From Mono- to Tetraphosphines A Contribution to the ... · PDF fileTo my wife 'Asma' and my...

From Mono- to Tetraphosphines – A Contribution to the Development of

Improved Palladium Based Catalysts for Suzuki- Miyaura Cross Coupling

Reaction

Von der Fakultät für Naturwissenschaften der Technischen Universität Chemnitz

genehmigte Dissertation zur Erlangung des akademischen Grades

Doktor rerum naturalium

(Dr. ret. nat.)

Vorgelegt von M. Sc. Albara I. S. Alrawashdeh

geboren am 22.05.1981 in Al Tafila- Jordanien

Chemnitz, eingereicht am 26.07.2011

Gutachter: Prof. Dr. Heinrich Lang

Prof. Dr. Wolfgang Weigand

Tag der Verteidigung: 09.11.2011

http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-80110

http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-80110

Die vorliegende Arbeit wurde in der Zeit von August 2008 bis Juli 2011 unter Leitung von Herrn Prof. Dr. Heinrich Lang am Lehrstuhl für Anorganische Chemie der Technischen Universität Chemnitz durchgeführt.

Herrn Prof. Dr. Heinrich Lang danke ich für die gewährte Freiheit bei der Bearbeitung des Themas, die anregenden Diskussionen und für die großzügige Unterstützung dieser Arbeit.

Dedication

To the spirit of my dear father,

To my great mother,

To my wife 'Asma' and my son 'Ibrahim'.

To my brothers; Alhassan, Alameen and Alrazi,

To my sisters; Lubaba and Afaq,

To The Hashemite Kingdome of Jordan.

Albara Alrawashdeh

Bibliographische Beschreibung und Referat

Albara I. S. Alrawashdeh

Von Mono- zu Tetraphosphane - Ein Beitrag zur Entwicklung von verbesserten

palladiumbasiereten Katalysatoren für die Suzuki–Miyaura Kreuzkupplung

Technische Universität Chemnitz, Fakultät für Naturwissenschaften

Dissertation 2011, 181 Seiten

Im ersten Teil der Arbeit wird die Synthese neopentyl- und neosilylsubstituierter Phosphane zur

Verwendung als Liganden in katalytisch aktiven Palladiumkomplexen beschrieben. Die Aktivität

wurde in der Suzuki-Miyaura Kreuzkupplungsreaktion getestet. Während die neosilylsubstituierten

Phosphane 2:1 Addukte (5b und 5d) mit geeigneten Palladiumsalzen bilden, welche moderate

Katalyseaktivität zeigen, untergehen die neopentylsubstituierten Komplexe schnelle

Cyclometalierungsreaktionen in Gegenwart von Basen und bilden die katalytisch wenig aktiven

Palladacyclen (6a, 6e, and 6g). Die deaktivierende Cylometallierung konnte durch Darstellung der

Palladiumcomplexe ausgehend von Pd(cod)Cl2 in Abwesenheit von Basen vermieden werden. Die

erhaltenen 2:1 Phosphaneaddukte zeigten deutlich verbesserte Aktivität. Daraus wurde gesch-

lossen, dass die Cyclomettalierung als Nebenreaktion eine wichtige Deaktiverungsmöglichkeit

darstellt, diese Überlegung veranlasste uns Trialkylphosphane mittlerer Größe, mit Substituenten die

nur schwer eine Cyclometallierungen eingehen können zu testen. Die Verwendung der

Phosphoniumsalze 4h (R = Cy, R‘ = neopentyl) und 4m (R = iPr, R‘ = CH2Cy) führt zu höheren

Aktivitäten in der Suzuki-Miyaura Kreuzkupplung, als bestes Katalysatorsystem hat sich die

Kombination aus Pd2(dba)3 oder Pd(OAc)2 und entsprechendem Phosphoniumsalz ergeben.

Im zweiten Teil dieser Arbeit werden Synthesen zu neuen biphenylbasierten Diphosphanen (70, 71,

76, and 77) vorgestellt. Die Palladiumkomplexe wurden ebenfalls auf ihre Eignung als Katalysatoren

in palladiumkatalysierten Suzuki-Miyaura Kreuzkupplungen getestet und zeigen für diese Klasse von

Komplexen gute Aktivität. Das Tetraphosphan 82 wurde für die Synthese des zweikernigen

Palladium(II)-komplex 83 eingesetzt. Durch die Koordination des D2h-symmetrischen

Tetraphosphanes an die Palladiumatome wird die Symmetrie des Moleküls erniedrigt und folglich

erhält man den formal D2-symmetrischen Komplex 83.

Stichworte: Cyclometallierung, Biphenyle, Suzuki-Kreuzkupplungen, Palladium(II), Platin(II),

Phosphane Komplexe, Palladacyclen, Diphosphanes, Tetraphosphane.

Abstract

From Mono- to Tetraphosphines – A Contribution to the development of Improved

Palladium Based Catalysts for Suzuki- Miyaura Cross Coupling Reaction


Technische Universität Chemnitz, Fakultät für Naturwissenschaften

In the first part of this thesis, the synthesis and catalytic activity of neopentyl and neosilyl

substituted phosphine palladium complexes is described. The complexes have been tested

in the Suzuki-Miyaura cross-coupling reaction. Whereas the neosilyl substituted phosphines

form 2:1 adducts (5b and 5d) with Palladium salts which showed moderate activity, the

neopentyl complexes quickly undergo cyclometallation in presence of bases to form

Palladacycles (6a, 6e, and 6g) which showed only moderate catalytic activity.

Cyclometallation could be avoided by the preparation starting from Pd(cod)Cl2 in the

absence of bases. The obtained 2:1 phosphine adducts showed superior activity. We

concluded that cyclometallation process is an important deactivation pathway, this

prompted us to test trialkyl phosphine ligands with medium size but substituents not

reliable to cyclometallation. We have been pleased to find that 4h (R = Cy, R‘ = neopentyl)

and 4m (R = iPr, R‘ = CH2Cy) showed good activity in the Suzuki-Miyaura cross-coupling

reaction. The best results have been obtained by in situ preparation of active catalyst from

Pd2(dba)3 or Pd(OAc)2 and the appropriate phosphonium salt.

In the second part of this thesis, the first synthesis of a new family of biphenyl based

bisphosphine ligands (70, 71, 76, and 77) has been reported. Their palladium complexes

were successfully tested as catalyst in the Suzuki cross-coupling reaction. Within the class of

bisphosphine based palladium complexes they show good activity in Suzuki-Miyaura cross-

coupling reaction. Systematically, was expanded our synthesis strategy and we were able to

introduce the first synthesis of a highly symmetric 2,2',6,6'-tetraphosphinobiphenyl.

Tetraphosphine 82 was used as ligand in a dinuclear palladium(II) complex 83. Upon

complexation the D2h symmetric 2,2’,6,6’-tetraphosphine lead to a chiral D2 symmetric

complex 83.

Keywords: Cyclometallation, Biphenyls, Suzuki Cross Coupling, Palladium(II), Platinum(II),

Phosphine Complexes, Palladacycles, Diphosphane, Tetraphosphane.

Table of Contents

i

• Table of Contents……………………………………………………………………………………………………… i • List of Figures………………………………………………………………………………………………………….… v • List of Tables…………………………………………………………………………………………………………….. vii • List of Schemes…………………………………………………………………………………………………………. viii • Abbreviations……………………………………………………………………………………………………........ x 1 INTRODUCTION AND MOTIVATION……………………………………………………………………….. 1 1.1 Catalysis…………………………………………………………………………………………………………….. 1 1.2 Organometallic Chemistry and Homogenous Catalysis………………………………………. 6 1.3 Palladium in Homogenous Catalysis…………………………………………………………………… 7 1.4 Palladium Catalyzed Cross Coupling Reactions…………………………………………………… 8 1.5 Palladium Catalyzed Suzuki –Miyaura Cross Coupling Reactions………………………… 13 1.5.1 Phosphorous Ligands in Suzuki – Miyaura Cross Coupling Reactions……… 16

1.5.1.1 Trialkylphosphines…………………………………………………………………… 16 1.5.1.2 Biaryl Based Phosphine Ligands………………………………………………. 23 1.5.1.3 Palladacycles in The Suzuki Cross Coupling Reaction………………. 29 2 RESULTS AND DISCUSSION……………………………………………………………………………………… 36 2.1 Synthesis, Characterization and Applications of Trialkyl Monophosphine Ligands

in Palladium Catalyzed Cross Coupling Reactions………………………………………………

36 2.1.1 Synthesis and Characterization of Substituted Neopentyl and Neosilyl

Phosphine Ligands and their Phosphonium Salts……………………………………

36 2.1.2 Synthesis and Characterization of Substituted iPropyl and tButyl

Phosphonium Salts…………………………………………………………………………………

41

2.1.3 Synthesis and Characterization of Palladium Complexes……………………… 43 2.1.3.1 Synthesis of Substituted Neopentyl and Neosilyl Palladium

Complexes 5a-5d………………………………………………………………………

43 2.1.3.2 Characterization of the Synthesized Complexes 5a-5d…………….. 44 2.1.3.3 Molecular Structures of 5b and 5d……………………………................ 46

2.1.4 Cyclopalladated and Non-Cyclopalladated Complexes of Substituted Neopentyl phosphine…………………………………………………………………............

48

2.1.4.1 Coordination Behavior of Phosphonium Salt 4a ……………………… 49 2.1.4.2 Molecular Structure of the Cyclopalladated Complex 6a.………… 51 2.1.4.3 Coordination Behavior of Phosphonium Salt 4e………………………. 52 2.1.4.4 Molecular Structure of the Cyclopalladated Complex 6e………… 54 2.1.4.5 Coordination Behavior of Cyclopalladated Complex 6e…………… 56 2.1.4.6 Coordination Behavior of Phosphonium Salt 4g…………………….… 59 2.1.4.7 Coordination Behavior of Phosphonium Salt 4h…………………….… 60

2.1.5 Synthesis and Characterization of Substituted iPropyl and tButyl Dinuclear Palladium Complexes 6i-6o……………………………………………………

61

2.1.6 Effective Suzuki Cross Coupling Reactions Using Prepared Phosphonium Salts and Palladium Complexes……………………………………………………………..

67

2.1.6.1 Neopentyl and Neosilyl Phosphines Based Catalysts for Suzuki-Miyaura Cross-Coupling Reactions………………………………………....

67

2.1.6.2 Cyclometallated Palladium Complexes in Suzuki-Miyaura Cross-Coupling and Buchwald Amination Reactions………………..

75

Table of Contents

ii

2.1.6.3 Substituted Trialkylphosphonium Salts in Suzuki-Miyaura Cross

Coupling Reaction……………………………………………………………………

87 2.2 Synthesis, Characterization and Applications of New 2,2'-Bisphosphine and

2,2',6,6'-Tetraphosphine Biaryl Ligands in Palladium Catalyzed Suzuki Cross Coupling Reaction………………………………………………………………………………………………

97 2.2.1 Synthesis and Characterization of New 2,2'-Bisphosphine Ligands and

their Palladium and Platinum Complexes………………………………………………

97 2.2.1.1 Synthesis and Characterization of New 2,2'-

Bis(dimethylamino)-6,6'-Bisphosphinobiphenyl Ligands and their Palladium and Platinum Complexes…………………………………

97 2.2.1.2 Synthesis and Characterization of New 2,2'-Bis(dibromo)-6,6'-

Bisphosphino biphenyl Ligands and their Palladium and Platinum Complexes………………………………………………………………..

104 2.2.2 Bisphosphinbiphenyl Palladium Complexes in Suzuki-Miyaura Cross-

Coupling Reaction…………………………………………………………..........................

113 2.2.3 Synthesized and Characterization of a 2,2’,6,6’-Tetraphosphinobiphenyl

and a related Dinuclear Palladium Complex…………………………………………..

115 3 Experimental Section……………………………………………………………………………………………… 124 3.1 General Remarks: Equipment, Chemicals and Work Technique…………………………. 124

3.1.1 Chemicals and Work Technique……………………………………………………………. 124 3.1.2 NMR Spectroscopy………………………………………………………………………….……. 125 3.1.3 Mass Spectroscopy…………………………………………………………………………….…. 125 3.1.4 Infrared spectroscopy (IR)………………………………………………………………….…. 125 3.1.5 Elementary analysis…………………………………………………………………………….… 125 3.1.6 Melting Points………………………………………………………………………………………. 125 3.1.7 Gas chromatography-Mass spectrometry…………………………………………….. 125 3.1.8 Single crystal X-ray analysis…………………………………………………………………… 125 3.1.9 Column chromatography………................................................................... 126

3.1.10 TLC………………………………………………………………………………………………………… 126 3.2 Experimental Procedures and Spectroscopic Data…………………………………………….. 126

3.2.1 Synthesis of [Ph2PCH2C(Me)3] 3c……………………………………………………........ 126 3.2.2 Synthesis of Ph 2PCH2SiMe3 3d………………………………………………………………. 126 3.2.3 Synthesis of [Hi-Pr2PCH2C(Me)3][BF4] 4a……………………………………………….. 127 3.2.4 Synthesis of [Hi-Pr2PCH2SiMe3][PF6] 4b………………………………………………….. 128 3.2.5 Synthesis of [HtBu2PCH2C(Me)3][BF4] 4e………………………………………………… 129 3.2.6 Synthesis of [Ht-Bu2PCH2SiMe3][PF6] 4f……………………………………………….…. 130 3.2.7 Synthesis of [HP(CH2C(Me)3)3][BF4] 4g…………………………………………………… 131 3.2.8 Synthesis of [HCy2PCH2CMe3][BF4] 4h…………………………………………………… 131 3.2.9 Synthesis of [Ht-Bu(iPr)2P][BF4] 4i…………………………………………………………… 132

3.2.10 Synthesis of [Ht-Bu3P][BF4] 4k……………………………………………………………… 133 3.2.11 Synthesis of [HiPr2P(3-pentane)][BF4] 4l……………………………………………… 133 3.2.12 Synthesis of [HiPr2PCH2Cy][PF6] 4m…………………………………………………… 134 3.2.13 Synthesis of [HtBu2PCH2Cy][PF6] 4n…………………………………………………… 135 3.2.14 Synthesis of [Hi-Pr2PCH2CH(Me)2][BF4] 4o…………………………………………… 136 3.2.15 Synthesis of complex (iPr2PCH2C(Me)3)2PdCl2 5a………………………………… 137 3.2.16 Synthesis of complex (i-Pr2PCH2SiMe3)2PdCl2 5b…………………………………. 137 3.2.17 Synthesis of complex (Ph2PCH2C(Me)3)2PdCl2 5c………………………………… 138

Table of Contents

iii

3.2.18 Synthesis of complex (Ph2PCH2SiMe3)2PdCl2 5d………………………………….. 138 3.2.19 Synthesis of Palladacycle 6a.………………………………………………………………. 139 3.2.20 Synthesis of Palladacycle 6e……………………………………………………………….. 139 3.2.21 Synthesis of Palladacycle 6g……………………………………………………………….. 140 3.2.22 Synthesis of (Cy2PCH2CMe3)2Pd2Cl4 6h………………………………………………. 141 3.2.23 Synthesis of (iPr2PtBu)2Pd2Cl4 6i………………………………………………………….. 141 3.2.24 Synthesis of (iPrPtBu2)2Pd2Cl4 6j…………………………………………………………. 142 3.2.25 Synthesis of Palladacycle 6k……………………………………………………………….. 142 3.2.26 Synthesis of (iPr2P(3-pentane)2Pd2Cl4 6l…………………………………………… 143 3.2.27 Synthesis of complex (iPr2PCH2Cy)2Pd2Cl4 6m…………………………………… 143 3.2.28 Synthesis of complex (iPr2PCH2CH(Me)2)2Pd2Cl4 6o…………………………… 144

3.2.29 Synthesis of Palladacycle 9e……………………………………………………………… 144 3.2.30 Synthesis of Palladacycle 9k……………………………………………………………… 145 3.2.31 Synthesis of Palladacycle 10e……………………………………………………………. 145 3.2.32 Synthesis of Palladacycle 10k…………………………………………………………….. 146 3.2.33 Synthesis of Palladacycle 11e…………………………………………………………….. 146 3.2.34 Synthesis of Palladacycle 12e…………………………………………………………….. 147 3.2.35 Synthesis of Pd(0) 13e……………………………………………………………………….. 147 3.2.36 Synthesis of PdCl2(tmeda) …………………………………………………………………. 148 3.2.37 Synthesis of PdMe2(tmeda) ………………………………………………………………. 148 3.2.38 Synthesis of 2-bromo-4-methyl-6-nitroaniline 65………………………………. 148 3.2.39 Synthesis of 1-bromo-2-iodo-5-methyl-3-nitrobenzene 66………………… 149 3.2.40 Synthesis of 2,2'-dibromo-4,4'-dimethyl-6,6'-dinitrobiphenyl 67………… 149 3.2.41 Synthesis of 6,6'-dibromo-4,4'-dimethylbiphenyl-2,2'-diamine 68…… 150 3.2.42 Synthesis of 2,2'-dibromo-6,6'-diiodo-4,4'-dimethylbiphenyl 75………… 150 3.2.43 Synthesis of 6,6'-dibromo-N,N,N',N',4,4'-hexamethylbiphenyl-2,2'

diamine 69……………………………………………………………………………………..… 151 3.2.44 Synthesis of bisphosphine 77……………………………………………………………… 151 3.2.45 Synthesis of bisphosphine 76……………………………………………………………… 152 3.2.46 Synthesis of bisphosphine 70……………………………………………………………… 153 3.2.47 Synthesis of bisphosphine 71……………………………………………………………… 154 3.2.48 Synthesis of PdCl2 (71) 73…………………………………………………………………… 154 3.2.49 Synthesis of PdCl2(70) 72…………………………………………………………………… 155 3.2.50 Synthesis of PtCl2 (70) 74…………………………………………………………………… 155 3.2.51 Synthesis of PdCl2(77) 79…………………………………………………………………… 156 3.2.52 Synthesis of PdCl2 (76) 78…………………………………………………………………… 156 3.2.53 Synthesis of PtCl2 (76) 80…………………………………………………………………… 157 3.2.54 Synthesis of PtCl2 (77) 81…………………………………………………………………… 157 3.2.55 Synthesis of 2,2',6,6'-tetraphosphinebiphenyl 82……………………………… 158 3.2.56 Synthesis of Dinuclear Palladium Complex of 2,2',6,6'

tetraphosphinebiphenyl 83………………………………………………………………..

159 3.3 General Procedure for the Suzuki-Miyaura coupling…………………………………………. 160 3.4 General Procedure for the Buchwald-Hartwig coupling……………………………………. 160 3.5 General Procedure for the Suzuki-Miyaura coupling (Kinetic investigations)……. 161 3.6 General Procedure of 31P{1H} NMR studies of the Pd(0), 13e, complex……………… 161

4 SYMMARY……………………………………………………………………………………………………… 162 REFERENCES …………………………………………………………………………………………………. 165

Table of Contents

iv

APPENDIX…………………………………………………………………………….……………………………. 172 PERSONAL DATA……………………………………………………………………………………………….. 177 ACKNOWLEDGAMENT……………………………………………………………………………………….. 179

List of Figures

v

• List of Figures.

Figure 1.1: Effect of the catalysts in a thermodynamically favorable reaction…………... 2 Figure 1.2: History of catalysis of industrial process………………………………………………….. 4 Figure 1.3: The principle of cross coupling reaction……………………………………………..…... 9 Figure 1.4: Major cross coupling reactions…………………………………………………………..….… 11 Figure 1.5: Mechanism of a cross coupling reaction………………………………………………….. 13 Figure 1.6: General catalytic cycle for Suzuki-Miyaura coupling………………………………… 15 Figure 2.1: Molecular structure of 5b…………………………………………………………………….….. 47 Figure 2.2: Molecular structure of 5d…………………………………………………………………….….. 48 Figure 2.3: Molecular Structure of 6a (Cyclometallated palladium complex of

phosphine salt 4a (R = iPr, R' = Neopentyl))………………………………………….…..

51 Figure 2.4: Molecular Structure of 6e…………………………………………………………………….….. 54 Figure 2.5: Coordination behavior of cyclopalladated complex 6e……………………….….. 56 Figure 2.6: Molecular structure of 13e………………………………………………………………..….… 58 Figure 2.7: Molecular structure of 6m…………………………………………………………………..….. 64 Figure 2.8: Kinetic investigation of complex in the Suzuki Miyaura cross-coupling

reaction of 2-bromotoluene with phenylboronic acid ……………………..….…

72 Figure 2.9: Kinetic investigation of complexes 5 in the Suzuki Miyaura cross-coupling

reaction of 2-bromotoluene with phenylboronic acid ……………………….…...

73 Figure2.10: Kinetic investigation of complexes 5 in the Suzuki Miyaura cross-coupling

Reaction of 4-chloroacetophenone with phenylboronic acid…………………..

73 Figure 2.11: 31P{1H}-NMR investigation (25°C or 50°C, CD3CN) on the oxidative

addition of bromo benzonitrile to Pd(0) complex 13e in CD3CN……..………


addition of 3,5-CF3-bromobenzene to Pd(0) complex 13e in CD3CN……..


addition of iodobenzene to Pd(0) complex 13e in CD3CN…………………..…..


addition of iodobenzene to Pd(0) complex (no.) in CD3CN ……………………..

80 Figure 2.15: Kinetic Investigation of 6k and 9k in the Buchwald-Hartwig amination

reaction of 2-bromotoluene with morpholine…………………………………………

83 Figure 2.16: Kinetic Investigation of 6k and 9k in the Buchwald- Hartwig amination

reaction of bromobenzene with diethyl amine………………………………..………

84 Figure 2.17: Kinetic investigation of the Suzuki Miyaura cross-coupling reaction of 4-

bromoacetophenone with phenylboronic acid with 0.5 mol%Pd(OAc)2/1 mol% 4 ……………………………………………………………………..…………………………….


chloroanisol with phenylboronic acid with 0.5 mol% Pd(OAc)2/1 mol% 4


bromotoluene with phenylboronic acid with 0.5 mol% Pd(OAc)2/1mol% 4

92 Figure 2.20: 1H-NMR spectrum of bisphosphine ligand 71 CDCl3………………………………. 99 Figure 2.21: Variable temperature 1H NMR (500MHz) of 74 in CD2Cl2…………………..… 101 Figure 2.22: Variable temperature 31P{1H} NMR of 74 in CD2Cl2……..................………. 102 Figure 2.23: Molecular structure of 72…………………………………………………………………..…… 103 Figure 2.24: Molecular structure of 73 ………………………………………………………………………. 103

List of Figures

vi

Figure 2.25:

Molecular structure of 74……………………………………………………………………..…

104

Figure 2.26: Variable temperature 31P{1H} NMR of 79 in CD2Cl2/DMF........................ 108 Figure 2.27: The 31P{1H} NMR of 84 in CDCl3…………………….…………………………….….….. 108 Figure 2.28: Molecular structure of bisphosphinebiphenyl 77 ……………………………..……. 110 Figure 2.29: Molecular structure of palladium complex 78……………………………………..…. 110 Figure 2.30: Molecular structure of palladium complex 79 …………………………………..…… 111 Figure 2.31: Kinetic investigation of 72, 73, 78 and 79 in the Suzuki cross coupling

reaction of 2-bromotoluene with phenylboronic acid……………………….……

113 Figure 2.32: Kinetic Investigation of 79 in the Suzuki cross coupling reaction of 4-

bromoanisole with phenylboronic acid……………………………………………….….

114 Figure 2.33: Variable temperature 31P{1H} NMR spectra of complex 83 in d7-dmf

solution at 178, 198, 223, 248, 273, 298, 323, 348, and 373 K ……………...

117 Figure 2.34: Standard proton nmr spectrum, of 83, (top) and 1H selective NOE

spectrum (buttom) with irradiation at the aromatic proton at δ = 8.25 a mixing time of 0.5 sec and 64 transients recorded in d7-dmf at 398K……………………………………………………………………………………………………..…

118 Figure 2.35: 31P{1H} NMR spectrum of complex 83 in d7-dmf at 223K, signals were

grouped based on the signal intensity and line broadening…………………....

119 Figure 2.36: 31P{1H} EXSY spectrum of complex 83 at 208K in d7-DMF/CH2Cl2 mixture

(ratio 1:2)…………………………………………………………………………………………………

120 Figure 2.37: Molecular structure of complex 83………………………………………………………..… 121 Figure 2.38: Ortep drawing of the complete asymmetric unit of crystals of complex

83…………………………………………………………………………………………………..…………

122 Figure 3.1: Photo for preparation of Li/Na alloy…………………………………………..………….… 127

List of Tables

vii

• List of Tables.

Table 1.1: Types of the cross coupling reaction…………………………………………………….. 10 Table 1.2: Suzuki cross-couplings of aryl bromides by Fu………………………………………. 18 Table 1.3: Suzuki cross-couplings of aryl iodides by Fu………………………………………….. 18 Table 1.4: Suzuki cross-couplings of aryl chlorides by Fu………………………………………. 19 Table 1.5: Suzuki cross-couplings of aryl triflates by Fu…………………………………………. 19 Table 1.6: Suzuki cross-couplings of different aryl chlorides with phenylboronic 6

acid by Beller ligand 14………………………………………………………………………….

20 Table 1.7: Suzuki cross-couplings of aryl halides with phenylboronic 6 acid by

Shaughnessy ligands 15, 16 and 17……………………………………………………….

22 Table 1.8: Suzuki cross-couplings of aryl halides by Buchwald………………………………. 26 Table 1.9: Suzuki Cross-Couplings of Aryl Halides by Herrmann……………………………. 32 Table 2.1: 31P NMR data of phosphonium salts……………………………………………………… 43 Table 2.2: Selected bond lengths (Å) and angles (°) of 5b……………………………………… 47 Table 2.3: Selected bond lengths (Å) and angles (°) of 5d……………………………………… 48 Table 2.4: Data for single crystal X-ray structure analysis of 5b and 5d…………………. 172 Table 2.5: Selected bond lengths (Å) and angles (°) of palladacycle 6a.………………… 52 Table 2.6: Selected bond lengths (Å) and angles (°) of palladacycle 6e……………….… 55 Table 2.7: Data for single crystal X-ray structure analysis for 6a, 6e, 6m, and 13e.. 173 Table 2.8: Selected bond lengths (Å) and angles (°) of 12……………………………….…..… 58 Table 2.9: 31P NMR data of phosphonium salts and its dimeric palladium

complexes………………………………………………………………………………………….….

62 Table 2.10: Selected bond lengths (Å) and angles (°) of 6m…………………………………….. 65 Table 2.11: Selected bond lengths (Å) and angles (°) of 72-74, 77, 78 and 79…………. 112 Table 2.12: Selected bond lengths (Å) and angles (°) of 83………………………….………….. 121 Table 2.13: Data for single crystal x-ray structure analysis of 72-74, 77-79, and 83 … 174

List of Schemes

viii

• List of Schemes.

Scheme 1.1: The principle of catalysis…………………………………………………………………..…… 3 Scheme 1.2: Classification of catalysts………………………………………………………………………. 9

Scheme 1.3 : Wacker process…………………………………………………………………………………….. 8 Scheme 1.4 : Tsuji-Trost process………………………………………………………………………………… 8 Scheme 1.5 : Kumada Coupling………………………………………………………………………………….. 10 Scheme 1.6 : Corriu Coupling……………………………………………………………………………………… 10 Scheme 1.7 : Suzuki cross coupling reaction………………………………………………………………. 14 Scheme 1.8 : Suzuki coupling of aryl chloride…………………………………………………………….. 16 Scheme 1.9 : Common phosphines for Suzuki cross coupling…………………………………..… 17

Scheme 1.10: Common phosphines for Suzuki cross coupling by Shaughnessy …………… 21

Scheme 1.11: Atropisomerism of biaryl and biphenyl diphosphines……………………………. 23

Scheme 1.12: 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (BINAP)……………………………. 24

Scheme 1.13: Common dialkyl(biphenyl)phosphine for Suzuki cross coupling reactions 25

Scheme 1.14: Synthesis of biaryl backbone phosphines by Buchwald……………………….…. 27

Scheme 1.15: Synthesis of 2,2'-diphosphanesbiaryl…………………………………………………….. 28 Scheme 1.16: 2,2'-diphosphanesbiaryl bu Takaya and Achiwa…………………………………….. 28 Scheme 1.17: Structural definition of cyclometallation……………………………………………….. 29 Scheme 1.18: The first cyclometallated compound by Kleimann, Dubeck and Cope……. 30 Scheme 1.19:

Formation of trans-di(µ-acetato)-bis[di-o-tolylphosphino) benzyl] dipalladium by Hermann and co-workers………………………………………………….

31

Scheme 1.20: Ortho-metallated palladium complexes by Bedford and co-workers…….. 31

Scheme 1.21: Postulated mechanism for the formation of the catalytically active species [Pd{P(o-tol)3}2] during the amination reaction by Hartwig et al…

32

Scheme 1.22: Cyclometallated platinum complexes by Shaw et al. …………………………….. 33

Scheme 1.23: Cyclometallated palladium complexes by Kraus et al. …………………………… 34

Scheme 1.24: Cyclometallated palladium and platinum complexes by Kraus et al. ……… 34

Scheme 2.1: Synthesis of substituted neopentyl and neosilyl phosphines…………………. 37

Scheme 2.2: The mechanism of organomagnesium and organolithium compounds generation …………………………………………………………………………………………….

37

Scheme 2.3: Synthesis of substituted neopentyl and neosilyl phosphonium salts……… 39 Scheme 2.4: Substiuted iPropyl and tButyl phosphonium salts………………………………….. 42 Scheme 2.5: Synthesis of palladium complexes 5a, 5b, 5c and 5d via free phosphine

ligands 3a, 3b, 3c and 3d………………………………………………………………………

44 Scheme 2.6: Synthesis of palladium complexes 5a and 5b via phosphonium salts 4a

and 4b……………………………………………………………………………………………………

44 Scheme 2.7: Coordination behavior of phosphonium salts……………………………………….. 49 Scheme 2.8: Cyclopalladation of the phosphonium salt 4a by Pd(OAc)2……………………. 50

Scheme 2.9: Cyclopalladation of the phosphonium salt 4e by Pd(OAc)2……………………. 53 Scheme 2.10: Synthesis of palladium(0) complex 13e…………………………………………………. 57

Scheme 2.11: Cyclopalladation of the phosphonium salt 4g by Pd(OAc)2……………………. 59 Scheme 2.12: The dinuclear palladium complex of 4h………………………………………………… 60

List of Schemes

ix

Scheme 2.13: Coordination behavior of phosphonium salt's 4i-4o……………………………… 62 Scheme 2.14: Coordination behavior of phosphonium salt 4k…………………………………….. 65 Scheme 2.15: Coordination behavior of cyclopalladated complex 6k…………………………. 66 Scheme 2.16: Suzuki cross-coupling reaction of bromobenzene with phenylboronic

acid catalyzed by palladium complex 5b and 5d …………………………………….

68 Scheme 2.17:

Suzuki cross-coupling reaction of 4-bromoacetophenone with phenyl boronic acid catalyzed by palladium complex 5b and 5d ………………………

69

Scheme 2.18:

Suzuki cross-coupling reaction of 4-bromoanisole with phenylboronic acid catalyzed by 5………………………………………………………………………………..

70

Scheme 2.19:

Suzuki cross coupling reaction of 2-bromotoluene with phenylboronic acid catalyzed by palladium complexes 5 ………………………………………………

71

Scheme 2.20:

Suzuki cross coupling reaction of 2-chlorotoluene with phenylboronic acid catalyzed by palladium complexes 5 ………………………………………………

72

Scheme 2.21:

Screening of bases for Suzuki cross-coupling of 4-bromoacetophenon with phenylboronic acid using catalyst 5b and 5c…………………………………..

74

Scheme 2.22: Postulated mechanism for the formation of the catalytically active monophosphine palladiumd(0) species in Suzuki cross-coupling……………

76

Scheme 2.23: Proposed reaction pathways for the oxidative additions of aryl halides to the Pd(0) complex 13e……………………………………………………………………….

77

Scheme 2.24:

Suzuki coupling of 4-chloroacetophenon with phenylboronic acids catalyzed by mixtures of complex 6e and two equivalents of PPh3 or PPh2(o-tolyl)…………………………………………………………………………………………..

81 Scheme 2.25:

Suzuki cross-coupling reaction of 4-chloroacetophenone with phenyl boronic acid catalyzed by 6k, 9k and 10k………………………………………………..

82

Scheme 2.26: Amination of aryl bromides and chlorides catalyzed by 6k…………………….. 85 Scheme 2.27:

Influence of catalyst loading of 6m ((P(iPropyl)2CH2Cy)2Pd2Cl4) in Suzuki coupling of 4-bromocetophenon with phenylboronic acid ……………………

86

Scheme 2.28:

Suzuki coupling of 4-bromoacetophenon with phenylboronic acids catalyzed by mixtures of Pd(OAc)2 and two equivalents of phosphonium salts [HPR2R'][BF4]; 4b, 4k, 4l, 4m, 4n and 4o.......................................

89 Scheme 2.29:

Suzuki coupling of 2-bromotoluene with phenylboronic acids using phosphonium salts 4………………………………………………………………………………

93

Scheme 2.30:

Suzuki coupling of aryl halides with phenylboronic acids catalyzed by 4h([HPCy2CH2C(CH3)3])/Pd(OAc)2…………………………………………………………….

94

Scheme 2.31:

The comparison of a variety of phosphine ligands as reported by Fu et al. and phosphonium salts 4h, 4m and 4n in Suzuki coupling of 4-chlorotoluene and Phenylboronic acid …………………………………………….……

95 Scheme 2.32: Synthesis of Biaryl backbone phosphines 70 and 71…………………….………… 98 Scheme 2.33: Synthesis of palladium and platinum biarylbackbone phosphines

complexes 72-74……………………………………………………………………………….……

100 Scheme 2.34: Synthesis of biaryl backbone phosphines 76 and 77………………………….…… 105 Scheme 2.35: Synthesis of palladium and platinum biaryl backbone phosphines

complexes 78-81……………………………………………………………………………….……

106 Scheme 2.36: Synthesis of 2,2’,6,6’-tetraphosphinobiphenyl 82 and its related complex

83…………………………………………………………………………………………………………..

115

Abbreviations

x

• Abbreviations.

Ac acetyl

Å angstrom

Ar aryl

br broad

Cat catalysis

CataCXium® A di-1-adamantyl-n-butylphosphine

COSY correlated spectroscopy

Cy cyclohexyl

d doublet (1H NMR)

dd

dt

doublet of doublet

doublet of triplet

DMF dimethylformamide

DMSO dimethylsulfoxide

dppf 1,1'-bis(diphenylphosphino)ferrocene

dsept doublet of septet

DTBNP ditertbutyl neopentyl phosphine

Et ethyl

Et2O diethyl ether

EWG electron with drawing group

EXSY exchange spectroscopy

Hz hertz iPr Iso-propyl

J coupling constant

L ligand

m medium (IR)

M metal

m multiplet (1H NMR)

M.p melting point

MeOH methanol

MHz mega hertz

mmol millimol

MS mass spectrometry nBu n-butyl nBuLi n-butyllithium

nm nanometer

NMR nuclear magnetic resonance

http://chem.ch.huji.ac.il/nmr/techniques/other/dynamic/dynamic.html#ms

Abbreviations

xi

NOESY

nuclear over hauser and exchange spectroscopy

o ortho

p para

Ph phenyl

ppm parts per million

q quartet

R organic group

s singlet (1H NMR)

st strong (IR)

t

td

triplet

triplet of doublet

TBDNPP tert-butyl di-neopentylphosphine tBu tert-butyl

THF tetrahydrofuran

TLC thin layer chromatography

TMEDA tetramethylethylene diamine

TMS trimethylsilane

TNPP trineopentyl phosphine

TOF turnover frequency

TON turnover number

TTBP tritbutyl phosphine

VT variable temperature (NMR)

z charge

δ chemical shift

Chapter 1: Introduction and Motivation

1

Chapter

1

1. Introduction and Motivation.

1.1 Catalysis

A broad definition of catalyst stands for ''any compound which lowers the activation energy

of a chemical reactions without being consumed in them''.[1] The modern definition of a

catalyst was given by Wilhelm Ostwald in 1894: ''A catalyst is a substance that changes the

rate of a reaction without itself appearing in the products''. Ostwald received the Nobel

Prize in chemistry in 1909 for his work on understanding catalytic processes. In addition, a

large number of chemists those received the Nobel Prize in the field of the role of metal

catalysts, for example Haber (1918), Bergius and Bosch (1931), Natta and Ziegler (1963),

Fischer and Wilkinson (1973), Knowles, Noyori and Sharpless (2001)[1], Chauvin, Grubbs and

Schrock (2005), Ertl (2007), and most recently Suzuki, Heck and Negishi (2010).[2] One of the

most important industrial processes involving catalysts was discovered by a German chemist

called Fritz Haber in 1914, when he established an industrial process for the manufacture of

ammonia.[2] This process utilizes atmospheric nitrogen and hydrogen in presence of iron

oxide catalyst at high temperature and pressure. Since their discover in the mid-1850s by

Baron J. J. Berzelius catalyst have represented a very interesting topic of applied science and

involves many areas of chemistry, notably in organometallic chemistry and materials science

research.[3]

In general, catalysts can be gases, liquids or solids and the most widely used catalysts are

liquids or solids. The key rule of the catalyst is kinetic; catalysts work by providing an

alternative mechanism that involves a different transition state and lower activation energy

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2

(Figure 1.1). The effect is that more molecular collisions have the energy needed to reach

the transition state. In general, for every chemical reaction to proceed well; a certain

quantity of activation energy is needed. For some reactions when the difference is very high

between the free enthalpy of the substrate and the free enthalpy of the transition state;

they are kinetically slowed down and cannot be observed to a significant extend. In other

words, catalysts can carry out reactions which take place much faster, more specifically, and

at lower temperatures.

Figure 1.1. Effect of the catalysts in a thermodynamically favorable reaction.[1c]

Catalysts generally react with one or more reactants to form intermediates that

subsequently give the final reaction product, in the process regenerating the catalyst

(Scheme 1.1). The complex XC of the substrate X and the catalyst C reacts with substrate Y

to give the product XY while releasing the catalyst C. This sequence consists the generation

of the substrate-catalyst-complex, the product formation and the release of the catalyst is

called a catalytic cycle.[4]


3

Scheme 1.1: The principle of catalysis.

After the catalyst is released, it can re-enter the cycle. As a catalyst is regenerated in a

reaction, often only small amounts are needed to increase the rate of the reaction. In

practice, however, catalysts are sometimes consumed in secondary processes. Moreover,

catalysts are often deactivated over the course of the reaction due to side reactions and are

then not able to participate in new sessions of the catalytic cycle. Hence, the productivity of

a catalyst can be described by the turn over number (or TON) which equals the ratio of the

substrate concentration to the active catalyst concentration. The catalytic activity described

by the turn over frequency (TOF), which is the TON per time unit.

One of the most important properties of catalytic reactions is that they proceed at milder

conditions, produce less waste, less energy and are less time-consuming than their

stoichiometric analogues. Moreover, with help of catalysis, few steps are required to reach a

target molecule by enabling the reaction of former relatively inert substrates. In addition,

production of most industrially important chemicals involves catalysis.[5,7] Similarly, most

biochemically significant processes are catalysed. Catalyst plays a key role in the most

industrial synthesis of liquid fuels and bulk chemicals such as nitric acid (from ammonia),

sulfuric acid (from sulfur dioxide to sulfur trioxide by the chamber process) and acrylonitrile

from propane and ammonia. In addition, most carbonylation processes require metal

catalysts, such as Monsanto acetic acid process and hydroformylation.[6]

In addition to their use in previous processes, catalysts have been employed for broad range

of chemical processes. The brief historical survey given in figure 1.2 shows the development

of catalysis in industrial chemistry.[5-8] Furthermore, the importance of catalysis in industry

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http://en.wikipedia.org/wiki/Nitric_acid

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http://en.wikipedia.org/wiki/Sulfur_trioxide

http://en.wikipedia.org/wiki/Chamber_process

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4

is shown by the fact that the most chemicals are synthesized in the presence of catalysis. [9-

18]

Figure 1.2. History of catalysis of industrial process.

In general, catalysts can be either homogeneous, heterogeneous or biocatalysts (which are

defined as catalytic proteins) depending on whether a catalyst exists in the same phase as

the reactant or not (Scheme 1.2).[19-21] If they are present in the same phase, the term

homogeneous is used and typically homogeneous catalysts are dissolved in a solvent with

the reactant. In heterogeneously catalyzed reactions, the catalyst exists in a different phase

than the reactant (s), and most heterogeneous catalysts can dissolve into the solution in a

solid-liquid system or evaporate in a solid-gas system. Biocatalysts are often defined as a

‘blend’ of homogeneous and heterogeneous catalysis; about 4,000 reactions are known to

be catalyzed by enzymes.[22]

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5

Catalysis

Homogeneous Catalysts

BiocatalystsHeterogeneous Catalysts

Transitionmetal-catalysts

Acid/basecatalysts

Supportedcatalysts

Bulkcatalysts

Scheme 1.2: Classification of catalysts.

The major advantage of the heterogeneous catalysts is the simplicity of catalyst separation

from reaction media. The catalyst is either automatically removed in the process (e.g., gas

phase reactions in fixed-bed reactors), or separated by simple methods such as filtration or

centrifugation. On the other hand, the separation of the homogeneous transition metal

catalysts is difficult and often almost not feasible. Therefore, complicated processes such as

distillation, liquid-liquid extraction, and ion exchange must often be used. This has been

improved by using organometallic complexes which are soluble in both organic media and

water, ionic liquids or super-critical CO2.[23] By the end of the reaction the media containing

the homogeneous catalyst is easily separated from the organic phase using similar

procedures as in the case of the heterogeneous catalysts. Moreover, the most widely used

catalyst is the heterogeneous type, in addition, mild reaction conditions (50-200°C)

employed in homogeneous catalysis comparing with severe conditions (eg., often <250 °C).

in the case of heterogeneous catalysis. [19-21]

In summary, homogeneous and heterogeneous catalysts should be used to complement one

another and not regarded as competitors, since each group has its special characteristics

and properties. Furthermore, the importance of homogeneous and heterogeneous catalysts

in industry is shown by the fact that more than 75% of all types of chemicals are synthesized

in the presence of them, and its importance has grown up to the present day. Therefore,

many products can be synthesised by means of homogeneous and heterogeneous catalysts

much more efficiently than before.


6

1.2 Organometallic Chemistry and Homogeneous Catalysis

Organometallic compounds are defined as materials having bonds between one or more

metal atoms and one or more carbon atoms of an organyl group.[24] This bond can be either

a direct carbon to metal bond (σ bond or sigma bond) or a metal complex bond (π bond or

pi bond). The first metal complex identified as an organometallic compound was a salt,

K[CH2=CH2)PtCl3 , obtained from reaction of ethylene with platinum(II)chloride by William

Zeise in 1820s[25]. Since their discovery in 1820s organometallic compounds have grown

enormously, although most of their applications have only been developed in recent

decades. The most important key points in the fast expansion of organometallic chemistry

are the selectivity of organometallic complexes in organic synthesis (discovered with

Grignard reagents at the end of the 19th century) as well as biological systems (e.g.

enzymes, hemoglobin, etc)[26]. One of the most interesting things about organometallic

compounds is that they are very useful as homogeneous catalysts in the synthesis of organic

compounds.

According to the established definitions, homogeneous catalysis can be divided into two

different classes; the first one are metal complex-catalyzed reactions and the second are

acid\base catalyzed reactions (which play an important function in condensation, and

oxidation reactions).[27-30] Furthermore, homogeneous catalysts are usually employed in the

fine-chemical and pharmaceutical industries because of their ability to produce highly

selective and reproducible products as well as lower reaction temperatures in many types of

chemical transformation.[28-35] Homogeneous catalysts have become widely used in

industrial processes to obtain fine chemicals and polymers, such as oxidation of toluene and

xylene to acids, oxidation of ethene to aldehyde, condensation of ester to polyesters,

carbonylation of methanol, polymerization of dienes to unsaturated polymers,

hydroformylation of alkenes, oligomerization of alkenes, asymmetric hydrogenation,

asymmetric isomerization, asymmetric epoxidation, co-dimerization of ethene,

hydrosilylation of alkenes, ring opening metathesis polymerization of dicyclopentadiene and

norbornene, alternating copolymerization of ethane, carbon monoxide, and biological

applications etc.[9-18] Furthermore, homogeneous catalysts have acquired enormous

importance in all type of cross coupling reactions.[35-43] Since the early uses of the palladium

compounds in the Heck-Mizoroki reaction[39,43]; many strategies through last few decades


7

have been used homogeneous palladium catalyzed cross-coupling reactions as an ideal way

on the formation of carbon-carbon or carbon-heteroatom bonds and its importance has

grown up to the present day.[35-44]

1.3 Palladium in Homogenous Catalysis

Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46.

It is a rare silvery-white (even more rare than gold), noble metal, part of the platinum group

of metals (PGM) and having a weight similar to gold. Palladium can exist in a number of

different oxidation states, useful organic methods are dominated by the use of Pd(0) and

Pd(II).[47-49,50-52] Palladium has a relative high electronegativity of 2.20 (according to Pauling).

Consequently, Pd–C bonds are quite unpolar, and organopalladium complexes are relatively

stable. Palladium is able to form d8 and d10 complexes as well as d6 complexes.

Palladium catalysts facilitate unique transformations that cannot be readily achieved using

classical techniques, and in many cases palladium-catalyzed reactions proceed under mild

reaction conditions and nearly every area of organic synthesis has been impacted by this

novel transition metal. Therefore, it has become one of the most extensively studied metals

in organometallic chemistry, in the syntheses of natural products, agrochemicals polymers,

and pharmaceuticals. In fact there is a large number of famous reactions those employ this

metal, mainly including many type of C-C, C-N, C-O and C-S coupling reactions,

hydrogenation, hydrogenolysis, carbonylation and even cycloisomerization, as well as the

Wacker process (the oxidation of ethylene to acetaldehyde catalysed by PdCl2 and CuCl2)[45],

and the Tsuji-Trost allylation Scheme 1.3 and 1.4 respectively .[10-46]

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8

Scheme 1.3 : Wacker process[45]

Scheme 1.4: Tsuji-Trost process[46]

A large number of chemical reactions are facilitated by catalysis with palladium compounds.

Therefore, the most important properties of palladium which make it suitable metal for

catalytic reactions are:

a) Because palladium has moderate size; palladium complexes are often relatively stable.

b) Palladium primarily exists in the 0, +2 oxidation states (the most common), that plays an

important role in the oxidation and reduction operations in any kind of catalytic cycles.

c) Much easily accessible HOMO and LUMO orbitals enable participation in a range of

concerted processes with low activation energies.

d) Its complexes behavior can be adjusted easily through changing the electronic and steric

nature of ligands which coordinated to the metal centre.

e) Finally, the general lack of toxicity, high tolerance to different functional groups and ease

of handling make palladium catalysis a useful tool for modern organic chemistry.[7,49]

1.4 Palladium Catalyzed Cross Coupling Reactions.

The process of the formation a new bond between two carbon or carbon-hetero atoms have

been widely used in synthetic organic chemistry and extensively developed. One of the most

important examples of these processes is Palladium-catalyzed cross-coupling reactions. In

general, cross coupling can be simply defined as a reaction of an organometallic reagent R'-

M, such as boronic acids,[36,40,53,55] organostannanes[37,55-56,66], organosiloxanes[58,59],

organozinc,[60-63] and Grignard reagents[64,65] (where R' = alkyl, alkenyl, alkynyl, aryl), with an

organic compound X-R (R = alkyl, alkenyl, alkynyl, aryl; X = bromide, iodide, and common


9

X-R M-R'+

X-M R-R'+

Pd

halogen-like or pseudo-halide groups including trifluoromethanesulfonate) resulting in the

generation of new C–C or C-hetero atom bond present in the product R-R' (Figure 1.3).[10-66]

Figure 1.3: The principle of cross coupling reaction.

Some applications have been extended to the industrial scale to facilitate the formation of a

large variety of organic molecules. The suitable solvents for many type of the cross coupling

reactions are often polar aprotic ones such as dimethylformamide, acetonitrile, toluene,

tetrahydrofuran and 1,4-dioxane as well as water, because they allow for best solubility of

both, the substrates and the catalyst. This helps to achieve high conversions in short periods

of time and mild conditions with higher selectivities. Over the last few decades, the

pioneering work in the field of palladium-catalysed cross coupling reactions was carried out

by a huge number of studies, and there are a number of well-known name cross coupling

reactions which the most common ones are shown in table 1.1. and figure 1.5. Moreover,

since their discovery in the 1970s it has represented a very interesting topic of research, and

at the same time, many research groups started to tackle the lack of functional group

tolerability by investigating different metals including Nickel and Palladium.


10

Table 1.1: Types of the cross coupling reaction

Cross coupling reaction Discovery year

Kumada coupling 1972

Heck coupling 1972

Sonogashira coupling 1975

Negishi coupling 1977

Stille cross coupling 1978

Suzuki coupling 1979

Hiyama coupling 1988

Buchwald-Hartwig coupling 1994

In Pd-catalyzed C–C cross-coupling reactions, organometallics based on various metals have

been studied in details during the last few decades. These metals include magnesium, boron

(Suzuki-Miyaura coupling), [36, 40, 53, 55] tin (Stille coupling),[37, 55, 66] zinc (Negishi coupling)[60-

63], copper (Sonogashira-Hagihara coupling)[66, 67] and silicon (Hiyama coupling)[70-72] among

others[68-69,73-76]. The starting point of cross coupling process was reported independently by

two groups in 1972[77], and was named after Makoto Kumada, they reported the reaction of

a Grignard reagent (phenylmagnesium bromide 1) with alkenyl or aryl halides (such as vinyl

chloride 2) to form the coupled product (styrene 3) which catalyzed by a Ni-phosphine

complex (Scheme 1.5). In 1972, Corriu reported that the reaction of β-bromostyrene 4 with

phenylmagnesium bromide 1 proceeded neatly to form trans-stilbene 5 also with nickel

catalysts (Scheme 1.6). [78]

Scheme 1.5 : Kumada Coupling[77]

Scheme 1.6: Corriu Coupling [78]

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Recently, attention moved from the well-known formation of C-C or C-H bonds to the most

suitable formation of C-N or C-O functional groups as well as certain difficult reactions in

classical syntheses, e.g. the formation of a new chemical bond between unsaturated carbon

centers, can be carried out easily using novel cross-coupling reactions promoted by

transition metal. A general scheme of a transition metal-catalyzed cross coupling reactions is

shown in figure 1.5.[36-76]

Figure 1.5: Major cross coupling reactions.

A general catalytic cycle for the cross-coupling reaction of organometallics, which involves

three main processes: oxidative addition, transmetallation and reductive elimination

sequences, is depicted in Figure 1.6. It is significant that the great majority of cross-coupling

reactions catalyzed by nickel and palladium are rationalized in terms of this common

catalytic cycle. A transition metal (M, usually palladium) with a certain oxidation number


12

initiates a cross coupling reaction and usually this is achieved in a dissociative approach. In

general, the fundamental reactions of the catalytic cycle can be described as follows by four

sequential steps. In the first step, the transition metal inserts into the R–X bond while

breaking the bond connecting them (the reactivity order of aryl halides and triflates (I > OTf

> Br >> Cl), follows the bond strength of the C–X bonds to be broken.[85] With respect to the

organic halide, this step becomes faster with decreasing C–X (X = I, Br, Cl) bond dissociation

energy DE (DECCl > DECBr > DECCI). Since the oxidation number of transition metal M will

increase by 2, this step is referred to as oxidative addition (basically defined as the typical

reaction of transition metal complexes, in which the formal oxidation state of the metal is

increased after the reaction of the complex with a substrate molecule).

The intermediate from the oxidative addition step then goes through the next step which is

called transmetallation (basically known as the transfer of an organic group from one metal

centre (mostly a main group metal) to another (mostly a transition metal)), where a ligand

exchange takes place with the R2 group, then replacing the halide X. A byproduct, salt MX, is

produced in this step. Next, given a characteristic square planar configuration of M, a trans-

cis isomerisation step must occur before the formation of a new C–C bond to permit the

following step; reductive elimination. Reductive elimination can be considered to be the

reverse process to oxidative addition. During this step, the final cross coupling product R1-R2

is released and the transition metal catalyst M is regenerated with the oxidation number as

same as of the M at the beginning of the catalyst cycle, which allows further catalytic cycle

processes.

Furthermore, the properties of the palladium catalysts can be modified by changing the

ligands. Numerous applications appear every year applying novel ligands for catalytic active

transition metal complexes. One of the most important types of ligands become more and

more popular with researchers namely phosphine, amine and carbene ligands which are

used to tune the catalysts. In addition, special modifications in the substtituents in the

ligand design can provide fine tuning of the catalysts.


13

Figure 1.6: Mechanism of a cross coupling reaction.

1.5. Palladium Catalyzed Suzuki-Miyaura Cross-Coupling Reaction.

The cross coupling of organic halides (act as electrophiles) with organoboron compounds

(act as nucleophiles) is indeed useful in synthetic chemistry. These compounds are very

susceptible to undergo transmetallation, usually if a base is present, with many different

metals (silver, magnesium, zinc, aluminum, tin, copper, mercury). Transmetallation with

palladium complexes and subsequent reductive elimination affords a very useful generalized

cross coupling method. Organoboron compounds are readily available and several

advantages can be attributed to the popularity of this reaction in organic synthesis. Boronic

derivatives are widely available, easy to handle (can be stored indefinitely), and exhibit high

functional group tolerance. Furthermore, excellent reactivity and chemo selectivity have

been achieved under mild reaction conditions with a wide range of substrates as well as the

products are non-toxic. This reaction has been given the name of the 'Suzuki cross coupling

reaction' [36, 40, 53, 55, 84] (Scheme 1.7).


14

Scheme 1.7: Suzuki cross coupling reaction. [36, 40, 53, 55, 84]

This process can be simply defined as a cross-coupling reaction between organoboron

compounds 6 and organic electrophiles, such as aryl or alkenyl halides 7 (where R can be

many functional groups including hydrogen, alkyl, alkenyl, alkynyl, or aryl groups and X = I,

Br or Cl) in the presence of a certain amount of a base (to facilitate the reduction of

palladium and also aid in the transmetallation step of the catalytic cycle and normally,

mineral bases such as alkali metal carbonates are used) to get the coupling product 8,

scheme 1.7. The active catalyst is often a palladium(0) source; however, the precatalyst can

also be a palladium(II) source (such as catalysts formed from triarylphosphine and Pd(II)

precursor) which is reduced under catalytic conditions. Furthermore, Suzuki-Miyaura cross-

coupling reactions generally use organic solvents such as toluene, tetrahydrofuran, 1,4-

dioxane and diethyl ether in the presence of Pd(II) or Pd(0) catalyst which are soluble in

these solvents. Subsequently a lot of papers were published, where different solvent

mixtures were used for the reactions such as acetonitrile/water, 1,4-dioxane/water and

DMF/water mixtures. [53, 55, 85] The use of water either as a solvent or additive helps with the

solvation of the organic insoluble materials.

The typical Suzuki cross coupling catalytic cycle which involves three main steps: oxidative

addition, transmetallation and reductive elimination, is depicted in figure 1.8. In the first

step, the Palladium catalyst A (LnPd0) inserts into the Ar1–X bond B, while breaking the bond

connecting them; to form the organopalladium species C (LnPdIIAr1X). Since the oxidation

number of palladium metal will increase by 2, this step is referred as oxidative addition. In

the next step the halide ion is displaced from the organopalladium species C (LnPdIIAr1X) by

the suitable base D (the role of the base is to form a more electron-rich intermediate with

the boronic acid H resulting in a more reactive than the original boronic acid G (Ar2BY2)

towards attack of the palladium(II) complexes making the transmetallation step easier to

give the more reactive species F (LnPdIIAr1OR). This step is followed by transmetallation of

the electron-rich intermediate F (LnPdIIAr1OR) with the boronic acid H to provide the

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15

diarylpalladium species J (LnPdII(Ar1)(Ar2)). Reductive elimination of this intermediate leads

to formation of a carbon-carbon single bond between the two different aryl groups Ar1-Ar2

(coupling product K) and the palladium catalyst A (LnPd0) is regenerated for the next

catalytic cycle.[80]

In general, in the most cross-coupling reactions, the oxidative addition of an aryl halide to a

low coordinated Pd(0) complex is followed by relatively fast transmetallation and reductive

elimination. Accordingly, transmetallation adducts have only been isolated when reductive

elimination was impossible.

Figure 1.8: General catalytic cycle for Suzuki-Miyaura coupling.

At the beginning of the development of this process, most reports involved the usage of aryl

bromides, aryl iodides, and electron-deficient aryl chlorides. On the other hand, prior to

1998, there was no report of an effective catalyst system for palladium catalyzed Suzuki-

Miyaura reactions of electro-neutral or electron-rich aryl chlorides. Recently there has been

renewed research interest in the development of efficient catalytic system for Suzuki

coupling process. The use of cheap aryl chlorides in transformations has received increasing

attention, and a lot of effective catalytic systems have been developed to achieve this

http://en.wikipedia.org/wiki/Reductive_elimination


16

purpose. In most cases, these systems have been designed to facilitate one or more steps in

the catalytic cycle.[80-83]

1.5.1 Phosphorous Ligands in Suzuki-Miyaura Cross-Coupling Reaction.

1.5.1.1 Trialkylphosphines.

In palladium-catalyzed cross coupling reactions, ligand plays a key rule in modulation and

improvement of the given catalytic capacity of the metal. Especially phosphines were found

to impart highly beneficial properties onto palladium such as stability, electron-richness and

steric shielding of the complexes, which are now known to be the most important

properties of high activity catalysts. Triarylphosphines (such as PPh3) were the principal

ligands during the early years of cross coupling chemistry [41, 87]. However, the development

of new phosphine ligands, whose palladium complexes enable the facile activation of

difficult substrates such as aryl chlorides, initiated vigorous research, which has now led to a

huge number of powerful and more specialized ligands with different abilities in various

coupling reactions.

The first significant breakthrough has discovered in 1997 by Shen when he reported that

palladium complexes of bulky electron rich phosphines PdCl2(PCy3)2 catalyzed the coupling

reaction of several activated chloroarenes 7a with phenylboronic acid 6I to get 8a in

moderate to good yield in presence of CsF as a base (Scheme 1.8).[80-83, 86]

Scheme 1.8: Suzuki coupling of aryl chloride.

Traditionally, triphenyphosphine (PPh3) 9 ligand was one of the first ligands used for the

earliest catalytic precursors in cross-coupling reactions, practically in Suzuki and Heck. [41, 87]


17

when this ligand is used in sterically demanding couplings the chemical yield is low, if

successfully forming the coupling product at all. Indeed, this pre-catalyst with

triphenylphosphine as the ligand was use in most coupling protocols until the mid 1990’s

when several groups have established that other ligands show better results. In 1997, Shen

and co-worker showed that mixture of P(Cy)3 10 (Scheme 1.9) and palladium precursor

could activate aryl chlorides in Suzuki cross coupling reaction[80-83, 86]. One year later,

another sterically demanding and electron rich trialkylphosphine, P(tBu)3 11 (Scheme 1.9),

was used for the first time by Fu and Littke. They reported that a mixture contained P(tBu)3

11 and [Pd2(dba)3] (dba = dibenzylideneacetone) was highly active as a catalyst for Suzuki

cross coupling reaction of arylboronic acids (substrates 6I, 6II or 6III) and a broad

spectrum of aryl bromides (Table 1.2; substrates 7b, 7c and 7d), aryl iodide (Table 1.3,

substrates 7e, 7f and 7g), and aryl chlorides (Table 1.4, substrates 7h, 7i and 7j), in very

good yield, typically at room temperature. The high activity of P(tBu)3 was attributed to the

electron-rich nature and the steric bulk of the ligand. [82] Moreover, through use of

Pd(OAc)2/PCy3, a diverse array of aryl and vinyl triflates react cleanly at room temperature

too (Table 1.5, substrates 7k, 7l and 7m).[42, 53, 63, 82, 83, 89, 90]

Scheme 1.9: Common phosphines for Suzuki cross coupling reaction.


18

Table 1.2: Suzuki cross-couplings of aryl bromides by Fu.[83, 82, 89, 90]

Table 1.3: Suzuki cross-couplings of aryl iodides by Fu. [83, 82, 89, 90]


19

Table 1.4: Suzuki cross-couplings of aryl chlorides by Fu. [83, 82, 89, 90]

Table 1.5: Suzuki cross-couplings of aryl triflates by Fu. [83, 82, 89, 90]


20

Fu and Littke also discovered that the sterically hindered aryl chlorides (7h, Table 1.4) can

react efficiently with mono, di, or tri-substituted arylboronic acids (such as 6III, Table 1.4)

to form the hindered biaryls (8e, Table 1.4 with excellent yields at 60–90°C using a

Pd2(dba)3/P(t-Bu)3 or Pd2(dba)3/PCy3 catalyst system). [90, 91, 92] More recently, a great

attention has focused on the use of electron rich and bulky ligands that improve the

catalytic activity of palladium complexes in coupling reactions. That helps a lot to make the

palladium complexes more able to activate the strong C-Cl bond. Together, these catalyst

systems cover a broad spectrum of commonly encountered substrates for Suzuki couplings.

In spite of these phosphine ligand have a positive influence on the stability and catalytic

activity of palladium, because it increase the electron density on the metal which will

increase the rate of the oxidative addition, they are oxidativly sensitive, often toxic,

unrecoverable, and can disturb the isolation and purification of the products formed. On the

other hand, P(iPr)3 12 as well as tricyclopentylphosphine 13 (Scheme 1.9) those are sterically

and electronically similar to P(Cy)3 10 were found to be poor in the Suzuki-Miyaura reaction

of alkyl chlorides.[89] In 2000, Beller et al. have described an easy way for preparing a new

class of bulky and electron rich phosphines ligand, namely diadamantyl-n-butyl phosphine

14 [93, 94, 95], and they have reported that this bulky and electron rich ligand when conjugated

with Pd(OAc)2; acts as an effective catalysts system for Suzuki cross coupling reactions of

broad spectrum of aryl bromides and chlorides with excellent yields, table 1.6.[93, 94]

Table 1.6: Suzuki cross-couplings of different aryl chlorides with phenylboronic 6I acid by

Beller ligand 14.[93, 94]


21

Moreover, Shaughnessy and co-worker have reported recently that di-tbutyl(neopentyl)

phosphine 15, tbutyl-di(neopentyl)phosphine 16 or trineopentyl phosphine 17 (Scheme

1.10) in conjunction with Pd2(dba)3 acts as an effective catalyst system for Suzuki cross

coupling reactions of aryl bromides and chlorides (Table 1.7).[4]

Of the most important properties of these phosphines ligands are; di-tbutyl(neopentyl)

phosphine (DTBNpP) 15, like tbutyl-di(neopentyl)phosphine (TBPDNp) 16, is pyrophoric in

pure form and highly air-sensitive, for example, after exposure of di-tbutyl(neopentyl)

phosphine (DTBNpP) to air for 3h, 75% of DTBNpP had been oxidized (by 1H NMR

spectroscopy). After 6 h, nearly 90% had been oxidized, while no DTBNpP was present after

exposure to air for 30 h, tbutyl-di(neopentyl)phosphine (TBPDNp) showed a similar,

although slower, rate of decomposition upon exposure to air. After 3 h only 56% of the

phosphine remained, while 28% remained after 30 h. In contrast, TNpP is quite stable in air,

a pure sample of TNpP when exposed to air for 9 days, the percentage of TNpP in the

sample have remained essentially unchanged.

Scheme 1.10: Common phosphines for Suzuki cross coupling reaction by Shaughnessy et al.


22

Table 1.7: Suzuki cross-couplings of aryl halides with phenylboronic 6I acid by Shaughnessy

ligands 15, 16 and 17.[4]

Finally, there are many factors responsible for the widespread use of the trialkylphosphine

ligands by researchers over the past years in this area of chemistry (cross coupling

reactions), including:

a) Their electron-rich nature: the electron donating ligands increase the electron

density in the metal complex; which will generate an electron-rich metal complex

and undergoes faster oxidative addition reaction, which is the rate determination

step in many cross coupling reactions, particularly with less reactive bromide and

chloride substrates. In addition, with bulky alkylphosphines (such as P(t-Bu)3), the

mechanism of oxidative addition to L2Pd species proceeded cleanly toward stable

three coordinate species LPd(Ar)X (where X = Br), rather than either four coordinate

L2Pd(Ar)X in the case of PPh3 or dimeric [LPd(Ar)X]2 complexes in the case of P(o-

Tol)3.[96, 97]

b) Their steric bulk which plays a key role in the rate of reductive elimination.


23

1.5.1.2 Biaryl Based Phosphine Ligands.

In general, biaryls are the results of two aryl groups joined together by an sp2-sp2 carbon

bond. When the positions ortho to this bond are occupied by large substituents, free

rotation around the axis may be limitid and the biaryl system is locked into a specific

conformation. In the case that these orto substituents are different, two stereoisomers are

possible. In this way X and Y are enantiomers. This steroisomerism is known as

atropisomerism, where X and Y are known as atropisomers which was introduced by Kuhn in

1920's, has a roots in a Greek language ''a'' meaning ''not'' and ''tropos'' meaning ''turn''

(Scheme 1.11). One of the most important biaryl systems are biaryl based phosphine.

According to the literature, several strategies have been developed to synthesis (biaryl

backbone) phosphine ligands. They play a prominent role in modern transition metal

catalysts, for enantioselective catalysis. In addition, biaryl backbones are very interesting

due to the chiral atropisomerism inherent to the molecule (Scheme 1.11). This has led to the

development of the stereoselective synthetic methodologies for their preparation. [98, 99]

Scheme 1.11: Atropisomerism of biaryl and biphenyl diphosphines.

Most prominent derivative of the Biaryl phosphine ligands is 2,2’-Bis(diphenylphosphino)-

1,1’-binaphthyl (BINAP) 18 (Scheme 1.12), firstly synthesized by Noyori and coworkers[101]

Noyori was not only encouraged to the synthesis of BINAP by the fascinating applications in


24

asymmetric chemistry [101] but was also inspired by “its molecular beauty” due to the high

symmetry.[102] Nowadays hundreds of derivatives have been synthesized [106, 107] and

numerous publication appear every year using biarylbackbone phosphines as ligands for

catalytic active transition metal complexes. On of the one important examples of the use of

these biaryl phosphine is Suzuki cross coupling process of a wide range of aryl halides which

was brought about by Buchwald's development of dialkyl(biphenyl)phosphine ligands 19,

20, 21, 22, 23, 24, 25, 26, 27, 28 and 29 (Scheme 1.13) which started from the work on the

BINAP ligand 18. Buchwald and co-workers demonstrated that catalyst system generated

from these biarylbackbone phosphine ligands and Pd(OAc)2 or Pd(dba)2 are highly useful for

carbon-carbon bond forming reactions with aryl halides including the Sonogashira, Negishi,

Hiyama, Kumada, Suzuki and Heck reaction.[101, 102, 103-134, 141]

The outstanding catalytic performance of these ligands in conjunction with a palladium

source has been attributed to a combination of both electronic properties, which facilitates

the oxidative addition, and steric hindrance, which favours the reductive elimination steps

in the catalytic cycle. For example, ligand 19, 20, and 24 were successfully employed in the

Suzuki coupling of activated aryl bromides and chlorides as well as sterically hindered and

electron-rich ones in which all the reactions proceeded at room temperature (or other

mentioned temperature) to give the cross coupling products in good yield (Table 1.8). [126,

141]

Scheme 1.12: 2,2’-Bis(diphenylphosphino)-1,1’-binaphthyl (BINAP).


25

Scheme 1.13: Common dialkyl(biphenyl)phosphines for cross coupling reactions.


26

Table 1.8: Suzuki cross-couplings of aryl halides by Buchwald. [126]

Of the most important properties that singled out these types of phosphine biaryl backbone

ligands, in addition to its high performance in cross coupling reactions, are:

(a) Air and thermal stable ligands.

(b) Crystalline materials.

(c) Many of these ligands are commercially available.


27

(e) The second ring in some of them could coordinate to a palladium centre and this should

facilitate reductive elimination.

(f) The processes that yield these ligands are operationally simple, not requiring the use of a

glove box, for example, ligands 20 and 21 were synthesised starting from substituted aryl

halides 2-bromoaniline 30, scheme 1.14. Reductive alkylation to get 2-bromo(N,N-

dimethylamino)benzene 31, then metal-halogen exchange using n-butyllithium followed by

quenching with triisopropyl borate gave the boronate ester which was hydrolyzed during

work up to get the arylboronic acid 32 which by Suzuki cross coupling with 2-

bromoiodobenzene 33 in presence of tetrakis- (triphenylphosphine)palladium(0) biphenyl;

34 was obtained. Once again metal-halogen exchange with n-butyllithium followed by

quenching with P(tBu)2Cl to yield 20 or with P(Cy)2Cl to give 21 (Scheme 1.14). [63, 74, 92, 91,

135,136]

Scheme 1.14: Synthesis of biaryl backbone phosphines by Buchwald.

Another strategy that has been mentioned in numerous publications over the past two

decades is the synthesis of biarylbackbone bisphosphine ligands and their applications as

ligands for catalytic active transition metal complexes. In 1980's, the groups of Shmid and

Frejd have independently reported the preparation of a new class of biarylbackbone

bisphosphine 38 starting from 6-methyl-2-nitroaniline 35 followed by diazotization-

iodination, Ullman coupling and catalytic hydrogenation to afford 36, and then the diamine

was converted by Sandmeyer reaction into dibromide 37. Dilithination of 37 followed by the


28

reaction with PPh2Cl afforded 38 (Scheme 1.15).[137] While the dialkylbiaryl phosphine 39 has

been reported by Takaya in 1989 by the same way.[138] Few years later, Jenedralla have

described the first example of an electron poor diphenylbiaryl phosphine ligand 40 (Scheme

1.16). Moreover, similar electron deficient biaryl phosphine 41 (Scheme 1.16), was also

reported by Achiwa and co-worker in 1991, and many of these ligands 38-41 have been

applied in asymmetric chemistry, such as asymmetric hydrogenations and asymmetric

isomerisation. [139, 140]

Scheme 1.15: Synthesis of 2,2'-diphosphanesbiaryl.

Scheme 1.16: 2,2'-diphosphanesbiaryl by Takaya and Achiwa.


29

1.5.1.3 Palladacycles in Suzuki Cross Coupling Reaction.

The oxidative addition of metals to carbon-hydrogen bonds has been studied extensively

over the last five decades and have represented a very interesting topic of research.

Organometallic compounds are often highly reactive compounds because they have an

unstable metal–carbon bond. However, organometallic intramolecular compounds with

organic rings that form chelates are comparatively stable. In other word, transition metal

complexes of a polydentate ligand are more stable than those containing an equivalent

number of monodentate ligands containing the same donor atoms. This is particularly true

in the case of complexes with multidentate ligands in which one or more of the donor atoms

is carbon. Such complexes represent the interface between classical coordination chemistry

and organometallic chemistry, and usually described as cyclometallated, orthometallated or

organometallic intramolecular coordination compounds.[53, 82, 93, 142, 143, 144, 148] Often

cyclometallation lead to organometallic compounds by the formation of a new chelating

ligand (Scheme 1.17).

Scheme 1.17: Structural definition of cyclometallation.

According to the literature, these compounds can be divided into different classes based on

the organic fragment: the two common ones are four-electron (X') and six-electron

donor(Y').[144]

Metallacycles ( M = Pd or Pt ) of type X' often exist as acetate or halogen bridged dimmer as

two geometric isomers, namely cisoid A and transoid B conformers. [144, 145]


30

These compounds can be synthesized in a very facile manner, making it possible to

modulate both their steric and electronic properties which play a key role in organic

synthesis. Moreover, they have been used as mesogenic, photoluminescent agents as well

as biological applications for cancer treatment and as catalyst precursor for palladium

catalyzed cross coupling reactions. [149, 150 - 157] In 1963 Kleinman and Dubeck reported the

first example of these compounds, when they reacted azobenzene 42 with NiCp2 to obtain a

five - membered metallacycle 43 (Scheme 1.18). In addition, by the reaction of 42 with

palladium chloride, the dimmer 44 is formed, which was reported by Cope and co-

worker.[158] In 1995, Beller, Hermann and co-workers reported that palladium acetate 46 can

be treated with the sterically demanding tri-o-tolyl-phosphine P(o-tol)3 45 in toluene to give

the yellow, air and moisture stable cyclometallated complex 47 (trans-di(µ -acetato)-bis[ di-

o-tolylphosphino)benzyl]diPalladium) by the C-H activation of one ortho-methyl group in

P(o-tol)3 (Scheme 1.19).[147]

Scheme 1.18: The first cyclometallated compound by Kleimann, Dubeck and Cope.[158]


31

In addition, analogue complexes using P(Mes)3 or PR2(o-tolyl) with R = tBu 48, Cy and Ph as

ligand could be obtained likewise.

Interestingly, Palladacycle 47 was the initial Palladacycle used in the Suzuki cross coupling

reaction for the coupling of aryl bromides and chlorides.[147, 159]

Scheme 1.19: Formation of trans-di(µ-acetato)-bis[di-o-tolylphosphino)benzyl]diPalladium

by Hermann and co-workers. [159]

Also, Bedford et al. have shown that 49 an orthocyclopalladated complex of the ligand di-

iPropyl-2,4-di-tButylphosphate (Scheme 1.20), which can be prepared by the direct reaction

of di-iPropyl-2,4-di-tButylphosphate with PdCl2, and found that this complex was a very

active precursor in Suzuki cross coupling reactions of aryl bromides (with both electronically

activated and deactivated) and chlorides with phenylboronic acid, extremely high turnover

numbers of up 1*106 and turnover frequencies of approximately 9*105 were observed

(Table 1.9). [159]

Scheme 1.20: Ortho-metallated palladium complexes by Bedford and co-workers. [146, 159, 160,]

Also, Bedford and co-workers prepared the ortho-metallated Pd(II)-triarylphosphite complex

50 , which proved to be an extremely active catalyst for Suzuki cross-coupling reaction .[146,

159, 160, 163]


32

Table 1.9: Suzuki cross-couplings of aryl halides by Herrmann. [159, 162]

Interestingly, Herrmann and co-worker reported that there is no doubt about the reduction

mechanism of Palladacycle 47 toward Pd(0) species via Suzuki cross coupling. In other hand,

Hartwig et al. found a suitable mechanism, in the amination reaction, for the formation of

Pd(0) species by reduction of Palladacycle 47 in presence of secondary amine HNEt2 to form

the monometallic amine complex 51, which is crystalline material and could be isolated

easily (Scheme 1.21). [163, 164, 165]

Scheme 1.21: Postulated mechanism for the formation of the catalytically active species

[Pd{P(o-Tol)3}2] during the amination reaction by Hartwig et al. [164, 165]


33

Moreover, they suggested, by low temperature NMR studied and crystal structure

determination, compound 51 exhibiting strong hydrogen bonding between the acetic acid

carbonyl oxygen and amine NH proton which was confirmed in the crystal structure and by

IR data. Then amine complex 51 is deprotonated by base such as NaOtBu and generate a

Pd(II) species 52, followed by β-H elimination to generate compound 53 which undergo

reductive elimination to generate [Pd{P(o-Tol)3}2] 55 in about 50% yield based on the

number of phosphines (Scheme 1.21).[164, 165]

Intramolecular oxidative addition to ortho-carbon-hydrogen bonds of tertiary phosphine

ligands was particularly well documented for aromatic or benzylic carbon atoms, but a few

structural characterizations have been reported where a purely aliphatic chain has been

metallated. In 1976 Shaw reported that few complexes of platinum(II) of type trans [PtX2L2],

(where X = halogen and L = bulky aliphatic phosphines ligand) undergo cyclometallation to

give complex of type [PtX(P-C)L], where (P-C) = cyclometallated tertiary phosphines, by

sometimes very slowly compared with the cyclometallation process by aryl bulky

phosphines (Scheme 1.22).[166] Shaw reported that the treatment of [PtCl2(NCtBu)2] with di-

tbutyl(ibutyl)phosphine (1 : 1 mol per platinum atom) in boiling 2-methoxyethanol gave after

a few hours, a white cyclometallated complex 56 (where X = Cl) in excellent yield (Scheme

1.22). In addition, he reported the corresponding iodide, bromide and acetylacetonate

complexes by the same way, and the 31P (1H} NMR spectrum of this complex showed a

central singlet at 68.7 ppm with two sets of 195Pt satellites, with 1J(Pt-P) 5042 and 5117 Hz

respectively.[166] Moreover, Shaw have shown that the treatment of chlorobridged complex

56 with either PtBu2iBu or PPh3, the bridged split mononuclear complexes 57 were obtained

(Scheme 1.22).

Scheme 1.22: Cylometallated platinum complexes by Shaw et al. [166]


34

A few years later, Clark and Goel have reported that cyclometallated complex 58 can be

prepared by the direct reaction of P(tBu)3 with [K2PdCl4] in N,N-dimethylformamide or with

(PhCN)2PdCl2 in dichloromethane.[167] In 1980's Kraus and co-worker, have showed that

reaction of complex 58 with TlC5H5, in benzene occurred with chloride-bridge cleavage to

give the cyclopentadienyl complex 59 and analogously, treatment of 58 with LiC5Me5

produced the pentamethylcyclopentadienyl complex 60 ( Scheme 1.23).

Scheme 1.23: Cylometallated palladium complexes by Kraus et al. [167]

In 1987, Simms and Ibers reported that when the ditbutylcyclobutylmethylphosphine is

combined with Zeise's salt (K[PtCl3(C2H4)]) in presence of LiBr in ethanol and heated at reflux

for several hours, the cyclometallated platinum complex 61 formed.[168] In 2005, the

reactivity of 62 as a catalyst for the arylation of the α-silyl nitrile have been tested by

Hartwig and co-worker. They found that the reaction of p-tert-butylbromobenzene with

trimethylsilyl acetonitrile in the presence of 2 mol % of complex 62 was much slower than

the reaction initiated with Pd(OAc)2 and PtBu3 in a 1:2 ratio (Scheme 1.24).[169]

Scheme 1.24: Cylometallated palladium and platinum complexes 61-63. [168-169]


35

Recently, in 2010 some reactions of 63 with various anionic ligands have been investigated

by Dey and Jain, but without mentioning that if it have had applications or not.[169]

Finally, in most of the previous studies concerning cyclometallation process, we noted that

there is no publication almost usage of these complexes (i.e.cyclometallated complexes via

purely aliphatic phosphines) as a catalyst in cross coupling reactions. Therefore, we should

mention here that a part of this thesis started from this point; to find out what is the

effectiveness of such complexes as catalysts.

Chapter 2: Results and Discussion

36

Chapter

2

2. Results and Discussion.

2.1 Synthesis, Characterization and Applications of Trialkyl Monophosphine Ligands

in Palladium Catalyzed Cross Coupling Reactions.

2.1.1 Synthesis and Characterization of Substituted Neopentyl and Neosilyl

Phosphine Ligands and their Phosphonium salts.

One of the most applied methods for the synthesis of tertiary phosphines is the reaction of

halogenophosphine as an electrophilic phosphorus reagent with an excess of Grignard or

organolithium reagent. We used Gringard or organolithium reagents 2 which have been

prepared from organic halides 1a or 1b (which are commercially available) as sources of the

neopentyl or neosilyl sub – skeleton to the overall organic architectural backbone of the

phosphine ligands 3a-h (Scheme 2.1).


37

Scheme 2.1: Synthesis of substituted neopentyl and neosilyl phosphines.

According to generally accepted theory, the generation of organomagnesium and organo-

lithium compounds takes place according to a simple mechanism, whereby an anion radical

[R.-X]-, resulting from a single electron transfer from a metal (Mg or Li) to an organohalide

(R-X), which is present on the metal surface before the formation of organomagnesium or

organolithium compound. This anion radical will then evolve into a familiar pair of radicals,

R-MgX or R-Li, to yield the organomagnesium and organolithium compounds, respectively

(Scheme 2.2). [180, 181]

Scheme 2.2: The mechanism of organomagnesium and organolithium compounds

generation.

Although Gringard and organolithium reagents were found brought use in organic

syntheses, not all organohalides are easily convertible into Gringard or organolithium

reagents. Complications are caused by the sensitivity of such reagents toward oxygen and

mosture, inactivation of the metal surface and side reactions (homocoupling, reduction or

elemination).


38

In our attempted preparations, just phosphine 3a was prepared according to the published

procedure by adding the diisopropylphosphinechloride to an excess of the Grignard reagent

in ether. However, organolithiums may be more reactive as a result of the more ionic and

hence more polar nature of the C-Li bond than the C-Mg bond in the corresponding

Grignard reagent.[183] In particular, the use of the more reactive organolithium reagent was

applied in the synthesis of sterically hindered phosphines too, such as di-tertbutyl

(diphenyl)methylphosphine as well as tri-tert-butylphosphine.[182]

The preparation of 2a and 2b was first attempted by modified a method to speed up the

grinding of lithium\sodium pieces. It is obvious that the teflon stirring bar used for

pulverization is relatively light, its surface is very smooth and therefore barely scores the

lithium\sodium pieces. We added glass splinters from fragmented pipettes to the pieces

before stirring. Stirring overnight is satisfactory to give a charcoal-colored mixture of

powder and pieces of reduced size; to increase the reactive surface. This modification alone

only gave reasonable yield for 2b. The formation of 2a and 2b was judged by reacting it with

an aliquot of P(tBu)2Cl and recording 31P{1H} NMR data of the crude mixture. In addition,

integral intensities of the signals were also noted from the 1H NMR spectra.

However, the yield of organolithium reagent 2a has been considerably improved by the

application of lithium doped with 4% sodium according to the literature.[180, 181] The success

of this modification prompted us to use the doped lithium also for the preparation of 2b

which has been obtained in considerable improved yields. Reaction of organolithium

reagents with the phosphinechlorides occurred smoothly in ether or hexane at ambient

temperature. The success of this synthetic method was further evident from the yield of 62-

78% after work-up. All phosphines were unstable with respect to atmospheric oxidation but

could be isolated as thermally stable colorless oils or white solids. In the case of preparation

of phosphine 3d; the product was noted to display an observable but insignificant level of

instability after the process of work-up, by the appearance of weak and unidentified peaks

(from 31P{1H} NMR data) of side-products previously not observed in the crude mixture.

The rapid oxidation of phosphines 3 made the work up and handling difficult especially in

small scale synthesis. It occurred to us that a simple but powerful strategy for the handling


39

of these phosphines would be to protect them by converting them to air stable

phosphonium salts 4a-h. In addition, this strategy is easy to crystallize and store these

compounds which are in contrast to free phosphine not odorous and spontaneously

inflammable, moreover the low vapor pressure allows the handling of the toxic phosphine

on the bench top.[194 - 196]

Scheme 2.3: Synthesis of substituted neopentyl and neosilyl phosphonium salts.

These salts can be synthesized in quantitative yield simply by treating a solution of the

phosphine in CH2Cl2 with diluted HCl (3 eq. based on expected phosphine). Exchange of the

chloride with BF4-/PF6

- made the resulting salt extractable in organic solvents and non

hygroscopic. The organic layer was then separated from the aqueous layer, dried over

MgSO4, and filtered. Removal of the solvent provided the phosphonium salts as white solid,

which after recrystallization from CH2Cl2\diethyl ether (or pentane) gave an analytically pure

colorless crystal.

Neither 4a-f have shown any sign of deterioration after exposure to air for several months

(> 6 months) (31P, and 1H NMR; elemental analysis). Indeed, NMR spectroscopy reveals no

significant decomposition even after heating them in air at 100°C for more than 5h. In view

of the sensitivity of the free phosphines, the air-stability of these salts is particularly

remarkable. On the other hand, we haven't succeeded to get the phosphonium salts of

phosphine 3c and 3d, the reasons behind such limitations are most probably due to the

lower basicity.

A survey of the literature revealed a precedent for the use of a phosphonium salt as a

precursor to a phosphine reagent.[194-196] All of the synthesized phosphonium salts were

characterized by 1H, 13C, 31P{1H} NMR, IR, elemental analysis, mass spectroscopy as well as


40

melting point. For instance, in preparation of phosphonium salt 4e (R = tBu, R' = Neopentyl),

a good indication of the presence of the product was provided by the appearance of one

singlet at δ = 1.19 ppm for CH3 of neopentyl group, as well as a simple doublet of doublet

resonance representative of the CH2 protons in the 1H NMR spectrum at δ = 2.08 ppm, in

which the splitting pattern of the NMR resonance is a result of the spin – spin coupling with

the 31P{1H} nucleus over two bonds and with the proton at phosphorus atom with 2JPH

coupling constant of 10 Hz, and 3JHH = 5 Hz. In addition, one doublet appeared at δ = 1.49

ppm for the CH3 of tButyl group, also with spin-spin coupling with phosphorus atom (3JPH =

20 Hz). Finally, one doublet was appeared at δ = 6.17 ppm which belongs to the proton on

the phosphorus atom, with 1JPH coupling constant = 422 Hz. The magnitude of this coupling

constant is in agreement with those observed for the analogous phosphines [HPtBu3][BF4]

(465Hz. at 6.07 ppm).[194, 195, 196] Moreover, the 31P{1H} NMR spectrum of analytical pure

product revealed one singlet peak at δ = 29.38 ppm.

On the other hand, in preparation of phosphonium salt 4f (R = tBu, R' = Neosilyl), the 31P{1H}

NMR spectrum of analytically pure product revealed one singlet peak at δ = 38.27 ppm. In

addition, a good indication of the presence of product was provided by the appearance of

one singlet at δ = 0.3 ppm for CH3 of neosilyl group, as well as a simple doublet of doublet

resonance representative of the CH2 protons in the 1H NMR spectrum (δ = 1.87 ppm), in

which the splitting pattern of the NMR resonance is a result of the spin – spin coupling with

the 31P{1H} nucleus over two bonds and with proton on phosphorus atom with 2JPH coupling

constant = 13.3 Hz and 3JHH = 5.84 Hz. In addition, one doublet appearance at δ = 1.43 ppm

for the CH3 of tButyl group, also with spin-spin coupling with the phosphorus atom with a

3JPH coupling constant = 16.7 Hz. Finally, one doublet of triplet was appeared at δ = 5.95

ppm which belong to the proton on the phosphorus atom, with 1JPH coupling constant = 470

Hz.

All of the phosphonium salts showed good solubility in dichloromethane and

dimethylsulfoxid, on the other hand, they were insoluble in ether, hexane and slightly

soluble in chloroform.

Moreover, in preparation of phosphonium salt 4h (R = Cy, R' = Neopentyl), a good indication

of the presence of the product was provided by the appearance of one singlet at δ = 1.15

ppm for CH3 of neopentyl group, as well as a simple doublet of doublet resonance


41

representative of the CH2 protons in the 1H NMR spectrum at δ = 2.11 ppm, in which the

splitting pattern of the NMR resonance is a result of the spin – spin coupling with the 31P{1H}

nucleus over two bonds and with proton in phosphorus atom with coupling constant 2JPH =

11.8 Hz and 3JHH = 4.5 Hz. In addition, multiplets appearance in the range of δ = 1.3-2.48

ppm for the cyclohexyl group. Finally, one duplet of pentet was appeared at δ = 6.05 ppm

which belong to the proton on the phosphorus atom, with 1JPH

coupling constant = 469 Hz.

Moreover, the 31P{1H} NMR spectrum of analytically pure product revealed one singlet peak

at δ = 13.05 ppm.

2.1.2 Synthesis and Characterization of Substiuted iPropyl and tButyl Phosphonium

Salts.

In the second part of our investigation, we began to study the synthesis and behaviors of a

broad range of substituted iPropyl and tButyl phosphonium salts (4i-o); whereas they

undergo cyclometallation to form four or five membered palladacycles or the dimeric non-

cyclometallated palladium complexes (vide Libra). The preparation of substituted iPropyl

and tButyl phosphonium salts 4i-o were achieved by using the similar procedures described

for the preparation of phosphonium salts 4a-h (Scheme 2.1, 2.3 and 2.4).


42

Scheme 2.4: Substiuted iPropyl and tButyl phosphonium salts.

The 31P NMR spectra of the phosphonium salts each show one single resonance in the

region δ = -14.64 to 51.58 ppm and well removed from the chemical shift of the free

phosphine starting material. The 31P NMR spectroscopic data for new and known

phosphonium salts are shown in Table 2.1. In addition, treatment of the air stable

phosphonium salts with a suitable base led to the free phosphines. Advantageously, the

resulting phosphines were isolated without contamination by phosphine oxides or other

impurities.

All products described in Tables 2.1 were fully characterized by 1H, 13C, and 31P NMR, IR and

MS (most of them). Correct elemental analyses were obtained in case of the phosphonium

salts, but not for the free phosphines because of their oxygen sensitivity.


43

Table 2.1: 31P NMR data of phosphonium salts*

*: 4a (R = iPr, R' = Neopentyl); 4b (R =

iPr, R' = Neosilyl); 4e (R =

tBu, R' = Neopentyl), 4f (R =

tBu, R' = Neosilyl),

4g (R =, R' = Neopentyl), 4h (R = Cy, R' = Neopentyl), 4i (R = iPr, R' =

tBu), 4j (R =

tBu, R' =

iPr), 4k (R = R' =

tBu), 4l

(R = iPr, R' = CH(Et)2, 4m (R =

iPr, R' = CH2Cy), 4n (R =

tBu, R' = CH2Cy), and 4o (R =

iPr, R' =

iBu).

2.1.3 Synthesis and Characterization of Palladium Complexes.

2.1.3.1 Synthesis of Substituted Neopentyl and Neosilyl Palladium Complexes 5a-

5d.

Complexes 5a-5d were prepared by either reacting the corresponding phosphine ligand (3a,

3b, 3c and 3d) with Pd(cod)Cl2 in the ratio of 2:1 ligand to palladium (Scheme 2.5), or the

reaction of phosphonium salts (only for 4a (R = iPr, R' = Neopentyl) and 4b (R = iPr, R' =

Neosilyl)) with palladium acetate via a ligand to palladium ratio of 2:1 in presence of sodium

acetate, then the resulting mixture was washed with sodium chloride solution to afford the

palladium complexes (Scheme 2.6). All the new palladium dichloride complexes 5a, 5c, 5b

and 5d, were isolated as yellow solids in moderate to high yields. Moreover, these

complexes were characterized by 1H, 13C, 31P{1H} NMR, IR, elemental analysis, mass


44

spectroscopy as well as melting point. Complexes 5b and 5d were further characterized by

single crystal X-ray analysis.

Scheme 2.5: Synthesis of palladium complexes 5a, 5b, 5c and 5d via

free phosphine ligands 3a, 3b, 3c and 3d respectively.

Scheme 2.6: Synthesis of palladium complexes 5a and 5b via

phosphonium salts 4a and 4b respectively.

2.1.3.2 Characterization of the synthesized complexes 5a-5d. All of the synthesized complexes contain a plane of symmetry. Thus one would except the

interpretation of 1H NMR spectra to be simple. For example, 5a (R = iPr, R' = Neopentyl) the

31P{1H} NMR spectrum showed signal at δ = 22.47 ppm as compared to δ = 21.3 ppm in the

corresponding ligand. Moreover, in the 1H NMR of the complex 5a (R = iPr, R' = Neopentyl),

the CH3 protons of the neopentyl group appears at δ = 1.28 ppm as compared to δ = 1.16

ppm in the corresponding ligand. Consequently the methylene linker protons appears as a


45

doublet of doublet in the ligand at δ = 2.15 ppm whereas in the complex they appear at δ =

1.91 with coupling constant 3JPH = 11 Hz and 3JHH = 7.20 Hz. Moreover, peaks due to the

methyl protons of the iPropyl group appears in the free phosphine ligand at δ = 1.41 ppm

with coupling constant 3JHP = 15 Hz and 2JHH = 7.4 Hz, whereas in the complexes they appear

at δ = 1.32 with coupling constant 3JHP = 13.6 Hz and 2JHH = 7.7 Hz ppm. These data were

clearly signs that complexation has taken place.

In the case of complex 5b (R = iPr, R' = Neosilyl), the CH3 protons of the neosilyl group

appear at δ = 0.29 ppm as compared to δ = 0.31 ppm in the corresponding ligand. While the

methylene linker protons in the ligand appears at δ = 1.27 ppm, whereas in the complex

they appear as a duplet at δ = 1.14 ppm. Moreover, peaks due to the methyl protons of the

iPropyl group appears at δ = 1.39 ppm in the ligand whereas in the complexes appears at δ =

1.26 ppm. These data are clearly signs that complexation has taken place, which is also

simply indicated by 31P{1H} NMR spectrum of the ligand (29.41 ppm) and the complex (33.37

ppm).

The 31P{1H} NMR spectra of complexes 5c (R = Ph, R' = Neopentyl) and 5d (R = Ph, R' =

Neosilyl) were appeared as a singlet at δ = 3.21 ppm and δ = 13.47 ppm, respectively. Which

were shifted downfield when compared to those for 4c (δ = -5.2 ppm) and 4d (δ = -22.75

ppm), respectively.

Looking at the 1H NMR spectra in the alkyl region of complexes 5c (R = Ph, R' = Neopentyl)

and 5d (R = Ph, R' = Neosilyl), the peaks due to CH3 protons of the neopentyl group

appeared as a singlet at δ = 0.98 ppm of the complex 5c, while in the case of 5d the methyl

protons of the neosilyl group appeared at δ = -0.7 ppm. Moreover, peaks due to the phenyl

group, in both complexes 5c and 5d, were shifted downfield when compared with those

belong to the ligand. These are clearly signs that complexation has taken place, which also

confirmed by the clearly shift in 31P{1H} NMR spectra of complexes 5c and 5d, compared

with the free phosphine, that appeared as a singlet at δ = 6.61 ppm in 5c (R = Ph, R' =

Neopentyl) and at δ = 13.46 ppm in 5d (R = Ph, R' = Neosilyl). The structures of 5b (R = iPr, R'

= Neosilyl) and 5d (R = Ph, R' = Neosilyl) were confirmed by X-ray crystallography.

Elemental analysis data for all complexes suggested that one palladium atom is bond to two

phosphine ligands.


46

2.1.3.3 Molecular Structures of 5b and 5d. The solid state structures of 5b (R = iPr, R' = Neosilyl) and 5d (R = Ph, R' = Neosilyl) were

determined by single crystal X-ray crystallography. Crystals suitable for X-ray studies of

complexes 5b and 5d were grown by slow diffusion of pentane vapour into a solution of

dichloromethane containing the complexes at room temperature. The molecular structures

of 5b and 5d are shown in figure 2.1, and figure 2.2, respectively. Selected bond lengths and

angels are given in table 2.2 and table 2.3 for 5b and 5d, respectively. Crystal data, together

with the data collection and refinement parameters are presented in table 2.4 (in the

appendix).

The palladium atom in complex 5b (Figure 2.1) is in d.square planner configuration with the

bond angels around the palladium atom of 351°. Palladium metal has four atoms in its

coordination sphere; two phosphorus and two chlorides. The Pd-Cl bond length was

2.316(5), while the Pd-P bond length was 2.338(6). The Pd-P and Pd-Cl bond lengths fall in

the expected range of values for similar palladium complexes.[184]

Similarly, the palladium atom in complex 5d (Figure 2.2) is in square planner configuration

with the bond angels around the palladium atom of 359.4°. Palladium metal has four atoms

in its coordination sphere; two phosphorus and two chlorides. The Pd-Cl bond length is

2.3062(5), while the Pd-P bond length is 2.3131(6). The Pd-P and Pd-Cl bond lengths fall in

the expected range of values, but are quite long, compared to similar palladium complexes

[184, 197].

One feature of note was the response of the neosilyl substituent to changes in the

coordination environment at the metal center; the Pd-P-C-Si(Me)3 dihedral angles in

complexes 5b was 62.94(15)°, while in complex 5d it was 73.90(14)°, and these values were

important to allow free space for the other substituents at the Pd centre and reflects the

additional steric strain of these systems. Indeed, it is clear from the structure of both

palladium complexes 5b and 5d that the phosphine ligand is attached to the palladium

centre as a monodentate one.


47

Figure 2.1: Molecular structure of 5b (Pd; orange, P; yellow, Si; pink, Cl; green and C; gray).

Table 2.2: Selected bond lengths (Å) and angles (°) of 5b.

Pd-P 2.3382(6) P-Pd-P 172.33(3)

Pd-Cl 2.3156(5) Cl-Pd-Cl 188.57(3)

P-C5 1.853(2) Cl-Pd-P 90.05(2)

P-C1 1.819(2) P1-C1-Si 123.30(13)

P-C8 1.853(2) Pd-P-C1 115.57(7)


48

Figure 2.2: Molecular structure of 5d (Pd; orange, P; yellow, Si; pink, Cl; green and C; gray).

Table 2.3: Selected bond lengths (Å) and angles (°) of 5d.

Pd-P 2.3132(6) P-Pd-P 180(14)

Pd-Cl 2.3062(5) Cl-Pd-Cl 180(4)

P-C1 1.890(4) Cl-Pd-P 86.33(19)

P-C5 1.823(2) P-C1-Si 119.47(11)

P-C11 1.821(2) Pd-P-C1 116.08(8)

2.1.4 Cyclopalladated and Non-Cylopalladated Complexes of Substituted Neopentyl

Phosphines.

As mentioned in the last section, when phosphines 3a, 3b, 3c or 3d were allowed to react

with Pd(cod)Cl2 in a 2:1 molar ratio in dichloromethane, the bisphosphine palladium

dichloride complexes were obtained. An easy and common way to obtain most

metallacycles is the direct formation from the free ligand and a metal salt in protic solvents

at ambient temperature.[178, 185] In our study, we were able to implement a novel and

powerful strategy that allowed us to synthesize of a new type of cyclometallated and non-


49

cyclometallated palladium complexes with purely aliphatic, trialkyl phosphine backbone.

The best results were achieved by converting the air sensitive trialkyl-phosphines into their

stable salts via simple protonation on phosphorus, then followed by direct reaction of this

salts with palladium acetate in a 1:1 molar ratio in tetrahydrofuran at 50°C in presence of

sodium acetate as a base, followed by washing the resulting mixture with sodium chloride

solution gave the dinuclear palladium complexes in very good yield as bench top stable

yellow crystalline materials. This complexes were obtained either as five membered ring

metallated palladium complexes (Type A), or the dimeric non-cyclometallated palladium

complexes (Type B), scheme 2.7.

[HPR2R'][BF4]

Cl

Pd

Cl

Pd

PR2R'

R'R2P

Cl

Cl

Cl

Pd

Cl

Pd

PR2R'

R'R2P

NaOAc, thf, reflux

NaCl

NaOAc, thf, reflux

NaCl

Pd(OAc)2Type A

Type B

Scheme 2.7: Coordination behavior of phosphonium salts.

2.1.4.1 Coordination Behavior of Phosphonium Salt 4a (R = iPr, R' = Neopentyl).

When the prepared phosphonium salt 4a (R = iPr, R' = Neopentyl) is directly treated with a

stoichiometric amount of palladium(II) acetate (1:1 molar ratio) in tetrahydrofuran in the

presence of sodium acetate as a base, followed by chloride ion metathesis; the

cyclopalladated dimmer 6a was formed. In fact, it was possible to isolate this binuclear

complex as analytically pure, fine, pale yellow crystals in an overall yield of 78 % after work-

up by this procedure (Scheme 2.8).


50

Scheme 2.8: Cyclopalladation of the phosphonium salt 4a by Pd(OAc)2.

By a combination of 1H and 31P{1H} NMR spectroscopic analyses of the crude product, it was

immediately obvious that we got the cyclometallated palladium complex 6a. For instance, in

solution, the 31P{1H} NMR spectrum (CDCl3) of the analytically pure product was presented

as a singlet peak at δ = 80.13 ppm at room temperature, whereas in the corresponding

phosphine appeared as singlet at δ = 21.44 ppm, and from this value thus is indicative of

two important points. Firstly, the coordination shift (Δδ) of the phosphine ligand

approximately δ = 58.69 ppm, was supportive of the five – membered chelate ring

formation upon cyclopalladation of the phosphoine ligand generated from 4a (R = iPr, R' =

Neopentyl) and therefore provided support to cyclopalladated structure of the ligand via

oxidative addition to a carbon-hydrogen bonds of the methyl in neopentyl group. Secondly,

the appearance of one singlet peak (δ = 80.13 ppm) was in accordance with the dimeric

structure of complex 6a. In addition, the 1H NMR signals were clear and easily to be

resolved. For instance, the CH3 protons of the rest of the neopentyl group was appeared as

singlet at δ = 1.17 ppm. Consequently, the doublet resonance of the CH2 (δ = 1.63 ppm)

protons is adequately resolved though, and the efficiency of the spin – spin coupling with

the adjacent phosphorus nucleus has improved as a consequence of C-H palladation. This

was noted from the 2JPH coupling constant of 9.18 Hz for the palladated structure, which is,

approximately, more than twice as large as that of the uncoordinated ligand, at 4.9 Hz.

Moreover, the methyl protons of the iPropyl protons were appeared as duplet of duplet at δ

= 1.37 ppm and δ = 1.22 ppm with coupling constants 3JPH = 14 Hz, 2JHH = 5.74 Hz; 3JPH = 14

Hz, and 2JHH = 6.69 Hz, respectively. Finally, the CH(CH3)2 was appeared at δ = 1.37 ppm.


51

2.1.4.2 Molecular Structure of the Cyclopalladated Complex 6a. The solid state structures of 6a (Cyclometallated palladium complex for phosphnume salt 4a

(R = iPr, R' = Neopentyl) was determined by single crystal X-ray analysis. Crystals suitable for

X-ray studies for complexes 6a were grown by slow diffusion of pentane or diethyl ether

into a solution of dichloromethane containing the complex at room temperature. The

molecular structure of 6a is shown in Figure 2.3, selected bond lengths (Å) and angels (°) are

given in Table 2.5. Crystal data, together with the data collection and refinement

parameters are presented in Table 2.7 (in the appendix). The structure of palladacycle 6a

consists of two halves, in which each half of the dimer is the inverted mirror image of the

other. Moreover, the central four – membered {Pd2(μ-Cl)2} cycle was flat and the four atoms

(two Pd and two Cl) form a perfect plane. Each palladium atom in complex 6a (Figure 2.3) is

in a square planner configuration with the total bond angel around each palladium atom;

360°, and each of them has four atoms in its coordination sphere; one phosphorus, the

metallated carbon and two chlorides. The Pd-Cl (trans to P) bond length was 2.4176(4) Å

(compared with 2.4168(6)Å in Palladacycle 6e), while the Pd-Cl (trans to metallated C) bond

length was 2.4626(4) Å (compared with 2.4754(6) Å in Palladacycle 6e). In addition the Pd-P

bond length was 2.1974(4) Å (compared with 2.2318(6) Å in Palladacycle 6e) and all of them

fall in the expected range of values for similar phosphametallacycle complexes.[166]

Figure 2.3: Molecular structure of 6a (Cyclometallated palladium complex of phosphonium

salt 4a (R = iPr, R' = Neopentyl)), (Pd; orange, P; yellow, Cl; green and C; gray).


52

Table 2.5: Selected bond lengths (Å) and angles (°) of palladacycle 6a.

The Pd – Pd distance within the dimer 6a (Cyclometallated palladium complex of phosphine

salt 4a; R = iPr, R' = Neopentyl) was 3.510 Å (compared with 3.61 Å in Palladacycle 6e;

cyclometallated palladium complex of phosphine salt 4e; R = tBu, R' = Neopentyl) and like

those of the Palladacycle 6e, the crystal structure also confirms the trans-geometry of the

phosphorous atoms along the Pd–Pd axis. As expected for a d8 complex, both palladium

centers were found to be in square planar coordination geometries (the sum of the angles

around Pd in the complex 6a was 360°). Due to the steric strain between a square planar Pd

coordination and an almost planar five membered metallacycle, the Pd–P bond lengths in

cyclometallated palladium complexes 6a were shorter than that expected for a non-

cyclometallated palladium complex 6m (R = iPr, R' = CH2Cy; 2.236 Å) as well as

cyclometallated palladium complex 6e (2.232 Å). On the other hand, the Pd-Cl-Pd-P dihedral

angles was 167.48(15)°, while the Pd-Cl-Pd-C (metallated carbon atom) was 179.67(6)°.

2.1.4.3 Coordination Behavior of Phosphonium Salt 4e.

In common with the previous method used for the cyclopalladation of ligand 4a, the

prepared phosphonium salt 4e was directly treated with a stoichiometric amount of

palladium(II) acetate (1:1 molar ratio) in tetrahydrofuran in the presence of sodium acetate

Pd-P 2.1974(4) Cl-Pd-Cl 98.165(15)

Pd-Cl(trans to P) 2.4176(4) Pd-Pd 3.510

Pd-Cl(trans to metallated C) 2.4626(4) Cl-Pd-P (trans to metallated C) 98.165(15)

Pd-C3 2.0436(18) P-Pd-Cl (trans to p) 173.670(16)

P-C1 1.8373(18) C3 Pd1 Cl1 92.87(5)

P- C6 1.8393(17) C3 Pd1 P1 80.94(5)

P-C9 1.8412(18) Pd-P-C1 106.77(6)

C2 C3 Pd1 115.15(16) C3 Pd1 Cl1 179.06(5)


53

as a base, to yield the cyclopalladated dimer 6e as analytically pure pale yellow crystals in an

overall yield of 83 % after work-up (Scheme 2.9).

Scheme 2.9: Cyclopalladation of the phosphonium salt 4e by Pd(OAc)2.

Like those of the palladacycle 6a, the 31P{1H} NMR spectroscopic observations were thus

indicative of two important points. Firstly, the coordination shift (Δδ) of the phosphine

ligand was supportive of the five – membered chelate ring formation upon cyclopalladation

of the phosphonium 4e and, therefore, provided support to palladated structure of the

ligand via oxidative addition to carbon-hydrogen bonds of methyl in neopentyl group.

Secondly, the appearance of one singlet peak (δ = 94.02 ppm) was in accordance with the

dimeric structure of complex 6e.

Looking at the 1H NMR of the dimeric complex 6e, the CH3 protons of the rest of the

neopentyl group appeared as singlet at δ = 1.21 ppm. Consequently the metallated methyl

protons of the neopentyl group appears as a singlet at δ = 2.35 ppm. Moreover, peak due to

the methyl protons of the tButyl group was appeared as a doublet at δ = 1.44 ppm due to

the spin-spin coupling with the phosphorus atom with coupling constant of 3JHP = 10 Hz,

whereas in the ligand 4e was appeared at δ = 1.49 ppm with coupling constant of 3JHP = 20

Hz. These data clearly sign that complexation has taken place. Finally, the linker methyl

group adjacent the phosphorus atom was appeared as a doublet at δ = 1.83 ppm with

coupling constant of 3JHP = 10 Hz. The 1H NMR signals of the dimer 6e in solution were clear

and easily to be resolved which helped us to get full NMR spectroscopic characterization of

the cyclopalladated structure of the phosphine ligand 4e as mentioned in the above

paragraph. The doublet resonance of the CH2 protons is adequately resolved though and the

efficiency of the spin – spin coupling with the adjacent phosphorus nucleus has improved as


54

a consequence of C-H palladation. This was noted from the 2JPH coupling constant of 10 Hz

for the palladated structure, which is more than twice as large as that of the uncoordinated

ligand (5Hz).

2.1.4.4 Molecular Structure of the Cyclopalladated Complex 6e.

The solid state structure of 6e was determined by single crystal X-ray crystallography.

Crystals suitable for X-ray studies for complexe 6e were grown by slow diffusion of pentane

diethyl ether into a solution of dichloromethane containing the complex at room

temperature. The molecular structure of 6e is shown in Figure 2.4, selected bond lengths (Å)

and angels (°) are given in table 2.6. Crystal data, together with the data collection and

refinement parameters are presented in table 2.7 (in the appendix). Each palladium atom in

complex 6e (Figure 2.4) has four atoms in its coordination sphere; one phosphorus, the

metallated carbon and two chlorides. The Pd-Cl bond length was 2.4168(6) Å, while the Pd-P

bond length was 2.2318(6) Å.

Figure 2.4: Molecular structure of 6e (Pd; orange, P; yellow, Cl; green and C; gray).


55

Table 2.6: Selected bond lengths (Å) and angles (°) of palladacycle 6e.

The Pd–Pd distance within the dimer 6e was 3.610 Å. The crystal structure also confirms the

trans-geometry of the phosphorous atoms along the Pd–Pd axis. As expected for a d8

complex, both palladium centers were found to be in square planar coordination geometries

(the sum of the angles around Pd in the complex 6e was 360°). Due to the steric strain

between a square planar Pd coordination and an almost planar five membered metallacycle,

the Pd–P bond lengths in cyclometallated palladium complexes 6e were shorter than

expected for a non-cyclometallated palladium complex 6m (2.236 Å).

The structure of palladacycle 6e consists of two halves, in which each half of the dimer is the

inverted mirror image of the other. Moreover, the central four – membered {Pd2(μ-Cl)2}

cycle was flat and the four atoms (two Pd and two Cl) form a perfect plane. The Pd-C, Pd-P

and Pd-Cl bond lengths fall in the expected range of values for similar phosphametallacycle

complexes.[166] Looking at the bond lengths and angels, the Pd-C (metallated atom), Pd-P,

Pd-Cl (bridging trans to P) and Pd-Cl (bridging trans to metallated carbon atom) in

palladacycle 6e were 2.043(2) Å, 2.2318(6) Å, 2.4754(6) Å and 2.4168(6) Å , respectively. On

the other hand, the Pd-Cl-Pd-P dihedral angles was 174.43(17)°, while the Pd-Cl-Pd-C

(metallated carbon atom) was 179.81(7)°.

Pd-P 2.2318(6) Cl-Pd-Cl 84.92(2)


Pd-Cl(trans to metallated C) 2.4754(6) Cl-Pd-P (trans to metallated C) 102.47(2)

Pd-C3 2.043(2) P-Pd-Cl (trans to p) 172.57(2)

P-C1 1.853(2) C3 Pd1 Cl1 175.95(7)

P- C6 1.886(2) C3 Pd1 P1 81.58(7)

P-C11 1.879(2) Pd-P-C1 115.57(7)

C2 C3 Pd1 115.15(16) C3 Pd1 Cl1 91.03(7)


56

2.1.4.5 Coordination Behavior of Cyclopalladated Complex 6e. The metal-carbon σ bond in cyclometalated palladium complexes is remarkably robust[185],

and a variety of conventional reactions can be successfully carried out. For example, the

chlorine-bridged dimer 6e undergoes the usual adduct formation at mild reaction conditions

with either triphenylphosphine via cleavage of the μ-chloro bridges to yield 9e, or with

PPh2(o-Tolyl) to yield 10e. Both of the mononuclear complexes 9e and 10e were crystalline

and well-characterized product with a trans-configuration whith respect to the phosphorus.

As usual, this geometries were indicated by the 31P{1H} NMR spectra for 9e and 10e which

were presented as a pair of doublets with slightly different 31P-31P couplings. Such that the

coupling constant has a large value (2JPP = 379 Hz, trans PPh3 ligand and 2JPP = 377 Hz, trans

PPh2(o-tolyl) ligand). In addition, the chlorine anions in palladacycle complex 6e were

exchanged easily by salt metathesis with silver acetate and silver trifloroacetate to give the

dimeric complexes 11e and 12e respectively (Figure 2.5).

Figure 2.5: Coordination behavior of cyclopalladated complex 6e.


57

Looking at the 1H NMR of the dimeric complex 11e and 12e, the CH3 protons of the rest of

the neopentyl group were appeared as a singlet at δ = 1.21 ppm and at δ = 1.18 ppm,

respectively. Consequently the metallated methyl protons of the neopentyl group appears

as a singlet at δ = 2.16 ppm in 11e and at δ = 2.29 ppm in 12e. Moreover, peaks due to the

methyl protons of the tButyl group was appeared as a doublet in 11e at δ = 1.41 ppm due to

the spin-spin coupling with the phosphorus atom with coupling constant of 3JHP = 13.5 Hz,

whereas in the complex 12e was appeared at δ = 1.49 ppm with coupling constant of 3JHP =

13.8 Hz. Finally, the linker methyl group adjacent the phosphorus atom was papered as a

doublet, in 11e, at δ = 1.80 ppm with coupling constant of 3JHP = 9 Hz, and at δ = 1.80 ppm in

12e with coupling constant of 3JHP = 8 Hz. These data clearly signs that chloride displacement

has taken place. The methyl protons of acetate group in 11e were appeared at δ = 2.35 ppm

too. On the other hand, we reported the synthesis and the structure of 14VE palladium(0)

complex of ligand 4e, firstly by deprotonation of phosphonium salt 4e by means of a base to

regenerate the free phosphine 3e, then by the reaction of this phosphine with

(tmeda)PdMe2, which was prepared according to the published procedure, to yield

(PtBu2CH2CCMe3)2Pd 13e as colourless solid in an overall yield of 88 % after work-up.

As usual, the reaction of phosphine with (tmeda)PdMe2[186] (tmeda; tetramethylethylene

diamine) often give bisphosphine-dimethylpalladium complexes, but in our case for bulky

phosphine, like 3e, these readily reductively eliminate ethane to yield a slightly air-sensitive

(PtBu2CH2CMe3)2Pd(0) 13e (Scheme 2.10).

Scheme 2.10: Synthesis of palladium(0) complex 13e.

The room temperature 31P{1H} NMR spectra of 13e in C6D6 showed one sharp signal at 45.09

ppm, in addition, the 1H NMR spectra at room temperature showed three peaks appears at

δ = 1.51 ppm as doublet, δ = 1.48 ppm as singlet and at δ = 1.43 ppm. In June 2010, at the

same period of our investigation of palladium (0) complex 13e, Shaughnessy and co-worker


58

[184] have synthesized the same complex by different procedure; they added a methanolic

solution of NaOH to Pd(cod)Br2 suspended in toluene at -5°C. Then they reacted the

resulting solution with phosphine in toluene at a certain temperature, and they succeeded

to precipitate the complex as off-white solid by methanol.

The solid state structure of 13e was determined by single crystal X-ray crystallography.

Crystals suitable for X-ray studies of complex 13e were grown upon recrystallization from

cold pentane at -20°C. The molecular structure of 13e is shown in figure 2.6, selected bond

lengths (Å) and bond angels (°) are given in table 2.8. Crystal data, together with the data

collection and refinement parameters are presented in table 2.7. An obvious different of

this structure and those of the few other reported structure of (PR3)2Pd was the (C2-C1-P-

Pd) dihedral angel near the zero (-0.17(18) Å)[184], whereas in the palladium(II) dichloride

complex of phosphine 3e this angle was 126.52(9) Å[184], due to the steric strain in this

system.

Figure 2.6: Molecular structure of 13e (Pd; orange, P; yellow, and C; gray).

Table 2.8: Selected bond lengths (Å) and angles (°) of 13e.

Pd-P 2.2974(6) C2-C1-P 120.03(15)

P-C1 1.865(2) P-Pd-P 180(5)

P- C6 1.890(2) Pd-P-C6 111.32(7)

P-C10 1.892(2) Pd-P-C1 117.93(7)


59

The Pd-P bond length was 2.2974(6) Å (compared with 2.2318(6) Å in palladacycle 6e, and

2.4148(4) Å in the palladium (II) dichloride complex of phosphine 3e [184]), while the P-C1

bond length was 1.865(2) Å (compared with 1.853(2) Å in palladacycle 6e, and 1.8522(14) Å

in the palladium(II)dichloride complex of phosphine 3e [184]). In addition the C2-C1-P bond

angel was 120.03(15)° (compared with 126.24(9)° in the palladium(II) dichloride complex of

phosphine 3e [184]) .

2.1.4.6 Coordination Behavior of Phosphonium Salt 4g.

Like those of the phosphapalladacycle 6a and 6e, the cyclometallated palladium complex 6g

have been prepared by a direct treatment of the phosphonium salt 4g with a stoichiometric

amount of palladium(II) acetate (1:1 molar ratio) in tetrahydrofuran in the presence of

sodium acetate as a base, followed by chloride ion metathesis (by washing the reaction

mixture a couple of times with sodium chloride solution) to yield the cyclopalladated dimer

as analytically pure off white crystals in an overall yield of 86 % after work-up (Scheme

2.11).

Scheme 2.11: Cyclopalladation of the phosphonium salt 4g by Pd(OAc)2.

By a combination of 1H and 31P{1H} NMR spectroscopic analyses of the crude product, a

good indication of the presence of the product as cyclometallated palladium complex 6g (R

= trineopentyl) was provided, by the appearance of one singlet at δ = 1.28 ppm for CH3 of

two neopentyl group, as well as a simple doublet of doublet resonance representative of the

CH2 protons of neopentyl arms which appeared at δ = 1.93 ppm. In addition, one doublet

appeared at δ = 2.47 ppm for the CH2 protons of the third neopentyl arm which was


60

responsible for cyclometallation process, also with spin-spin coupling with phosphorus atom

with coupling constants 3JPH = 11.7 Hz. Finally, one singlet was appeared at δ = 1.179 ppm-

which belong to the two methyl group of the rest of the cyclometallated neopentyl arm.

Moreover, the room temperature 31P{1H} NMR spectrum (CDCl3) of the analytically pure

product was presented as a singlet peaks at δ = 33.66 ppm.

2.1.4.7 Coordination Behavior of Phosphonium Salt 4h.

In the case of phosphonium salt 4h, when palladium acetate was treated with this salt like

the above protocol which described for preparation of cyclometallated palladium complexes

6a, 6e and 6g, it only afforded the 1:1 dinuclear, chlorine-bridged palladium complexe (non-

cyclometallated palladium complex) 6h as a pale yellow powder in an over yield of 84%

(Scheme 2.12).

Scheme 2.12: The Dinuclear Palladium Complex of 4h.

The 1H NMR signals of the dimmer 6h in solution were clear and easily to be resolved. For

instance, the CH3 protons of the neopentyl group was appeared as a singlet at δ = 1.33 ppm,

whereas in the ligand 4h was appeared at δ = 1.15 ppm. Moreover, the linker CH2 group

adjacent the phosphorus atom was appeared as a doublet at δ = 2.314 ppm due to the spin-

spin coupling with the phosphorus atom with coupling constant of 3JHP = 11.8 Hz, whereas in

the ligand 4h (R = Cy, R' = Neopentyl) was appeared at δ = 2.11 ppm with coupling constant

of 3JHP = 12 Hz. More two set of multiplet was appeared in the range of δ = 1.4-2.48 ppm for

the cyclohexyl group. The 31P{1H} NMR spectroscopic observations were thus indicative of

two important features. Firstly, the coordination shift (Δδ) of the phosphine ligand at


61

approximately δ = 4.28, was supportive of the formation dimmer complex 6h. Secondly, the

appearance of one singlet peaks (δ = 17.33 ppm) was in accordance with the dimeric

structure of complex 6h (non-cyclometallated palladium complex) and clearly signs that

complexation has taken place.

2.1.5 Synthesis and Characterization of Substituted iPropyl and tButyl Dinuclear

Palladium Complexes 6i-6o.

An easy and common way to obtain most metallacycles is the direct formation from the free

ligand and a metal salt in protic solvents at ambient temperature. [14, 29]

In this part of our investigation, we began studying the behaviors of a broad range of

substituted iPropyl and tButyl phosphonium salts to know weather they undergo

cyclometallated to form four or five membered ring metallated palladium complexes (type

A), or the dimeric non-cyclometallated palladium complexes (type B).

We showed that when palladium acetate was treated with phosphonium salts (4i, 4j, 4l, 4m,

4n or 4o), by approved protocol to prepare the cyclometallated palladium complexes, they

only afforded the 1:1 dinuclear complexes (6i, 6j, 6l, 6m, 6n or 6o), (Scheme 2.13).


62

Scheme 2.13: Coordination behavior of phosphonium salts 4i-o.

The 31P NMR spectra of the dimmer complexes (6i-l and 6m-n) each show one single

resonance, which suggests the presence of only one isomer in solution, in the region δ = -

10.54 to 94.02 ppm and well removed from the chemical shift of the phosphonium salts

starting materials 4. In addition, there is a significant difference between the chemical shift

of cyclometallated and non cyclometallated palladium complexes. The 31P NMR

spectroscopic data for new complexes, together with that for the parent new and known

phosphonium salts are shown in table 2.9.

Table 2.9: 31P NMR data of phosphonium salts and its dimeric palladium complexes.


63

The dinuclear palladium complexes described in table 2.9 were fully characterized by 1H, 13C,

and 31P NMR, and IR, elemental analyses and MS as well as melting point.

In the case of phosphonium salt 4m (R = iPr, R' = CH2Cy), when palladium acetate was

treated with this salt; it only afforded the 1:1 dinuclear chlorine-bridged palladium

complexe 6m (non-cyclometallated palladium complex) as a pale yellow powder in an over

all yield of 79% (Scheme 2.13).

By a combination of 1H and 31P{1H} NMR spectroscopic analyses of the crude product, it was

immediately obvious that we got the non-cyclometallated palladium complex 6m (non-

cyclometallated palladium complex of phosphonium salt 4m (R = iPr, R' = CH2Cy). For

instance, in solution, the 31P{1H} NMR spectrum (CDCl3) of the analytically pure product was

presented as a singlet peak at δ = 57.36 ppm at room temperature, whereas in the ligand

appeared at δ = 27.41 ppm, and from this value thus indicative of an important point; the

appearance of one singlet peaks (δ = 57.36 ppm) was in accordance with the dimeric

structure for the complex 6m. In addition, the 1H NMR signals were cleared and easily to

resolved. For instance, the doublet resonance of the CH2 (δ = 2.25 ppm) proton is

adequately resolved though and the efficiency of the spin – spin coupling with the adjacent

phosphorus nucleus has improved as a consequence of non C-H palladation. This was noted

from the 2JPH coupling constant of 12 Hz for the non cyclometallated structure. Moreover,

the methyl protons of the isopropyl protons were appeared as duplet of duplet at δ = 1.43

ppm and δ = 1.38 ppm with coupling constants 3JPH = 13.6 Hz and 3JPH = 12 Hz, respectively,

In addition, 2JHH = 6.9 Hz and 2JHH = 6 Hz, respectively. Also the protons of cyclohexyl group

were appeared in the range of δ = 1.21-1.87ppm. Finally, the CH(CH3)2 protons were

appeared at δ = 2.39 ppm.

The solid state structure of 6m was determined by single crystal X-ray crystallography.

Crystals suitable for X-ray studies for complex 6m was grown by slow diffusion of pentane

into a solution of dichloromethane containing the complex 6m at room temperature. The

molecular structure of 6m is shown in figure 2.7, selected bond lengths (Å) and angels (°) are

given in table 2.10. Crystal data, together with the data collection and refinement

parameters are presented in table 2.7. The structure of palladacycle 6m consists of two

halves, in which each half of the dimer is the inverted mirror image of the other.


64

Like those of the cyclometallated palladium complexes 6a, 6e and 6g, in the non-

cyclometallated palladium complex 6m (Figure 2.7), each palladium atom in complex was

in a square planner configuration with the total bond angels around each palladium atom =

360°, and each of them has four atoms in its coordination sphere; one phosphorus and

three chlorides. The Pd–Pd distance within the dimer 6m was 3.50 Å (compared with 3.61 Å

and 3.510 Å in palladacycle 6e and 6a, respectively.) and like those of the palladacycle 6e

and 6a, the crystal structure also confirms the trans-geometry of the phosphorous atoms

along the Pd–Pd axis. The Pd–P bond lengths in non cyclometallated palladium complexes

6m were longer than expected for a cyclometallated palladium complex 6e (2.232 Å) as well

as in the cyclometallated palladium complex 6a (2.197 Å). On the other hand, the Pd-Cl-Pd-P

dihedral angles was 175.04(3)°, while the torsion angel Cl2-Pd-Cl1-Pd was 10.4(3)°. The

structure of non-cyclometallated palladium complex 6m consists of two halves, in which

each half of the dimer is the inverted mirror image of the other. Moreover, the Pd-P and Pd-

Cl bond lengths fall in the expected range of values for similar phospha metallacycle

complexes.[166]

Figure 2.7: Molecular structure of 6m (Pd; orange, P; yellow, Cl; green and C; gray).


65

Table 2.10: Selected bond lengths (Å) and angles (°) of 6m.

Looking at the bond lengths, the Pd-P, Pd-Cl1 (bridging trans to P), Pd-Cl1 (bridging trans to

Cl2 atom) and Pd-Cl2 in 6m were 2.2356(8) Å, 2.3190(7) Å, 2.4754(6) Å, 2.4353(8) Å and

2.2751(8) Å, respectively.

In the case of the phosphonium salt 4k, we were pleased to find that the reaction of this salt

proceeded cleanly to afford four membered ring cyclometallated palladium complex 6k as a

pale yellow solid in an over all yield of 95% (Scheme 2.14). In addition to our work, Goel and

co-worker have prepared the cyclometallated palladium complex 6k directly by treatment of

the free phosphine P(tBu)3 with PdCl2 or Na2PdCl4 in DMF, and stirring at room temperature

for long period of time (48h).[177]

Compared to previous protocol for the synthesis of 6k, the procedure does not require

stirring for long period of time. An investigation on the preparation and characterization of

authentic samples of 6k showed that it readily undergoes intramolecular metalation in

solution.

Scheme 2.14: Coordination behavior of phosphonium salt 4k.

Pd-P 2.2356(8) Cl1-Pd-Cl2 175.19(3)


Pd-Cl(trans to Cl2) 2.4754(6) P-Pd-Cl1(trans to P) 174.96(3)

Pd-Cl2 2.2751(8) P-Pd-Cl1(trans to Cl2) 93.83(3)

P-C1 1.839(3) P-Pd-Cl2 90.80(3)

P- C5 1.837(3) Pd-P-C7 116.17(10)

P-C7 1.834(3) Pd-Cl1-Pd 94.78(3)


66

The metal-carbon σ bond in cyclometalated palladium complex 6k is remarkably robust, and

a variety of conventional reactions can be successfully carried out. For example, the

treatment of a dichloromethane solution of 6k with two equivalents of either PPh3 or

PPh2(o-Tolyl) resulted in the precipitation of monomeric palladium complexes 9k and 10k,

respectively (Scheme 2.15). In addition, a color changes from pale yellow to light yellow was

observed. After evaporation, an off-white solid was obtained whose 31P NMR spectrum in

CDCl3 showed a pair of doublets with different 31P-31P couplings. Such that the coupling

constant has a large value (2JPP = 379 Hz, trans PPh3 ligand and 2JPP = 252 Hz, trans PPh2(o-

Tol) ligand) and the chemical shift being consistent with the formation of the monomeric

complexes 9k and 10k.

Scheme 2.15: Coordination behavior of cyclopalladated complex 6k.

From above results, it can be stated that a broad range of trialkylphosphonium salts

undergo cyclometallation either as five and four membered ring metallated palladium

complexes or the dimeric non-cyclometallated palladium complexes. Interestingly, the tri-

tButyl substituted phosphonium salt 4k, [HP(tBu)3][BF4], undergo cyclometallation process

via C-H activation. In contrast, the mono and di-substituted tButyl phosphonium salt 4i (R =

iPr, R' = tBu) and 4j (R = tBu, R' = iPr) afforded only the 1:1 dinuclear complexes. In summery

the formation of five membered palladacycle by cyclometallation of a neopentyl group

proceeds more easily than the same process leading to four membered palladacycle on

tButyl group. Obviously steric crowding on the phosphine as well as methyl groups in the

right position to form five membered palladacycle lead to very fast and easy C-H activation

and subsequent cyclopalladation.


67

2.1.6 Effective Suzuki Cross Coupling Reactions Using Prepared Phosphonium Salts

and Palladium Complexes.

Interest in the studying of palladium (II) complexes mainly focuses on the ability to

exploitation their electronic and steric effects to tune the acidity and reactivity of such

complexes for their probable utility as catalysts [159, 162]. It has been shown that the catalytic

activity depends on the donor atom around the metal present in the complex as well as the

steric environment around the metal too. In general, an electron rich metal complex

accelerates the oxidative addition and the steric around the metal center facilitates

reductive elimination and stabilizes the complex. Therefore, phosphines serve as useful

reagents and catalysts, in a wide array of important organic synthesis resulting from

different types of cross coupling reaction. In the early studies, triarylphosphines (e.g., PPh3),

which are typically air stable, have been the predominant focus of study over

trialkylphosphines, probably as a result in large part of the fact that many of them are air-

sensitive, which makes them more difficult to handle than triarylphosphines.[4,89, 93]

Therefore, we focused our interest, in the second part of this thesis, in a simple but

powerful strategy for handling these phosphines would be to protect them as their

conjugate acids. According to this approach, a stable, easily handled phosphonium salt

would be employed as a precursor, and insitu deprotonation in the reaction mixture would

liberate the desired free phosphine. In this section we described the application and efficacy

of prepared complexes and phosphonium salts in the Suzuki Miyaura cross coupling

reaction.

2.1.6.1 Neopentyl and Neosilyl Phosphines based Catalysts for Suzuki-Miyaura Cross-Coupling Reaction. As an obvious model reaction we have examined the formation of substituted biphenyls

from phenylboronic acid and different types of alkyl halides in the presence of palladium

complex 5 ((PR2R')2Pd Cl2); 5a (R = iPr, R' = Neopentyl), 5b (R = iPr, R' = Neosilyl), 5c (R = Ph, R'

= Neopentyl) or 5d (R = Ph, R' = Neosilyl), and using different reaction conditions. In all cases

no homocoupling product was formed. For initial studies, 4-bromoanisole was chosen as the

main test substrate as it is electronically inactivated and is usually difficult to be activated in


68

cross-coupling reactions. We were delighted to see that all complexes 5a, 5b, 5c or 5d

catalyzed the reaction between 4-bromoanisole and phenylboronic acid smoothly at mild

reaction conditions. It was established that using dioxan/water and K2CO3 at 80°C shows

excellent yields of the product at the catalyst loading of 0.5mol% Pd (Scheme 2.16). We next

investigated the relationship between the reactions time and yield, kinetic study, of Suzuki

cross-coupling reaction product at the following reaction conditions: aryl halides (1.0 mmol),

phenylboronic acid (1.2 mmol), K2CO3 (3 equiv.), palladium complex 0.5 mol%, dioxan/water

(2:1), reaction temperature of 80°C. Complex 5b (R = iPr, R' = Neosilyl) proved to be an

extremely efficient catalyst for Suzuki–Miyaura cross-coupling reaction, and led to very good

reaction rates and yields in short reaction times and with 0.5 mol% catalyst loading.

Remarkably, complex 5d (R = Ph, R' = Neosilyl) generally shows significantly lower activities

than 5b (R = iPr, R' = Neosilyl) and the higher catalytic activity of complex 5b over 5d is

attributed to electronic factors as well as steric factors, the metal center of 5b (R = iPr, R' =

Neosilyl) being more electron-rich than 5d (R = Ph, R' = Neosilyl). For example,

bromobenzene and phenylboronic acid in the presence of K2CO3 underwent 85% C-C

coupling in dioxan/water at 80°C with only 0.5 mol% of catalyst 5b (R = iPr, R' = Neosilyl)

within 5 hours (Scheme 2.16, entry 1). No induction period was required; approximately 40

% conversion was observed after 3 hours. In contrast, 50% of conversion was achieved

under the same reaction conditions by 5d (Scheme 2.16, entry 2).

Scheme 2.16: Suzuki cross-coupling reaction of bromobenzene with phenylboronic acid catalyzed by palladium complexs 5b (R = iPr, R' = Neosilyl) and 5d (R = Ph, R' = Neosilyl).


69

Higher conversion rates were realized with 5b and 5d when activated aryl bromides were

used as substrates, scheme 2.17. Coupling reactions performed with 4-bromoacetophenone

yielded 94% 4-acetylbiphenyl after approximately less than 30 minutes by 5b, while

complete conversion into 4-acetylbiphenyl was achieved after 60 minutes. In contrast, 89%

of conversion was achieved under the same reaction condition by 5d, while complete

conversion into 4-acetylbiphenyl was obtained after 90 minutes.

Scheme 2.17: Suzuki cross-coupling reaction of 4-bromoacetophenone with phenylboronic

acid catalyzed by palladium complex 5b (R = iPr, R' = Neosilyl) and 5d (R = Ph, R' = Neosilyl).

In addition, the activity only slightly decreases with increasing electron density on the aryl

bromide. For example, when the electronically deactivated 4-bromoanisole was employed

(Scheme 2.18), 75% and 83% conversions were obtained within 30 and 60 min, respectively,

by palladium complex 5b (R = iPr, R' = Neosilyl), while 52% and 63% conversions were

obtained within 30 and 60 min, respectively, by palladium complex 5d (R = Ph, R' = Neosilyl).

While complete conversion into 4-methoxybiphenyl 8f was achieved after 90 minutes

(Scheme 2.18, entry 2 and 4). In contrast, 100% and 93% conversion were achieved within

60 minutes by neopentyl substituted palladium complex 5a (R = iPr, R' = Neopentyl) and 5c

(R = Ph, R' = Neopentyl), respectively. A further decrease in activity, in both substituted


70

neopentyl and neosilyl phosphine-based catalysts 5a, 5b, 5c and 5d, was obtained by using

sterically hindered substrates. Coupling reactions with 2-bromotoluene led to 96%, 75%,

91% and 30% conversion within 30 minutes by 5a, 5b, 5c and 5d, respectively (Scheme 2.19,

entries 1-4). Less than 16% conversion was obtained after 1h using 2-bromomesitylene as

the substrate by 5b and 5d. Reactions carried out with 4-chloroacetophenone also showed

some conversion rates. For example, complete conversion of 4-chloroacetophenone at 80°C

with 0.5 mol% catalyst 5a, 5b and 5d were observed after 90, 180 and 240 minutes,

respectively. In contrast, coupling reaction with deactivated or sterically hindered aryl

chlorides, such as 2-chlorotoluene, was less successful and only led to approximately 24%

and 37% conversions by 5a, in boiling toluene, after 24h and 48h, respectively. On the other

hand, only 14 % conversion was observed by 5b after 24h and no significant conversion was

observed with 5c and 5d even at high temperature for long period of time (Scheme 2.20).

Scheme 2.18: Suzuki cross-coupling reaction of 4-bromoanisole with phenylboronic acid catalyzed by 5 (5a (R = iPr, R' = Neopentyl), 5b (R = iPr, R' = Neosilyl), 5c (R = Ph, R' = Neopentyl) or 5d (R = Ph, R' = Neosilyl).


71

In the examples of the Suzuki–Miyaura cross-coupling reactions performed (in particular

when aryl bromides as well as activated and unactivated aryl chlorides were employed);

catalyst 5a (and to a minor extent 5b) were more efficient than the others.

In general, according to above results it was observed that the more electron rich catalysts

were the most active in catalyzing the reactions. To put the results in a proper context, time

dependent experiments were performed in order to evaluate the difference in activity of

different catalyst over time. Figurers 2.8, 2.9 and 2.10 show the profile of these time

dependent reactions.

Scheme 2.19: Suzuki cross coupling reaction of 2-bromotoluene with phenylboronic acid catalyzed by palladium complexes 5 (5a (R = iPr, R' = Neopentyl), 5b (R = iPr, R' = Neosilyl), 5c (R = Ph, R' = Neopentyl) and 5d (R = Ph, R' = Neosilyl)).


72

Scheme 2.20: Suzuki cross coupling reaction of 2-chlorotoluene with phenylboronic acid catalyzed by palladium complexes 5 (5a (R = iPr, R' = Neopentyl), 5b (R = iPr, R' = Neosilyl), 5c (R = Ph, R' = Neopentyl) and 5d (R = Ph, R' = Neosilyl)).

0 50 100 150 200 250 3000

20

40

60

80

100

% C

on

vers

ion

Time(min)

5a

5b

5f

5e

Figure 2.8: Kinetic investigation of complex 5 (5a (R = iPr, R' = Neopentyl), 5b (R = iPr, R' = Neosilyl), 5c (R = Ph, R' = Neopentyl) and 5d (R = Ph, R' = Neosilyl) in the Suzuki Miyaura cross-coupling reaction of 2-bromotoluene with phenylboronic acid (0.5 mol% [Pd], 80°C).


73

0 50 100 150 200 250 3000

20

40

60

80

100

% C

on

vers

ion

Time(min)

5a

5b

5f

5e

Figure 2.9: Kinetic investigation of complexes 5 (5a (R = iPr, R' = Neopentyl), 5b (R = iPr, R' = Neosilyl), 5c (R = Ph, R' = Neopentyl) and 5d (R = Ph, R' = Neosilyl)) in the Suzuki Miyaura cross-coupling reaction of 4-bromoanisol with phenylboronic acid (0.5 mol% [Pd], 80°C).

0 50 100 150 200 250 3000

20

40

60

80

100

% C

on

vers

ion

Time(min)

5a

5b

5f

5e

Figure 2.10: Kinetic investigation of complexes 5 (5a (R = iPr, R' = Neopentyl), 5b (R = iPr, R' = Neosilyl), 5c (R = Ph, R' = Neopentyl) and 5d (R = Ph, R' = Neosilyl)) in the Suzuki Miyaura Cross-Coupling Reaction of 4-chloroacetophenone with phenylboronic acid (0.5 mol% [Pd], 80°C).


74

It was observed that the initial activity of 5a was much higher than for 5b, 5c or 5d (Figure

2.8, 2.9 and 2.10). Complex 5d clearly showed one of the lowest starting activities (in the

coupling of 4-bromoanisol and 2-bromotoluene), which culminates in a weaker overall

performance. It is interesting to observe that, in cross coupling of 4-bromanisol with

phenylboronic acid, all complexes (5a, 5b, 5c and 5d) reached 50% conversion in less than

60 minutes. Moreover, Suzuki cross coupling reaction was influenced by the base. For

example, in the cross coupling of 4-bromoacetophenone with phenylboronic acid, replacing

K2CO3 by NaOAC, Cs2CO3 or K3PO4 led to a detectable drop in the reactions rate. No

significant activity of understudy catalysts was observed at room temperature with

activated and deactivated aryl bromides during 2h (Scheme 2.21).

Scheme 2.21: Screening of bases for Suzuki cross-coupling of 4-bromoacetophenon with

phenylboronic acid using catalyst 5b (R = iPr, R' = Neosilyl) and 5c (R = Ph, R' = Neopentyl).


75

The low conversions observed with these catalysts can be ascribed to the reduced donor

ability of phosphorus atom in the neosilyl phosphine ligands compared with neopentyl ones.

In other words, the less sterically crowded complexes were the most active (but to a minor

exception with 5c).

2.1.6.2 Cyclometallated Palladium Complexes in Suzuki-Miyaura Cross-Coupling

and Buchwald Amination Reactions.

There has recently been considerable interest in the development of high-activity catalysts

those can be used at low loadings in Suzuki cross coupling reaction, and phosphorus-based

palladacycle complexes, which derived from triarylphosphine have played a significant role

in this regard. [147, 159, 162]

In our investigations on the cyclometallated palladium complexes 6a(R = iPr, R' = Neopentyl)

and 6e (R = tBu, R' = Neopentyl) as catalyst in Suzuki cross coupling reaction; the presence of

palladium carbon bond in these complexes doesn't in anyway help in increasing the reaction

rate in which the Suzuki cross coupling proceeds compared with related bisphosphine

palladium(II) complexes (5a (R = iPr, R' = Neopentyl), 5b (R = iPr, R' = Neosilyl), 5c (R = Ph, R'

= Neopentyl) and 5d (R = Ph, R' = Neosilyl); section 2.4.1) or Beller and Herrmann

Palladacycle. [147, 159, 162] Unfortunately, this system doesn't showed any significant catalytic

activity in Suzuki cross coupling and failed to yield any isolable product in the applied

conditions, except in the case of activated aryl bromide. Coupling reactions performed with

4-bromoacetophenone just showed some limited activity (21% conversion by 2 mol% Pd of

6e) after more than 48h at 100°C. In contrast, 8% conversion was achieved by use of 6a

(cyclometallated palladium complex of phosphonium salt 4a (R = iPr, R' = Neopentyl)) under

the same conditions. The very low conversions observed with these catalysts can be

ascribed to the difficultness to generate the Pd(0) active species by reductive C-H or C-C

elimination.[87, 147, 188]. The P-based palladacyclic Suzuki catalysts rapidly generate Pd(0) by

nucleophilic attack of the aryl boronic acid at the palladium center, followed by reductive

elimination and C-C bond formation to yield the catalytic active Pd(0) monophosphine

species [87, 188-189]. We suggested a similar process which is operative in the case of

trialkylphosphines based palladacycles (Scheme 2.22).


76

Scheme 2.22: Postulated mechanism for the formation of the catalytically active

monophosphine Palladiumd(0) species in Suzuki cross-coupling of 4-bromoacetophenon

with phenylboronic acid by reductive C-C bond formation from cyclometallated palladium

complex 6e.

To obtain a detailed and clear view about the nature and the role of P(tBu)2CH2C(CH3)3

ligand 3e in catalytic cycle steps; the oxidative addition process of the Pd(0) complex 13e of

this ligand have been studied. The oxidative addition of haloarenes to d10 Pd(0) phosphine

complexes is a key step in Suzuki cross coupling reaction process.[87, 147, 188] Therefore, we

have examined this reaction by 31P{1H} NMR monitoring. Firstly, we tried to achieve

oxidative addition of activated aryl bromide (Scheme 2.23), such as bromobenzonitrile, to

the 14VE Pd(P(tBu)2CH2C(CH3)3)2 13e. Figure 2.11 shows the 31P{1H} NMR spectroscopic

monitoring. The reaction of Pd(P(tBu)2CH2C(CH3)3)2 13e with bromobenzonitrile is

accompanied by the growth of a singlet at δ = 15.98 ppm and of a singlet at δ = 53.59 ppm,

while the signals of Pd(P(tBu)2CH2C(CH3)3)2 13e at δ = 41.26 ppm constantly decrease. We


77

assigned the signal at δ = 53.59 ppm to oxidative addition product 13c and the singlet at δ =

15.98 ppm to free phosphine 3e. Next we tried to achieve oxidative addition of 3,5-CF3-

bromobenzene to Pd(0) complex 13e. Similarly upon addition of an excess of 3,5-CF3-

bromobenzene to a solution of Pd(0) complex 13e in CD3CN; we observed a change in the

31P{1H}-NMR resonances (Figure 2.12). The signal for Pd(0) decrease with time and two new

signals appeared in a ratio of about 1:1, the free Phosphine and the postulated complex

13d. In the case of oxidative addition of iodobenzen to the Pd(0) a direct formation of two

sharp signal were observed at room temperature (Figure 2.13 and 2.14). As the sole

products in oxidative addition were only the free phosphine and the complex 13f, we tried

to force this reaction to completeness by increasing the temperature to 70°C in hope to

isolate the pure complex 13f by simple removing the free phosphine, solvent as well as the

iodobenzene by oil pump vacuum. These attempts were hampered by the formation of

another two sharp signals after 20 minutes at 70°C. We know from our investigation (vide

supra) that Pd(II) complexes with neopentyl decorated phosphines do easily undergo

cyclometallation by C-H activation. Indeed the signal at δ = 91.80 ppm (compared with δ =

94.02 ppm of related cyclometallated palladium complex 6e, where X = Cl) can be assigned

to complex 13g. Another typical side reaction is the reductive elimination of a biaryl by C-C

bond formation accompanied by the formation of a dimeric Pd(I) complex 13h (Figure 2.14),

we assigned the signal at δ = 58.34 ppm to this complex based on the reported shifts for

similar complexes.[87, 188-189]

Scheme 2.23: Proposed reaction pathways for the oxidative additions of aryl halides to the

Pd(0) complex 13e.


78

Figure 2.11: 31P{1H}-NMR investigation (25°C or 50°C, CD3CN) on the oxidative addition of bromobenzonitrile to Pd(0) complex 13e in CD3CN solution by using PPh3 as external standard: (A) at the start; (B) after 48h at 25°C; (C) after 48h at 60°C.

Figure 2.12: 31P{1H}-NMR investigation (25°C or 60°C, CD3CN) on the oxidative addition of 3,5-CF3-bromobenzene to Pd(0) complex 13e in CD3CN solution by using PPh3 as external standard: (A) at the start at 25°C; (B) after 48h at 25°C; (C) after 48h at 60°C.


79

Figure 2.13: 31P{1H}-NMR investigation (25°C or 50°C, CD3CN) on the oxidative addition of

iodobenzene to Pd(0) complex 13e in CD3CN solution by using PPh3 as external standard: (A)

after 5min. at 25°C; (B) after 10min. at 25°C; (C) after 5min. at 60°C; (D) after 10min. at 60°C;

(E) after 20min. at 60°C.


80

Figure 2.14: 31P{1H}-NMR investigation (25°C or 50°C, CD3CN) on the oxidative addition of iodobenzene to Pd(0) complex 13e in CD3CN solution by using PPh3 as external standard: (F) after 22min. at 60°C; (G) after 25min. at 60°C; (H) after 5min. at 70°C; (I) after 10min. at 70°C; (J) after 20min. at 70°C.


81

In an effort to determine whether phosphine adducts of the complex 6e (either PPh3 or

PPh2(oTolyl) generally perform better than palladacycle analogue 6e, we compared the

performances of catalysts formed in situ with these phosphines with activated aryl chloride

substrate. The P : Pd ratios were maintained at 2 : 1 for both phosphines used and the

results are summarised in scheme 2.24. As can be seen, in all cases the PPh2(o-Tolyl) ligand

did indeed performed better than PPh3. As mentioned earlier, the activity shown with these

substrates is not as high as that shown by triarylphosphine-based Palladacycle. [159, 162]

Scheme 2.24: Suzuki coupling of 4-chloroacetophenon with phenylboronic acids catalyzed

by mixtures of complex 6e and two equivalents of PPh3 or PPh2(o-Tolyl).

In order to test the catalytic activity of the four membered palladacycles, we have used the

dimmer 6k (cyclometallated palladium complex of P(tBu)3) and monomeric palladium

complexe 9k (monomeric phosphane adduct 6k with PPh3) and 10k (monomeric phosphane

adduct of 6k with PPh2P(o-Tolyl)) in the Suzuki coupling reaction of 4-chloroacetophenone

with phenyl boronic acid to get the coupling product 4-acetylbiphenyl. Coupling reactions

performed with 4-chloroacetophenone just show some limited activity (31% conversion by 1

mol% Pd of 6k) after more than 20h at 100°C. In contrast, 36% and 38% conversion were

achieved by monomeric palladium complex 9k and 10k, respectively, under the conditions

employed here too (Scheme 2.25). From these limited data, we cannot rule out a specific


82

rule on the effectiveness of four and five membered ring cyclometallated palladium

complexes 6e or 6k as catalyst in Suzuki cross coupling reaction, but we can judge from

these limited examples that the cyclometallated palladium complexes 6e (cyclometallated

palladium complex of 4e (R = tBu, R' = Neopentyl) and 6k (R = R' = tBu) have been found to

be less effective in Suzuki cross coupling reaction than ortho metallated palladium

complexes.[159, 162] In addition, the very low conversions observed with the using of either

four or five membered palladacycles 6e and 6k as catalysts in such cross coupling reaction

may be ascribed to the difficultness of generating the palladium active species through

reductive elimination.[159, 164-165]

Scheme 2.25: Suzuki cross-coupling reaction of 4-chloroacetophenone with phenyl boronic

acid catalyzed by 6k, 9k and 10k.

From this limited data set (Scheme 2.24), it would appear as though no significant different

between using dimmer or monomer palladium complexes in Suzuki cross coupling of

activated aryl chloride 7i. In addition, without further studies we could not completely rule

out the efficiency of cyclometallated palladium complexes 6k in Suzuki cross coupling

reaction. However, we then decided to examine the dimmer 6k and monomer 9k as catalyst

in Buchwald amination coupling reaction of different types of aryl halides with amines. In


83

general, the test reactions were performed in dioxan using KOtBu as a base at 95°C and 1

mol% catalyst loading. In the first example, we reacted 2-bromotoluene with morpholine in

order to evaluate the difference in activity of the dimmer palladium complex 6k as well as

the monomer one 9k over time. Figurer 2.15 shows the profile of these time dependent

reactions. We also reported kinetic investigation of the amination cross coupling reaction of

diethyl amine with bromobenzene (Figure 2.16). Each pair of substrates was heated at 95°C

with vigorous stirring. After 2.5, 5, 10, 20, 30, 60, 90, 120, 150, 180, 210, 240 and 300 min,

samples (~1 mL) were taken for characterization. The conversions were determined by

GC/MS spectroscopy.

0 20 40 60 80 100 120 140 1600

20

40

60

80

100

% C

on

vers

ion

Time(min)

30

30b

6k

9k

Figure 2.15: Kinetic Investigation of 6k and 9k in the Buchwald- Hartwig amination reaction

of 2-bromotoluene with morpholine (1 mol% [Pd], 95°C).

As shown in figure 2.15, we observed that the coupling reaction with deactivated or

sterically hindered aryl bromide, for example; 2-bromotoluene, was successfully coupled

after less than 120min by using of 6k (cyclometallated palladium complex of P(tBu)3) and the

monomeric palladium complexes 9k (monomer of 6k/PPh3) as catalysts. Moreover, no

significant differences were observed by using the di- or mononuclear palladium complexes

6k and 9k, respectively. Also an over all yield of 93% within 2.5h was achieved. Fu et al. also

reported the use of Pd(OAc)2 with a sterically hindered and electron rich trialkylphosphine


84

ligand, PtBu3, yielded the cross coupling product in excellent yield, 96%, within 6h at

elevated temperature.[83, 89-90]

0 50 100 150 200 250 3000

20

40

60

80

100

% C

on

vers

ion

Time(min)

30

30b

6k

9k

Figure 2.16: Kinetic Investigation of 6k and 9k in the Buchwald- Hartwig amination reaction

of bromobenzene with diethyl amine (1 mol% [Pd], 95°C).

In contrast, coupling reaction of diethyl amine with neutral aryl halide, such as

bromobenzene, was less successful and only led to approximately 49% and 16% conversions

after 120min by 6k and 9k, respectively. In contrast to previous studies [200], simple acyclic

secondary amines were poor substrates. Reactions carried out with 4-bromoacetophenone

and 4-chloroacetophenone with morpholine also showed some conversion rates.

For example, complete conversion of 4-bromoacetophenone at 95°C with 1 mol% catalyst

6k was observed in overall yield of 90% (Scheme 2.25, entry 3). In contrast, complete

conversion of 4-chloroacetophenone was less successful and only led to approximately 59%

(Scheme 2.25, entry 5). By using 6k and KOtBu in dioxane in the coupling reaction of

morpholine with 4-bromotoluene the product was obtained in 61% isolated yield (Scheme

2.26, entry 1). On the other hand, the cross coupling reaction of morpholine and

deactivated aryl chloride (such as 2-chlorotoluene) in presence of either 6k or 9k was

unsuccessful and yielded no product (just 14% conversion was observed) when our


85

optimized conditions were used. In addition, coupling reaction with more crowded and

sterically hindered aryl bromides, such as bromomesitylene, was less successful and only led

to approximately 24% isolated yield by 6k in boiling dioxane.

Scheme 2.26: Amination of aryl bromides and chlorides catalyzed by 6k (R = R' = tBu).

It was known from the work of Herrmann and co-worker that the using of orthometallated

triaryl phosphine palladium complexes in amination reactions of a wide range of aryl halides

and amines can be easily be achieved at high temperatures (100-135°C) in good yields. [162]

From this limited data set it would appear as though that cyclometallated palladium

complex 6k has been found to be less effective, for the coupling of aryl halides with amine,

than ortho metallated palladium complexes in spite of the presence of the electron rich and

sterically demanding ligand in cyclometallated palladium complex 6k. This result may be

suggests that the steric property could be more important in determining catalyst activity

toward aryl halides than the electronic properties of the ligand.

Then we expand our investigation to see what is the behaviour of the dinuclear

noncyclometallated palladium complex 6m ((P(iPr)2CH2Cy)2Pd2Cl4) as catalyst in Suzuki cross


86

coupling reaction. Firstly, the dinuclear palladium complex 6m was screened for their ability

to promote the Suzuki coupling of 4-bromoacetophenone and phenylboronic acid using

0.5% mol/Pd and sodium carbonate in dioxane/water mixture. This complex served as an

air-stable precatalyst that is highly effective for the coupling of 4-bromoacetophenone and

phenylboronic acid. In this reaction; complex 6m ((P(iPr)2CH2Cy)2Pd2Cl4) gave complete

conversion within 20 minutes. It is significant to accomplish good conversion and/or yields

using minimum amounts of catalysts. Therefore, we have examined the effect of catalyst

loading, of 6m ((P(iPr)2CH2Cy)2Pd2Cl4), on a convenient coupling between 4-bromoaceto-

phenone and phenylboronic acid at 80°C. Good conversion (100%, 98% and 93%) was

obtained from normal catalyst loads (0.5% mol) down to a level of 0.1 and 0.05 mol%,

respectively (Scheme 2.27). A low conversion (18%) was obtained even at catalyst loading as

low as 0.01 with a TON and TOF of 1800 and 3600, respectively. These are the indications of

an effective catalytic system that merits more downstream explorations.

Scheme 2.27: Influence of catalyst loading of 6m ((P(iPr)2CH2Cy)2Pd2Cl4) in Suzuki coupling of

4-bromocetophenon with phenylboronic acid .


87

Based in success of 6m in the test reaction, coupling of aryl bromides and chlorides with

phenylboronic acid were carried out. Complete conversions were obtained with activated

and deactivated aryl bromide as well as deactivated aryl chlorides. For example, complete

conversions of 4-chloroacetophenone at 90°C and 4-bromoanisol at 80°C with 0.5 mol%

catalyst 6m was observed within 120 min and 300 min, respectively. No significant

conversions to product occurred in attempts to couple sterically hindered aryl chloride using

0.5 mol% of 6m even at high temperature (110°C in toluene).

From this limited data set it would appear as though the dinuclear palladium complex 6m

has the greatest effect on the couplings involving electron deficient aryl bromide and

chloride than the cyclometallated one (e.g.; 6e and 6k). In addition, no significant effect on

the coupling of electron rich aryl chloride was obtained.

2.1.6.3 Substituted Trialkylphosphonium Salts in Suzuki-Miyaura Cross Coupling

Reaction.

As mentioned in the first chapter of this thesis, several groups have established that the

combination of bulky and electron rich phosphines with different type of palladium salts

show high catalytic activity in cross coupling reactions.[4, 89, 93-95] In our investigations,

selected examples of the prepared phosphonium salts were shown to be excellent ligands

for the palladium catalyzed Suzuki cross-coupling reaction, may be due to the possibility of

in situ deprotonation of the phosphonium salts under catalytic conditions. In order to test

the catalytic activity of phosphonium salts 4a (R = iPr, R' = Neopentyl), 4b (R = iPr, R' =

Neosilyl), 4f (R = tBu, R' = Neosilyl), 4i (R = iPr, R' = tBu), 4j (R = tBu, R' = iPr), 4l (R = iPr, R' =

CH(Et)2, 4m (R = iPr, R' = CH2Cy), and 4n (R = iPr, R' = CH2Cy), we have started to test the

Suzuki coupling reaction of activated aryl halides (such as 7c) with phenylboronic acid

(Scheme 2.28). This is a useful benchmark reaction to test new phosphonium salts as ligands

in such cross coupling reaction; because in the presence of standard aromatic

phosphines,[41] which are most often applied for Suzuki reactions of aryl halides, no

significant conversion takes place.

In general, the test reactions were performed in dioxan/water or toluene using K2CO3 or

Cs(CO3)2 as a base at 80°C, 90°C or 100°C at catalyst loading (0.5 mol% (or 1.5 mol%) of


88

palladium precursor (Pd(OAc)2 or [Pd2(dba)3]) and 1 mol% (or 3.6 mol%) of the respective

phosphonium salts.

As shown in Scheme 2.28, all tested phosphonium salts lead to active catalyst systems.

Hence, at least partial deprotonation of the phosphonium salts seem to occur under the

applied reaction conditions. Among the different phosphonium salts the tButyl derivative 4k

and 4n as well as the iPropyl derivative 4l (Scheme 2.28, entries 2, 3 and 4) showed

significant better catalytic activity compared to other phosphonium salts (except 4h). In

addition, time dependent experiments were performed in order to evaluate the difference

in activity of different catalyst systems over time (Figure 2.17).


89

Scheme 2.28: Suzuki coupling of 4-bromoacetophenon with phenylboronic acids catalyzed

by mixtures of Pd(OAc)2 and two equivalents of phosphonium salts [HPR2R'][BF4]; 4b (R = iPr,

R' = Neosilyl); 4k (R = R' = tBu), 4l (R = iPr, R' = CH(Et)2, 4m (R = iPr, R' = CH2Cy), 4n (R = tBu, R'

= CH2Cy) and 4o (R = iPr, R' = iBu).


90

0 20 40 60 80 1000

20

40

60

80

100

% C

on

vers

ion

Time(min)

4b

31

32

33

34

4b

4l

4m

4n

4o

Figure 2.17: Kinetic investigation of the Suzuki Miyaura cross-coupling reaction of 4-bromo-

acetophenone with phenylboronic acid with 0.5 mol% Pd(OAc)2/1 mol% 4 (4b (R = iPr, R' =

Neosilyl), 4l (R = iPr, R' = CH(Et)2, 4m (R = iPr, R' = CH2Cy), 4n (R = tBu, R' = CH2Cy) and 4o (R =

iPr, R' = iBu).

Reactions carried out with 3-chloroanisol also showed some conversion rates at 95°C with

0.5 mol% Pd(OAc)2/1 mol% phosphonium salt in presence of K2CO3 as a base and dioxane as

a solvent. For instance, we observed that the electron donating aryl chloride can couple

with the electron neutral boronic acid, by combination of Pd(OAc)2 and phosphonium salts

(4b, 4l, 4n and 4o), to generate 3-methoxybiphenyl in 11%, 21%, 10% and 4% conversions

within 60 minutes by 4b, 4l, 4n and 4o, respectively (Figure 2.18). Moreover, just 26%, 33%,

22% and 14% conversions within 240 minutes by 4b, 4l, 4n and 4o, respectively, were

observed too. Also 51% conversion was observed after 300 minutes by the catalyst system

which derived from phosphonium salt 4l. In contrast, coupling reaction with deactivated or

sterically hindered aryl chlorides, such as 2-chlorotoluene, was less successful and only led

to approximately 52% conversions by 4a, in boiling toluene after 48h, compared with 90%

within 5h at 80°C which have been reported by Fu and co-worker by using (1.5%

Pd2(dba)3/3.6% PtBu3) catalytic system in presence of cesium carbonate as a base and

dioxane as a solvent.[83, 84, 190]. On the other hand, only 7% conversion was observed by 4l

after 24h and no significant conversion was observed with 4b even at high temperature for

long period of time.


91

0 50 100 150 200 2500

20

40

60

80

100

% C

on

vers

ion

Time(min)

4b

31

33

34

4b

4l

4n

4o

Figure 2.18: Kinetic investigation of the Suzuki Miyaura cross-coupling reaction of 3-

chloroanisol with phenylboronic acid with 0.5 mol% Pd(OAc)2/1 mol% 4 (4b (R = iPr, R' =

Neosilyl), 4l (R = iPr, R' = CH(Et)2), 4n (R = iPr, R' = CH2Cy) and 4o (R = iPr, R' = iBu).

In order to test and compare the catalytic activity of substituted iso-propyl phosphonium

salts 4a, 4b and 4o, we have used these phosphonium salts in the Suzuki coupling reaction

of 2-bromotoluene with phenylboronic acid with 0.5 mol% Pd(OAc)2/1 mol% phosphonium

salt in presence of K2CO3 as a base and dioxane/water (2:1) as a solvent (Figure 2.19). We

were pleased to find that the coupling reaction with 2-bromotoluene led to 98%, 8.7% and

71% conversions within 10 minutes by phosphonium salts 4a, 4b and 4o, respectively. On

the other hand, complete conversions of 2-bromotoluene at 80°C with 4a, 4b and 4o were

observed after 20, 240 and 45 minutes, respectively (Figure 2.19).

Reactions carried out with 4-chloroacetophenone also showed some conversion rates. For

example, complete conversions of 4-chloroacetophenone, at 90°C with 0.5 mol% Pd(OAc)2

/1 mol% phosphonium salts in presence of K2CO3 as a base and dioxane/water(2:1) as a

solvent, were observed after 60, 120, 90 and 90 minutes by 4a, 4i, 4l and 4o, respectively.


92

0 50 100 150 200 2500

20

40

60

80

100

4a

4b

34

% C

on

vers

ion

Time(min)

4a

4b

4o

Figure 2.19: Kinetic investigation of the Suzuki Miyaura cross-coupling reaction of 2-bromotoluene with phenylboronic acid with 0.5 mol% Pd(OAc)2/1 mol% 4 (4a (R = iPr, R' = Neopentyl), 4b (R = iPr, R' = Neosilyl), and 4o (R = iPr, R' = iBu). From this limited data set it would appear as though the phosphonium salts have the

greatest effect on the couplings involving electron deficient aryl bromide and chloride and

low (or not significant) effect on the coupling of electron rich aryl chloride. A comparison of

the catalytic activity of the phosphonium salts, (Scheme 2.27, Figures 2.17, 2.18 and 2.19)

shows that in general the phosphonium salts 4l (R = iPr, R' = CH(Et)2) and 4o (R = iPr, R' = iBu)

gave better results in cross coupling of activated aryl halides compared to non or

deactivated ones. Nevertheless, with regard to a general use, the combinations of

phosphonium salts and Pd(OAc)2 constitute interesting catalyst systems due to the high

stability of all components towards air and water and thus the easy handling of the catalyst.

Next, the best two phosphonium salts 4l and 4m of substituted iPropyl were used for Suzuki

reactions of various activated and deactivated aryl halides. For electron-deficient aryl

bromides, e.g., acetyl substituted bromobenzene; excellent yields are obtained both in the

presence of substituted iPropyl and tButyl phosphonium salts. In the case of more

challenging substrates, e.g. 3-chloroanisole (Figure 2.18) the using of phosphonium salt 4l (R

= iPr, R' = CH(Et)2) gave the best result. In addition, the catalyst derived from phosphonium

salt 4a and Pd(OAc)2 gave very good yield of coupled product in the coupling of 2-


93

bromotoluene with phenylboronic acid. Similar yields are obtained by the catalyst system 4n

(R = iPr, R' = CH2Cy)/Pd(OAc)2, while the catalyst system derived from phosphonium salt 4l (R

= iPr, R’ = CH(Et)2) and Pd(OAc)2 gave the low yield of cross coupling product 2-

methylbiphenyl (Scheme 2.29).

Scheme 2.29: Suzuki coupling of 2-bromotoluene with phenylboronic acids using

phosphonium salts 4; 4a (R = iPr, R' = Neopentyl); 4b (R = iPr, R' = Neosilyl), 4f (R = tBu, R' =

Neosilyl), 4i (R = iPr, R' = tBu), 4l (R = iPr, R' = CH(Et)2, 4m (R = iPr, R' = CH2Cy), 4n (R = iPr, R' =

CH2Cy), 4o (R = iPr, R' = iBu).

Based on the success of the 4h ([HPCy2CH2C(CH3)3][BF4])/Pd2(dba)3 system (Scheme 2.28) in

the coupling of activated aryl bromide (4-bromoacetophenone) with phenylboronic acid

(Scheme 2.28), coupling of deactivated (4-bromoanisol) and sterically hindered (2-

bromotoluene) aryl bromide as well as activated (4-chloroacetophenone) and non-activated

(4-chlorotoluene) aryl chloride were carried out, scheme 2.30. Catalyst derived from the


94

cyclohexyl phosphonium salt 4h ([HPCy2CH2C(CH3)3][BF4]) showed modest activity toward

aryl chloride in the presence of cesium carbonate in dioxane. One of the most important

parts in our investigations was the success to get coupling product of the 4-chlorotoluene

with phenylboronic acid under Fu et al. conditions.[83-84, 190]

Scheme 2.30: Suzuki coupling of aryl halides with phenylboronic acids catalyzed by

4h([HPCy2CH2C(CH3)3])/Pd(OAc)2.

We were pleased to find that 4-chlorotoluene 7u and phenylboronic acid are efficiently

cross-coupled in the presence of 1.5% [Pd2(dba)3] (dba = dibenzylideneacetone), 3.6%

phosphonium salts 4h, 4m or 4n, and two equivalents of Cs2CO3 in dioxane; 86%, 56% and

69% yield have been observed by 1HNMR after 5.0h (Scheme 2.31, entry 10, 11 and 12)


95

compared with reported GC yield by Fu and co-worker for the same reaction. As shown in

scheme 2.31, good conversions of coupled products were obtained in the coupling of a non

activated aryl chloride 7u with phenylboronic acid using phosphonium salts 4h (R = Cy, Y =

Neopentyl), 4m (R = iPr, R' = CH2Cy) and 4n (R = iPr, R' = CH2Cy), although the catalyst

derived from phosphonium salt 4m (R = iPr, R' = CH2Cy) gave a lower conversion than the

catalyst employing 4h (R = Cy, R' = Neopentyl) or 4n (R = iPr, R' = CH2Cy). High temperatures

were required for those reactions.

1.5% [Pd2(bda)3]

3.6% Phosphane

Cl

+

B(OH)2

16

35

36

Entry Phosphane GC Yield, %ref

1 -

a:BINAP: 2,2'-bis(diphenylphosphanyl)-1,1'-binaphthyl.

b:1,1'-bis((diphenylphosphanyl)ferrocene.

c:100°C, 1HNMR Yield.

4 dppf

2 equiv Cs2CO3Dioxane, 80°C, 5h

2 PPh3

5 P(otol)3

6 Ph2P(CH2)3PPh2

7 Cy2P(CH2)3PCy2

8 PCy3

9 PtBu3

10 [HPCy2CH2C(CH3)3][BF4], 4h

11 [HPiPr2CH2Cy][BF4], 32

12 [HPtBu2CH2Cy][BF4], 33

3 BINAPa

b

c

c

c

0

0

0

0

10

0

0

75

86

86

56

69

Scheme 2.31: The comparison of a variety of phosphine ligands as reported by Fu et al.[83-84,

190]and our phosphonium salts 4h, 4m and 4n in the Suzuki coupling of 4-chlorotoluene and

phenylboronic acid.


96

Finally, despite of most of the catalyst systems depending upon their electronic and steric

properties proceed cleanly toward cross coupling product; there is a large range of them

cannot be regionalized simply by looking on their electronic and steric properties but also

must be related to the resistance of phosphine ligands toward side reaction. For example,

cyclometallation (vide supra). As we observed from our investigations, the less electron

donating and electron crowding performed, in some examples, better than the more

electron donating monophosphine system.


97

2.2. Synthesis, Characterization and Applications of New 2,2'-Bisphosphine and

2,2',6,6'-Tetraphosphine Biaryl Ligands in Palladium Catalyzed Suzuki Cross

Coupling Reaction.

2.2.1 Synthesis and Characterization of New 2,2'-Bisphosphine Ligands and their

Palladium and Platinum Complexes.

Monodentate, bulky, and electron-rich dialkylbiarylphosphines[126, 141] as well as 2,2'-

bisphosphine biaryles have seen wide use as supporting ligands in a variety of

transformations, especially in Pd-catalyzed carbon-carbon, carbon-nitrogen, and carbon-

oxygen bond-forming processes.[136, 143, 191-193] The biphenyl framework has two major

advantages that supported the use of such ligand in cross coupling reaction. One is that the

dihedral angles of the biaryls may be easily fine tuned by controlling the size of the

substituents at the 6 and 6' positions. Another advantage is that the basicity at phosphorus

can be adjusted simply by introducing substituents with differing electronic properties onto

the biaryl. Based on these ideas, in this part of our work we presented the synthesis of new

family of biarylphosphines.

2.2.1.1 Synthesis and Characterization of New 2,2'-Bis(dimethylamino)-6,6'-bis-

phosphinebiphenyl Ligands and their Palladium and Platinum Complexes.

We were able to implement a powerful strategy that allowed us to synthesize a new family

of 2,2'-bis(dimethylamino)-6,6'-bisphosphinebiphenyles in good yield through a series of

steps (Scheme 2.32) by employing known synthesis strategies starting from the

commercially available 4-methyl-2-nitroaniline 64. Bromonation of 64 to get 2-bromo-4-

methyl-6-nitroaniline 65, then simple diazotization–iodination process to get 2-bromo-4-

methyl-6-nitroaniline 66 which by Ullman coupling was converted to biarylbackbone 67;

2,2'-dibromo-4,4'-dimethyl-6,6'-dinitrobiphenyl. Reduction of 67 by means of Zn\H+, to

afforded 6,6'-dibromo-4,4'-dimethylbiphenyl-2,2'-diamine 68. The diamine 68 proceeds

cleanly through methalation, by Me2SO4 in presence of NaH, to get 6,6'-dibromo-

N,N,N',N',4,4'-hexamethylbiphenyl-2,2'-diamine 69, then metal-halogen exchange using n-


98

butyllithium followed by reaction either with PPh2Cl to afforded 6,6'-

bis(diphenylphosphine)-N,N,N',N',4,4'-hexamethylbiphenyl-2,2'-diamine 70, or with PiPr2Cl

to get 6,6'-bis(di-iPropylphosphine)-N,N,N',N',4,4'-hexamethylbiphenyl-2,2'-diamine 71.

Scheme 2.32: Synthesis of biaryl backbone phosphines 70 and 71.

Looking at the 1H NMR of the bisphosphine 71 (Figure 2.20), the protons of the CH3 group on

the phenyl ring appeared as a singlet at δ = 2.39 ppm (compared with δ = 2.27 ppm of

bisphosphine 70), while the protons of the N(CH3)2 group was appeared as singlet at δ = 2.42

ppm (compared with δ = 2.08 ppm of bisphosphine 70). Moreover, duplet of duplet of

CH(CMe2)2 were appeared at 1.38 with 3JPH = 11 Hz and 3JHH = 6.9 Hz as well as at 1.17 with

3JPH = 15 Hz, 3JHH = 7.4 Hz, and at δ = 1.26 with 3JPH = 21 Hz and 3JHH = 6.90 Hz. The 31P{1H}

NMR spectrum of pure 71 revealed one singlet peak at δ = -1.39 ppm, while was appeared

as singlet at δ = -11.60 of the bisphosphine biphenyl 70. In addition, the two different


99

protons on the biphenyl group were appeared as a singlet at δ = 7.31 ppm (compared with

broad singlet at δ = 6.80 ppm of bisphosphine 70) and as a duplet at δ = 6.90 ppm.

Figure 2.20: 1H-NMR spectrum of bisphosphine ligand 71 in CDCl3.

The appropriate palladium dichloride complexes 72 and 73 are accessible by treatment of

biaryl phosphine ligands with Pd(cod)Cl2 in CH2Cl2 at room temperature (Scheme 2.33).

Moreover, the platinum dichloride complex 74 was obtained by direct reaction of

bisphosphinebiphenyl 70 with one equivalent of Pt(Et2S)2Cl2 in CH2Cl2 at room temperature

too.


100

Scheme 2.33: Synthesis of palladium and platinum biarylbackbone phosphines complexes

72-74.

Looking at the1H NMR of the complexes 72 and 73, the protons of CH3 group on the phenyl

ring was appeared as singlet at δ = 2.01 ppm and δ = 2.38 ppm, respectively (compared

with δ = 2.39 ppm and δ = 2.27 of bisphosphine 70 and 71, respectively), while the protons

of the N(CH3)2 group was appeared as singlet at δ = 2.32 ppm and δ = 2.56 ppm in 72 and 73,

respectively (compared with δ = 2.08 ppm and δ = 2.42 of bisphosphine 70 and 71,

respectively ). Moreover, duplet of duplet of CH(CMe2)2, in 73, were appeared at δ = 1.01

with 3JPH = 15 Hz and 3JHH = 7.15 Hz as well as broad signal at δ = 1.28, and broad signal at δ =

1.55 ppm. Moreover, the 31P{1H} NMR spectra of pure 72 and 73 revealed one singlet peak

and broad singlet at δ = 31.64 ppm and broad at δ = 46.40 ppm, respectively. In addition the

two different protons on the biphenyl group of the complexes 72 and 73 were appeared as

a singlet at δ = 6.038 ppm and δ = 6.86 ppm, respectively (compared with δ = 6.90 ppm and

δ = 6.80 of bisphosphine 70 and 71, respectively), and as a duplet at δ = 6.54 ppm with 3JPH =

13 Hz and δ = 7.08 ppm with 3JPH = 9 Hz, respectively.


101

In the case of platinum complex 74, the 31P{1H} NMR spectrum of 74 in CDCl3 showed a

singlet at δ = 11.79 ppm with platinum satellites (1JPt-P = 3640 Hz). Similarly, variable-

temperature (VT) 1H NMR spectroscopic studies (figure 2.21) as well as 31P{1H} NMR (figure

2.22) were performed in order to gain more information on the dynamic behaviour of

complex 74. (VT) 1H NMR was measured in CD2Cl2 in the temperature range of 183 - 273K.

Only one feature was observed; splitting of the signals assigned to the phenyl group,

suggesting a hindered rotation on the time scale of the NMR experiments at low

temperature (183 K). Note that the ease of rotation is almost unaffected by the introduction

of the methyl group in 4 and 4'-positions in the biphenyl backbone. On the other hand, at all

temperature no significant features were observed by the (VT) 31P{1H} NMR studies and the

spectra were almost identical.

Figure 2.21: Variable temperature 1H NMR (500MHz) of 74 in CD2Cl2.


102

-6-30246811141720232629

273 K

253 K

233 K

213 K

193 K

138 K

Figure 2.22: Variable temperature 31P{1H} NMR of 74 in CD2Cl2.

The solid state structures of 72, 73 and 74 were determined by single crystal X-ray

crystallography. Crystals suitable for X-ray studies for complexes 72, 73 and 74 were grown

by slow diffusion of pentane vapour into solutions of dichloromethane containing the

complexes at room temperature. The molecular structures of 72, 73 and 74 are shown in

Figure 2.23, 2.24, and 2.25. Selected bond lengths and bond angels of 72, 73 and 74 are

given in table 2.11. Crystal data, together with the data collection and refinement

parameters for all complexes are presented in the appendix.

The palladium atom in complex 72 (Figure 2.23) is in square planner configuration with the

bond angels around the palladium atom of 360°. Palladium metal has four atoms in its

coordination sphere; two phosphorus and two chlorides. The Pd-Cl bond length was

2.3592(8) Å, while the Pd-P bond length was 2.2466(8) Å. The Pd-P and Pd-Cl bond lengths

fall in the expected range of values for similar palladium complexes.[187]


103

Figure 2.23: Molecular structure of 72 (Pd; orange, P; yellow, N; blue, Cl; green and C; gray).

Figure 2.24: Molecular structure of 73 (Pd; orange, P; yellow, N; blue, Cl; green and C; gray).


104

Figure 2.25: Molecular structure of 74 (Pt; pink, P; yellow, N; blue, Cl; green and C; gray).

2.2.1.2 Synthesis and Characterization of New 2,2'-bis(dibromo)-6,6'-bisphosphine-

biphenyl Ligands and their Palladium and Platinum Complexes.

We have prepared new biphenyl backbone phosphine ligands using of the same strategy

which we described for the synthesis of biphenylbisphosphine 70 and 71 (Scheme 2.32),

starting from synthesis of 2,2'-dibromo-6,6'-diiodo-4,4'-dimethylbiphenyl 75 by simple

diazotization–iodination[179a] of the diamine 68, then upon treatment of 75 with two

equivalents of n-BuLi and subsequent with excess amount of either PPh2Cl to afforded 2,2'-

dibromo-6,6'-bis (diphenylphosphine)-4,4'-dimethylbiphenyl 76 [179b], or PiPr2Cl to get 2,2'-

dibromo-6,6'-bis (diiPropylphosphine)-4,4'-dimethylbiphenyl 77 as colourless oil which after

recrystallization from ethanol yielded the analytical pure compound as a white powder

(Scheme 2.34). Of good advantage of the lithination process of biphenyl back bone 75 over

the lithination of 69; that this process tacks place quickly and only effected the iodine

substrate subsequently the transformation to bisphosphine proceed smoothly at relatively

low temperature.


105

Scheme 2.34: Synthesis of biaryl backbone phosphines 76 and 77.

The 31P{1H} NMR spectrum of analytically pure products of 76 and 77 revealed one singlet

peak at δ = -12.04 ppm and a broad at δ = 45.02 ppm, respectively. Similarly the 1H NMR

spectrum of 76 and 77 shows two signal at δ = 6.98 ppm, 7.38 ppm and δ = 7.23 ppm, 7.41

ppm, respectively, for the four aromatic protons as well as one resonance at δ = 2.27 and at

δ = 2.01 ppm, respectively, which can be assigned to the two equivalent methyl groups in

the 4,4’ position at the biphenyl moiety. Moreover, two set of signal was appeared, for 77,

as duplet of septet at δ = 2.20 ppm with 2J(P,H) = 6.50 Hz and 3J(H,H) = 7.3 Hz which can be

assigned to the CH(Me)2 group. Finally, the protons of phenyl group of phosphorus were

appeared in the range of (δ = 7.129 – 7.76 ppm). All synthesized phosphines were

characterized by 1H, 13C, 31P{1H} NMR, IR, elemental analysis, mass spectroscopy as well as

melting point and single-crystal X-ray structure analysis for 77 (Figure 2.28).

Then we gained access to the phenyl and isopropyl decorated bisphosphinebiphenyl 78 and

79 palladium complexes by treatment of the new bisphosphinebiphenyl 76 and 77 with

[Pd(cod)Cl2] (cod = 1,5-cyclooctadiene) in dichloromethane at room temperature (Scheme

2.35). Both complexes 78 and 79, isolated as air stable yellow powders, have been


106

characterized by NMR (1H, 13C, 31P) and mass-spectroscopic data, by satisfactory elemental

analysis data and by single-crystal X-ray structure analysis (Figures; 2.29 and 2.30).

Scheme 2.35: Synthesis of palladium and platinum biaryl backbone phosphines complexes

78-81.

The 31P{1H} NMR spectrum of analytically pure product of 78 revealed one singlet peaks at δ

= 30.50 ppm. Similarly the 1H NMR spectrum of 78 shows two signals at δ = 7.03 ppm (s, Ar-

H, biph) and 6.90 ppm (d, 3JPH = 11.7 Hz, Ar-H, biph) for the four aromatic protons as well as

one resonance at δ = 2.05 ppm, which can be assigned to the two equivalent methyl groups

in the 4,4’ position at the biphenyl moiety. Finally, the protons of phenyl group of

phosphorus were appeared at 8.01, 7.81, 7.37, 6.97-6.94 ppm. In the case of palladium

complex 79, the 31P{1H} NMR spectrum of pure product revealed one broad singlet peak at δ

= 45.07 ppm. In addition, the 1H NMR spectrum of 79 shows two signal at δ = 7.50 ppm (as a

singlet) and 7.50 ppm (as a duplet with 3JPH = 9.10 Hz) for the four aromatic protons as well

as one resonance at δ = 2.46 ppm, which can be assigned to the two equivalent methyl

groups in the 4,4’ position at the biphenyl moiety. Finally four signals were appeared in the

alkyl region, one of them as duplet of duplet at δ = 1.05 ppm (3J(P,H) = 9.7 and 2J(H,H) = 6.5

Hz) which can be assigned to the methyl group of the iPropyl fragment, the second one was


107

appeared as broad signal at δ = 1.25 ppm which can be assigned to the second methyl group

of isoprpyl fragment, the third one was appeared as duplet of duplet at δ = 1.58 ppm

(3J(P,H) = 16 Hz and 2J(H,H) = 6.9 Hz) which can be assigned to the two methyl (CH(Me)2)

group. Finally, one resonance at δ = 2.35 ppm which can be assigned to the two equivalent

methyl groups in the 4,4’ position at the biphenyl moiety. Important properties that singled

out these types of phosphine biaryl backbone ligands including: (a) They are air and thermal

stable ligands (except 71 and 77) and (b) They are crystalline materials.

In the case of platinum complex 79, the 1H NMR spectra was cleared to assigned the signal

for every proton and in order to obtain more information on the dynamic behaviour of

complex 79; variable-temperature (VT) 31P{1H} spectroscopic studies (Figure 2.26) was

performed. (VT) 31P{1H} NMR were measured in CD2Cl2/DMF in the temperature rang (183 -

373K). Only one feature was observed; the broad singlet found in 31P{1H} NMR spectra

which can be assigned to the average signal for phosphorus atoms splits into four broad

signals at low temperature due to presence of two conformers with C1-symmetry (178 K).

Two coalescences were found (Figure 2.26). The platinum complexes 80 and 81 were

obtained by reacting Pt(Et2S)2Cl2 with the new bisphosphinebiphenyl 76 and 77 in

methylene chloride at room temperature. Both complexes 80 and 81 were isolated as air

stable pale yellow to off-white powders. The 31P{1H} NMR spectrum of 80 in CDCl3 showed a

singlet at δ = 11.58 ppm with platinum satellites (1JPt-P = 3600.50 Hz), figure (2.27). While

was appeared in the case of platenium complex 81 at δ = 22.51 ppm with platinum satellites

(1JPt-P = 4000.80 Hz).


108

178 K

198 K

223 K

248 K

273 K

298 K

323 K

338 K

373 K

38.039.040.041.042.043.044.045.046.047.048.049.050.051.0

Figure 2.26: Variable temperature 31P{1H} NMR of 79 in CD2Cl2/DMF.

Figure 2.27: The 31P{1H} NMR of 80 in CDCl3.


109

The solid state structures of 77, 78 and 79 were determined by single crystal X-ray

crystallography. Crystals suitable for X-ray studies for bisphosphinebiphenyl 77 was grown

at low temperature (-20°C) from ethanol solution containing the ligand. While crystals

suitable for X-ray studies for complexes 78 and 79 were grown by slow diffusion of pentane

vapour into solutions of dichloromethane containing the complexes at room temperature.

The molecular structure of 77 is shown in Figure 2.28, 78 in Figure 2.29, while 79 in Figure

2.30. Selected bond lengths and bond angels are given in table 2.11 for all

bisphosphinebiphenyl deratives. Crystal data, together with the data collection and

refinement parameters for all complexes are presented in the appendix.

The palladium atom in complex 78 (Figure 2.29) is in distorted square planner configuration

with the bond angels around the palladium atom of 368°. The palladium metal has four

atoms in its coordination sphere; two phosphorus and two chlorides. The Pd-Cl bond length

was 2.373(3), while the Pd-P bond length was 2.243(3). In other hand, the palladium atom in

complex 79 (Figure 2.30) was in square planer configuration with the bond angel around the

palladium atom 360,2°. Palladium metal has four atoms in its coordination sphere; two

phosphorus and two chlorides. The Pd-Cl bond length was 2.3721(7), while the Pd-P bond

length was 2.2920(8). The Pd-P and Pd-Cl bond lengths fall in the expected range of values,

but quite long, for similar palladium complexes. [187]


110

Figure 2.28: Molecular structure of bisphosphinebiphenyl 77 (P; yellow, Br; red and C; gray).

Figure 2.29: Molecular structure of palladium complex 78 (Pd; orange, P; yellow, Br; red, Cl;

green and C; gray).


111

Figure 2.30: Molecular structure of palladium complex 79 (Pd; orange, P; yellow, Br; red, Cl;

green and C; gray).

Selcted bond lengths and bond angles of all synthesized palladium complex (72, 73, 78 and

79), platinum complex 74 as well as bisphosphinobiphenyl 77 are presented in table (2.11).


112

Table 2.11: Selected bond lengths (Å) and angles (°) of 72, 73, 74, 77, 78 and 79.


113

2.2.2 Bisphosphinbiphenyl Palladium Complexes in Suzuki-Miyaura Cross-Coupling

Reaction.

The key compound in the reaction is the catalyst. Thus we employed all prepared palladium

complexes 72, 73, 78 or 79 as catalyst for simple Suzuki cross coupling. In expansion to our

work on mono phosphines we used the formation of substituted biphenyls from

phenylboronic acid and different types of alkyl halides in the presence of palladium complex

72, 73, 78 or 79. For initial studies, 4-bromotoluene was chosen as the main test substrate,

we were delighted to see that all complexes 72, 73, 78 or 79 catalyzes the reaction between

4-bromotoluene and phenylboronic acid smoothly at mild reaction conditions (palladium

complex 0.5 mol%, Dioxan\Water (2:1) and at 85°C), figure (2.31).

0 20 40 60 80 1000

20

40

60

80

100

% C

on

vers

ion

Time(min)

72

73

78

79

Figure 2.31: Kinetic investigation of biarylbackbone palladium complexes 72 (NMe2, Ph), 73

(NMe2, iPr), 78 (Br, Ph), and 79 (Br, iPr) in Suzuki cross coupling reaction of 2-bromotoluene

with phenylboronic acid (0.5 mol% [Pd], 85°C).

Most properly the effectiveness of these complexes was attributed to a combination of

electronic and steric properties of the bisphosphinebiphenyl ligand that favor both the

oxidative addition and reductive elimination steps in the catalytic cycle. In addition, higher


114

conversion rates were realized with all complexes 72, 73, 78 or 79 when activated aryl

bromide and chloride were used as substrates. Coupling reactions performed with 4-

bromoacetophenone yielded 64% 4-acetylbiphenyl after 10 minutes by 72, while complete

conversion was achieved after 30 minutes. Moreover, complete conversion was achieved

under the same reaction condition by 73, 78 and 79 after 20 min, 60 min and 30 min,

respectively.

In other hand, complete conversions of 4-chloroacetophenone at 80°C with 0.5 mol%

catalysts 72, 73, 78 or 79 were observed within less than 1h. In addition, we also reported

the kinetic investigation of cross coupling of 4-bromoanisol with phenyl boronic acid at

catalyst loading of 0.5% mol 79, figure 2.32.

From this limited data set it would appear as though the bisphosphinebiphenyl backbone

palladium complexes 72, 73, 78 or 79 perform nearly as well as the monophosphine

palladium complexes presented in the previous chapter 2.1. However, we cannot rule out of

the use of these complexes as effective catalyst in cross coupling reactions without further

investigations.

0 20 40 60 80 1000

20

40

60

80

100

% C

on

ve

rsio

n

Time(min)

79

Figure 2.32: Kinetic Investigation of 79 in the Suzuki cross coupling reaction of 4-

bromoanisole with phenylboronic acid.


115

2.2.3. Synthesized and Characterization of 2,2’,6,6’-tetraphosphinobiphenyl and a

Related Dinuclear Palladium Complex.

Having synthesized mono and diphosphines we have been encouraged to prepare a highly

symmetric 2,2’,6,6’-tetraphosphinobiphenyl. Employing the same synthesis strategies as

described a bove in preparation of biphosphine biphenyl 76 and 77, we gained access to the

isopropyl decorated tetraphosphane 82 by a “one-pot-two-step” synthesis starting from the

2,2'-dibromo-6,6'-diiodo-4,4'-dimethylbiphenyl 75, scheme 2.35. Upon treatment of 75 with

two equivalents of n-BuLi and subsequent reaction with excess of iPr2PCl molecule 77 is

formed. Diphosphane 77 gives upon reaction with another two equivalents of n-BuLi and

subsequently with iPr2PCl a crude product of 82. Column chromatography and crystallization

from ethanol yields pure 82 (Scheme 2.36).

Scheme 2.36. Synthesis of 2,2’,6,6’-tetraphosphinobiphenyl 82 and its related complex 83.


116

The 31P{1H} NMR spectrum of the 2,2’,6,6’-tetraphosphinobiphenyl 82, showed the high

symmetry of 82, only one signal at δ = 9.29 ppm was appeared. Similarly the 1H NMR

spectrum of 82 shows one set of signals for the eight equivalent isopropyl groups, one signal

for the four equivalent aromatic protons was appeared at δ = 7.25 ppm as well as one

resonance which can be assigned to the two equivalent methyl groups in the 4,4’ position at

the biphenyl moiety was appeared at δ = 2.38 ppm. The number of signals is consistent with

the expected D2h symmetry of 82 with three C2-axis (C2(z)-axes in line with the central C-C

bond of the biphenyl moiety and the two symmetry equivalent axis C2(x) and C2(y)

perpendicular to the central C-C bond) as well as a S4-axis and two mirror planes.

Interestingly, 82 is only sparingly soluble in DMSO but well soluble in ether/hexane.Due to

the high proximity of the phosphane moieties in 82 the lone pairs of the phosphorous atoms

are effectively shielded what is also reflected by the low reactivity of 82 towards Pd(cod)Cl2

(cod = cycloocta-1,5-diene). Therefore, molecule 82 was reacted with the more reactive

palladium acetate followed by addition of sodium chloride solution to yield the desired

dinuclear palladium complex 83. Complex 83 shows a fluxional behavior and a site exchange

is observed indicated by highly temperature dependent NMR spectra. Coordination of 82 to

palladium caused large conformational changes in the ligand and lead to a hindrance of the

free rotation of the isopropyl groups in 83. This becomes apparent in very broad lines in all

NMR spectra recorded at ambient temperature and in order to obtain more information on

the dynamic behaviour of complex 83; variable-temperature (VT) 31P{1H} spectroscopic

studies were performed (Figure 2.33). For example, one signal with line widths about 600 Hz

is found at 51 ppm in the 31P{1H} NMR spectrum. Recording the spectra at 473 K in d7-DMF

decreases the broadening and the averaged signal over all conformers at δ = 53.9 again

shows the high symmetry of 83 (Figure 2.33).


117

Figure 2.33: Variable temperature 31P{1H} NMR spectra of complex 83 in d7-dmf solution at

178, 198, 223, 248, 273, 298, 323, 348, and 373 K respectively (from bottom to top), the

spectra have been scaled in order to make the broad signals visible, spectrum at 178 K has

been recorded in CD2Cl2/d7-dmf mixture.

In addition, due to the coordination of phosphine 82 to palladium the eight isopropyl groups

split into two sets of four equivalent isopropyl groups. A selective NOE NMR experiment

(Figure 2.34) with excitation on the aromatic proton showed contact to the axial isopropyl

groups that allowed the assignment to the axial array and the equatorial side (axial array:

CH at δ = 4.04 (dsep; 2J(P,H) = 10.4 Hz, 3J(H,H) = 7.1 Hz); CH3 at δ = 1.97 (dd, 3J(P,H) = 17 Hz,

3J(H,H) = 7.2 Hz), 1.81 (dd, 3J(P,H) = 15 Hz, 3J(H,H) = 7.1 Hz) and equatorial side: CH at δ =

2.15 (dsep; 2J(P,H) 8.7 Hz, 3J(H,H) = 7.1 Hz); CH3 at δ = 1.47 (dd, 3J(P,H) = 20.6 Hz, 3J(H,H) =

7.2 Hz), 1.40 (dd, 3J(P,H) = 14 Hz, 3J(H,H) = 7.2 Hz)).

The found number of signals at 373 K is consistent with the lower D2 symmetry of complex

83 compared to the free ligand 82. Decreasing the symmetry from D2h to D2 leads to the loss

of the S4-axes and the mirror planes. In consequence, the dinuclear palladium complex 83 is

chiral with three perpendicular C2 axes. The axis C2(x) (through the Pd-atoms and middle of


118

the central C-C bond) and C2(y) (perpendicular to C2(x) and C2(z)) are not symmetry

equivalent.

Figure 2.34: Standard proton nmr spectrum, of 83, (top) and 1H selective NOE spectrum [198]

(buttom) with irradiation at the aromatic proton at δ = 8.25 a mixing time of 0.5 sec and 64

transients recorded in d7-dmf at 398K. Peaks marked with * are water, residual solvent

protons, and CH2Cl2.

Similarly, cooling the solution results in a splitting of the broad signal in the 31P{1H} NMR

spectrum into 14 detected signals (Figure 2.35). Based on the intensities the signals found at

223 K can be assigned to four conformers: three C1 symmetric conformers A, B, C giving rise

to 4 signals each: A1-4 (δ = 54.2; 49.9; 46.0; 42.3 ppm), B1-4 (δ = 61.0; 40.5; 64.4; 45.2 ppm),

C1-4 (δ = 53.5; 40.4; 49.7; 46.2 ppm) and one D1-2 (δ = 51.9; 48.3) with two signals indicating

that one C2 axis is still appropriate (Figures 2.35 and 2.36). Conformers A - D are found in the

ratio of 13:21:17:49 at 223 K; at lower temperature signals for conformers A, and B,

respectively, are weaker and the signals for C and D become dominant (at 198 K:

11:17:20:51 and at 178 K: 11:8:24:57). That means the energy minimum conformer of

complex 83 is either C or D. Down to the lowest accessible temperature for solution studies

the signals sharpen which indicate that the rotation of the isopropyl groups is frozen at the


119

31P NMR time scale (Figure 2.38). P-P exchange in conformer D must occur through at least

one conformer higher in energy and lower in symmetry, which might be one assigned to the

signal groups A, B, or C, respectively. To deepen knowledge of this process, we recorded 2D

31P{1H} EXSY NMR spectra at 208 K in a d7-DMF/CH2Cl2 mixture (ratio 1:2) (Figure 2.36).

Figure 2.35: 31P{1H} NMR spectrum of complex 83 in d7-dmf at 223K, signals were grouped based on the signal intensity and line broadening.

The observed exchange signals for the direct P-P exchange are very small, although they

should be the strongest as conformer D is the dominant species. Exchange crosses peaks of

signal D1 with B1/2 and C1/2 as well as D2 with B3/4 and C3/4, respectively, are found. However,

this alone does not explain the P-P exchange. Due to limitation in the solubility of complex

83 and the necessary low temperatures we have not been able to obtain a signal to noise

ratio allowing detection of cross peaks between other conformers. However, a good guess

of the reaction rate is the coalescence point, and that gives k = 0.5 kHz at 298K for the P-P

exchange.


120

Figure 2.36: 31P{1H} EXSY spectrum of complex 83 at 208K in d7-DMF/CH2Cl2 mixture (ratio 1:2), the cross peaks for the P-P exchange within conformer D is marked with green boxes, note that this cross peaks would have higher intensity due to the dominant conformer D if the P-P exchange would be comparable fast within D. The colored lines on the top should indicate the correlation between the exchanging signals. This spectrum has been recorded with 2048 transients in F2 and 128 transients in F1 and a mixing time of 0.6 sec. Conformer A does not show exchange signals in this spectrum.

By diffusion of n-pentane vapor into a solution of complex 83 in CH2Cl2/MeOH crystals

suitable for single crystal X-ray structure determination could be obtained. Complex 83

crystallized in the monoclinic crystal system, space group P1 (Figure2.37) and selected bond

lengths (Å) and bond angles (°) of 83 are presented in table 2.12. Crystal data, together with

the data collection and refinement parameters for all complexes are presented in the

appendix (Table 2.13). The asymmetric unit includes two molecules of 83 and five molecules

of CH2Cl2 and one of methanol (Figure 2.38). In contrast to the results of the low

temperature NMR spectra, in the solid state none of the molecules of complex 83 has

crystallographic symmetry. The isopropyl groups of the ligand are tightly packed and show


121

short contacts to neighboring methyl groups as well as to the aromatic protons at the

biphenyl moiety.

Figure 2.37: Molecular structure of complex 83.

Table 2.12: Selected bond lengths (Å) and angles (°) of 83.

Pd1-Pd2 7.7430(4) C27-P3 1.857(4)

Cl1-Pd1 2.3738(9) P1-Pd1-P2 91.46(3)

Cl2-Pd1 2.3628(9) P1-Pd1-Cl2 170.51(4)

Cl3-Pd2 2.3640(9) P2-Pd1-Cl2 95.37(3)

Cl4-Pd2 2.3327(12) P1-Pd1-Cl1 86.78(3)

C32-P4 1.853(4) P2-Pd1-Cl1 176.01(4)

C30-P3 1.855(4) Cl2-Pd1-Cl1 85.98(3)

P1-Pd1 2.2744(9) P4-Pd2-P3 92.80(4)

P2-Pd1 2.2782(9) P4-Pd2-Cl3 167.49(4)

P3-Pd2 2.2993(11) P3-Pd2-Cl4 172.56(4)

P4-Pd2 2.2492(9) P4-Pd2-Cl4 90.84(4)

C36-P4 1.853(4) P4-Pd2-P3 92.80(4)

C21-P2 1.873(4) P3-Pd2-Cl3 89.65(4)

C24-P 1.860(4) Cl4-Pd2-Cl3 88.18(4)


122

Figure 2.38: Ortep drawing of the complete asymmetric unit of crystals of complex 83.

Not unexpectedly one of the molecules shows disorder that could not be fully resolved;

however, the other has been refined without disordered parts (Figure 2.38). The most

striking feature is the almost square planar coordination of the two palladium complex

fragments. Contrary to the expectation for a 2,2’-diphosphine biphenyl ligated palladium

complex but in accordance with NMR spectroscopy the palladium atoms are bent away from

the expected C2(x) axes through the midpoints of the phosphorus atoms in 2,2’- and 6,6’-

positions, respectively, and the centroid of the central C-C bond in the biphenyl moiety.

Therefore, the two palladium complex fragments are C1 symmetric, similar observations

have been found in mononuclear transition metal complexes with related structure.[199] The

isopropyl groups do not show clear preference for edge or face orientation, however, in

nearly all PdP-CH(Me)2 moieties stacked conformation is found. The found multitude of

orientations of the isopropyl groups in the solid state raises the question which conformer is

the dominant one assigned to signal group D observed in the low temperature 31P NMR


123

spectrum. As the crystals have been grown at ambient temperature different conformers

are thermally accessible. Moreover, the one with the highest entropy will become the

dominant conformer in solution and also the one fitting the best in the crystal lattice will be

depicted from the mixture and subsequently found in the solid state structure. For those

reasons it is not wise to draw too many correlations between conformers observed in

solution and in solid state. But if one omits the orientation of the isopropyl groups, the

molecular structure of all molecules found in solid state point to the assumption that the

former C2(z)-axes remain valid. Hence, most likely conformer D is C2-symmetric with the C2-

axis in line with the central C-C bond. However, clearly the spatial arrangement of the

isopropyl groups is highly interdependent as the observation of only four conformers in the

31P NMR spectrum with the C2 symmetric conformer D as the dominant species

demonstrates. The two complex fragments combined in 83 cannot simply be treated as

combination of two fluxional fragments but are cross linked and sense each other.

In summary, we have for the first time synthesized a highly symmetric 2,2’,6,6’-

tetraphosphane biphenyl and a related dinuclear palladium complex 83 employing 82 as

ligand. The complex shows complicate temperature dependent NMR spectra that have been

rationalized by intramolecular interaction of the isopropyl groups (gear effect). Only a minor

number of possible conformers of complex 83 are observed at low temperatures with more

than 50 % of the molecules adopting the C2 symmetric conformation D.

As the spatial arrangement of the ligands around a metal center often controls the reactivity

and properties (e. g. color, spin state) the found interaction can be recognized as a kind of

communication or coupling pathway between the palladium complex fragments through

the ligand skeleton similar to the allosteric interaction in enzymes. Systems that are able to

couple magnetic or electronic properties of metal complexes are of high interest in material

science.

Chapter 3: Experimental Section

124

Chapter

3

3. Experimental Section.

3.1 General Remarks: Equipment, Chemicals and Work Technique. 3.1.1 Chemicals and Work Technique.

All reactions handling sensitive chemicals were carried out under an argon inert gas

atmosphere using standard Schlenk and cannula techniques. All solvents were distilled by

standard methods. Tetrahydrofuran and diethyl ether were freshly distilled from sodium

benzophenone ketyl under argon, and solvents that are commercially available, ethanol and

dimethylforamide, were used without further purification unless otherwise noted.

Methylene chloride was distilled freshly from calcium hydride under argon. All other

chemicals were purchased by commercial suppliers (Merck®, Aldrich®, Arcos® and others)

and were used without further purification. Silica gel (230-400 mesh) 122 was used for flash

column chromatography. All air stable compounds were concentrated using a rotary

evaporator and reduced pressure.


125

3.1.2 NMR Spectroscopy.

All NMR spectra have been recorded on a 500MHz Bruker AVANCE III spectrometer. Proton

spectra are referenced to the residual protons of the deuterated solvent (d7-dmf: δ = 8.18

ppm formyl proton; CDCl3: δ = 2.26 ppm; d6-DMSO: δ = 2.50 ppm; C6D6: δ = 7.16 ppm);

31P{1H} NMR spectra are referenced to 85% H3PO4 as external standard. 13C-NMR are

referenced internally to the 13C-NMR signal for the deuterated solvent. In variable

temperature investigating; temperature of the sample has been measured by the internal

sensor of the probe head and is not corrected. Before accumulating data probe head and

spectrometer were allowed equilibrate for 10 min at the desired temperature.

3.1.3 Mass Spectroscopy.

All mass spectra were recorded on a Bruker micrOTOF-QIIa mass spectrometer operating in

ESI mode.

3.1.4 Infrared Spectroscopy (IR).

All Infrared spectra were recorded with a Nicolet IR200 FT-IR spectrometer.

3.1.5 Elementary Analysis.

Elemental analyses were performed using a Thermo FlashAE 1112 analyser.

3.1.6 Melting Points.

All Melting point's were recorded with a type MFB 595 010 type. Melting points were not

corrected.

3.1.7 Gas Chromatography-Mass Spectrometry.

All GC/MS investigations were recorded with a varian, star 3400 Cx spectrometer.

3.1.8 Single crystal X-ray Analysis.

Reflection data have been collected on an Oxford Gemini S diffractometer with graphite-

monochromatized Mo Kα radiation (λ = 0.71073 Å). All structures have been solved by direct

methods (SIR92)[171] and refined against ΙFoΙ2 with the SHELXS 97[172] and SHELXL 97[173],


126

respectively. Ortep-3 for Windows[174] and Mercury were employed for structure

presentation.

3.1.9 Column Chromatography.

Chromatography was performed over Merck silica gel 60 (0,063 -0,200 mm, 70 - 230 mesh).

Some solvent were distilled before use.

3.1.10 TLC.

Merck DC finished foils silica gel 60 F254 on aluminum foil and Macherey finished foils

Alugram® Sil G/UV254. Detection under UV light with 254 nm.

3.2 Experimental Procedures and Spectroscopic Data.

3.2.1 Synthesis of [Ph2PCH2C(Me)3] 3c :

To a 200 mg (63.4mmol, 2.2 equiv) of Lithium\ 4% sodium alloy in 25 mL diethyl ether (5 mL)

was added at -40°C during a period of 15 min. a solution of neopentylbromide (4.35g, 28.82

mmol, 1.0 equiv). The resulting mixture was stirred for 45 min at -40 °C and 2h at r.t., then

filtration over Celite under argon to remove unreacted lithium/sodium pieces, after cooling

to -45°C a solution of (6.35 g, 28.28 mmol) of diphenylphosphinochloride was added. The

resulting mixture was stirred for 30 min. at -95 °C allowed to warm to r.t. and stirred

overnight. The mixture was filtrated over Celite then quenched by addition of 10 ml of

degassed H2O, extracted with diethyl ether (3 × 10 mL) under argon. The combined organic

extracts were dried with MgSO4 and concentrated under reduced pressure yielding

phosphine 3c as colourless oil (Yield; 62%). The NMR data for this colourless oil agree well

with previously published results.[175]

3.2.2 Synthesis of Ph 2PCH2SiMe3 3d [175]

.

Magnesium turnings (0.866g, 45.58 mmol) and a catalytic amount of iodine were added in

anhydrous ethyl ether (25 mL). Then, (Chloromethyl)trimethylsilane (4.3g, 3.5mmol) in


127

diethyl ether (10 mL) was added dropwise by syringe and the resulting mixture was stirred

for 3h at room temperature. Filtration over celite under argon to remove unreacted Mg

turnings. To the cooled filtrate; diphenylphosphinochloride (24.2mmol) in diethyl ether (10

mL) was added dropwise and stirred for 1h at -40°C and 6 h at room temperature. The

mixture was filtrated over Celite, and the two layers were separated under argon.

Ammonium chloride in degassed water (2 g/15 mL) was added, stirring continued for a

further 30 min, the mixture was extracted with dry ether (3 * 20 mL), and the washings

combined with each other. The resulting organic phase was dried over anhydrous MgSO4,

and reduced to low volume under vacuum affording the product as colourless oil.

Ph2PCH2SiMe3; Yield: 78%. 31P{1H} NMR (202.5 MHz, C6D6, 25°C): δ = -22.75. The NMR data

for 3d agree well with previously published results. [175, 176]

We have synthesized all type of free ligand and phosphonium salts employing Li/4% Na alloy

instead of Mg to speed up the grinding of lithium\sodium pieces. We added glass splinters

from fragmented pipettes to the pieces before stirring. Stirring overnight is satisfactory to

give a charcoal-colored mixture of powder and pieces of reduced size (Figure 3.1).

Figure 3.1: Photo for Preparation of Li/Na alloy.

3.2.3 Synthesis of [Hi-Pr2PCH2C(Me)3][BF4] 4a.

As the same procedure described above; to a solution of 90 mg (28.53mmol, 2.2 equiv.) of

Lithium\ 4% sodium alloy in 15 mL diethyl ether was added at -50 °C during a period of 15

min a solution of neopentylbromide (1.958g, 12.96 mmol, 1.0 equiv.). The resulting mixture

was stirred for 45 min at -50 °C and 1.5h at r.t., followed by filtration over Celite under


128

argon to remove unreacted lithium/sodium pieces. After cooling to -45 °C a solution of (1.98

g, 12.95 mmol) of di-iPropylphosphinochloride was added. The resulting mixture was stirred

for 30 min. at -45 °C allowed to warm to r.t. and stirred overnight. The mixture was filtrated

over Celite then quenched by addition of 10 ml of degassed H2O, extracted with diethyl

ether (3 × 10 mL) under argon. The combined organic extracts were dried with MgSO4 and

concentrated under reduced pressure yielding di-iPropyl(neopentyl) phosphine 4a as

colourless oil. The NMR data for this colourless oil agree well with previously published

results. HCl (1\10 eq. based on Li\Na) was added to a solution of di-iPropyl(neopentyl)

phosphine in CH2Cl2 (15mL), and the resulting mixture was stirred vigorously for 10 min.

then aqueous solution of NaBF4 (4 equiv. of HCl) was added. The organic layer was then

separated from the aqueous layer, dried over MgSO4, and filtered. Removal of the solvent

provided the title compound as white solid, which after recrystallization from CH2Cl2\diethyl

ether gave analytically pure colourless crystal. Yield: 83 %. M.p.: 195°C. 1H NMR (500 MHz,

CDCl3, 25°C): δ = 1.16 (s, C(Me3)3, 9H); 2.14 (dd, CH2C(Me3), 3J(H,H) = 4.5 Hz 3J(H,P) = 7.5 Hz,

2H); 6.1 (dpent, PH, 1H); 3.5 (m, 3J(H,H) = 3.6 Hz, 3J(H,P) = 7.5 Hz CH(Me)2, 2H) 1.4 (dd,

3J(H,H) = 7 Hz, 3J(H,P) = 7.5 Hz CH(Me)2, 12H); 31P{1H} NMR (202.5 MHz, CDCl3, 25 °C): δ =

21.44 ppm; 13C{1H} NMR (126 MHz, CDCl3, 25°C): 30.76 (d, 1JPC = 5 Hz, C(Me)3), 30.54 (d, 3JPC

= 6 Hz, CH(Me)3), 26.98 (d, 1JPC = 39 Hz, C(Me)3), 20.31 (d, J = 43 Hz,1C), 21.10 (d, CH(Me)2),

17.03 (dd, 3JPC = 8,6 Hz, 2.54 Hz CH(Me)2). IR (KBr): 793,9 (s, νP-C Alkyl), 2942 (s), 1032,3 (m),

1373,4(m), 2960,7 (s), 1373,4 (s). Elemental analysis calcd (%) for C11H25BF4P (275.095

g∙mol-1): C 48.03, H 9.16; found C 47.85, H 9.49.

3.2.4 Synthesis of [Hi-Pr2PCH2SiMe3][PF6] 4b.

To a 200 mg (28.9mmol, 2.0 equiv) of Lithium\ 4% sodium alloy in 25 mL diethyl ether was

added at -45°C during a period of 15 min a solution of chloromethyl-trimethylsilane (12.31

mmol, 1.0 equiv). The resulting mixture was stirred for 45 min at -40 °C and 2h at r.t.,

followed by filtration over Celite under argon to remove unreacted lithium/sodium pieces,

after cooling to -95 °C a solution of (1.87g, 12.29 mmol) of di-ipropylphosphinochloride was

added. The resulting mixture was stirred for 30 min. at -95 °C allowed to warm to r.t. and

stirred overnight. The mixture was filtrated over Celite then quenched by addition of 10 ml

of degassed H2O, extracted with diethyl ether (3 × 10 mL) under argon. The combined


129

organic extracts were dried with MgSO4 and concentrated under reduced pressure yielding

phosphine 4b as colourless oil. The NMR data for this colourless oil agree well with

previously published results. [175, 176] HCl (3eq. based on excepted phosphine) was added to a

solution of 4b in CH2Cl2 (30mL), and the resulting mixture was stirred vigorously for 5 min.

then aqueous solution of NaBF4 (4 equiv. of HCl) was added. The organic layer was then

separated from the aqueous layer, dried over MgSO4, and filtered. Removal of the solvent

provided the title compound as white solid, which after recrystallization from CH2Cl2\diethyl

ether gave an analytically pure colourless crystal (Yield; 78%) M.p.: 140°C. 1H NMR (500

MHz, CDCl3, 25°C): δ = 0.29 (s, SiMe3, 9H); 2.5 (m, CH(Me)2, 2H); 1.14 (dd, 3J(H,H) = 18.7 Hz,

CH(Me)2, 12H), 1.13 (dd, 3J(H,H) = 6.7 Hz, Me, 2H); 31P{1H} NMR (202.5 MHz, CDCl3, 25 °C): δ

= 29.41 ppm; 13C{1H} NMR (126 MHz, CDCl3, 25°C): 0.39 (SiMe3), 21.00 (d, CH(Me)2), 16.91

(d, CH(Me)2), 21.10 (d, CH2(SiMe3). IR (KBr): 1468 (st), 1254 (st), 834 (st), 704 (st). ESI-TOF

MS calc (m/z) for [C10H26PSi] 205.163 found 205.163 [C10H26PSi]+. Elemental analysis calcd

(%) for C10H26F6P2Si (349.329 g∙mol-1): C 34.28, H 7.48; found C 34.42, H 7.56.

3.2.5 Synthesis of [HtBu2PCH2C(Me)3][BF4] 4e.

To a 90 mg (28.5mmol, 2.2 equiv) of Lithium\4% sodium alloy in 15 mL diethyl ether was

added at -45 °C during a period of 10 min. a solution of neopentylbromide (1.958g, 12.96

mmol, 1.0 equiv). The resulting mixture was stirred for 45 min at -60 °C and 1.5h at r.t.,

followed by filtration over Celite under argon to remove unreacted lithium/sodium pieces,.

After cooling to -45°C a solution of (2.39 g, 13.31mmol) of di-tButylphosphine chloride was

added. The resulting mixture was stirred for 30 min. at -45 °C, allowed to warm to r.t. and




di-tButyl(neopentyl)phosphine as white solid. The NMR data for this solid agree well with

previously published results. [ref] Then HCl (3 eq. based on excepted phosphine) was added

to a solution of di-tert-butylphosphine- neopentylphosphine in CH2Cl2 (15mL), and the

resulting mixture was stirred vigorously for 10 min. then aqueous solution of NaBF4 (4 equiv.

of HCl) was added. The organic layer was then separated from the aqueous layer, dried over

MgSO4, and filtered. Removal of the solvent provided the title compound as white solid,


130

which after recrystallization from CH2Cl2\pentane gave a colourless crystal. Yield: 71.2%.

M.p.: 189°C. 1H NMR (500 MHz, CDCl3, 25°C): δ = 1.19 (s, C(CMe3), 9H), 1.49 (d, C(Me3)3,

3J(H,P) = 20 Hz, 18H); 2.08 (dd, 3J(H,H) = 5 Hz, 3J(H,P) = 10 Hz, 2H); 6.17 (dt, PH, 1J(H,P) = 422

Hz, 1H); 31P{1H} NMR (202.5 MHz, CDCl3, 25 °C): δ = 29.38 ppm; 13C{1H} NMR (126 MHz,

CDCl3, 25°C): 32.2 (d, 2JPC = 36 Hz, C(Me)3), 30.5 (d, 3JPC = 5.81 Hz, C(Me)3), 22.12 (d, 1JPC = 41

Hz, C(Me)3), 31.0 (d, 1JPC = 5.26 Hz, CH2C(Me)3), 25.05 (d, C(Me)3), 37.04); 27.3 (C(Me)3). IR

(KBr): 2969,6 (s), 2887,4 (vs), 782 (st, νP-C Alkyl), 1380,8 (st), 1484 (st), 1287 (st), 1232 (s).

ESI-TOF MS calc (m/z) for [C13H28P]+ 215.192 found 215.198 [C13H28P+ nH]+. Elemental

analysis calcd (%) for C13H30BF4P (304.155 g∙mol-1): C 51.34, H 9.94; found C 49.68, H 9.73.

3.2.6 Synthesis of [Ht-Bu2PCH2SiMe3][PF6] 4f.

To a 200 mg (28.9mmol, 2.0 equiv) of Lithium\4% sodium alloy in 25 mL diethyl ether (5 mL)

was added at -45 °C during a period of 15 min a solution of chloromethyl-trimethylsilane

(12.31 mmol, 1.0 equiv). The resulting mixture was stirred for 45 min at -40 °C and 2h at r.t.,

followed by filtration over Celite under argon to remove unreacted lithium/sodium pieces,

after cooling to -95 °C a solution of (106 mg, 0.698 mmol) of di-tButyl phosphinochloride

was added. The resulting mixture was stirred for 30 min. at -95 °C allowed to warm to r.t.

and stirred overnight. The mixture was filtrated over Celite then quenched by addition of 10

ml of degassed H2O, extracted with diethyl ether (3 × 10 mL) under argon. The combined

organic extracts were dried with MgSO4 and concentrated under reduced pressure yielding t-

Bu2PCH2SiMe3 as colourless oil. The NMR data for this colourless oil agree well with

previously published results. HCl (1\10 eq. based on Li\Na) was added to a solution of 2 in

CH2Cl2 (30mL), and the resulting mixture was stirred vigorously for 5 min. then aqueous

solution of NaBF4 (4 equiv. of HCl) was added. The organic layer was then separated from

the aqueous layer, dried over MgSO4, and filtered. Removal of the solvent provided the title

compound as white solid, which after recrystallization from CH2Cl2\diethyl ether gave an

analytically pure colourless crystal. Yield: 72%. M.p.: 213 (dec.) °C. 1H NMR (500 MHz, CDCl3,

25°C): δ = 1.49 (d, C(CMe3), 2J(H,P) = 12 Hz, 18H); 1.88 (dd, CH2C(SiMe3), 2J(H,P) = 12 Hz,

3J(H,H) = 5.84 Hz, 2H); 0.30 (s, SiMe3); 5.91 (dt, PH, 1J(H,P) = 476 Hz, 1H); 31P{1H} NMR (202.5


131

M Hz, CDCl3, 25 °C): δ = 38.26 ppm. ESI-TOF MS (m/z): 233.19 (C12H30PSi). Elemental

analysis calcd (%) for C12H30P2F6Si (320.230 g∙mol-1): C 45.01, H 9.44; found C 44.71, H 9.918.

3.2.7 Synthesis of [HP(CH2C(Me)3)3][BF4] 4g.

To a solution of 430 mg (136.32mmol, 2.2 equiv) of Lithium\ 4% sodium alloy in 15 mL

diethyl ether was added at -60 °C during a period of 10 min. a solution of neopentylbromide

(9.35 g 61.95mmol, 1.0 equiv). The resulting mixture was stirred for 45 min at -60 °C and

1.5h at r.t., then filtration over Celite under argon to remove unreacted lithium/sodium

pieces,. After cooling to -45°C a solution of (2.50 g, 18.7 mmol) of Phosphortrichlorid was

added. The resulting mixture was stirred for 30 min. at -65 °C, allowed to warm to r.t. and




tri(neopentyl)phosphine as white solid. The 31P{1H} NMR data for this solid agree well with

previously published results. [4] Then HCl (3 eq. based on Phosphine) was added to a solution

of tri(neopentyl)phosphine in CH2Cl2 (15mL), and the resulting mixture was stirred

vigorously for 10 min. then aqueous solution of NaBF4 (4 equiv. of HCl) was added . The

organic layer was then separated from the aqueous layer, dried over MgSO4, and filtered.

Removal of the solvent provided the title compound as white solid, which after

recrystallization from CH2Cl2\diethyl ether gave an analytically pure colourless crystal. Yield:

76%. M.p.: 235 °C. 1H NMR (500 MHz, CDCl3, 25°C): δ = 1.19 (d, C(CMe3), 4J(H,P) = 1.35Hz,

27H); 2.50 (dd, CH2C(CMe3), 3J(H,H) = 5.3 Hz, 6H); 5.93 (dsep, PH, 1J(H,P) = 430 Hz, 1H);

31P{1H} NMR (202.5 M Hz, CDCl3, 25 °C): δ = -14.64 ppm; 13C{1H} NMR (126 MHz, CDCl3,

25°C): 34.94 (d, JPC = 42 Hz, CH2C(Me)3), 31.91 (d, JPC = 5 Hz, C(Me)3), 30.82 (d, JPC = 7.7 Hz,

C(Me)3). IR (KBr): 2295 (s), 2966 (s), 2878 (s), 1448 (m), 1372 (st), 1282 (st), 1241 (st), 819

(st, νP-C Alkyl). ESI-TOF MS calc (m/z) for [C15H34P] 245.239 found [C17H34P] 245.239.

Elemental analysis calcd (%) for C15H34BF4P (332.208 g∙mol-1): C 54.23, H 10.32; found C

54.22, H 10.74., Elemental analysis calcd (%) for the oxide, OP(CH2C(Me)3)3, C15H33OP

(332.208 g∙mol-1): C 69.19, H 12.77; found C 68.77, H 13.56.

3.2.8 Synthesis of [HCy2PCH2CMe3][BF4] 4h.


132

As described in the above procedures, to a solution of 200 mg (28.9mmol, 2.0 equiv) of

Lithium\ 4% sodium alloy in 25 mL diethyl ether (5 mL) was added at -45 °C during a period

of 10 min a solution of neopentylbromide (12.31 mmol, 1.0 equiv). The resulting mixture

was stirred for 45 min at -45 °C and 2h at r.t., then filtration over Celite under argon to

remove unreacted lithium/sodium pieces, after cooling to -95°C a solution of (106 mg, 0.698

mmol) of di-cyclohexylphosphinochloride was added. The resulting mixture was stirred for

30 min. at -95 °C allowed to warm to r.t. and stirred overnight. The mixture was filtrated

over Celite, after cooling to 0.0°C ; 10 ml of degassed H2O and HCl (1\10 eq. based on Li\Na)

was added, and the resulting mixture was stirred vigorously for 5 min. then aqueous

solution of NaBF4 (4 equiv. of HCl) was added. The organic layer was then separated from

the aqueous layer, dried over MgSO4, and filtered. Removal of the solvent provided the title

compound as white solid, which after recrystallization from hexane at -20°C gave an

analytically pure colourless crystal. Yield: 77.4%. 1HNMR (500 MHz, CDCl3, 25°C): δ = 1.15 (s,

C(CMe3, 9H); 2.12 (dd, CH2C(CMe3), 3J(H,P) = 12 Hz 3J(H,H) = 4.41 Hz, 6H); 2.49 (m, CHCy,

2H); 1.78 (d), 1.28-2.21 (ca, cyclohexyl group) 31P{1H} NMR (202.5 M Hz, CDCl3, 25 °C): δ =

13.05 ppm; 13C{1H} NMR (126 MHz, CDCl3, 25°C): 25.25 (s), 26.17 (dd, J = 13.53, 6.25 Hz),

26.71 (s), 27.47 (d, J = 3.5 Hz), 27.20 (s), 26.88 (s), 30.62 (d, J = 6.7 Hz), 30.92 (d, J = 4.8 Hz).

IR (KBr): 2854 (m), 2295,8 (s), 1375 (s), 1462 (s), 1238 (s), 1452 (s), 2931 (st). ESI-TOF MS

calc (m/z) for [C17H34P] 269.239 found [C17H34P] 269.239. Elemental analysis calcd (%) for

C17H34BF4P (356.230 g∙mol-1): C 57.32, H 9.62; found C 57.34, H 10.23.

3.2.9 Synthesis of [Ht-Bu(iPr)2P][BF4] 4i.

To a solution of (10 mL, 48mmol, 2equiv) of of iPrLi (2.4 M) in 20 mL diethyl ether was added

at -40 °C during a period of 10 min a solution of t-BuLi (10 mL, 2.4 M, 24 mmol, 1.0 equiv).

The resulting mixture was stirred for 45 min at -40 °C allowed to warm to r.t. and stirred

overnight. The mixture was filtrated over Celite, after cooling to 0.0°C ; 10 ml of degassed

H2O and HCl (3equiv.) was added, and the resulting mixture was stirred vigorously for 30

min. then aqueous solution of NaBF4 (4 equiv. of HCl) was added. The mixture was extracted

with diethyl ether (3 × 10 mL) and the combined organic extracts were dried with MgSO4

and concentrated under reduced pressure to afford 4i as white powder. M.p.: 264°C. 1H

NMR (500 MHz, CDCl3, 25°C): δ = 2.86 (m, 2J(P,H) 12 Hz, 3J(H,H) 6.87 Hz, CH(Me)2, 2H), 1.49


133

(d, 2J(P,H) 10 Hz, 3J(H,H) 7.98 Hz, C(Me)3, 9H), 1.45 (d, 3J(P,H) 15 Hz, 3J(H,H) 3.93 Hz,

CH(Me)2, 12H), 5.79 (d, 1J(H,H) = 469 Hz, PH, 1H); 31P{1H} NMR (202.5 M Hz, CDCl3, 25 °C): δ

= 45.54 ppm. IR (KBr): 2972 (m), 2873 (s), 1475 (st), 1378 (st), 1287 (s), 1197 (s), 816 (st),

2899 (m), 1470 (st), 1393 (m), 1362 (m), 807 (st). Elemental analysis calcd (%) for C10H24BF4P

(261.068 g∙mol-1): C 45.83, H 9.23; found C 45.86, H 9.47.

3.2.10 Synthesis of [Ht-Bu3P][BF4] 4k.

To a solution of (2 g, 11 mmol) of tBu2PCl in 20 mL diethyl ether was added at -40 °C during a

period of 15 min a solution of t-BuLi (6.9 mL, 11 mmol, 1.0 equiv). The resulting mixture was

stirred for 45 min at -40 °C allowed to warm to r.t. and stirred overnight. The mixture was

filtrated over Celite, after cooling to 0.0°C ; 10 ml of degassed H2O and HCl (15mmol) was

added, and the resulting mixture was stirred vigorously for 30 min. then aqueous solution of

NaBF4 (4 equiv. of HCl) was added. The mixture was extracted with diethyl ether (3 × 10 mL)

and the combined organic extracts were dried with MgSO4 and concentrated under reduced

pressure to afford 2.96 g (93%) of 4k as white powder[ref]. M.p.: 260°C. 1H NMR (500 MHz,

CDCl3, 25°C): δ = 1.67 (d, 3J(P,H) = 15 Hz, C(CH3)3, 27H), 6.18 (d, 1J(H,H) = 430 Hz, PH, 1H);

13C{1H} NMR (126 MHz, CDCl3, 25°C): 37.22 (d, 1JPC = 28 Hz, C(Me)3), 30.22 (s, C(Me)3; 31P{1H}

NMR (202.5 M Hz, CDCl3, 25 °C): δ = 51.58 ppm. IR (KBr): 2966 (m), 2899 (m), 1470 (st), 1393

(m), 1362 (m), 807 (st). Elemental analysis calcd (%) for C12H27BF4P (290.129 g∙mol-1): C

49.68, H 9.73; found C 49.79, H 9.94.

3.2.11 Synthesis of [HiPr2P(3-pentane)][BF4] 4l.

In a similar procedure described above, to a 90 mg (28.53mmol, 2.2 equiv) of Lithium\ 4%

sodium alloy in 15 mL diethyl ether was added at -35 °C during a period of 10 min. a solution

of 3-bromopentane (1.95 g, 12.96 mmol, 1.0 equiv). The resulting mixture was stirred for 45

min at -40 °C and 1.5h at r.t., then filtration over Celite under argon to remove unreacted

lithium/sodium pieces, after cooling to -40 °C a solution of (1.97 g, 12.95 mmol) of di-

iPropylphosphinochloride was added. The resulting mixture was stirred for 30 min. at -45 °C,

allowed to warm to r.t. and stirred overnight. The mixture was filtrated over Celite, after

cooling to 0.0°C ; 10 ml of degassed H2O and HCl was added, and the resulting mixture was


134

stirred vigorously for 30 min. then aqueous solution of NaBF4 (4 equiv. of HCl) was added.

The mixture was extracted with diethyl ether (3 × 10 mL) and the combined organic extracts

were dried with MgSO4 and concentrated under reduced pressure provided the title

compound as white solid, which after recrystallization from CH2Cl2\diethyl ether gave an

analytically pure colourless crystal (Yield; 73%). M.p.: 198-200°C. 1H NMR (500 MHz, CDCl3,

25°C): δ = 1.41 (dd, CH(CMe2), 3J(H,P) = 11.5 Hz, 3J(H,H) = 4.48, 12H); 2.87 (dsept, 2J(H,P) = 14

Hz, 3J(H,H) = 6.94 Hz, CH(CMe2), 2H), 2.45(m, 2J(H,P) = 12.50, 3J(H,H) = 6.59 Hz, CH(CH2CH3)2,

1H), 1.74 (dpent, 3J(H,P) = 13 Hz, 3J(H,H) = 6.63 Hz CH(CH2CH3)2, 4H); 1.033 (t, 3J(H,H) = 7.38

Hz, CH(CH2CH3)2); 5.89 (m, 1J(H, P) = 469 Hz, PH, 1H); 13C{1H} NMR (126 MHz, CDCl3, 25°C):

30.73 (d, 1JPC = 39.7 Hz, CH(CH2CH3)2), 30.51 (d,2JPC = 6.77 Hz, CH(CMe2), 20.27 (d,2JPC = 43.6

Hz, CH(CH2CH3)2), 26.93 (d, 1JPC = 39.9 Hz, CH(CMe2), 17.35 (s, CH(CH2CH3)2), 31P{1H} NMR

(202.5 M Hz, CDCl3, 25 °C): δ = 33.54 ppm. Elemental analysis calcd (%) for C11H26BF4P

(276.102 g∙mol-1): C 47.85, H 9.51; found C 48.08, H 10.46.

3.2.12 Synthesis of [HiPr2PCH2Cy][PF6] 4m.

In a similar procedure described above, to a 90 mg (28.53mmol, 2.2 equiv) of Lithium\ 4%

sodium alloy in 15 mL diethyl ether was added at -45 °C during a period of 10 min. a solution

of cyclohexylmethylbromide (1.148 g, 12.97mmol, 1.0 equiv.). The resulting mixture was

stirred for 45 min at -40 °C and 1.5h at r.t., then filtration of the product under argon to

remove if there un reacted lithium sodium pieces, after cooling to -40 °C a solution of 12.40

mmol) of iPr2PCl was added. The resulting mixture was stirred for 30 min. at -45 °C, allowed

to warm to r.t. and stirred overnight. The mixture was filtrated over Celite, after cooling to

0°C; 10 ml of degassed H2O and HCl (3eq. based on phosphine) was added, and the resulting

mixture was stirred vigorously for 30 min. then aqueous solution of NaBF4 (4 equiv. of HCl)

was added. The mixture was extracted with diethyl ether (3 × 10 mL) and the combined

organic extracts were dried with MgSO4 and concentrated under reduced pressure provided

the title compound as white solid, which after recrystallization from CH2Cl2\diethyl ether

gave an analytically pure colourless crystal (Yield: 69.47%). M.p.: 166°C. 1H NMR (500 MHz,

CDCl3, 25°C): δ = 1.40 (dd; 2J(P,H) = 11 Hz, 3J(H,H) = 7.2 Hz, CH(Me)2, 12H); 2.71 (m, 2J(H,P) =

11 Hz, 3J(H,H) = 6.82 Hz, (CHMe2), 2H), 2.06 (dd, 2J(H,P) = 12 Hz, 3J(H,H) = 6.27 Hz, PCH2Cy,

2H), 1.13 (m, CH(Cy), 1H); 5.78 (d, 1J(H,P) = 465 Hz, PH, 1H);protons of Cyclohexyl in the


135

range of 1.10 to 2.10. 13C{1H} NMR (126 MHz, CDCl3, 25°C): δ(s or d, coupling constant):

34.149 (d, 5.26), 34.05 (d, 8.31), 25.87 (s), 25.56 (s), 20.63 (d, 41.14), 19.77 (d, 43.12), 17.35

(d, 2.56); 31P{1H} NMR (202.5 MHz, CDCl3, 25 °C): δ = 27.41 ppm. IR (KBr): 2933 (st), 2859(s),

1465 (st), 1380 (st), 1398 (st), 1407 (st), 884 (st). ESI-TOF MS calc (m/z) for [C13H28P] 215.192

found 215.192 [C15H32P]+. Elemental analysis calcd (%) for C13H28F6P2 (360.299 g∙mol-1): C

43.34, H 7.83; found C 42.88, H 7.25.

3.2.13 Synthesis of [HtBu2PCH2Cy][PF6] 4n.

In a similar procedure described above, to a of 110 mg (34.87mmol, 2.2 equiv) of Lithium\

4% sodium alloy in 15 mL diethyl ether was added at -45 °C during a period of 10 min. a

solution of cyclohexylmethylbromide (2.8 g, 15.85 mmol, 1.0 equiv). The resulting mixture

was stirred for 45 min at -30 °C and 1.5h at r.t., then filtration over Celite under argon to

remove unreacted lithium/sodium pieces, after cooling to -40 °C a solution of (2.86 g,

15.85mmol) of tBu2PCl was added. The resulting mixture was stirred for 30 min. at -45 °C,

allowed to warm to r.t. and stirred overnight. The mixture was filtrated over Celite, after

cooling to 0.0°C ; 10 ml of degassed H2O and HCl (3 eq. based on a phosphine) was added,

and the resulting mixture was stirred vigorously for 30 min. then aqueous solution of NaBF4

(4 equiv. of HCl) was added. The mixture was extracted with diethyl ether (3 × 10 mL) and

the combined organic extracts were dried with MgSO4 and concentrated under reduced

pressure provided the title compound as white solid, which after recrystallization from

CH2Cl2\diethyl ether gave an analytically pure colourless crystal. (Yield; 70%). M.p.: 213°C. 1H

NMR (500 MHz, CDCl3, 25°C): δ = 1.29 (s, C(CMe3), 27H); 1.51 (d, 3J(H,P) = 16 Hz, (CMe3),

18H), 2.47 (dt, 2J(H,P) = 11 Hz 3J(H,H) = 5.91 Hz, PCH2Cy, 2H), 6.38 (d, 1J(H,H) = 468 Hz, PH,

1H); protons of Cyclohexyl group in the range of 0.72 to 2.22, 5.81 (d, 1J(H,H) = 456 Hz, PH,

1H); 13C{1H} NMR (126 MHz, CDCl3, 25°C): 34.99 (d, 1JPC 5 Hz, CH2C(Me)2), 33.14 (d, 1JPC =

7.68 Hz, C(Me)3), 31.84 (d,3JPC= 35.5 Hz, CH(Cyclohexyl cycle)), 26.34 (s, C(Me)3), 25.04 (s,

Cyclohexyl cycle), 20.98 (s, Cyclohexyl cycle); 31P{1H} NMR (202.5 M Hz, CDCl3, 25 °C): δ =

39.59 ppm. IR (KBr): 2849 (s), 2920 (st), 1468 (s), 1391 (s), 1172 (m), 1364 (s), 1019 (m), 761

(s), 1276 (s), 810 (m). ESI-TOF MS calc (m/z) for [C15H32P]+ 243.223 found 243.223 [C15H32P]+.


136

Elemental analysis calcd (%) for C15H32F6P2 (422.900 g∙mol-1): C 46.39, H 8.31; found C 47.65,

H 9.05.

3.2.14 Synthesis of [Hi-Pr2PCH2CH(Me)2][BF4] 4o.

As the same procedure described above; to a 200 mg (63.4mmol, 2.2 equiv)of Lithium\ 4%

sodium alloy in 25 mL diethyl ether (5 mL) was added at -45 °C during a period of 15 min a

solution of isobutyl bromide (28.81 mmol, 1.0 equiv). The resulting mixture was stirred for

45 min at -40 °C and 2h at r.t., then filtration over Celite under argon to remove unreacted

lithium/sodium pieces, after cooling to -95 °C a solution of (28.82 mmol, 1.0 equiv) of di-

iPropylphosphinochloride was added. The resulting mixture was stirred for 30 min. at -95 °C

allowed to warm to r.t. and stirred overnight. The mixture was filtrated over Celite then

quenched by addition of 10 ml of degassed H2O, extracted with diethyl ether (3 × 10 mL)

under argon. The combined organic extracts were dried with MgSO4 and concentrated

under reduced pressure yielding colourless oil. Then HCl (3eq. based on excepted

phosphine) was added to a solution of 2 in CH2Cl2 (30mL), and the resulting mixture was

stirred vigorously for 5 min. then aqueous solution of NaBF4 (4 equiv. of HCl) was added. The

organic layer was then separated from the aqueous layer, dried over MgSO4, and filtered.

Removal of the solvent provided the title compound as white solid, which after

recrystallization from CH2Cl2\diethyl ether gave an analytically pure colourless crystal. Yield:

68%. M.p.: 195°C. 1H NMR (500 MHz, CDCl3, 25°C): δ = 1.086 (d, CH(Me2)3, 6H); 2.14 (dd,

3J(H,H) = 4.5 Hz, 3J(H,P) = 7.5 Hz, 2H); 6.1 (dpent, PH, 1H); 2.722 (m, 3J(H,H) = 4.92 Hz, 3J(H,P)

= 11.82 Hz CH(Me)2, 2H), 2.066 (m, 3J(H,H) = 5.89 Hz, 3J(H,P) = 11.93 Hz CH(Me)2, 1H), 1.37

(dt, 3J(H,H) = 5.89 Hz, 3J(H,P) = 11.92 Hz CH(Me)2, 12H); 31P{1H} NMR (202.5 MHz, CDCl3, 25

°C): δ = 27.72 ppm; 13C{1H} NMR (126 MHz, CDCl3, 25°C): 25.40 (d, 2JPC = 4.90 Hz, C(Me)3),

23.53 (d, 3JPC = 9 Hz, CH(Me)3), 22.12 (d, 1JPC = 41 Hz, C(Me)3), 19.76 (d, 3JPC = 43 Hz,

CH(Me)2), 17.05 (d, CH(Me)2), 17.03 (dd, 2JPC = 86 Hz, 2.54 Hz CH(Me)2). IR (KBr): 2279,6 (s),

1002,0 (m), 794,6 (m, νP-C Alkyl), 2942 (s), 1032,3 (m), 1373,4(m), 2964 (s), 2960,7 (s),

1468,4 (s), 1373,4 (s), 1375,3 (s), 1237,5 (s) 3052 (s, νC-H Alkyl). Elemental analysis calcd (%)

for C10H24BF4P (262.076 g∙mol-1): C 45.83, H 9.23; found C 46.79, H 9.52.


137

3.2.15 Synthesis of complex (iPr2PCH2C(Me)3)2PdCl2 5a.

2.0 equivalent iPr2PCH2C(Me)3 (500 mg, 2.656 mmol) was dissolved in CH2Cl2 (10 mL), and

one equivalents of PdCl2(COD) (380 mg , 1.328 mmol) in CH2Cl2 (5 mL) was added dropwise

at r. t. The orange-yellow suspension was stirred for 5h at room temperature. The resulting

solution was evaporated under vacuum, washed 2 times with diethyl ether to precipitate the

product, which was then dried under high vacuum to obtain the product 5a in 82 % yield as

pale yellow powder. 1H NMR (500 MHz, CDCl3, 25°C): δ = 0.99 (s, CMe3, 18H); 2.67 (m,

2J(H,P) = 7.2Hz, 2J(H,H) = 3.70 Hz, CH2, 4H); 1.94 (t, 2J(H,H) = 3.59 Hz, CH2, 4H); (td; 3J(P,H) 10

Hz, 3J(H,H) 6.7 Hz, CH(Me)2, 4H); 1.35 (s, C(CMe3), 18H); 31P{1H} NMR (202.5 MHz, CDCl3, 25

°C): δ = 22.46 ppm; 13C{1H} NMR (126 MHz, CDCl3, 25°C): 36.87 (CH2), 32.71 (CMe3), 31.96

(CMe3), 24.18 (CH(Me)2, 20.9, 19.37 (CH(Me)2. IR (KBr): 2983 (sm), 2869,7 (m), 1466,7 (m),

801,9 (s, νP-C Alkyl). Elemental analysis calcd (%) for C20H50P2Cl2Pd (553.905 g∙mol-1): C

47.70, H 9.10; found C 47.68, H 9.34.

3.2.16 Synthesis of complex (i-Pr2PCH2SiMe3)2PdCl2 5b.

The same procedure of preparation of 6 was followed; 2.0 equivalent of i-Pr2PCH2SiMe3

(1.96 mmol) was dissolved in CH2Cl2 (10 mL), and one equivalents of palladium dichloro(1,5-

cyclooctadiene) (0.100g , 1mmol) in CH2Cl2 (5 mL) was added dropwise at r. t. The dark

yellow suspension was stirred for 4h at room temperature. The resulting solution was

evaporated under vacuum, washed 2 times with cold hexane to precipitate the product,

which was then dried under high vacuum to obtain the product 5b in 84% yield as pale

yellow powder. M.p.: 176-178 °C. 1HNMR (500 MHz, CDCl3, 25°C): δ = 0.291 (s, SiMe3, 18H);

1.14 (t, 3J(H,P) = 11 Hz, CH2, 24H); 2.1 (brm, 2J(P,H) = 7.8, 2J(H,H) = 3.12 Hz, CH(Me)2, 4H);

1.34 (t, 2J(P,H) = 8 Hz, J(H,H) = 7.5 Hz, CH2(Me)2, 4H); 31P{1H} NMR (202.5 MHz, CDCl3, 25 °C):

δ = 33.37 ppm; 13C{1H} NMR (126 MHz, CDCl3, 25°C): 2.06 (SiMe3), 19.02 (CH(Me)2), 4.84

(CH2), 24.98 (CH(Me)2. IR (KBr): 1158,0 (s), 2960,7 (s), 1367,3 (s), 1457,1 (m), 797,4 (s), 1567

(m), 838,1 (s). ESI-TOF MS calc (m/z) for [C20H50P2PdSi2Cl2-Cl]+ 551.164 found 551.169

[C20H50P2PdSi2Cl2-Cl + nH]+. Elemental analysis calcd (%) for C20H50P2Cl2PdSi2 (586.055 g∙mol-

1): C 40.99, H 8.60; found C 40.23, H 8.30.


138

3.2.17 Synthesis of complex (Ph2PCH2C(Me)3)2PdCl2 5c.

The same procedure of preparation of 6 was followed, 2.0 equivalent of Ph2PCH2C(Me)3 (60

mg, 0.468 mmol) was dissolved in CH2Cl2 (10 mL), and one equivalents of palladium

dichloro(1,5-cyclooctadiene) (66 mg, 0.234 mmol) in CH2Cl2 (5 mL) was added dropwise at r.

t.. The orange-yellow suspension was stirred for 5h at room temperature. The resulting

solution was evaporated under vacuum, washed 2 times with diethyl ether to precipitate the

product, which was then dried under high vacuum to obtain the product 5c in 80% yield as

pale yellow powder M.p.: 194-198°C. 1H NMR (500 MHz, CDCl3, 25°C): δ = 0.992 (s, CMe3,

18H); 2.71 (t, 2J(H,P) = 4 Hz, 2J(H,H) = 3.99 Hz, CH2, 4H); 7.75 (ddd, 2J(H,H) = 3.38 Hz, Ph, 8H);

7.36 (t, 2J(H,H) = 7.19 Hz, Ph, 4H); 7.27 (t, 2J(H,H) = 7.27 Hz, Ph, 8H); 31P{1H} NMR (202.5

MHz, CDCl3, 25 °C): δ = 6.61 ppm; 13C{1H} NMR (126 MHz, CDCl3, 25°C): 32.078 (CMe3),

31.623 (CMe3), 37.45 (CH2), 128.2, 131, 133.7. IR (KBr): 2950,3 (s), 2884,6 (s, νC-H Aryl-CH3),

1572,5 (s, νc-c ring) 3052 (s, νC-H Aryl)1158,0 (s), 2960,7 (s), 1367,3 (s), 1457,1 (m), 1430,1 (s),

797,4 (s), 1567 (m), 838,1 (s), 3067,2 (s, νC-H Aryl). ESI-TOF MS calc (m/z) for (C17H21PPd)

361.033 found 361.033 (C15H32P]+. Elemental analysis calcd (%) for C34H42P2Cl2Pd (689.970

g∙mol-1): C 59.19, H 6.14; found C 59.35, H 6.27.

3.2.18 Synthesis of complex (Ph2PCH2SiMe3)2PdCl2 5d.

Two equivalent of Ph2PCH2SiMe3 (0.94 g, 1.96 mmol) was dissolved in CH2Cl2 (10 mL), and

one equivalents of PdCl2(COD) (0.100g , 1mmol) in CH2Cl2 (5 mL) was added dropwise at r. t..

The dark yellow suspension was stirred for 4h at room temperature. The resulting solution

was evaporated under vacuum, washed 2 times with cold hexane to precipitate the product,

which was then dried under high vacuum to obtain the product 5d in 84 % yield as yellow

powder M.p.: 179°C. 1HNMR (500 MHz, CDCl3, 25°C): δ = 0.077 (s, SiMe3, 18H); 2.53 (t,

2J(H,P) = 5.4 Hz, CH2, 4H); 7.74 (d, 2J(H,H) = 6.23 Hz CHPh, 8H); 7.35 (t, 2J(H,H) = 7.35 Hz,

CH(Me)2, 8H), 7.38 (t, 2J(H,H) = 6.74 Hz, Me, 4H); 31P{1H} NMR (202.5 MHz, CDCl3, 25 °C): δ =

13.46 ppm; 13C{1H} NMR (126 MHz, CDCl3, 25°C): 0.535 (SiMe3), 12.67 (CH2(SiMe3), 128.21,

130.25, 133.69. IR (KBr): 1243 (s), 849 (s), 1435 (s), 3052 (s, νC-H Aryl), 1567 (m), 789 (s), 695

(s).ESI-TOF MS calc (m/z) for [C32H42P2PdSi2Cl2-Cl]+ 685.102 found 685.094[C32H42P2PdSi2Cl2-

Cl +nH]+. Elemental analysis calcd (%) for C32H42P2 PdSi2 (722.120 g∙mol-1): C 53.22, H 5.86;

found C 53.28, H 5.788.


139

3.2.19 Synthesis of Palladacycle 6a.

In a similar procedure as described above, one equivalent of [HiPr2PCH2CMe3][BF4] (65 mg,

0.1945 mmol) and 3 equivalents of NaOAc were dissolved in CH2Cl2 (5 mL), one equivalents

of palladium acetate (44 mg, 0.1945 mmol) in CH2Cl2 (5 mL) was added dropwise at r. t.. The

resulting solution was stirred for 1h at room temperature and 4h at 55°C. The mixture was

allowed to attain r.t., the resulting solution was reduced to low volume under vacuum, and

the residue was washed a couple of times with sodium chloride solution and extracted with

CH2Cl2 (3 × 10 mL). The combined organic extracts were dried over MgSO4 and concentrated

under reduced pressure, purified by column chromatography on silica gel using 0.5mL:10mL

ratio of CH2Cl2/hexane to provide the desired product as very pale yellow powder 6a (Yield;

78 %). M.p.: 190-194°C. 1HNMR (500 MHz, CDCl3, 25°C): δ = 1.22 (dd, CH(CMe2), 3J(H,P) =

7.82, 3J(H,H) = 6.78, 6H); 1.37 (dd, CH(CMe2), 3J(H,P) = 11 Hz, 3J(H,H) = 5.3 Hz, 6H); 2.11 (m,

CH(CMe2), 2.27 (s, CH2-Pd), 2H); 1.63 (d, 3J(H,P) = 9 Hz, CH2-P, 2H); 1.80 (d, 3J(H,P) = 10 Hz,

2H); 13C{1H} NMR (126 MHz, CDCl3, 25°C): 47.54 (s, CH2-Pd), 43.47 (d, 1JPC = 10.7 Hz,

CH2C(Me)2), 36.50 (d, 2JPC = 27 Hz, C(Me)2CH2-Pd), 31.98 (d, 3JPC = 14.7 Hz, CH2C(Me)2), 25.19

(d, 1JPC = 23.5 Hz, C(Me)3), 19.1 (d, 2JPC = 3 Hz, CH(Me)2); 31P{1H} NMR (202.5 M Hz, CDCl3, 25

°C): δ = 80.13 ppm. IR (KBr): 2869 (s), 2908 (s), 2925 (s), 2955 (s), 1734 (st), 1460 (st), 1355

(m), 1373 (m), 1387 (m), 1250 (s), 758 (st). ESI-TOF MS calc (m/z) for [C22H48P2Cl2Pd2-Cl]+

623.099 found 623.108 [C22H48P2Cl2Pd2-Cl+ nH]+). Elemental analysis calcd (%) for

C22H48P2Cl2Pd2 (658.310 g∙mol-1): C 40.15, H 7.36; found C 43.29, H 8.07.

3.2.20 Synthesis of Palladacycle 6e.

One equivalent of [Ht-Bu2PCH2CMe3][BF4] (520 mg, 1.634 mmol), 3 equivalents of NaOAc

and one equivalents of palladium acetate (366 mg, 1.634 mmol) were dissolved in thf (10

mL). The yellow brown suspension was stirred for 1h at room temperature and 4h at 55°C.

The mixture was allowed to attain r.t., the resulting solution was reduced to low volume

under vacuum, and the residue was washed a couple of times with sodium chloride solution

and extracted with CH2Cl2 (3 × 10 mL). The combined organic extracts were dried over

MgSO4 and concentrated under reduced pressure, purified by column chromatography on

silica gel using 0.5mL/10mL ratio of CH2Cl2/hexane to provide the desired product as pale

yellow powder 6e. Yield 83%; M.p.: 207°C. 1HNMR (500 MHz, CDCl3, 25°C): δ = 1.44 (d,


140

C(CMe3), 3J(H,P) = 10 Hz, 18H); 2.35 (s, CH2-Pd), 2H); 1.18 (s, CMe2, 6H); 1.80 (d, 3J(H,P) = 10

Hz, CH2Me2, 2H); 13C{1H} NMR (126 MHz, CDCl3, 25°C): 47.65 (s, CH2-Pd), 43.22 (d, 1JPC = 10

Hz, CH2C(Me)2), 37.52 (d, 2JPC = 23 Hz, C(Me)2 CH2-Pd), 35.42 (d, 3JPC = 16 Hz, CH2C(Me)2),

32.38 (d, 1JPC = 13 Hz, C(Me)3), 30.01 (d, 2JPC = 4.5 Hz, C(Me)3); 31P{1H} NMR (202.5 M Hz,

CDCl3, 25 °C): δ = 94.02 ppm. IR (KBr): 3003 (s), 2955 (s), 2924 (s), 2364 (s), 1732 (st), 1466

(st), 756 (st). ESI-TOF MS calc (m/z) for [C26H58P2Cl2Pd2-Cl]+ 679.161 found 679.167

[C26H58P2Cl2Pd2-Cl+ nH]+. Elemental analysis calcd (%) for C26H58P2Cl2Pd2 (714.416 g∙mol-1): C

43.71, H 7.9; found C 44.27, H 8.01.

3.2.21 Synthesis of Palladacycle 6g.

In a similar procedure as described above, an oven-dried Schlenk flask was charged with one

equivalent of [P(CH2CMe3)3][HBF4] (93 mg, 0.298 mmol), 3 equivalents of NaOAc and one

equivalents of palladium acetate (63mg, 0.298 mmol). The Schlenk flask was sealed and 10

mL of thf was added. The yellow brown suspension was stirred for 1h at room temperature

and 4h at 55°C. The mixture was allowed to attain r.t., the resulting solution was reduced to

low volume under vacuum, and the residue was washed a couple of times with sodium

chloride solution and extracted with CH2Cl2 (3 × 10 mL). The combined organic extracts were

dried over MgSO4 and concentrated under reduced pressure to provide the desired product

as off-white powder 6g. After few days off-white crystal of 6g were obtained at room

temperature from CH2Cl2/pentane. Yield 86 %. 1H NMR (500 MHz, CDCl3, 25°C): δ = 1.288 (s,

C(CMe3), 27H); 1.931 (dd, 3J(H,P) = 12 Hz, CH2(CMe3), 4H), 2.47 (s, CH2-Pd, 2H), 1.11 (s,

C(Me)2CH2-Pd, 6H); 13C{1H} NMR (126 MHz, CDCl3, 25°C): 49.98 (s, CH2-Pd), 46.66 (d, 1JPC =

22.56 Hz, CH2C(Me)2), 43.42 (d, 2JPC = 12 Hz, C(Me)2CH2-Pd), 32.28 (d, 3JPC = 5.7 Hz,

CH2C(Me)2CH2Pd), 32.14 (d, 3JPC = 6.5 Hz, C(Me)3), 31.32 (d, 3JPC = 6.5 Hz, CH2C(Me)2), 32.38

(d, 1JPC = 13 Hz, C(Me)3), 30.91 (d, 2JPC = 16 Hz, C(Me)3), 30.01 (d, 2JPC = 5 Hz, C(Me)3), 34.94

(d, 1JPC = 43 Hz, CH2C(Me)3), 31.91 (d, 2JPC = 5.6 Hz, C(Me)3), 30.82 (d, 3JPC = 8 Hz, C(Me)3);

31P{1H} NMR (202.5 M Hz, CDCl3, 25 °C): δ = 33.66 ppm. IR (KBr): 2953 (s), 2865 (m), 1486 (s)

1238 (m), 821,9 (m, νP-C Alkyl). ESI-TOF MS calc (m/z) for [C30H64P2Pd2Cl2- Cl]+ 735.224 found

[C30H64P2Pd2Cl2- Cl + nH]+ 735.207. Elemental analysis calcd (%) for C30H64P2Cl2Pd2 (770.523

g∙mol-1): C 46.76, H 8.37; found C 47.89, H 8.56.


141

3.2.22 Synthesis of (Cy2PCH2CMe3)2Pd2Cl4 6h.

One equivalent of [HCy2PCH2CMe3][BF4] (67g, 0.188 mmol) and 3 equivalents of NaOAc

were dissolved in CH2Cl2 (5 mL), 0.5 equivalents of palladium acetate (43 mg, 188 mmol) in

CH2Cl2 (5 mL) was added dropwise at r.t. The yellow brown suspension was stirred for 1h at

room temperature and 3h at 55°C. The mixture was allowed to attain r.t., then was washed

a couple of times with sodium chloride solution and extracted with CH2Cl2 (3 × 10 mL). The

combined organic extracts were dried over MgSO4 and concentrated under reduced

pressure, recrystallized from CH2Cl2\pentane to yield a yellow powder (Yield 84%). M.p.: 257

(deco.)°C. 1H NMR (500 MHz, CDCl3, 25°C): δ = 1.33 (s, C(CMe3, 9H); 2.34 (dd, CH2C(CMe3),

3J(H,P) = 11.8 Hz, 4H); 1.93 (dd, 2J(H,P) = 7 Hz, CHCy, 2H); 1.78 (d), 1.18-1.98 (ca, cyclohexyl

group) 31P{1H} NMR (202.5 M Hz, CDCl3, 25 °C): δ = 17.33 ppm; 13C{1H} NMR (126 MHz,

CDCl3, 25°C): 26.79, 27.69, 29.757, 31.087, 32.017, 32.702 and 35.21. Elemental analysis

calcd (%) for C17H34P2Pd2Cl4.3CH3CN (1014.640 g∙mol-1): C 47.35, H 7.45; found C 47.89, H

8.56.

3.2.23 Synthesis of (iPr2PtBu)2Pd2Cl4 6i.

In a similar procedure described above, one equivalent of [HiPr2PtBu][BF4] (50g, 0.181 mmol)

and 3 equivalents of NaOAc were dissolved in CH2Cl2 (5 mL), 0.5 equivalents of palladium

acetate (42mg, 0.187 mmol) in CH2Cl2 (5 mL) was added dropwise at r. t. The resulting

mixture was stirred for 1h at room temperature and 3h at 55°C. The mixture was allowed to

attain r.t., then was washed a couple of times with sodium chloride solution and extracted

with CH2Cl2 (3 × 10 mL). The combined organic extracts were dried over MgSO4 and

concentrated under reduced pressure, recrystallized from CH2Cl2\pentane to yield an

orange powder. Yield 71% M.p.: 257°C. 1H NMR (500 MHz, CDCl3, 25°C): δ = 1.44 (dsep,

CH(CMe2), 3J(H,P) = 15 Hz, 3J(H,H) = 6.87, 4H); 1.70 (d, 3J(H,P) = 12.5 Hz, 3J(H,H) = 6.87 Hz);

1.162 (brd, 3J(H,P) = 11.5 Hz); 13C{1H} NMR (126 MHz, CDCl3, 25°C): 21.89 (d, JPC = 39 Hz),

19.78 (d, JPC = 3.5 Hz,) 25.72 (d,2JPC = 25 Hz), 25.99 (d, JPC = 40 Hz), 25.99; 31P{1H} NMR (202.5

M Hz, CDCl3, 25 °C): δ = 70.80 ppm.


142

3.2.24 Synthesis of (iPrPtBu2)2Pd2Cl4 6j.

In a similar procedure described above, one equivalent of [HiPrPtBu2][BF4] (55 mg, 0.200

mmol) and 3 equivalents of NaOAc were dissolved in CH2Cl2 (5 mL), one equivalents of

palladium acetate (44.7 mg, 0.200 mmol) in CH2Cl2 (5 mL) was added dropwise at r. t.. The

resulting mixture was stirred for 1h at room temperature and 3h at 55°C. The mixture was

allowed to attain r.t., then was washed a couple of times with sodium chloride solution and

extracted with CH2Cl2 (3 × 10 mL). The combined organic extracts were dried over MgSO4

and concentrated under reduced pressure, recrystallized from CH2Cl2\pentane to yield an

orange powder 6j. Yield 79%. 1H NMR (500 MHz, CDCl3, 25°C): δ = 3.78 (brm, CH(CMe2), 2H);

1.63 (brd, C(CMe3), 3J(H,P) = 14.8 Hz, 36H), 1.46(dd, CH(CH3)2, 3J(H,P) = 13.29, 3J(H,H) = 6.68

Hz, 12H),; 13C{1H} NMR (126 MHz, CDCl3, 25°C): 32.10 (d, JPC = 3.5 Hz), 29.87 (d, JPC = 5 Hz),

29.53 (d, JPC = 25.01 Hz), 14.34 (d, JPC = 11 Hz), 25.99 (s, CH(CH2CH3)2), 31P{1H} NMR (202.5 M

Hz, CDCl3, 25 °C): δ = 50.27 ppm. IR (KBr): 1459 (st), 1387 (s), 1369 (s), 1248 (s), 1176 (m).

Elemental analysis calcd (%) for C22H50Pd2P2Cl4 (731.231 g∙mol-1): C 36.14, H 6.89; found C

36.07, H 7.27.

3.2.25 Synthesis of Palladacycle 6k.

One equivalent of [HPtBu3][BF4] (400 mg, 1.38mmol) and 339.6 mg (3 equivalents) of NaOAc

and 1.1 equivalents of palladium acetate (340.8 mg, 1.52 mmol) were dissolved in thf (10

mL), at r. t.. The resulting mixture was stirred for 1h at room temperature and 3h at 50°C.

The mixture was allowed to attain r.t., then was washed a couple of times with sodium

chloride solution and extracted with CH2Cl2 (3 × 10 mL). The combined organic extracts were

dried over MgSO4 and concentrated under reduced pressure afforded a pale yellow powder

6k (450.2 mg, 95 % based on 19. M.p.: 190 (dec.)°C. 1H NMR (500 MHz, CDCl3, 25°C): δ =

1.10 (d, 3J(H,H) = 5 Hz, CH2(CH3)2Pd, 2H); 1.56 (d, 3J(H,P) = 15 Hz, C(CH3), 18H); 1.47 (d,

3J(H,P) = 10 Hz, C(CH3)2, 6H); 13C{1H} NMR (126 MHz, CDCl3, 25°C): 49.49 (d, 2JPC = 19.80, CH2-

Pd), 38.16 (d, 1JPC = 9.9 Hz, C(Me)3), 32.31 (d, 2JPC = 3 Hz, C(Me)3), 31.18 (d, C(Me)2CH2-Pd),

11.75 (d, 1JPC = 29.7 Hz, C(Me)2CH2-Pd), 30.01 (d, 2JPC = 4.5 Hz,C(Me)3); 31P{1H} NMR (202.5 M

Hz, CDCl3, 25 °C): δ = -10.54 ppm. IR (KBr): 2924 (s), 1460 (st), 1367(st), 1267 (m), 1229 (s),


143

757 (m, νP-C Alkyl). Elemental analysis calcd (%) for C24H52P2Pd2Cl2 (686.363 g∙mol-1): C

42.00, H 7.64; found C 42.32, H 7.96.

3.2.26 Synthesis of (iPr2P(3-pentane)2Pd2Cl4 6l.

One equivalent of [HiPr2P(3-pentane)][BF4] (50 mg, 0.181 mmol), 3 equivalents of NaOAc,

and one equivalents of palladium acetate (44.7 mg, 0.199 mmol) were dissolved in thf (10

mL). The resulting mixture was stirred for 1h at room temperature and 3h at 35°C. The

mixture was allowed to attain r.t., then was washed a couple of times with sodium chloride

solution and extracted with CH2Cl2 (3 × 10 mL). The combined organic extracts were dried

over MgSO4 and concentrated under reduced pressure, afforded an orange powder 6l. Yield:

76%. M.p.: 200-204°C. 1H NMR (500 MHz, CDCl3, 25°C): δ = 1.441 (dd, CH(CMe2), 3J(H,P) = 15

Hz, 3J(H,H) = 6.52, 24H); 2.87 (dsept, 2J(H,P) = 14 Hz, 3J(H,H) = 7 Hz, CH(CMe2), 2H), 2.15(m,

2J(H,P) = 14 Hz, 3J(H,H) = 7.36 Hz, CH(CH2CH3)2, 2H), 1.89 (pent, CH(CH2CH3)2, 84H); 1.16 (t,

3J(H,H) = 7.40 Hz);; 13C{1H} NMR (126 MHz, CDCl3, 25°C): 39.22 (d, 1JPC = 21.89 Hz,

CH(CH2CH3)2), 25.72 (d,2JPC = 25.01 Hz, CH(CMe2), 19.78 (d,2JPC = 3.5 Hz, CH(CH2CH3)2), 15.14

(d, 1JPC = 11 Hz, CH(CMe2), 25.94 (s, CH(CH2CH3)2), 31P{1H} NMR (202.5 M Hz, CDCl3, 25 °C): δ

= 70.82 ppm. IR (KBr): 2967 (st), 2908 (m), 1459 (m), 1383 (s), 763 (s). Elemental analysis

calcd (%) for C22H50Cl4P2Pd2 (731.231 g∙mol-1): C 36.14, H 6.89; found C 36.06, H 7.32.

3.2.27 Synthesis of complex (iPr2PCH2Cy)2Pd2Cl410 6m.

One equivalent of [iPr2P(3-pentane)][HBF4] (55 mg, 0.182 mmol), 3 equivalents of NaOAc,

and one equivalents of palladium acetate (41 mg, 0. 182 mmol) were dissolved in thf (10

mL). The resulting mixture was stirred for 1h at room temperature and 3h at 35°C. The

mixture was allowed to attain r.t., then was washed a couple of times with sodium chloride

solution and extracted with CH2Cl2 (3 × 10 mL). The combined organic extracts were dried

over MgSO4 and concentrated under reduced pressure, afforded an orange powder 6m.

Yield: 79%. M.p.: 169°C (not corrected). 1H NMR (500 MHz, CDCl3, 25°C): δ = 1.437 (dd;

3J(P,H) = 13.6 Hz, 3J(H,H) = 6.90 Hz, CH(Me)2, 24H); 1.388 (dsept, 3J(H,P) = 12 Hz, 3J(H,H) = 6

Hz, (CHMe2), 4H), 2.25 (dd, 2J(H,P) = 11.7 Hz, 3J(H,H) = 6.0 Hz, PCH2Cy, 4H), 1.61 (m, CH(Cy),

1H); protons of Cyclohexyl in the range of 1.14 to 2.13. 31P{1H} NMR (202.5 M Hz, CDCl3, 25


144

°C): δ = 57.36 ppm. Elemental analysis calcd (%) for C26H54Cl4P2Pd2 (783.304 g∙mol-1): C

39.87, H 6.95; found C 39.88, H 6.74.

3.2.28 Synthesis of complex (iPr2PCH2CH(Me)2)2Pd2Cl410 6o.

One equivalent of [HiPr2PCH2CH(Me)2][BF4] (70 mg, 0.267 mmol) and three equivalents of

NaOAc were dissolved in CH2Cl2 (5 mL), 1 equivalents of palladium acetate (60 mg, 0.267

mmol) in thf (5 mL) was added dropwise at r. t.. The yellow brown suspension was stirred

for 1h at room temperature and 2h at 55°C. The mixture was allowed to attain r.t., then was

washed a couple of times with sodium chloride solution and extracted with CH2Cl2 (3 × 10

mL). The combined organic extracts were dried over MgSO4 and concentrated under

reduced pressure, recrystallized from hexane\ether to yield a yellow powder 6o (81%).

M.p.: 135(dec.) °. Elemental analysis calcd (%) for C20H46P2Cl4Pd2 (703.178 g∙mol-1): C 34.16,

H 6.59; found C 34.77 H 6.66.


In a similar procedure as described above, to a CH2Cl2 (10 mL) solution of Palladacycle 6e

(71.3 mg, 0.10 mmol), triphenylphosphine (54.5 mg, 0.208 mmol) was added with stirring.

The mixture was heated under reflux for 10 min after which all the material had dissolved.

The resulting mixture was stirred for 1h at room temperature, the solvent was removed

under reduced pressure to give an off-white solid which, on recrystallization from

dichloromethane/ methanol, yielded off-white crystals of 9e (97.9mg, 79% based on 24.

M.p.: 180-185°C. 1H NMR (500 MHz, CDCl3, 25°C): δ = 1.39 (d, C(CMe3), 3J(H,P) = 13.6 Hz,

18H); 1.73 (d, 3J(H,P) = 8.82 Hz , CH2-Pd), 2H); 0.97 (s, CMe2, 6H); 1.548 (d, 3J(H,P) = 7 Hz,

CH2CMe2CH2-Pd, 2H); 7.53-7.67 (m, Ph);13C{1H} NMR (126 MHz, CDCl3, 25°C): 44.66 (dd, 2JPC

= 15.76 and 3.56, CH2-Pd), 48.20 (CH2C(Me)2), 35.77 (dd, 3JPC = 11 Hz and 4.00 Hz,

C(Me)2CH2-Pd), 33.25 (d, 3JPC = 12 Hz, CH2C(Me)2), 30.58 (d, 2JPC = 4 Hz, C(Me)3), 33.30 (d, 1JPC

= 4 Hz, C(Me)3), 132.32 (dd, 1JPC = 2.5 Hz and 3JPC = 35.5 Hz, P-Pd-P-C-Ph), 134.992 (d, 2JPC =

12.09 Hz, P-C-C in Ph), 128.208 (d, 3JPC = 9.6 Hz, P-C-C-C in Ph) ;31P{1H} NMR (202.5 M Hz,

CDCl3, 25 °C): δ = 82.021 (d, JPP = 379 Hz), 25.767 (d, JPP = 380 Hz). IR (KBr): 3052 (s), 2947

(st), 2900 (s), 1435 (st), 1391 (s), 1093 (s), 1032 (m), 753 (st). Elemental analysis calcd (%)

for C31H43ClP2Pd (619.493 g∙mol-1): C 60.10, H 7.00; found C 59.34, H 7.22.


145


To a dichloromethane (20 mL) solution of Palladacycle 6k (0.09 g; 0.34 mmol), triphenyl

phosphine (85.3 mg, 0.34 mmol) was added with stirring. The mixture was heated under

reflux for 10 min after which all the material had dissolved. The resulting mixture was stirred

for 1h at room temperature; the solvent was removed under reduced pressure to give an

off-white solid which, on recrystallization from dichloromethane/ methanol, yielded off-

white crystals of 9k NMR data were in agreement with literature values [ref].

M.p.: 161-163°C( 165°C literature value)[177, 178], Elemental analysis calcd (%) for

C30H41ClP2Pd : C 59.51, H 6.83; found C 58.46, H 7.09 (found C 59.55, H 6.80 literature value)

ref, 31P{1H} NMR (202.5 M Hz, CDCl3, 25 °C): δ = 19.60 ppm.[177, 178] IR (KBr): 3068 (s, νC-H

Aryl), 2958 (s), 1479 (m), 1391 (s), 1254 (s), 1267 (m), 1229 (s), 750 (s, νP-C Alkyl). 1435 (m,

νP-C Aryl).


Diphenyl(o-tolyl)phosphine (54.14 mg; 0.196 mmol), was added to a suspension of

palladacycle 6e (70 mg; 0.10 mmol), in dichloromethane (10 mL). The mixture was heated

under reflux for 60 min after which all the material had dissolved. The solvent was removed

under reduced pressure to give an pale yellow solid which, on recrystallization from hexane,

yielded pale yellow crystals of 10e (99.33 mg, 82. M.p.: 182-184°C. 1H NMR (500 MHz, CDCl3,

25°C): δ = 1.494 (d, C(CMe3), 3J(H,P) = 13.50 Hz, 18H); 1.74 (d, 3J(H,P) = 8.80 Hz , CH2-Pd),

2H); 0.93 (s, CMe2, 6H); 1.61 (d, 3J(H,P) = 7 Hz, CH2CMe2CH2-Pd, 2H); 2.55 (s, CH3 group of o-

tolyl), 7.69 (t, 3J(H,H) = 8.58 Hz, Ph , 4H), 7.10 (t, 3J(H,H) = 7.48 Hz, o-tolyl , 1H), 7.00 (t,

3J(H,H) = 8.51 Hz, o-tolyl , 1H), 7.3 (d, 3J(H,H) = 7.41 Hz, o-tolyl , 1H), 7.23 (t, 3J(H,H) = 7.07

Hz, Ph , 1H), 7.30-7.39 (m, Ph) ;13C{1H} NMR (126 MHz, CDCl3, 25°C): 44.50 (dd, 2JPC = 15.80

and 3.27 CH2-Pd), 47.32 (d, JPC = 2 Hz, (CH2C(Me)2), 35.78 (dd, 3JPC = 12 Hz and 3.78 Hz,

C(Me)2CH2-Pd), 33.07 (d, 3JPC = 12.07 Hz, CH2C(Me)2), 30.51 (d, 2JPC = 4.40 Hz, C(Me)3), 35.97

(C(Me)3), 23.40 (d, 3JPC = 12 Hz, CH3 of o-tolyl) 131.607 (dd, JPC = 2 Hz and 3JPC = 37 Hz, P-Pd-P-

C(o-tolyl)), 129.967 (dd, 3JPC = 7.6 Hz and 1.750 Hz, P-Pd-P-C(Ph)), (131.139 (d, 3JPC = 8 Hz),

132.928 (d, 3JPC = 3.5 Hz), 125.99 (d, 3JPC = 6.7 Hz), 135.707 (d, 3JPC = 12.05 Hz, P-C-C in Ph),

128.26 (d, 3JPC = 9.95 Hz, P-C-C-C in Ph) ;31P{1H} NMR (202.5 M Hz, CDCl3, 25 °C): δ = 82.86


146

(d, 2JPP = 377.34 Hz), 19.891 (d, 2JPP = 377.27 Hz). Elemental analysis calcd (%) for

C32H45ClP2Pd (633.520 g∙mol-1): C 60.67, H 7.10; found C 60.50, H 7.26.


Diphenyl(o-tolyl)phosphine (0.09 g; 0.34 mmol), was added to a suspension of Palladacycle

6k (0.15 g; 0.17 mmol), in dichloromethane (10 mL). The mixture was heated under reflux

for 5 min after which all the material had dissolved. The solvent was removed under

reduced pressure to give an pale yellow solid which, on recrystallization from hexane,

yielded pale yellow crystals (Yield; 86%). 1H NMR (500 MHz, CDCl3, 25°C): δ = 1.622 (d,

C(CMe3), 3J(H,P) = 13.33 Hz, 18H); 0.49 (d, 3J(H,P) = 6 Hz , CH2-Pd), 2H); 1.39 (d, 3J(H,P) = 13

Hz,CMe2, 6H), 2.62 (s, CH3 group of o-tolyl), 7.76 (t, 3J(H,H) = 8.53 Hz, Ph , 4H), 7.09 (t,

3J(H,H) = 7.45 Hz, o-tolyl , 1H), 6.81 (t, 3J(H,H) = 8.56 Hz, o-tolyl , 1H), 7.25 (d, 3J(H,H) = 6.45

Hz, o-tolyl , 1H), 7.31 (t, 3J(H,H) = 7.36 Hz, Ph , 1H), 7.34-7.40 (m, Ph) ;13C{1H} NMR (126

MHz, CDCl3, 25°C): 49.81 (dd, 2JPC = 17 Hz and 2.26 CH2-Pd), 31.85 (brd, C(Me)2CH2-Pd),

23.37 (dd?, 3JPC = 12 Hz, C(Me)2), 30.51(bd, C(Me)3), 38.23 (dd, 1JPC = 3.68 Hz and 3JPC = 6.33

Hz C(Me)3), 16.39 (d, 3JPC = 27 Hz, CH3 of o-tolyl), 132.94 (dd, JPC = 2 Hz and JPC = 4.4 Hz, P-Pd-

P-C(o-tolyl)), 132.07 (dd, JPC = 2.80 and 34.61 Hz, P-Pd-P-C(Ph)), 135.36 (d, 3JPC = 12 Hz),

128.54 (d, 3JPC = 9.50 Hz), 131.23 (d, 3JPC = 7.50 Hz), 130.10(d, JPC = 1.96 Hz), 129.89 (d, JPC =

1.40 Hz), 125.63 (d, JPC = 6.81 Hz); 31P{1H} NMR (202.5 M Hz, CDCl3, 25 °C): δ = -13.94 (d, 2JPP

= 410.23 Hz), 14.20 (d, 2JPP = 410.51 Hz). IR (KBr): 3057 (s, νC-H Aryl), 2989 (s), 2959 (s), 2867

(s), 759 (st, νP-C Alkyl). 1466 (m), 1437 (m, νP-C Aryl), 1373 (m), 1179 (m). Elemental analysis

calcd (%) for C31H43ClP2Pd (619.493 g∙mol-1): C 60.10, H 7.00; found C 60.29, H 7.33.


To a dichloromethane (20 mL) solution of Palladacycle 6e (72.4 mg, 0.1013 mmol), solid

AgOAc (25.3 mg, 0.2026 mmol) was added with stirring. After 4 h, the white precipitate

formed was separated by centrifugation and the supernatant was filtered through a celite

column. The filtrate was dried and the yellow residue was recrystallized from hexane to

yield pale yellow crystals of 11e. (Yield; 73.1mg; 95%). 1H NMR (500 MHz, CDCl3, 25°C): δ =

1.41 (d, C(CMe3), 3J(H,P) = 13.50 Hz, 18H); 2.16 (s, CH2-Pd), 2H); 1.18 (s, CMe2, 6H); 1.806 (d,

3J(H,P) = 9 Hz, CH2CMe2CH2-Pd, 2H), 2.35 (s, Me in the OAc bridge group); 13C{1H} NMR (126


147

MHz, CDCl3, 25°C): 44.23 (s, CH2-Pd), 42.44 (d, 1JPC = 10.7 Hz, CH2C(Me)2), 37.66 (d, 2JPC =

24.6 Hz, C(Me)2 CH2-Pd), 35.30 (d, 3JPC = 17.9 Hz, CH2C(Me)2), 32.40 (d, 1JPC = 13 Hz, C(Me)3),

29.65 (d, 2JPC = 4.27 Hz, C(Me)3, 130.90 (s, in the bridge group); 31P{1H} NMR (202.5 M Hz,

CDCl3, 25 °C): δ = 93.01 ppm.


To a dichloromethane (8 mL) solution of Palladacycle 6e (72.2mg, 0.1012 mmol), solid

AgCOOCF3 (25.3mg, 0.2 mmol) was added with stirring. After 4 h, the white precipitate

formed was separated by centrifugation and the supernatant was filtered through a celite

column. The filtrate was dried and the yellow residue was recrystallized from hexane to

yield pale yellow crystals (Yield; 65.6 mg, 95%). 1H NMR (500 MHz, CDCl3, 25°C): δ = 1.409 (d,

C(CMe3), 3J(H,P) = 14 Hz, 18H); 2.29 (s, CH2-Pd), 2H); 2.168 (s, CMe2, 6H); 1.87 (d, 3J(H,P) = 9.

Hz, CH2CMe2CH2-Pd, 2H), 1.23 (s, Me in the bridge group); 13C{1H} NMR (126 MHz, CDCl3,

25°C): 44.23 (s, CH2-Pd), 42.44 (d, 1JPC = 10.7 Hz, CH2C(Me)2), 37.66 (d, 2JPC = 24.6 Hz, C(Me)2

CH2-Pd), 35.30 (d, 3JPC = 17.9 Hz, CH2C(Me)2), 32.40 (d, 1JPC = 12.7 Hz, C(Me)3), 29.65 (d, 2JPC =

4 Hz, C(Me)3, 144.90 (s, in the bridge group), 206.8(s, CF3, in the bridge group); 31P{1H} NMR

(202.5 M Hz, CDCl3, 25 °C): δ = 92.81 ppm. Elemental analysis calcd (%) for C30H56F6O4P2Pd2

(869.54 g∙mol-1): C 41.44, H 6.49; found C 41.9, H 7.12.

3.2.35 Synthesis of Pd(0) 13e.

A solution of PdMe2(tmeda) (32 mg, 0.127 mmole, 1equiv) in hexane (3 mL) was added to

PtBu2CH2C(CH3)3, 3e, (55 mg, 0.254 mmol, 2 equiv) suspended in hexane (3 mL) at room

tempreture. The resulting mixture was stirred for 1h at room temperature and 24h at 50°C.

The mixture was allowed to attain r.t., solvent was removed in vacuum to leave a foamy

white solid .To this solid, additional amount of diethyl ether was added to precipitate the

product, removed the ether under reduced pressure to leave colourless crystals which was

direct washed with cold pentane, and dried under high vacuum to give final product as

colourless crystals (Yield; 88%). 1H NMR (500 MHz, C6D6, 25°C): δ = 1.47 (s, C(CMe3, 18H),

1.39 (br, C(Me3)3), 1.38 (brs, CH2C(Me3)3); 31P{1H} NMR (202.5 MHz, CDCl3, 25 °C): δ = 45.5

ppm. Elemental analysis calcd (%) for C26H58P2Pd (539.105 g∙mol-1): C 57.93, H 10.84; found

C 57.137, H 11.02.


148

3.2.36 Synthesis of PdCl2(tmeda).

PdCl2 (1.76 g, 10 mmol) was dissolved in acetonitrile (50 mL) at reflux. After the solution was

cooled to 20°C, N,N,N',"-tetramethylethanediamine (2 mL, 15 mmol) was added and the

yellow precipitate of 40 that formed was filtered off, washed two times with diethyl ether,

and dried in vacuo, afforded an yellow powder yield (90%), Physical data were in agreement

with literature values.[186]

3.2.37 Synthesis of PdMe2(tmeda).

PdCl2(tmeda) (2.37 g, 8 mmol) was suspended in diethyl ether (30 mL). The stirred

suspension was cooled to -30°C and treated with an diethyl ether solution of salt-free MeLi

(12 mL of a 1.44 M solution, 17 mmol). With continued stirring the mixture was allowed to

warm slowly to 0.0°C and was kept for 1 h at that temperature. A grayish white suspension

formed. Then, ice cold degassed water (10 mL) was slowly added with stirring until a clear

diethyl ether layer and a black water layer had formed. The organic layer was separated,

dried over MgSO4 and concentrated under reduced pressure, afforded colourless crystals of

41 yields varied between 1.20 and 1.70 g (60-85%); mp 125-130°C .Physical data were in

agreement with literature values.[186]

3.2.38 Synthesis of 2-bromo-4-methyl-6-nitroaniline 65.

4-methyl-2-nitroaniline (10.0 g, 65.67 mmol) in glacial acetic cacid (100 mL) was heated at

50°C in an oil bath until a clear orange solution was formed. The bath was removed, and

bromine (3.6 mL, 11.22 g, 70.15 mmol) was added slowly. An exothermic reaction took

place, maintained the temperature < 15°C, and an orange precipitate was obtained. The

suspension was stirred for 1h at room temperature, and then poured into water at 0.0°C.

The solid was collected, washed with water and dried in vacuo to give 2-bromo-4-methyl-6-

nitroaniline (14.9 g, 98%) as an orange solid. M.p.: 72-74. 1H NMR (500 MHz, CDCl3, 25°C): δ

= 2.26 (s, Ar-CH3, 3H) 6.37 (brs, NH2, 2H); 7.92 (s, Ar-H, 1H); 7.55 (s, Ar-H, 1H); 13C{1H} NMR

(126 MHz, CDCl3, 25°C): 20.01 (s, Ar-CH3), 112.02, 125.58, 126.56, 132.7, 140.08, 140.32. IR

(KBr): 3484 (st, νC-NH2 Aryl-NH2), 3368 (st), 1576 (s), 1509 (st, νC-NO2 Aryl-NO2), 1347 (st, νC-N


149

Aryl-N), 1085 (m). Elemental analysis calcd (%) for C14H14Br2N2 (231.047 g∙mol-1): C 36.93, H

3.05, N 12.12; found C 36.40, H 3.01, N 12.13.

3.2.39 Synthesis of 1-bromo-2-iodo-5-methyl-3-nitrobenzene 66.

A solution of 2-bromo-4-methyl-6-nitroaniline (14.9 g, 64.5 mmol) and concentrated H2SO4

(72 mL) in water (120.0 mL) was cooled to 0.0°C. Next, (4.53g, 64.71 mmol) of NaNO2 in 40

mL of water was added dropwise to the diamine solution over a period of 30 min, keeping

the temperature at 0.0°C. After the addition of NaNO2 was complete, the resulting mixture

was stirred for an additional 30 min. and an aqueous solution of KI (16.37 g in 50 mL of

water) at -5°C was added dropwise over 30 min. The reaction mixture was then stirred for 1

h at r.t and 2h at 110°C, giving a dark brown solution. The solution was then cooled to 25 ºC

and washed a couple of times with water and 10% NaHCO3, then with Na2SO3 and extracted

with CH2Cl2 (3 × 10 mL), dried over MgSO4, and filtered. Removal of the solvent provided the

title compound as brown solid. The crude brown solid was then purified by column

chromatography (silica gel, hexane) yielding the title compound in good yield (21.56g, 84%).

M.p.: 70-73°C. 1H NMR (500 MHz, CDCl3, 25°C): δ = 2.37 (s, Ar-CH3, 3H), 7.66 (s, Ar-H, 1H);

7.34 (s, Ar-H, 1H); 13C{1H} NMR (126 MHz, CDCl3, 25°C): 20.75 (s, Ar-CH3), 90.66, 123.64,

133.02, 136.20, 141.32, 156.28. IR (KBr):, 1530 (st) 1347 (st), 1048 (s), 1259 (st).

3.2.40 Synthesis of 2,2'-dibromo-4,4'-dimethyl-6,6'-dinitrobiphenyl 67.

To a stirring solution of 1-bromo-2-iodo-5-methyl-3-nitrobenzene (4.05 g, 11.8 mmol) in

DMF (20 mL) was added copper powder (4.02 g, 63.26 mmol), and the reaction mixture was

heated at 125°C. After 3 h, the mixture was allowed to cool to room temperature. After

most of the DMF was evaporated under high vacuum at 60°C, the residue was dissolved in

CH2Cl2 (30mL) and the excess copper next removed by filtration through Celite. The filtrate

was washed with water and 10% NaHCO3, then with Na2SO3, extracted with CH2Cl2 (3 × 10

mL), dried over MgSO4, and filtered. Removal of the solvent provided the title compound as

brown solid. The crude solid was then purified by column chromatography (silica gel,

hexane) yielding the title compound as yellow solid, which was recrystallized from ethanol

to yield 1.95g of pure product (Yield 76 %). 1H NMR (500 MHz, CDCl3, 25°C): δ = 2.51 (s, Ar-

CH3, 3H) 8.01 (s, Ar-H, 1H); 7.79 (s, Ar-H, 1H); 13C{1H} NMR (126 MHz, CDCl3, 25°C): 21.13 (s,

Ar-CH3), 124.83, 125.16, 131.34, 138.62, 141.47, 149.44. IR (KBr): 3075 (st, νC-H, Aryl-H),


150

1528 (st, νC-NO2 Aryl-NO2), 1352 (st, νC-N Aryl-N), 1040 (s). Elemental analysis calcd (%) for

C14H10Br2N2O4 (430.049 g∙mol-1): C 39.10, H 2.34, N 6.51.; found C 40.9, H 2.36, N 6.79.

3.2.41 Synthesis of 6,6'-dibromo-4,4'-dimethylbiphenyl-2,2'-diamine 68. To a solution of 2,2'-dibromo-4,4'-dimethyl-6,6'-dinitrobiphenyl (4.2 g, 9.66 mmol) in 25 mL

of absolute ethanol was added 32 % w/w aqueous HCl (15.0 mL). Zink powder (4.93g, 75.3

mmol) was then added in portions over 15 min, and the reaction mixture was heated to

reflux at 100°C for 2 h. After cooling, the mixture was poured into ice water (50 mL) and

then made alkaline with 20% w/w aqueous NaOH solution(or ammonia) until pH = 9.0. The

product was next extracted with CH2Cl2, and the organic layer was washed with brine, dried

over anhydrous MgSO4, filtered, and then evaporated to dryness to give crude product as

brown solids, then purified by column chromatography (Alox., hexane) yielding the title

compound as light-brown crystals, (3.62g, 72%). M.p.: 131-134°C. 1H NMR (500 MHz, CDCl3,

25°C): δ = 2.28 (s, Ar-CH3, 3H), 6.95 (s, Ar-H, 1H); 6.56 (s, Ar-H, 1H); 3.57 (br, NH2, 2H);

13C{1H} NMR (126 MHz, CDCl3, 25°C): 32.2 (s, Ar-CH3), 115.24, 120.73, 123.40, 125.56,

140.89, 145.99. IR (KBr): 3361 (s, νC-NH2), 3010 (s, νC-H Aryl), 1612 (st), 1549 (s, νCH3 Aryl-CH3),

1034 (s, νC-Br Aryl-Br), 1302 (s, νC-N Aryl). ESI-TOF MS: calcd (m/z) for [C14H14Br2N2+nH]+

370.957 found 370.955 [C14H14Br2N2+nH]+. Elemental analysis calcd (%) for C14H14Br2N2

(370.082 g∙mol-1): C 45.44, H 3.81, N 7.57; found C 46.04, H 3.80, N 7.66.

3.2.42 Synthesis of 2,2'-dibromo-6,6'-diiodo-4,4'-dimethylbiphenyl 75.

A solution of 6,6'-dibromo-4,4'-dimethylbiphenyl-2,2'-diamine (1.5g, 4.05 mmol) and conc.

HCl (4.05 mL) in water (17 mL) was cooled to 0.0°C. Next, (0.84g, 12.17 mmol) of NaNO2 in

10 mL of water was added dropwise to the diamine solution over a period of 30 min,

keeping the temperature at 0.0°C. After the addition of NaNO2 was complete, the resulting

mixture was stirred for an additional 30 min. and an aqueous solution of KI (2.01 g in 10 mL

of water in presence of 0.1g I2) at -5°C was added dropwise over 30 min. The reaction

mixture was then stirred for 1 h at r.t and 2.5 h at 70°C, giving a dark brown solution. The

solution was then cooled to 25 ºC and the brown precipitate was collected by filtration. The

crude brown solid was then purified by column chromatography (silica gel, hexane) yielding

the title compound as a white solid (1.71 g, 71.3 % yield). 1H NMR (500 MHz, CDCl3, 25°C): δ


151

= 2.37 (s, Ar-CH3, 3H), 7.75 (s, Ar-H, 1H); 7.51 (s, Ar-H, 1H); 13C{1H} NMR (126 MHz, CDCl3,

25°C): 20.63 (s, Ar-CH3), 100.15, 122.98, 133.49, 139.03, 141.75, 145.40. IR (KBr): 2906 (m,

νC-H Aryl-H), 1521 (s, νCH3 Aryl-CH3), 1612 (st), 1580 (s), 1030 (s, νC-Br Aryl-Br). Elemental

analysis calcd (%) for C14H10Br2I2 (591.846 g∙mol-1): C 28.41, H 1.70; found C 29.00, H 1.69.

3.2.43 Synthesis of 6,6'-dibromo-N,N,N',N',4,4'-hexamethylbiphenyl-2,2'-diamine 69.

To a solution of 68 (7.6 g, 20.5 mmol, 1.0 equiv.) in thf (20 mL) was added at 25°C within

10min a NaH (5 g, 6 equiv.). The resulting mixture was stirred for 10min, and then (11.7 mL,

15.52 g, 123 mmol) of Me2SO4 was added. The mixture was allowed to reflux for 24h at

60°C. After cooling, the mixture was poured into ice water (50 mL) and then made alkaline

with 20% w/w aqueous NaOH solution (or ammonia) until pH = 9.0. The product was next

extracted with CH2Cl2, and the organic layer was washed with brine, dried over anhydrous

MgSO4, filtered, and then evaporated to dryness to give crude product as brown solids, then

purified by column chromatography (Alox., hexane) yielding the title compound as light-

brown crystals, (Yield; 73 %) of 69). M.p.: 137-140°C 1H NMR (500 MHz, CDCl3, 25°C): δ =

2.34 (s, Ar-CH3, 6H), 2.49 (s, Ar-NMe2, 12H), 7.15 (s, Ar-H, 2H); 6.85 (s, Ar-H, 2H); 13C{1H}

NMR (126 MHz, CDCl3, 25°C): 21.37 (s, Ar-CH3), 43.78 (s, Ar-NMe2), 153.98, 139.27, 132.62,

127.19, 126.87, 119.82. IR (KBr): 3053 (s), 1593 (st), 1544 (st), 1346 (s), 1303 (m), 1210 (m),

1046 (m), 783 (st). ESI-TOF MS: calcd (m/z) for [C18H22Br2N2+nH]+ 427.02 found 427.02

[C14H14Br2N2+nH]+, Elemental analysis calcd (%) for C18H22Br2N2 (426.188 g∙mol-1): C 50.73, H

5.20, N 6.57; found C 50.72, H 5.27, N 6.41.

3.2.44 Synthesis of bisphosphine 77.

To a solution of 75 (400 mg, 0.676 mmol, 1.0 equiv.) in diethyl ether (6 mL) was added at -

95°C within 5min a solution of n-BuLi (0.887 mL, 1.6 M n-hexane, 1.42 mmol, 2.1 equiv.).

The resulting slightly opaque mixture was stirred for 25min at -95°C, and then a solution of

iPr2PCI (216.6 mg, 1.42 mmol) in diethyl ether (5 mL) was added. The mixture was allowed

to attain r.t. within 2h. At ca. -65°, the precipitation of a white solid started. After stirring for

3h at r.t., the mixture was reduced to dryness under reduced pressure (oil pump vacuum)

for 1h, then a new portion of Et2O (5 mL) was added. The mixture was quenched by addition

of 10 ml of degassed H2O, extracted with diethyl ether (3 Х 10 mL) under Ar. The combined


152

organic extracts were dried with MgSO4 and concentrated under reduced pressure. The

crude material obtained was purified by column chromatography on silica gel using THF as

eluent, then concentrated under reduced pressure. The resulting colorless oil was

recrystallized from EtOH to yield 363 mg (93 % based on 75) of 77 as white crystals. M.p.:

192°C. 1H{31P} NMR (500 MHz, C6D6, 25 °C): δ = 7.41 (s, Ar-H, 2H); 7.22 (s, Ar-H, 2H); 2.17

(sep; 3J(H,H) = 6.8 Hz, CH(Me)2, 2H); 2.07 (sep; 3J(H,H) = 7.4 Hz, CH(Me)2, 2H); 2.01 (s,

biphen-CH3, 6H), 1.23 (d; 3J(H,H) = 7.0 Hz, CH(Me)2, 6H), 1.115 (d; 3J(H,H) = 6.9 Hz, CH(Me)2,

6H); 1.08 (d; 3J(H,H) = 7.2 Hz, CH(Me)2, 12H). 13C{1H} NMR (125.8 MHz, C6D6, 25 °C): δ =

144.2 (m, central C-C); 141.1 (m, Ar-C-P(iPr)2; 138.7 (Ar-C-Me); 133.7 (Ar-C-H); 131.8 (Ar-C-

H); 127.3 (t, J(C,P) = 4.5 Hz, Ar-C-Br); 25.35 (dd, J(C,P) = 7.0/9.5 Hz, CH(Me)2); 22.3 (t, J(C,P) =

10 Hz, CH(CH3)2); 22.1 (m, CH(Me)2); 22.0 (d, J(C,P) = 11 Hz, CH(CH3)2); 20.85 (biphen-CH3);

20.4 (t, J(C,P) = 11 Hz, CH(CH3)2); 17.75 (t, J(C,P) = 2.5 Hz, CH(CH3)2). 31P{1H} NMR (202.5

MHz, C6D6, 25 °C): δ = 2.01 ppm. IR (KBr): 1452 (s), 1309 (s), 2942 (s), 2815 (s), 1589 (s),

1134 (s), 3052 (s). ESI-TOF MS: calcd (m/z) for [C26H38Br2P2+H]+ (100%) 573.0873 found

573.076 [C26H38Br2P2+H]+ with expected isotopic pattern. Elemental analysis (%) for

C26H38Br2P2 (572.335 g∙mol-1): C 54.56, H 6.69; found C 54.13, H 6.82.



95°C within 5min a solution of n-BuLi (0.665 mL, 1.6 M n-hexane, 1.06 mmol, 2.1 equiv.).

The resulting slightly opaque mixture was stirred for 25min at -95°C, and then a solution of

Ph2PCI (232.6 mg, 1.06 mmol) in diethyl ether (5 mL) was added. The mixture was allowed

to attain r.t. within 2h. At ca. -65°, the precipitation of a white solid started. After stirring for

4h at r.t., the mixture was reduced to dryness under reduced pressure (oil pump vacuum)

for 1h, then a new portion of Et2O (5 mL) was added. The mixture was quenched by addition

of 10 ml of degassed H2O, extracted with diethyl ether (3 Х 10 mL) under Ar. The combined

organic extracts were dried with MgSO4 and concentrated under reduced pressure. The

crude material obtained was filtrated through silica gel using THF as eluent, then

concentrated under reduced pressure. The resulting colourless oil was recrystallized from

EtOH to yield 358 mg (98 % based on 3) of 4 as white crystals. 1H NMR (500 MHz, C6D6, 25

°C): δ = 7.38 (d, Ar-H, 2H); 6.97 (s, Ar-H, 2H); 2.01 (s, biphen-CH3, 6H); 7.08-7.70 (m’s; Ph);


153

31P{1H} NMR (202.5 MHz, CDCl3, 25 °C): δ = -11.95 ppm; 13C{1H} NMR (126 MHz, CDCl3,

25°C): 21.28 (s, Ar-CH3), 128.79 (d, JPC = 11 Hz), 128.98 (s), 128.07 (s), 128.35 (s), 128,36 (dd,

JPC = 6.49 Hz and JPC = 3 Hz), 130.98 (d, JPC = 9 Hz), 134.99 (brd), 134.64 (s), 139.58 (s),

133.159 (brd). IR (KBr): 3051 (s, νC-H Aryl-H), 1580 (m), 1478 (m, νCH3 Aryl-CH3), 1434 (st),

1208 (st), 1068 (s, νC-Br Aryl-Br). ESI-TOF MS: calcd (m/z) for [C38H30Br2P2+H]+ (100%) 709.25

found 709.011 [C38H30Br2P2+H]+. Elemental analysis (%) for C38H30Br2P2 (708.400 g∙mol-1): C

64.43, H 4.27; found C 64.60, H 4.59.



20°C within 5min a solution of n-BuLi (1.012 mL, 1.6 M n-hexane, 1.62 mol, 2.3 equiv.). The

resulting slightly opaque mixture was stirred for 30min at -50°C, and then was added to a

solution of PPh2CI (266 mL, 1.62 mol, 2.3 equiv) in diethyl ether (5 mL). The mixture was

allowed to attain r.t. within 2h. At ca. -20°, the precipitation of a white solid started. After

stirring for 5h at r.t., the mixture was reduced to dryness under reduced pressure (oil pump

vacuum) for 1h, then a new portion of Et2O (5 mL) was added. The mixture was quenched by

addition of 10 ml of degassed H2O, extracted with diethyl ether (3 Х 10 mL) under Ar. The

combined organic extracts were dried with MgSO4 and concentrated under reduced

pressure. The crude material obtained was purified simply on silica gel using THF as eluent,

then concentrated under reduced pressure. The resulting off white solid was recrystallized

from EtOH to yield 226 mg (Yield 50.2 %) of titled compound as off white crystals. M.p.: 229

(dec.)°C. 1H NMR (500 MHz, C6D6, 25 °C): δ = 6.80 (br, Ar-H, 4H), 2.27 (s, biphen-CH3, 6H),

2.08 (s, biphen-N(CH3)2, 12H), 7.28 (d, biphen-CH3, JPH = 7 Hz), 6.95 (t, PPh, JPH = 6 Hz, 4H),

7.27-7.37 (m’s; Ph); 31P{1H} NMR (202.5 MHz, CDCl3, 25 °C): δ = -11.60 ppm; 13C{1H} NMR

(126 MHz, CDCl3, 25°C): 21.91 (s, Ar-CH3), 42.46 (s, Ar-N(CH3)2), 120.59 (s), 127.25 (d, JPC =

1.42 Hz), 128.98 (s), 128.07 (s), 127.99 (d, JPC = 5.5 Hz), 127.9 (d, JPC = 6 Hz), 131.43 (d, JPC =

2.6 Hz), 132.82 (d, JPC = 18.5 Hz), 133.39 (d, JPC = 19 Hz), 140.85 (dd, JPC = 15 Hz); IR (KBr):

3051 (m, νC-H Aryl-H), 1589 (st), 1545 (m, νCH3 Aryl-CH3), 1476 (m), 1309 (st, νC-N Aryl-N ),

1429 (st), 1130 (st, νC-N Alkyl-N). ESI-TOF MS: calcd (m/z) for [C42H42N2P2+H]+ (100%)

637.289 found 637.275 [C42H42N2P2+H]+. Elemental analysis (%) for C42H42N2P2 (636.743

g∙mol-1): C 79.33, H 6.56, N 4.40; found C 71.32, H 6.49, N 3.65.


154

3.2.47. Synthesis of bisphosphine 71.

To a solution of 69 (100 mg, 234 mmol, 1.0 equiv.) in diethyl ether (6 mL) was added at -

50°C within 5min a solution of n-BuLi (0.3 mL, 1.6 M n-hexane, 492 mmol, 2.1 equiv.). The

resulting slightly opaque mixture was stirred for 30min at -70°C, and then a solution of

iPr2PCI (75.2 mg, 492 mmol, 2.1 equiv) in diethyl ether (5 mL) was added. The mixture was

allowed to attain r.t. within 2h. At ca. -20°, the precipitation of a white solid started. After

stirring for 5h at r.t., the mixture was reduced to dryness under reduced pressure (oil pump

vacuum) for 1h, then a new portion of Et2O (5 mL) was added. The mixture was quenched by

addition of 10 ml of degassed H2O, extracted with diethyl ether (3 Х 10 mL) under Ar. The


pressure. The crude material obtained was purified by column chromatography on silica gel

using THF as eluent, then concentrated under reduced pressure. The resulting off white

solid was recrystallized from EtOH to yield 47% of titled compound as off white crystals. 1H

NMR (500 MHz, C6D6, 25 °C): δ = 2.39 (s, biphen-CH3, 6H), 6.90 (d, Ar-H, 2H); 7.31 (s, Ar-H,

2H); 2.42 (s, N(CH3)2, 12H), 2.22 (dsep; 3JPH = 11 Hz and 3JHH = 6.9 Hz, CH(Me)2, 2H).1.26 (dd;

3JPH = 11 Hz and 3JHH = 7 Hz, CH(Me)2, 6H) 1.38 (dd, 3JPH = 11 Hz and 3JHH = 6.9 Hz, CH(CMe2)2,

6H), 1.17 (dd, 3JPH = 15 Hz, 3JHH = 7.38 Hz, CH(Me)2, 6H); 1.24 (dd; 3JPH = 11 Hz and 3JHH = 6.9

Hz, CH(Me)2, 6H).31P{1H}NMR (202.5 MHz, CDCl3, 25 °C): δ = -1.39 ppm.

3.2.48 Synthesis of PdCl2 (71) 73.

One equivalent of the bisphosphine biphenyl 71 (80 mg, 0.159 mmol) was dissolved in

CH2Cl2 (5 mL), and one equivalents of palladium dichloro(1,5-cyclooctadiene) (45.6mg ,

0.159 mmol) in CH2Cl2 (5 mL) was added drop wise at r. t.. The yellow suspension was

stirred for 5h at room temperature. The reaction mixture concentrated under reduced

pressure, recrystallized from CH2Cl2/diethyl ether to yield 73 as yellow powder. (77.6 mg, 75

%). 1H NMR (500 MHz, C6D6, 25 °C): δ = 2.38 (s, biphen-CH3, 6H), 2.56 (s, N(CH3)2, 12H), 1.01

(dd, 3JPH = 15 Hz and 3JHH = 7.15 Hz CH(CMe2)2, 6H), 1.28 (br, CH(Me)2, 6H); 1.55 (br,

CH(Me)2, 12H); ), 7.08 (d, 3JPH = 9 Hz, Ar-H, 2H); 6.86 (s, Ar-H, 2H);. 31P{1H} NMR (202.5 MHz,

CDCl3, 25 °C): δ = (br, 46.40 ppm). Elemental analysis (%) for C30H50Cl2N2P2Pd (678.00 g∙mol-

1): C 53.14, H 7.43, N 4.13; found C 52.53, H 7.79, N 3.56.


155

3.2.49 Synthesis of PdCl2(70) 72.


CH2Cl2 (5 mL), and one equivalents of palladium dichloro(1,5-cyclooctadiene) (44.8mg ,



pressure, recrystallized from CH2Cl2/diethyl ether to yield an orange powder (93 mg, 85.9

%). M.p.: 260 (dec.)°C. 1H NMR (500 MHz, C6D6, 25 °C): δ = 2.01 (s, biphen-CH3, 6H), 2.39 (s,

biphen-N(CH3)2), 7.28 (d, JPH = 7 Hz), 6.04 (s, Ar-H, 4H), 7.16-7.92 (m's; Ph); 31P{1H} NMR

(202.5 MHz, CDCl3, 25 °C): δ = 31.637 ppm; 13C{1H} NMR (126 MHz, CDCl3, 25°C): 21.69 (s,

Ar-CH3), 42.18 (s, Ar-N(CH3)2), 120.468 (s), 124.78 (d, JPC = 10.83 Hz), 130.63 (d, JPC = 13.06),

135.40 (d, JPC = 9.86), 136.193 (d, JPC = 12 Hz), 138.50 (d, JPC = 13. Hz), 149.52 (d, JPC = 11 Hz);

IR (KBr): 3057 (s, νC-H Aryl-H), 1589 (st), 1543 (st, νCH3 Aryl-CH3), 1433 (st), 1349 (st, νC-N Aryl-

N ), 1591 (st), 1093 (st, νC-N Alkyl-N). ESI-TOF MS: calcd (m/z) for [C42H42ClN2P2Pd2-Cl+H]+

777.155 found 777.140 [C42H42ClN2P2Pd2-Cl+H]+. Elemental analysis (%) for C42H42Cl2N2P2Pd

(814.069 g∙mol-1): C 61.97, H 5.20, N 3.44; found C 55.73, H 5.00, N 2.87.

3.2.50 Synthesis of PtCl2 (70) 74.


CH2Cl2 (5 mL), and one equivalents of platinum dichlorobis(diethylsulfide) (0.159 mmol) in

CH2Cl2 (5 mL) was added drop wise at r. t.. The yellow suspension was stirred for 5h at room

temperature. The reaction mixture concentrated under reduced pressure, recrystallized

from CH2Cl2/diethyl ether to yield an orange powder (Yield; 91%). M.p.: 218 (dec.)°C. 1H

NMR (500 MHz, C6D6, 25 °C): δ = 2.00 (s, biphen-CH3, 6H), 2.37 (s, biphen-N(CH3)2), 6.58 (d,

JPH = 10.4 Hz, 4H), 5.94 (s, Ar-H, 4H), 7.86 (dt, JPH = 12 Hz, JHH = 4.39 Hz, Ph), 7.39 (brm, Ph),

7.30 (t, JHH = 6.99 Hz, Ph), 7.22 (t, JHH = 6.57Hz) ; 31P{1H} NMR (202.5 MHz, CDCl3, 25 °C): δ =

11.79 ppm with JPt-P = 3600 Hz); ESI-TOF MS: calcd (m/z) for [C42H42ClN2P2Pd2-Cl+H]+ 867.216

found 867.201 [C42H42ClN2P2Pt2-Cl+H]+. Elemental analysis (%) for C42H42Cl2N2P2Pt (902.733

g∙mol-1): C 55.88, H 5.69, N 3.10; found C 53.23, H 4.78, N 2.74.


156

3.2.51 Synthesis of PdCl2(77) 79.

One equivalent of bisphosphine biphenyl 77 (72 mg, 0.125 mmol) was dissolved in CH2Cl2 (5

mL), and one equivalents of palladium dichloro(1,5-cyclooctadiene) (36 mg , 0.125 mmol) in

CH2Cl2 (5 mL) was added drop wise at r. t.. The yellow suspension was stirred for 5h at room

temperature. The reaction mixture concentrated under reduced pressure, recrystallized

from CH2Cl2/pentane to yield a yellow powder (70 mg, 77.3). M.p.: 168-172°C. 1H NMR (500

MHz, C6D6, 25 °C): δ = 7.51 (d, 3JPH) = 9 Hz, Ar-H, 2H); 7.70 (s, Ar-H, 2H); 2.45 (s, biphen-CH3,

6H); 2.35 (m, CH(Me)2, 2H), 1.23 (br, CH(CMe2)2, 6H), 1.029 (dd, 3JPH = 16 Hz, 3JHH = 6.41 Hz,

CH(Me)2, 6H); 1.239 (br, CH(Me)2, 12H). 31P{1H} NMR (202.5 MHz, CDCl3, 25 °C): δ = (br,

45.02) ppm. IR (KBr): 3030 (s, νC-H Aryl-H), 2969 (m), 2876 (m), 1534 (m, νCH3 Aryl-CH3), 1583

(st), 1452 (st), 1375 (st), 1221 (st), 1156 (s), 1041 (s, νC-Br Aryl-Br). ESI-TOF MS: calcd (m/z)

for [C26H38Br2Cl2P2Pd-Cl+H]+ 714.951 found 714.941 [C26H38Br2Cl2P2Pd-Cl+H]+. Elemental

analysis (%) for C26H38Br2Cl2P2Pd (749.661 g∙mol-1): C 41.66, H 5.12; found C 41.45, H 5.17.

3.2.52 Synthesis of PdCl2 (76) 78.


CH2Cl2 (5 mL), and one equivalents of palladium dichloro(1,5-cyclooctadiene) (44.4 mg,



pressure, recrystallized from CH2Cl2/pentane to yield a yellow powder (117 mg, 85.2 %).

M.p.: 268 (dec)°C. 1H NMR (500 MHz, C6D6, 25 °C): δ = 6.90 (d, 3JPH) = 11.74 Hz, Ar-H, 2H);

7.03 (s, Ar-H, 2H); 2.05 (s, biphen-CH3, 6H); 8.01 (dd, 3JPH = 12.45 Hz, 3JHH = 7.64 Hz, Ph); 7.81

(m, Ph, 2H), 7.41-7.49 (m, Ph), 7.37 (br, Ph). 31P{1H} NMR (202.5 MHz, CDCl3, 25 °C): δ = (br,

31.64) ppm. IR (KBr): 3013 (m, νC-H Aryl-H), 1586 (s, νCH3 Aryl-CH3), 1523 (m), 1479 (m), 1435

(st), 1097 (st, νC-Br Aryl-Br).13C{1H} NMR (126 MHz, CDCl3, 25°C): 21.08 (s, Ar-CH3), 128.1 (d,

JPC = 10.83 Hz), 128.7 (d, JPC = 11.8 Hz), 131.41 (d, JPC = 2.7 Hz), 131.98 (s), 133.71 (d, JPC =

9.02), 135.31 (d, JPC = 10 Hz), 136.10 (d, JPC = 13 Hz), 136.98 (s), 139.98 (d, JPC = 10.71 Hz);

141.961 (d, JPC = 17.50 Hz). ESI-TOF MS: calcd (m/z) for [C26H38Br2Cl2P2Pd-Cl+H]+ 850.889

found 850.866 [C38H30Br2Cl2P2Pd-Cl+H]+. Elemental analysi (%) for C38H30Br2Cl2P2Pd (885.726

g∙mol-1): C 51.53, H 3.41; found C 51.05, H 3.42.


157



CH2Cl2 (5 mL), and one equivalents of platinum dichlorobis(diethylsulfide) (54.6mg , 0.122

mmol) in CH2Cl2 (5 mL) was added drop wise at r.t.. The yellow suspension was stirred for

24h at room temperature. The reaction mixture concentrated under reduced pressure,

recrystallized from CH2Cl2/pentane to yield a off-white powder (101mg, 81%). 1H NMR (500

MHz, C6D6, 25 °C): δ = 6.96 (br, Ar-H, 4H); 2.05 (s, biphen-CH3, 6H); 7.34 (t, JPH = 7 Hz, JHH =

6.98 Hz, Ph); 7.41-7.48 (m, Ph), 7.77 (t, JHH = 8 Hz, Ph), 7.96 (br, Ph). 31P{1H} NMR (202.5

MHz, CDCl3, 25 °C): δ = 11.58 ppm. 13C{1H} NMR (126 MHz, CDCl3, 25°C): 33.91 (s, biph-CH3),

127.74, 128.49, 129.52, 131.35, 131.85, 133.266, 135.53, 135.86, 139.75, 137.37. IR (KBr):

3051 (s), 1589 (st), 1482 (st), 1024 (s) 1095. ESI-TOF MS: calcd (m/z) for [C38H30Br2Cl2P2Pt-

Cl+H]+ 938.950 found 983.930 [C38H30Br2Cl2P2Pt-Cl+H]+. Elemental analysis (%) for

C38H30Br2Cl2P2Pt (974.390 g∙mol-1): C 46.84, H 3.10; found C 47.92, H 3.93.



CH2Cl2 (5 mL), and one equivalents of platinum dichlorobis(diethylsulfide) (35.6 mg , 0.113

mmol) in CH2Cl2 (5 mL) was added drop wise at r.t., the yellow suspension was stirred for

24h at room temperature. The reaction mixture concentrated under reduced pressure,

recrystallized from CH2Cl2/pentane to yield a off-white powder (Yield; 80 %). M.p.: 267°C

(dec.). 1H NMR (500 MHz, C6D6, 25 °C): δ = 7.47 (d, 3JPH = 8.7 Hz, Ar-H, 2H); 7.66 (s, Ar-H, 2H);

2.45 (s, biphen-CH3, 6H); 1.01 (brm, CH(Me)2, 6H), 1.25 (brm, CH(Me)2, 6H), 1.56 (brm,

CH(Me)2, 12H), 1.67 (br, CH(Me)2, 2H); 3.67 (br, CH(Me)2, 2H), 31P{1H} NMR (202.5 MHz,

CDCl3, 25 °C): δ = (br, 22.36) ppm. IR (KBr): 2963 (m), 2921 (st), 2869 (st), 1583 (st), 1454

(st), 1156 (s), 1076 (s, νC-Br Aryl-Br), 733 (m). ESI-TOF MS: calcd (m/z) for [C26H38Br2Cl2P2Pt-

Cl+H]+ 803.013 found 802.997 [C26H38Br2Cl2P2Pt-Cl+H]+. Elemental analysis (%) for

C26H38Br2Cl2P2Pt (838.325 g∙mol-1): C 37.25, H 4.57; found C 38.03, H 4.68.


158

3.2.55 Synthesis of 2,2',6,6'-tetraphosphinebiphenyl 82.

Method A

n-BuLi (2.5 M in n-hexane, 0.887 mL, 2.19 mmol, 2.1 equiv.) was added at -95 °C dropwise

over a period of 5 min. to a solution of 75 (400 mg, 1.0 mmol) in diethyl ether (6 mL). The

mixture was stirred for 25 min at -95 °C, and then a solution of i-Pr2PCI (432 mg, 2.84 mmol)

in in diethyl ether (6 mL) was added at this temp. The mixture was allowed to attain r.t.

within 2h, at ca. -65 °C the precipitation of a white solid started. After stirring for 3 h at r.t.,

the solvent was reduced to dryness under reduced pressure (oil pump vacuum) for 1 h, and

then a new portion of diethyl ether (6 mL) was added. After stirring for 2 h at r.t., the

mixture was filtered under Ar, and washed 2 times with diethyl ether (3 mL). At -95 °C n-

BuLi (2.5 M in n-hexane, 0.887 mL, 2.19 mmol, 2.1 equiv.) was added. The mixture was

stirred for 35 min at -95 °C and 1h at r.t., chilled to -95 °C again; a solution of iPr2PCI (432

mg, 2.84 mmol) in diethyl ether (5 ml) was added. The resulting mixture was stirred for 45

min at -95 °C allowed to attain r.t. and stirred overnight, the mixture was quenched by

addition of degased H2O (10 ml), extracted with diethyl ether (3 × 10 mL) under Ar. The


pressure. The crude material obtained was purified by column chromatography on silica gel

using dichloromethane as eluent, concentrated under reduced pressure to obtain a

colorless oil which was recrystallized from EtOH to afford 423.2 mg (96 % based on 75) of 82

as white powder. M.p.: 206 °C. 1H{31P} NMR (500 MHz, C6D6, 25 °C): δ = 7.58 (s, Ar-H, 4H);

2.53 (s, biphen-CH3, 6H); 2.29 (dt; 3J(H,H) = 7.2 Hz, 3J(H,H) = 6.7 Hz, CH(Me)2, 8H); 1.14 (d,

3J(H,H) = 7.2 Hz, Me, 24H), 1.13 (d, 3J(H,H) = 6.7 Hz, Me, 24H); 31P{1H} NMR (202.5 MHz,

C6D6, 25 °C): δ = -4.08; 13C{1H} NMR (125.8 MHz, C6D6, 25 °C): δ = 148.9 (m, central C-C);

139.1 (m, Ar-C-P(iPr)2; 134.8 (Ar-C-Me); 133.2 (Ar-C-H); 23.4 ppm (m, CH(Me)2); 23.1 (m, Me,

iPr); 21.5 (biphen-CH3); 18.8 ppm(Me, iPr). IR (KBr): 1457 (s), 1358 (s), 2975, 2947, 2915 (s),

2865 (s), 1583 (s), 1150 (s), 3046 (s). ESI-TOF MS: calcd (m/z) for [C38H66P4+H]+ 647.4193

found 647.405 [C38H66P4+H]+ with expected isotopic pattern. Elemental analysis calcd (%)

for C38H66P4∙1/2 CH2Cl2 (572.335 g∙mol-1): C 67.09, H 9.80; found C 67.08, H 9.60.


159

Method B

To a solution of 200 mg (0.349 mmol, 1 equiv.) of 77 in diethyl ether (5 mL) was added at -95

°C during a period of 5 min a solution of n-BuLi (0.436 ml, 1.6 M n-hexane, 0.698 mmol, 2.0

equiv.). The resulting mixture was stirred for 30 min at -95 °C and 1h at r.t., after cooling to -

95 °C a solution of (106 mg, 0.698 mmol) of iPr2PCI was added. The resulting mixture was

stirred for 45 min at -95 °C, allowed to warm to r.t. and stirred overnight. The mixture was

quenched by addition of 10 ml degassed H2O, extracted with diethyl ether (3 × 10 mL) under

Ar. The combined organic extracts were dried with MgSO4 and concentrated under reduced

pressure. The resulting colorless oil was recrystallized from EtOH to afford 218.5 mg (96%)

of 2 as white powder.

3.2.56 Synthesis of dinuclear palladium complex of 2,2',6,6'-tetraphosphinebiphenyl 83.

One equivalent of ligand 82 (46 mg, 0.0712 mmol) was dissolved in CH2Cl2 (5 mL), and 2

equivalents of palladium acetate (32 mg, 0.1424 mmol) in CH2Cl2 (5 mL) were added

dropwise at r. t.. The yellow brown suspension was stirred for 6h at room temperature. The

reaction mixture was washed a couple of times with sodium chloride solution and extracted

with CH2Cl2 (3 × 10 mL). The combined organic extracts were dried over MgSO4 and

concentrated under reduced pressure, recrystallized from chloroform to yield complex 5 as

yellow powder (60 mg, 84 % based on 2). M.p.: 208 °C. 1H NMR (500 MHz, d7-dmf, 100°C): δ

= 8.25 (d, 3J(P,H) = 10 Hz, Ar-H, 4H); 4.04 (dsep; 2J(P,H) = 10.4, 3J(H,H) = 7.1 Hz, CH(Me)2, 4H);

2.85 (s, biphen-CH3, 6H); 2.15 (dsep; 2J(P,H) 8.7, 3J(H,H) 7.1 Hz, CH(Me)2, 4H); 1.97 (dd,

3J(P,H) = 17.0, 3J(H,H) = 7.2 Hz, Me, 12H), 1.81 (dd, 3J(P,H) = 15 Hz, 3J(H,H) = 7.1 Hz, Me,

12H); 1.47 (dd, 3J(P,H) = 20.6 Hz, 3J(H,H) = 7.2 Hz, Me, 12H), 1.40 (dd, 3J(P,H) = 14 Hz, 3J(H,H)

= 7.2 Hz, Me, 12H); 31P{1H} NMR (202.5 MHz, d7-dmf, 100°C): δ = 53.9 ppm. IR (KBr): 1447

(s), 1385 (s), 2965 (s), 2865 (s), 1627 (s), 1173 (s), 3039 (s). ESI-TOF MS: calcd (m/z) for

[C38H66P4Pd2Cl3-Cl+H]+ 966.1333 found 966.102 [C38H66P4Pd2Cl3-Cl+H]+ with expected

isotopic pattern. Elemental analysis calcd (%) for C38H66P4Pd2Cl2∙1/2 CHCl3 (1001.477 g∙mol-

1): C 43.58, H 6.32; found C 43.39, H 6.35.


160

3.3. General procedure for the Suzuki-Miyaura coupling.

An oven-dried Schlenk tube was charged with either palladium complex, Pd2(dba)3

/phosphine or Pd(OAc)2)/phosphine, the boronic acid (1.2 mmol, 1.2 equiv.), and base (3.0

mmol, 3.0 equiv) The Schlenk tube was capped with a rubber septum and then evacuated

and backfilled with argon (this sequence was repeated three times). Dry solvent (10 mL) was

added through the septum via syringe and the resulting mixture was stirred at ambient

temperature for 5 min. The aryl halide (1.0 mmol, 1.0 equiv.) was added via syringe (solid

aryl halides were added during the initial charge, prior to securation). The reaction mixture

was heated at the given temperature with vigorous stirring for the given time. After cooling

to ambient temperature, the reaction mixture was diluted with water (25 mL) and extracted

with diethyl ether (3 x 25 mL). The combined organic extracts were dried over MgSO4 and

concentrated under reduced pressure. The crude material obtained was purified by column

chromatography on silica (diethyl ether).

3.4. General procedure for the Buchwald-Hartwig coupling.

An oven-dried Schlenk tube was charged with palladium complex 1%, powdered, base (3.0

mmol, 3.0 equiv.), and acetnaphthene (1.0 mmol) as internal standard. The Schlenk tube

was capped with a rubber septum and then evacuated and backfilled with argon (this

sequence was repeated three times). Dry solvent (10 mL) was added through the septum via

syringe and the resulting mixture was stirred at ambient temperature for 5 min. The aryl

halide (1.0 mmol, 1.0 equiv.) was added via syringe (solid aryl halides were added during the

initial charge, prior to securation). Next, amine was added via syringe too, the reaction

mixture was heated at the given temperature with vigorous stirring for the given time. After

cooling to ambient temperature, the reaction mixture was diluted with water (25 mL) and

extracted with diethyl ether (3 x 25 mL). The combined organic extracts were dried over

MgSO4 and concentrated under reduced pressure. The crude material obtained was purified

by column chromatography on silica (diethyl ether).


161

3.5. General procedure for the Suzuki-Miyaura coupling (Kinetic investigations).

An oven-dried Schlenk flask was evacuated and back-filled with argon and charged with aryl

halides (1.0 mmol), phenylboronic acid (1.2 mmol), K2CO3 (0.414 g, 3 mmol) and 114 mg (0.5

mmol) of acetylferrocene and were dissolved in 9 mL of a 1,4-dioxan/water mixture (2:1),

thf or toluene. After addition (0.1-1 mol %) of the respective catalyst (or Pd:L), the reaction

mixture was heated at the given temperature with vigorous stirring for the given time. After

3, 8, 15, 20, 30, 60, 90, 120, 150, 180, 210, 240 and 300 min, samples (~1 mL) were taken for

characterization, evaporate the solvent and chromatographed on silica gel with diethyl

ether (or CH2Cl2) as eluent, and all volatiles were evaporated under reduced pressure. The

conversions were determined by 1H NMR spectroscopy.

3.6. General procedure of 31P{1H} NMR studies of the Pd(0), 13e, complex:

Kinetic experiments were performed at room temperature, 50°C, 60°C and 70°C with 0.013

M solutions of palladium(0) complex, Pd[(tBu2)PCH2C(CH3)3] 13e, in CD3CN with two drops of

THF. After addition of the aryl halides at certain temperature, spectra were then recorded at

regular time intervals until the conversion reached about 50%. The data were acquired by

following the growing of the free phosphine signals, decreasing the intensity of Pd(0)

complex and formation of new signals as described in details in the chapter 2; section

(2.1.6.2).

Chapter 4: Symmary

162

4. Summary.

Bulky, electron-rich phosphines are effective ligands in palladium-catalyzed cross-coupling

reactions, which are most useful organic transformations. For industrial palladium-catalyzed

processes, phosphine ligands have to be stable and easy to be synthesized from cost-

effective starting materials. For these and other reasons, new and excellent precursors for

the generation of new phosphines are required, especially those which are stable, easy to

produce and handle and very efficient in a wide range of organic synthesis under mild

conditions. In this study, a new method that fulfils most of these requirements had been

developed.

In the first part of the this thesis, we were pleased to find that neopentyl and neosilyl

substituted phosphines palladium complexes, as well as additionlly trialkylphosphine ligand,

were conveniently prepared by a modular synthesis and successfully tested in Suzuki

coupling of different type of aryl halides under mild reaction conditions. Their efficiency

prompted us to study their coordination behaviour to afford cyclometallated palladium

complexes. Whereas the neosilyl substituted phospines form 2:1 adducts with palladium

salts which showed moderate activity, the neopentyl complexes quickly undergo

cyclometallation in presence of bases to form palladacycles (6a, 6e, and 6g) which showed

only moderate catalytic activity. Cyclometallation could be avoided by the preparation

starting from Pd(cod)Cl2 in the absence of bases. The obtained 2:1 phosphine adducts

showed superior activity. We concluded that cyclometallation process is an important

deactivation pathway; this prompted us to test trialkyl phosphine ligands with medium size

but substituents not reliable to cyclometallation. We have been pleased to find that (4h, 4l

and 4m) showed good activity in Suzuki cross-coupling reaction. The best results have been

obtained by in situ preparation of active catalyst from Pd2(dba)3 or Pd(OAc)2 and the

appropriate phosphonium salt. In addition, the palladacycle complexes 6k and 9k have been

tested in Buchwald amination and showed moderate to good activity.

Chapter 4: Symmary

163

We then set our focus on the development of a new family of novel phosphine ligands being

suitable for Pd-catalyzed cross couplings (especially Suzuki cross coupling reaction).

Encouraged by the success of the biphenyl-based phosphines (70, 71, 76, and 77) and their

dichloride palladium and platinum complexes (72, 73, 74, 78, 79, 80 and 81). Ligand (70 and

76) were remarkably stable towards air, while ligands 71 and 77 were high sensitive to air.

Systematically, the scope of the novel phosphine ligands was expanded to other class of

phosphine; the first synthesis of a highly symmetric 2,2',6,6'-tetraphosphinobiphenyl 82 has

been reported, and used as ligand in a dinuclear palladium(II) complex 83. We gained access

to the isopropyl decorated tetraphosphane 82 by a one-pot-two-step synthesis starting

from 2,2'-dibromo-6,6'-diiodo-4,4'-dimethylbiphenyl followed by a convenient lithiation-

phosphorylation method to afforded the tetraphosphine as analytical pure white solid in

over yield of 84%. We reported that the 2,2’,6,6’-tetraphosphane had D2h symmetric, while

the dinuclear palladium complex was D2 symmetric and hence chiral. Due to the crowded

phosphine substituent's in 2,2’,6,6’-tetraphosphane; different conformers are observed at

low temperature with either C2 or C1 symmetry. Herein, it was demonstrated that all steps

of the synthesis protocol of the 2,2'-dibromo-6,6'-diiodo-4,4'-dimethylbiphenyl and its

dinuclear palladium complex can proceed under very special conditions. Within the class of

bisphosphine based palladium complexes they show good activity, especially the isopropyl

substituted phosphines are promising chiral ligands in Suzuki-Miyaura cross-coupling

reaction.

As the spatial arrangement of the ligands around a metal center often controls the reactivity

and properties (e. g. colour, spin state) the found interaction can be recognized as a kind of

communication or coupling pathway between the palladium complex fragments through

the ligand skeleton similar to the allosteric interaction in enzymes. Systems that are able to

couple magnetic or electronic properties of metal complexes are of high interest in material

science and they may have good applications in spin crossover studies, so spin crossover

studies can be carried out employing 2,2’,6,6’-tetraphosphinobiphenyls as bridging ligands

by using other metal ions such as nickel.

Chapter 4: Symmary

164

Finally, despite of most of the catalyst systems depending upon their electronic and steric

properties proceed cleanly toward cross coupling product; there is a wide range of them can

not be regionalized simply by looking on their electronic and steric properties but also must

be related to on the resistance of phosphine ligands toward side reaction. As we observed

from our investigations, the less electron donating and electron crowding performed, in

some examples, better than the more electron donating monophosphine system.

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Appendix

172

Table 2.4. Data for single crystal X-ray structure analysis of 5b and 5d.

5b 5d

Empirical formula C20H50Cl2P2PdSi2 C32H42Cl2P2PdSi2

Formula weight (g∙mol-1) 390.68 722.08

T/K 293(2) 153(2)

Crystal system Orthomobic Triclinic

Space group(No.) Pbcn Pbca

a/ Å 13.6200(8) 17.9450(4)

b/ Å 18.563(3) 9.1770(2)

c/ Å 11.5612(10) 21.2925(6)

α/° 90 90

β/° 90 90

γ/° 90 90

V/Å3 2922.9(5) 3506.48(15)

Z 6 4

ρ (g∙cm-3) 1.332 1.368

µ (cm-1) 1.015 0.861

Reflections collected 7409 6690

Independent Reflections / Rint 2824/0.0338 3354/0.0262

Parameters/restrains 124/0 181/0

Θmin/max 3.19°/26.00° 2.97°/26.00°

Completeness to Θ 98.0 97.2

wR2 (all reflections F2)[a]) 0.0688 0.0563

R1 (I > 2σ(I))[a]) 0.0271 0.257

GooF[b]) 0.952 0.912

Extrema ΔF (e∙Å-3) 0.595/-0.489 0.369/-0.497

Absorption correction multi-scan multi-scan

Tmin/max - -

[[a] Definition of R indices: R1 = (Fo-Fc)/Fo wR2 = {[w(Fo2-Fc

2)

2]/[w(Fo

2)

2]}

1/2 with w

-1 =

2(Fo

2) + (aP)

2.[b] =

{[w(Fo2-Fc

2)

2]/(No-Np)}

1/2.

Appendix

173

Table 2.7. Data for single crystal X-ray structure analysis of 6a, 6e, 6m, and 13e.

6a 6e 6m 13e

Empirical formula C22H48Cl2P2Pd C26H58Cl2P2Pd C26H54Cl4P2Pd2 C26H58P2Pd

Formula weight (g∙mol-1) 685.310 714.416 703.178 539.105

T/K 123(2) 293(2) 123(2) 123(2)

Crystal system monoclinic triclinic triclinic orthomobic

Space group(No.) P1 12/c 1 P-1 P-1 Pbca

a/ Å 7.6177(2) 8.3033(7) 7.2384(6) 8.5727(3)

b/ Å 16.1067(3) 9.0979(7) 10.4306(9) 16.0019(6)

c/ Å 11.8408(3) 10.6666(9) 11.3811(8) 21.494(4)

α/° 90 77.073(7) 93.038(7) 90

β/° 104.176(2) 82.720(7) 98.813(6) 90

γ/° 90 89.982(6) 106.491(7) 90

V/Å3 1408.58(6) 778.70(11) 809.98(11) 2948.6(6)

Z 4 2 2 8

ρ (g∙cm-3) 1.552 1.480 1.606 1.214

µ (cm-1) 1.587 1.441 1.554 0.748

Reflections collected 6130 5756 5654 7743

Independent Reflections / Rint

2754/0.0163 3030/0.0263 3154/0.0264 2884/0.0291

Parameters/restrains 133/0 153/0 154/0 142/0

Θmin/max 3.03°/26.00° 3.35°/ 25.99° 3.21°/26.00° 3.04°/26.00°

Completeness to Θ 99.1 99.1 99.1 99.3

wR2 (all reflections F2)[a]) 0.0461 0.0604 0.0634 0.0502

R1 (I > 2σ(I))[a]) 0.0171 0.0251 0.0267 0.0242

GooF[b]) 1.044 0.998 1.007 0.853

Extrema ΔF (e∙Å-3) 0.358/0.489 0.522/-0.698 0.944/-0.498 0.339/-0.319

Absorption correction multi-scan multi-scan multi-scan multi-scan

Tmin/max 0.76067/1 0.85921/1 - -

[a] Definition of R indices: R1 = (Fo-Fc)/Fo wR2 = {[w(Fo2-Fc

2)

2]/[w(Fo

2)

2]}

1/2 with w

-1 =

2(Fo

2) + (aP)

2.[b] =

{[w(Fo2-Fc

2)

2]/(No-Np)}

1/2.

Appendix

174

Table 2.13. Data for single crystal X-ray structure analysis of 72-74, 77-79, and 83.

72 73 74

Empirical formula C42H42Cl2N2P2Pd C30H50Cl2N2P2Pd C42H42Cl2N2P2Pt

Formula weight (g∙mol-1) 814.069 678.004 902.733

T/K 293(2) 123(2) 293(2)

Crystal system monoclinic monoclinic monoclinic

Space group(No.) C12/c1 P121/n1 P121/n1

a/ Å 23.3473(9) 14.3438(3) 10.9743(6)

b/ Å 16.0796(4) 14.2343(4) 18.6298(4)

c/ Å 24.0921(7) 15.6768(4) 22.4283(9)

α/° 90 90 90

β/° 95.853(3) 95.242(2) 101.388(5)

γ/° 90 90 90

V/Å3 8997.4(5) 3187.41(14) 4495.2(3)

Z 8 4 4

ρ (g∙cm-3) 1.453 1.413 1.961

µ (cm-1) 7.534 0.872 8.114

Reflections collected 27174 17547 14812

Independent Reflections / Rint

7071/0.0438 6242/0.0326 6964/0.0284

Parameters/restrains 572/154 348/0 506/271

Θmin/max 3.34°/62.00° 2.85°/ 26.00° 4.02°/62.21°

Completeness to Θ 99.8 99.6 97.8

wR2 (all reflections F2)[a]) 0.0906 0.0748 0.2745

R1 (I > 2σ(I))[a]) 0.0352 0.0299 0.1062

GooF[b]) 1.007 1.019 1.111

Extrema ΔF (e∙Å-3) 1.029/-1.145 0.638/-0.570 10.888/-2.546

Absorption correction multi-scan multi-scan multi-scan

Tmin/max 0.235/1 0.835/1 -


2)

2]/[w(Fo

2)

2]}

1/2 with w

-1 =

2(Fo

2) + (aP)

2.[b] =

{[w(Fo2-Fc

2)

2]/(No-Np)}

1/2.

Appendix

175

Table 2.13. Continue.

77 78 79

Empirical formula C26H38Br2P2 C38H30Br2Cl2P2Pd C26H38Br2Cl2P2Pd

Formula weight (g∙mol-1) 572.335 885.726 749.62

T/K 293(2) 123(2) 153(2)

Crystal system Orthomobic triclinic orthomobic

Space group(No.) Pbcn P-1 Pbcn

a/ Å 10.7852 19.402(4) 14.0318(3)

b/ Å 16.0491 15.404(13) 14.3546(4)

c/ Å 16.3899 12.312(4) 14.4404(3)

α/° 90 90 90

β/° 99.889(3) 111.76(3) 92.383(2)

γ/° 90 90 90

V/Å3 2794.82 3418(3) 2906.08(12)

Z 4 4 4

ρ (g∙cm-3) 1.484 2.181 1.713

µ (cm-1) 0.302 3.187 3.697

Reflections collected 9762 8610 12529

Independent Reflections / Rint 4890/0.0236 3322/0.0596 5562/0.0329

Parameters/restrains 261/0 205/0 308/0

Θmin/max 2.89°/25.00° 3.19/26.00 3.16°/26.00°

Completeness to Θ 99.5 99.00 97.5

wR2 (all reflections F2)[a]) 0.0624 0.1866 0.056

R1 (I > 2σ(I))[a]) 0.0277 0.0755 0.0277

GooF[b]) 0.902 1.137 0.905

Extrema ΔF (e∙Å-3) 0.455/-0.325 2.369/-1.777 0.443/-0.6950

Absorption correction ‘multi-scan’ ‘multi-scan’ ‘multi-scan’

Tmin/max - - 0.85120/1


2)

2]/[w(Fo

2)

2]}

1/2 with w

-1 =

2(Fo

2) + (aP)

2.[b] =

{[w(Fo2-Fc

2)

2]/(No-Np)}

1/2.

Appendix

176

Table 2.13. Continue.

83

Empirical formula C37H62Cl4 P4Pd2

Formula weight (g∙mol-1) 985.435

T/K 153(3)

Crystal system monoclinic

Space group(No.) P1 21/c 1

a/ Å 23.3722(4)

b/ Å 11.6540(2)

c/ Å 38.7341(6)

α/° 90

β/° 99.158(2)

γ/° 90

V/Å3 10415.9(3)

Z 2

ρ (g∙cm-3) 1.542

µ (cm-1) 1.304

Reflections collected 51728

Independent Reflections / Rint 18391/0.0329

Parameters/restrains 1095/43

Θmin/max 3.10°/25.05°

Completeness to Θ 99.8

wR2 (all reflections F2)[a]) 0.1058

R1 (I > 2σ(I))[a]) 0.0377

GooF[b]) 1.072

Extrema ΔF (e∙Å-3) 1.687/-0.879

Absorption correction multi-scan

Tmin/max 0.79940/1.0000 [a] Definition of R indices: R1 = (Fo-Fc)/Fo wR2 = {[w(Fo

2-Fc2)2]/[w(Fo

2)2]}1/2 with w-1 = 2(Fo2) + (aP)2.[b] = {[w(Fo

2-Fc

2)2]/(No-Np)}1/2.

Personal Data

177

Al-baraa Ibrahim Salim Alrawashdeh

Date of Birth: 22.05.1981

Place of Birth: Al Tafila, Jordan.

Status: Married, one son 'Ibrahim'

Nationality: Jordanian.

E-mail1 : [email protected]

E-mail2: [email protected]

School and University Educations

PhD Student: 2008 - Present / Supervisor: Prof.Dr. Heinrich.Lang

Technische Universität Chemnitz, Institut für Chemie, Lehrstuhl für Anorganisch Chemie.

M.Sc. in Applied Chemistry, 06-2003, Mu’tah University, Jordan. Title: (The effect of

substituents (F, OH, CN, NH2, NO2, CH3, CF3 and CHO) on the relative stability of methylene

cyclobutane and 1-Methyl- cyclobutene Tautomerism).

B.Sc. in Chemistry, 03-1999, Mu’tah University, Jordan.

Ain Albida Secondary School Tafila Governorate, Jordan, 1989-1999.

Work Experience and Training

23/08/2003 - 11/03/2004: Lecturer. Directorate of Education, Ain Albida Secondary School

Tafila Governorate, Jordan.

06-09/2004: Practical Training, Mu’tah University, Karak Governorate, Jordan.

12\2004–02\2006: Teacher and Research Assistant, Faculty of science, Department of

Chemistry, Albalqa Applied University, Amman, Jordan.

03\2006-07\2008: Teacher and Research Assistant, Faculty of science , Department of

Chemistry, Tafila Technical University, Tafila, Jordan.

04-07/2010 and 02-05/2011: Teacher Assistant, Faculty of science, Department of

Chemistry, Technische Universität Chemnitz, Chemnitz, Germany.

Computer Skills

ICDL (International Computer Driving License, 2003.

mailto:[email protected]

Personal Data

178

Memberships

Member of the Jordanian Chemical Society, since 2003.

Scientific Work

List of publications

E. Al-Rawajfeh, M. Al-Garalleh, G. Al-Mazaideh, A. AL-Rawashdeh, and S. Khalil*,

Understanding CaCO3-Mg(OH)2 Scale Formation: A Semi-empirical MINDO-Forces Study of

CO2-H2O System, Chem. Eng. Comm. 2008, 195, 1026–1038

Holm Petzold, A. I. S. Alrawashdeh, Chem. Commun. 2012, 48 (1), 160 - 162.

Further manuscripts are in preparation.

Poster Presentation

New Biaryl Phosphine Ligands in Palladium Catalyzed Suzuki Cross-Coupling Reaction, Albara

Alrawashdeh, Holm Petzold, 9th Ferrocene Colloquium, 14.–16.02.2011, Chemnitz, Germany.

New Cyclo- and Non Cyclometallated Palladium Complexes. Synthesis and Solid State Study,

Albara Alrawashdeh, Holm Petzold, 13th JCF-Frühjahrssymposium, 23-25.03.2011, Erlangen-

Nuremberg, Germany.

Acknowledgement

179

Acknowledgment

The present study was carried out at the Department of Inorganic Chemistry, Institute of

Chemistry, Chemnitz University of Technology, Germany, in the period 2008 - 2011.

Before I started making a PhD, I already knew that this will be my most memorable journey

in my life, because I can devote myself totally to the scientific research. It is my great

pleasure to thank the following people for their contributions to this work contained in this

thesis. It is my privilege to acknowledge that without their efforts and assistance, this work

would never have been accomplished. First of all, I would like to express my deep thanks

and gratitude to my supervisor Prof. Dr. Heinrich Lang who welcomed me in his research

group, giving me this great opportunity to do the research in his research group, his

continuous encouragement, support and constructive discussion, which enriched my

knowledge, skills and experience. It is difficult to overstate my gratitude to Dr. Holm

Petzold, with his inspiration, and his great efforts to explain things clearly and simply, he

helped to make chemistry fun for me, and successfully guided me through this work.

Throughout my thesis-writing period, he provided encouragement, sound advice, good

teaching, and lots of good ideas. I would have been lost without him.

I would like to express my gratitude to Prof. Dr. Wolfgang Weigand for reading my thesis

and being a member of the committee. In particular, thanks are extended to Dr.T.Rüffer for

the X-ray crystallographic work. Special thanks go to Dr. R. Buschbeck and Fr. Kempe for

mass spectrometric studies and many thanks for Fr. Ute Stöß and Fr. Janine Fritzsch for

carrying out elemental analysis. I would also like to thank all my colleagues and whole staff

in the Department of Inorganic Chemistry; Jutta Ruder, Mohammad Abdulmalic, Silvio

Heider, Dr. Alexander Jakob, Dr. F. Meva, Colin Georgi, Carola Mende, Ron Claus, Sascha

Dietrich, Manja Lohan, Bianca Milde, Robert Mothes, Dieter Schaarschmidt, Sascha Tripke,

André Tuchscherer, Alexander Hildebrandt, Dunja Grimm, Astride Kammoe, Ch. Schliebe, U.

Pfaff, Frank Strehler, Dominique Miesel, Karoline Rühlig, and Michael Reichel, for the warm

and supportive environment. I offer my regards and blessings to his excellency Prof. Dr.

Sultan Abu-Orabi, president of the Yarmouk University, Irbid, Jordan, who encouraged and

supported me to complete my PhD.

http://www.tu-chemnitz.de/chemie/anorg/mitarbeiter/alja.php

http://www.tu-chemnitz.de/chemie/anorg/mitarbeiter/mecar.php

http://www.tu-chemnitz.de/chemie/anorg/mitarbeiter/ronc.php

http://www.tu-chemnitz.de/chemie/anorg/mitarbeiter/sasd.php

http://www.tu-chemnitz.de/chemie/anorg/mitarbeiter/sasd.php

http://www.tu-chemnitz.de/chemie/anorg/mitarbeiter/lohan.php

http://www.tu-chemnitz.de/chemie/anorg/mitarbeiter/mibi.php

http://www.tu-chemnitz.de/chemie/anorg/mitarbeiter/rmot.php

http://www.tu-chemnitz.de/chemie/anorg/mitarbeiter/diete.php

http://www.tu-chemnitz.de/chemie/anorg/mitarbeiter/sat.php

http://www.tu-chemnitz.de/chemie/anorg/mitarbeiter/antu.php

http://www.tu-chemnitz.de/chemie/anorg/mitarbeiter/dugr.php

http://www.tu-chemnitz.de/chemie/anorg/mitarbeiter/domm.php

http://www.tu-chemnitz.de/chemie/anorg/mitarbeiter/ruek.php

http://www.tu-chemnitz.de/chemie/anorg/mitarbeiter/remich.php

Acknowledgement

180

Also have a great debt on my life due to the enormous sacrifices of my mother, my brothers

and sisters for their divine love, prayers, constant care, encouragement and continuous

support throughout my studies and understanding of why being too far from them.

To my wife Asma and my son Ibrahim. Asma perhaps only you know the amount you have

contributed and sacrificed to see this thesis to completion. Your support and

encouragement, and kept me going, through the good and bad times, until the end. This is

yours as much as mine. Thanks are extended to Chemnitz University of Technology.

Finally I thank Tafila Technical University for financial support.

181

Selbständigkeitserklärung

Hiermit erkläre ich, dass ich die vorliegende Arbeit selbständig und nur unter Verwendung

der angegebenen Literatur und Hilfsmittel angefertigt habe.

Chemnitz, den 26.07.2011


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