Indi an Journal of Chemistry Vol. 42A. September 2003. pp. 2422-2426

Pall adium-carbon a -bonded complexes bearing diphosphazane and diphosphazane monosulphide ligands t

Swadhin K Mandai , Setharampattu S Kri shnamurth y* & Munirathinam Nethaj i

Department of Inorganic and Physical Chemistry, Indian Insti tute of Science, Bangalore 560 0 12. India

Received 23 Ma rch 2003

The reac ti ons of the e1i phosphazanes and diphosphazane monosulphidcs. Ph2P(E)N(R)PPh2 rE '" lone pair. R = CHMec (1): E = lone pair. R = (S)-*CHMePh (2): E = S, R = CHMe2 (.1): E = S, R = (S)-*CHMePh (4)] with [PdM eCI(COD)1 yie ld the neulral chelate complexes of the type [PdMe{ K2-Ph2P(E)N(R)PPh2 ICI] (5. 6. 8 and 9). The reactions of 1 -3 wi th chlorobridged cyc lometallated pa lladium azobenzene dimers. [Pel {(C6H3-R' -4)-N=N-(C6H.,-R ' -4)( ).I -C I ) 1 ~ (R' = H or OCr,H 13) in the presence of N H4PF6 yield cationic cyclopalladated complexes, r { ~-(C6H , - R'-4)-N=N-(C6H~-R ' -4) I Pd {K

C_

Ph2P(E)N(R)PPh2 I ](PF6 ) (10-15). The molecular structure of [Pdf K2_(C6Hr OC6H 1.l-4)- N=N -(C(, H~-OC6H w4) I {K2_ Ph2P(S)N(CHMe2)PPh2 I l(PF6) (15) has been determi ned by X-ray diffraction: the pall ad ium bound carbon atom occupie~ the ( raIlS po ition with respect to the sulphur atom of the chelated diphosphazane monosulphi ele li ganel.

Introduction The pallad i um-carbon (J-bonded co mplexes are

very important f rom the point o f view of the ir ability to undergo fac ile insertion reactio ns into the palladi ull1-carbon bond. T hi s type of reacti vity finds unique appli cations in vari o us catalytic reactio ns especia lly in the pall ad ium catalysed a lternating co­polymerisation reactio ns of alkenes and carbon monox ide l

. The cyclometa ll ated pa ll ad ium co mplexes hJve enge nde red considerable inte rest in recent yea rs because of their utili ty in various sy nthetica ll y important react iolls and also their ab ility to show Il1ctallomesogenic properties if designed properll. Recently Pringle and coworket's have used the Pd(J I) complexes of diphosphazane ligands of the type, Ar~PN(Me)pA r2 (Ar = C6Hs, C6H40Me-2, C6H4M e-2, Cc, H4Et-'2 or C6H4iPr-2) to carry o ut catalytic alternating copolymeri sati on reactions of carbon monox ide and ethylene3

.

As a part of our research programme o n the organo metallic chemi stry of d iphosphazane and related iigands4

, we had earlier reported that the reaction of Ph2PN(CHMe2)PPh2 w ith [Pdidbah] in the presence of Mel y ields the (iodo)( methyl)pall adium complex, [Pd(l\1e)(l){ K2_ Ph2PN(C HM e2)PPh21]sO, whil e the (chloro) methy l

platinu m com plex. lPt(Me)(Cl ){ K2 -Ph2PN«S)­CHMePh)PPh2}] was reported by Payne and

E-mail : ,skrish@ipc. iisc.ernet. in; Fax: 91-80-3600683/3601552 Organometalli c chemistry of diphosphazanes. Part 19 49

Stephan5b. In this paper, we report the syntheses and

structural charac te ri sati o n o f pa ll adiu m(ll) -carbon (j­

bo ded complexes of d iphosphazanes and d iphosphazane mo nosulphides, Ph2P(E)N(R)PPh2 IE = lone pair or S ; R = C HMe2 or (S)-*C HM e Ph ].

Materials and Methods Al l reactio ns and manipul atio ns were carried out

under an atmosphere of dry ni trogen using standa rd Schl enk and vacuum·line techniques. The so lvents were puri f ied by standard p roced ureso and dis till ed under nitrogen. The ch loro(methy l) pallad ium complex, [PdM eCI (COD)]. was prepared as p reviou sly described

7• Tht' chl o robridged

cyclo meta ll ated pall adiu m azobenzene d imers .

[{ (C6H4)-N= N-(C6Hs) I Pd(/J.-CI)J2 and I Pd {(Cc, H 1-

OC6H w4)-N= -(C6H4-0C(iH Jr4)}(~I-C I )h were prepared accordi ng to the li teralUre proceduresx. The ligands, Ph2PN(CHMe2)PPh2 (ref. 9), Ph2PN((S)­*CHM ePh)PPh2 (ref. 10) Ph2 P(S)N (CHMe2)pPh ~

(ref. 11) and Ph2P(S)N((S)-*CHMePh)PPh/ i were prepared by literature methods. The NMR spect ra were recorded at 298 K using Bruker AMX -400 MH z or Bruker ACF-200 MHz spectrometers. Chemi ca l sh ifts downfield from the reference standard were ass igned positi ve va lues . E lemental ana lyses were carried out using a Perkin-Elmer 2400 C HN analyser.

Synthesis oJ[PdMe{ K2-Ph2PN(CH Mc::)pPh2 leI] (5 ) A mi xture o f 0 .026 g (0.98x I O .. j mo l) 01

[PdMeCI(COD)] and 0.045 g (l.05x l O-~ mol) or

MANDAL et al.: PALLADIUM-CARBON a -BONDED COMPLEXES 2423

Ph2PN(CHMe2) PPhz was dissolved in 20 cm3 of toluene. The solution was stirred for I hour at 25 °C and rhe title compound 5 was precipitated as a colourl ess solid during the reaction . The mother liquor was removed using a syringe and the precipitate was repeatedly (3x 10 cm)) washed with cold to luene to remove liberated COD and any unreacted starting materials.

The other (chl oro) methyl complexes, 6, 8 and 9, were synthes ised as described above for 5 using the appropriate starting material s. The yield, melting po int , CHN analytical data are given in Table I. The I H, I3C and 31 P MR data are li sted in Table 2. Complexes 6 and 7 could not be isolated in pure form and were ident ified by ' H and 31p NMR spectroscopy .

Syllthesis of {Pd{'! -{(C6H.;)-N=N-(C6HS)j (,!-Ph2PN(CHMe2)PPh2}J(PF6) (10)

A mixture of 0.064 g (0.99x lO-4 mol) of [{ (C6H4) ­

N= -(C6HS)} Pd()..t-CI) h, 0.033 g (2.02x 1 0-4 mol ) of H~PF6 and 0.090 g (2.lOx I 0-4 mol) of

Ph2PN (C HM e2)PPhz was dissolved in 20 cm3 of acetone. The sol ution was stirred for 12 hours at 25°C and the white precipitate fo rmed during the reaction was filte red off. The resul ting orange filtrate was evaporated under reduced pressure to dryness. The residue was d issolved in 10 cm3 CHCI2 and the solution was layered by addi ng 10 cm3 of hexane (b. p.

40-60°C) to y ield orange crystals of title compound 10.

The other cyclometallated palladi um complexes (11-15) were synthesised as described above for 10. The yields , m. pt. and CHN analytical data are g iven in Table I . The 13C MR data are unexceptional and are not listed. The 31p NMR data are li sted in Table 2.

X-ray Clyslallography The X-ray data for complex 15 was collected using

Enraf-Nonius CAD-4 diffractometer. The crystallographic data and details of data collection have been depos ited wi th the Cambridge Crystallographic Dara Centre. CCDC No. 208844. The structure was solved by Patterson heavy atom method using the program SHELXS-8612 and refined on F2 val ues by full- matrix least-squares usi ng SHELXS-9i 3. The C6 al kyl chain carbon atoms, C(48) ~lI1d C(49), exhibited high thermal disorder showing erratic variations in the bond-lengths of C(47)-C(48) 0.213(2)), C(48)-C(49) (1.852(2)) , C( 49)-C(50) (1.248(2)) and C(50)-C(51) (1.644(2)) and they were refined isotropically. As a

consequence, the hydrogens attached to these carbons (C(47), C(48), C(49), C(50) and C(51)) were not fixed, while the remaining hydrogen atoms were geometrically fixed and allowed to ride.

Results and Discussion

Reactions of Ph2P( E)N( R)P Ph2 (1-4) \\"ith (PdMeCl(COD)

In the present study , the chloro(methyl)palladium cyclooctadiene complex, [PdMeCI (COD)] was used as a precursor for the synthesi s of palladium methyl complexes of diphosphazane ligand. , PhzP(E)N(R)PPh2 [E = lone pair, R = CHMe2 (1 ) or (S)-*CHMePh (2); E = S, R = CHMe2 (3) or (S) ­*CHMePh (4)].

The reactions of [PdMeCI(COD)] with 1-4 in

toluene at 25°C yielded the palladium methyl complexes (5 , 6, 8 and 9). These reactions are shown in Scheme I . The reaction with Ph2PN«S)­*C HMePh)pPh2 gave a mi xture of two compl exes 6 and 7 . The 3\p and 'H NMR data fo r 7 are identical to those reported for this complex syn thesised by a diffe rent method 10. Apparently the chl oro(methyl)­pall adium compl ex 6 undergoes disproprtionation to give the dichloro complex 7 . Complexes 6 and 7 could not be separated ; the other complexes 5, 8 and 9 were iso lated as colourl ess solids.

These complexes have been characteri sed by I H. 13C, and 31p NMR spectra and elemental analyses. The 31 P NMR spectra show an AX spin syste m: the data are li sted in Tab le 1. For complexes 5 and 6, the

chemical shifts of the -PPh2 phosphorus at the t rails

pos ition to the ch loride are 50. 1 and 56.0 ppm respecti vely and those for the -PPh2 phosphorus t rails

to the methyl group are 61.6 and 67.7 ppm

respectively. The magnitude of coordi nation shift. t.O [t.O = 0 (complex) - 0 (free ligand)] is higher for the phosphorus trails to the palladium bound methyl

Ph . I' .

[PdMeCl(COD)] _(i)_ / ',- /C I

+ R- N I'd " ,,/ CI

I' Ph,

7: R = (S)· *CHMel'h.

5: R = CHMe,. E = 10lle pair 7: R = (s)·*r HMel'h .

6: R = (S)·*CHM ePh, E = lone pair 8: R = CHMe" E = S 9: R = (S) -*CHMePh. E = S

(i) Ph, P(E)N(R)PPh,/lo iuene/25"CIi h

Scheme 1

2424 INDIAN J CHEM. SEC A, SEPTEMBER 2003

Table I- Analytical data for palladium (II ) complexes (5, 8-15) of diphosphazanes and diphosphazane monosulphides

Complex Yield M.p. Ana l~s i s data t

('!'o ) (DC) C H N

5 88 137-40 (d) 58.1 5.3 2.2 (57.6) (5.2) (2.4)

8 91 184-87 (d) 54.7 4.7 2.2 (54.6) (4.9) (2.3)

9 92 161-64 (d) 58.3 4.9 2.0 (58.5) (4.7 ) (2.1 )

10 79 195-97 (d) 54.4 4.1 4.8 (54.5) (4.2) (4.9)

11 70 169-72 (d) 57.2 3.6 4.5 (57.3) (4. 1) (4.6)

12 80 2 10-12 52.1 3.4 4.1 (52.5) (4.0) (4 .7)

13 61 190-92 57.7 5.4 3.7 (57 .8) (5.7) (4.0)

14 74 173-75 59.6 5.4 3.4 (59.9) (5.5) (3 .7)

IS 67 193-95 56.2 5.4 3.7 (56.1 ) (5.5) (3.8)

tThe ca lculated values are in parantheses

group ; ev idently the trails influence of the palladi um bound methyl is higher than that exhibited by the chloride ligand which acts both as cr- and n-donor. The palladium bound methyl protons resonate at 0.58 ppm and 0.52 ppm as a doublet of doublets for 5 and 6 respect ively (Table I). The three-bond t ra il s

coup ling constant of the phosphorus nucleus with the palladium bound methyl protons is higher (9.6 Hz) than the cis coupling constant (2.1 Hz). Such a trend is also generally observed for other methyl palladium complexes of bisphosphane ligands 14.

The reactions of [PdMeCI(COD)] with the diphosphazane monosulphide ligand s, Ph2P(S) (R)PPh2 [R = CHMe2 (3) or (S)-*CHMePh (4)] can give rise to two isomeric palladium methyl complexes. The palladium bound methyl group can be located (rail S to either the coordinated -PPh2 group or the -P(S)Ph 2 group. The :1 1 P NMR spectrum of the reaction mixture reveals the formation of a single product in each case. Only one AX type pattern is observed for each of the complexes 8 and 9. The chemical shifts of the -PPh2 phosphorus nucleus of 8 and 9 are at 98.6 and 96.3 ppm with 1'18 vaiues 44.4 and 41.9 ppm respectively. On the other hand, the - P(S)Ph2 phosphorus chemical shifts lie at 70.5 and 70.9 ppm with a small coordination shift of 3.0 and - 2.0 ppm respectively . The I H NMR spectra show a doubl et and the average value of 3J(p, H) is 3.9 Hz which is close to the three-bond cis coupling between phosphorus and palladium bound methyl protons .

JI'~ + F>h: I h

/ '" . ),... ( il R- N I'd " ', \ j\.)' PrE) N

Ph ~ ¢

10: R = CHMe, . E = lonepair ( I.p ). R' = H

II : R = (S)-*C HM cPh. E = I.p. R' = H 12 : R = CHM c1• E = S, R' = H

13: R = CHM e1. E = I.p. R' = OC"HI) 14; R = (S)- *CHM ePh. E = I.p. R' = Ol . H"

15: R = CHM c1, E = S. R' = OCOHI)

( i) Ph,P(E)N(R)PPh,lN H,PFJ 25"CIJ ~ h

Scheme 2

R'

Hence, the methyl group is at the cis positi on with respect to the coordi nated phosphorus (see Scheme I ). The formation of a single isomer is the resu lt of the electronic effect of two di fferent donor centre ~.

phosphorus and sulphur. The pall ad ium bound methyl group prefers to occupy the trans position with respect to the sulphur atom, which has a lesser Jr ­

acceptor capability than that of phosphorus.

Synthesis and characterisation (}f cyci(}lI lct({ll(// cd palladium complexes

The reactions of the chl orobridged cyclopalladalCd dimers, [Pd {(C6H)-R'-4)-N=N-(Cc,H .. -R'-4 ) ( ).l -CI ) J: (R' = H or OC6HI)) derived from zobenzene wit h Ph2P(E)N(R)PPh2 (1-3) in the presence of NH .. PFr. yielded cation ic cyclopalladated complexes, I { KC

_

(C6H]-R'-4)-N = N-(C6H~-R'-4)) Pd{ KC -Ph2P(E)N(R)

PPhl ) ](PF6) (10-15) as shown in Scheme 2.

These complexes (10-15) are air-stable. intense orange soli ds and isolated in pure form in good y i e l cl~

(-80 %). They are characteri sed by lheir :1 lp. ' :1C and IH NMR spectroscopy and elemental analyses . The ) Ip NMR spectra show an AB or AX spin system. Thc 31p chemical shifts (Table 2) for these cyclopallaclatcd complexes fo llow a simi lar trend as th at observed for the ch loro(methy l)palladium comple 'es (5, 6, 8 and 9).

The complexes 12 and 15 bearing a heterodonor diphosphazane monosulphide ligand can exist as a mixture of two geometrical isomers. The " P{ III ) spectra of the reaction mixture point to the formati oJl of on ly one isomer. The solid sta te structure of 15 (see below) reveals that the palladium bound cyclo-

MANDAL et 01.: PALLADIUM-CARBON a-BONDED COMPLEXES 2425

Table 2-Selected 1 H, DC { 1 H I and 3 1 P { 1 HI NMR spectroscopic data for palladium complexes (5. 6. 8-15) of diphosphazanes and diphosphazane monosulfides

Complex IH NMR'

Pd-Me

5 0.58 dd (9.6)C (2.I)d 6 0.52 dd (9.6)< (2 .I )d 8 9

Complex

10 11 12 13 14 IS

d. doublet: br. s. broad singlet "CDC!, was used as so lvent.

0.59 d (3.9)d 0.52 d (3.9)d

PA 46.2 d 52.3 d 97.8 d 49.1 d 52.6 d 97.9 d

13C NMR

Pd- Me

7.5 ddc

11.5 br.s 11.0 br. s

L'./) (P A) -2.6 -0.1 43A 0.3 OA 43.5

3I p(I H I NMRh

PA L'./) (P A) Px L'./) (Px )

50.ld(75.1 ) 1.3 61.6 d 12.8 56.0 d (79.1 ) 3.8 67 .7 d 15.5 98.6 d (58.3) 44A 70.5 d 3.0 96.3 d (57 .8) 41.9 70.9 d -2 .0

3I p{'HI NMR"J

Px L'.O (Px) lJ Ax 55.8 d 7.0 80.9 61.9 d 9.7 76.3 69. 1 d 1.6 49.1 51\.8 d 10.0 73.8 62.6 d lOA 75.0 69.1 d 1.6 52.0

hCH1CI1 was used as solvent. Coupling constants in Hz are given in parentheses. PA is phosphorus nucleus trailS to the chl oride and p\ i, phosphorus nucleus lrallS to methyl; L'.O = /) (complex) - /) (li gand). " ' J(P.H ),ra",, ' d'J(PJ ·I),·i.\. < 21 (C-P) = 115.7,9.7 Hz. d, doublet. r PA is phosphoru s nucleus lrallS to the coordinated nitrogen centre and Ph is phosphorus nucleus IrallS to cyclometallated carbon centre.

Fig. I- The molccular structu re of [{K"_(C6Hr OC6Hu-4)-N=N­(C6H~-OCr,l-1 u-4) I Pd (K" -Ph2P(S)N(CHMel)PPh211(PF6) (15). Hydrogen atoms and the hexafluorophosphate anion have been omilled for clarity.

metallated carbon centre occupies the irans position with respect to suiphur. This is a result of the e lectronic se lection of one of the two poss ible geometrical isomers. Such a feature is also observed in the case of palladium methyl complexes (8 and 9).

X-ray crys/a/ structllre of [{ K2_(C6H3-0C6H u-4)­

N=N-(C(lH~-OC6H w 4)} Pd {K2 -Ph2P (S)N(CHMe2) PPh2 } ](PF6) (15)

The structu re of complex 15 has been determined by si ngle crystal X-ray diffraction and its molecular structure is shown in Fig.I. It reveals a trails di sposition of the coordinated sulphur and cyciometallated carbon centre. Selected bond di stances and angles are listed in Table 3. The coordination geometry around the palladium centre

Table 3-Selected bond di stances and bond angles in [(KC-Cr,l-l,­OC6H w4-N=N-C6H4-0C6H u-4)Pd (K1-Ph1P(E) N(R )PPh11 I(PFr.)

( IS)

Pd( I )-C(28) 2.015(4) S( I )- PcI( I )-P( I ) ':JU( I )

PcI( I )-N(2) 2.103(3) N(2)-Pd( I )- C(28) 711.9(2) Pd( I )- P( I ) 2.246( I) S( I )-PcI( I )- N(2) 95.7( I )

Pd( I )- S( I) 2.386( I) P( I )-Pd( I )-C(28) 955( I ) P(l )-N(l) 1.724(3) S( I )- Pd( I )- C(28) 169A( I ) P(2)-N(I) 1.669(3) P( I )-Pd\ I )-N(2) 168.9( I ) P(2)-S( I) 1.995(2) P(2 )- S( I )- Pd( I ) 98.3( I ) N(2)-N(3) 1.272(4) N( I )-P( I )-PcI( I) ! 103( I )

P(I )- N( I )-P(2) 11J.7(2 )

can be considered as distorted square planar. The S(l)-Pd(l)-P(l) and N(2)-Pd( I )-C(28) ang les are 91.2(5)° and 78.9(6)° respecti vely. The S( I )-Pd( I )­C(28) and P(I )-Pd(J )- N(2) angles deviate from the

ideal value by -10°. The P(I )-N(I )-P(2) ang le is J 13 .7(2)°, which is comparable with that observcd fo r the free ligand [116.0(3)°]\(;" and the metal complexes, [RhCI(CO)( 4)t f and [PdCl 2( 4) ] 16h

[110.1(8) and 116.0(3) respectively]. The

Pd(l)-C(28) di stance is 2.019(S)A, which is in the range of palladium-cyclopall adated carbon bond distances observed for other cyclopalladu\ed complexes containing a phosphorus li gand ' 7

.

Conclusions The reactions of pa Il adium-carbon a-bonded

complexes with diphospha2.ane liganth have been

2426 INDIAN J CHEM, SEC A, SEPTEMBER 2003

studied. The operation of a pronounced electronic effect is strikingly illustrated by the formation of a single isomer in the case of diphosphazane monosulphide ligands Ph2P(S)N(R)PPh2 (R = CHMe2 or (S)-*C HMePh) in which the palladium carbon (J­

bond is located trans to sulphur with its less n­electron acceptor nature than the phosphorus centre. These complexes would be potentially useful in various homogeneously catalysed reactions. In parti cular, the chiral chloro(methyl) palladium co mpl exes may find applications in enantioselective palladium catalysed alternating copolymerisation reactions of styrene type monomers and CO I8

.

Acknowledgement We thank the

Technology (DST), support.

References

Department of Science and New Delhi, India, for financial

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