This document is confidential and is proprietary to the American Chemical Society and its authors. Do not copy or disclose without written permission. If you have received this item in error, notify the sender and delete all copies.

NMR and EPR Spectroscopic Identification of Intermediates

Formed upon Activation of 8-mesitylimino-5,6,7-

trihydroquinolylnickel dichloride with AlR2Cl (R = Me, Et)

Journal: Organometallics

Manuscript ID: om-2015-00263t

Manuscript Type: Article

Date Submitted by the Author: 27-Mar-2015

Complete List of Authors: Soshnikov, Igor; G. K. Boreskov Institute of Catalysis, Semikolenova, Nina; G. K. Boreskov Institute of Catalysis, Bryliakov, Konstantin; Boreskov Institute of Catalysis, Zakharov, Vladimir; Boreskov Institute of Catalysis, Sun, Wen-Hua; Chinese Academy of Sciences, Institute of Chemistry Talsi, Evgenii; Boreskov Institute of Catalysis, Siberian Branch, Russian Acad. of Sci.

ACS Paragon Plus Environment

Submitted to Organometallics

1

NMR and EPR Spectroscopic Identification of Intermediates Formed upon Activation of

8-mesitylimino-5,6,7-trihydroquinolylnickel dichloride with AlR2Cl (R = Me, Et).

Igor E. Soshnikov,a,b Nina V. Semikolenova,a Konstantin P. Bryliakov,a,b Vladimir A. Zakharov,a,b Wen-Hua Sun,c Evgenii P. Talsia,b *

a Boreskov Institute of Catalysis, Pr. Lavrentieva 5, Novosibirsk 630090, Russian Federation b Novosibirsk State University, Pirogova 2, Novosibirsk 630090, Russian Federation c CAS Key Laboratory of Engineering Plastics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China

ABSTRACT: The intermediates formed upon activation of 8-mesitylimino-5,6,7-trihydroquinolylnickel dichloride [LNiCl2] with AlR2Cl (R = Me, Et) have been studied by 1H NMR and EPR spectroscopy. Activation of LNiCl2 with AlEt2Cl has been shown to afford diamagnetic ion pair [LNiIIEt]+[AlEt3Cl]−, while the use of AlMe2Cl as activator yields the paramagnetic ion pair with pro-posed structure [LNiII(µ-R)2AlMeCl]+[AlMe3Cl]− (R = Cl or Me). Both ion pairs convert with time into bis-ligated Ni(I) complexes with proposed structures [L2NiI]+[A]-, where [A]- = AlEt3Cl- and AlMe3Cl-, respectively. Ethylene reactivity examination witness that ion pairs [LNiIIEt]+[AlEt3Cl]− and [LNiII(µ-R)2AlMeCl]+[AlMe3Cl]− are the closest precursors of the active species of polymer-ization.

INTRODUCTION

Highly-branched ethylene oligomers have been attracting growing interest as components of lubricants or surface modi-fies.1,2 Such oligomers can be obtained using cationic or neu-tral Ni(II) catalysts,1-27 capable of relatively rapid (comparable to propagation) β-hydride elimination and 2,1-reinsertion, resulting in extensive chain walking.26,28 In 2010, some of us employed bulky substituents to modify α-diiminonickel pre-catalysts, which resulted in highly active and thermally stable ethylene polymerization catalysts, capable of forming elasto-meric polyethylenes.29,30 An alternative approach assumed the design of 8-arylimino-5,6,7-trihydroquinolinylnickel chlorides that demonstrated high activities in ethylene polymerization upon activation with MAO and AlEt2Cl, to form highly branched polyethylenes with narrow molecular weight distri-bution.31 Further modifications led to catalysts affording branched polyethylene waxes, potentially interesting as addi-tives to lubricants and pour-point depressants.32 The nature of active species operating in those catalyst systems has remained unclear.

Previously, some of us showed that activation of bis(imino)pyridine nickel(II) dichloride complexes LNiCl2 and vanadium(III) trichloride complexes LVCl3 with methyl-alumoxane (MAO) afforded ion pairs [LNiMe]+[Me-MAO]− 33 and [L(R)V(µ-R)2AlMe2]

+[Me-MAO]− (R =Me or Cl)34 capa-ble of conducting olefin polymerization. However, until now there have been no examples of spectroscopic characterization of intermediates formed upon the activation of post-metallocene catalysts with AlR2Cl (R = Et, Me). In this work, we present the 1H NMR and EPR spectroscopic detection and characterization of species formed upon the activation of 1 (Chart 1) with AlMe2Cl and AlEt2Cl. The nature of closest precursors of active sites of ethylene polymerization, and of catalyst deactivation products is discussed.

Chart 1. The structure of the complex 1.

RESULTS AND DISCUSSION

Ethylene polymerization data

The activation of 1 with AlMe2Cl and AlEt2Cl leads to ac-tive ethylene polymerization catalysts (Table 1). The rate pro-files of the ethylene polymerization by 1/AlMe2Cl and 1/AlEt2Cl systems (Figure 1) were rather similar, exhibiting high initial polymerization rates followed by gradual decay. The catalyst system 1/AlMe2Cl exhibited higher initial activi-ty; whereas the deactivation rates of both catalyst systems were close (the rate of polymerization for both catalyst sys-tems decreases almost 3 times within 30 min period). The polymers obtained had low Mw values (~600 g/mol) and high number of branches (ca. 60/1000 C), with Mw/Mn ~ 2, which is evidence of the presence of only one type of active sites of ethylene polymerization.

Page 1 of 6

ACS Paragon Plus Environment

Submitted to Organometallics

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

2

Table 1. Ethylene polymerization catalyzed by 1/AlR2Cl.a

No n(Ni), µmol co-catalyst m(PE), g activity,

gPE/(mmolNi·bar·h) Mn, g/mol Mw, g/mol Mw,/Mn branches/1000Cb

1 1.8 AlMe2Cl 6.8 756 310 620 2.0 44 (Bn)

17 (B1)

2 2.0 AlEt2Cl 5.7 570 310 580 1.9 45 (Bn)

17 (B1) a Conditions: heptane (50 mL), 50 °C, PC2H4= 5 bar, [Al]/[Ni] = 200, polymerization time 60 min. b By 13C NMR spectroscopy.

Figure 1. The kinetic profile of the ethylene polymerization over the catalyst systems 1/AlMe2Cl (curve 1) and 1/AlEt2Cl (curve 2). Curve numbers correspond to experiment numbers in Table 1.

Spectroscopic Monitoring of Activation of 1 with Al-

Me2Cl

Pre-catalyst 1 displays broad paramagnetically shifted 1H NMR resonances spread over the +250 to −45 ppm range (Figure 2a). Most part of them can be readily assigned on the basis of integral values and analysis of line widths (Table 2).

Mixing 1 with AlMe2Cl ([Al]/[Ni] = 120) in toluene-d8 for one minute at 0 °C results in the conversion of 1 into a new paramagnetic complex 2 (Figure 2b, Table 2). 2 is the major product (> 70% yield) of the reaction between 1 and AlMe2Cl. In addition to 1H NMR resonances of the ligand, a new broad resonance from AlMeCl moiety at δ ~3 (3H, ∆ν1/2 ~ 540 Hz) was found, which could reflect the formation of either a neu-tral heterobinuclear complex LNiIIR(µ-R)2AlMeCl (R = Cl or Me) or ion pair [LNiII(µ-R)2AlMeCl]+[AlMe3Cl]−. An attempt to discriminate between these two possibilities using Al-Me3/[Ph3C]+[B(C6F5)4]

− as an ion-pair-forming activator was not successful: even at -40 °C, the reaction of 1 with Al-Me3/[Ph3C]+[B(C6F5)4]

− immediately afforded EPR active (S = 1/2) Ni(I) species with uninformative NMR spectra. Fur-ther warming the sample of 1/AlMe2Cl ([Al]/[Ni] = 120) to +25 °C leads to a disappearance of 2 and formation of an EPR-active complex 3. The EPR spectrum of frozen solution of 3 is characteristic of Ni(I) species35 (Figure 3). The EPR spectrum of 3 exhibits almost axial g-tensor anisotropy (g1 = 2.225, g2 = 2.075, g3 = 2.044), which is evidence of nearly axial symmetry of the ligand environment of the Ni(I) species.

Figure 2. 1H NMR spectrum (0 °C, acetone-d6) of 1 ([1] = 10-3 M) (a); 1H NMR spectra (0 °C, toluene-d8) of catalyst systems 1/AlMe2Cl ([Al]/[Ni] = 120, [1] = 10-2 M) (b) and 1/AlEt2Cl ([Al]/[Ni] = 20, [1] = 10-2 M) (c). Asterisks denote signals of diamagnetic complex 5 (see Figure 4). “s” marks residual sol-vent peak.

Time, min

10 20 30 40 50 60 0

500

1000

1500

1

2

Activity,

g P

E/(

mm

ol N

i�ba

r�h

)

ppm

-45-25-15 -551525354555657585

230260

A

B C F

I

B

F

I

G

C

D, E, H

* *

AlMe2Cl

H2O

230260

A

B F

200230

A AlEt2Cl

G

AlMeCl

I

D, E, H

C

G

D, E, H

s

-35

a

b

c

Page 2 of 6

ACS Paragon Plus Environment

Submitted to Organometallics

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

3

Table 2. 1H NMR data (δ, ppm and ∆ν1/2, Hz) for complexes 1, 2, 4 in toluene-d8 at 0 °C.

A B C D, E, H a F G I AlRCl

1 δ ~247 79.5 25.6 19.4 15.2 13.0 -41.7 8.4 28.9 -

∆ν1/2 (~1300) (350) (190) (90) (160) (50) (330) (230) (210) -

2 δ ~208 63.4 17.1 19.5 14.3 9.7 -32.1 18.6 26.4 ~3

∆ν1/2 (~4300) (350) (80) (140) (160) (100) (340) (410) (190) (~540)

4 δ 220÷205 67÷62 17.7÷17.0 20.8÷20.0 15.4÷13.9 10.2÷9.2 -31÷-34 20÷17 28.4÷26.1 NF a Resonances D, E and H protons cannot be unambiguously distinguished. NF – not found (signals of Et protons overlap with the

intense peak of AlEt2Cl).

The g2 and g3 components of the EPR spectrum display par-tially resolved hyperfine splitting aN

2 = aN3 ≈ 10.5±0.5 G from

nitrogen atoms. Although the exact number of nitrogen atoms in the coordination sphere of nickel cannot be identified from the EPR spectrum, the nearly axial g-tensor symmetry sug-gests bis-ligated structure for 3, which can thus be tentatively assigned to an ion pair of the type [L2NiI]+[AlMe3Cl]-. Pro-longed storing the sample 1/AlMe2Cl ([Al]/[Ni] = 120) at room temperature leads to a decrease of the EPR resonances of Ni(I), accompanied by visible formation of Ni black on the NMR-tube walls.

Figure 3. Frozen solution (-196 °C, toluene-d8) EPR spectrum of the sample 1/AlMe2Cl ([Al]/[Ni] = 120, [1] = 10-2 M) after 30 min storing at 0 °C.

Spectroscopic Monitoring of Activation of 1 with AlEt2Cl

The reaction of 1 with AlEt2Cl in toluene results in the for-mation of new Ni(II) species: paramagnetic complexes of the type 4 and diamagnetic complex 5. The ratio between 4 and 5 strongly depends on the temperature and the [Al]/[Ni] ratio. At [Al]/[Ni] = 20, paramagnetic complexes 4 predominate in the reaction solution at 0 °C, and only small amount of 5 is ob-served (Figure 2c). Raising the temperature up to 25 °C leads to a complete conversion of 4 into 5. At [Al]/[Ni] > 50, only species 5 was found even at -20 °C (Figure 4). 1H NMR reso-nances of 4 resemble those of 2. However, several (at least two) resonances are observed for each particular proton of 4 instead of one resonance for 2 (Table 2, Figure 2c). This may be due to the existence of several structurally similar species of the type 4. The spectrum of diamagnetic complex 5 (see Experimental section) corresponds to a Ni(II) complex bearing one bidentate ligand and one Ni-CH2-CH3 moiety (Figure 4). The assignment of Ni-CH2-CH3 was confirmed by the 1H-1H

COSY experiment. Most probably, 5 is an outer-sphere ion pair of the type [LNiIIEt]+[AlEt3Cl]−. The diamagnetic nature of 5 is evidence of its square-planar topology. 1H NMR char-acterization of a similar diamagnetic species [L1NiIIEt]+[BAr'4]

− (L1 = neutral bidentate α-diimine ligand, Ar' = 2.6-C6H3Me2) was previously reported by Brookhart and co-workers.26

Prolonged storing 5 at -20 °C results in a decrease of its con-centration (ca. 3 times within 2 h), accompanied by formation of EPR active Ni(I) species 3′ (with EPR parameters coincid-ing with those of 3), which can be tentatively assigned to [L2NiI]+[AlEt3Cl]- structure. Warming the sample containing species 5 accelerates the reduction to Ni(I).

Figure 4. 1H NMR spectrum (-20 °C, toluene-d8) of the sample 1/AlEt2Cl recorded after 10 min mixing the reagents ([Al]/[Ni] = 50, [1] = 10-2 M). Asterisks mark signals of AlEt2Cl. “s” mark residual solvent peaks.

Overall, NMR and EPR spectroscopic studies of the catalyst systems 1/AlMe2Cl and 1/AlEt2Cl have shown that nickel complexes 2-5 can be observed in these systems. Diamagnetic ion pair 5 ([LNiIIEt]+[AlEt3Cl]−) can be reliably characterized by NMR. The structures of species 2 and 4, due to their para-magnetism, are less firmly established. According to 1H NMR spectroscopic data, 2 and 4 contain one ligand L at Ni(II), as well as NiII(µ-R)2AlR1Cl moiety (for complex 2, R = Cl or Me, R1 = Me; for complexes 4, R = Cl or Et, R1 = Et). Howev-er, based on the NMR data, one cannot conclude whether complexes 2 and 4 are neutral complexes LNiIIR(µ-R)2AlR1Cl or ion pairs [LNiII(µ-R)2AlR1Cl]+[Al(R1)3Cl]−. However, tak-ing into account the high ethylene polymerization activity of species 2 and 4 (see below), we favor the assignment of 2 and 4 to the ion-pair structure of the type [LNiII(µ-R)2AlR1Cl]+[Al(R1)3Cl]−. Proposed reactions in systems 1/Al(Alk)2Cl are shown in Scheme 1.

ppm

6.57.0 7.5 8.0

Py-Ho

-0.8 -0.4 00.4 0.8 1.21.62.02.4

Ar-Hm

8.5

Py-Hm

Py-Hp

s

sNi-CH2-CH3

N=C-CH2-

Ar-Meo * *

~

~

~

~

2900 3000 3100 3200 3300 3400 3500

2.225 2.075

2.044

Page 3 of 6

ACS Paragon Plus Environment

Submitted to Organometallics

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

4

Scheme 1. Proposed reactions in systems 1/Al(Alk)2Cl/(C2H4).

The major distinction between the systems 1/AlMe2Cl and 1/AlEt2Cl is the formation of temperature-unstable species 5 which was only observed in the latter system. Apparently, in the system 1/AlMe2Cl, the corresponding intermediate 5′ is too unstable and either rapidly undergoes reduction (detected by the formation of the EPR active bis-ligated complex 3) or accumulates in the form of the ion pair [LNiII(µ-Me)2AlMeCl]+[AlMe3Cl]−. In the intermediate 5, β-agostic interaction of the Et with the Ni center is possible, which may stabilize the intermediate 5 as compared to 5′.

Catalyst Systems 1/AlR2Cl/C2H4 (R = Me, Et)

Catalyst systems 1/AlMe2Cl and 1/AlEt2Cl display similar activities in ethylene polymerization and produce PEs with the same molecular structures (Table 1). However, according to NMR data, different Ni(II) species predominate in the 1/AlMe2Cl and 1/AlEt2Cl systems at room temperature: para-magnetic ion pair with proposed structure [LNiIIR(µ-R)2AlMeCl]+[AlMe3Cl]− (R = Me, Cl) (2), and diamagnetic ion pair [LNiIIEt]+[AlEt3Cl]− (5), respectively (Scheme 1).

Adding C2H4 (200 eq.) to the sample 1/AlEt2Cl ([Al]/[Ni] = 50) at -20 °C lead to immediate disappearance of 5 and rapid ethylene polymerization. During 4-5 min ethylene was com-pletely consumed and the 1H NMR resonances of 5 were re-stored.

A similar result was obtained for the system 1/AlMe2Cl ([Al]/[Ni] = 120). After the addition of 200 equiv. of ethylene to the sample 1/AlMe2Cl ([Al]/[Ni] = 120) at 0 °C, complex 2 immediately disappeared. After ethylene consumption, the NMR pattern of 2 appeared again.

Brookhart and co-workers have shown that cationic complex [L1NiIIMe]+[BAr'4]

− generated in the model system L1NiIIMe2 + [H(OiPr2)2]

+[BAr'4]− is capable of inserting ethylene into the

Ni-Me bond to form complex [L1NiIIPr]+[BAr'4]−. Further eth-

ylene insertion into the Ni-Pr bond yields complex [L1NiII(C5H11)]

+[BAr'4]−. The cationic [L1NiII(alkyl)]+[BAr'4]

− complexes were postulated as the active species of ethylene

polymerization.26 Based on this analogy, intermediate [LNiIIEt]+[AlEt3Cl]− (5) may be considered as the true direct precursor of the active species of polymerization. In the case of 1/AlMe2Cl system, the corresponding [LNiIIMe]+[AlEt3Cl]− (5′) was not observed, presumably, due to its much lower sta-bility. In this system, the heterobinuclear ion-pair intermediate [LNiIIR(µ-R)2AlMeCl]+[AlMe3Cl]− (R = Me, Cl) (2), predom-inating in the reaction solution, is the last detectable precursor of the active sites of ethylene polymerization, which is ex-pected to convert to the [LNiII(polymeryl)]+[A]− species upon substitution of the RAlMeCl with ethylene, followed by eth-ylene insertion.

CONCLUSIONS

Using NMR and EPR spectroscopy, the activation of eth-ylene polymerization pre-catalyst based on [LNiCl2] complex (L = 2,4,6-trimethyl-(N-5,6,7-trihydroquinolin-8-ylidene) phenylamine) with dialkyl aluminum chlorides AlR2Cl (R = Me, Et) in toluene has been investigated at -20…0 °C. At the initial stage of activation (at Al/Ni ≈ 20), paramagnetic ion pairs with heterodinuclear cationic parts [LNiII(µ-R)2AlR1Cl]+[Al(R1)3Cl]− (R = Cl, Me, Et; R1 = Me, Et) are formed. In the system [LNiCl2]/AlMe2Cl, this ion pair remains the major Ni(II) species in solution even at high Al/Ni (100-120). In the system containing AlEt2Cl, raising the Al/Ni ratio to 50 or higher results in the formation diamagnetic ion pair [LNiIIEt]+[AlEt3Cl]−. Addition of ethylene to either [LNiII(µ-R)2AlMeCl]+[AlMe3Cl]− or [LNiIIEt]+[AlEt3Cl]− results in fast reaction with formation of PE (which is in agreement with virtually identical catalytic properties of the systems [LNiCl2]/AlMe2Cl/C2H4 and [LNiCl2]/AlEt2Cl/C2H4); after complete ethylene consumption, [LNiII(µ-R)2AlMeCl]+[AlMe3Cl]− or [LNiIIEt]+[AlEt3Cl]− restore their concentrations.

In the absence of C2H4, [LNiII(µ-R)2AlMeCl]+[AlMe3Cl]− and [LNiIIEt]+[AlEt3Cl]− species gradually reduce to bis-

Page 4 of 6

ACS Paragon Plus Environment

Submitted to Organometallics

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

5

ligated nickel(I) species [L2NiI]+[AlMe3Cl]-, and to Ni(0) black. One could expect that similar reduction processes ac-count for the catalysts deactivation processes under practical polymerization conditions.

EXPERIMENTAL SECTION

All manipulations with air-sensitive materials were performed in an argon-filled glovebox. All solvents used were dried with 4 Å molecu-lar sieves and distilled under dry argon. Complex 1 was synthesized according to published procedure.31 AlMe3, AlEt3, AlMe2Cl, and AlEt2Cl were purchased from Aldrich.

Ethylene polymerization was performed in a 0.3 L steel reactor. The pre-catalyst 1 (2 µmol) was introduced into the reactor in an evacuated sealed glass ampoule. The reactor was evacuated at 80 °C, cooled down to 20 °C and then charged with the freshly prepared solution of AlR2Cl or AlR3 (R = Me, Et) in heptane (50 cm3), [Al]/[Ni] = 200. After setting up the desired polymerization tempera-ture (50 °C) and ethylene pressure (5 bar), the reaction was started by breaking the ampoule with the pre-catalyst. During the polymeriza-tion, ethylene pressure, temperature and stirring speed were main-tained constant. The experimental unit was equipped with an automat-ic computer-controlled system for the ethylene feed, maintaining the required pressure, recording the ethylene consumption and providing the kinetic curve output both in the form of a table and as a graph.

1H NMR spectra were measured on a Bruker Avance 400 MHz NMR spectrometer at 400.130, using 5 mm o.d. glass NMR tubes. 1H chemical shifts were referenced to the residual CD2HC6D5 peak at δ 2.09. The samples for NMR spectroscopy were prepared as follows. Desired amounts of the complex 1 were weighed in the glove-box and transferred into the NMR tube, which was then closed with septum stopper. The solutions of AlMe2Cl and AlEt2Cl in toluene-d8 were then added via gas-tight syringe upon proper cooling (−40 °C).

EPR spectra were measured on a Bruker ER-200D spectrometer at 9.3 GHz, modulation frequency 100 kHz, modulation amplitude 4 G. Periclase crystal (MgO) with impurities of Mn2+ and Cr3+, which served as a side reference, was placed into the second compartment of the dual cavity. EPR spectra were quantified by double integration with TEMPO toluene solution as standard. The relative accuracy of the quantitative EPR measurements was ±30 %.

Species 5: NMR data (toluene-d8, −20 °C), δ 8.49 (br.d., 1H, Py-Ho), 6.98 (m, 1H, Py-Hm), 6.64 (d, JHH = 6.8Hz, 1H, Py-Hp), 6.59 (s, 2H, Ar-Hm), 2.04 (s, 6H, Ar-CH3 (ortho)) 1.89 (t, JHH = 5.9Hz, 2H, -N=C-CH2-CH2-), 0.71 (q, JHH = 5.8Hz, 2H, Ni-CH2-CH3), -0.60 (t, JHH = 5.8Hz, 3H, Ni-CH2-CH3). The resonance of Ar-CH3 (para) overlaps with the intense peak of CD2HC6D5.

AUTHOR INFORMATION

Corresponding Author

* Evgenii P. Talsi, Boreskov Institute of Catalysis, Pr. Lavrentieva 5, Novosibirsk 630090, Russian Federation, Fax: +7 383 3308056, e-mail: talsi@catalysis.ru

ACKNOWLEDGMENT

This work was partially supported by the Ministry of Science and Education of the Russian Federation and by the Russian Founda-tion for Basic Research (Grant RFBR 14-03-91153 / NSFC 21211120163). The authors are grateful to Dr. D. E. Babushkin for fruitful discussions, Dr. M. A. Matsko for the analysis of the polymers’ MWD, and Mrs. O. K. Akmalova for assistance with the ethylene polymerization experiments.

REFERENCES

(1) Wiedemann, T.; Voit, G.; Tchernook, A.; Roesle, P.; Göttker-Schnetmann, I.; Mecking, S. J. Am. Chem. Soc. 2014, 136, 2078-2085.

(2) Dong, Z.; Ye, Z. Polym. Chem. 2012, 3, 286-301.

(3) Wang, C.; Friedrich, S.; Younkin, T.R.; Li, R.T.; Grubbs, R.H.; Bansleben, D.A.; Day, M. W. Organometallics 1998, 17, 3149-3151.

(4) Johnson, L.K.; Bennett, A.M.A.; Ittel, S.D.; Wang, L.; Partha-sarathy, A.; Hauptman, E.; Simpson, R.D.; Feldman, J.; Coughlin, E.B. (DuPont), WO98/30609, 1998.

(5) Tomov, A.; Spitz, R.; Saudemont, T.; Drujon, X. (Elf Atochem, S.A.), French Patent 98.12476, 1998.

(6) Held, A.; Bauers, F.M.; Mecking, S. Chem. Commun. 2000, 301-302.

(7) Gates, D.P.; Svejda, S.A.; Onate, E.; Killian, C.M.; Johnson, L.K.; White, P.S.; Brookhart, M. Macromolecules 2000, 33, 2320-2334.

(8) Leatherman, M.D.; Brookhart, M. Macromolecules 2001, 34, 2748-2750.

(9) Soula, R.; Broyer, J.P.; Llauro, M.F.; Tomov, A.; Spitz, R.; Claverie, J.; Drujon, X.; Malinge, J.; Saudemont, T. Macro-

molecules 2001, 34, 2438-2442. (10) Gibson, V.C.; Tomov, A.; White, A.J.P.; Williams, D.J.

Chem. Commun. 2001, 719-720. (11) Zuideveld, M.; Wehrmann, P.; Rohr, C.; Mecking, S. Angew.

Chem. Int. Ed. 2004, 43, 869-873. (12) Zhang, L.; Brookhart, M.; White, P.S. Organometallics 2006,

25, 1868-1874. (13) Kuhn, P.; Sémeril, D.; Jeunesse, C.; Matt, D.; Neuburger, M.;

Mota, M. Chem. Eur. J. 2006, 12, 5210-5219. (14) Göttker-Schnetmann, I,; Wehrmann, P.; Röhr, C.; Mecking,

S. Organometallics 2007, 26, 2348-2362. (15) Yu, S.M.; Berkefeld, A.; Göttker-Schnetmann, I.; Müller, G.;

Mecking, S. Macromolecules 2007, 40, 421-428. (16) Lavanant, L.; Rodriguez, A.S.; Kirillov, E.; Carpentier, J.F.;

Jordan, R.F. Organometallics 2008, 27, 2107-2117. (17) Song, D.P.; Ye, W.P.; Wang, Y.X.; Liu, J.Y.; Li, Y.S.

Organometallics 2009, 28, 5697-5704. (18) Popeney, C.S.; Rheingold, A.L.; Guan, Z. Organometallics

2009, 28, 4452-4463. (19) Camacho, D.H.; Guan, Z. Chem. Commun. 2010, 46, 7879-

7893. (20) Song, D.P.; Wang, Y.X.; Mu, H.L.; Li, B.X.; Li, Y.S. Orga-

nometallics 2011, 30, 925-934. (21) Weberski, M.P.; Chen, C.; Delferro, M.; Marks, T.J. Chem.

Eur. J. 2012, 18, 10715-10732. (22) Weberski, M.P.; Chen, C.; Delferro, M.; Zuccaccia, C.; Mac-

chioni, A.; Marks, T.J. Organometallics 2012, 31, 3773-3789. (23) Stephenson, S.J.; Mclnnis, J.P.; Chen, C.; Weberski, M.P.;

Motta, A.; Delferro, M., Marks, T. J. ACS Catal. 2014, 4, 999-1003.

(24) Johnson, L.K.; Killian, C.M.; Brookhart, M. J. Am. Chem.

Soc. 1995, 117, 6414-6415. (25) Killian, C.M.; Tempel, D.J.; Johnson, L.K.; Brookhart, M. J.

Am. Chem. Soc. 1996, 118, 11664-11665. (26) Leatherman, M.D.; Svejda, S.A.; Johnson, L.K.; Brookhart,

M. J. Am. Chem. Soc. 2003, 125, 3068-3081. (27) Wang, S.; Sun, W. H.; Redshaw, C. J. Organomet. Chem.

2014, 751, 717-741. (28) Möhring, V.M.; Fink, G. Angew. Chem. Int. Ed. 1985, 24,

1001-1003. (29) Liu, H.; Zhao, W.; Hao, X.; Redshaw, C.; Huang, W.; Sun,

W. H. Organometallics 2011, 30, 2418-2424. (30) He, Z.; Liang, Y.; Yang, W.; Uchino, H.; Yu, J.; Sun, W. H.;

Han, C. C. Polymer 2015, 56, 119-122. (31) Yu, J.; Zeng, Y.; Huang, W.; Hao, H.; Sun, W. H. Dalton

Trans. 2011, 40, 8436-8443. (32) Sun, Z.; Yue, E.; Qu, M.; Oleynik, I. V.; Oleynik, I. I.; Li, K.;

Liang, T.; Zhang, W.; Sun, W. H. Inorg. Chem. Front. 2015, 2, 223-227.

(33) Antonov A. A., Samsonenko, D. G., Talsi, E. P., Bryliakov, K. P. Organometallics 2013, 32, 2187.

(34) Soshnikov, I. E.; Semikolenova, N. V.; Antonov, A. A.; Bryliakov, K. P.; Zakharov, V. A.; Talsi E. P. Organometallics 2014, 33, 2583.

Page 5 of 6

ACS Paragon Plus Environment

Submitted to Organometallics

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

6

(35) See, for example, Gagne, R.R.; Ingle, D.M. Inorg. Chem. 1981, 20, 420-425.

For graphical abstract

Page 6 of 6

ACS Paragon Plus Environment

Submitted to Organometallics

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960