Cationic Zirconocene Olefin Polymerization Catalysts Based on the Organo-Lewis Acid Tris(pentafluorophenyl)borane. A Synthetic, Structural, Solution Dynamic, and Polymerization Catalytic Study

Xinmin Yang, Charlotte L. Stern, Tobin Jay Marks

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838 Scopus citations

Abstract

The reaction of B(C6F5)3with zirconocene dimethyl complexes L2ZrMe2in hydrocarbon solvents affords base-free cationic zirconium complexes L2ZrMe+MeB(C6F5)3- (L = η5-C5H5, 1; η5-Me2C5H3, 2; η5-Me5C5, 3; η5- (TMS)2C5H3, 4) in quantitative yields. A similar reaction using (tBu2C5H3)2ZrMe2results in the formation of the cationic metallacyclic product tBu2C5H3) [tBuC5H3(Me2)CH2Zr+MeB(C6F5)3- (6) through what is presumably an intramolecular C-H activation process. Complexes 3 and 6 undergo rapid hydrogenolysis to yield the corresponding cationic hydrido complexes (Me5C5)2ZrH+MeB(C6F5)3- (7), (Me5C5)2ZrH+HB(C6F5)3- (8) (stepwise), and (tBu2C5H3)2ZrH+MeB(C6F5)3- (9), respectively. Complex 2 undergoes slow conversion to {[(Me2C5H3)2ZrMe]2(μ- F)]+MeB(C6F5)3- (12) in C6D6under an inert atmosphere at 25 °C. Complexes 2, 3, 4, 6, 8, and 12 have been characterized by X-ray diffraction (crystal data: 2, monoclinic, P21/n, a = 12.261(2) Å,b = 20.010(6) Å, c = 13.053(5) Å, β = 90.80(2)°, R = 0.027; 3, monoclinic, P21/n, a = 9.405(1) Å, b = 19.336(3) Å, c = 10.382(1) Å, β - 96.54(1)°, R = 0.039; 4, triclinic, Pi, a = 11.639(4) Å, b = 12.877(4) Å, c = 19.224(4) Å, α = 77.89(2)°, β = 74.33(2)°, γ = 77.04(3)°, R = 0.043; 6, monoclinic, P21a = 12.610(5) Å, b = 20.995(4) Å, c = 21.389(5) Å, β = 106.13(3)°, R = 0.066; 8, triclinic, Pi, a = 11.899(4) Å, b = 12.643(4) Å, c = 13.681(4) Å, α = 84.47(2)°, β = 76.12(3)°, γ = 65.34(3)°, R = 0.060; 12, triclinic, P1a = 12.308(1) Å, b = 13.898(3) Å, c = 15.182(2) Å, α = 101.63(1)°, β = 90.42(1)°, γ = 115.22(1)°,R = 0.031). These structure determinations allow detailed analysis of the metrical aspects of L2ZrMe+MeB(C6F5)3- ion pairing on the solid state. As revealed by dynamic1H NMR, complexes 1-4 undergo rapid intramolecular Zr-Me/B-Me exchange (∆G*(σ, kcal/mol, °C, complex) = 18.7(2, 80, 1); 19.7(2, 80, 2); 19.8(2, 80, 3); 18.0(2, 35, 4)) and for 2 and 4, symmetrizing ion-pair dissociation-recombination processes (∆G*(σ, kcal/mol, °C, complex) = 18.3(2, 80, 2); 14.4(2, 35, 4)). Complexes 1-4, 7, and 8 are highly active homogeneous catalysts for the polymerization of ethylene with activities (3.2-6.8 X 106g polyethylene/mol Zr h atm at 25 °C) comparable to methylalumoxane-based zirconocene catalysts. Complexes 1-3, 7 and 8 are also active for the atactic polymerization of propylene. In regard to polymerization chain transfer mechanisms, NMR endgroup analysis and labeling experiments using CH2=CH13CH3indicate the predominant pathway for 1 and 2 is 0-H elimination, while for 3 it is 0-CH3elimination. These experiments unambiguously rule out propylene C-H activation processes as an important chain transfer pathway. Complex 9 is highly active for the catalytic dimerization of propylene (Nt= 0.25 s-1at 20 °C) to form a mixture of 2-methyl-l-pentene and 2-methyl-2-pentene.

Original languageEnglish (US)
Pages (from-to)10015-10031
Number of pages17
JournalJournal of the American Chemical Society
Volume116
Issue number22
DOIs
StatePublished - Nov 1 1994

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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