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 J Marks

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Abstract

The reaction of B(C6F6)3 with zirconocene dimethyl complexes L2ZrMe2 in 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)2ZrMe 2 results in the formation of the cationic metallacyclic product (tBu2C5H3)[tBuC 5H3C(Me2)CH2]Zr +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(C6F 5)3- (7), (Me5C5)2ZrH+HB(C6F 5)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 C6D6 under 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, P1̄, 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, P21, a = 12.610(5) Å, b = 20.995(4) Å, c = 21.389(5) Å, β= 106.13(3)°, R = 0.066; 8, triclinic, P1̄, 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, P1, a = 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 dynamic 1H NMR, complexes 1-4 undergo rapid intramolecular Zr-Me/B-Me exchange (ΔG‡(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 (ΔG‡(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 × 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=CH13CH3 indicate the predominant pathway for 1 and 2 is β-H elimination, while for 3 it is β-CH3 elimination. 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-1 at 20 °C) to form a mixture of 2-methyl-1-pentene and 2-methyl-2-pentene.

Original languageEnglish
Pages (from-to)10015-10031
Number of pages17
JournalJournal of the American Chemical Society
Volume116
Issue number22
Publication statusPublished - Nov 2 1994

ASJC Scopus subject areas

  • Chemistry(all)

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