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Displacement of weakly coordinating anions from zirconocene alkyl cations by trialkyl phosphine : a model for olefin coordination in homogeneous Ziegler-Natta catalysis

Displacement of weakly coordinating anions from zirconocene alkyl cations by trialkyl phosphine : a model for olefin coordination in homogeneous Ziegler-Natta catalysis

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BECK, Stefan, Marc-Heinrich PROSENC, Hans-Herbert BRINTZINGER, 1998. Displacement of weakly coordinating anions from zirconocene alkyl cations by trialkyl phosphine : a model for olefin coordination in homogeneous Ziegler-Natta catalysis. In: Journal of Molecular Catalysis A: Chemical. 128(1-3), pp. 41-52. ISSN 1381-1169. Available under: doi: 10.1016/S1381-1169(97)00161-1

@article{Beck1998Displ-23878, title={Displacement of weakly coordinating anions from zirconocene alkyl cations by trialkyl phosphine : a model for olefin coordination in homogeneous Ziegler-Natta catalysis}, year={1998}, doi={10.1016/S1381-1169(97)00161-1}, number={1-3}, volume={128}, issn={1381-1169}, journal={Journal of Molecular Catalysis A: Chemical}, pages={41--52}, author={Beck, Stefan and Prosenc, Marc-Heinrich and Brintzinger, Hans-Herbert} }

Beck, Stefan Brintzinger, Hans-Herbert eng 2013-07-04T07:10:24Z deposit-license Prosenc, Marc-Heinrich Displacement of weakly coordinating anions from zirconocene alkyl cations by trialkyl phosphine : a model for olefin coordination in homogeneous Ziegler-Natta catalysis 2013-07-04T07:10:24Z Prosenc, Marc-Heinrich Journal of Molecular Catalysis A: Chemical ; 128 (1998), 1-3. - S. 41-52 Brintzinger, Hans-Herbert Beck, Stefan Displacement of the anion H<sub>3</sub>C–B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub><sup>−</sup> from the zirconocene contact-ion pair [(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>Zr(CH<sub>3</sub>)+⋯(μ-H<sub>3</sub>C)–B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub><sup>−</sup>] by a series of phosphines and formation of a bisphosphine complex by uptake of a second phosphine ligand have been studied by NMR methods in C<sub>6</sub>D<sub>6</sub> solutions. Evidence is presented that associated, outer-sphere ion pairs [(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>Zr(CH<sub>3</sub>)(PR<sub>3</sub>)]<sup>+</sup> H<sub>3</sub>C–B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub><sup>−</sup> predominate at zirconocene concentrations up to ca. 2 mM; higher aggregates become apparent at higher zirconocene concentrations. Equilibrium constants for the formation of mono- and bis-PMe3 complexes have been determined; the latter are found to be highly sensitive to steric perturbations. These data, together with density-functional estimates for reaction enthalpies, lead to the following qualitative conclusions with regard to olefin coordination in zirconocene-based polymerization catalysts: (i) The olefin substrate displaces the borate anion only from a small equilibrium fraction of the zirconocene alkyl cations present; (ii) the predominant fraction of the resulting zirconocene alkyl olefin cation remains in an outer-sphere association with the counteranion; (iii) mutual displacement of olefin and counteranion from the Zr center is slow compared to typical olefin insertions; (iv) uptake of a second olefin under formation of a cationic zirconocene alkyl diolefin complex is rather unlikely even at elevated olefin concentrations. 1998

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