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Anion exchange in alkyl-zirconocene borate ion pairs : are solvated alkyl-zirconocene cations relevant intermediates?

Anion exchange in alkyl-zirconocene borate ion pairs : are solvated alkyl-zirconocene cations relevant intermediates?

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BECK, Stefan, Susanna LIEBER, Frank SCHAPER, Armin GEYER, Hans-Herbert BRINTZINGER, 2001. Anion exchange in alkyl-zirconocene borate ion pairs : are solvated alkyl-zirconocene cations relevant intermediates?. In: Journal of the American Chemical Society. 123(7), pp. 1483-1489. ISSN 0002-7863. eISSN 1520-5126

@article{Beck2001Anion-23733, title={Anion exchange in alkyl-zirconocene borate ion pairs : are solvated alkyl-zirconocene cations relevant intermediates?}, year={2001}, doi={10.1021/ja003531w}, number={7}, volume={123}, issn={0002-7863}, journal={Journal of the American Chemical Society}, pages={1483--1489}, author={Beck, Stefan and Lieber, Susanna and Schaper, Frank and Geyer, Armin and Brintzinger, Hans-Herbert} }

Ion pairs of the type Cp<sup>x</sup><sub>2</sub>ZrMe<sup>+</sup>***A<sup>-</sup> containing various ansa-zirconocene methyl cations in contact with Me-B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub><sup>-</sup> or B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub><sup>-</sup> anions have been studied with regard to their anion exchange kinetics by 2D-NMR methods in benzene or toluene solutions. The resultsacceleration of anion exchange by added Li<sup>+</sup>***Me−B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub><sup>-</sup>, substantial nonproductive exchange between added and Zr-bound Me-B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub><sup>-</sup> anions, an increase of exchange rates at increased zirconocene concentrations, and the exclusively entropic origin of this rate increaseall indicate that anion exchange occurs by way of ion quadruples or higher ionic aggregates, rather than via dissociation to solvent-separated ions. These findings imply that solvent-separated (i.e. anion-free) alkyl zirconocene cations are unlikely to be relevant intermediates in reaction systems containing Cp<sup>x</sup><sub>2</sub>ZrMe<sup>+</sup>***A<sup>-</sup> ion pairs and, hence, also in zirconocene-based catalyst systems for the polymerization of α-olefins. eng Schaper, Frank Geyer, Armin Beck, Stefan Brintzinger, Hans-Herbert 2013-06-24T14:37:32Z deposit-license 2013-06-24T14:37:32Z Lieber, Susanna Anion exchange in alkyl-zirconocene borate ion pairs : are solvated alkyl-zirconocene cations relevant intermediates? Schaper, Frank Brintzinger, Hans-Herbert Lieber, Susanna Geyer, Armin 2001 Journal of American Chemical Society ; 123 (2001), 7. - S. 1483-1489 Beck, Stefan

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