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Zr-alkyl isomerization in ansa-zirconocene-catalyzed olefin polymerizations. Contributions to stereoerror formation and chain termination

Zr-alkyl isomerization in ansa-zirconocene-catalyzed olefin polymerizations. Contributions to stereoerror formation and chain termination

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LECLERC, Margarete K., Hans-Herbert BRINTZINGER, 1996. Zr-alkyl isomerization in ansa-zirconocene-catalyzed olefin polymerizations. Contributions to stereoerror formation and chain termination. In: Journal of the American Chemical Society. 118(38), pp. 9024-9032. ISSN 0002-7863. eISSN 1520-5126. Available under: doi: 10.1021/ja961157n

@article{Leclerc1996Zralk-23759, title={Zr-alkyl isomerization in ansa-zirconocene-catalyzed olefin polymerizations. Contributions to stereoerror formation and chain termination}, year={1996}, doi={10.1021/ja961157n}, number={38}, volume={118}, issn={0002-7863}, journal={Journal of the American Chemical Society}, pages={9024--9032}, author={Leclerc, Margarete K. and Brintzinger, Hans-Herbert} }

2013-06-24T16:48:50Z deposit-license 1996 Leclerc, Margarete K. Brintzinger, Hans-Herbert 2013-06-24T16:48:50Z Leclerc, Margarete K. eng Zr-alkyl isomerization in ansa-zirconocene-catalyzed olefin polymerizations. Contributions to stereoerror formation and chain termination Brintzinger, Hans-Herbert Journal of the American Chemical Society ; 118 (1996), 38. - S. 9024-9032 In polymers made from (E)- or (Z)-[1-D]propene with methyl alumoxane (MAO)-activated ansa-zirconocene catalysts, signals of deuterium-labeled mrrm pentads document that stereoerrors arise mainly from an isomerization of the Zr-bound chain end. Reduced D-atom redistribution in poly([2-D]propene) indicates a kinetic isotope effect of k<sub>H</sub>/k<sub>D</sub> ≈ 3 for the β-H/D transfer associated with the isomerization reaction. In all poly([1- and [2-D]propenes) studied, D-labeled mmmm pentads occur with a probability similar to that of D-labeled mrrm pentads; this observation requires further mechanistic clarification. Olefinic chain ends of polymers obtained with C<sub>2</sub>H<sub>4</sub>(thind)<sub>2</sub>ZrCl<sub>2</sub>-MAO from (E)- or (Z)-[1-D]propene deviate in their D-label distributions from the expected stereochemistry. Isomerization of the Zr-bound chain end, probably via a Zr-bound tertiary alkyl intermediate, thus contributes also to chain-growth termination. With the sterically hindered catalyst Me<sub>2</sub>Si(2-Me-4-tBu-C<sub>5</sub>H<sub>2</sub>)<sub>2</sub>ZrCl<sub>2</sub>-MAO, almost all chain terminations appear to occur via chain-end isomerization, which does not lead to stereoerrors here. With the high-performance catalyst Me<sub>2</sub>Si(2-Me-benz[e]indenyl)<sub>2</sub>ZrCl<sub>2</sub>-MAO, finally, no D-label is found in the mrrm and mmmm pentad signals; here, Zr-alkyl isomerization can apparently not compete with the high rate of olefin insertion.

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