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Yoder JC, Bercaw JE. Chain epimerization during propylene polymerization with metallocene catalysts: mechanistic studies using a doubly labeled propylene. J Am Chem Soc. 2002;124(11):2548-55doi: 10.1021/ja0123296.
Yoder, J. C., & Bercaw, J. E. (2002). Chain epimerization during propylene polymerization with metallocene catalysts: mechanistic studies using a doubly labeled propylene. Journal of the American Chemical Society, 124(11), 2548-55. https://doi.org/10.1021/ja0123296
Yoder, Jeffrey C, and Bercaw, John E. "Chain epimerization during propylene polymerization with metallocene catalysts: mechanistic studies using a doubly labeled propylene." Journal of the American Chemical Society vol. 124,11 (2002): 2548-55. doi: https://doi.org/10.1021/ja0123296
Yoder JC, Bercaw JE. Chain epimerization during propylene polymerization with metallocene catalysts: mechanistic studies using a doubly labeled propylene. J Am Chem Soc. 2002 Mar 20;124(11):2548-55. doi: 10.1021/ja0123296. PMID: 11890805.
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J Am Chem Soc. 2002 Mar 20;124(11):2548-55. doi: 10.1021/ja0123296.

Chain epimerization during propylene polymerization with metallocene catalysts: mechanistic studies using a doubly labeled propylene.

Journal of the American Chemical Society

Jeffrey C Yoder, John E Bercaw

Affiliations

  1. Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena, CA 91125, USA.

PMID: 11890805 DOI: 10.1021/ja0123296

Abstract

The mechanisms of chain epimerization during propylene polymerization with methylaluminoxane-activated rac-(EBTHI)ZrCl(2) and rac-(EBI)ZrCl(2) catalysts (EBTHI = ethylenebis(eta(5)-tetrahydroindenyl); EBI = ethylenebis(eta(5)-indenyl)) have been studied using specifically isotopically labeled propylene: CH(2)=CD(13)CH(3). These isospecific catalysts provide predominantly the expected [mmmm] pentads with [minus signCH(2)CD(13)CH(3)(-)] repeating units ((13)C NMR). Under relatively low propylene concentrations at 50 and 75 degreesC, where stereoerrors attributable to chain epimerization are prevalent, (13)C NMR spectra reveal (13)C-labeled methylene groups along the polymer main chain, together with [CD(13)CH(3)] units in [mmmr], [mmrr], and [mrrm] pentads and [CH(13)CH(3)] units in [mmmmmm] and [mmmmmr] heptads, as well as [mrrm] pentads. The isotopomeric regiomisplacements and stereoerrors are consistent with a mechanism involving beta-D elimination, olefin rotation and enantiofacial interconversions, and insertion to a tertiary alkyl intermediate [Zr-C(CH(2)D)((13)CH(3))P] (P = polymer chain), followed by the reverse steps to yield two stereoisomers of [Zr-CHDCH((13)CH(3))P] and [Zr-(13)CH(2)CH(CH(2)D)P], as well as unrearranged [Zr-CH(2)CD((13)CH(3))P]. The absence of observable [-CH(2)CH(13)CH(2)D-] in the [mrrm] pentad region of the (13)C NMR spectra provides evidence that an allyl/dihydrogen complex does not mediate chain epimerization.

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