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Published May 26, 2008 | Supplemental Material
Journal Article Open

Catalyst Site Epimerization during the Kinetic Resolution of Chiral α-Olefins by Polymerization

Abstract

A new enantiopure C1-symmetric olefin polymerization precatalyst, (1,2-SiMe_2)_2{η^5-C_5H_2-4-((S)-CHEtCMe_3)}{η^5-C_5H-3,5-(CHMe_2)_2}ZrCl_2, (S)-2, was synthesized, and its use for the kinetic resolution of 3-methyl-substituted racemic α-olefins was investigated. Upon activation with methyl aluminoxane (MAO), selectivity factors for most olefins were greater when (S)-2 was used as the catalyst as compared to its previously reported methylneopentyl analogue, (1,2-SiMe_2)_2{η^5-C_5H_2-4-((S)-CHMeCCMe_3)}{η^5-C_5H-3,5-(CHMe_2)_2}ZrCl_2, (S)-1. Pentad analysis of polypropylene produced by the two catalysts at various propylene concentrations indicates that (S)-2 undergoes more efficient site epimerization (polymeryl chain swinging prior to subsequent monomer enchainment) at intermediate propylene concentrations compared to (S)-1. At high and low propylene concentrations, however, the two catalysts behave similarly. On the other hand, polymerization of 3,5,5-trimethyl-1-hexene at different olefin concentrations and temperatures illustrated that selectivity differences between the two catalysts are likely not a consequence of inefficient site epimerization for (S)-1.

Additional Information

© 2008 American Chemical Society. Received 31 July 2007. Published online 25 April 2008. Published in print 1 May 2008. This work was supported by USDOE Office of Basic Energy Sciences (Grant No. DE-FG03-85ER13431) and the National Science Foundation (Grant No. CHE-0131180). We thank Professors Steve Miller and Jay Labinger for help with the statistical modeling of polymerizations of propylene with catalysts (S)-1 and (S)-2. We would also like to thank Dr. Larry Henling and Dr. Mike Day for their work in solving the X-ray crystal structure of (S)-2 and Steven Baldwin for help with the characterization of some of the compounds.

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