期刊
ORGANOMETALLICS
卷 35, 期 1, 页码 47-54出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.organomet.5b00866
关键词
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资金
- SABIC Netherlands
- NSERC [RGPIN 04766-14]
- Dutch Polymer Institute [641]
Growing chain orientational preference is one of the key factors determining the stereoselectivity of olefin polymerization and related 'reactions such as carboalumination; alpha-agostic interactions are an important component of this preference. Using insertion of ethene in the M-CH3 bond as a model, the intrinsic orientational preference was evaluated for a number of important catalyst types through determination of the energy profile for methyl group rotation at the insertion TS. Ti and Zr metallocenes show a pronounced preference (Ti, 10 kcal/mol; Zr, similar to 6 kcal/mol) for a classical alpha-agostic arrangement with a single short M center dot center dot center dot CH contact and an elongated C-H bond; on CH3 rotation the agostic elongation mostly disappears. In contrast, for all non-metallocene systems studied the orientational preference is much smaller or even opposite that of metallocenes. Moreover, on CH3 rotation the agostic C-H bond elongation gets spread out over two C-H bonds rather than disappearing. These results point to greater chain orientation flexibility for nonrnetallocene catalysts.
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