A Combined ab Initio MO−MM Study on Isotacticity Control in Propylene Polymerization with Silylene-Bridged Group 4 Metallocenes. C2 Symmetrical and Asymmetrical Catalysts
A Combined ab Initio MO−MM Study on Isotacticity Control in Propylene Polymerization with Silylene-Bridged Group 4 Metallocenes. C2 Symmetrical and Asymmetrical Catalysts
复制标题
甲硅烷基桥接第 4 族茂金属催化剂的全同立构规整度控制的从头开始 MO−MM 研究。
DOI：
10.1021/om9504009
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发表时间：
1996
期刊：
影响因子：
2.8
通讯作者：
K. Morokuma
中科院分区：
文献类型：
--
作者：
Tohru Yoshida;N. Koga;K. Morokuma
采用组合的从头算 MO−MM 方法评估了各种取代柄型茂金属丙烯聚合中的全同立构控制能力。控制过渡态全同立构规整度的空间能分为直接项（由于催化剂-烯烃相互作用而产生的空间能）和间接项（由于催化剂-聚合物和聚合物-烯烃相互作用而产生的空间能）。在第4族双(茚基)和双(四氢茚基)配合物中，由于中心金属的原子尺寸小，钛配合物通常比锆和铪类似物具有更好的产生全同立构序列的能力。为了获得良好的立体规整性，茚基茂金属的2-位和4-位上的取代基非常重要。然而，对拥挤的茚基催化剂的分析表明，虽然拥挤的过渡结构通常提供更好的立体控制，但过度拥挤可能会降低灵活性并降低立体调控差异。
The isotactic control capabilities in propylene polymerization of various substituted ansa-metallocenes are evaluated with a combined ab initio MO−MM method. Steric energy controlling the isotacticity at the transition state is divided into the direct term (steric energy due to the catalyst−olefin interaction) and the indirect term (steric energy due to the catalyst−polymer and polymer−olefin interaction). Among group 4 bis(indenyl) and bis(tetrahydroindenyl) complexes, titanium complexes in general have a substantially better capability of producing an isotactic sequence over zirconium and hafnium analogs, due to the small atomic size of the central metal. To attain good stereoregulation, the substituents at the 2- and 4-positions of the indenyl-based metallocene are very important. However, analysis among congested indenyl-based catalysts suggests that, though the crowded transition structures in general provide better stereocontrol, overcrowding could reduce flexibility and lower stereoregulatory discr...