Extent of Structural Change during the Reaction and Its Relationship to Isoselectivity in Polypropylene Polymerization with ansa-Zirconocene/Borate Catalyst: A Computational Study
Extent of Structural Change during the Reaction and Its Relationship to Isoselectivity in Polypropylene Polymerization with ansa-Zirconocene/Borate Catalyst: A Computational Study
复制标题
使用柄型锆茂/硼酸盐催化剂进行聚丙烯聚合时，反应过程中结构变化的程度及其与同选择性的关系：计算研究
DOI：
10.1002/jcc.26040
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
and Y. Aoki
中科院分区：
文献类型：
--
作者：
Y. Orimoto;S. Shirane;and Y. Aoki
采用量子化学（QC）计算方法，对（R，R）-柄型二茂锆/硼酸盐催化体系聚合等规聚丙烯（iPP）的反应机理进行了研究。对于单体配位的四种可能的反应路径，即1，2-re、1，2-si、2，1-si和2，1-re，比较迁移插入的活化能Ea，直到第七单体插入步骤，明确包括硼酸根阴离子助催化剂。这表明，1，2-repath是最有利的，除了第一步，有利于1，2-si。在第一步反应中，1，2-sides的产物与1，2-repath的产物是构象异构体，1，2-sides特殊的可拆分性并不影响异构选择性。这些结果支持以前的研究，除了我们的研究结果解决了未经探索的第七插入步骤与硼酸根阴离子助催化剂通过QC计算。异构选择性与反应过程中整个体系的结构变化程度有关。详细的分析表明，与其它路径相比，1，2-重链的优势在于其空间位阻小，结构变化小.相反，在其他路径中涉及的系统中的较大排斥导致较大的结构变化以最小化结构应变。然而，由于强制四元环过渡态结构的结构限制，弛豫似乎不足。硼酸根阴离子助催化剂打破了二茂锆电子结构的C2对称性，导致单体插入的奇偶性。分子轨道分析表明，d-π轨道重叠可以解释烯烃配位的接近方向和二茂锆的弯曲结构，提供了与以往研究不同的观点。根据我们的研究结果，催化剂控制的潜力进行了讨论。© 2019 Wiley Periodicals，Inc.
The mechanism of isotactic polypropylene (iPP) polymerization with an (R,R)‐ansa‐zirconocene/borate catalyst system was analyzed using quantum chemistry (QC) calculations by focusing on the extent of structural change during monomer insertion. The activation energy for migratory insertion,Ea, was compared for four possible reaction paths with regard to monomer coordination, that is, 1,2‐re, 1,2‐si, 2,1‐si, and 2,1‐re, until the seventh monomer insertion step, explicitly including a borate anion cocatalyst. This indicated that the 1,2‐repath was most favorable, except for the first step, which favored 1,2‐si. As far as the first step, the product of 1,2‐siis a conformational isomer to that of the 1,2‐repath, and the exceptional favorability of 1,2‐sidoes not affect the isoselectivity. These results support previous studies, except that our results address the unexplored seventh insertion step with a borate anion cocatalyst by QC calculations. The isoselectivity correlated with the extent of structural change in the whole system during the reaction. It was proved from our detail analysis that the advantage of 1,2‐rewith a smallEais attributed to its smaller structural changes due to low steric repulsion in the system compared with other paths. Conversely, larger repulsion in the systems involved in other paths results in larger structural changes to minimize the structural strain. However, the relaxation appears insufficient due to structural restriction of the enforced four‐membered ring transition state structure. A borate anion cocatalyst broke theC2symmetry of the electronic structures of zirconocene, resulting in an odd–evenEafrequency for the monomer insertion. Molecular orbital analysis demonstrated that the d–π orbital overlaps can explain the approach direction of the olefin coordination and the bent structure of zirconocene, providing a different viewpoint from previous studies. The potential for catalyst control was discussed based on our results. © 2019 Wiley Periodicals, Inc.