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DFT Studies on cis-14-Polymerization of Dienes Catalyzed by a Cationic Rare-Earth Metal Complex Bearing an Ancillary PNP Ligand

机译：DFT研究带有辅助PNP配体的阳离子稀土金属配合物催化的二烯的顺式14-聚合

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摘要

Dnsity functional theory (DFT) calculations have been carried out for the highly selective cis-1,4-polymerization of butadiene catalyzed by a cationic rare-earth metal complex bearing an ancillary PNP ligand. It has been found that the chain initiation and propagation of butadiene polymerization occurs via the favorable cis-1,4-insertion route. The trans-1,4 and 1,2-insertion are unfavorable both kinetically and thermodynamically. The chain growth follows the π-allyl-insertion mechanism. The analyses of energy decomposition of transition states indicate that the likelihood of rival insertion pathways is predominantly controlled by the interaction energy of butadiene with a metal center and the deformation energy of butadiene moiety. The electronic factor of the central metal has a decisive influence on the cis- vs. trans-insertion and the regioselectivity (cis-1,4- vs. cis-1,2-insertion) is mainly determined by steric hindrance. Tetrahydrofuran (THF) coordination made monomer insertion less favorable compared with THF-free case and had more noticeable impact on the trans-monomer insertion compared with the cis case. During the chain propagation, cis-insertion of monomer facilitates THF de-coordination and the THF molecule could therefore dissociate from the central metal.
机译：已经对带有辅助PNP配体的阳离子稀土金属络合物催化的丁二烯的高选择性顺式1,4-聚合进行了密度函数理论（DFT）计算。已经发现丁二烯聚合的链引发和扩散通过有利的顺式1，4-插入途径发生。反式1、4和1，2-插入在动力学和热力学上都是不利的。链增长遵循π-烯丙基插入机制。过渡态能量分解的分析表明，竞争插入途径的可能性主要由丁二烯与金属中心的相互作用能和丁二烯部分的变形能控制。中心金属的电子因子对顺式-反式插入有决定性的影响，区域选择性（顺式-1,4-顺式-1,2插入）主要由空间位阻决定。与无THF的情况相比，四氢呋喃（THF）配位使单体插入效果不佳，与顺式情况相比，四氢呋喃（THF）对反式单体的插入影响更大。在链增长过程中，单体的顺式插入会促进THF的去配位作用，因此THF分子可能会从中心金属上解离。

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