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首页> 外文期刊>Chemistry: A European journal >Organolanthanide-mediated ring-opening Ziegler polymerization (ROZP) of methylenecycloalkanes: A theoretical mechanistic investigation of alternative mechanisms for chain initiation of the samarocene-promoted ROZP of 2-phenyl-1-methylenecyclopropane
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Organolanthanide-mediated ring-opening Ziegler polymerization (ROZP) of methylenecycloalkanes: A theoretical mechanistic investigation of alternative mechanisms for chain initiation of the samarocene-promoted ROZP of 2-phenyl-1-methylenecyclopropane

机译：亚甲基有机锡介导的亚甲基环烷烃的开环齐格勒聚合（ROZP）：由三茂铁促进的2-苯基-1-亚甲基环丙烷的ROZP链引发的替代机理的理论机理研究

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摘要

A detailed theoretical investigation of alternative mechanisms for chain initiation of the organolanthanide-promoted ring-opening polymerization of 2-phenyl-1-methylenecyclopropane (PhMCP) with an archetypical [Cp2SmH] model catalyst is presented. Several conceivable pathways for important elementary steps, which also included ring-opening isomerization of PhMCP to phenylbutadienes, were critically scrutinized for a tentative course of the catalytic reaction. The operative mechanism starts with the first exomethylene C=C insertion into the SmH bond in a 1,2 fashion and is followed by shift-based β-alkyl eliminative cyclopropyl ring opening by cleavage of a proximal bond, while the alternative mechanism that commences with 2,1-insertion and subsequent ring opening by distal bond scission is revealed to be almost entirely precluded. The facile and irreversible insertion process is not found to occur in a regioselective fashion. Tne ring-opening process is analyzed as the critical step that discriminates between the two conceivable mechanisms. Opening of the cyclopropyl ring is kinetically easy and proceeds readily for the 1,2-insertion species, while a prohibitively large barrier must be overcome for ring opening of 2,1-insertion species. The isomerization of PhMCP in a ring-opened fashion, which would afford phenylbutadienes as possible products, is predicted to be a less likely process, owing to both kinetic and thermodynamic factors. The phenyl functionality has been demonstrated to distinguish between the regioisomeric ring-opening pathways, both kinetically and thermodynamically, thereby rendering this process selective with regard to the regiochemistry. Overall, chain initiation of the samarocene-mediated ring-opening polymerization of PhMCP is predicted to be a smooth, kinetically facile process.
机译：提出了详细的理论研究的替代机制，用典型的[Cp2SmH]模型催化剂，进行有机镧系元素促进的2-苯基-1-亚甲基环丙烷（PhMCP）开环聚合的链引发反应。重要的基本步骤的几种可能途径，包括PhMCP开环异构化为苯基丁二烯，也已严格审查了催化反应的初步过程。其作用机理始于将第一个Exomethyl C = C以1,2方式插入SmH键，然后通过裂解近端键而使基于移位的β-烷基消除环丙基开环，而替代机理始于几乎完全排除了2,1-插入和随后的远端键断裂造成的开环。没有发现以区域选择性方式发生容易且不可逆的插入过程。分析开环过程是区分这两种可能机制的关键步骤。环丙基环的打开在动力学上很容易，并且对于1,2-插入物种而言很容易进行，而2,1-插入物种的开环必须克服过大的障碍。由于动力学和热力学因素，PhMCP的开环异构化将产生苯丁二烯作为可能的产物，因此预计该过程不太可能发生。已证明苯基官能团可在动力学和热力学上区分区域异构体开环途径，从而使该过程对于区域化学具有选择性。总的来说，PhMCP的三茂铁介导的开环聚合的链引发预计是一个平稳，动力学上容易的过程。

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