Mechanistic and Kinetic Studies of the Ring Opening Metathesis Polymerization of Norbornenyl Monomers by a Grubbs Third Generation Catalyst
Mechanistic and Kinetic Studies of the Ring Opening Metathesis Polymerization of Norbornenyl Monomers by a Grubbs Third Generation Catalyst
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DOI：
10.1021/jacs.9b09752
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发表时间：
2019-11-06
影响因子：
15
通讯作者：
Guironnet, Damien
中科院分区：
文献类型：
--
作者：
Hyatt, Michael G.;Walsh, Dylan J.;Guironnet, Damien
研究了Grubbs第三代预催化剂[（H（2）IMes）（pyr）（2）（Cl）（2）Ru=CHPh]引发的一系列功能化双烯基单体的开环易位聚合（ROMP）机理。通过一系列的C-12/C-13和H-1/H-2动力学同位素效应研究，确定聚合的速率控制步骤是金属环丁烷环的形成。通过密度泛函理论计算进一步验证了这一实验结果，表明最高能量的过渡态是金属环丁烷的形成。研究了两种酯取代单体的立体化学（exo vs endo）对聚合物性能的影响。动力学和光谱证据支持形成的六元螯合物通过协调的近端聚合物酯的Ru中心。这种螯合作用及其对聚合速率的影响显示出根据所采用的单体及其立体化学而变化。这些知识的结合导致了描述由Grubbs第三代催化剂引发的异戊二烯单体的聚合速率的通用速率定律的推导。
The mechanism of ring-opening metathesis polymerization (ROMP) for a set of functionalized norbornenyl monomers initiated by a Grubbs third generation precatalyst [(H(2)IMes)(pyr)(2)(Cl)(2)Ru=CHPh] was investigated. Through a series of C-12/C-13 and H-1/H-2 kinetic isotope effect studies, the rate -determining step for the polymerization was determined to be the formation of the metallacyclobutane ring. This experimental result was further validated through DFT calculations showing that the highest energy transition state is metallacyclobutane formation. The effect of monomer stereochemistry (exo vs endo) of two types of ester substituted monomers was also investigated. Kinetic and spectroscopic evidence supporting the formation of a six-membered chelate through coordination of the proximal polymer ester to the Ru center is presented. This chelation and its impact on the rate of polymerization are shown to vary based on the monomer employed and its stereochemistry. The combination of this knowledge led to the derivation of a generic rate law describing the rate of polymerization of norbornene monomers initiated by a Grubbs third generation catalyst.