Examining the Effects of Monomer and Catalyst Structure on the Mechanism of Ruthenium-Catalyzed Ring-Opening Metathesis Polymerization.
Examining the Effects of Monomer and Catalyst Structure on the Mechanism of Ruthenium-Catalyzed Ring-Opening Metathesis Polymerization.
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DOI：
10.1021/jacs.9b08835
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发表时间：
2019-10
影响因子：
15
通讯作者：
W. Wolf;Tzu-Pin Lin;R. Grubbs
中科院分区：
文献类型：
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作者：
W. Wolf;Tzu-Pin Lin;R. Grubbs
利用两种具有不同空间构型的N-杂环卡宾(NHC)配体的第三代Ru催化剂，详细研究了Ru催化开环歧化聚合(ROMP)的反应机理。实验证据表明，在使用这些快速引发催化剂的情况下，降冰片烯单体的聚合机理依赖于单体，聚合物与Ru中心发生了螯合作用。一系列的动力学实验，包括ROMP的速率测量、引发速率的测量、单体相关的动力学同位素效应和活化参数，有助于区分螯合和非螯合单体，并确定螯合作用对聚合机理的影响。络合金属环的形成是由NHC的空间主体和单体的几何构型共同推动的，导致基态稳定，减缓了聚合速度，也改变了共聚中Ru中心对不同单体的反应性。本文的结果补充了烯烃复分解反应的机理工作，并可能为ROMP催化剂的继续设计提供参考，以获得新的聚合物结构和材料。
The mechanism of Ru-catalyzed ring-opening metathesis polymerization (ROMP) is studied in detail using a pair of third generation ruthenium catalysts with varying sterics of the N-heterocyclic carbene (NHC) ligand. Experimental evidence for polymer chelation to the Ru center is presented in support of a monomer-dependent mechanism for polymerization of norbornene monomers using these fast-initiating catalysts. A series of kinetic experiments, including rate measurements for ROMP, rate measurements for initiation, monomer-dependent kinetic isotope effects, and activation parameters were useful for distinguishing chelating and nonchelating monomers and determining the effect of chelation on the polymerization mechanism. The formation of a chelated metallacycle is enforced by both the steric bulk of the NHC and by the geometry of the monomer, leading to a ground-state stabilization that slows the rate of polymerization and also alters the reactivity of the propagating Ru center toward different monomers in copolymerizations. The results presented here add to the body of mechanistic work for olefin metathesis and may inform the continued design of catalysts for ROMP to access new polymer architectures and materials.