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Mechanistic Insights into Chromium-Catalyzed Ethylene Trimerization
ACS Catalysis ( IF 12.9 ) Pub Date : 2018-06-08 00:00:00 , DOI: 10.1021/acscatal.8b00468
Thilina Gunasekara 1, 2 , Jungsuk Kim 3 , Andrew Preston 1, 2 , D. Keith Steelman 1 , Grigori A. Medvedev 3 , W. Nicholas Delgass 3 , Orson L. Sydora 4 , James M. Caruthers 3 , Mahdi M. Abu-Omar 2, 5
Affiliation  

The kinetics of ethylene trimerization by a chromium N-phosphinoamidine (Cr-(P,N)) precatalyst activated by modified methylaluminoxane (MMAO) has been investigated by high-pressure NMR techniques. An in-depth kinetic analysis of this metallacyclic mechanism has been conducted. It was found that an intermediate in the trimerization catalytic cycle, proposed in this study as the chromium alkenyl hydride species, degrades into a polymer active site where this degradation step is independent of ethylene concentration and is first order in catalyst. Additionally, we report that at least one of the first two ethylene coordination steps must be reversible in order to predict the features of the monomer consumption profiles. The reaction order in ethylene is dependent on the reversibility of the ethylene coordination steps. The observation of these details of the mechanism explains many of the challenges inherent in the examination of this and similar catalyst systems and emphasizes the usefulness of operando high-pressure NMR studies and a quantitative kinetic modeling approach in the study of such systems.

中文翻译:

铬催化乙烯三聚反应的机理分析

N-膦-(Cr-(P,N))已通过高压NMR技术研究了由改性甲基铝氧烷(MMAO)活化的预催化剂。已经对该金属环机理进行了深入的动力学分析。已经发现,在本研究中提出的三聚催化循环中的中间体称为氢化链烯基铬,可降解成聚合物活性位点,该降解步骤与乙烯的浓度无关,并且是催化剂的一级反应。此外,我们报告说,前两个乙烯配位步骤中的至少一个必须是可逆的,以便预测单体消耗曲线的特征。乙烯中的反应顺序取决于乙烯配位步骤的可逆性。
更新日期:2018-06-08
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