Rapidly initiating ruthenium olefin-metathesis catalysts
Rapidly initiating ruthenium olefin-metathesis catalysts
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DOI：
10.1002/anie.200461374
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发表时间：
2004-01-01
影响因子：
16.6
通讯作者：
McDonald, R
中科院分区：
文献类型：
--
作者：
Romero, PE;Piers, WE;McDonald, R
烯烃歧化反应是化学合成中最有力的碳-碳键断裂和生成反应。[1]根据反应伙伴的性质，烯烃歧化反应可用于开环聚合(ROMP)，[2]可用于制造先进的聚合物材料，[3]可用于将非环二烯底物转化为复杂的环状有机分子(在闭环歧化反应(RCM)中)[4]或聚合物(在非环二烯歧化反应(ADMET)中)[5]或在交叉复分解反应(CM)中生成不对称的烯烃。而CM依靠最简单的烯烃--乙烯的消除作为热力学驱动力。[8，9]烯烃歧化反应单独使用或与其他合成反应一起使用，是现代合成化学家的一种通用方法。人们普遍认为，需要一个金属卡宾物种，{LNM=CRR‘}，与烯烃底物相互作用，通过2+2环加成生成四元金属环丁烷中间体或过渡态{LNM(CRR’)3}；该中间体的裂解与其形成的相反意义导致烯烃歧化反应，产生新的碳-碳双键，并重新生成活性金属卡宾。金属卡宾通常被归类为在卡宾碳原子上的亲核(富电子)或亲电(贫电子)性质，但有效的烯烃歧化催化剂表现出介于这两个极端之间的行为。两类经过精心调整的介体已发展成为烯烃歧化反应的首选催化剂。Schrock催化剂[10，11]是钼或钨基烷基烯，具有一套相当特定的配位体，旨在调节卡宾的性质(图1)。这些催化剂表现出高活性和稳定性，但对环境空气和湿度敏感，相对不能容忍极性官能团。格拉布斯催化剂产品组合[12]由多种基于Ru的体系组成。
Olefin metathesis is arguably the most powerful carbon–carbon bond breaking and making reaction in chemical synthesis.[1] Depending on the nature of the reacting partners, olefin metathesis can be used for ring-opening polymerization (ROMP),[2] to create advanced polymeric materials,[3] transformation of acyclic diene substrates into complex cyclic organic molecules (in ring-closing metathesis (RCM))[4] or polymers (in acyclic diene metathesis (ADMET))[5] or in cross metathesis (CM) to generate unsymmetrical olefins.[6, 7] Although olefin metathesis is fully reversible, RCM, ADMET, and CM rely on the elimination of ethylene, the simplest olefin, as a thermodynamic driving force. Used by itself or in tandem with other synthetic transformations,[8, 9] olefin metathesis is a versatile method for the modern synthetic chemist.It is generally acknowledged that a metal carbene species,{LnM= CRR’}, is required and that interaction with an olefin substrate leads to four-membered metallacyclobutane intermediates or transition states,{LnM (CRR’) 3}, by a 2+ 2 cycloaddition; cleavage of this intermediate in the opposite sense by which it was formed leads to olefin metathesis, creating a new carbon–carbon double bond and regenerating an active metal carbene. Metal carbenes are generally classified as being nucleophilic (electron rich) or electrophilic (electron poor) in character at the carbene carbon atom, but an effective olefin-metathesis catalyst exhibits behavior between these two extremes. Two carefully tuned classes of mediator have evolved into the catalysts of choice for olefin metathesis. Schrock catalysts [10, 11] are molybdenum-or tungsten-based alkylidenes with a fairly specific ligand set designed to modulate the properties of the carbene (Figure1). These catalysts display high activities and stabilities, but are sensitive to ambient air and moisture and are relatively intolerant of polar functionalities. The Grubbs-catalyst portfolio [12] consists of a variety of ruthenium-based systems of