双金属促进的均相碳氢键活化反应(英文)

Bimetallic C―H Activation in Homogeneous Catalysis

近年来,过渡金属催化的碳氢键活化反应得到了快速的发展,已成为构建碳碳键及碳杂原子键的重要手段之一。利用双金属之间的协同效应,发展的双金属促进的碳氢键活化反应也引起了广泛的关注,并在均相催化领域里取得了良好的应用。双金属促进的碳氢键活化反应与单金属催化的碳氢键活化反应相比,能够表现出不同的化学选择性、区域选择性以及立体选择性,体现了其独特之处。本综述总结了各种双金属促进的碳氢键活化体系,同时依据实验和理论研究结果对可能的反应机理进行了探讨。

The strategy of transition-metal-catalyzed C―H activation has been greatly developed in recent years.Direct transformations of inert C―H bonds undoubtedly provide powerful ways to construct various C―C and C―X(X=heteroatom)bonds,with enhanced atom-and step-economy.Impressive efforts have been devoted to this research all along.However,concerns about reactivity and selectivity remain to be tackled,due to their strong dependence on directing groups and acidic reactive sites.In this regard,more effective catalytic systems are of great importance and therefore in high demand.Bimetallic C―H activation,by virtue of the cooperative effect,has emerged as a promising solution to this issue.The intriguing interactions between two metals with substrates afford exceptional reaction efficiency and selectivity.Intensive interest in both experimental and computational studies has been recently triggered.In this minireview,diverse bimetallic catalytic reactions are summarized into three categories according to the initiator in the C―H activation step,namely,bimetallic catalyses based on palladium,nickel,and other metals.Experimental results as well as density functional theory(DFT)calculations are invoked in the plausible mechanistic considerations.In the first part,collaborative modes based on palladium are described,in which magnesium,chromium,cobalt,and silver are successfully engaged as accessory partners.Most of them stabilize the C―H activation transition states by decreasing the energy,thus facilitating the cleavage of C―H bonds.Notably,some reactions previously reported as examples of monomeric palladium catalysis are now reinvestigated as bimetallic scenarios,in light of computational discussions.In the second part,reactions based on the synergy of nickel,and zinc or aluminum,are generalized,in which zinc or aluminum acts as a Lewis acid to increase the acidity of C―H bonds.It has been shown that the choice of different kinds of Lewis acids and ligands has a great influence on the reaction chemo-,regio-,and stereoselectivity.Gratefully,even enantioselective transformations can be achieved using the cooperation of nickel and aluminum.Moreover,a key reaction intermediate in the bimetallic C―H activation by nickel and aluminum has been isolated,providing guidance for this bimetallic catalytic system in further mechanistic studies and applications.In the last part,synergetic catalysis based on various other metals is presented.Bimetallic regimes of ruthenium/copper,rhodium/bismuth,iridium/aluminum,manganese/zinc,and zirconium/aluminum have been elegantly applied to C―H activation reactions.Multifarious action modes are proposed on account of the mechanistic research.