Computational mechanistic studies of acceptorless dehydrogenation reactions catalyzed by transition metal complexes
Computational mechanistic studies of acceptorless dehydrogenation reactions catalyzed by transition metal complexes
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DOI：
10.1360/zb2012-42-10-1487
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发表时间：
2012-09
期刊：
影响因子：
--
通讯作者：
Li Haixia;Wang Zhixiang
中科院分区：
文献类型：
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作者：
Li Haixia;Wang Zhixiang
无受体脱氢（AD）是一种无毒、无废物的催化反应，是走向绿色化学的重要途径。无受体醇脱氢（AAD）是构建新键（如C-C和C-N键）的关键步骤，其中醇需要活化成更具反应性的酮或醛。AD反应也可用于从生物质或其发酵产物（主要是醇）生产氢。可逆的氢化/脱氢和氢的吸收/释放是实现潜在的有机氢化物储氢的关键。本文综述了近年来各种过渡金属配合物催化AD反应的计算机理研究和实验进展。这些反应包括无受体的醇加成反应、含氮杂环的可逆脱氢/氢化反应、醇与胺形成C-N键的缩合偶联反应以及醇与不饱和底物形成C-C键的缩合偶联反应。对于具有金属-配体双功能活性中心的催化剂（如本文中的28、45、86、87和106），它们更倾向于“双功能双氢转移”机理，而不是普遍接受的b-H消除机理。然而，由铱络合物121催化的甲醇和丙二烯的C-C偶联反应中涉及的甲醇脱氢经由b-H消除机理发生，因为配体的对烯丙基部分或羧基的刘易斯碱性太弱而不能发挥高的刘易斯碱性反应性。揭示AD反应的催化机理有助于开发新的催化剂。
Acceptorless dehydrogenation (AD) that uses non-toxic reagents and produces no waste is a type of catalytic reactions toward green chemistry. Acceptorless alcohol dehydrogenation (AAD) can serve as a key step in constructing new bonds such as C-C and C-N bonds in which alcohols need to be activated into more reactive ketones or aldehydes. AD reactions also can be utilized for hydrogen production from biomass or its fermentation products (mainly alcohols). Reversible hydrogenation/ dehydrogenation with hydrogen uptake/release is crucial to realization of the potential organic hydride hydrogen storage. In this article, we review the recent computational mechanistic studies of the AD reactions catalyzed by various transition metal complexes as well as the experimental developments. These reactions include acceptorless alcohol dehydrogenations, reversible dehydrogenation/hydrogenation of nitrogen heterocycles, dehydrogenative coupling reactions of alcohols and amines to construct C-N bonds, and dehydrogenative coupling reactions of alcohols and unsaturated substrates to form C-C bonds. For the catalysts possessing metal-ligand bifunctional active sites (such as 28 , 45 , 86 , 87 , and 106 in the paper), the dehydrogenations prefer the “bifunctional double hydrogen transfer” mechanism rather than the generally accepted b-H elimination mechanism. However, methanol dehydrogenation involved in the C-C coupling reaction of methanol and allene, catalyzed by the iridium complex 121 , takes place via the b-H elimination mechanism, because the Lewis basicity of either the p-allyl moiety or the carboxyl group of the ligand is too weak to exert high Lewis basic reactivity. Unveiling the catalytic mechanisms of AD reactions could help to develop new catalysts.