A Unified Mechanism to Account for Manganese- or Ruthenium-Catalyzed Nitrile alpha-Olefinations by Primary or Secondary Alcohols: A DFT Mechanistic Study
A Unified Mechanism to Account for Manganese- or Ruthenium-Catalyzed Nitrile alpha-Olefinations by Primary or Secondary Alcohols: A DFT Mechanistic Study
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伯醇或仲醇锰或钌催化的腈 α-烯烃化的统一机制：DFT 机制研究
DOI：
10.1002/chem.201806016
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Wang Zhi Xiang
中科院分区：
文献类型：
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作者：
Lu Yu;Zhao Ruihua;Guo Ji;ong;Liu Zheyuan;Menberu Wasihun;Wang Zhi Xiang
无受体双偶联（ADC）反应通常涉及亲核试剂（例如，胺）作为偶联配体。有趣的是，已经报道了腈也可以在ADC反应中充当亲核试剂，通过分别使用锰或钌钳形络合物作为催化剂来实现腈与伯醇或仲醇的α-烯烃化。虽然已经假设了两种催化体系的不同机制，但本文报道的我们的DFT机理研究的结果使我们能够提出一种统一的机制来解释两种腈α-烯烃化。反应分四个阶段进行，即醇脱氢，腈活化生成亲核金属物质，醛或酮与金属物质偶联形成C−C键并将腈（Cα−）H原子转移到羰基，以及通过将质子（N−）H转移到羟基进行脱水。偶联阶段的一个显著特征是水或醇的活化，得到具有OH−或OR−-样基团的中间体，其活化腈Cα−H键。此外，该机制甚至可以应用于碱（KOtBu，由（KOtBu）4簇）催化的腈与酮的Knoevenagel缩合反应，这进一步表明了该机制的普遍性以及金属钳配合物与（KOtBu）4碱的相似性。我们期望这些深入的机理见解以及金属钳形络合物与（KOtBu）4簇的相似性的发现可以帮助开发新的ADC反应。
Acceptorless dehydrogenative coupling (ADC) reactions generally involve a nucleophile (e.g., amine) as a coupling partner. Intriguingly, it has been reported that nitriles could also act as nucleophiles in ADC reactions, achieving the α‐olefination of nitriles with primary or secondary alcohols by employing a manganese or ruthenium pincer complex as the catalyst, respectively. Although different mechanisms have been postulated for the two catalytic systems, the results of our DFT mechanistic study, reported herein, have allowed us to propose a unified mechanism to account for both nitrile α‐olefinations. The reactions take place in four stages, namely alcohol dehydrogenation, nitrile activation to generate a nucleophilic metal species, coupling of an aldehyde or ketone with the metal species to form a C−C bond and to transfer a nitrile (Cα−)H atom to the carbonyl group, and dehydration by transferring the protonic (N−)H to the hydroxy group. A notable feature of the coupling stage is the activation of water or alcohol to give an intermediate featuring an OH−‐ or OR−‐like group that activates a nitrile Cα−H bond. Moreover, the mechanism can even be applied to the base (KOtBu, modeled by the (KOtBu)4cluster)‐catalyzed Knoevenagel condensation of nitriles with ketones, which further indicates the generality of the mechanism and the resemblance of the metal pincer complexes to the (KOtBu)4base. We expect these in‐depth mechanistic insights and the finding of the resemblance of the metal pincer complexes to the (KOtBu)4cluster could assist the development of new ADC reactions.