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首页> 外文期刊>Chemistry: A European journal >Mechanistic investigation of the ruthenium-N-heterocyclic-carbene-catalyzed amidation of amines with alcohols
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Mechanistic investigation of the ruthenium-N-heterocyclic-carbene-catalyzed amidation of amines with alcohols

机译：钌-N-杂环卡宾催化胺与醇酰胺化反应的机理研究

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摘要

The mechanism of the ruthenium-N-heterocyclic-carbene-catalyzed formation of amides from alcohols and amines was investigated by experimental techniques (Hammett studies, kinetic isotope effects) and by a computational study with dispersion-corrected density functional theory (DFT/M06). The Hammett study indicated that a small positive charge builds-up at the benzylic position in the transition state of the turnover-limiting step. The kinetic isotope effect was determined to be 2.29(±0.15), which suggests that the breakage of the C-H bond is not the rate-limiting step, but that it is one of several slow steps in the catalytic cycle. Rapid scrambling of hydrogen and deuterium at the α position of the alcohol was observed with deuterium-labeled substrates, which implies that the catalytically active species is a ruthenium dihydride. The experimental results were supported by the characterization of a plausible catalytic cycle by using DFT/M06. Both cis-dihydride and trans-dihydride intermediates were considered, but when the theoretical turnover frequencies (TOFs) were derived directly from the calculated DFT/M06 energies, we found that only the trans-dihydride pathway was in agreement with the experimentally determined TOFs. On the right pathway: Experimental and theoretical investigations indicate that the Ru-catalyzed amidation of amines with alcohols (see scheme) proceeds by alcohol coordination, β-hydride elimination, nucleophilic attack, and β-hydride elimination to the amide.
机译：通过实验技术（Hammett研究，动力学同位素效应）和色散校正的密度泛函理论（DFT / M06）的计算研究，研究了钌-N-杂环卡宾催化由醇和胺形成酰胺的机理。 。 Hammett研究表明，在周转限制步骤的过渡态中，苄基位置会积累少量正电荷。确定的动力学同位素效应为2.29（±0.15），这表明C-H键的断裂不是限速步骤，而是催化循环中几个缓慢的步骤之一。用氘标记的底物观察到氢和氘在醇的α位上的快速加扰，这表明催化活性物质是二氢化钌。通过使用DFT / M06表征可能的催化循环，为实验结果提供了支持。顺式-二氢化物和反式-二氢化物中间体均被考虑，但是当理论周转频率（TOFs）直接从计算出的DFT / M06能量中推导时，我们发现只有反式-二氢化物途径与实验确定的TOF一致。在正确的途径上：实验和理论研究表明，Ru催化的胺与醇的酰胺化反应（参见方案）是通过醇配位，β-氢化物消除，亲核攻击和β-氢化物消除酰胺而进行的。

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