The nitrile hydration reaction mechanism catalyzed by a Mn^I(NH)-OH complex has been elucidated by means of DFT computations, first exploring three mechanistic hypotheses experimentally suggested in the literature and then proposing a novel catalytic cycle proceeding along a combination of two pathways, suitable to describe the whole process. The results show that the reaction proceeds through a nucleophilic attack by the hydroxide to the Mn-coordinated nitrile substrate, leading to amide formation, ultimately released as the iminol tautomer upon a Mn–N to Mn–O switching step. A rapid tautomerization to yield the amide product closes the cycle. An explanation of the enhancement of the experimental turnover number (TON) with the electron-withdrawing properties of the substituents was also provided by comparing the free energy profiles obtained for the hydration of benzonitrile (PhCN), p-N-dimethylbenzonitrile (NMe₂PhCN) and p-trifluoromethylbenzonitrile (CF₃PhCN) substrates, which nicely combines experimental and theoretical results. In addition, to introduce a further advance in this novel field and to gain useful insights for the design of more efficient Mn^I catalysts, a newly designed Mn(NCH₃)-OH complex is investigated herein and proposed for the nitrile hydration reaction, interestingly showing an improved catalytic activity in comparison with the previous Mn^I(NH)-OH complex.

中文翻译：

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Mn-OH配合物催化芳香腈的水合：量子化学研究的合理化

Mn ^I催化腈水合反应机理（NH）-OH配合物已通过DFT计算得以阐明，首先探索了文献中实验上提出的三个机理假说，然后提出了一种新颖的催化循环，沿着两种途径的组合进行，适于描述整个过程。结果表明，该反应通过氢氧化物对Mn配位的腈底物的亲核进攻而进行，导致酰胺的形成，最终在Mn–N到Mn–O转换步骤中作为亚氨基互变异构体释放。快速互变异构产生酰胺产物结束了该循环。通过比较为苯甲腈（PhCN）的水合而获得的自由能曲线，还提供了用取代基的吸电子性质提高实验周转数（TON）的解释，p - Ñ -dimethylbenzonitrile（NME ₂ PHCN）和p -trifluoromethylbenzonitrile（CF ₃ PHCN）底物，其结合了很好的实验和理论的结果。另外，为了在该新领域中引入进一步的进展并获得对设计更有效的Mn ^I催化剂有用的见识，本文对新设计的Mn（NCH ₃）-OH配合物进行了研究，并提出了用于腈水合反应的方法。与以前的Mn ^I（NH）-OH配合物相比，具有更高的催化活性。