The nitrile hydration reaction mechanism catalyzed by a MnI(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 MnI 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 MnI(NH)-OH complex.
Prejano, M., Alberto, M., Russo, N., Marino, T. (2020). Hydration of aromatic nitriles catalyzed by Mn-OH complexes: A rationalization from quantum chemical investigations. ORGANOMETALLICS, 39(18), 3352-3361 [10.1021/acs.organomet.0c00436].
Hydration of aromatic nitriles catalyzed by Mn-OH complexes: A rationalization from quantum chemical investigations
Alberto, ME;
2020
Abstract
The nitrile hydration reaction mechanism catalyzed by a MnI(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 MnI 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 MnI(NH)-OH complex.
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