Enantioselective reduction of prochiral ketones promoted by amino amide ruthenium complexes: A DFT study

The origin of enantioselectivity in the reaction of chiral Ru amino amide complexes in the asymmetric transfer hydrogenation of acetophenone was investigated using DFT calculations. For the most stable active catalysts, the full free energy profiles for the reaction were calculated according to the concerted hydrogen transfer mechanism. We succeeded in reproducing the experimentally observed enantioselectivity for the studied Ru amino amide complexes. Our results indicate that the high enantioselectivity can be explained by a stabilizing CH-pi interaction existing between the phenyl group of acetophenone and the aromatic substituent of the catalyst, which plays a significant role in selectivity. Finally, our results show that important insights can be obtained with such a theoretical approach not simply to explain the origin of the reaction asymmetry but also to predict the enantiomeric excess. This can help experimentalists to design new enantioselective catalysts. (C) 2021 Published by Elsevier B.V.