DFT Mechanistic Study of RuII-Catalyzed Amide Synthesis from Alcohol and Nitrile Unveils a Different Mechanism for Borrowing Hydrogen

Abstract

Using RuII complex as a mediator, Hong and co-workers recently developed a redox-neutral synthetic strategy to produce amide from primary alcohol and nitrile with complete atom economy. Intrigued by the novel strategy, we performed DFT computations to unravel the catalytic mechanism of the system. The transformation is catalyzed by RuIIH2(CO)(PPh3)(IiPr) (IiPr = 1,2-diisopropylimidazol-2-ylidene) via four stages including nitrile reduction, alcohol dehydrogenation, C–N coupling, and amide production. Generally, alcohol dehydrogenation in dehydrogenative coupling (DHC) or borrowing hydrogen methodology (BHM) takes place separately, transferring the Hα and hydroxyl HOH atoms of alcohol to the catalyst to form the catalyst-H2 hydride. Differently, the alcohol dehydrogenation in the present system couples with nitrile hydrogenation; alcohol plays a reductant role to aid nitrile reduction by transferring its HOH to nitrile N atom directly and Hα to the catalyst and meanwhile becomes partially oxidized. In our ...