The present work prepared a copper N-heterocyclic carbene complex that could be used in catalyzing the homogeneous hydrogenation of carboxylic acid with ammonia borane (hydrogen source) to synthesize primary alcohols. Various aromatic and aliphatic carboxylic acids with diverse functional groups were transformed to respective alcohols in moderate to high yields. The process can be easily scaled up (TON up to 14545) and exhibit a high compatibility with different sensitive functional groups, including fluorine, chlorine, bromine, iodine, hydroxyl, cyano and nitro groups. IMesCuCl/NH3·BH3 combination can selectively reduce aromatic and aliphatic esters. Mechanistic studies indicate that Cu-H species produced in situ are the active intermediates.

Herein, we present a method for the homogeneous hydrogenation of nitroarenes to produce aromatic amines using low catalyst loading (1 mo%) of air-stable copper N-heterocyclic carbene complexes as the catalyst and ammonia borane as the source of hydrogen. A wide range of nitroarenes, featuring diverse functional groups, were selectively transformed into their corresponding primary aromatic amines with high yields. This process can be readily scaled up and exhibits compatibility with various sensitive functional groups, including halogen, trifluoromethyl, aminomethyl, alkenyl, cyano, ester, amide, and hydroxyl. Notably, this catalytic methodology finds application in the synthesis of essential drug compounds. Mechanistic investigations suggest that the in-situ-generated Cu-H species may serve as active intermediates, with reduction pathways involving species such as azobenzene, 1,2-diphenylhydrazine, nitrosobenzene, and N-phenylhydroxylamine.