Chemoselective Transfer Hydrogenation of Nitroarenes with Ammonia Borane
Catalyzed by Copper N-heterocyclic Carbene Complexes
Abstract
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.