Homogeneous cobalt catalyzed reductive formylation of N-heteroarenes with formic acid

• A novel homogeneous cobalt complex for reductive formylation of N-heteroarenes to generate N-formyltetrahydroquinolines. • Formic acid as an abundant and easy to handle transfer hydrogenation reagent under cobalt catalysis. • Low catalyst loading, high efficiency and broad substrate scope. • Metal ligand cooperated dehydrogenation of formic acid. Herein, we report a cobalt N,N-bidentate complex catalyzed reductive formylation of N-heteroarenes for the generation of N-formyltetrahydroquinoline (FTHQ) derivatives, formic acid was employed as a transfer hydrogenation reagent that was safe, abundant and easy to handle. This work represented the first homogeneous system for reductive formylation of N-heteroarenes, the metal ligand cooperated dehydrogenation was the key to the success of this transformation. Deuteration labelling experiments and Hammet analysis were conducted and a plausible mechanism was suggested.