Synthesis of Secondary Amines from One-Pot Reductive Amination with Formic Acid as the Hydrogen Donor over an Acid-Resistant Cobalt Catalyst

Developing new heterogeneous non-noble metal catalysts to replace noble-metal catalysts in organic transformations is of high importance in modern synthetic chemistry. Herein, nitrogen-doped carbon embedded Co catalysts (abbreviated as Co@CN-T-AT, in which T represents the pyrolysis temperature, AT represents the acid-leaching process) were prepared through the simple pyrolysis of graphene oxide-supported cobalt-based zeolitic imidazolate-frameworks, followed by the acid-leaching process. The Co@CN-600-AT catalyst demonstrated the highest catalytic activity among the synthesized Co catalyst toward the reductive amination of carbonyl compounds with nitro compounds by transfer hydrogenation with formic acid as the hydrogen donor, which integrated three consecutive steps into a one-pot reaction. By applying this catalyst, structurally diverse secondary amines were produced in good to excellent yields without the reduction of other functional groups. The transfer hydrogenation of the imines (C═N bonds) was the rate-determining step. Furthermore, the catalyst was highly stable and could be reused without decrease of the catalytic activity.