Cobalt-Catalyzed Synthesis of Aromatic, Aliphatic, and Cyclic Secondary Amines via a “Hydrogen-Borrowing” Strategy

The replacement of precious metals with inexpensive, less toxic, and earth-abundant elements in typical noble-metal-mediated organic transformations is a major goal in current synthetic chemistry and industries. The metal-catalyzed N-alkylation of amines with other amines through a “hydrogen-borrowing” principle represents a green and atom-economical reaction for the synthesis of secondary amines. However, catalysts developed thus far that are effective for this process remain quite scarce and are only limited to a few ruthenium and iridium complexes. In this work, we present a cobalt-catalyzed selective alkylation of amines with amines to synthesize a large variety of secondary amines. A range of amine substrates have been converted to the corresponding products through hetero- or homocoupling between amines. Cyclic sec-amines are also achieved from diamine precursors as rare examples.