Nickel-Catalyzed Transfer Hydrogenation of Benzonitriles with 2-Propanol and 1,4-Butanediol as the Hydrogen Source

The homogeneous transfer hydrogenation of benzonitrile with 2-propanol or 1,4-butanediol produced N -benzylidene benzylamine (BBA, 85% yield) using 5 mol % [Ni(COD) 2 ] as a catalytic precursor and a mixture of Cy 2 P(CH 2 ) 2 PCy 2 and Cy 2 P(CH 2 ) 2 P(O)Cy 2 as ancillary ligands, under mild reaction conditions (120 °C, 96 h, tetrahydrofuran). 1,4-Butanediol performed better than 2-propanol as a hydrogen donor and yielded γ-butyrolactone as the product of transfer dehydrogenation. Selectivity toward dibenzylamine (DBA, 62% yield) was achieved by varying the amount of 1,4-butanediol in the catalytic system. A reaction mechanism was proposed, involving a ligand-assisted O-H bond activation, end-on substrate coordination, and a key dihydrido-Ni(II) intermediate, leading to the in situ formation of primary imines and amines to ultimately yield the secondary imines observed.