A New Phenoxide Chelated Ir-III N-Heterocyclic Carbene Complex and Its Application in Reductive Amination Reactions

A new phenoxide chelated [Ir(NHC)Cp*Cl] (NHC = Nhetero cyclic carbene; Cp* = pentamethylcyclopentadienyl) complex (3) has been prepared by reaction of [IrCp*Cl-2](2) with an in situ prepared NHC-Ag complex in dichloromethane at ambient temperature. The Ir-III complex was stable toward air and moisture and was fully characterized by H-1, C-13 NMR, HRMS, and single-crystal X-ray diffraction. The new complex was found to be an active catalyst for transfer hydrogenative reductive amination under aqueous conditions with formate as hydrogen source as well as hydrogenative reductive amination reactions using H-2. Various carbonyl compounds such as aliphatic and aromatic ketones and aldehydes were successfully reacted with amines to give new amines. In comparison with transfer hydrogenative reductive amination, the reductive amination with H2 is faster and permits higher molar ratios of the substrate to the catalyst (S/C).