Primary Amine Functionalized N‑Heterocyclic Carbene Complexes of Iridium: Synthesis, Structure, and Catalysis

The square-planar iridium­(I) complex [Ir­(cod)­(C–NH2)]­PF6 (3·PF6) containing a primary amine based N-heterocyclic carbene ligand (C–NH2) ligand was synthesized by a transmetalation reaction of the nickel­(II) complex [Ni­(C–NH2)2]­(PF6)2 (1) with [Ir­(cod)­Cl]2 (cod = 1,5-cyclooctadiene). An addition reaction of HCl with 3·PF6 afforded a mixture of two isomers of the octahedral iridium­(III) hydrido chloride complex [IrHCl­(cod)­(C–NH2)]­PF6 (5). One of the isomers, 5-cis-HCl, was found to have a rare geometry containing trans-H–Ir–NH2 and cis-H–Ir–Cl moieties. All of these iridium complexes were tested in the hydrogenation of molecules with unsaturated bonds. They are active catalysts in the H2-hydrogenation of acetophenone, with activity superior to that of the phosphine–amine (P–NH2) complex [Ir­(cod)­(P-NH2)]­PF6 (4) and half-sandwich complexes [Ir­(C5Me5)­(C–NH2)­Cl]­PF6 (2a) and [Ir­(C5H5)­(C-NH2)­Cl]­PF6 (2b). Complex 3·PF6, however, was ineffective as a catalyst for the hydrogenation of trans-α-methylstilbene and N-(1-phenylethylidene)­aniline.