N -Alkylation and N -Methylation of Amines with Alcohols Catalyzed by Nitrile-Substituted NHC-Ir(III) and NHC-Ru(II) Complexes.

A series of nitrile-modified N -heterocyclic carbene (NHC) complexes of Ir(III) ( 2a - e ) and Ru(II) ( 3a - d ) have been prepared by transmetallation of [IrCp*Cl 2 ] 2 and [RuCl 2 ( p -cymene)] 2 forming an in situ NHC-Ag complex. The structures of all complexes were characterized by 1 H NMR, 13 C NMR, and Fourier transform infrared (FT-IR) spectroscopies. And the structures were clearly elucidated by performing X-ray diffraction studies on 2b , 3a , and 3c single crystals. The complexes of NHC-Ir(III) ( 2a - e ) and NHC-Ru(II) ( 3a - d ) were investigated in the N -alkylation reaction of aniline derivatives with benzyl alcohols to form N -benzyl amines and in the N -methylation reaction of aniline derivatives with methanol. Both reactions were performed in solvent-free media. The Ir(III) complexes ( 2a - e ) were found to perform essentially better than similar Ru(II) complexes ( 3a - d ) in the N -alkylation and N -methylation reactions. Among the Ir(III) complexes ( 2a - e ), the best results were obtained with 2b . The catalytic mechanisms of both reactions were revealed by 1 H NMR study. Formation of Ir-hydride species was observed for both reactions. This new report provides useful information to evaluate the activity of complexes and the differences in sensitivity between the NHCs.