Cyclometalation of Secondary Benzyl Amines by Ruthenium(II) Complexes

Abstract

The cyclometalation of chiral secondary amines through ortho-metalation of an aryl group occurred readily with [(η6-benzene)RuCl2]2 in acetonitrile. Reasonable to good yields of the expected cationic products of the form [(η6-benzene)Ru(N−C)(NCMe)](PF6), in which N−C represents the cyclometalated ligands, were obtained with bis-(R)-phenylethylamine, bis-(R)-1-naphthylethylamine, and (2R,5R)-2,5-diphenylpyrrolidine. Variable proportions of the expected four diastereoisomers were found according to NMR studies. The stereochemistry of complexes was investigated by 2D NMR in solution and by X-ray diffraction of single crystals. The (S) configuration at the metal was generally associated with a δ conformation of the metallacycle, and conversely, the (R) configuration with the λ conformation.