Cyclometalation of primary benzyl amines by ruthenium(II), rhodium(III), and iridium(III) complexes

The cyclometalation of chiral and achiral primary amines occurred readily with Ru(II), Rh(III), and Ir(III) derivatives. Thus, the metalation of (R)-1-phenylethylamine by [(eta(6)-benzene)RuCl2](2), [(eta(5)-Cp*)RhCl2](2), and [(eta(5)-Cp*)IrCl2](2) was studied. Good yields of the expected cationic products in which the phenyl group was ortho-metalated were obtained for the rhodium and the ruthenium derivatives, whereas a mixture of products was formed in the case of the iridium complex. Benzylamine, (R)-1-phenylpropylamine, (R)-1-(1-naphthyl)ethylamine, and (R)-1-aminotetraline afforded also the cycloruthenation products whose general formula is [(eta(6)-benzene)Ru(N-C)(NCMe)]PF6 where N-C represents the ortho-metalated ligands. Substitution of the acetonitrile ligand by PMe2Ph occurred readily on the ruthenium complexes, affording stable compounds that were characterized by X-ray diffraction studies on single crystals, thus ascertaining the existence of the cycloruthenated five-membered rings. Accurate analyses of the structure of the complexes were implemented in solution and in the solid state. The (S) configuration at the metal was usually associated with a delta conformation of the metallacycle, and conversely, the (R) configuration with the lambda conformation. The study of the conformation of the five-membered rings revealed that the orientation of the NH2 group is such that one NH unit is oriented toward the eta(6)-benzene ring (roughly parallel to the Ru-centroid benzene vector), whereas the second NH is parallel to the Ru-L bond, L = NCMe or PMe2Ph.