Investigation of the coordination chemistry of multidentate azine Schiff-base ligands towards d6 half-sandwich metal complexes

Abstract

The reaction of multidentate azine Schiff-base ligands was investigated towards d6 half-sandwich metal complexes. Tetradentate azine ligand L1 reacts with [(arene)MCl2]2 (arene = p-cymene, Cp*; M = Ru, Rh and Ir) in 1:2 or 1:1 M ratio to give mononuclear complexes having formula [(arene)M{L1к3(N,N′,N´´)}]2+ whereas the reaction of one equivalent of [(arene)MCl2]2 with four fold excess of hexadentate azine ligand L2 afforded mononuclear complexes bearing formula [(arene)M{L2к2(N,N′)}]+. The reaction of L2 with [(p-cymene)RuCl2]2 in 1:1 M ratio gave dinuclear complex [(p-cymene)2Ru2Cl2L2к4(N,N′,N´´,N´´´)]2+ whereas the reaction of L2 with [Cp*MCl2]2 yielded two coordination isomers (dinuclear and mononuclear). The coordination isomers were separated by column chromatography and characterized by spectral and structural studies. In mononuclear complexes with ligand L1 it acted as tridentate chelating ligand coordinating metal center in a tridentate к3 fashion through both the pyridine and one azine nitrogen atom leading to the formation of five and six membered chelated rings. Ligand L2 in mononuclear complexes coordinated metal in a bidentate к2 mode coordinating through both the pyridine nitrogen's whereas in dinuclear complexes L2 acted as tetradentate bridging ligand coordinating both metal atoms in a bidentate к2 fashion through pyridine nitrogen's thus forming a six membered metallacycle with both the metal centers. In the other isomer of rhodium and iridium complexes L2 acted as tridentate chelating ligand having bonding properties similar with complexes of ligand L1.