Pyridyl azine Schiff-base ligands exhibiting unexpected bonding modes towards ruthenium, rhodium and iridium half-sandwich complexes: Synthesis and structural studies

Abstract

The reaction of multidentate azine Schiff-base ligands was investigated towards p-cymene ruthenium, Cp*Rh and Cp*Ir complexes. The reaction of [(arene)MCl2]2 (arene = p-cymene, Cp*; M = Ru, Rh and Ir) with azine Schiff-base ligands (L1-L3) in 1:2 M ratio led to the formation of mononuclear complexes of the type [(arene)M(L)Cl]+ whereas the reaction of [Cp*MCl2]2 (M = Rh/Ir) with azine Schiff-base ligands (L1-L3) in 1:1 M ratio afforded dinuclear rhodium and iridium complexes bearing formula [{Cp*MCl}2(μ-L)]+ (M = Rh/Ir). The ligands in dinuclear complexes exhibited interesting coordination modes towards the metal atom. The reaction of ligand L3 with [Cp*IrCl2]2 dimer yielded two coordination isomers whereas with [Cp*RhCl2]2 yielded exclusively one isomer. The molecular structure of both the isomers of the iridium complex has been established. In rhodium and iridium complexes the ligand L3 acted as uninegative pentadentate bridging ligand coordinating one metal center in a tridentate fashion and the other metal in a bidentate fashion. In the other isomer the ligand L3 behaved as uninegative tetradentate bridging ligand coordinating both iridium centers in a bidentate fashion. In the mononuclear complexes, the ligands are coordinated to the metal atom in a bidentate N∩N fashion through pyridine nitrogen and azine nitrogen. The ligand (L1 and L2) acted as tetradentate bridging ligand in dinuclear complexes. All these complexes were isolated and characterized by spectroscopic and analytical techniques.