Structural diversity and solution behavior of low-valent iridium complexes bearing 1,4-diazabutadiene ligands

Three types of 1,4-diazabutadiene stabilized low-valent iridium complexes, namely [IrCl(cod)(MesDAB)] (1), [IrCl(coe)(MesDAB)] (2) and [IrCl(MesDAB)2] (3), have been prepared from 1,4-bis(2,4,6-trimethylphenyl)-1,4-diaza-1,3-butadiene (MesDAB) and [IrCl(cod)]2 or [IrCl(coe)2]2, respectively. The complexes have been investigated by NMR spectroscopy and X-ray diffraction experiments. While tetra-coordinated 2 and penta-coordinated 3 maintain their solid state structure in solution, penta-coordinated 1 shows fluxional behavior. The crystal structures determined indicate strong π-backbonding towards the MesDAB ligand in all cases.