Mono- and Bis(iminoxolene)iridium Complexes: Synthesis and Covalency in π Bonding

N-(2,6-Diisopropylphenyl)-4,6-di-tert-butyl-o-iminobenzoquinone (Diso) reacts with the (cyclooctadiene)iridium chloride dimer to form a monoiminoxolene complex, (Diso)­Ir­(cod)­Cl. Reaction of 2 equiv of the iminoquinone with chlorobis­(cyclooctene)­iridium dimer affords the bis-iminoxolene (Diso)₂IrCl. This five-coordinate complex adopts a distorted square pyramidal structure with an apical chloride ligand and undergoes halide exchange to form an air-stable iodide complex. (Diso)₂IrCl can be reduced by one electron to form neutral, square planar (Diso)₂Ir, while oxidation with PhICl₂ gives octahedral trans-(Diso)₂IrCl₂. The cis isomer can be prepared by air oxidation of (Diso)₂IrCl; cis/trans isomerization is not observed even on prolonged heating. Structural and spectroscopic features of the complexes are consistent with the presence of strong, covalent π bonding between the metal and the iminoxolene ligands, with structural data suggesting between 45 and 60% iridium character in the π bonding orbitals, depending on the ancillary ligands. The spectroscopic similarity of (Diso)₂Ir and (Diso)₂IrCl to their cobalt congeners suggests that the first-row metal complexes likewise have appreciably covalent metal-iminoxolene π bonds.