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) 2 IrCl. 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) 2 IrCl can be reduced by one electron to form neutral, square planar (Diso) 2 Ir, while oxidation with PhICl 2 gives octahedral trans -(Diso) 2 IrCl 2 . The cis isomer can be prepared by air oxidation of (Diso) 2 IrCl; 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) 2 Ir and (Diso) 2 IrCl to their cobalt congeners suggests that the first-row metal complexes likewise have appreciably covalent metal-iminoxolene π bonds.