Modulation of Isomerization and Ligand Exchange Rates by π Bonding in Bis(iminoxolene)iridium Pyridine Complexes.

The bis(iminoxolene)iridium complex (Diso)IrCl (Diso = -(2,6-diisopropylphenyl)-4,6-di--butyl-2-imino--benzoquinone) reacts with pyridine to give -(Diso)Ir(py)Cl as the kinetic product, with -(Diso)Ir(py)Cl formed as the exclusive thermodynamic product upon heating. Electronic spectra and density functional theory calculations point to very similar electronic structures for the cis and trans isomers, with a nonbonding iminoxolene-centered HOMO and a metal-iminoxolene π* LUMO. The triplet states of -(Diso)Ir(py)Cl and -[(Diso)Ir(py)] (but not -(Diso)Ir(py)Cl) are unusually low in energy (1000-1500 cm above the singlets), as shown by variable-temperature NMR spectroscopy.