Halogen Photoreductive Elimination from Metal-Metal Bonded Iridium(II)-Gold(II) Heterobimetallic Complexes

Halogen oxidation of [(IrAuI)-Au-I(dcpm)(2)(CO)X](PF6) (dcpm = bis(dicyclohexylphosphino)methane, X = Cl, Br) and [(IrAuI)-Au-I(dppm)(2)((CNBu)-Bu-t)(2)](PF6)(2) (dppm = bis(diphenylphosphino)methane) furnishes the heretofore unknown class of d(7)-d(9) compounds comprising an (IrAuII)-Au-II heterobimetallic core. A direct metal-metal bond is evident from a 0.2 angstrom contraction in the intermetallic distance, as determined by X-ray crystallography. The photophysical consequence of iridium-gold bond formation, as elucidated by experimental and computational investigations, is an electronic structure dominated by a sigma -> sigma* transition that possesses significant ligand-to-metal charge transfer (LMCT) character. Accordingly, these compounds are non-emissive but photoreactive. Excitation of (IrAuII)-Au-II complexes in the presence of a halogen trap prompts a net photoreductive elimination of halogen and the production of the two-electron reduced (IrAuI)-Au-I species with about 10% quantum efficiency. The (IrAuII)-Au-II complexes add to a growing library of d(7)-d(9) heterobimetallic species from which halogen elimination may be driven by a photon.