Halogen photoreductive elimination from metal-metal bonded iridium(II)-gold(II) heterobimetallic complexes

Article abstract of DOI:10.1021/ic902590u

Halogen oxidation of [Ir^IAu^I(dcpm) ₂(CO)X](PF₆) (dcpm = bis(dicyclohexylphosphino)methane, X = Cl, Br) and [Ir^IAu^I (dppm)₂(CN ^tBu)₂](PF₆)₂ (dppm = bis(diphenylphosphino)methane) furnishes the heretofore unknown class of d ⁷-d⁹ compounds comprising an Ir^IIAu ^II heterobimetallic core. A direct metal-metal bond is evident from a 0.2 A 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 σ → σ* transition that possesses significant ligand-to-metal charge transfer (LMCT) character. Accordingly, these compounds are non-emissive but photoreactive. Excitation of Ir^IIAu^II complexes in the presence of a halogen trap prompts a net photoreductive elimination of halogen and the production of the two-electron reduced Ir^IAu^I species with about 10% quantum efficiency. The Ir^IIAu^II complexes add to a growing library of d⁷-d⁹ heterobimetallic species from which halogen elimination may be driven by a photon.