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

摘要

Halogen oxidation of [(Ir~IAu~I)(dcpm)_2(CO)X](PF_6) (dcpm = bis(dicyclohexylphosphino)methane, X = Cl, Br) and [(Ir~IAu~I)(dppm)_2((CN~tBu)_2](PF_6)_2 (dppm = bis(diphenylphosphino)methane) furnishes the heretofore unknown class of d~7-d~9 compounds comprising an (Ir~(II)Au~(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~(II)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 (Ir~IAu~I) species with about 10% quantum efficiency. The (Ir~(II)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.