Metal-oxo photooxidants. Crystal structure, spectroscopy and photophysical properties of neutral luminescent trans-dioxoosmium(VI) complexes with cyanide and mesityl ligands

Abstract

A series of neutral osmium(VI)-oxo complexes having mesityl (mes) and cyanide ligands have been prepared and the crystal structures of [OsVI(py)2(CN)2(O)2] (py = pyridine), [OsVI(tmen)(CN)2(O)2] (tmen = N,N,N′,N′-tetramethylethylenediamine), [OsVI(mes)2 (phen = 1,10-phenanthroline)] and [OsVI(mes)2(tmen)(O)2] determined. While [Os(mes)2(L-L)(O)2] (L-L = chelating aromatic diimines and diamines) are non-emissive, the related [Os(L-L)(CN)2(O)2], complexes have long-lived and emissive excited states in solution at room temperature. The [Os(4,4′-Me2bipy)(CN)2(O)2] (4,4′-Me2bipy = 4,4′-dimethyl-2,2′-bipyridine) complex has a E°(OsVI*-OsV) value of 1.77 V vs. normal hydrogen electrode and is capable of oxidizing alkenes to the corresponding epoxides upon irradiation with UV/VIS light at room temperature.