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.

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