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 [Os^VI(py)₂(CN)₂(O)₂](py = pyridine), [Os^VI(tmen)(CN)₂(O)₂](tmen =N,N,N′,N′-tetramethylethylenediamine), [Os^VI(mes)₂(phen = 1,10-phenanthroline)] and [Os^VI(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°(Os^VI*–Os^V) 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.