Dioxygen activation and catalytic aerobic oxidation by a mononuclear nonheme iron(II) complex.

We have used dioxygen, not artificial oxidants such as peracids, iodosylarenes, and hydroperoxides, in the generation of a mononuclear nonheme oxoiron(IV) complex, [Fe(IV)(TMC)(O)]2+ (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), from its corresponding Fe(II) complex, [Fe(TMC)(CF3SO3)2]. The formation of oxoiron(IV) species by activating dioxygen was markedly dependent on iron(II) complexes and solvents, and this observation was interpreted with the electronic effect of iron(II) complexes on dioxygen activation to form oxoiron(IV) species. A catalytic aerobic oxidation of organic substrates was demonstrated in the presence of the [Fe(TMC)]2+ complex. By carrying out 18O-labeled water experiment, we were able to conclude that the oxidation of organic substrates was mediated by an oxoiron(IV) intermediate, not by a radical type of autoxidation process.