O2 Activation and Double C-H Oxidation by a Mononuclear Manganese(II) Complex

A Mn-II complex, [Mn(dpeo)(2)](2+) (dpeo= 1,2-di(pyridin-2-yl) ethanone oxime), activates O-2, with ensuing stepwise oxidation of the methylene group in the ligands providing an alkoxide and ultimately a ketone group. X-ray crystal-structure analysis of an intermediate homoleptic alkoxide Mn-III complex shows tridentate binding of the ligand via the two pyridyl groups and the newly installed alkoxide moiety, with the oxime group no longer coordinated. The structure of a Mn-II complex of the final ketone ligand, cis-[MnBr2(hidpe)(2)] (hidpe=2-(hydroxyimino)-1,2-di(pyridine-2-yl)ethanone) shows that bidentate oxime/pyridine coordination has been resumed. (H2O)-O-18 and O-18(2) labeling experiments suggest that the inserted O atoms originate from two different O-2 molecules. The progress of the oxygenation was monitored through changes in the resonance-enhanced Raman bands of the oxime unit.