A Non-Heme Iron Photocatalyst for Light-Driven Aerobic Oxidation of Methanol

Non-heme (L)Fe-III and (L)Fe-III-O-Fe-III(L) complexes (L=1,1-di(pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)-ethan-1-amine) underwent reduction under irradiation to the Fe-II state with concomitant oxidation of methanol to methanal, without the need for a secondary photosensitizer. Spectroscopic and DFT studies support a mechanism in which irradiation results in charge-transfer excitation of a Fe-III-mu-O-Fe-III complex to generate [(L)Fe-IV=O](2+) (observed transiently during irradiation in acetonitrile), and an equivalent of (L)Fe-II. Under aerobic conditions, irradiation accelerates reoxidation from the Fe-II to the Fe-III state with O-2, thus closing the cycle of methanol oxidation to methanal.