Light-mediated aerobic oxidation of C(sp3)–H bonds by a Ce(iv) hexachloride complex

Abstract

A photochemical C(sp³)–H oxygenation of alkane and arene substrates catalyzed by [NEt₄]₂[Ce^IVCl₆] under mild conditions (1 atm, 25 °C) is described. Time-course studies reveal that the hydrocarbons are oxidized in a stepwise fashion to afford alcohols, aldehydes, ketones, and carboxylic acids. The catalyst resting state, [Ce^IVCl₆]²⁻, is observed by UV-visible spectroscopy. On/off light-switching experiments, quantum yield measurements, and the absence of a kinetic isotope effect on parallel C–H/C–D functionalization suggest that ligand-to-metal charge transfer of [NEt₄]₂[Ce^IVCl₆] to generate Cl˙ is the turnover-limiting step. The involvement of a highly reducing excited-state [NEt₄]₃[Ce^IIICl₆]* species as well as photo-excited aldehyde, under black light irradiation appears to facilitate the conversion of primary alcohols and aldehydes to carboxylic acids. Remarkably, this approach is found to be capable of direct activation of light alkanes, including methane and ethane.