C–O Bond Cleavage of Alcohols via Visible Light Activation of Cobalt Alkoxycarbonyls

A strategy for the activation of C–O bonds in alcohols via a carbonylation–homolysis–decarboxylation process is described. Using readily available cobalt­(II) porphyrin precursors, carbonylation of simple alcohols provides access to alkoxycarbonyl cobalt­(III) complexes. Spectroscopic, crystallographic, and computational methods are used to provide structural details and an estimate for the Co–C bond dissociation energy of an alkoxycarbonylcobalt­(III) complex of 39.8 kcal/mol for the first time. Visible light irradiation in the presence of the radical trapping agent TEMPO and a thiol reducing agent demonstrates the cleavage of the alcohol C–O bond under oxidative and reductive conditions, respectively. Addition of a stoichiometric reducing agent allows the use of a catalytic amount of hindered thiol for the reduction of a benzylic alcohol to the corresponding hydrocarbon.