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

Abstract

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.