Catalysis of Cobalt Schiff Base Complexes for the Oxygenation of Olefins. Mechanisms for the Ketonization Reaction

Abstract

Cobalt Schiff base complexes are interesting because in aprotic solvents they exhibit dioxygenase-like activities as well as the reversible formation of dioxygen complexes. Our recent findings on oxidation-reduction reactions of cobalt Schiff base complexes, Co(L¹)-Co(L⁶), are now found to catalyze effeciently, in primary or secondary alcohols under an atmospheric pressure of O₂ at 60°C, the oxygenations of olefin substrates 1, 5, and 6, which result in ketonization without carbon-carbon bond cleavage (Table 1). In the Co(L¹)-catalyzed oxygenation of 1a in PhCH₂OH, a mixture composed of 2a, 3a, and PhCHO was obtained. Time course of the reaction proceeded as a co-oxidation of 1a and PhCH₂OH with with a 1:1 stoichiometry (98% selectivity).