Aerobic Oxidation of Primary Alcohols Catalyzed by Copper Salts and Catalytically Active μ-Hydroxyl-Bridged Trinuclear Copper Intermediate

We have developed a new protocol involving the "copper(II) chloride-cesium carbonate" system for the aerobic oxidation of primary alcohols. Cesium carbonates and the solvents such as toluene and 1,2-dichloroethane play important roles to form a catalytically active intermediate containing a mu-hydroxyl-bridged trinuclear copper moiety (complex 1). From the X-ray crystal structure of complex 1, an electrostatic interaction between chloride anions and cesium cations was observed, which stimulated us to understand the roles of cesium carbonate in this reaction as a base, stabilizing and "solvating" intermediates in toluene and 1,2-dichloroethane.