Additive-Mediated Selective Oxidation of Alcohols to Esters via Synergistic Effect Using Single Cation Cobalt...

The direct catalytic oxidation of alcohols to esters is very appealing, but the economical-friendly catalysis systems are not yet well established. Herein, we show that a pure inorganic ligand-supported single-atomic cobalt compound, (NH₄)₃[CoMo₆O₁₈(OH)₆] (simplified as CoMo₆), could be used as a heterogeneous catalyst and effectively promote this type of reaction in the presence of 30% H₂O₂ using KCl as an additive. The oxidative cross-esterification of various alcohols (aromatic and aliphatic) could be achieved under mild conditions in nearly all cases, affording the corresponding esters in high yields, including several drug molecules and natural products. Detailed studies have revealed that chloride ion is able to bind to the CoMo₆ to form a supramolecular dimer 2(CoMo₆∙Cl), which can effectively catalyze the reaction via a synergistic effect from chloride ion and CoMo₆. Mechanism studies and control reactions demonstrate that the esterification proceeds via the key oxidative immediate of aldehydes.