Additive-Mediated Selective Oxidation of Alcohols to Esters via Synergistic Effect Using Single Cation Cobalt Catalyst Stabilized with Inorganic Ligand.

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.