Aerobic Electrochemical Oxygenation of Light Hydrocarbons Catalyzed by an Iron-Tungsten Oxide Molecular Capsule

The selective oxidation of light hydrocarbons and their valorization with only dioxygen (O₂) are important transformations toward development of efficient chemical processes. Monooxygenase enzymes can catalyze selective aerobic reactions under reducing and protic conditions. The translation of such enzymatic pathways to the practical electrocatalytic oxidation of light, gaseous hydrocarbons, using O₂ as sole oxidant is now reported. An iron-tungsten oxide inorganic molecular catalyst with a capsular structure {Fe₃₀W₇₂} stabilized inside by sulfate/bisulfate anions provides a protic environment where three iron atoms are located at each of the pores of the capsule leading to a unique and potent active site for the oxidation reactions. Under mild electrochemical conditions, 1.8 V, in water at room temperature, using O₂ from air, we demonstrate the low-pressure (1-2 bar) hydroxylation of alkanes, notably ethane to acetic acid, and the ozone like cleavage of the carbon-carbon double bonds of alkenes. Typical turnover frequencies were 300-400 min^-1. Initial mechanistic studies support a reaction through a very active iron-oxo species.