Lewis Acid Enhanced Dioxygen Activation by Iron (II) Complex for Short‐ to Middle‐Length Aliphatic Aldehyde Oxidations to the Corresponding Acids

Efficient catalytic oxidation through dioxygen activation under gentle conditions is a long‐standing challenge in industry. The present work introduces a catalytic oxidation of short‐ to middle‐length aliphatic aldehydes to the corresponding acids through Lewis acid enhanced dioxygen activation by iron (II) complex. It was found that the presence of a modest Lewis acid such as Ca (OTf) 2 could substantially improve the catalytic efficiency, and an unusual odd‐even effect in catalysis was observed for the corresponding acid formation. The quenching experiments with 1,4‐benzoquinone indicated that the iron (III) superoxo species, which is the primary active oxygen species after dioxygen activation, was one of the key active oxygen species for the oxidation. The promotional effect of Ca (OTf) 2 was attributed to its electrostatic interaction with the iron (III) superoxo species, that is, LFe III ‐O 2 ‐• ···Ca 2+ , which stabilized this intermediate, thus drove dioxygen activation to its formation and improved the catalysis. A simplified mechanism was proposed to rationalize this Lewis acid enhanced dioxygen activation by iron (II) complex for aliphatic aldehyde oxidations to the corresponding acids.