Green synthesis of bimetallic MIL-100(Fe,Cu) MOFs and their catalytic application in an aerobic Baeyer–Villiger oxidation of cyclic ketones

Baeyer–Villiger oxidation is an efficient method of synthesizing value-added esters or lactones by inserting of an oxygen atom into ketones. Inexpensive bimetallic MIL-100(Fe,Cu) catalysts are prepared with a green and mild experimental technique. The catalysts have been comprehensively characterized and tested their catalytic performance of aerobic Baeyer–Villiger oxidation. Screening experiments are conducted to evaluate the effects of reaction time, temperature, the molar ratio of benzaldehyde to cyclohexanone, and catalyst mass on the oxidation of cyclohexanone. Surprisingly, it is observed that a catalyst in a ratio of 6:1 (Fe to Cu) exhibits high catalytic activity (99 % cyclohexanone conversion and 99 % ε-caprolactone yield). The scope of substrates indicates that the screened catalyst demonstrates moderate to high activity for five- and six-membered cyclic ketones. Furthermore, the prepared catalyst is thermally stable and exhibits significant recycling activity (>96 %). The reaction mechanism and the role of the catalyst are clarified through computational study. The catalyst can first trap and activate O₂ to oxidize benzaldehyde towards benzoyl peroxy acid. Significantly, the high catalytic activity would be attributed to the copper-modulated morphology of the catalyst. The activation energy is estimated to be 19 kcal/mol in the kinetic experiments. Consequently, we have developed an inexpensive MIL-100(Fe,Cu) catalyst via a green synthetic method for an aerobic Baeyer-Villiger oxidation of cyclic ketones to lactones.