A Multisite Molecular Mechanism for Baeyer–Villiger Oxidations on Solid Catalysts Using Environmentally Friendly H₂O₂ as Oxidant

The molecular mechanism of the Baeyer-Villiger oxidation of cyclohexanone with hydrogen peroxide catalyzed by the Sn-beta zeolite has been investigated by combining molecular mechanics, quantum-chemical calculations, spectroscopic, and kinetic techniques. A theoretical study of the location of Sn in zeolite beta was performed by using atomistic force-field techniques to simulate the local environment of the active site. An interatomic potential for Sn/Si zeolites, which allows the simulation of zeolites containing Sn in a tetrahedral environment, has been developed by fitting it to the experimental properties of quartz and SnO2(rutile). The tin active site has been modeled by means of a Sn(OSiH3)3OH cluster, which includes a defect in the framework that provides the flexibility necessary for the interaction between the adsorbates and the Lewis acid center. Two possible reaction pathways have been considered in the computational study, one of them involving the activation of the cyclohexanone carbonyl group by Sn (1) and the other one involving hydrogen peroxide being activated through the formation of a tin-hydroperoxo intermediate (2). Both the quantum-chemical results and the kinetic study indicate that the reaction follows mechanism 1, and that the catalyst active site consists of two centers: the Lewis acid Sn atom to which cyclohexanone has to coordinate, and the oxygen atom of the Sn-OH group that interacts with H2O2 forming a hydrogen bond.