Comparison of Epoxidation and Baeyer−Villiger Reaction Pathways for Ti(IV)−H2O2 and Sn(IV)−H2O2

Density functional theory has been used to study model epoxidation and Baeyer−Villiger reaction mechanisms for Ti(IV)−H2O2 and Sn(IV)−H2O2 catalytic oxidation systems. The titanium and tin catalysts have been modeled with unconstrained single coordination sphere clusters using a B3LYP/ECP methodology. Activation of hydrogen peroxide via formation of a metal hydroperoxo intermediate proceeds with similar energetics over titanium and tin. The overall reaction kinetics for epoxidation of either ethylene or 2,3-dimethyl-1-butene are also similar for Ti(IV)−H2O2 and Sn(IV)−H2O2. The intrinsic reaction rate for Baeyer−Villiger oxidation of either acetone or 2-methyl-3-pentanone is approximately 5 orders of magnitude slower with Ti(IV)−H2O2 than with Sn(IV)−H2O2. The greater Lewis acidity of tin relative to titanium enhances adsorption of the ketone substrate on the metal active site and reduces the rate-determining activation barrier for Baeyer−Villiger rearrangement of the chelated Criegee intermediate. These calculations provide insight into experimental results obtained previously for the oxidation of unsaturated ketones with hydrogen peroxide using titanium- and tin-containing redox molecular sieve catalysts.