Mechanistic insights into the ruthenium-catalyzed site-selective oxidation of alcohols

Abstract

The site-selective oxidation of alcohols has attracted extensive research interest due to its potential application in the conversion of natural products to value-added chemicals. Herein, the mechanism of the ruthenium-catalyzed site-selective Oppenauer-type oxidation of alcohols has been systematically investigated by DFT calculations. It was found that this reaction proceeds via an inner-sphere pathway, which involves the formation of the Ru–alkoxide complex, the β-H elimination (which generates a Ru–H complex and ketone), the hydride transfer from the Ru–H complex to acetone, and the protonation of isopropoxide. It was found that both the β-H elimination and the protonation of isopropoxide can be the rate-determining steps, depending on the properties of the substrate. Large steric hindrance and low electron density around the hydroxyl group would increase the barrier of β-H elimination, while an adjacent coordinating group has the opposite effect. Meanwhile, the relative stability of the oxidation product also weighs on the overall barrier. All the above factors contribute to the selectivity of the hydroxyls in different environments. In addition, the reactive site in a polyhydroxy complex is well predicted, demonstrating the potential of theoretical conclusions in practical applications.