Epoxidation of Alkenes with H2O2 Catalyzed by Dititanium‐Containing 19‐Tungstodiarsenate(III): Experimental and Theoretical Studies

Abstract

AbstractEpoxidation of a range of alkenes with aqueous H2O2 easily proceeds in the presence of the dititanium‐containing 19‐tungstodiarsenate(III) [Ti2(OH)2As2W19O67(H2O)]8– (1), which contains five‐coordinate Ti atoms. The results of product and kinetics studies support a mechanism that involves a reversible interaction between H2O2 and the Ti–OH group of 1 to produce a titanium hydroperoxo complex followed by electrophilic oxygen atom transfer from the hydroperoxo ligand to the alkene substrate in the rate‐limiting step. The effect of the alkene substrate nature has been investigated at the DFT level. A clear correlation between the energy of πC=C orbitals in the alkene and the turnover frequency values has been found, thereby indicating that the higher nucleophilicity of the alkene, the higher the reactivity. ONIOM (ONIOM = our own n‐layered integrated molecular orbital and molecular mechanics) calculations have been employed to evaluate the role of steric effects of alkene substituents. The calculations show that the steric bulk can play a secondary role and tunes the activity in specific cases such as trans‐stilbene.