Mechanistic study of the co-ordination of hydrogen peroxide to methylrhenium trioxide

Abstract

The activation parameters (ΔH^‡, ΔS^‡, ΔV^‡) for the co-ordination of hydrogen peroxide to methylrhenium trioxide have been determined. They indicate a mechanism involving nucleophilic attack. The protons lost in converting H₂O₂ to a co-ordinated η²-O₂^2– group are transferred to one oxide oxygen, which remains on the metal as an aqua ligand. The rate of reaction is not pH dependent, consistent with the deuterium kinetic isotope effect (k_H/k_D= 2.8). The method used to study the reaction is based on the ability of ReMeO₃ to catalyse the reaction between Br^– and H₂O₂. The activation parameters for the uncatalysed reaction of Br^– and H₂O₂ were also determined. The value found for ΔV^‡ is consistent with the accepted mechanism, proton-assisted nucleophilic displacement.