Oxygen-Transfer Reactions of Methylrhenium Oxides

Methylrhenium dioxide, CH 3 ReO 2 (or MDO), is produced from methylrhenium trioxide, CH 3 ReO 3 (or MTO), and hypophosphorous acid in acidic aqueous medium. Its mechanism is discussed in light of MTO's coordination ability and the inverse kinetic isotope effect (kie): H 2 P(O)OH, k = 0.028 L mol - 1 s - 1; D 2 P(O)OH, k = 0.039 L mol - 1 s - 1 . The Re(V) complex, MDO, reduces perchlorate and other inorganic oxoanions (XO n -, where X = Cl, Br, or I and n = 4 or 3). The rate is controlled by the first oxygen abstraction from perchlorate to give chlorate, with a second-order rate constant at pH 0 and 25 °C of 7.3 L mol - 1 s - 1 . Organic oxygen-donors such as sulfoxides and pyridine N -oxides oxidize MDO to MTO as do metal oxo complexes: VO 2+ (aq), VO 2 + (aq), HOMoO 2 + (aq), and MnO 4 - . The reaction between V 2+ (aq) with MTO and the reduction of VO 2+ with MDO made it possible to determine the free energy for MDO/MTO. Oxygen-atom transfer from oxygen-donors to MDO involves nucleophilic attack of X−O on the electrophilic Re(V) center of MDO; the reaction proceeds via an [MDO·XO] adduct, which is supported by the saturation kinetics observed for some. The parameters that control and facilitate the kinetics of such oxygen-transfer processes are suggested and include the force constant for the asymmetric stretching of the element−oxygen bond.