OXYGEN-TRANSFER REACTIONS OF METHYLRHENIUM OXIDES

Methylrhenium dioxide, CH3ReO2 (or MDO), is produced from methylrheniu m trioxide, CH3ReO3 (or MTO), and hypophosphorous acid in acidic aqueo us medium. Its mechanism is discussed in light of MTO's coordination a bility and the inverse kinetic isotope effect (kie): H2P(O)OH, k = 0.0 28 L mol(-1) s(-1); D2P(O)OH, k = 0.039 L mol(-1) s(-1). The Re(V) com plex, 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 th e first oxygen abstraction from perchlorate to give chlorate, with a s econd-order rate constant at pH 0 and 25 degrees C of 7.3 L mol(-1) s( -1). Organic oxygen-donors such as sulfoxides and pyridine N-oxides ox idize MDO to MTO as do metal oxo complexes: VO(aq)(2+), VO2(aq)(+), HO MoO2 (aq), and MnO4-. The reaction between V-(aq)(2+), With MTO and th e reduction of VO2+ with MDO made it possible to determine the free en ergy for MDO/MTO. Oxygen-atom transfer from oxygen-donors to MDO invol ves nucleophilic attack of X-O on the electrophilic Re(V) center of MD O; the reaction proceeds via an [MDO . XO] adduct, which is supported by the saturation kinetics observed for some. The parameters that cont rol 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.