Kinetics of reactions of pentane-2,4-dionato complexes of manganese(III) with glyoxylate anion in aqueous perchlorate media

Abstract

Glyoxylate (gox) catalyses the reduction of [Mn(pd)₃] to Mn^II in aqueous perchlorate media (pH 5.5–7.5) containing excess of pentane-2,4-dione (Hpd). In this process, 1 mol of Hpd, but no gox, is consumed per mol of Mn^III reduced. E.p.r. studies indicate the generation of a pd˙ radical in a cyclic redox process. The kinetically active manganese(III) species are [Mn(pd)₂(gox)] and [Mn(pd)₂(H₂O)(OH)]; [Mn(pd)₃] makes no appreciable contribution to the rate. The rate constants for the [Mn(pd)₂(gox)] and [Mn(pd)₂(H₂O)(OH)] paths are (1.27 ± 0.03)× 10^–4s^–1 and (9.58 ± 0.26)× 10^–2 dm³ mol^–1 s^–1 respectively while the formation constant for [Mn(pd)₂(gox)] from [Mn(pd)₂(H₂O)₂]⁺ and gox is 902 ± 42 dm³ mol^–1 at 30°C, I= 1.0 mol dm^–3. Inner-sphere paths seem reasonable.