Kinetics of reduction of μ-amido-μ-superoxo-bis[tetraamminecobalt(III)]4+ complex with hydroxylamine derivatives

Hydroxylamine-N-monosulfonate (HAMS) and hydroxylamine-N,N′-disulfonate (HADS) react with the title superoxo complex 1 in acetate buffer media. In the presence of 3.0 mM dipicolinic acid, the decay of 1 follows first order kinetics in [1] and in the [reductant] but is inverse first order in [H+]. The observed first order rate constants (ko) decrease with increasing mol% of D2O in the solvent: kH2O/kD2OkH2O/kD2O 3.5 for HAMS and 1.6 for HADS. The H atom at the –OH end of a hydroxylamine derivative is essential for the reactions to occur. Each mole of HADS and HAMS reduces 3 mol of 1 to its hydroperoxo derivative 2 and is itself converted to SO42− and NO. Plots of ko versus [H+]−1 are linear with intercepts; intercepts yield the reactivity of 1 and the slopes give the reactivity of 1-H (1-H is the deprotonated form of 1) at 25 °C and ionic strength 1.0 mol L−1. HADS reacts faster than HAMS. The simplest possible mechanism has been suggested.

Graphical abstractThe μ-amido-μ-superoxo-bis[tetraamminecobalt(III)]4+ complex (1) deprotonates in the solution and, both 1 and its deprotonated form (1-H) are kinetically active towards the sulfonated hydroxylamine derivatives (hydroxylamine monosulfonate, HAMS and hydroxylamine disulfonate, HADS) via a PCET path.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Sulfonated hydroxylamine derivatives reduce the superoxo ion by the –OH end. ► Superoxo complex deprotonates in aqueous solution. ► Both superoxo and its deprotonated form are kinetically reactive. ► Reactions are proceed via a PCET path.