RuIII(edta) complexes as molecular redox catalysts in chemical and electrochemical reduction of dioxygen and hydrogen peroxide: inner-sphere versus outer-sphere mechanism

The reduction of molecular oxygen (O-2) and hydrogen peroxide (H2O2) by [Ru-II(edta)(pz)](2-) (edta(4-) = ethylenediaminetetraacetate; pz = pyrazine) has been studied spectrophotometrically and kinetically in aqueous solution. Exposure of the aqua-analogue [Ru-II(edta)(H2O)](2-) to O-2 and H2O2 resulted in the formation of [Ru-III(edta)(H2O)](-) species, with subsequent formation of the corresponding Ru-V = O complex. A working mechanism for the O-2 and H2O2 reduction reactions mediated by the Ru-II(edta) complexes is proposed. The role of the coordinated water molecule (by its absence or presence in the primary coordination sphere) in controlling the mechanistic pathways, outer-sphere or inner-sphere, is discussed.

Automated summary

In this study, the reduction of molecular oxygen and hydrogen peroxide by [Ru-II(edta)(pz)](2-) was investigated in aqueous solution. The formation of [Ru-III(edta)(H2O)](-) species and subsequent Ru-V = O complex was observed. A proposed working mechanism for the O-2 and H2O2 reduction reactions mediated by the Ru-II(edta) complexes was discussed, along with the role of coordinated water molecules in controlling mechanistic pathways.