RoemelingMargoBiochemBiophysicsMechanisticInsightPeroxydisulfateSupportingInfo.pdf

Abstract

One-electron oxidation of the μ-oxo dimer (cis,cis-[Ruᴵᴵᴵ(bpy)₂(OH₂)]₂O⁴⁺, {3,3}) to {3,4} by S₂O₈²⁻ can be described by three concurrent reaction pathways corresponding to the three protic forms of {3,3}. Free energy correlations of the rate constants, transient species dynamics determined by pulse radiolysis, and medium and temperature dependencies of the alkaline pathway all suggest that the ratedetermining step in these reactions is a strongly nonadiabatic dissociative electron transfer within a precursor ion pair leading to the {3,4}|SO₄²⁻|SO₄•− ion triple. As deduced from the SO₄•− scavenging experiments with 2-propanol, the SO₄•− radical then either oxidizes {3,4} to {4,4} within the ion triple, effecting a net two-electron oxidation of {3,3}, or escapes in solution with ∼25% probability to react with additional {3,3} and {3,4}, that is, effecting sequential one-electron oxidations. The reaction model presented also invokes rapid {3,3} + {4,4} → 2{3,4} comproportionation, for which kcₒₘ ∼5 × 10⁷ M⁻¹ s⁻¹ was independently measured. The model provides an explanation for the observation that, despite favorable energetics, no oxidation beyond the {3,4} state was detected. The indiscriminate nature of oxidation by SO₄•− indicates that its fate must be quantitatively determined when using S₂O₈²⁻ as an oxidant