The violet superoxo complex, [(H20)4(OH)Rh11r(02)Rh111(OH) (H20)4I3+, formed by treatment of (Rh11)24+ with 0 2 in HC104, is converted to a le-reduction product, the corresponding p-peroxo complex, by the reductants I-, IrCls3-, and the trinuclear aquamolybdenum(II1) cation, (MOrrr)3. Each reaction is firstorder in both redox partners, and the le-reduction by IrCls3-is followed by a much slower conversion to a peroxide-free complex. Among the rapid reductions of the superoxo derivative examined here and in a previous study, only that by IrClc3is accelerated by increases in acidity; the rate law for this reaction features both an acid-independent and a [H+l-proportional component, the latter stemming from partial conversion of the oxidant to its conjugate acid (PKA < -1.0). Rate laws for reductions by other metal-center reagents generally exhibit inverse-[H+] terms, reflecting deprotonation of the reductant. All reductions thus far observed involving this superoxo species appear to be outer-sphere. Treatment of acid-independent rate constants within the framework of the Marcus model, allows estimates of the self-exchange rate, K11, for the (Rhrrr)2-bound superoxo-peroxo couple. Because values of k11 calculated from the several reductions span a range of 104.5, reductions of the superoxo complex cannot be taken to conform satisfactorily to the Marcus treatment, being in this respect comparable to the systems VO(OH)+/2+, MI?+'^+, Eu2+l3+, and Ti(OH)2+/3+, each of which exhibits similar divergences. The wide range of calculated self-exchange rates appears to invalidate an earlier suggestion that reduction of the superoxo complex by Fez+ proceeds primarily through a bridged path.