Mechanisms of reduction of trans-cyclohexane-1,2-diamine-NNN′N′-tetra-acetatomanganate(III) by hydrazine, hydroxylamine, and substituted benzene-1,2-diols

Abstract

The kinetics and mechanism of reduction of trans-cyclohexane-1,2-diamine-NNN′N′-tetra-acetatomanganate(III), [Mn^III(cdta)(H₂O)]^–, by hydrazine, hydroxylamine, and a series of substituted benzene-1,2-diols C₆H₃(OH)₂R (R = H, 4-Me, 4-CO₂H, or 3-CO₂H) have been investigated by the stopped-flow technique. Simple first-order dependence on Mn^III complex and reductant concentrations has been observed for hydrazine, which shows a rate with [H⁺]^–1 dependence. For hydroxylamine, complex kinetic dependences on reductant and hydrogen-ion concentration suggest a composite inner-sphere mechanism. Also, in the case of the diols an inner-sphere mechanism, through intermediate association, is proposed; for these substrates experimental rates, higher than those computed with the Marcus cross relation, and limiting kinetics are in agreement with the lability of the oxidizing complex.