Kinetics and mechanisms of reduction of a sexidentate di(oxime–imine) complex of nickel(IV) with two-electron reductants, 1,2-di-hydroxybenzene and 1,4-dihydroxybenzene

Abstract

The kinetics and mechanisms of reduction of a nickel(IV) di(oxime–imine) complex, [Ni^IVL]²⁺(H₂L = 3,14-dimethyl-4,7,10,13-tetra-azahexadeca-3,13-diene-2,15-dione dioxime), by 1,2-dihydroxybenzene (H₂Z) and 1,4-dihydroxybenzene (H₂Q) are reported. Both reactions proceed by consecutive one-electron transfers and kinetic traces are biphasic with quantitative formation of nickel(III) intermediates, [Ni^IIIL]⁺ and [Ni^III(HL)]²⁺ depending on the pH. The dominant pathways for reduction of both nickel(IV) and nickel(III) involve the reductant anions HZ^– and HQ^–. Reactions of nickel(IV) are outer-sphere in nature while those of nickel(III) proceed by an inner-sphere pathway. Preliminary results on the oxidation of the corresponding nickel(II) complex by thallium(III) indicate that no detectable intermediate oxidation-state species is formed in this reaction.