Iron(II) reduction of trans-bis(dimethylglyoximato)halogeno-pyridinecobalt(III) complexes: kinetics and mechanism

Abstract

The iron(II) reduction of cobaloximes of the type trans-[Co(Hdmg)₂L(X)][Hdmg = dimethylglyoximate(1–); L = pyridine (py), nicotinamide (na) or isonicotinamide (isna), X = Cl, Br or I] was studied in 1%(v/v) dimethyl sulfoxide–water at 27 ± 0.1 °C and I= 0.25 mol dm^–3(LiClO₄) in the range [H⁺] 0.007–0.100 mol dm^–3 under pseudo-first-order conditions using an excess of the reductant. The inverse dependence of rate on [H⁺] suggests an equilibrium between the protonated and unprotonated forms of the complex, the protonated from reacting slower than the unprotonated form. The rate constants are in the order Cl^– < Br^– < I^– and py < na ≈ isna for the axial ligands.