Studies in nickel(IV) chemistry. Part 2. Kinetics of proton-assisted decomposition of tris(dimethylglyoximato)nickelate(IV) with concomitant intramolecular electron transfer in aqueous media

Abstract

The kinetics of proton-assisted decomposition of tris(dimethylglyoximato)nickelate(IV), [Ni(dmg)₃]^2–, with concomitant Intramolecular electron transfer forming bis(dimethylglyoximato)nickel(II) and/or hexa-aquanickel (II) have been studied. The values of pseudo-first-order rate constants (k_ad) corresponding to the solvent-assisted and proton-assisted decomposition satisfy the expression (1)k_ad=k_od+k_1dK_1H[H⁺]+k_2dK_1HK_2H[H⁺]²//_{1 +K1H[H⁺]+K1HK2H[H⁺]²}(1) at I= 0.57 and 0.25 mol dm^–3, where k_od, k_1d, and k_2d, respectively, refer to the pseudo-first-order rate constants for the solvent-assisted, first protonation-assisted, and second protonation-assisted decomposition paths, and K_1H and K_2H are the first and second protonation equilibrium constants of [Ni(dmg)₃]^2–. Results are interpreted in terms of a mechanism involving formation of protonated nickel(IV) species prior to axial ring-opening and concomitant Intramolecular electron transfer.