Mechanistic implications of kinetic data for the acid-catalysed dissociation of a tetraazamacrocyclic ligand complex of nickel(II)

Abstract

The dissociation kinetics of [NiL]²⁺(L = 2,4,4,10,12,12-hexamethyl-1,5,9,13-tetraazacyclohexadeca-1,9-diene) has been studied spectrophotometrically in 0.10–2.25 mol dm^–3 HClO₄ at 25 °C. The reaction scheme (i) is followed with k₁= 1.4 × 10^–4[H⁺]+ 1.1 × 10^–5 s^–1, k_–1=(9.2 × 10^–5[NiL]²⁺ [graphic omitted] Ni²⁺+ H_nLⁿ⁺(i) 8.8 × 10^–4[H⁺]/(1 + 24[H⁺]) s^–1, K_H= 24 dm³ mol^–1 and k₂=(1.9 × 10^–5+ 6.7 × 10^–4[H⁺]+ 3.8 × 10^–5[H⁺]²)/(1 + 24[H⁺]). Possible pathways for the cleavage and reformation of the Ni–N bonds, the factors influencing the dissociation rates, and the factors affecting the relative importance of each of the pathways are discussed.