Kinetics and mechanism of the acid dissociation of copper (II) complex of novel C-functionalized macrocyclic dioxotetraamines

Article abstract of DOI:10.1016/S0277-5387(96)00516-5

The kinetics of the acid dissociation of copper(II) complex of a novel C-functionalized macrocyclic dioxotetraamine has been studied using a stopped-flow spectrophotometer. It was proven that substituents decrease the acid dissociation rates. The dissociation rate follows the law v_d = C_comkK₁K₂H²/ (1 + K₁H + K₁K₂H²). On the intermediates we have obtained, the dissociation kinetics are interpreted by a mechanism involving the negatively charged carbonyl oxygen of the complex being rapidly protonated in a pre-equilibrium step, the rate-determining step being intramolecular hydrogen(enolic tautomer) migration(to imine nitrogen). The dissociation rate reached a plateau in strongly acidic solution. By means of temperatures coefficient method, K₁, K₂ of the pre-equilibrium step and ΔH≠ and ΔS≠ of the rate-determining step were obtained and the results discussed. It is the strong in-plane ligand field that increased ΔH of the rate-determining step and thus decreases the dissociation rate constant. The Broensted type linear free energy relationships do exist in this C-functionalized dioxotetraamine copper(II) complex. The results clarify insights into acid dissociation mechanisms for the 14-membered macrocyclic dioxotetraamine copper(II) complex.