KINETICS AND MECHANISM OF THE ACID DISSOCIATION OF COPPER(II) COMPLEXOF NOVEL C-FUNCTIONALIZED MACROCYCLIC DIOXOTETRAAMINES

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 decre ase the acid dissociation rates. The dissociation rate follows the law upsilon(d) = C(com)kK(1)K(2)H(2)/(1 + K1H + K1K2H2). On the intermedi ates we have obtained, the dissociation kinetics are interpreted by a mechanism involving the negatively charged carbonyl oxygen of the comp lex being rapidly protonated in a pre-equilibrium step, the rate-deter mining step being intramolecular hydrogen(enolic tautomer) migration(t o imine nitrogen). The dissociation rate reached a plateau in strongly acidic solution. By means of temperatures coefficient method, K-1, K- 2 of the pre-equilibrium step and Delta H-not equal and Delta S not eq ual of the rate-determining step were obtained and the results discuss ed. It is the strong in-plane ligand held that increased Delta H of th e rate-determining step and thus decreases the dissociation rate const ant. The Bronsted type linear free energy relationships do exist in th is C-functionalized dioxotetraamine copper(II) complex. The results cl arify insights into acid dissociation mechanisms for the 14-membered m acrocyclic dioxotetraamine copper(II) complex. (C) 1997 Published by E lsevier Science Ltd.