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

The kinetics of the acid dissociation of copper(II) complexed of novel C-fu nctionalized macrocyclic dioxotetraamines has been studied by means of a st opped-flow spectrophotometer. The acid dissociation rate follows the law V- d = C(com)kK(1)K(2)H(2)/(1 + K1H + K1K2H2). From the experimental facts we have obtained, the dissociation kinetics are interpreted by a mechanism inv olving the negatively charged carbonyl oxygen of the complex being rapidly protonated in a pre-equilibrium step, the rate-determining step being intra molecular hydrogen (enolic tautomer) migration (to imine nitrogen). The dis sociation rare reached a plateau in the strongly acidic solution. By means of temperature coefficient method, Delta H-phi, Delta S-phi of the pre-equi librium step and Delta H-not equivalent to, Delta S-not equivalent to of th e rate-determining step were obtained. The results of 13-membered macrocycl ic dioxotetraamines have been discussed. The influence of the substituents to the acid dissociation rates has also been discussed. The Bronsted type l inear flee energy relationships do also exist in these C-functionalized dio xotetraamine copper(II) complexes. (C) 1998 Elsevier Science Ltd. All right s reserved