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

• Published in: Polyhedron 1998-01, Vol.17 (25), p.4331-4337
• Main Authors: Lin, Huakuan, Zhu, Shourong, Kondiano, Appolin Bave, Su, Xuncheng, Kou, Fuping, Chen, Yunti
• Format: Article
• Language: English
• Subjects: acid dissociation; copper(II) complex; kinetics; macrocyclic dioxotetraamines; mechanism
• ISSN: 0277-5387
• DOI: 10.1016/S0277-5387(98)00199-5

The kinetics of the acid dissociation of copper(II) complexes of novel C-functionalized macrocyclic dioxotetraamines has been studied by means of a stopped-flow spectrophotometer. The acid dissociation rate follows the law V d = C com kK 1 K 2 H 2 /(1+ K 1 H+ K 1 K 2 H 2 ). From the experimental facts 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 the strongly acidic solution. By means of temperature coefficient method, Δ H φ , Δ S φ of the pre-equilibrium step and Δ H ≠, Δ S ≠ of the rate-determining step were obtained. The results of 13-membered macrocyclic dioxotetraamines have been discussed. The influence of the substituents to the acid dissociation rates has also been discussed. The Bronsted type linear free energy relationships do also exist in these C-functionalized dioxotetraamine copper(II) complexes.