Collect. Czech. Chem. Commun. 2008, 73, 258-274

Kinetic Study of Dissociation of a Copper(II) Complex of A 14-Membered Tetraaza-Macrocyclic Ligand Containing Pyridine and Pendant N-Carboxymethyl Arms

Přemysl Lubala,b,*, Anne-Marie Albrecht-Garyb, Sylvie Blancc, Judite Costad,e and Rita Delgadod,f,*

a Department of Chemistry, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic
b Laboratoire de Physico-Chimie Bioinorganique, UMR 7509 CNRS, ECPM, 25, rue Bequerel, 67200 Strasbourg, France
c Laboratoire de Chimie Theorique et Physico-Chimie Moleculaire, UMR 5624 CNRS, Université de Pau et des Pays de l'Adour, 2, rue Jules Ferryl, 64000 Pau, France
d Instituto de Tecnologia Química e Biológia, Universidade Nova de Lisboa, Apartado 127, 2781-901 Oeiras, Portugal
e Centro de Estudos de Ciencias Farmaceuticas, Faculdade de Farmácia de Lisboa, Av. Prof. Gama Pinto, 1649-003 Lisboa, Portugal
f Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal


The kinetics of acid-catalyzed dissociation of the copper(II) complex with 7-methyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene-3,11-diacetic acid (ac2Me[14]pyN4) at [H+] = 0.05-0.25 mol l-1, I = 0.25 mol l-1 (Na, H)ClO4, and T = 298.16 K was studied with conventional and stopped-flow UV/VIS spectroscopy. Three steps of consecutive complex reaction were observed. The very fast first and second steps characterized by k1 = 70 ± 10 and k2 = 0.23 ± 0.01 l mol-1 s-1 depend on the H+ concentration. The third step is very slow, k3 = (1.08 ± 0.03) × 10-3 s-1, and does not depend on the H+ concentration. Latter rate-determining step involves an isomerisation process forcing the copper(II) ion to leave rapidly the macrocyclic cavity. The reaction mechanism of the complex dissociation has been proposed, taking into account the results obtained for related systems by independent methods: potentiometry, UV/VIS and EPR spectroscopies, X-ray diffraction analysis, and molecular mechanics calculations.

Keywords: Copper(II) complexes; Pendant acetate arms; Tetraaza-macrocyclic ligands; Aza-crown macrocycles; Pyridinylbackbone; Stability constants; Kinetics.

References: 42 live references.