resumo
The synthesis of the cross-bridged cyclen CRpy(2) {4,10-bis((pyridin-2-yl)methyl)-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane}, a constrained analogue of the previously described trans-methylpyridine cyclen Cpy(2) is reported. The additional ethylene bridge confers to CRpy(2) proton-sponge type behaviour which was explored by NMR and potentiometric studies. Transition metal complexes have been synthesized (by complexation of both ligands with Co2+, Cu2+ and Zn2+) and characterized in solution and in the solid state. The single crystal X-ray structures of [CoCpy(2)](2+), [CuCpy(2)](2+) and [ZnCpy(2)](2+) complexes were determined. Stability constants of the complexes, including those of the cross-bridged derivative, were determined using potentiometric titration data and the kinetic inertness of the [CuCRpy(2)](2+) complex in an acidic medium (half-life values) was evaluated by spectrophotometry. The pre-organized structure of the cross-bridged ligand imposes an additional strain for the complexation leading to complexes with smaller thermodynamic stability in comparison with the related non-bridged ligand. The electrochemical study involving cyclic voltammetry underlines the importance of the ethylene cross-bridge on the redox properties of the transition metal complexes.
palavras-chave
TOPOLOGICALLY CONSTRAINED TETRAAZAMACROCYCLES; IN-VIVO STABILITY; COPPER(II) COMPLEXES; CRYSTAL-STRUCTURES; X-RAY; MACROCYCLIC LIGANDS; KINETIC INERTNESS; POTENTIOMETRIC TITRATIONS; ELECTROCHEMICAL-BEHAVIOR; THERMODYNAMIC STABILITY
categoria
Chemistry
autores
Bernier, N; Costa, J; Delgado, R; Felix, V; Royal, G; Tripier, R
nossos autores
Vítor Félix
Professor Associado com Agregaçãoagradecimentos
This research work was supported by the Ministere de l'Education Nationale et de la Recherche and by the Comite National pour la Recherche Scientifique. The authors acknowledge the financial support from Fundacao para a Ciencia e a Tecnologia (FCT) with coparticipation of the European Community fund FEDER (Project PTDC/QUI/67175/2006). We also thank Nelly Kervarec for contribution in the 2D NMR measurements.