Synthesis and properties of new polymetalated porphyrins / Sintese e propriedades de novas porfirinas polimetaladas

AUTOR(ES)

Koiti Araki

DATA DE PUBLICAÇÃO

1989

RESUMO

Metalloporphyrins containing peripheral meta l complexes attached to the macrocyclic ring can exhibit an interesting supramolecular chemistry, modeling , for instance, photosynthetic systems in their ability to undergo intramolecular photocatalyzed electron transfer; and cytochrome-c oxidase , by acting as multielectron redox catalysts in the reduction of molecular oxygen. In view of its relevance , we have investigated a new series of polynuclear porphyrins derived from meso-tetra(4-pyridyl)porphyrin , [4-TPyP], by complexing the pyridine residues with ruthenium-ammines or ruthenium-EDTA íons. Typical species , containing three pentaammineruthenium (III) or four EDTA-ruthenium(III) ions attached to the porphyrin , were isolated and characterized based on spectroscopic and electrochemical techniques. The electronic spectra exhibited the characteristic Soret , α and β bands in the visible region. In the reduced species a new band , consistent with a Ru(II)-to-pyridine charge transfer transition , was detected in the 440-470 nm region. Cyclic voltammetry measuremen ts provided direct evidence of the attached ruthenium ions, displaying reversible waves, slightly shifted to less cathodic potentials with respect to the non-coordinated species. The electrochemical behaviour was also investigated in the presence of dimethyl sulfoxide , wich is a scavenger for RuII (edta)(H2 O) complex. In the presence of dioxygen, a strong catalytic wave was observed for the polymetallated iron-porphyrin , almost coinciding with the electrachemical wave for the iron centre. The electrochemical behaviour was consistent with the reduction of dioxygen to water, at the iron-porphyrin centre. The process is assisted by the four ruthenium(II) ions which act as a source of electrons, improving the catalytic efficiency by means of the supramolecular interactions.

ASSUNTO(S)

supramolecular chemistry porphyrins ruthenium complexes porfirinas química supramolecular complexos de rutênio

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