Changing the electrochemical behavior of catechols by means of their conversion into the corresponding ruthenium(III)-dioxolene complexes

The rather complicated electrochemical behavior, in aqueous solution, exhib ited by catechol(1,2-dihydroxybenzene) and its derivatives containing carbo xylate and sulphonate groups, can be conveniently controlled by means of th eir conversion into the corresponding blue ruthenium(III)-edta complexes (e dta = ethylenedinitrilotetraacetate ligand). In the free form, the catechol species undergo a primary electrochemical oxidation process in the range o f 0.3-0.6 V versus SHE, yielding quinone products susceptible to a number o f pH dependent, secondary chemical reactions. When coordinated to the ruthe nium(III)-edta unit, their electrochemical and spectroelectrochemical behav ior is dramatically changed, approaching that of metal complexes with non-i nnocent dioxolene ligands. In this case, the reduction of the ruthenium(III ) metal ion proceeds reversibly above pH 9, in the -(0.5-0.6) V range and t he oxidation process centered on the catecholate ligands becomes reversible , leading exclusively to the formation of the semiquinone species, with no evidence of complications from the secondary reactions. (C) 2000 Elsevier S cience B.V. All rights reserved.