Electron transfer and autoxidation kinetics of the bis(imidazole)bis(dimethylglyoximato)iron(II) complex

Abstract

. Can. J. Chem. 64, 1280Chem. 64, (1986. The properties and reactivity of the bis(imidazo1e)bis-(dimethylglyoximato)irn(II) complex have been studied based on spectroelectrochemistry, cyclic voltammetry, and stopped-flow kinetics in aqueous solution. The autoxidation reaction was found to be inhibited by the imidazole ligand in excess but susceptible to copper(I1) catalysis. In this case a mechanism has been proposed, consisting of a rapid electron transfer followed by the reoxidation of the resulting Cu(1) species by 02. HENRIQUE E. TOMA et ANTONIO CARLOS C. SILVA. Can. J. Chem. 64, 1280Chem. 64, (1986.OpCrant en solution aqueuse et faisant appel i la spectroClectrochirnie, i la voltarnktrie cyclique et i la cinCtique par flux stoppC, on a CtudiC les propriCtCs et la rCactivitC du complexe bis(imidazo1e) bis(dimCthyg1yoximato) fer(I1). On a trouvC que la rCaction d'auto-oxydation est inhibCe par le ligand irnidazole qui est 1jrCsent en excks, alors qu'elle est susceptible i la catalyse par le cuivre(I1). Dans ce cas, on propose un mCcanisme d'aprks lequel il se produit une transfert rapide d'Clectron qui est suivi d'une rkoxydation, par le 0 2 , de l'espkce Cu(1) qui rCsulte.[Traduit par la revue]. IntroductionDioxime complexes of iron(II) are interesting examples of coordination compounds which mimic hemoglobin and mioglobin in their ability t o reversibly bind carbon monoxide (1-4).Among the several dioxime complexes, the bis(dimethylg1y-oximato)bis(irnidazole)iron(II) complex [Fe(Hdmg)2(Him)J, because of its well known molecular structure (5) which resembles the porphyrin species with biologically important ligands, has attracted our attention. O n the other hand, in contrast with the pyridine analogues, the imidazole complex is soluble enough in water for comparative studies with the biological hemes. In this work we have studied the properties and reactivity of the [Fe(Hdmg)2(Him)2] complex, with particular emphasis o n the electrochemistry and redox kinetics in aqueous solution. We have also investigated the autoxidation mechanisms, including the copper-catalyzed reaction, because of their possible relevance to the understanding of the biological oxidation processes (6)(7)(8). Experimental The electronic spectra of the complexes in the visible and uv region were recorded on a Cary 17 or a Hewlett-Packard 8451 diode-may spectrophotometer fittedwith thermostatted cell compartments. Cyclic voltammetry measurements were carried out with a Princeton Applied Research instrument, consisting of a 173 potentiostat and a 175 universal programmer. A platinum electrode was employed for the measurements, using the conventional Luggin capillary with the Ag/AgC1(1 M KCl) reference electrode in a non-isothermic mangement. A platinum wire was used as the auxiliary electrode.Spectroelectrochemica1 measurements were carried out using the diode-may spectrophotometer and the 173 potentiostat, with a transparent electrochemical cell of 0.03 cm internal optical pathlength. A gold minigrid was employed as the working electro...

Ferroxime(II)-catalysed oxidation of 3,5-di-tert-butylcatechol by O2. Kinetics and mechanism †

“…2, 3 The nature and modelling of active oxidising species in nonheme iron proteins prompted studies on the reduction of oxo-bridged diiron species derived from difluoro(dimethylglyoximato)borate 4, 5 and on the autoxidation of bis(dimethylglyoximato)bis(imidazole)iron(). 6 In a search for square planar iron() complexes with 4N donor equatorial ligands, expected to mimic the porphyrin moiety, we have investigated the catalytic properties of bis(dimethylglyoximato)bis(N-methylimidazole)iron(),…”

Thermal decomposition of bis(dimethylglyoximate) iron(II) complexes containing axial N-heterocyclic ligands

“…These complexes are interesting examples of coordination compounds which mimic biologically important heme groups in their ability to bind carbon monoxide reversibly [1][2][3][4].The axial ligands in these maerocyclic complexes are highly important, influencing their redox and kinetic properties and their affinity for unsaturated bases in solution [5][6][7]. The role of the N-heteroeyelie ligands in the thermal behaviour of the iron(II)-dioximate complexes is discussed in this paper.…”