Electrochemistry of organometallic compounds: Part III. Oxidations of methyl derivatives of organocobalt(III) complexes with delocalized electronic structure in dimethylformamide

The influence of the equatorial ligand on the electrochemical oxidation of the compounds H₃CCo(chel)B], where chel is bis (dimethylglyoximato), (DH)₂; bis(salicylaldehyde)ethylenediimine, salen; bis(salicylaldehyde) o-phenylenediimine, salophen; bis(salicylaldehyde)cyclohexylenediimine, salcn; bis(acetylacetone) ethylenediimine, bae; and where B is pyridine when chel is (DH₂), and dimethylformamide (DMF) when chel represents a Schiff base (salen, salcn, salophen and bae), was studied by means of cyclic voltammetry in DMF, 0.2 M in tetraethylammonium perchlorate, between 25 and ?25°C, with a platinum disk working electrode. Absorption spectra in the visible and near ultraviolet regions for these compounds in DMF at 25°C were obtained. The complexes exhibit a reversible one-electron oxidation, at ?20°C with scan rates >0.5 V s^?; chemical reactions following electron transfer are not detected under these conditions. At slower potential or higher temperatures, the oxidized product decomposes chemically in a solvent-assisted (or nucleophile-assisted) reaction, yielding products which are electroactive in the applied potential range. The behavior of the H₃CCo (DH₂)py] derivative is better described as a quasi-reversible charge transfer followed by an irreversible chemical reaction. Experimental evidence suggests that in the case of the H₃CCo(bae)] derivative at ?20°C, the reactive -species is pentacoordinated and weakly adsorbed at the electrode surface. The value of E${}_1\text{2}$ and the energies of the first two absorption bands in the visible spectra reveal the ability of the studied complexes to donate and to delocalize electronic charge.