Redox chemistry and valence tautomerism of cobalt-quinone complexes in nonaqueous solvents

Abstract

The electrochemistry and valence tautomerism of Co-III(N-N)(SQ)(Cat), [N-N=N,N,N',N'-tetramethylethylenediamine (TMEDA); SQ=3,5- or 3,6-di-tert-butyl-semiquinone, Cat=3,5- or 3,6-di-tert-butyl-catechol], have been investigated by spectroscopic, electrochemical, spectroelectrochemical methods in nonaqueous solvents under anaerobic condition. The transition temperature between tautomers is dependent upon the donation effect of substituted quinone ligand and solvent. It increases with the increase of donation effect of solvent and quinone ligand. Co-III(TMEDA)(SQ)(Cat) is reduced to [Co-II(TMEDA)(SQ)(Cat)](-), and then reduces to [Co-II(TMEDA) (Cat)(2)](2-). Co-III(TMEDA)(SQ)(Cat) is oxidized to [Co-III(TMEDA)(SQ)(2)](+), but the stability of the oxidized form in DMF is dependent upon the solution temperature. With the increase of solution temperature the oxidized form may be converted to [Co-II(TMEDA)(SQ)(BQ)](+) by intramolecular electron transfer from SQ ligand to Co-III.