REDOX CHEMISTRY AND VALENCE TAUTOMERISM OF COBALT-QUINONE COMPLEXES IN NONAQUEOUS SOLVENTS

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-t ert-butyl-semiquinone, Cat=3,5- or 3,6-di-tert-butyl-catechol], have b een investigated by spectroscopic, electrochemical, spectroelectrochem ical methods in nonaqueous solvents under anaerobic condition. The tra nsition temperature between tautomers is dependent upon the donation e ffect of substituted quinone ligand and solvent. It increases with the increase of donation effect of solvent and quinone ligand. Co-III(TME DA)(SQ)(Cat) is reduced to [Co-II(TMEDA)(SQ)(Cat)](-), and then reduce s to [Co-II(TMEDA) (Cat)(2)](2-). Co-III(TMEDA)(SQ)(Cat) is oxidized t o [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(TMED A)(SQ)(BQ)](+) by intramolecular electron transfer from SQ ligand to C o-III.