Design of reversible one-electron redox systems using five-membered heterocycles containing sulfur, selenium, and tellurium

Stable 4,7-disubstituted benzotrichalcogenoles containing sulfur, selenium, and tellurium atoms in the five-membered ring were systematically and selectively prepared in good yields by reaction of the corresponding benzodichalcogenastannoles or benzodichalcogenatitanoles, synthetic equivalents of benzenedichalcogenols, with an S-1 or Se-1 source. Characterization of these new trichalcogenole frameworks was performed by multi-nuclear Sn-119, Se-77, Te-125 NMR studies and X-ray crystallographic analyses. The cyclic voltammograms of the trichalcogenoles showed well-defined reversible electrochemical redox couples with low oxidation potential. Novel radical ions were isolated in quantitative yields in the one-electron oxidation of the trichalcogenoles with 1 equiv. of NOPF6 as a one-electron oxidant. The structures of the radical cation salts were analyzed by P-31 NMR and ESR spectroscopies, and elemental analyses. The salts underwent one-electron reduction on treatment with I equiv. of samarium(II) iodide to give the neutral starting trichalcogenoles quantitatively.