Synthesis, properties, oxidation, and electrochemistry of 1,2-dichalcogenins

Syntheses are presented of the 1,2-dichalcogenins: 1,2-dithiin, 1,2-diselenin, and 2-selenathiin, both substituted and unsubstituted. 1,2-Dithiin and 1,2-diselenin are prepared by reaction of PhCH2XNa (X = S or Se) with 1,4-bis(trimethylsilyl)-1,3-butadiyne followed by reductive cleavage and oxidation. 2-Selenathiin is similarly prepared using a mixture of PhCH2SeNa and PhCH2SNa. Reaction of titanacyclopentadienes with (SCN)(2) or (SeCN)(2) followed by bis(thiocyanate) or bis(selenocyanate) cyclization affords substituted 1,2-dithiins or 1,2-diselenins, respectively. With S2Cl2, 1,2-dithiins an directly formed from titanacyclopentadienes. Oxidation of 1.2-dithiins and 1,2-diselenins gives the corresponding I-oxide and, with 1,2-dithiins and excess oxidant 1,1-dioxides; oxidation of 2-selenathiin gives the 2-oxide. Electrochemical oxidation of 1,2-dichalcoenins, which have a twisted geometry, affords planar radical cations by an EC mechanism. One-electron AlCl3 oxidation of 3,6-diphenyl-1,2-dithiin gives the corresponding radical cation, characterized by EPR spectroscopy. Theoretical calculations result in a flattened structure for the 1,2-dithiin radical cation and a fully planar structure for the 1,2-diselenin radical cation. The Se-77 NMR chemical shifts of 1,2-diselenin an characteristically high-field-shifted with respect to open chain diselenides in good agreement with results of GIAO-DFT calculations based on MP2 and DFT optimum geometries.