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Synthesis, Properties, Oxidation, and Electrochemistry of 1,2-Dichalcogenins

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journal contribution
posted on 2000-05-16, 00:00 authored by Eric Block, Marc Birringer, Russell DeOrazio, Jürgen Fabian, Richard S. Glass, Chuangxing Guo, Chunhong He, Edward Lorance, Quangsheng Qian, T. Benjamin Schroeder, Zhixing Shan, Mohan Thiruvazhi, George S. Wilson, Xing Zhang
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 are directly formed from titanacyclopentadienes. Oxidation of 1,2-dithiins and 1,2-diselenins gives the corresponding 1-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-dichalcogenins, 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 77Se NMR chemical shifts of 1,2-diselenin are 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.

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