Benzo-bridged bis(1,2,3-dithiazoles) and their selenium analogues. Preparation, molecular and electronic structures, and redox chemistry

The condensation of diaminobenzenedithiol with sulfur monochloride leads to the chloride salt of the radical cation of 3,6-dichlorobenzo[l,2-d:4,5-d']bis(1,2,3-dithiazole), dichloro-[BB-123-DTA][Cl], which can be reduced to neutral dichloro-[BB-123-DTA] with triphenylantimony. A similar condensation with selenium tetrachloride leads, upon reduction, to the corresponding bis(l,2,3-thiaselenazole) dichloro-[BB-123-TSA]. The crystal and molecular structures of both compounds have been determined by X-ray diffraction. Both compounds, which are formally antiaromatic 16 pi-systems, exhibit internal bond lengths consistent with a quinoid formulation; The radical cations of both rings have been characterized by ESR spectroscopy; for dichloro-[BB-123-DTA](+) g = 2.0114 and a(N) = 0.201 mT, while for dichloro-[BB-123-TSA](+) g = 2.021 and a(N) = 0.44 mT. Further oxidation of both rings affords the corresponding dications, both of which have been characterized crystallographically as their AlCl4- salts. The structural features of these compounds are consistent with those expected for dithiazolylium (or thiaselenazolylium) derivatives. The structure and redox chemistry of the benzo[l,2-d:4,5-d']bis(l,2,3-dithiazole) framework is discussed in the light of the results of ab initio calculations.