CHEMISTRY OF DICATIONS AS A NOVEL UNUSUAL VALENCY OF CHALCOGEN ELEMENTS (S, SE, TE)

Dications bonded by two positively charged heteroatoms have received a little attention, and study of their properties is of great interest. This article presents the preparation, structure, and properties of sigma-bonded dications from the medium-sized cyclic compounds containing S, Se and Te atoms. Both the oxidation of 1,5-dithiacyclooctane (1,5-DTCO), the related selenium and tellurium derivatives (1,5-DSeCO, 1,5-DTeCO), and their dibenzocyclooctane derivatives using either concd H2SO4 or oxidizing agent such as NOBF4 and the treatment of their monooxide in concd H2SO4 or with (CF3SO2)2O revealed the formation of dications containing transannular bond between two heteroatoms. The structures of the dication salts of 1,5-DTCO and 1,5-DSeCO were determined by X-ray crystallographic analysis. These dications act as an oxidant or as an electrophile depending on the added reagents. These new species are of particular interest and become attractive if one could prepare the analogous derivatives bearing multiheteroatoms. As typical example, inspection of the spectrum of the dication of the tris-sulfide, 1,11-(methanothiomethano)-5 H, 7 H-dibenzo[b, g][1, 5] dithiocin, and its oxides in concd D2SO4 indicated that the central sulfur atom should have a hypervalent bonding structure composed of two sulfur and two carbon ligands i.e., 10-S-4(C2S2).