Trichalcogen-Dications

Generation of disulfonium dications involves stabilization of the cationic centers on the sulfur atoms through formation of a new S-S bond between the two sulfonium centers. When such an interaction involves more than two chalogen atoms, it leads to formation of new interesting types of dications, which contain hypervalent central atoms, such as sulfurane, selenurane or tellururane.94 

One can use the same methods for generation of trithiodications as for synthesis of disulfonium dications, i.e. oxidation of suitable trisulfides with concentrated sulfuric acid or with nitrosonium salts as well as reaction of a 

The structure of compounds 135 was established by NMR spectroscopy and by X-ray analysis. According to the X-ray data,137 triselenium dication 135 (X = Y = Se) has a bent structure with the C(Ar)-Se-C(Ar) angle equal to 95.6°. 

The only example of an organic dicationic system with participation of oxygen was described for the selenuranium dication 145 prepared by reaction of selenoxide 146 with triflic anhydride.144 X-ray analysis of this dication confirmed formation of a hypervalent structure with an almost collinear 

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The chemical properties of trichalcogen dications are, in many ways, analogous to the properties of dichalcogen dications, but are considerably less studied. Hydrolysis of chalcogenurane dications occurs preferentially at the onium chalcogen atom. Similar to the usual dichalcogen dications, trichalcogen dications also display oxidative properties. For example, reduction of selenu-rane dication 135 (X = Y = Se) is observed in reactions with Sm(II) salts, triphenylphosphine or thiophenol (Scheme 54).135... 

An interesting way to generate telluronium dications involves electron transfer through a 71-conjugated system to a spatially remote sulfoxide sulfur atom in a domino manner. Treatment of substrate 141 with triflic anhydride results in reduction of the terminal sulfoxide group with simultaneous oxidation of the tellurium atom in the para-position and formation of a trichalcogen dicationic moiety 144143 through the intermediate sulfonium salt 142 and quinoid structure 143 (Scheme 52). 

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