Heavy atom analogues of 1,2,3-dithiazolylium salts: Preparation, structures and redox chemistry

Article abstract of DOI:10.1021/ic8013738

Synthetic routes to salts of the benzo[1,2,3]thiatellurazolylium cation [2c]⁺ and its selenium analogue [2b]⁺ are described. Access to the cation frameworks involves the intermediacy of N,N,S-trisilylated 2-aminobenzenethiol. The latter reacts smoothly with selenium and tellurium halides ECl₄ (E = Se, Te) to afford the desired heterocyclic benzo cations [2b]⁺ and [2c]⁺ as their chloride salts. Anion exchange provides the corresponding GaCl₄^-, OTf ^- and TeCl₅^- salts of [2c]⁺, all of which have been characterized by X-ray crystallography. While the gallate salts of the sulfur and selenium cations [2a]⁺ and [2b]⁺ crystallize as ion-paired cations and anions, salts of [2c]⁺ adopt solid-state structures that display strong association of the cations via short intermolecular Te-N′ bonds. However, crystallization of [2c]⁺ salts in dichloroethane in the presence of GaCl₃ leads to cleavage of the dimers and the formation of a Lewis acid adduct at nitrogen. Reduction of the benzo cations [2a,b]⁺ affords the respective radicals 2a,b, both of which have been characterized by electron paramagnetic resonance (EPR) spectroscopy. Attempts to generate the corresponding radical 2c have been unsuccessful, although a material of nominally correct elemental composition can be generated by chemical reduction. The energetics of association of [2a,b,c]⁺ in solution has been probed by means of density functional theory calculations using the polarized continuum model. The results suggest that the dimeric nature of the Te-centered cation is retained in solution. The strength of the interaction is, however, less than in N-alkylated tellurodiazolylium salts.