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摘要
Synthetic routes to salts of the benzol[,2,3]thiatellurazolylium cation [2c](+) and its selenium analogue [2b](+) are described. Access to the cation frameworks involves the intermediacy of NNS-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.
- 出版日期2008-11-3
