Aryltellurenyl halides

Halogenated derivatives of tellurium in the oxidation state +2, namely tellurenyl halides, are unfamiliar compounds compared to the well-known selenium analogues. 

These compounds are in principle easily accessible by the controlled halogenolysis of the parent ditellurides. However, the first compound obtained in 1959, 2-naphthyl-tellurenyl iodide, remained for a long time the only stable representative of this class until the preparation of other members of this class by a successful use of the same method.  

Several aryltellurenyl halides have been prepared, bearing an ortho carbonyl, nitro or another electron-attracting group, exhibiting a stabilizing effect by coordination to tellurium.  

With the exception of 2-naphthyltellurenyl iodide, the unsubstituted members are, however, thermally unstable in the solid state. Therefore, to exploit their highly electrophilic character, aryltellurenyl halides are not isolated, instead being generated in situ and used directly for further conversion. -  

A recent report describes the synthesis of Te-anisyl phosphorotellurolate esters by the reaction of anisyltellurium trichloride with trialkylphosphites. The intermediacy of the ani-syltellurenyl chloride, formed by the reduction of the trichloride at the expense of the excess of the trialkylphosphonite, rationalizes the result. 

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The conproportionation of diaryl ditellurides and aryltellurium trihalides, resulting in the formation of aryltellurenyl halides, has been investigated. The aryltellurenyl halides are, in general, unstable, and they disproportionate to diaryltellurium dihalides and elemental tellurium. ... 

Finally, an aryltellurenyl cation stabilized by an NHC was prepared by Beckmann et al. from the reactions of aryltellurenyl halides with ImMe4 (Figure 15.48). Both [ArTe-NHC][I] and [ArTe-NHC] [ArTeCl2] (Ar = 2,6-bis (2,4,6-trimethylphenyl)phenyl, X = Cl) were isolated and characterized. In the iodide salt the Te—C carbene bond length is 2.161(2) A, while in the [ArTeCy salt the length is 2.091(8)A. DFT calculations and NBO analyses were also carried out [274]. 

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