Aryltellurium tribromides

Aryltellurium tribromides are generally less reactive towards ketones. MeOC4H4Te(Br2)CH2COPh was prepared by this method. ... 

The reaction is usually performed with aryltellurium tribromides, generated in situ by the treatment of the corresponding diteUurides with bromine (although trichlorides, ditel-lurides/CuCl2 and teUmocyanates/CuCl2 are also effective). 

Tellurium tetrachloride and aryltellurium trichloride, as well as tellurium tetrabro-mide" and aryltellurium tribromides add to acetylenes to produce, respectively, 2-halovinyl tellurium trihalides and dihalides, which can be submitted to further manipulations. 

The addition of aryltellurium tribromides exhibits Z or configuration depending on the solvent, benzene or ethanol used in the reaction. 

Aryltellurium tribromides (Ar =p-MeOC6fl4) are also effective in these cycloetherification reactions. 

Aryltellurium trichlorides 5 (R = aryl, X = Cl) are usually yellow, very stable crystalline solids, with a slight odor of hydrochloric acid, which probably arises from the reaction of 5 with the air moisture. Contact of 5 with metallic spatulas, with moist solvents, or prolonged exposure to light must be avoided. These compounds, however, can be handled in the air with no risk of decomposition. Aryltellurium tribromides (5, R = aryl, X = Br) are yellow crystalline solids, and the triiodides (5, R = aryl, X = 1) are dark red solids. The aryltellurium tribromides and triiodides were less explored for synthetic purposes, in contrast to the aryltellurium trichlorides, which were frequently used in several synthetic transformations. The aliphatic tellurium trihalides are less stable than the aromatic ones and were much less studied and used for preparative purposes. 

The reactivity of aryltellurium trihalides decreases on going from the chlorides to the iodides, the same trend occurring for hydrolysis. Aryltellurium trichlorides are very sensitive to water and moisture and are easily hydrolysed, the tribromides being more stable, while the triiodides are unaffected by cold water and can be prepared even by aqueous procedures. Diaryltellurium dihalides are stable in water, and ionic exchange reactions allow the conversion of dichlorides into dibromides and diiodides. 

The ease of hydrolysis follows the order ArTeClj > ArTeBrj > ArTelj. Aryltellurium trichlorides and tribromides are converted into the oxohalides by simple treatment with cold water. The triiodides are unaffected under these conditions, and on treatment with boiling water give mixtures or undefined products in most cases. ... 

Like tellurium tetrachloride, aryltellurium (and alkyltellurium) trichlorides (and tribromides) nndergo condensation reactions with reactive organic substrates or metallo-organic reagents as well as addition reactions to C=C bonds, giving rise to tellnrinm dichlorides. 

Aryltellurium trichlorides and tribromides condense with aromatic compounds bearing electron-donating groups, giving unsymmetrical diaryltellurium dihalides. This electrophilic substitution therefore parallels that described for tellurium tetrachloride. 

Aryltellurium triiodides can be prepared by treating aryltellurium trichlorides, tribromides, oxohalides or aryltellnrinic anhydrides with aqneons sodium iodide. ... 

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