Diorganyl tellurides

On treatment with an equivalent amount of (Et2N)3P, thiotelluroxide 67a is reduced to give telluroazocine 65 in almost quantitative yield, which can be converted into telluroxide 68 by the usual procedures for a diorganyl telluride to telluroxide transformation. It is worth noting that when treated with Lawesson reagent, the telluroxide 68 forms thiotelluroxide 67a, whereas diaryl telluroxides are reduced by this reagent to diaryl tellurides. 

Sections 3.1-3.3 outline the principal preparative methods of diorganyl tellurides and ditellurides, organyltellurium trichlorides and diorganyltellurium dichlorides, which were the first classes of compounds investigated at the beginning of tellurium organic chemistry. 

Diorganyl tellurides have low molecular mass and are colourless or yellowish liquids with an unpleasant and penetrating odour. Dimethyl teUuride is a metabolite of tellurium and tellurium compounds in a variety of living organisms, including humans. Higher dialkyl tellurides and most diaryl tellurides are solids with low melting points (diphenyl telluride is a liquid). 

Diorganyl tellurides are soluble in common organic solvents. 

Because of the above-mentioned organoleptic properties, it is recommended that contact between dialkyl tellurides and the skin is avoided, and that, in general, all work involving diorganyl tellurides is performed under a well-ventilated hood. 

Diorganyl tellurides, compounds with two organic groups linked to a tellurium atom, constitute the most abundant and famihar class of organic tellurium compounds. The organic groups, of the most differentiated types, can be identical or different, giving rise to symmetrical or unsymmetrical tellurides. 

A different approach to unsymmetrical diorganyl tellurides, in which an electrophilic tellurium species is used, involves the nucleophilic attack of organomagnesium or organo-lithium reagents to diorganyl ditellurides. 

Unsymmetrical diorganyl tellurides (general procedure). A solution of the ditelluride (2 nunol) in THE (30 mL) is treated dropwise at 0°C under N2 with Br2 (0.32 g, 3 mmol)... 

The reaction with ethyl- and cyclohexytmercury chlorides requires heating for 24 h. 3.9.4 By addition of halogens to diorganyl tellurides... 

Diorganyl tellurides are easily oxidized to the corresponding telluroxides. Dialkyl tel-Inrides are especially sensitive to oxidation, and their exposnre to air, either neat or in soln-tion, canses the formation of dialkyl telluroxides. Diaryl tellnrides are much more stable and are oxidized only by chemical methods. 

Water-soluble diorganyl tellurides with thiolperoxidase and autoxidant activity have been prepared as depicted in the following scheme. ... 

Diorganyl tellurides add to alkynes via a radical mechanism in the presence of a catalytic amount of a radical initiator such as AIBN or 2,2 -azobis(4-methoxy-2,4-dimethyl-valeronitrile) (In), as well as under irradiation by visible light (tungsten lamp), affording vinylic tellurides in a variable ZIE ratio." ... 

The known property of diorganyl tellurides of reducing metallic salts, applied to tita-nium(IV) chloride, generates a titanium(III) species which is a useful reagent for some selective reductions. By this method benzaldehyde is reduced to dihydrobenzoin, and benzyl to benzoin, and successively to desoxybenzoin. ... 

Di-(j -methoxyphenyl telluride) had at first been used but better results have been achieved with electron-rich diorganyl tellurides, such as (p-Me2NCgH4)2Te, (CgHi3)2Te, 2(PhTe)CgH4CH2NMe2 associated to different reducing agents, reduced glutathione (GSH) or sodium ascorbate. ... 

By treatment of diorganyl tellurides with alkyllithiums in THF at -78°C, a hthium-tellurium exchange occurs, generating another organolithium if the latter is more stable than the former. 

The use of several diorganyl tellurides as initiators for controlled living radical polymerization of styrenes has been investigated. " ... 

Diorganyl tellurides are able to catalyse the reaction of H2O2 with thiols. p-Electron-donating substituents (OH, NH2, NMe2 and NHPh) enhance such activity, whereas the electron-withdrawing CFj group has the opposite effect. 

Because of their increased solubility in water, 4-sulphopropyl-substituted derivatives such as Li, Na, K and Me4N salts were found to be the most efficient tellurium-based inhibitors of thioredoxin reductase. Another active diorganyl telluride is characterized by p-OMOM, p-OTHP and (0CH2CH2)30THP, groups. 

Tellurolate anions possess the highest nucleophilicity in the series of analogous chalcogen derivatives. The same is true for diorganyl tellurides compared to their respective diorganyl sulfides and selenides. 

A two-coordinated tellurium center in 92 is susceptible to numerous transformations typical of those in diorganyl tellurides. 

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