Diaryl ditellurides

Diaryl ditellurides, which are more important as synthetic intermediates, are sohds, highly soluble in solvents such as petroleum ether, benzene, chloroform, ether, and tetrahy-drofuran (THF), but are less soluble in methanol and ethanol. 

Aryltellurium trichlorides are highly soluble in methanol and ethanol but less soluble in benzene. Diaryltellurium dichlorides exhibit inverse solubilities, being more soluble in benzene than in methanol or ethanol. These properties allow an easy separation of diaryl tellurides from diaryl ditellurides (frequently formed as by-products in the preparation of tellurides) the mixture is treated with SOjClj and the obtained mixed di- and trichlorides are separated by the appropriate solvents, and reduced back into the pure tellurides and ditellurides. 

The small amounts of diaryl ditellurides formed frequently as by-products can be converted into tellurides by treatment with copper powder in refluxing dioxane. For Ar=2H02CC6H4, the crude product is extracted with aqueous Na2C03 and precipitated with acid (yield 8%). 

From diaryl ditellurides by extrusion of a tellurium atom... 

Diaryl ditellurides are relatively thermolabile compounds and eliminate one tellurium atom by heating at 300°C. ° In the presence of copper metal, however, the extrusion of tellurium is achieved during reflux with toluene or dioxane. " " ... 

The reductive fission of diaryl ditellurides with sodium in liquid ammonia reported ear-lier has seldom been employed. More recently, aprotic solvents have been substituted for ammonia. 

Diaryl ditellurides, like diaryl disulphides and diselenides, undergo disproportionation into arene tellurolates and tellurinates by alkaline treatment. 

The low reactivity of aryl halides towards nucleophilic reagents makes their reaction with sodium ditelluride unattractive for the preparation of diaryl ditellurides. Low yields are obtained, like the similar reaction with sodium telluride (see Section 3.1.2.1). 

Early experiments to prepare diaryl ditellurides, employing arylUthium reagents generated by Uthium-halogen exchange using ether as the solvent, gave only modest yields. 

At present the most successful and general route to dialkyl and diaryl ditellurides employs the telluration of organyllithium compounds in THF. 

The following diaryl ditelluride can be prepared in the same maimer as in the foregoing procedure Ar=2-pyridyl, Ph and (halogen and Me) derivatives, p-(Me2N)CgH4, 1-naph-thyl, 4-biphenylyl (50-84%). 

The arylation of sodium teUuride in NMP (see Section 3.1.2.1) followed by air oxidation gives rise to diaryl ditellurides in medium to good yields. 

Diaryl ditellurides (general procedure) The aryltellurium trichloride is poured into 15 mol equiv of Na2S-9H20 heated (and melted) at 95-100°C in a beaker, with strong manual stirring. An exothermic reaction occurs. After 10 min at the same temperature, excess HjO is added. By cooling the ditelluride solidifies, and is collected by decantation or filtration. The yields are near to quantitative. 

Diaryl ditellurides from aryl boronic acids... 

Aryl boronic acids treated with TeCl4 generate aryltellurium trichlorides which are reduced to diaryl ditellurides without prior isolation. ... 

Starting materials for the preparation of aryl tellurides and diaryl ditellurides and, consequently, aryltellurols find wide use in the manipulation of several organic functionalities. 

A more convenient method due to the mild experimental conditions and high yields involves the reaction of diaryl ditellurides with diazomethane. ... 

Reaction of diaryl ditellurides with diazomethane-formation of diaryl telluroketals (typical procedure). Di-p-methoxyphenyl ditelluride (2.34 g, 5 mmol) in ether (30 mL) is treated dropwise, at 0°C and while stirring, with an ethereal solution of diazomethane until disappearance of the red colour of the ditelluride. Evolution of N2 ensues. The product is obtained by evaporation of the solvent. RecrystaUization from hexane or EtOH gives colourless crystals (2.41 g (100%) m.p. 98-99°C). 

Dialkyl and diaryl ditellurides are easily converted into the corresponding tellurium trichlorides by means of the fission of the Te-Te bond by a chlorinating reagent. This route is very suitable for the preparation of the alkyl derivatives in view of the easy accessibility of dialkyl ditellurides via the alkylation of sodium ditelluride (see Section 3.2.1). 

Arenetellurinic anhydrides are formed from the mixed anhydrides by hydrolysis, but a more convenient one-pot procedure for their preparation involves the reaction of phenyliodine(III) dicarboxylate with diaryl ditellurides in the two-phase system CH2CI2/H2O 10%. ... 

S.3 Reaction of diaryl ditelluride with arenediazonium salts/CuXj ... 

Addition of aryl tellurolates to acetylenic ketones (general procedure) NaBH4 (0.55 g, 15 mmol) is added in small portions, under N2, to a solution of the diaryl ditelluride (5 mmol) in EtOH (20 mL) at room temperature. A solution of the acetylenic ketone (10 mmol) in EtOH (10 mL) is then added to the reaction mixture, with stirring. The resulting precipitate of the 2-carbonylvinyl telluride is filtered off and recrystallized from EtOH. 

By treating alkynes with diaryl ditellurides and sodium arylsulphonates in AcOH/H O, an flnh-tellurosulphonation takes place. Some of the obtained tellurosulphones have been converted into the corresponding dibromides. In the case of R=Mc3Si a desilylate product is formed. ... 

Diaryl ditellurides are converted into biaryls (Ar=p-MeOCgH4) by treatment with an additional eqnivalent of Pd(0) (HMPA as solvent). 

An additional report describes Te/Zn exchange of diaryl tellurides and diaryl ditelluride by treatment with Zn under Ni catalysis." The resulting Zn derivatives submitted to trans-metallation with CuCN-2LiCl and subsequent allylation with aUyhc bromide, furnishes the expected product in high yield. 

In every case the product mixture was composed of the expected 2-((aryltelluro) methyl)chromanone as the very major product together with the corresponding elimination product and the diaryl ditelluride. Spectral analysis was facilitated by the possession of authentic samples of the ditellurides and, eventually, of the elimination products. The product ratios, and hence yields, were determined by integration of the NMR spectra. Attempted purification by chromatography on silica gel led only to less pure samples contaminated with increased amounts of ditelluride and elimination products. 

Diaryldifluorotellurium compounds, e.g. 19, are formed in high yield by reaction of sulfur tetrafluoride with either diaryl tellurides or diaryl ditellurides.221... 

It is also relevant to record that several iron-carbonyl complexes with bridging, and in one case terminal, aryltellurol ligands have been prepared by reaction of Fe(CO)5, Fe(CO)12 or [ji-CpFe(CO)2]2 with diaryl ditellurides and which, together with complexes containing other transition metal carbonyls, e.g, ruthenium, osmium and manganese, provide a substantial number of interesting compounds.2... 

For the first time, derivatives of the new tellurium-containing mesoionic system, 1,2-oxatellurolyl-l-ium halides 21, were prepared by Detty via cyclization of j8-aryltelluropropenoyl chlorides 22, which in turn were synthesized starting from diaryl ditellurides as shown in the scheme. Under the action of Lewis acids (A1C13) or upon heating, compounds 22 rearrange to 21 in 50-96% yields (83JA875). 

Reactions of diaryl ditellurides with [bis(acyloxy)iodo]arenes, on the other hand, lead to oxidative cleavage of the Te-Te bond, and afford aryltellurinic mixed anhydrides 15 (Scheme 8) [26]. When such oxidations are conducted in a medium containing aqueous sodium hydroxide, aryltellurinic anhydrides 16 are obtained [16]. 

Dihydrotellurophene-1,1-difluoride119 was formed in the low-temperature reaction of 2,5-dihydrotellurophene with xenon difluoride. Aryltellurium(Vl) fluoride was synthesized from diaryl ditelluride or aryltellurium(lV) fluoride120 while perfluorinated dimethyl or diphenyl tellurides are transformed only to difluorides121,122 (Scheme 51). 

Dialkyl (e.g., 30) and diaryl ditellurides (e.g., 31) are transformed into the corresponding diorganotellurium trichlorides (e.g., 32 and 33) by reaction with elemental chlorine,74,75 with thionyl chloride,4,76 or with sulphuryl chloride (Scheme 8).65,77... 

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