Halides tellurium

The first compound of this series, CeSI, was reported by Carter (68) in 1961, and later discussed by Dagron (93). It was obtained by the reaction of iodine with cerium sulfide at 430 C, or by direct synthesis from the elements at 500°C. This was the start of a detailed investigation of this group of compounds mainly by Dagron and co-workers. The present situation is presented in Table VII. No scandium compounds are known thus far, and the same is true for selenium and tellurium halides of these elements. 

Oxyacids containing selenium and tellurium are known, but they and their salts are generally less important than the sulfur compounds. When selenium and tellurium halides hydrolyze, the solutions contain selenous and tellurous acids. 

Okazaki247 also suggested a detailed mechanism for the preparation of 1,3,4-telluradiazoline from 1,1,3,3-tetramethylindanhydrazone and tellurium halides. The reaction produces a complicated mixture of products, including 12. 

Although cyclo-Tcg has not been isolated, this tellurium homocycle has been tentatively identified by the observation of a Te NMR resonance in the 820-870 ppm region for (a) the product of the decomposition of thermally unstable tellurium halides 702X2 (X = C1, Br), (b) the cyclocondensation product of the reaction of two equivalents of Te2Cl2 with Cp 2Ti(p-Te2)2TiCp 2 (Cp = MeC5H4) and (c) a molten S-Se-Te mixture at 145... 

Tellurium Halides. Tellurium forms the dihalides TeCl and TeBi, but not Tel2. However, it forms tetrahalides with all four halogens. Tellurium decafluoride [53214-07-6] and hexafluoride can also be prepared. No monohalide, Te2X2, is believed to exist. Tellurium does not form well-defined oxyhalides as do sulfur and selenium. The tellurium halides show varying tendencies to form complexes and addition compounds with nitrogen compounds such as ammonia, pyridine, simple and substituted thioureas and anilines, and ethylenediamine, as well as sulfur trioxide and the chlorides of other elements. 

Organic tellurium halides 7 are normally unstable and cannot be isolated. Attempts to isolate organotellurium halides lead to their disproportionation, giving a mixture of organotellurium trihalides 5 and the corresponding diorganoditellurides 4 (Equation (1)). In this way, they are generated and used in situ.5 11 12... 

When tris[fluoroalkoxy] tellurium halides were treated with four molar equivalents of N-trimethylsilylmorpholine in anhydrous diethyl ether, the crystalline, colorless dimorpholino fluoroalkoxy tellurium halides were obtained1. 

Tellurium tetrakis[fluoroalkoxides] reacted with tellurium tetrahalides in benzene or tetrahydrofuran to yield fluoroalkoxy tellurium halides with one, two, or three flu-oroalkoxy groups in the molecule depending on the molar ratio of the reagents2. 

Phenyl tellurium halides, generated from diphenyl ditellurium and halogen in the presence or absence of thiourea, reacted with potassium selenocyanate to give bis[phenyltelluro] selenium3. 

The organo tellurium halides are the most investigated compounds among the tellurenic acid derivatives. 

Organo tellurium halides, also named organo tellurenyl halides, are in principle easily accessible through controlled halogenolysis of diorgano ditellurium compounds. However, 2-naphthyl tellurium iodide, prepared in 19592 from bis[2-naphthyl] ditellurium and iodine, remained the only compound of this type until 1971/72, when a series of ortho-carbonyl substituted phenyl tellurium halides were synthesized3-4. Aryl tellurium halides without substituents in the ortho-position to tellurium were isolated and characterized in 1975s. 

Crystal structures of ortho-substituted phenyl tellurium halides and of J-phenyl-3-(4 -methoxyphenyl)-l-propen-l-yl tellurium chloride6clearly show that tellurium interacts with the heteroatom, thus stabilizing the compounds. In the absence of a stabilizing group in the ortho-position, aryl tellurium halides are probably polymeric as solids and in solution with... 

Only a few unsubstituted, non-stabilized alkyl tellurium halides were characterized or isolated. /-Butyl tellurium chloride may have been detected by l2STe-NMR spectroscopy as a minor product of the controlled chlorination of di-/-butyl ditellurium6. 2-Chlorocarbon-ylbenzyl tellurium halides were obtained as rather unstable solids by halogenolysis of tellurophthalide7 (p. 246). Tris[trimethylsilyl methyl tellurium chloride, bromide and iodide were isolated as black-blue crystals that were stable in solution and as solids8. The stability of these compounds is attributable to the steric protection of the Te —X group by the trimethylsilyl substituents. 

Aryl tellurium bromides and iodides can be obtained by reaction of diaryl ditellurium compounds with an equimolar amount of bromine or iodine, when the solvent is able to dissolve the starting materials but not the aryl tellurium halide. The precipitation of the aryl tellurium halide prevents it from being converted to aryl tellurium trihalides. The aryl tellurium halides thus far isolated and suitable reaction media for their preparation are listed in Table 3 (p. 240). 

In contrast to the other aryl tellurium halides, 2-biphenyIyl tellurium bromide and iodide are only slightly associated in solution3. 

The aryl tellurium halides do not need to be isolated they can be generated in methanol or tetrahydrofuran and used in situ. 

The stable tris[trimethylsilyl]methyl tellurium halides were obtained in quantitative yields from the corresponding ditellurium and the elemental halogens4. 

The possibility of preparing aryl tellurium halides from equimolar amounts of diaryl ditellurium compounds and aryl tellurium trihalides has hardly been explored. Only phenyl tellurium iodide and 2-biphenylyl tellurium bromide could be obtained by this route. The other aryl tellurium halides (including 3,4-dimethoxyphenyl tellurium chloride) decomposed under the reaction conditions to give diaryl tellurium dihalides and tellurium5. 

A 4 1 molar ratio of thiosemicarbazone/aryl tellurium trichloride is necessary for the success of these reactions. No product was obtained with a 2 1 molar ratio of the reactants. The l,3-diphenyl-3-oxo-l-propen-1-yl tellurium trihalides were quantitatively reduced to the corresponding tellurium halides by hypophosphorous acid3. 

Hydrazine, lithium triethylborohydride, and sodium benzenethiolate produced the tellurium halides only in low yields3. 

Carbonyl-substituted phenyl organo tellurium compounds react with hydrohalic acids with cleavage of a Te —C bond and the formation of a stabilized aryl tellurium halide. 

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