Diorganyltellurium dihalides

Diorganyltellurium dihalides can also be prepared by the addition of halogens to the parent tellurides. 

Diorganyltellurium dihalides are often the primary products in the synthesis of organic derivatives of tellnrinm and are therefore immediate precnrsors of the corresponding tellnrides. 

With sodium sulphide hydrate (general procedure) The diorganyltellurium dihalide is mixed with a 15 times molar excess of Na2S 9H2O and the mixture heated at 95-100°C for 10 min or more, until aU the solid has melted. Sufficient HjO is added to dissolve the sulphide and then the mixture is filtered if the obtained telluride is a solid, or extracted with a solvent (ether or petroleum ether) if the telluride is a liquid. The products are purified by crystallization or distillation. Yields are high or quantitative (except for diphenyl telluride or di-p-tolyl telluride). 

With TUDO (general procedure). A mixture of diorganyltellurium dihalide (2 mmol) and 2 N NaOH (10 mL) is stirred at room temperature for 15 min. TUDO (0.432 g, 4 mmol)... 

Unsymmetrical diorganyltellurium dihalides are formed upon condensation of aryltellurium trichlorides with activated aromatic compounds and with ketones. The addition of the trichloride across carbon-carbon double bonds in alkenes, as well as the reaction with aryl(trimethyl)silane, hexaphenyldilead, and aryhnercury chlorides leads to the transfer of the aryl group to the tellurium atom. 

Most diorganyltellurium dihalides are stable in air. This facilitates a convenient method to purify diorganyl tellurides that are liquid at room temperature. The raw product is converted to a dichloride or dibromide by direct chlorination or bromination, and the pure dihalides are easily be reduced back to the original telluride." ... 

Diorganyl tellurides are starting materials for the preparation of diorganyltellurium dihalides, pseudohalides, and carboxylates, of telluroxides, and of telluronium salts, and are used as ligands for the synthesis of transition metal complexes. 

Reduction of Organoselenium and -tellurium Halides and Oxides. TUD reduces aryltellurium trihalides to diaryl ditel-lurides (eq 2) and diorganyltellurium dihalides and telluroxides to diorganyl tellurides (eq 3) in high yield. The corresponding selenium compounds are reduced similarly. Some examples are given in Table 2. The reduction is performed by premixing the substrate and 2 N NaOH at room temperature for 15 min prior to the addition of TUD in petroleum ether. 

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