Tellurium, with Grignard

The scope of the reaction of tellurium with Grignard reagents has not yet been delineated. Several aromatic and aliphatic Grignard reagents were reported to be unreactive toward tellurium. Bromomagnesium ethenetellurolates and vinylmethanetellurolate are the only aliphatic magnesium tellurolates are prepared. 

Thiols and sulfides are occasionally prepared by treatment of Grignard reagents with sulfur.318 Analogous reactions are known for selenium and tellurium compounds. Grignard reagents... 

Alkyl phenyl telluriums and diaryl telluriums react with Grignard reagents in THF or diethyl ether in the presence of catalytic amounts of nickel- or cobalt-phosphane complexes. Tellurium is precipitated. The organic groups combine to form in most cases all three possible coupling products in ratios determined by reaction conditions . The reaction of ( Z,)-phenylethenyl phenyl tellurium and phenyl magnesium bromide formed almost exclusively ( Zj-stilbene in quantitative yield. ( ZJ-Ethoxycarbonylethenyl phenyl tellurium and phenyl magnesium bromide reacted differently ( Fj-ethoxycarbonyl-(phenyl)-ethene and diphenyl tellurium were produced. Tellurium was not formed. ... 

The intennediates in these reactions are the corresponding triaryltelluronium halides (which react with an additional equivalent of Grignard reagent) or the unstable tetraaryl-tellurium derivatives. 

It mnst be pointed out that the reaction of tellurium tetrachloride with aryl Grignard or lithium reagents is inappropriate for the preparation of diorganyltellnrium dichlorides owing to the difficulty of stopping the reaction at the 1 2 stage. 

Alkanetellurolates, that can be obtained from an organic lithium compound or a Grignard reagent and tellurium, are oxidized to dialkyl ditellurium compounds on contact with air. Di-t-butyl ditellurium, that is difficult to prepare by other routes, was obtained by this method in excellent yield1 2. The reaction of /-butyl magnesium chloride with tellurium proceeded in THF solution only in the presence of hexamethylphosphoric triamide2. 

Arenetellurolates are obtained when tellurium is reacted with aromatic lithium compounds in THF or diethyl ether (p. 154) or with aromatic Grignard reagents in THF. The arenetellurolates thus formed are hydrolyzed to tellurols. The tellurols are oxidized to the diaryl ditellurium products. 

Bis[4-acetylphenyl] Ditellurium [Grignard Method] 1 The Grignard reagent is prepared from 4.09 g (0.0165 mol) of the 1,2-dihydroxycthane acetal of 4-acetylbromobenzene in 50 ml of tetrahydrofuran and the solution cooled to 0°. 3.15 g (0.025 mol) of powdered tellurium are added and the mixture is stirred in the flask, which is open to the atmosphere, for 10-15 h. 4 Molar aqueous hydrochloric acid is added to pH 2.5 and the ditcllurium compound is extracted with three 50 ml portions of diethyl ether. The combined extracts arc filtered, dried with sodium sulfate, the solvent is evaporated, and the residue is recryslallized from diethyl ether yield 0.36 g (9%, based on bromoacetal) m.p. 104-106°. 

The reactions between Grignard reagents and tellurium dihalides frequently reported in the older literature (Vol. IX, p. 1051) produced mixtures of diaryl tellurium products and other organic tellurium compounds that were difficult to separate. Tellurium dihalides are rather unstable compounds with a strong tendency to disproportionate to tellurium and tellurium tetrahalides. The Grignard reagents, which had to be used in excess of the stoichiometri-cally required amounts, then reacted with the tellurium (p. 172) and the tellurium tetrahalide and probably not with the tellurium dihalide. 

A detailed analysis of the NMR spectra of the product obtained from phenyl tellurium bromide and 4-methylphenyl magnesium bromide revealed that diphenyl tellurium and bis[4-methylphenyl] tellurium had been formed in addition to the expected unsymmetrical compound. Pure 4-methylphenyl phenyl tellurium was obtained with stoichiometrically insufficient amounts of bromine and Grignard reagent5. 

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