Tetramethyl tellurium

Tetrabutyl tellurium and tetramethyl tellurium were formed from tellurium tetrachloride and the appropriate alkyl lithium. 

Attempts to isolate the tetraalkyl tellurium compounds from their diethyl ether solutions led to decomposition5. However, tetramethyl tellurium was isolated in 77% yield when the reaction between tellurium tetrachloride and methyl lithium was carried out in the dark. 

Tetramethyl Tellurium6 A stirred suspension of 10.0 g (37 mmol) of powdered tellurium tetrachloride in 40 ml diethyl ether is cooled to — 78°. A solution of 155 mmol methyl lithium in diethyl ether(l 11 ml, 1.4 M) is dropped to the cool suspension. The reaction is warmed to 20° and stirred at this temperature in the dark for 12 h. The mixture is cooled to — 78° and filtered. The filter cake is washed with 25 ml diethyl ether. The filtrate and the washings are combined and fractionally distilled at 32° under a slight vacuum. The crude tetramethyl tellurium is collected at — 198° under vacuum and purified by vacuum distillation yield 77% b.p. 46 /20 torr. 

Tetramethyl tellurium is a malodorous, pyrophoric, yellow-orange liquid. Pure tetramethyl tellurium is extremely pyrophoric and sometimes explodes on contact with air. 

Tetraphenyl tellurium was similarly obtained in 34% yield from triphenyl telluronium iodide and phenyl lithium1,5. Solutions of tetramethyl tellurium were prepared from trimethyl telluronium iodide and methyl lithium3. The formation of butyl triphenyl tellurium was claimed in a reaction of triphenyl telluronium iodide and butyl lithium4. Equimolar amounts of triphenyl telluronium chloride and 3,3-bis[chloromercuro]-2,4-pentadione in refluxing methanol produced 3-[chloromercuro]-2,4-dioxopent-3-yl triphenyl tellurium6. 

Tetramethyl tellurium was found to be stable at 25° in the dark under an inert atmosphere9, but decomposed on exposure to intense visible light. At temperatures above 100° dimethyl tellurium, methane, and ethane were formed9. 

Hexamethyl tellurium is thus far the only known compound of this type. It was obtained from tetramethyl tellurium difluoride and dimethyl zinc2. Hexamethyl tellurium survived being heated at 140° for 4.5 hours. 

Tetraorgano tellurium compounds are thermally decomposed to diorgano tellurium compounds and hydrocarbons . Whereas tetramethyl tellurium, tetrabutyl tellurium, and diaryl dialkyl tellurium compounds already form diorgano tellurium compounds by loss of alkyl groups at or below 20° tetraphenyl tellurium tetrakis[pentafluoro-phenyl] telluriumtetrakis[4-methylphenyl] tellurium , and bis[2,2 -biphenyldiyl] tellurium must be heated to at least 100° to effect decomposition. 

V. Compounds with four tellurium-carbon single bonds or two tellurium-carbon single bonds and one tellurium-carbon double bond. Almost all of the tetraorgano tellurium Compounds are aromatic derivatives although tetramethyl tellurium was recently isolated. Aliphatic and aromatic tellurium ylides are known. 

When a toluene solution of trimethyl aluminum and bis[tributylstannyl] tellurium was kept at 90 for 15 h under argon, bis dimethylalumino tellurium was formed. In a similar reaction with bis[trimethylstannyl] tellurium the quantitative formation of tetramethyl tin was... 

Tetramethylammonium Tellurocyanate7 To 250 ml of acetonitrile are added 26.4 g (0.24 mol) or tetramethyl-ammonium chloride and 31.0 g (0.48 mol) of potassium cyanide and the mixture is stirred. Precipitated potassium chloride is filtered oil, 12.76 g (0.1 mol) of tellurium powder arc added to the filtrate, the resultant mixture is stirred at 20° for 3 h, and then filtered. The solvent is evaporated from the filtrate under reduced pressure and the residue is rccrystallized from dry acetone yield 10.6 g (50%). 

Similar reactions with tetramethyl lead, hexaphcnyl dilead, and triphenyl lead chloride yield aryl organo tellurium dichlorides4,5. 

Hexaphenyl dilead3, tetramethyl lead3, and triphenyl lead chloride4 donate phenyl groups to aryl tellurium trichlorides to produce aryl phenyl tellurium dichlorides in yields from 73 to 92%. The lead compounds are more reactive than the tin and silicon derivatives and even react at 20°. 

Ethoxyphenyl Methyl Tellurium Dichloride3 A two-necked, 250 ml flask is fitted with a dropping funnel and a magnetic stirrer. A solution of 1.06 g (3 mmol) of 4-ethoxyphenyl tellurium trichloride in 75 ml of toluene is placed in the nitrogen-flushed flask. 0.80 g (3 mmol) of tetramethyl lead dissolved in 20 ml of toluene are added dropwise to the stirred solution of the tellurium compound. The mixture is stirred overnight, then filtered, and the solvent distilled from the filtrate. The residue is recrystallized from absolute methanol yield 0.75 g (75%) m.p. 95°. ... 

The barriers to methyl group rotation in tetramethyl silane and dimethylselenane are 1.4 and 1.5 kcal/mol respectively ). Bond lengths are carbon-silicon, 1.94, carbon-selenium 1.94, carbon-tellurium 2.14 based on the sum of covalent radii ). 

The tellurocyanate ion is stabilized by bulky onium cations. The reactions of tellurium with tetraethylammonium cyanide in dimethylformamide or acetonitrile , with tetramethyl-ammonium cyanide in acetonitrile , with tetraphenylarsonium cyanide in acetonitrile , or with bis[triphenylphosphane]iminium cyanide in acetone produced onium tellurocyanates that were isolated by evaporation of the solvent. The dry salts are reported to be unaffected by oxygen . Moist air and wet solvents decompose the tellurocyanates with depostion of tellurium . 

The heavier elements of the group, S, Se and Te all form tetralluorides, EF4 and hexafluorides, EF6- If the central atom in these compounds form Lewis electron pair bonds to all the ligating fluorine atoms, it must accommodate five or six electron pairs in the valence shell, and we refer to the atoms as hypervalent. Sulfur forms no further homoleptic hypervalent derivatives. Selenium forms a solid tetrachloride, but as mentioned in the last paragraph, it decomposes on evaporation. Tellurium forms a solid tetrachloride, which may be evaporated without decomposition, as well as tetraphenyl-, tetramethyl- and hexamethyl- derivatives. 

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