Tellurocarboxylate

Coupling sodium tellurocarboxylates with R SiCl gives the unstable silyl derivative which isomerizes to the more thermodynamically stable RC(Te)OSiR 3 through a facile rearrangement that can be readily followed by 13C NMR spectroscopy. This contrasts with the reaction of alkali metal thiocarboxylates which give the O-silyl ester directly. There is no evidence for the S-silyl intermediate101. 

A large number of stable /e-organo tellurocarboxylates were prepared from tellurolates and aliphatic1,2 or aromatic2 carboxylic acid chlorides or aliphatic carboxylic acid anhydrides . The tellurolates were obtained by reduction of diorgano ditelluriums with sodium borohydride. 

From Sodium or Piperidinium Tellurocarboxylates and Alkyl Iodides... 

The red, oily sodium tellurocarboxylates (p. 162) react with an excess of an alkyl iodide at temperatures between — 63 and — 30° to give alkyl tellurobenzoates, yellow to orange oils or crystals, that are relatively stable thermally and hydrolytically. They can be stored at — 20° under argon for weeks but they are very sensitive towards oxygen. The methyl tellurobenzoates are the least stable of the tellurobenzoates1,2. 

Examples of similarly prepared alkyl tellurocarboxylates are1 ... 

When phenyl trimethylsilyl tellurium and acyl chlorides are mixed in dry tetrahydrofuran under an argon atmosphere at 20°, phenyl tellurocarboxylates are obtained in almost quantitative yields. The tellurobenzoates are relatively stable and can be purified by recrystallization or column chromatography. The telluroalkanoates are too unstable for isolation in pure form3. 

Diphenyl ditellurium in acetonitrile reacted at 125° with carbon monoxide at 100 atm in the presence of octacarbonyldicobalt to give phenyl tellurohenzoate in 52% yield. Carbon monoxide at only one atmosphere and 0° effected the same conversion when benzoyl(tetracarbonyl)cobalt was used instead of octacarbonyldicobalt. Addition of triphenylphosphane to the reaction mixture prevented the formation of phenyl telluroben-zoate. Attempts to carry out this carbonylation catalytically with respect to the cobalt compound failed. Bis[4-methoxyphenyl] ditellurium and didodecyl ditellurium did not produce any tellurocarboxylic esters under these conditions2. 

Only a few representatives of tellurocarboxylic acid anhydrides have been prepared from tellurium, sodium telluride, or bis[trimethylsilyl] tellurium and alkanoyl or arenoyl chlorides. Diacyl telluriums are stable at 20°, however, they are very sensitive to air and moisture. 

Whether the tellurocarboxylates are present in the tellurono- or the tellurolo-form is not known. Alkylation with alkyl iodides produces Te-alkyl tellurolocarboxylates1,2, while reaction with 2,4-dinitrobenzenesulfenyl chloride gives 7e-benzoyl. S-2,4-dinitrophenyl telluride sulfides. Oxidation with benzenesulfonyl chloride gives dibenzoyl ditelluriums2. The tellurocarboxylates are red, oily substances of low thermal stability and great sensitivity toward oxygen. 

Te-Esters of tellurocarboxylic acids were prepared from tellurolates and carboxylic acid chlorides or anhydrides, and from sodium telluride and aroyl chlorides". The following types of 7e-organo tellurocarboxylates have thus far been synthesized ... 

Irradiation of benzene solutions of 7e-aryl arenetellurocarboxylates with light from a mercury lamp generated radicals via homolytic cleavage of the Te—CO bond. The free radicals subsequently formed aldehydes, diorgano tellurium compounds, and diorgano ditellurium compounds via hydrogen abstraction, dimerization and elimination of tellurium, or dimerization -. The products of the photo-induced reaction of Te-4-methylphenyl 2-methylthiobenzene(tellurocarboxylate) are given as an example . ... 

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