Nucleophilic tellurium reagents

A different approach to unsymmetrical diorganyl tellurides, in which an electrophilic tellurium species is used, involves the nucleophilic attack of organomagnesium or organo-lithium reagents to diorganyl ditellurides. 

The main routes to symmetrical diorganyl tellurides involve the direct reaction of nucleophilic telluride dianions (usually as Nii Tc) with alkylating or arylating reagents. Otherwise the electrophilic tellurium tetrahalides react with aryhnagnesium reagents, giving diaryl tellurides. 

Since PPS is prepared by reaction of p-dichlorobenzene (I) and Na2S in N-methyl-2-pyrrolidone (NMP) at ca, 240° (13), the reaction of p-dlhalobenzenes with Na Se and Na2Te appeared to be at attractive approach. We note that an unsuccessful attempt to synthesize PPSe from p-dibromobenzene (2) and Na2Se has been reported. (14) As we have recently found (la-b) that alkali metals react directly with selenium and tellurium in 1 1 and 2 1 atomic ratios in dipolar aprotic solvents, thus avoiding the use of liquid NH3 commonly used for the preparation of these reagents, and that these reagents react readily with aromatic halides, which are not activated in the usual sense for a nucleophilic... 

Two acids with mixed three-membered chains are known, namely selenopentathionic and telluropentathionic acid. They are derived from pentathionic acid by substitution of selenium or tellurium for the middle sulfur atom of the latter, and behave in reactions with nucleophilic reagents as thiosulfates of divalent selenium and tellurium. The first salts of scleno-pentathionic (84) and telluropentathionic (85) acid were isolated in 1949, although the formation reactions in aqueous solutions had been known earlier. Wood (229) has by paper electrophoresis shown that the preparative methods lead to pure products. 

The nucleophilic displacement of active halogens in allylic halides to give allylic tellurides is effected by an even simpler reagent than either (300) or (301), i.e. Te -. Once formed, the allylic tellurides decompose spontaneously to allyl radicals which couple to form 1,5-dienes, a reaction in which tellurium appears to be far superior to selenium. 

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