Unsymmetrical tellurides

Diorganyl tellurides, compounds with two organic groups linked to a tellurium atom, constitute the most abundant and famihar class of organic tellurium compounds. The organic groups, of the most differentiated types, can be identical or different, giving rise to symmetrical or unsymmetrical tellurides. 

The magnesium aryl tellurolates described earlier have seldom been employed for the preparation of unsymmetrical tellurides." ... 

In contrast, tellurium insertion in alkyl- or aryllithium compounds followed by alkylation is a useful method for the synthesis of unsymmetrical tellurides. (For a tabulation of unsymmetrical tellurides prepared by alkylation of organyl tellurolates, see ref. 8.)... 

The reaction of organyltellurium trichlorides with NaBH followed by the in situ treatment of the generated tellurolate with alkyl halides is a useful method to prepare several types of unsymmetrical telluride ... 

Palladium(0) converts symmetrical and unsymmetrical tellurides into coupled compounds under mild conditions. ... 

Alkali tellurides 13 and 14, or ditellurides 15, are potent nucleophiles and react rapidly with alkyl halides. Table 1 presents some representative examples of such reactions leading to dialkyl tellurides 3 and dialkyl ditellurides 4. Alkali organotellurolates 2 are also potent nucleophiles and are used to prepare symmetrical and unsymmetrical tellurides (Table 2). 

Treatment of alkali metal alkyl or aryltellurolates (Sections) with alkyl halides, aryl halides, alkenes, or alkynes have been nsed to prepare unsymmetrical tellurides, as exemplified by the reaction of sodium phenyl teUurolate or paramethylphenyl tellnrolate with PhC CHCOPh. ... 

Elemental tellurium reacts with organometallic compounds, i.e. RM, to furnish metal tellurolates (Scheme 15.19) these are widely used as useful sources of tellurium for synthesis of a variety of unsymmetrical tellurides [57]. 

Although unsymmetrical tellurides are obtained by stepwise alkylation of Na2Te... 

Unsymmetrical telluro-substituted fatty esters (of biological interest) are obtained in about 40% yield after chromatographic separation from the symmetrical tellurides. ... 

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. 

Unsymmetrical diorganyl tellurides (general procedure). A solution of the ditelluride (2 nunol) in THE (30 mL) is treated dropwise at 0°C under N2 with Br2 (0.32 g, 3 mmol)... 

The protocol shown in Section 3.1.2.7 is also usefnl to prepare unsymmetrical diaryl tellurides. ... 

Another application of the above hydrotellnration protocol involves the synthesis of unsymmetrical divinyl tellurides by the addition of sodinm vinyhc teUnrolates, generated... 

The discovery of efficient methods for the reduction of tellurium in organic media to disodium telluride, which can be alkylated in situ, led to the preparation of many dialkyl telluriums. The greatest progress has been achieved, however, in the preparation of unsymmetrical diorgano telluriums by alkylation or arylation of tellurolates or by modification of the organic groups in diorgano telluriums. 

Unsymmetrical dialkyl tellurium derivatives were prepared by mixing an aqueous disodium telluride solution with equimolar amounts of two different alkyl halides. All three possible dialkyl tellurium products are formed. The unsymmetrical dialkyl tellurium is the predominant species. It can be separated from the symmetrical compounds by chromatography1. This one-pot procedure takes less time to complete than the alternative route employing alkyl tellurolates (p. 387) and was used to prepare unsymmetrical dialkyl telluriums containing radioactive tellurium. Sequential addition of two alkyl halides produced only symmetrical dialkyl telluriums. 

Diorganyl mono- and ditellurides are the best-known classes of organic tellurium compounds comprising symmetric and unsymmetric alkyl, aryl, and alkyl-aryl tellurides. In addition to acyclic tellurides, heterocychc aliphatic telluroethers as well as aromatic tellurophene-derivatives are known (for a review, see Ref 36). 

Ten /13-TePh ligands adopt an unsymmetrical pattern of one shorter , one longer and one intermediate Cu-Te bonding distances. These distances (2.552(3)-2.708(3) A) are, expectedly, shorter than their Ag-Te counterparts, and reflect the difference between the ionic radii of the two metals.This contraction of the metal-tellurium bonding distances is reflected in the overall size of the cluster frame. Thus, for comparison, the Te4 - Te7 distance is 12.29 A in 5 and 12.95 A in 3a similarly the telluride ligands Tel5-- Tel6 are 7.72 A apart in the copper complex whereas they are separated by 8.81 A in the silver cluster 3a. 

Table 4.9 Synthesis of Unsymmetrical Sulfides, Selenides, and Tellurides ...

---