Tellurium Dihalides

Imino tellurium dihalides are moisture-sensitive solids with melting or decomposition points above 100°. 

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Tellurium dihalide complexes L2TeX2 (L=ligand) tend to give planar 4-coordi-nated structures.2,3,9 From bidentate phosphine selenides dppmSe2 [Ph2P(=Se)CH2P(=Se)Ph2] and dppeSe2 two different kinds of 1 1 complexes... 

Some new Supramolecular Aspects of Diorganylselenium and -tellurium Dihalide Structures... 

This method is an efficient modification of the early method of Lederer, employing tellurium dihalides (unstable compounds which disproportionate in elemental tellurium and tellurium(IV) halides). 

DIORGANYL TELLURIUM DIHALIDES 3.9.1 From elemental tellurium... 

The dialkyl tellurium dihalides have given rise to considerable discussion in recent years. Vernon6 stated that he isolated two distinct forms of dimethyl tellurium di-iodide, from which two bases were prepared. He formulated these substances as follows,... 

Dimethyl tellurium dichioride, (CH3)2TeCl2, is prepared by similar methods to those used for the dibromide. It is the most stable of the dimethyl tellurium dihalides, and crystallises from water or alcohol in leaf-like crystals, M.pt. 92° C.3... 

The following work on diethyl tellurium dihalides 1 was carried out before Drew s discovery that the corresponding dimethyl compounds do not exist in isomeric form. It is therefore possible that the ]8-compounds to be described should be represented by formulae of the type (C2H5)3TeI.C2H5TeI3 and not by (C2H5)2TeI2 as shown. 

The following physical constants have been determined3 for the preceding diethyl compounds Extinction coefficients of diethyl tellurium dihalides molecular conductivities of diethyl tellurium compounds at 25° C., and potentiometric titrations carried out on the two bases. 

Tellurium derivatives of inorganic nature, such as tellurium dihalides, that form coordination compounds with organic ligands, such as thiourea and ethylenethiourea, are not included in this section. 

Tellurium dithiocyanate is known only in the form of its yellow complexes with thioureas. These complexes were prepared from bis[thiourea]tellurium dihalides and potassium or ammonium thiocyanate in aqueous or methanolic media. 

Bis[thiourea]tdlurium bis[thiosulfonates were obtained when thiourea-tellurium dihalide complexes were reacted with potassium thiosulfonates or when tellurium bis[thiosulfon-atcs] were treated with thioureas. Methanol or dimethylformamide served as the reaction medium. 

Bis[dialkylamino] tellurium dihalides are moisture-sensitive liquids (R = C2HS) or solids. Bis[diethylamino] tellurium difluoride decomposes at 20°. 

When bis[fluoroalkoxy] tellurium dihalides and W-Y-bis[trimethylsilyl]benzenesulfonami-de were stirred at 110° and halotrimethylsilane and fluoroalkoxytrimethylsilane removed under a vacuum of 0.003 torr, bis[benzenesulfimino] tellurium was isolated in 70 to 80% yield1. 

The possibility of preparing aryl tellurium halides from equimolar amounts of diaryl ditellurium compounds and aryl tellurium trihalides has hardly been explored. Only phenyl tellurium iodide and 2-biphenylyl tellurium bromide could be obtained by this route. The other aryl tellurium halides (including 3,4-dimethoxyphenyl tellurium chloride) decomposed under the reaction conditions to give diaryl tellurium dihalides and tellurium5. 

Aryl alkyl tellurium dihalides will lose alkyl halides on heating. The aryl tellurium halide products will disproportionate to the corresponding diaryl ditellurium in a basic environment (p. 154, 387). 

The reduction of aryl alkyl tellurium dihalides in which the alkyl group bears an electronegative substituent (chlorine, oxygen) on the /1-carbon, cleaves the alkyl group and forms diaryl ditellurium compounds. Sodium sulfide4-6, sodium hydrogen sulfite, hydrazine sulfate, and zinc effect this conversion. 

Diaryl ditellurium compounds were similarly obtained from the following aryl alkyl tellurium dihalides ... 

Aryl tellurium trichlorides are easily converted to symmetrical or unsymmetrical diaryl tellurium dihalides via reactions with organometallic compounds (see p. 549). Trimethyl(aryl)silanes transfer only the aryl group to tellurium1. 

Aryl tellurium trihalides and equimolar amounts of diaryl ditcllurium compounds in refluxing dichloromethane produce diaryl tellurium dihalides and elemental tellurium9,10. 

Organo magnesium halides and organo lithium compounds are readily accessible alkylation and arylation reagents. However, they have little practical importance for the preparation of diorgano tellurium derivatives. Tellurium tetrachloride cannot be alkylated or arylated stepwise to give, for instance, diorgano tellurium dihalides, which could... 

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. 

To facilitate the isolation and purification of the diaryl tellurium products, their conversion to diaryl tellurium dihalides is recommended1. The dihalidcs can then be reduced to the diorgano tellurium products. 

Diorgano tellurium dihalides are often the primary products of reactions producing compounds with two tellurium-carbon bonds. Such reactions arc the condensation of tellurium tetrachloride with aromatic compounds (p. 527), the addition of tellurium tetrachloride or organo tellurium trichlorides to carbon-carbon multiple bonds (p. 530, 544), and the alkylation or arylation of organo tellurium trihalides (p. 549). The symmetrical and unsymmetrical diorgano tellurium dihalides are convenient starting materials for the preparation of diorgano tellurium derivatives. 

Reaction of Diorgano Tellurium Dihalides with Sodium Sulfide General Procedure A 15-fold molar excess of sodium sulfide nonahydrate is mixed with the diorgano tellurium di halide and the mixture is heated at 90-95° on a boiling water bath. When the mixture has become liquid, it is stirred for an additional 10 min. and then cooled. Water is added to dissolve the sulfide and the mixture is filtered to collect the solid diorgano tellurium product. Liquid diorgano tellurium products are extracted into petroleum ether. Products are purified by recrystallization or distillation. 

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