Tellurium compounds tetravalent

Electrophilic addition reactions of tetravalent tellurium compounds have been reviewed.64 2-Naph-thyltellurium trichloride (ArTeCb) adds to alkenes in an anti stereospecific manner (equation 11), whereas tellurium tetrachloride gives mixtures of 2 1 adducts with both syn and anti addition.72 A one-pot alkene inversion procedure has been developed, based upon TeCU addition to alkenes followed by treatment of the (3-chloroalkyltellurium trichloride adduct with aqueous Na2S (Scheme 37).73 Tellurium compounds such as tellurinyl acetates, ArTe(0)0Ac, prepared in situ through reaction of tellurinic acid anhydrides with acetic acid, can be employed in oxytelluration and aminotelluration procedures (Schemes 38 and 39).74 In the oxytelluration reaction intermediate triacetates of the type RCH2Te(OAc)2Ph are reduced with hydrazine to the corresponding tellurides. 

Tellurium compounds that do not have a tellurium-carbon bond but contain at least one carbon atom in the molecule, in which the tellurium atom is divalent, tetravalent, or hexavalent, have been prepared. The tellurium atom in these compounds is linked to carbon atoms via one or more heteroatoms such as B, Al, Si, Ge, Sn, Pb, P, As, S, Se, and Hg. The derivatives of divalent tellurium can be considered to be derived from the unknown telluroxylic acid (H2Te02), those of tetravalent tellurium from the unknown orthotellurous acid (H4Te04), and those of hexavalent tellurium from the well known orthotelluric acid (H6Te06). 

This section presents the methods for the preparation of tetravalent tellurium compounds that fulfill the following conditions the tellurium atom is not directly bonded to a carbon atom and the molecule contains at least one carbon atom. These orthotellurous acid derivatives are arranged according to the groups in the periodic table to which the atom... 

Only a few representatives of this class of tetravalent tellurium compounds are known. Dithiocarbamate acts as a bidentate ligand in these compounds. The two halogen atoms are... 

Organic tellurium compounds with one Te—C bond containing divalent, tetravalent, or hexavalent tellurium have been prepared. The most widely investigated and best characterized compounds are the diorgano ditellurium derivatives and the organo tellurium trihalides. Pentafluoroethyl tellurium chloride tetrafluoride is the only known example of a hexavalent tellurium compound with one Te-C bond in the molecule. 

The class of organic tellurium compounds with two Te —C bonds contains divalent, tetravalent, and hexavalent tellurium derivatives. 

V-Bromosuccinimide and similar. V-halo compounds5 oxidize diaryl telluriums to tetravalent tellurium compounds with one halogen atom and the nitrogen-containing group bonded to tellurium. 

Tetravalent diorgano tellurium compounds with one hydroxide and one perchlorate ... 

Vanado-tellurites.—These compounds are of interest in that they are the only heteropoly-acid compounds containing tetravalent tellurium. They are prepared by mixing hydrochloric acid solutions of tellurium dioxide with solutions of vanadium pentoxide in caustic soda and then neutralising with more hydrochloric acid, or by mixing strongly alkaline... 

When tellurium tetrakis[diisopropyldithiocarbamate] (0.17 mmol) in dichloromethane was stirred with a mixture of tellurium (0.4 mmol) and iodine (0.4 mmol) for three hours, reddish-brown, plate-like crystals of the composition [(H3C)2CH]2N-CSJ3Te2I3, containing one divalent and one tetravalent tellurium atom, were formed. The structure of this compound was ascertained by X-ray crystallography1. 

Tellurinic acids and their derivatives contain tetravalent tellurium. The following types of compounds are known ... 

The elements yield tetravalent derivatives m special circumstances, iu which they function as the basic elements. In the case of oxygen they are termed oxonium salts sulphur yields sulphonium salts whilst selenium and tellurium offer an even wider range of derivatives. Thus, the following types of compounds are now well known ... 

Essentially all the reactions so far reported which result in the formation of a C—Tc bond at a stereogenic carbon center involve addition of tetravalent perhalotellurium compounds (see also Houben-Weyl Vol. E12b, p299ff) to alkenes. The earliest report which examined the stereochemical aspects of such additions found that addition of tellurium tetrachloride and aryltellurium trichloride to cyclohexene affords (1,S, 2,S )-2-chlorocyclohexyltellurium trichloride (1) and aryl(lS, 2S )-2-chlorocyclohexyl]tellurium dichloride 2, respectively85 86. 

During the search for homogeneous systems in which the tetravalent perhalotellurium compounds would undergo addition to an alkene, trimethylchlorosilane, acetyl chloride, or acetyl bromide were found to be a convenient source of halogens for the conversion of tellurium dioxide to a tellurium tetrahalide88. Addition of twice the stoichiometrically required amount of cyclohexene to a solution of tellurium tetrahalide, thus generated in either acetic acid, dichloromethane or ethanol-free chloroform leads to the formation of (fra i-2-halocyclo-hexyl)tellurium trihalides in ca. 70% yield. When dry methanol is used as solvent, trans-2-... 

Compounds containing tetravalent tellurium in which the tellurium atom is bonded via one or more heteroatoms to at least one carbon atom, can formally be considered as condensation products formed from orthotellurous acid and compounds with one or two active hydrogen atoms in the molecule. 

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