Tellurium species

Aryl derivatives of the heavier group 6 derivatives can also serve for the synthesis of arylmercury compounds.52 For instance, treatment of the diaryltellurium complex 30 with HgCl2 leads to the formation of a coordination complex which undergoes a slow dismutation reaction to afford the arylmercury chloride derivative 31 and the corresponding tellurium species (Scheme 3).53... 

The analogous selenium and tellurium species are best formed directly as their alkali-metal or ammonium salts, since the acids themselves tend to be much more unstable towards decomposition than the dithio-phosphorus acids, and are hence difficult to store and handle. Diselenophosphates can be prepared from refluxing a suspension of phosphorus(V) selenide in alcohol followed by treatment with potassium hydroxide or ammonia gas to give the... 

In this method, the electrophilic tellurium tetrachloride is employed as starting material to introduce tellurium in organic substrates, in contrast to the preceding methods using nucleophilic tellurium species. 

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. 

Like vinylic tellurides, acetylenic tellnrides can be prepared by two general approaches, starting respectively from nncleophilic or electrophilic tellurium species. 

The numbering system used for selenophene (1), tellurophene (2), benzo[6]selenophene (3) and benzo[6]tellurophene (4) is shown in Figure 1. Positions 2 and 5 in selenophene and tellurophene are referred to as a-positions and positions 3 and 4 are termed /3-positions. Alternative names for tetrahydroselenophene and tetrahydrotellurophene are selenolan and tellurolan, respectively. Benzo[c]selenophene (5), dibenzoselenophene (6) and diben-zotellurophene (7) are numbered as shown. The C4H3Se radicals (8) and (10) derived from selenophene are named 2-selenienyl and 3-selenienyl the corresponding tellurium species are named 2-tellurienyl (9) and 3-tellurienyl (11). 

Deoxypolypropionates, via ZACA reaction, 10, 273 13-Deoxyserratine, via Pauson-Khand reaction, 11, 360 2-Deoxy sugars, via rhodium(II)-catalyzed intramolecular nitrene C-H insertions, 10, 203-204 Deprotection reactions, by nucleophilic tellurium species,... 

Elemental tellurium, into nucleophilic tellurium species,... 

Lindemann, T., A. Prange, W. Dannecker, and B. Neidhart. 2000. Stability studies of arsenic, selenium, antimony and tellurium species in water, urine, fish and soil extracts using HPLC/ICP-MS. Fresenius J. Anal. Chem. 368 214-220. 

X-Ray structures of a number of tetravalent tellurium species 16 <2000JOM96>, 17 <2004JOM194>, and 18 <2002JOM34> have also been reported. 

Numerous oxidative additions of halogens to cyclic selenium- and tellurium-containing heterocycles have been reported. Treatment of the telluropyranone 66 with iodine affords crystalline tetravalent tellurium species 67 (Equation 24) <19950M1442>. The kinetics of this reaction <19950M1442> and analogous oxidations of 68 and 69 with bromine <19940M3338> have been studied using stopped-flow methods. These results indicate that the oxidative additions occur by stepwise mechanisms. 

Interaction of Nucleophilic Tellurium Species with Organic Substrates 598... 

The classes of organic tellurium compounds mentioned above are prepared by interaction of nucleophilic or electrophilic tellurium species with different classes of organic compounds. Such species are generated from elemental tellurium or from diorganoditellurides 4, as will be discussed in the following sections. 

Preparation of Nucleophilic Tellurium Species 9.13.3.1 From Elemental Tellurium and Reducing Agents... 

Preparation of Electrophilic Tellurium Species 9.13.4.1 Tellurium Tetrachloride... 

This class of organotellurium compounds is an important source of nucleophilic (Sections 9.13.3.1 and 9.13.3.2) or electrophilic (Sections 9.13.4.2.4 and 9.13.4.3) tellurium species. Diorganoditellurides can also behave as electrophiles, but in such cases normally one organotellurium group is lost. In this way, the corresponding organotellurium halides (Section 9.13.4.3) are prepared as source of electrophilic tellurium. In the past, the title compounds were prepared mainly by reduction of aryltellurium trihalides, in some cases under drastic reaction conditions5 9 11 12 (Scheme 11). 

Tellurium species are also useful to remove several different types of substituents from organic compounds. In some cases, variation of the experimental conditions allows the reductive removal of a substituent to be performed selectively in the presence of other functional groups. Scheme 26109 113 shows the removal of different substituents mediated by nucleophilic tellurium species.6,11,12... 

Similarly, the regeneration of phenols 52 from carboxylates 53,115 carbonates 54,116 or allyl ethers 55114 derivatives is performed with nucleophilic tellurium species (Scheme 28). 

Although not widely used as a route to organic tellurium compounds, the arylation of nucleophilic tellurium species has been considered for this purpose. In Scheme 32, some illustrative examples of such methods are... 

Another approach to aryl tellurides involving nucleophilic tellurium species consists in the use of aryldiazonium salts as substrates. Arenediazonium tetrafluoroborates 64 react with sodium telluride,128 potassium tellurocyanate 65, sodium 0,0-diethylphosphorotellurolate 66, or aryl tellurolate 2 to give the corresponding diaryl tellurides 3 in moderate yields (Scheme 33).129,130... 

In this section, the reactions of electrophilic tellurium species will be considered. Among these species are tellurium tetrachloride 16, organotellurium halides 7, organotellurium trihalides 5, and also diorganoditellurides 4, since these species can be attacked by carbanions. Diorganotellurium oxides 8, arenetellurinic acid anhydrides 9, and other oxidizing agents will also be discussed in Section 9.13.6.3, since in these species the tellurium atom is electron deficient. 

Dialkyl, alkyl aryl, and diaryl tellurium dichlorides were reduced by thiourea dioxide in a 2 molar aqueous solution of sodium hydroxide to the corresponding diorgano tellurium compounds4,5. The tellurium species actually reduced are the diorgano tellurium oxides or dihydroxides that are formed from the dichlorides in the basic medium. 

Fia. 6. Absorption spectra of HSOaF solution of the red tellurium species A and the yellow tellurium species B. 

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