Selenium dihalides

Recently, the first structural characterization of mixed sulfur selenium dihalides, SeSX2 (X = Br, Cl), has been reported in mixtures of S2C12 and Se2X2 (X = Br, Cl).29,30 In addition, two-dimensional NMR exchange... 

A remarkable stabilization of selenium dihalides is achieved if the central Se atom is coordinated with anionic (see Section 4.2) or neutral Lewis bases as ligands. 

Oxidation of the adducts formed from propargyl alcohols and selenium dihalides leads to formation of spiro selenuranes such as 102 and 103 (14S119). 

According to the calculations at the B3LYP/6-311-l-G(d,p) level, the addition of selenium dihalides to vinyl ethers proceeds in two steps via the seleniranium intermediate. The high selectivity stems from the consistent effects of the charge and orbital factors." ... 

Similarities are noted between the mass spectra of aliphatic and aromatic selenides with analogous sulphides and phosphines. " Selenoxides show the expected fragments derived from the selenate rearrangement product " " Extensions of these studies cover selenium dihalides (no moleculm ion is seen " ), seleninic acids and esters, " and selenones. Mass spectra of diaryl tellurides are very much like those of S and Se analogues. ... 

By contrast to the selenium systems, tert-butylimidotellurium dihalides ( BuNTeX2)n (X = Cl, Br) are thermally stable in the solid state. They are obtained in good yields in THE solution by the redistribution reaction depicted in Eq. 8.19. ... 

Fig. 1 Representative trigonal bipyramidal diaryltellurium(IV) and selenium(IV) dihalides that have been characterized by X-ray crystallography.

The lO-E-4 chalcogen(IV) species diphenylselenium(IV) dibromide (1, Fig. 1) and diphenyltellurium(IV) dibromide (2, Fig. 1) oxidize thiophenol to diphenyl disulfide in nearly quantitative yield as shown in equations (13) and (14). Tellurium(IV) dihalides 6-11 also oxidize thiophenol to diphenyl disulfide and benzene selenol to diphenyl diselenide. Similarly, the 12-Te-5 molecule dioxatellurapentalene 45 (Fig. 19) is a mild oxidant for ethylmercaptan, thiophenol, and benzene selenol giving diethyl disulfide, diphenyl disulfide, and diphenyl diselenide in essentially quantitative yield. As shown in equation (15), 1,1,5,5,9,9-hexachloro-1,5,9-tritelluracyclododecane oxidizes six molecules of thiophenol to diphenyl disulfide and 1,5,9-tritelluracyclododecane in 90% yield. In contrast, 12-Te-5 pertellurane 44 and 12-Se-5 perselenane 46 do not oxidize thiophenol to diphenyl disulfide. Instead, these molecules undergo a nucleophilic addition of thiophenol followed by cleavage of the tellurium-carbon or selenium-carbon bond. ... 

Halides, 7 1-26 actinide elements, 2 195-233 anion dependence, 39 139 berkelium, 28 48, 51-53 beryllium, 14 255-332 binary, 35 237-246, 274-280 decomposition, 35 277 dichalcogen dihalides, 35 279-280 equilibrium studies, 35 242 mixed-ligand halides, 35 244-246 reactions, 35 246 selenium halides, 35 240-241... 

Tellurium Halides. Tellurium forms the dihalides TeCl and TeBi, but not Tel2. However, it forms tetrahalides with all four halogens. Tellurium decafluoride [53214-07-6] and hexafluoride can also be prepared. No monohalide, Te2X2, is believed to exist. Tellurium does not form well-defined oxyhalides as do sulfur and selenium. The tellurium halides show varying tendencies to form complexes and addition compounds with nitrogen compounds such as ammonia, pyridine, simple and substituted thioureas and anilines, and ethylenediamine, as well as sulfur trioxide and the chlorides of other elements. 

Selenium hexafluoride, SeFg, the only clearly defined hexahalide, is formed by reaction of fluorine with molten selenium, It is more reactive than the corresponding sulfur compound, SFs, undergoing slow hydrolysis. Selenium forms tetrahalides with fluorine, chlorine, and bromine, and dihalides with chlorine and bromine. However, other halides can be found in complexes, e.g,. treatment of the pyridine complex of SeF/i in ether solution with HBr yields (py)2SeBrc Selenium tetrafluoride also forms complexes with metal fluorides, giving MSeF complexes with the alkali metals. 

As compared to the chemistry of the selenium(IV) and tellurium(IV) halides, knowledge of the reactions and stability of the corresponding halides with divalent chalcogens (oxidation number +2 for the normal dihalides, or +1 for the halides Y-X-X-Y) is less well developed. 

A number of studies of interest on other functional derivatives of the chalcogen dihalides include the preparation of novel haloselenium and halotellurium trithiocarbonates, RSC(S)SSeBr, RSC(S)STeBr, and RSC(S)STeI, as bromination and iodination products of selenium and tellurium bis(trithiocarbonates) [RSC(S)S]2X (X = Se, Te) (216), the synthesis of corresponding dithiocarboxylates RC(S)SSeY (Y = Br, I) and RC(S)STeY (Y = Cl, Br, I) by similar reactions with selenium and tellurium dithiocarboxylates as starting materials (215), the preparation of the C-brominated sulfenyl bromide, (CF3)2C(Br)SBr, by the reaction of (CF3)2C=SO with hydrogen bromide (409), and an electron diffraction study of C1SC(0)C1 (411). 

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