Selenium-Oxygen-Halogen Compounds

The noble-gas compounds xenon bis(pentafluoro-orthoselenate) and xenon bis(pentafluoro-orthotellurate) are the most thermally stable of the Xe(OR)2 compounds so far known. The first decomposition products of these compounds have now been shown291 to be SeOFs and TeOF5, as shown by e.s.r spectra at low temperatures. U.v. irradiation of the xenon bis(fluoro-orthochalcogenates) at room temperature results in the quantitative formation of the peroxides F5MOOMF5 (M = Se or Te). Attempts to prepare the compound FOTeFs were unsuccesful, but the compound ClOTeFs was prepared by the reaction of mercury bis(pentafluoro-ortho-tellurate) with C1F. 

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The chemical properties of selenium fall between sulfur and tellurium. Thus, selenium reacts with oxygen similarly to sulfur, forming two oxides, selenium dioxide, Se02 and trioxide, SeOs. The metal combines with halogens forming their halides. With nonmetals, selenium forms binary compounds exhibiting oxidation states +4 and -i-6. 

Selenium-oxygen bonds. The Se chemical shifts of some inorganic selenium-oxygen compounds are listed in the Tables 2 and 3. It is apparent that Se (Vl)-species are much more shielded (5 = 944-1076 Table 2) than the Se (IV)-species (5 = 1263-1559 Table 3). This holds as well for SeO3, the anhydride of selenic acid (H2SeO4), the halogen derivatives and its alkyl esters and amides. 

Since dioxiranes are electrophilic oxidants, heteroatom functionalities with lone pair electrons are among the most reactive substrates towards oxidation. Among such nucleophilic heteroatom-type substrates, those that contain a nitrogen, sulfur or phosphorus atom, or a C=X functionality (where X is N or S), have been most extensively employed, mainly in view of the usefulness of the resulting oxidation products. Some less studied heteroatoms include oxygen, selenium, halogen and the metal centers in organometallic compounds. These transformations are summarized in Scheme 10. We shall present the substrate classes separately, since the heteroatom oxidation is quite substrate-dependent. 

Metallated polystyrenes are versatile intermediates for the preparation of a number of polystyrene derivatives. Metallated polystyrene has been prepared from haloge-nated polystyrenes by halogen-metal exchange [41,42,65,66] and by direct metallation of polystyrene [67-69] (see Chapter 4). Electrophiles suitable for the derivatization of metallated polystyrene include carbon dioxide, carbonyl compounds, sulfur, trimethyl borate, isocyanates, chlorosilanes, alkyl bromides, chlorodiphenylphosphine, DMF, oxirane, selenium [70], dimethyldiselenide [71], organotin halides [69], oxygen [72], etc. [41,42,65-67],... 

The direct electrophilic addition of the elements H—X to aikenes, dienes and alkynes, where X = halogen, nitrogen, oxygen, sulfur and selenium, is among the oldest known and most important synthetic methods used to prepare the corresponding addition compounds. Unfortunately, much of the early lit-... 

Unlike many other type of radical addition reactions, the product is most often an alkyl-cobalt(III) species capable of further manipulation. These product Co—C bonds have been converted in good yields to carbon-oxygen (alcohol, acetate), carbon-nitrogen (oxime, amine), carbon-halogen, carbon-sulfur (sulfide, sulfinic acid) and carbon-selenium bonds (equations 179 and 180)354. Exceptions to this rule are the intermolecular additions to electron-deficient olefins, in which the putative organocobalt(III) species eliminates to form an a,/ -unsaturated carbonyl compound or styrene353 or is reduced (under electrochemical conditions) to the alkane (equation 181)355. 

General Properties of Compounds of Cobalt—Cobalt and the Halogens—Oxy-Halogon Derivatives—Cobalt and Oxygen—Cobalt and Sulphur—The Alums—Cobalt and Selenium, Tellurium, Chromium, and Molybdenum—... 

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