Xenon-carbon bonds

In the following section two aspects are discussed a) the syntheses of fluorinated and non-fluorinated alkynylxenonium salts, [XCsCXe][BF4], and b) the syntheses of polyfluoroalkenylxenonium salts [XCF=CFXe][BF4] and [CF2=CXXe][BF4]. These topics will provide further insight into the fundamental aspects regarding xenon-carbon bond formation. 

Compounds with bonding between carbon and Xe (II, TV) rely npon the maintenance of a partial positive charge on the Xe atom. A recent review detailed the full range and reactivity of these compounds so oifly a representative gronp will be described here. The first established stable system with a xenon-carbon bond is the salt [C6F5Xe]+ [C6F5BF3]... 

The noble gases were once called inert gases because they were thought to be completely unreactive. But in 1962, chemists were able to get xenon to react, making the compound XePtF6. In 1979, chemists were able to form the first xenon-carbon bonds. 

Since noble-gas chemistry was initiated in 1962, there has been interest in the possibility of making a xenon-carbon bond. Experiments in 1979 appeared to have provided a solution. When xenon difluoride was bled into the tail of a trifluoromethyl radical plasma, a volatile, waxy white solid was produced and trapped at — 196°C. The reported properties of this material are consistent with the formulation, Xe(CFi3)2 (164), but until this is independently confirmed, some doubt remains about its authenticity. 

Xenon-carbon bond formation is now quite well exemplified, and many products contain fluorinated aryl substituents, e.g. (C6F5C02)Xe(C6F5), [(2,6-F2C5H3N)XeC6F5]+ (Figure 17.7a), [(2,6-F2C6H3)Xe][Bp4] (Figure 17.7b), [(2,6-... 

In 1989, two groups working independently prepared pentafluoro-phenylxenon borates by nucleophilic displacement of fluorine in XeFa using BiCeFs), as an aryl-transfer reagent. The resulting colorless solid, which has a stable xenon-carbon bond, was characterized in solution by Xe and F NMR [e.g., Eq. (22)] (165, 166) ... 

In 1979, Lagow and co-workers reported the first evidence for a compound with a bond between xenon and carbon, namely Xe(CF3)2 (90). While the evidence for this compound still receives much scrutiny, the groups of Frohn and Naumann independently synthesized the first definitive examples of compounds with a xenon-carbon bond (91-96). Until recently all of the examples of xenon-carbon bonds were cationic species. However, earlier this year Frohn reported the preparation, characterization, and structure of C6F5Xe02CC6F5, the first truly covalent compound with not only a xenon-carbon bond, but a xenon-oxygen bond as well (97). 

Alkylaluminium compounds were transformed by xenon difluoride mainly to fluorides, while Al-carbon bond cleavage is accompanied with bright chemiluminescence141-144. 

The use of a difluoroborane, RBF2, precursor has proved to be a successful strategy for alkyl, alkenyl and aUcynyl derivatives of xenon(II). Xenon-carbon(alkene) and Xe-C(alkyne) bond formation is illustrated by reactions 18.20 and 18.21. 

Xenon Bonded to Carbon. A number of stmcturally well-characterized compounds containing Xe—C bonds are known. In all cases these occur as colorless salts of xenonium cations, R—Xe" where R is a fluorophenyl or alkynyl group. The formation of the pentafluorophenylxenon(II) cation, CgFgXe+ [121850-39-3] (-30W) and CHgC N (0°C) solutions with the anions B(C3F3)3F [121850-40-6], B(CgFg) 2F- [123168-25-2], and... 

Xenon difluoride fluorinates adamantane in low yield [45] (equation 22) When the carbon-hydrogen bond is activated by an a-sulfur atom, fliiorination occurs readily The reactions involve intermediates that contain sulfur-fluorine bonds. At-Fluoropyridinium reagents behave similarly [99, 100, 101, 102] (equations 55-57)... 

Radon forms a series of clathrate compounds (inclusion compounds) similar to those of argon, krypton, and xenon. These can be prepared by mixing trace amounts of radon with macro amounts of host substances and allowing the mixtures to crystallize. No chemical bonds are formed the radon is merely trapped in the lattice of surrounding atoms it therefore escapes when the host crystal melts or dissolves. Compounds prepared in this manner include radon hydrate, Rn 6H20 (Nikitin, 1936) radon-phenol clathrate, Rn 3C H 0H (Nikitin and Kovalskaya, 1952) radon-p-chlorophenol clathrate, Rn 3p-ClC H 0H (Nikitin and Ioffe, 1952) and radon-p-cresol clathrate, Rn bp-CH C H OH (Trofimov and Kazankin, 1966). Radon has also been reported to co-crystallize with sulfur dioxide, carbon dioxide, hydrogen chloride, and hydrogen sulfide (Nikitin, 1939). 

Xenon difluoride reacts with carbon-carbon single, double, and triple bonds giving addition fluoroorganic compounds, e.g.,... 

Koresh and Soffer (1980) used fibers or cloth (Carbone-Lorraine, France) for adsorption experiments with molecules like COj, Oj, Ar, N2, CjHj and H2. The carbon samples were filled with bonded water at room temperature. On thermal treatment in vacuum at 700°C it was observed that the largest molecule which could be adsorbed was xenon. Treatment at higher... 

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