Fluoride, catalysis

Xenon difluoride [4, 5, 7, 8,10] is a white crystalline material obtained through the combination of fluorine and xenon m the presence of light The reagent is commercially available and possesses a relatively long shelf-life when stored cold (freezer) Xenon difluoride is very effective for small-scale fluormation of alkenes and activated nucleophilic substrates. The reactions are usually conducted between 0 °C and room temperature in chloroform or methylene chloride solutions Hydrogen fluoride catalysis is sometimes helpful Xenon difluoride reacts in a manner that usually involves some complexation between the substrate and reagent followed by the formation of radical and radical cation intermediates... 

Diphenylsilane catalyzed by various salts promotes the 1,2-reduction of cinnamaldehyde.318 Cesium fluoride catalysis is particularly effective.320 It is possible to stop these reactions at the silyl ether stage.73,320 The 1,2-reduction of citral is accomplished in high yield with diphenylsilane and Wilkinson s catalyst (Eq. 262) 435 Interestingly, the trialkylsilanes, ethyldimethylsilane and triethylsilane, give high yields of the 1,4-reduction product whereas diisopropylsilane gives a 1 1 mixture of 1,2- and 1,4-reduction (Eq. 263)435... 

Hydrogen Fluoride Catalysis J. H. Simons Entropy of Adsorption Charles Kemball... 

Until recently, halogen substituted alkanes were thought to be inert to xenon difluoride, but detailed examination has shown that common solvents such as dichloromethane (3) and chloroform (4) undergo fluorine-chlorine and fluorine-hydrogen exchange at room temperature due to hydrogen fluoride catalysis.15... 

Cycloalkenes treated with xenon difluoride in dichloromethane form vicinal difluorides in high yield with hydrogen fluoride catalysis. Indene produces difluorides in 72% yield the preferred <7 t/-isomer is formed.36... 

Aromatic molecules with hydroxy, amino and alkoxy groups underwent ringfluorination by xenon difluoridc in the absence of hydrogen fluoride catalysis, functional groups being unaffected.63... 

At the time this mechanism was proposed it was considered that boron fluoride catalysis showed rather similar kinetics and activation energy, differing from the stannic chloride only in that chain transfer could occur but termination apparently was very slow or absent (13). Subsequent work with boron fluoride suggests however (14) that the apparent fractional order dependence on monomer may be spurious and thus tends to discredit the data for stannic chloride in spite of the fact that the rate expressions give an excellent account of the rate of disappearance of epoxide both within and between the individual experiments. The difference in behaviour between stannic chloride und boron fluoride remains one of the unsolved problems in this field. 

In the absence of hydrogen fluoride catalysis, anisole. phenol, 2-naphthol, 1,2-dimethoxybenzene, 1,2-dihydroxybenzene and 1,3-dihydroxybcnzene react with xenon difluoride to give monosubstituted products in fair to good yield (Table 15). ... 

Trimcthyl(pentafluoroethyl)- and -(heptafluoropropyl)silanes function as facile pentafluoro-ethylatingandheptafluoropropylating agents, respectively, for carbonyl compounds under fluoride catalysis. The products 9 are best isolated as the alcohols 10... 

Activated esters, such as oxalates, are also reactive towards trimethyl(perfluoroalkyl)silanes under fluoride catalysis as reported in the case of di-/cr/-butyl oxalate which affords tri-fluoropyruvic acid 26 (Rp = CFj) in hydrated fonn. ""... 

Lactones have also been reacted with trimethyl(trifluoromethyl)silane under fluoride catalysis in tetrahydrofuran however, only the silylated hemiketals could be isolated cleanly in the case of five- and six-membered ring lactones (in 70 and 75% yield, respectively). In the case of the seven-membered ring lactone, a mixture of products resulted. 

Table 3. Reaction ofTrimethyl(perfluorophenyl)silane with Fluorinated Alkenes and Arenes under Cesium Fluoride Catalysis in Acetonitrile...

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