Fluorinated organosilicon compounds

Fluorinated organosilicon compounds may be prepared from readUy available fluorohalocarbons by using phosphorous amides [84, 85, 86] or tetrakis(dimeth-ylamino)ethylene [57] for the generation of the fluoroorganic nucleophiles (equations 61-69). 

Title Fluorinated Organosilicon Compounds and Fluorochemical Surfactants... 

Replacements of one or two chlorine atoms and hydrogen by fluorine were observed in various organosilicon compounds in reactions with xenon difluoride99,135, while aryl-silicon bond cleavage was observed in the presence of potassium fluoride136,137 (Scheme 57). 

The first observation of penta- and hexaeoordinate silicon compounds was reported at the beginning of the 19th century by Gay-Lussac [87] and Davy [88], Subsequent investigation of hypercoordination in silicon compounds stimulated widespread use of nucleophilic activation and catalysis in the application of organosilicon compounds as reactive species in organic synthesis. Synthetic application for silicon-fluorine bond formation can be found in several reviews over the last two decades, and this section focuses on recent advances in the use of hypervalent organosilicon compounds in selective organic synthesis, in particular, selective carbon-carbon bond formation [89]. 

A wide variety of functional organosilicon compounds with the same built-in ligand have been synthesized. A trigonal bipyramidal (TBP) structure for these compounds has been proposed on the basis of the similarity of their spectra with those of known pentacoordinate germanium (134) and tin (41) compounds. Furthermore the TBP structure follows from the low temperature 19 F NMR study (134) of o-(Me2NCH2)C6H4SiF3 214 (Figure 40), which exhibits a triplet and a doublet of relative intensities 1 and 2 consistent with two equatorial and one apical fluorine atoms. 

A rapid procedure has been described10 based on sodium peroxide bomb fusion, for the determination of silicon and halogen in fluorine-containing organosilicon compounds and resins. The silicon is separated from the decomposition product as zinc silicate and estimated gravimetrically as silica. The filtrate is concentrated, acidified and, when necessary, reduced with sulphur dioxide. Chloride, bromide or iodide is then determined by the usual methods. Fluoride can be determined in neutral solution either gravimetrically as calcium fluoride, or volumetrically with zirconium tetrachloride or thorium nitrate, or directly in the decomposition solution by titration with zirconium tetrachloride. 

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