Phosphoranium salts

Fluorotnhalomethanes react with two equivalents of tnphenylphosphme or a tnalkylphosphine to form a fluonnated phosphoraniumsalt [5i] (equation 49). The formation of the phosphoranium salts depends upon the solvent system These salts may in turn be used for Wittig reactions [52, 5J] (equation 50) (Table 20). 

Table 20. Fluorine-Containing Phosphoranium Salts in Ftuoroolefin Syntheses [52, 53]...

The phosphoranium salt [CH(PPh2Me)2]TfO reacts with [Au(C6F5)(tht)] to afford its first metallic complex, [Au(C6F5) CH(PPh2Me)2 ]TfO, which, despite the weak nucleophilic character of the ylidic carbon, is stable.64... 

Phosphoranium salts have been shown to be very useful reagents in the Wittig olefination reaction The formation proceeds easily both when alkylphosphanes and arylphosphancs are utilized as reagents-... 

The phosphoranium salts obtained in this way are soluble in polar solvents and can be used without isolation in olefination reactions. For example, if triphenylphosphane is reacted with dibromodifluoromethane in diglyme at room temperature, the corresponding bromo(di-fluoro)methyl triphenylphosphonium salt precipitates quantitatively... 

E)-Styrenes. The phosphoranium salts are prepared by alkylation of the phosphine immediately after its generation from the corresponding phosphine oxide. The stereoselectivity of the Wittig reaction with ArCHO is very sensitive to the base used. Potassium hexamethyldisilazide is the preferred base for obtaining ( )-styrenes. 

The first examples of phosphirenium salts (129) have been prepared from the reactions of alkynes with the aluminium trichloride adducts of dichlorophos-phines. The reactions of phosphines with fluorotrihalogenomethanes lead to the first examples of fluorine-containing phosphoranium salts (130). The related nitrogen-bridged salt (131) is formed in the reactions of lithium bis(diphenyl-phosphino)amide with iodomethane. ... 

The hydrolysis of phospholanium salts based on the five-membered ring generally proceeds considerably faster than that of the corresponding phosphoranium salt based on the six-membered ring. 

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