RESUMO
The electrophilic phosphonium cation (EPC) salt [(3,5-(CF3)2C6H3)3PF][B(C6F5)4] (2) is prepared via oxidation of the precursor phosphine with XeF2 and subsequent abstraction of fluoride with [Et3Si(tol)][B(C6F5)4]. The Lewis acidity of 2 is evaluated by experimental and computational methods and by preliminary catalysis testing. Exchange reactions of 2 and [(C6F5)3PF][B(C6F5)4] with their respective difluorophosphoranes are studied by 2D 19F-19F NOESY/EXSY and selective 1D 19F NMR exchange spectroscopy (SEXSY) experiments affording comparative rates of fluoride exchange. Collectively, although these data show that 2 is less Lewis acidic than [(C6F5)3PF][B(C6F5)4], the improved access to the P center of 2 provides a kinetic acceleration for fluoride exchange and catalysis where the transition states are more sterically demanding.
RESUMO
A series of phosphines incorporating (C6Cl5) substituents, Ph2P(C6Cl5) 1, PhP(C6Cl5)22, P(C6Cl5)33 and (C6F5)P(C6Cl5)24 were prepared. In the case of 1, 2 and 4, these were converted to the corresponding aryl-difluorophosphoranes 5-7via reaction with XeF2, whereas reaction of 3 with XeF2 afforded only an inseparable mixture of products. The compounds 5-7 were converted to the fluorophosphonium cations 8-10, whereas the reaction of 3 with Selectfluor afforded (C6Cl5)2POF and (C6Cl5)2. The fluorophosphonium salts showed evidence of improved air stability as well as Lewis acid catalytic activity in hydrodefluorination, hydrosilylation, deoxygenation and dehydrocoupling chemistry.
RESUMO
Reactions of the boranes (C6F5)2BR (R = C6F5, Ph, H) with the nitrene-iodine reagents XC6H4SO2N=IPh, X = Me, Cl and MeSO2N=IPh effect the insertion of nitrene into the BC and BH bonds affording the species (C6F5)2BN(SO2C6H4X)R (X = Me, R = C6F5 1, Ph 3, H, 4, X = Cl, 5, X = NO2, 7) and (C6F5)2BN(SO2Me)H 6).
