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.
