Probing steric influences on electrophilic phosphonium cations: a comparison of [(3,5-(CF3)2C6H3)3PF]+ and [(C6F5)3PF].
作者： James H. W. LaFortune , Kevin M. Szkop , Farah E. Farinha , Timothy C. Johnstone , Shawn Postle
DOI: 10.1039/C8DT02594K
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摘要: 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 fluoride [Et3Si(tol)][B(C6F5)4]. Lewis acidity 2 evaluated by experimental computational methods preliminary catalysis testing. Exchange reactions [(C6F5)3PF][B(C6F5)4] their respective difluorophosphoranes are studied 2D 19F–19F NOESY/EXSY selective 1D 19F NMR exchange spectroscopy (SEXSY) experiments affording comparative rates exchange. Collectively, although these data show that less acidic than [(C6F5)3PF][B(C6F5)4], improved access to P center provides a kinetic acceleration for where transition states more sterically demanding.
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