Synthesis and Lewis acidity of fluorophosphonium cations

Abstract

A series of fluorophosphonium salts, [R₃PF][X] (R = alkyl or aryl; X = FB(C₆F₅)₃, [B(C₆F₅)₄]), have been prepared by reactions of phosphine/borane frustrated Lewis pairs (FLPs) with XeF₂ or difluorophosphoranes with [Et₃Si][B(C₆F₅)₄]. As the substituents bound to phosphorus become increasingly electron withdrawing, the corresponding fluorophosphonium salts are shown to be increasingly Lewis acidic. Calculations were also performed to determine the relative fluoride ion affinities (FIA) of these fluorophosphonium cations.