Phosphonium salts as room-temperature ionic liquids in organic synthesis

摘要

Applications of nitroqen-based room-temperature ionic liquids,including those based on ammonium,imidazolium or pyridinium cores,occupy centre stage in the rapidly expanding literature pertaining to their use as green solvents for a multitude of both catalytic and stoichiometric reactions.This situation is due both to the historical development of the field of molten salts,and the ready availability of quaternary nitrogen-based systems.In contrast,few applications have been reported pertaining to the use of phosphonium salt ionic liquids,several of which are now readily available in industrially relevant quantities.In this mini-review,we focus on the chemistry of phosphonium salts as benign and sustainable media for a variety of chemical transformations,highlight some of their unique properties in comparison with nitrogen-based systems,and describe their interesting chemical reactivity uncovered so far.