Electronic effects on the acidity of phosphorus(III) triflates

A range of chiral phosphorus(III) triflates has been prepared and their donor–acceptor behaviour towards the representative donor 4-phenylpyridine investigated. Correlations between 31P-NMR shifts, relative binding strengths (Kr) and the electronic nature of the phosphorus complex are observed. A scale of relative Lewis acidity (Ar) is proposed for this class of phosphorus compound towards donor molecules using 4-phenylpyridine as a reference.