Triorganophosphonium salts are normally air-stable and important reagents in transition metal-catalyzed organic synthesis, which can release air-sensitive triorganophosphines in situ in the presence of bases. Herein, a series of experimentally determined pKa values of P-H bonds of triorganophosphonium salts in toluene are reported. From the self-dissociation equilibrium constant of the anchor compound 2- (4-trifluoromethanesulfonato) phenylmalononitrile which is readily soluble in toluene, the pKa values of P-H bonds in 8 triorganophosphonium bistriflimides and 13 tool compounds (including 10 C-H acids, 2 O-H acids, and one N-H acid in toluene) were experimentally determined based on a combination of UV-visible and 31P1H NMR spectroscopic studies. These experimentally determined pKa values exhibit good linear correlations with the corresponding DFT-computationally determined values. In the future, it is expected that these experimentally determined pKa values of P-H bonds in toluene will provide guidelines for the rational design of catalytic reactions.
Liang et al. (Thu,) studied this question.