The p <i>K</i> _a Values of P–H Bonds of Triorganophosphonium Bistriflimides in Toluene

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 p<i>K</i>_a 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 p<i>K</i>_a 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 ³¹P{¹H} NMR spectroscopic studies. These experimentally determined p<i>K</i>_a values exhibit good linear correlations with the corresponding DFT-computationally determined values. In the future, it is expected that these experimentally determined p<i>K</i>_a values of P-H bonds in toluene will provide guidelines for the rational design of catalytic reactions.