The p K a Values of P–H Bonds of Triorganophosphonium Bistriflimides in Toluene

Key findings from this study

• The study determined experimentally the pKa values of P-H bonds in eight triorganophosphonium bistriflimides in toluene using UV-visible and 31P{1H} NMR spectroscopy.
• The authors report that these experimental pKa values show strong linear correlations with corresponding DFT-calculated values.
• The researchers demonstrate that the anchor compound method enables reliable thermodynamic characterization of phosphonium salt acidity in non-aqueous media.

Overview

Triorganophosphonium bistriflimides function as air-stable precursors to air-sensitive phosphines in transition metal catalysis. The study experimentally determined pKa values for P-H bonds of eight triorganophosphonium bistriflimides in toluene. These values were obtained through spectroscopic characterization and correlate with computational predictions.

Methods and approach

The researchers employed an anchor compound methodology using 2-(4-trifluoromethanesulfonato)phenylmalononitrile, which exhibits sufficient toluene solubility for self-dissociation equilibrium constant determination. UV-visible and 31P{1H} NMR spectroscopy provided experimental pKa data for the phosphonium salts and thirteen reference compounds. Density functional theory calculations were performed to validate experimental findings.

Results

Eight triorganophosphonium bistriflimides exhibited experimentally determined pKa values in toluene. The dataset included thirteen tool compounds spanning C-H, O-H, and N-H acidic species. Experimental pKa values demonstrated strong linear correlations with corresponding DFT-computed values, validating the computational approach for phosphonium salt acidity prediction.

Implications

The experimentally determined pKa values establish quantitative basicity requirements for releasing triorganophosphines from their bistriflimide salts in organic media. This thermodynamic framework enables rational selection of base strengths in catalytic system design. The linear correlation between experimental and computational values suggests DFT methods can predict phosphonium acidity reliably.

These pKa measurements provide benchmarks for phosphine generation in non-aqueous solvents where conventional aqueous pKa values prove inapplicable. Understanding P-H bond acidity in toluene facilitates optimization of in situ phosphine formation. Future catalytic applications may exploit this quantitative relationship to tune reactivity through phosphine ligand selection.

Scope and limitations

This summary is based on the study abstract and available metadata. It does not include a full analysis of the complete paper, supplementary materials, or underlying datasets unless explicitly stated. Findings should be interpreted in the context of the original publication.