Synthesis of Phosphine-Borane Derivatives

A dry round-bottomed flask, equipped with a magnetic stirring bar, sealed with a septum, and protected with an Ar balloon, was charged with 4- or 3-(trifluoromethyl)phenyl boronic acid (190 mg, 1.0 mmol or 570 mg, 3.0 mmol) in 1.0 mL of THF. A solution of 1.0 M diisobutyl aluminium hydride (DIBAL) in toluene (3.0 or 5.0 mmol) was added to the mixture, and the corresponding phosphine was added at 0 °C. The mixture was stirred at room temperature and monitored using TLC. Once completed, the reaction was quenched by the addition of a saturated aqueous potassium sodium tartrate solution and extracted with AcOEt. The organic layer was washed with brine and dried over Na₂SO₄. The solvent was evaporated, and the residue was purified using silica gel column chromatography (eluent = hexane/AcOEt) to generate the desired phosphine–borane derivatives. For compounds 20–22 and 32–34, the corresponding phosphines were prepared immediately before addition, without purification. The details of the characterization and spectra of the compounds are presented in the Supporting Information.