Biarylphosphine Ligands

1-[2-(Di-tert-butylphosphino)phenyl]-3,5-diphenyl-1H-pyrazole (1) is a useful biarylphosphine ligand. In the Pd-catalyzed amination of aryl halides, the desired coupling products can be obtained in high yields by using 1 as a ligand. This reaction has a fairly broad substrate scope.

Typical Procedure:
To a purple solution of Pd₂(dba)₃ (0.0500 mmol), 1 (0.125 mmol), and t-BuONa (3.00 mmol) in toluene (5.00 mL) are added the amine (3.13 mmol) and the aryl halide (2.50 mmol). The orange solution is heated to 85 °C for 2–16 h. The reaction is cooled to room temperature, quenched with H₂O (15 mL) and extracted with EtOAc (15 mL). The organic layer is washed with brine (10 mL), dried (Na₂SO₄) and concentrated in vacuo. The coupled product is isolated by flash chromatography on silica gel typically using a mixture of hexane and EtOAc as eluent.