Precatalyst Effects on Pd-Catalyzed Cross-Coupling Difluoromethylation of Aryl Boronic Acids

This is the authors' abstract. We don't add key points for this paper.

The Pd-catalyzed difluoromethylation of aryl boronic acids with difluoroiodomethane is shown to provide the difluoromethyl compounds in high to moderate yields by Pd(PPh 3 ) 2 /DPEphos catalyst in H 2 O/toluene. Mechanistic studies show that the oxidative addition by Pd(PPh 3 ) 4 rather than Pd 2 (dba) 3 precatalyst to difluoroiodomethane provides a square-planar trans -(PPh 3 ) 2 Pd(II)(CF 2 H)I complex defined by X-ray crystallographic analysis. The trans -(PPh 3 ) 2 Pd(CF 2 H)I complex is transformed to cis -(PPh 3 ) 2 Pd(CF 2 H)Ph detected by low temperature NMR analysis, via transmetalation with phenylboronic acids. The reductive elimination occurs via ligand exchange to DPEphosPd(CF 2 H)Ph to give Ph–CF 2 H ( t 1/2 = 144.7 min at 20 °C) with formation of the Pd(0)(PPh 3 ) 2 /DPEphos catalyst.