[Pd(L)Cl2]-Catalyzed Selective Hydroxylation of Arylboronic Acids to Phenols

The palladium complex [Pd(L)Cl-2] (1) has been prepared by the reaction of Pd(COD)Cl-2 (COD = 1,5-cyclooctadiene) with L [N,N'-bis(diphenylphosphanyl)-2-(diphenylphosphanyl)ethanamine]. The ligand L and complex 1 have been characterized by elemental analysis, mass spectrometry and H-1/P-31 NMR spectroscopy. In the presence of O-2, 1 selectively catalyzes the hydroxylation of a variety of arylboronic acids to the corresponding phenol derivatives in solvents with low-dielectric constants at 298 K, although in solvents with high dielectric constants the same reaction leads to the formation of both phenol and the coupled product, i.e. biaryl. The mechanistic aspects of the selective phenol formation from arylboronic acid with 1 have been addressed.