Homocoupling of Arylboronic Acids Catalyzed by a Simple Hydrophilic Palladium(II) Complex in Aqueous Media

Homocoupling of arylboronic acids has been successfully carried out by using the inexpensive hydrophilic palladium( II) complex PdCl2(NH2CH2COOH)2 as catalyst in i-PrOH/H2O (v/v=1:2) under aerobic atmosphere without elevated heating to give rise to symmetrical biaryls in moderate to good yields. The aqueous media, room temperature reaction and the low amounts of catalyst (0.5 mol%) show a practical and environmentally benign protocol. In addition, enhancement of yield was observed in the presence of 0.5 equiv. p-toluenesulfonyl chloride. Furthermore, the byproducts of this reaction were not observed while biaryl is the only product, which results in much more facile in the separation of the product symmetrical biaryls from arylboronic acids.