Highly efficient phosphine-free Suzuki aryl couplings mediated by an in situ generated Pd(OAc)2/metformin complex in green media

An in situ generated complex of palladium(II) and a biguanide, namely metformin, was found to be a highly efficient homogeneous catalyst for the phosphine-free Suzuki–Miyaura reaction. Significant rate acceleration of the palladium-catalyzed coupling was observed when a 1:1 mixture of ethanol/water was employed as the reaction solvent. Using this protocol, a variety of aryl halides (Cl, Br, I) were subjected to reaction with various arylboronic acids and the products were obtained in good to excellent yields under mild reaction conditions.