Investigation of the palladium catalyzed aromatic coupling of pyridine derivatives

The coupling reaction of 4-methylpyridine to form 4,4 ' -dimethyl-2,2 ' -bi pyridine using a carbon-supported palladium catalyst was studied. Whereas p revious research indicated that the reaction is catalyzed by palladium(0), we have found evidence that the reaction is catalyzed by palladium(II). Alt hough oxygen can be used as the oxidative agent, the reaction is ultimately Limited by catalyst deactivation. The major source of deactivation is most likely depletion of the palladium(II) oxide. The catalyst is reduced durin g the reaction and in the case of the oxygen-treated catalyst a small amoun t of palladium appears to be dissolved. In an investigation of the catalyst using X-ray photoelectron spectroscopy (XPS) and solid state nuclear magne tic resonance (NMR) it was found that deactivation is also caused by poison ing, the poison being either the product and/or the by-product. (C) 2000 El sevier Science B.V. All rights reserved.