Synthesis of N-heterocyclic carbene-PdCl-[(2-Pyridyl)alkyl carboxylate] complexes and their catalytic activities towards arylation of (benzo)oxazoles with aryl bromides

Four well-defined N-heterocyclic carbene-PdCl-[(2-Pyridyl)alkyl carboxylate] complexes have been conveniently synthesized through bridge-cleavage reactions of [Pd(mu-Cl)(Cl)(NHC)](2) with (2-pyridyl) alkyl carboxylic acids [2-(pyridin-2-yl)acetic acid and 3-(pyridin-2-yl)propanoic acid]. The new complexes have been fully characterized by NMR, elemental analysis, HR-MS and X-ray single-crystal diffraction. The catalytic performance of the complexes was screened and the obtained palladium (II) complexes shown effective catalytic activities for direct arylation of (benzo)oxazoles with aryl bromides. Moreover, the 2-(pyridin-2-yl)acetate stabilized NHC-Pd complexes were more efficient than the 3-(pyridin-2-yl)propanoate stabilized NHC-Pd analogues. Further studies exhibited that 2-(pyridin-2-yl)acetate, as ancillary ligand, could easily decarboxylate and transform into 2-methylpyridine in the reaction condition. (C) 2018 Elsevier B.V. All rights reserved.