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

Article abstract of DOI:10.1016/j.jorganchem.2018.07.029

Four well-defined N-heterocyclic carbene-PdCl-[(2-Pyridyl)alkyl carboxylate] complexes have been conveniently synthesized through bridge-cleavage reactions of [Pd(μ-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.