Unsymmetrical ONO-type pincer complexes of palladium(II) containing amino acid barbiturate derivatives: Synthesis, characterization, and catalytic applications in Suzuki–Miyaura cross-coupling reaction

Abstract

New two tridentate pincer ligands were prepared by the reaction between the selected amino acids and 1,3-dimethyl barbituric acid. The corresponding Pd(II) complexes were synthesized from the treatment of palladium(II) acetate with the prepared ligands in presence of an ancillary ligand such as pyridine, triphenylphosphine, or 1-methylimidazole. All ligands and Pd(II) complexes were characterized by standard spectroscopic and analytical techniques. The crystal and molecular structures of two complexes were determined by single-crystal X-ray diffraction revealing a slightly distorted square-planar geometry around the metal center to which the ligand bonded in an ONO-tridentate fashion. The catalytic activities of Pd(II) complexes were evaluated in the Suzuki-Miyaura coupling reaction of phenylboronic acid with the different aryl halides. They showed good activity for 4-substituted aryl bromide with phenylboronic acid.