Synthesis of non-classical O,N,O-pincer type transition metal (Pd, Zn, Cu) complexes and their applications

Objective: The aim of this study is the synthesis of novel Pd(II), Zn(II) and Cu(II) transition metal complexes derived from a non-classical, asymmetric and dianionic O,N,O-type pincer ligand and investigation of their catalytic activities. Material and Methods: The O,N,O-type tridentate ligand was prepared by the reaction of glycine and 1,3-diethyl-2-thiobarbituric acid. Non-classical O,N,O-type pincer complexes were synthesized by the treatment of this ligand with the selected transition metal salts in presence of pyridine, 1-methylimidazole or triphenylphosphine as ancillary ligands. Results: The structures of the obtained compounds were fully characterized by the standard spectroscopic methods. The catalytic activities of the novel pincer complexes were studied in the selected reactions. Pd(II) pincer complexes showed good catalytic activity in Suzuki-Miyaura (SM) coupling reactions and Cu(II) pincer complexes showed catalytic activity in peroxidative oxidation of cyclohexane. However, it was observed that both Pd(II) and Cu(II) complexes have no activity in transfer hydrogenation (TH) reaction of acetophenone. Conclusion: There are many studies in literature related to biological activity of pincer complexes bearing amino acid and barbituric acid arms on their backbones, however, publications regarding to the catalytic activities of such complexes are very limited. In this work, an O,N,O-type pincer ligand and its Pd(II), Zn(II) and Cu(II) complexes were synthesized, characterized by the standard spectroscopic methods and their catalytic activities were studied. It has been observed that the synthesized complexes have an important potential in catalytic applications. Keywords: Pincer, O,N,O-Pincer, Glycine, Thiobarbituric Acid, Catalytic Activity.