Synthesis of Novel Azo-Azomethine-Based Pd(II) Complexes and Catalytic Activities in the Synthesis of Vitamin K-3 (2-Methyl-1,4-Naphthoquinone)

Five types of azo-azomethine ligands (6-10) have been synthesized from the reaction of azo aldehyde derivatives with aniline. Structures of the synthesized ligand were characterized with C-13-NMR, H-1-NMR, UV-Visible spectroscopy, elemental analysis, and FT-IR. The Pd(II) complexes were synthesized from the reaction of free ligands with Na2PdCl4. From FTIR, UV-visible, C-13-NMR, H-1-NMR, elemental analysis, and HRMS analysis results, it was understood that palladium metal is bound by N and O atoms in the ligands. The catalytic activities of complexes were investigated in the synthesis of 2-methyl-1,4-naphthoquinone (vitamin K-3, 2MNQ, and menadione) with the oxidation of 2-methyl naphthalene (2MN) substrate. Acidic media (sulfuric acid, acetic acid, and hydrogen peroxide) was used as a strongly oxidizing agent in the reaction. Selectivities were reached over 75% with conversions over 89% using the Pd(II) complexes as catalysts.