Palladium(II) pyridoxal thiosemicarbazone complexes as efficient and recyclable catalyst for the synthesis of propargylamines by a three‐component coupling reactions in ionic liquids

The palladium(II) complexes (1 and 2) were obtained from the reaction of [PdCl2(PPh3)2] with the tridentate Schiff base ligands, pyridoxal thiosemicarbazone (L1), and pyridoxal N-methyl thiosemicarbazone (L2), respectively in ethanol. These complexes were characterized by elemental analyses, IR, UV–Vis, 1H NMR, 31P NMR and ESI-MS spectroscopy. The molecular structure of the complex [Pd(L2)PPh3] (2) was determined by single-crystal X-ray diffraction, which reveals a distorted square planar geometry around palladium(II) ion. To screen the catalytic properties of the synthesized complexes, palladium(II) complex catalyzed three-component coupling reaction of aldehydes, amines and phenylacetylenes under solvent free conditions in ionic liquid at 80 °C were done to synthesize propargylamines in high yields. The effect of solvent, time, temperature, catalyst loading and substituent on ligand moiety on the reaction was also studied. The results showed that the supported catalyst with low loading (1.0 mol%) showed high stability, which could be recovered also and reused for minimum 5 times without significant loss of its activity.