Schiff base and transition metal complexes containing methyl 6-acetamido-2-amino-4,5,6,7tetrahydrobenzo[b]thiophene-3-carboxylate: Synthesis, characterization and biological activities

The aim of this study is to synthesize and characterize the original Schiff bases and their Fe(II), Co(II), Ni(II), Ru(II), Pd(II) metal complexes and to examine their antioxidant properties. For this purpose, after synthesis of methyl 6-acetamide-2-amino-4,5,6,7-tetrahydrobenzo[b] thiophene-3-carboxylate, the starting material, 2-hydroxy-3-methoxybenzaldehyde and 5-bromo-2hydroxybenzaldehyde, two different aldehyde groups, and new Schiff base ligands were synthesized. After the Schiff base ligands are obtained, the metal complexes of the Schiff base ligands were prepared with FeCl2∙4H2O, CoCl2∙6H2O, NiCl2∙6H2O, [RuCl2(p-cymene)]2 and PdCl2(CH3CN)2 metal salts. Schiff base ligands and complexes were characterized using elemental analysis, 1H-NMR, 13C-NMR, FT-IR, LC-MS, UV-vis., magnetic susceptibility, thermal analysis methods. In order to determine the antioxidant activity of these ligands and complexes, DPPH∙ free radical removal activity, reduction force for ferric ions (Fe+3) to ferrous ions (Fe+2) according to the FRAP method, reducing force for cupric ions (Cu+2) to the cuprous ions (Cu+) with CUPRAC method and total antioxidant activities by ferric thiocyanate method were studied. It was determined that Fe(II), Co(II), Ni(II) and Ru(II) complexes had octahedral structure and Pd(II) complexes had square structure. It was also determined that complex compounds generally showed more effective antioxidant activity than ligands.