Synthesis and biological evaluation of arene ruthenium(II) complexes containing thiophene benzhydrazone derivative ligands

A convenient synthesis of eight new ruthenium(II) thiophene benzhydrazone complexes (1–8) having the general formula [(η 6-arene)Ru(L)Cl] (arene: benzene or p-cymene; L: bidentate substituted thiophenebenzhydrazone derivatives) has been described. They have been isolated as neutral mononuclear N∩O chelating ruthenium(II) complexes. When further reacted with sodium azide in methanol, these neutral ruthenium(II) thiophenebenzhydrazone complexes yielded corresponding azido ruthenium complexes (9–16). The complexes were characterized by IR, UV–Vis, NMR and ESI-MS spectral methods. The solid-state molecular structures of the representative complexes were determined using a single-crystal X-ray diffraction study and the geometry of complexes are pseudo octahedral and similar to the piano stool structures. The N∩O binding mode is through the azomethine nitrogen and the imidolate oxygen forming a five-membered chelating ring. All the complexes and the ligands were thoroughly screened out for antibacterial and antioxidant activity studies in which few of the complexes exhibited antibacterial activity against Gram-positive bacterial strains i.e., S. aureus and B. thuringiensis. Complex 7 shows the highest bacterial inhibition towards S. aureus, whereas complexes 7 and 8 show the highest inhibition towards B. thuringiensis. While for antioxidant activity study, it has been found that the antioxidant activity of the complexes is more prominent as compared to their respective ligands.