Synthesis and biological evaluation of some new class of benzothiazole–pyrazole ligands containing arene ruthenium, rhodium and iridium complexes

Metal complexes 1–9 have been synthesized by reacting the benzothiazole–pyrazole derivative ligands (L1, L2 and L3) with the metal precursors of ruthenium (Ru), rhodium (Rh) and iridium (Ir). The complexes have been isolated as cationic mononuclear N ∩ N chelating metal complexes having the general formula as [(arene)M(κ2(N∩N)-L)Cl]PF6 where L = L1, L2 and L3, M = Ru, Rh and Ir, arene = p-cymene, Cp*. Structural studies revealed the mode of binding of the ligands to the metal centers is through the nitrogen atom of the benzothiazole ring and the pyrazole nitrogen atom forming a five-membered ring. All these complexes were characterized by various spectroscopic techniques as well as by XRD analysis. These complexes, as well as the ligands, have been investigated for antibacterial and antioxidant activity studies where only a few of the complexes exhibited antibacterial activity against Gram-positive bacterial strains, i.e., Staphylococcus aureus and Bacillus thuringiensis with complex 6 showing the highest bacterial inhibition toward Staphylococcus aureus and complexes 3, 4 and 6 showing the highest inhibition toward Bacillus thuringiensis. While for the antioxidant activity study, all the compounds showed profound antioxidant potency with complexes 6 and 9 showing more the 50% DRSA activity with reference to ascorbic acid (100%) taken as a reference. The antioxidant activity of the complexes is more pronounced as compared to their respective ligands alone. Graphic abstractBenzothiazole–pyrazole derivative ligands upon complexation with the halide bridged metal precursors resulted in the formation of mononuclear N ∩ N chelating complexes. These complexes have been investigated for biological studies such as antibacterial and antioxidant studies, and they arrayed potential response against the bacterial strains under study as well as good antioxidant activity.