Versatile coordination modes of benzothiazole hydrazone derivatives towards Ru(II), Rh(III) and Ir(III) complexes and their reactivity studies with azides and activated alkynes

Abstract

Metal precursors of the type [(p-cymene)RuCl2]2 and [Cp*MCl2]2 (M = Rh/Ir) on reacting with benzothiazole hydrazones ligands (L1 = benzylidenehydrazinyl benzothiazole, L2 = 4-flourobenzylidenehydrazinyl benzothiazole and L3 = 4-methylbenzylidenehydrazinyl benzothiazole) in the ratio of 1:2 (M:L), leads to the formation of range of complexes. In the case of ruthenium precursor with ligand L1, a cationic complex [(p-cymene)Ru{κ2(NN’)L1}Cl]Cl (1) is formed whereas with L2 and L3 neutral complexes [(p-cymene)Ru{κ2(NN’)L2/L3}Cl2] (4 and 7) are obtained. Rhodium precursor with L1 and L2 forms mono dentate neutral complexes [Cp*Rh{κ1(N)L1/L2}Cl2] (2 and 5) while with L3 bidentate NN′ bonding complex [Cp*Rh{κ1(NN’)L3}Cl] (8) is obtained. However, iridium precursor with these ligands yielded neutral bidentate complexes (3, 6 and 9) having the general formula [Cp*Ir{κ2(NN’)L}Cl] where L = L1, L2 and L3 respectively. Some of these complexes have been treated with sodium azide to yield azido compounds. Conformational switching of the benzothiazole hydrazone derivatives of complexes 2 and 5 from trans (E) to cis (Z) are observed on treatment with sodium azide. These azido complexes obtained, have been treated with activated acetylenes of dimethyl and diethyl acetylene carboxylates, which undergo [3 + 2] cycloadditions to form arene ruthenium triazolato complexes. All these complexes have been characterized by analytical, spectroscopic and single crystal x-ray diffraction studies. These complexes have also been carried out for antibacterial studies, but unfortunately none of these compounds or ligands exhibits antibacterial activity towards gram-positive and gram-negative bacteria.