Arene ruthenium, rhodium and iridium complexes containing benzamide derivative ligands: Study of interesting bonding modes, antibacterial, antioxidant and DNA binding studies

Abstract The benzamide derivative ligands of benzothiazole (L1) and benzimidazole (L2) upon reaction with halide bridged metal precursors of platinum group yielded a series of complexes (1-6) formulated as [(arene)M(κ1(N)-L)Cl2], where, L = L1 and L2, M = Ru, Rh and Ir, arene = Cp*, p-cymene. Structural studies revealed the bonding of the ligands to the metal centers takes through the nitrogen donor atom of the benzothiazole and benzimidazole moiety in a monodentate fashion. Further reaction of rhodium and iridium complexes with NaN3 in methanol yielded di-azido κ1(N3) monodentate complexes by substituting two chlorides. In the case of ruthenium, azido complexes could not be isolated. Additional treatment of the di-azido complexes with diethyl acetylene dicarboxylate (DEAD) yielded two different bonded triazolo complexes of rhodium (11 and 13) and iridium (12 and 14). In rhodium triazolo complexes, the ligands displayed a chelating mode of bonding through the carbonyl oxygen and the nitrogen atom of the benzothiazole/benzimidazole ring while in iridium triazolo complexes, the ligands retained a monodentate bonding through the nitrogen atom of the benzothiazole/benzimidazole ring and formed two triazole rings. All these complexes were characterized by various spectroscopic techniques. NMR analysis revealed the triazolo ring coordinated to the metal center via the central nitrogen in both the rhodium and iridium triazolo complexes. These complexes as well as the ligands have been studied for antibacterial, antioxidant activity as well as DNA binding studies where a few of the compounds have shown good activity. Amongst these compounds, complex 7 possessed the highest antibacterial and radical scavenging activity while ligand L1 and complexes 1 and 2 showed good affinity as DNA binders.