Ruthenocycles of benzothiazolyl and pyridyl hydrazones with ancillary PAHs: synthesis, structure, electrochemistry and antimicrobial activity

Abstract

Two types of bivalent ruthenium complexes [RuL^Py(CO)Cl(PPh₃)₃] 3 and [RuL^Benz(CO)Cl(PPh₃)₃] 4 were synthesized starting from [RuH(CO)Cl(PPh₃)₃] and heterocyclic hydrazone ligands 1 and 2 respectively. X-ray diffraction studies reveal that in both types of complexes, the ligands behave as monoanionic bidentate N_hydrazonyl and N_pyridyl/N_{benzothiazolyl} donors towards ruthenium(II), thereby furnishing four-membered metallacycles. The multiple transitions in the electronic spectra have been elucidated by time dependent density functional theory (TDDFT). The redox active nature of both 3 and 4 has been substantiated from the well-defined oxidative responses and theoretical scrutiny corroborates that one of them is exclusively ligand centred while the other one is chiefly due to the Ru^II/Ru^III oxidation. Both the types of complexes exhibit a significant antimicrobial activity, although the activity of 4 is more prominent, particularly over Pseudomonas. These are analyzed by measuring ZOI, MIC as well as the extent of membrane damage and protein leakage studies. The complexes probably cause free-radical facilitated oxidative damage to the bacterial cells during the course of their activity.