Synthesis and antimicrobial studies of half-sandwich arene platinum group complexes containing pyridylpyrazolyl ligands

Abstract

The reaction of [(arene)MCl₂]₂ with pyridylpyrazolyl ligands (L1 and L2) in the presence of ammonium hexafluorophosphate leads to formation of cationic complexes having the general formula [(arene)M(L)Cl]PF₆ {M = Ru, arene = p-cymene (1, 4); Cp*, M = Rh (2, 5); Cp*, M = Ir (3, 6); L = 2-(1H-pyrazol-1-yl)pyridine (L1), 2-(3,5-dimethyl-1H-pyrazol-1-yl)pyridine (L2)}. Similarly the reaction of [CpRu(PPh₃)₂Cl] and [(ind)Ru(PPh₃)₂Cl] (ind = η⁵-C₉H₇) with L1 and L2 yielded cationic complexes which have been formulated as [(Cp/ind)Ru(L)PPh₃]PF₆ (7–10). All these complexes were characterized by analytical and spectroscopic techniques. The pyridylpyrazolyl ligands coordinated metal through pyridyl and pyrazolyl nitrogens forming a six-membered metallacycle. The ligands as well as the complexes were evaluated for their in vitro antibacterial activity by agar well diffusion method against two Gram negative bacteria (Escherichia coli and Pseudomonas aeruginosa) and two Gram positive bacteria (Staphylococcus aureus and Bacillus thuriengiensis). Results show that the ligands and the complexes have significant antibacterial activity against Gram negative bacteria.

Keywords:

• Ruthenium
• rhodium
• iridium
• pyridylpyrazolyl
• antibacterial

Acknowledgments

We thank DST-PURSE SCXRD, NEHU-SAIF, Shillong, India for providing Single crystal X-ray analysis and other spectral studies. JLT acknowledges the ICMR for JRF fellowship. KMP acknowledges the support of SERB-DST and DBT-IYBA for research funding.