Synthesis, characterization, and antimicrobial studies of half-sandwich η⁶-toluene ruthenium complexes with N,N′-bidentate ligands

Abstract

Nine new complexes [(η⁶-C₆H₅-CH₃)RuLCl]⁺(PF₆)ˉ (where L = N,N′-bidentate ligand; (C₅H₄NCH = N-Ar) where Ar = 4-methylphenyl (C₂₀H₂₀ClF₆N₂PRu, 1); 3,4-dimethylphenyl (C₂₁H₂₂ClF₆N₂PRu, 2); 2,4,6-trimethylphenyl (C₂₁H₂₄ClF₆N₂PRu, 3); 4-bromophenyl (C₁₉H₁₇ClBrF₆N₂PRu, 4); 2,5-dimethylphenyl (C₂₁H₂₂ClF₆N₂PRu, 5); 2-flourophenyl (C₁₉H₁₇ClF₇N₂PRu, 6), (4-methoxyphenyl)methylene (C₂₁H₂₂ClF₆N₂OPRu, 7); phenylmethylene (C₂₀H₂₀ClF₆N₂PRu, 8); and 3,5-dimethylphenyl (C₂₁H₂₂ClF₆N₂PRu, 9) were synthesized by reacting the corresponding N,N′-bidentate ligands with the ruthenium arene dimer in a 2:1 ratio. The compounds were fully characterized via ¹H NMR and ¹³C NMR, IR, and UV-vis spectroscopy and elemental analyses. The molecular structures of representative complexes (1, 7, and 8) were established by single-crystal X-ray diffraction studies. In the molecular structures of the complexes, the ligands coordinate to the Ru(II) centers via the pyridine nitrogen atom and the imine N atom in a bidentate manner. The other coordination sites of the Ru(II) center are occupied by the tolyl system in an η⁶ manner resulting in geometry often referred to as “pseudo-octahedral piano-stool.” All compounds were evaluated for their in vitro antibacterial activity by the disk diffusion method against a panel of Gram-negative and Gram-positive bacteria. The complexes showed promising bactericidal activity against methicillin-resistant Staphylococcus aureus ATCC 43300.

GRAPHICAL ABSTRACT

Keywords:

• Half-sandwich complexes
• bidentate ligands
• molecular structures
• antibacterial activity

Acknowledgements

We wish to extend our sincere thanks to the NRF and UKZN (URF) for financial support. Joel M. Gichumbi thanks Chuka University for the research visit leave.

Disclosure statement

No potential conflict of interest was reported by the authors.