Synthesis, structure, antibacterial studies and DFT calculations of arene ruthenium, Cp∗Rh, Cp∗Ir and tricarbonylrhenium metal complexes containing 2-chloro-3-(3-(2-pyridyl)pyrazolyl)quinoxaline ligand

Abstract

The ligand [2-chloro-3-(3-(2-pyridyl)pyrazolyl)quinoxaline] (L) have been prepared from 2,3-dichloroquinoxaline and 3-(2-pyridyl)-1H-pyrazole. The reaction of N,N′-bidentate chelating ligand (L) and the corresponding metal precursors [(arene)Ru(μ-Cl)Cl]2 {arene=p-cymene, benzene, hexamethylbenzene (HMB)}, [Cp∗M(μ-Cl)Cl]2 {Cp∗=pentamethylcyclopentadiene; M=Rh, Ir}, [CpRuCl(PPh3)2] {Cp=cyclopentadiene; PPh3=triphenylphosphine} and [Re(CO)5Br] leads to the formation of mononuclear metal complexes having the general formula [(arene)Ru(L)Cl]+ where, arene=p-cymene (1), C6H6 (2), C6Me6 (3), [Cp∗M(L)Cl]+ where, M=Rh (4), Ir (5), [CpRu(L)PPh3]+ (6) and [Re(L)(CO)3Br] (7). All these platinum group metal complexes were synthesized and isolated with PF6 counter anions except complex (6) whereas the complex (7) was isolated as a neutral complex. All these metal complexes were fully characterized by FT-IR, 1H NMR, UV–Vis and mass spectroscopic and analytical techniques. Moreover, the complexes (1–7) were determined by the single-crystal X-ray diffraction analysis. Single crystal X-ray data confirms that the coordination occurs to the N-atoms of the pyridyl and pyrazolyl moieties of the ligand. Agar well diffusion method reveals that complexes (1, 2, 4 and 5) are having good antibacterial activity against the three different bacteria, pathogenic test organisms Staphylococcus aureus subsp. aureus, Staphylococcus epidermidis and Escherichia coli. The electronic transitions and absorption band of the complexes calculated by using time-dependent DFT method are in good agreement with the experimental results.