Synthesis, structural characterization, and antibacterial activity of alkenyl functionalized imidazolium N-heterocyclic silver(I) and gold(I) carbene complexes

Abstract

Synthetic, structural, and antibacterial studies of a series of functionalized monocarbene NHC of silver(I) and gold(I) complexes are reported. Silver NHC compounds of general formula [AgCl{NHC}] 1a–e have been obtained in excellent yields by the traditional synthetic method using Ag2O, as starting material, and the corresponding 3-substituted 1-(2-methylallyl)imidazolium chloride salts L1–L5. NHC–Ag(I) compounds 1a–e were used as transmetalation agents to synthesize monocarbenes NHC–Au(I) complexes [AuCl{NHC}] 2a–e in good yields by using [AuCl(SMe2)] as a source of gold (I). All compounds were characterized by spectroscopic and analytic techniques. The molecular structures of seven compounds L3, 1a, 1d, 2a, 2a′, 2c and 2d were confirmed by a single-crystal X-ray diffraction method. Elemental analysis and powder X-ray diffraction (PXRD) experimental studies were also carried out. In addition, in vitro antibacterial assays, of the series NHC–Ag(I) 1a–e and NHC–Au(I) 2a–e were tested against three Gram positives: Staphylococcus aureus, Bacillus subtilis, and Enterococcus faecalis, and three Gram negatives: Pseudomonas aeruginosa, Escherichia coli and Salmonella typhi bacterial strains by Kirby–Bauer’s disk diffusion method. Silver compounds 1a, 1d, and all gold compounds showed excellent activity against S. aureus and S. typhi, though both types of complexes showed antibacterial activity, gold complexes were found to be the most active antibacterials. Good activity was shown by complexes 1a and 1d against P. aerouginosa, E. coli, S. typhi, S. aureus and E. feacalis and compounds 2b and 2e against E. faecalis. An excellent activity was shown by compound 2a against S. aureus with the highest inhibitory zone of 26 ± 0 mm.