N- Phenyl- substituted carbene precursors and their silver complexes: synthesis, characterization and antimicrobial activities

A series of unsymmetrically substituted N-heterocyclic carbene (NHC) precursors (1a, 1b, 1c, 1d, 1e) were synthesized from the reaction of N-phenylbenzimidazole with various alkyl halides. These compounds were used to synthesize NHC-silver(I) complexes (2a, 2b, 2c, 2d, 2e). The five new 1-phenyl-3-alkylbenzimidazolium salts (1a, 1b, 1c, 1d, 1e) and their NHC-silver complexes (2a, 2b, 2c, 2d, 2e) were characterized by the H-1 NMR, C-13 NMR and FT-IR spectroscopic methods and elemental analysis techniques. Also, the two NHC-silver complexes 2b and 2c were characterized by single-crystal X-ray crystallography, which confirmed the linear C?Ag?Cl arrangements. The antibacterial activities of the NHC precursor and NHC-silver complexes were tested against three Gram-positive bacterial strains (Bacillus subtilis, Listeria monocytogenes and Staphylococcus aureus) and three Gram-negative bacterial strains (Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa) using the microdilution broth method. The NHC-silver complexes showed higher antibacterial activity than the NHC precursors. In addition, silver complexes 2a, 2b, 2c, 2d showed high antibacterial activity against the Gram-positive bacteria L. monocytogenes and S. aureus compared to the standard, tetracycline. Copyright (c) 2014 John Wiley & Sons, Ltd.