New non-functionalized and nitrile-functionalized benzimidazolium salts and their silver(I) complexes: Synthesis, crystal structures and antibacterial studies

Abstract

Two series of new benzyl substituted benzimidazolium salts, non-functionalized series, 1-(2′/3′/4′-methylbenzyl)-3-(2″-propyl)benzimidazolium bromide/hexafluorophosphate (1–3·Br/PF6) and nitrile-functionalized series, 1-(2′/3′/4′-methylbenzonitrile)-3-(2″-propyl)benzimidazolium bromide/hexafluorophosphate (4–6·Br/PF6) were successfully synthesized as N-heterocyclic carbene (NHC) precursors. Reaction of 1–6·Br with Ag2O facilitate the in situ deprotonation of salt 1–6·Br that afforded the formation of a series of silver(I) complexes, [Ag(L)2]·PF6 (7–12), respectively (where L=2′/3′/4′-methyl/cyano benzyl). Both NHC ligand salts and Ag(I)–NHC complexes have been characterized using 1H and 13C NMR, FTIR spectroscopy and elemental analysis technique. Molecular structure of ligand salts 1, 2, and 4·PF6 and complexes 8, 10 and 11 were established by single crystal X-ray diffraction method. Qualitative antibacterial studies against the Gram-negative bacteria Escherichia coli (ATCC 25922) and the Gram-positive bacteria Staphylococcus aureus (ATCC 12600), were carried out on all the synthesized ligands salts (1–6·PF6) and complexes 7–12 using Kirby–Bauer disc diffusion method. All the ligand salts show negative result in this study while the antimicrobial activity of the Ag(I)–NHC complexes were varies with the nature of the ligands.