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

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)]center dot 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 H-1 and C-13 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 colt (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. (C) 2016 Elsevier Ltd. All rights reserved.