Synthesis, crystal structures, characterization and biological studies of nitrile-functionalized silver(I) N-heterocyclic carbene complexes

• A series of nitrile-functionalized benzimidazolium salts are reported.
• Ag complexes of nitrile-functionalized NHC are prepared.
• Crystal structure of two complexes are reported.
• Salts and complexes are evaluated for antibacterial and anticancer activity.
• Complexes showed promising activities.

The synthesis of a series of silver(I) complexes (3a–d), [1-(2′/3′-methylbenzyl)-3-(2″/3″-benzonitrile)benzimidazol-2-ylidenesilver(I)]PF6, of nitrile-functionalized N-heterocyclic carbenes (NHCs) based on benzimidazole core and their characterization and biological evaluations have been reported. The NHC precursors (1a–d and 2a–d) have been synthesized from successive N-alkylation of benzimidazole with appropriate substituted benzyl halides. Their corresponding bis-NHC silver(I) complexes, 3a–d, have been prepared from the reaction of the nitrile-functionalized benzimidazolium salts with silver(I) oxide in methanol/acetonitrile at mild reaction conditions in good yield (65–73%). Both, salts and complexes, were characterized by 1H and 13C NMR, FT-IR spectroscopic and elemental analysis techniques. The molecular structures of the silver(I)–NHC complexes, 3a and 3c, were elucidated by X-ray diffraction technique. Both the complexes displayed weak π–π stacking interactions between benzimidazole and benzyl benzene rings. All four silver(I) complexes exhibited potent antimicrobial activity against a Gram negative (Escherichia coli) and Gram positive (Staphylococcus aureus and Bacillus subtilis) bacteria. Also the IC50 values of both, salts (2a–d) and complexes (3a–d) have been determined by an MTT-based assay method against the human colon cancer cell line, HCT 116. Complexes 3a–d displayed three- to fivefold increase in the anticancer activity with the IC50 values 18.8 ± 1.3, 20.6 ± 1.5, 19.2 ± 1.0, 14.9 ± 0.8 μM compared to the anticancer potential of salts 2a–d (64.3 ± 2.5, 58.3 ± 4.5, 83.9 ± 1.5, 72.4 ± 1.0 μM), respectively.

Four nitrile-functionalized imidazolium salts and corresponding silver(I)–NHC complexes have been reported. All compounds were tested for antibacterial and anticancer activity showing all complexes are promising antibacterial and anticancer agents.Figure optionsDownload as PowerPoint slide