Nitrile functionalized silver(I) N-heterocyclic carbene complexes: DFT calculations and antitumor studies

A series of aliphatic nitrile functionalized benzimidazolium salts and their respective mononuclear N-heterocyclic carbene Ag(I)-NHC complexes are reported. The benzimidazolium salts were synthesized by N-alkylation of 1H-benzimidazole with an appropriate alkyl bromide, followed by reaction with either 5-bromovaleronitrile or 6-bromohexanenitrile. The respective mononuclear Ag(I)-NHC complexes were prepared by the reaction of the benzimidazolium salts with Ag2O. All the synthesized compounds were characterized by physico-chemical and spectroscopic techniques. The molecular structures of the two complexes were elucidated through single-crystal X-ray diffraction analyses. Density functional theory was used to model the structures of the other complexes. The benzimidazolium salts and their complexes were screened for cytotoxicity against a breast cancer cell line (MCF-7), using the MTT assay. All the Ag(I)-NHC complexes gave IC50 values ranging from 7.0 +/- 1.06 to 12.9 +/- 1.55 A mu M which are comparable to the standard drug, tamoxifen (IC50 = 11.2 +/- 1.84 A mu M), while all of the benzimidazolium salts proved to be inactive.