Topology control in nitrile-functionalized silver(I)–N-heterocyclic carbene complexes: Synthesis, molecular structures, and in vitro anticancer studies

A series of nitrile-functionalized N-heterocyclic carbene (NHC) proligands based on N-methyl-N′-benzonitrile and N,N′-dibenzonitrile imidazolium salts, 1–4, has been developed and investigated. Salts were obtained by the reaction of 2-bromomethylbenzonitrile with 1H-imidazole/1-methylimidazole in dioxane/ethanol at refluxing temperature. Following deprotonation, salts form mononuclear bis-NHC silver(I) complexes (6–8) with half an equivalent of silver(I) oxide. A dimeric silver(I) structure 5 was observed under similar conditions when NHC proligand 2 was treated with one equivalent of silver(I) oxide, however, similar complexation was not found in both the symmetrically substituted proligands 3 and 4. Compounds 2, 5 and 6 were additionally characterized by single crystal X-ray diffraction method. The dinuclear complex 5 is a symmetrical structure, with the two NHC ligands in identical chemical environment. Each silver center in 5 is coordinated by a carbene carbon atom of one ligand and nitrile nitrogen atom of another ligand unit. Preliminary in vitro anticancer studies against the human derived colorectal (HCT 116) cancer cell line using MTT-based assay method, were carried out on the reported compounds. The imidazolium proligand 3 and silver(I) complexes 5–8 revealed the following IC50 values, respectively, 5.0 ± 0.3, 1.7 ± 0.4, 6.0 ± 0.7, 1.7 ± 0.2 and 27.2 ± 1.1 μM.