New benzimidazolium salts (2, 3) and their silver (4, 5) and palladium (6, 7) N-heterocyclic carbene (Ag-and Pd-NHC) complexes were designed, synthesized and structurally characterized by NMR (H-1 and C-13), IR, HRMS and UV-Vis spectroscopic methods. All the synthesized compounds were tested in human colon cancer (DLD-1), breast cancer (MDA-MB-231) and embryonic kidney (HEK 293T) (non-cancerous) cell lines for in vitro cytotoxicity. Compound 4 specifically showed low IC50 values for these cell lines (IC50 values 12.41 +/- 2.89, 11.98 +/- 2.52 and 4.21 +/- 1.74 mu mol/L in DLD-1, MDA-MB-231 and HEK 293T cell lines, respectively). The Pd-NHC complexes (6, 7) did not exhibit cytotoxic activity (IC50 values > 200 in DLD-1, MDA-MB-231, HEK 293T cell lines). Therefore, Ag-NHC complexes can be further investigated as potential anticancer agents. (C) 2016 Elsevier B. V. All rights reserved.