Cytotoxic potential of silver, palladium, rhodium, ruthenium, and iridium complexes of a cycloheptyl-substituted lipophilic N-heterocyclic carbene ligand

Lipophilicity is a crucial parameter for cytotoxicity of metal complexes, in many cases associated with increased activity. In the present study, we synthesized a series of N-heterocyclic carbene (NHC) complexes of different metals with a lipophilic benzimidazolium chloride to investigate and compare their cytotoxicity. Rh- (4), Ru- (5), and Ir-NHC (6) complexes of a cycloheptyl-substituted benzimidazole-based NHC ligand (1) have been prepared by transmetalation reaction between Ag-NHC and the corresponding metal compound. The newly synthesized complexes have been characterized by NMR, IR, LC-MS spectroscopy, and elemental analyses. The anti-growth effects of the newly synthesized Rh-, Ru-, and Ir-NHC complexes and previously reported NHC precursor (1), Ag- (2), and Pd-NHC (3) complexes against human breast (MCF-7), colorectal (Caco-2), ovarian (A2780), and prostate (LNCaP) cancer cell lines have been investigated by MTT assay. The results revealed that the compounds provide stronger anti-growth effects against all cell lines compared to standard drug cisplatin. Among the compounds, benzimidazolium chloride, and Ag-NHC complex showed promising activities.