Cytotoxic Activities of Bis‐cyclometalated M(III) Complexes (M=Rh, Ir) Containing 5‐substituted 1,10‐Phenanthroline or 4,4’‐substituted 2,2’‐Bipyridine Ligands

The synthesis and characterization of eight new bis‐cyclometalated compounds [M(ptpy)2(N^N)]PF6 (ptpy=2‐(p‐tolyl)pyridinato; N^N=5‐chloro‐1,10‐phenanthroline: M=Rh, 1; M=Ir, 2); N^N=5‐methyl‐1,10‐phenanthroline: M=Rh, 3; M=Ir, 4; N^N=4,4’‐diphenyl‐2,2’‐bipyridine: M=Rh, 5; M=Ir, 6; N^N=4,4’‐diamino‐2,2’‐bipyridine: M=Rh, 7; M=Ir, 8) are described. All compounds were characterized by spectroscopic means. Additionally, the molecular structures of compounds 4, 5, 6, and 8 in the crystal were determined by single‐crystal X‐ray diffraction studies. To explore the cytotoxic properties of all new eight compounds, colorimetric assays (MTT assay) against prominent cancer cell lines, MCF‐7 and HT‐29, were performed. The determined IC50 values are in the low micromolar range, between 1.3‐5.6 μM. The most effective compounds are 1 and 2 with 5‐chloro‐substituted phenanthroline ligands, whereas the diamino‐substituted bipyridine ligands (5 and 6) are the least cytotoxic compounds. The tested complexes showed a significant increase in cytotoxicity, up to 25‐fold increase in MCF‐7 cancer cells, and up to 60‐fold increase in the HT‐29 cell line compared to the established anticancer compound cisplatin under identical conditions.