Synthesis, Characterization and Cytotoxic Activities of Half‐sandwich Pentamethylcyclopentadienyl Iridium(III) Complexes Containing 4,4'‐substituted 2,2'‐Bipyridine Ligands

Abstract The synthesis and characterization of six new organometallic half‐sandwich iridium(III) compounds containing modified 4,4'‐substituted 2,2'‐bipyridines as the bidentate co‐ligands were described. Thus the compounds [Ir(η 5 ‐C 5 Me 5 )(N^N)Cl]PF 6 [N^N: 4,4'‐bpy‐Ph, 1 ; 4,4'‐bpy‐Me, 2 ; 4,4'‐bpy‐nonyl, 3 ; 4,4'‐bpy‐CH 2 OH, 4 ; 4,4'‐bpy‐Cl, 5 ; 4,4'‐bpy‐NH 2 , 6 were obtained by bridge‐splitting reactions from the precursor [{Ir(η 5 ‐C 5 Me 5 )(μ‐Cl)Cl} 2 ] with the corresponding bidentate bipyridines. The X‐ray single‐crystal structures of compounds 1 , 2 , 4 and 6 in the solid state were determined. To evaluate the cytotoxic properties of all six compounds, colorimetric assays (MTT assay) against two cancer cell lines, MCF‐7 and HT‐29, were performed. Most promising results were achieved for compounds 1 and 3 with nonpolar phenyl or nonyl group attached to the bipyridine ligand, while the substitution with less lipophilic groups led to the inactivation of the compound. The most remarkable biological activity showed compound 3 with an IC 50 value in the low macromolecular range and >40‐fold enhanced toxicity compared to cisplatin against both cell lines.