Cytotoxic Activity of Some Half‐sandwich Rhodium(III) Complexes Containing 4,4’‐disubstituted‐2,2’‐bipyridine Ligands

Abstract

The synthesis and characterization of three compounds [Rh(η5‐C5Me5)Cl(N^N)]PF6 (N^N=4,4’‐disubstituted‐2,2’‐bipyridines, 1–3) are described. The cationic complexes contain the bidentate ligands N^N=4,4'‐di‐tert‐butyl‐2,2'‐bipyridine (1), N^N=4,4'‐dinonyl‐2,2'‐bipyridine (2) and N^N=4,4'‐diamino‐2,2'‐bipyridine (3). The complex salts were obtained by the bridge‐splitting reaction from the precursor [{Rh(η5‐C5Me5)(μ‐Cl)Cl}2] and subsequent salt metathesis affording their corresponding hexafluorido phosphate salts. All compounds were characterized by elemental analysis and spectroscopic means. Additionally, the molecular structure of compound 3 in the solid was determined by a single‐crystal X‐ray diffraction study. The cytotoxicity of all three compounds was examined by MTT assay against two cancer cell lines – HT‐29 (colon adenocarcinoma) and MCF‐7 (human breast adenocarcinoma) ‐ and normal human fibroblast cells (GM5657T). Compound 1 has moderate cytotoxicity against both cell lines, while compound 2 is seven to nine times more cytotoxic than cisplatin against MCF‐7 and HT‐29, respectively. In contrast to cisplatin, both compounds are more active against cancer cells than fibroblasts, thus showing some cancer selectivity.

N^N^C-Cyclometalated rhodium(iii) complexes with isomeric pyrimidine-based ligands: unveiling the impact of isomerism on structural motifs, luminescence and cytotoxicity

“…Our particular interest to rhodium complexes stems partly from our experience in rhodium chemistry 82–84 and partly from appealing properties this metal shows in the C–H bond activation and catalysis, 85–91 photochemistry 92–107 and bioinorganic chemistry. 108–128 Along with the synthesis of HL 2,5 and HL 2,6 and their rhodium( iii ) complexes [RhL 2,5 (Solv)Cl 2 ]· n EtOH and [RhL 2,6 (Solv)Cl 2 ]· n EtOH , here we report the impact of isomerism on molecular and supramolecular structures of these compounds, on the photophysical properties of the rhodium( iii ) complexes and on the cytotoxic activity of the ligands and complexes. These experimental studies are supplemented by the theoretical investigation of photophysical properties of the complexes and by theoretical modelling of the sp 2 C–H bond activation which occurs upon the coordination of HL 2,5 and HL 2,6 to RhCl 3 .…”