Abstract
Tris(ligand) complexes RuL~3~~2~ (L = 2‐phenylazopyridine or o‐tolylazopyridine) and mixed ligand RuL'~2~L''~2~ (L' and L'' are 2‐phenylazopyridine or 2,2'‐bipyridine) have been synthesized, structurally characterized and investigated for cytotoxic activity. These complexes are important to study the hypothesis that the compound α‐[Ru(azpy)~2~Cl~2~] (azpy = 2‐phenylazopyridine) exhibits a high cytotoxicity due to its two cis chloride ligands, which might be exchanged for biological targets as DNA. Molecular structures of mer‐Ru(azpy)~3~~2~ (1) and mer‐Ru(tazpy)~3~~2~ (5) (tazpy = o‐tolylazopyridine) have been determined by X‐ray diffraction. Series of complexes RuL~3~~2~ and RuL'~2~L''~2~ show interesting NMR spectroscopic data; e.g. the spectrum of mer‐Ru(azpy)~3~~2~ (1) shows extremely broadened resonances at room temp. but sharpened resonances at low temperature. In the ^1^H NMR spectra of compounds [Ru(azpy)~2~(bpy)]^2+^ and [Ru(bpy)~2~(azpy)]^2+^ (bpy = 2,2‐bipyridine), respectively, less broadened (room temp.) or completely sharp resonances (room temp.) occur in comparison to 1 (under same conditions). By selecting the right temperature and/or concentration, NMR spectra of these series of compounds have been resolved using 2D COSY and NOESY NMR spectroscopy. Remarkably, the cytotoxicity data against a series of human tumor cell lines (A498, EVSA‐T, H226, IGROV, M19, MCF‐7 and WIDR) show a moderate cytotoxicity for these series of tris(ligand) complexes. So, even though no chloride ligands are present in these tris(ligand) complexes, a considerable cytotoxic activity is observed. This would imply that the 2‐phenylazopyridine ruthenium(II) complexes act by a completely different mechanism than the well‐known cisplatin. This finding is important, because an anticancer compound acting via a different mechanism is a prerequisite in designing new anticancer drugs. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)