Bis-cyclometalated rhodium- and iridium-complexes with the 4,4′-dichloro-2,2′-bipyridine ligand. Evaluation of their photophysical properties and biological activity

The synthesis and characterization of new cyclometalated complex salts [M(C^N)2(4,4′-Cl2bpy)]PF6 (M = Rh and Ir; C^N = 2-(p-tolyl)pyridinato (1 and 2), 2-phenyl-5-chloro-pyridinato (3 and 4); 4,4′-Cl2bpy = 4,4′-dichloro-2,2′-bipyridine) is described. Compounds 1-4 were obtained by reaction of 4,4′-dichloro-2,2′-bipyridine with the complexes [{M(µ-Cl)(C^N)2}2] (M = Rh, Ir) in refluxing CH2Cl2/MeOH mixtures. The molecular structures of compounds 1 and 4 were confirmed by X-ray diffraction. The Ir compounds show phosphorescence in PMMA film and in solution at ambient temperature. Furthermore, all compounds display significant cytotoxicity against human cancer cell lines with the IC50 values in the 0.4-2 µM range.