Synthesis, molecular structure and cytotoxicity of molecular materials based on water soluble half-sandwich Rh(III) and Ir(III) tetranuclear metalla-cycles

Abstract

The neutral dinuclear complexes [(η5-C5Me5)2Rh2 (μ-dhnq)Cl2] (1) and [(η5-C5Me5))2Ir2 (μ-dhnq)Cl2] (2) (dhnqH2=5,8-dihydroxy-1,4-naphthoquinone) were obtained from the reaction of [(η5-C5Me5))M(μ-Cl)Cl]2 (M=Rh, Ir) with dhnqH2 in the presence of CH3COONa. Treatment of 1 or 2 in methanol with linear ditopic ligands L (L=pyrazine, 4,4'-bipyridine or 1,2-bis(4-pyridyl)ethylene), in the presence of AgCF3SO3, affords the corresponding tetranuclear metalla-rectangles [(η5-C5Me5))4M4 (μ-dhnq)2(μ-L)2]4+ (L=pyrazine, M=Rh, 3; M=Ir, 4; L=4,4'-bipyridine, M=Rh, 5; M=Ir, 6; L=1,2-bis(4-pyridyl)ethylene, M=Rh, 7; M=Ir, 8). All complexes were isolated as their triflate salts and were fully characterized by infrared, 1H and 13C NMR spectroscopy, and some representative complexes by single-crystal X-ray structure analysis. The X-ray structures of 3, 5 and 6 confirm the formation of the tetranuclear metalla-cycles, and suggest that complexes 5 and 6 possess a cavity of sufficient size to encapsulate small guest molecules. In addition, the antiproliferative activity of the metalla-cycles 3-8 was evaluated against the human ovarian A2780 (cisplatin sensitive) and A2780cisR (cisplatin resistant) cancer cell lines and on non-tumorigenic human embryonic kidney HEK293 cells. All cationic tetranuclear metalla-rectangles were found to be highly cytotoxic, with IC50 values in the low micromolar range. © 2013 by the authors; licensee MDPI, Basel, Switzerland.