Ferrocenoyl Pyridine Arene Ruthenium Complexes with Anticancer Properties: Synthesis, Structure, Electrochemistry, and Cytotoxicity

Reaction of the dimers [Ru(h6-arene)Cl2]2 (arene = C6H6, C6H5Me, p-iPrC6H4Me, C6Me6) with 2 equiv of the ferrocenoyl pyridine (NC5H4(OOCC5H4FeC5H5)-4) affords Ru(II) complexes [Ru(h6-arene)Cl2(NC5H4OOCC5H4FeC5H5)] (arene = C6H6 (1, 85% yield), C6H5Me (2, 81%), p-iPrC6H4Me (3, 91%), C6Me6 (4, 38%)) or with 1 equiv of the dipyridylferrocene deriv. ligand, 1,1'-ferrocene dicarboxylic acid pyridin-4-yl ester (NC5H4OOCC5H4FeC5H4COOC5H4N,) gives [Ru(h6-arene)Cl2]2(NC5H4OOCC5H4FeC5H4COOC5H4N) (arene = p-iPrC6H4Me (5, 74%), C6Me6 (6, 92%)). The mol. structures of these complexes was confirmed by single-crystal x-ray structure anal. of complex 4 as a representative example. The redox properties and in vitro anticancer activities of complexes 1-6 were studied. All the compds. are moderately cytotoxic toward the A2780 and A2780cisR (cisplatin-resistant) human ovarian carcinoma cell lines. The diruthenium arene complexes 5 and 6 are about twice as active as their mononuclear analogs 3 and 4. Cyclic voltammetry revealed a good correlation of the RuII/RuIII redox potentials of 1-4 and the no. of alkyl substituents in the arene ligand.