Synthesis, electrochemical, kinetic and thermodynamic studies of new ruthenocene-containing betadiketonato rhodium(I) complexes with biomedical applications

New ruthenocene-containing β -diketones 1-Ruthenocenyl-4,4,4,-trifluorobutan-1,3-dione [Hrctfa, pKa / = 7.31(3)], 1-ruthenocenylbutan-1,3-dione [Hrca, pKa / = 10.22(4)] 1-ruthenocenyl-3- phenylpropan-1,3-dione [(Hbrcm, pKa / = 11.31(4)], 1-ruthenocenyl-3-ferrocenylpropan-1,3-dione [(Hrcfcm; pKa / >13)], and 1,3-diruthenocenylpropane-1,3-dione [(Hdrcm, pKa / >13)], were prepared by the Claisen Condensation of acetylruthenocene and the appropriate ester under the influence of lithium diisopropylamide. The group electronegativity of the ruthenocenyl group (Rc) was determined from the linear relationship between the methyl ester (RCOOMe) infrared carbonyl stretching frequencies and the group electronegativities of known R groups, R = CF3, CH3, C5H5, H, Fc. The [Rh(β -diketonato)(cod)] complexes [Rh(rctfa)(cod)], [Rh(rca)(cod)], [Rh(brcm)(cod)], [Rh(rcfcm)(cod)] and [Rh(drcm)(cod)] were obtained by treating the appropriate β -diketones (Hrctfa, Hrca, Hbrcm, Hrcfcm and Hdrcm) with [Rh2(cod)2Cl2]. Kinetics results for the conversion of the β -diketones (Hrctfa, Hrca, Hbrcm, Hrcfcm and Hdrcm) from the enol to the keto form and vice versa are reported. Kinetics results for the substitution of β -diketonato ligand from the [Rh(β -diketonato)(cod)] complexes ( [Rh(rctfa)(cod)], [Rh(rca)(cod)], [Rh(brcm)(cod)], [Rh(rcfcm)(cod)] and [Rh(drcm)(cod)]) with 1,10-phenantroline in methanol are also presented. Large negative activation entropy values obtained, suggested an associative substitution mechanism. All substitution reactions had no observable mechanistic solvent pathway contribution. Oxidation potentials (Epa vs Ag/Ag + ) for the ruthenium core in the free β -diketones (Hrctfa, Hrca, Hbrcm, Hrcfcm and Hdrcm), as well as in the [Rh(β -diketonato)(cod)] complexes ([Rh(rctfa)(cod)], [Rh(rca)(cod)], [Rh(brcm)(cod)], [Rh(rcfcm)(cod)] and [Rh(drcm)(cod)]) are reported. The peak anodic potentials (Epa vs Ag/Ag + ) for oxidation of the rhodium(I) center were determined.