ic0503737_si_004.pdf (1.68 MB)
Tuning of Redox Properties for the Design of Ruthenium Anticancer Drugs: Part 2. Syntheses, Crystal Structures, and Electrochemistry of Potentially Antitumor [RuIII/IICl6-n(Azole)n]z (n = 3, 4, 6) Complexes†
journal contribution
posted on 2005-09-19, 00:00 authored by Erwin Reisner, Vladimir B. Arion, Anna Eichinger, Norbert Kandler, Gerald Giester, Armando J. L. Pombeiro, Bernhard K. KepplerA series of mixed chloro-azole ruthenium complexes with potential antitumor activity, viz., mer-[RuIIICl3(azole)3] (B),
trans-[RuIIICl2(azole)4]Cl (C), trans-[RuIICl2(azole)4] (D), and [RuII(azole)6](SO3CF3)2 (E), where azole = 1-butylimidazole
(1), imidazole (2), benzimidazole (3), 1-methyl-1,2,4-triazole (4), 4-methylpyrazole (5), 1,2,4-triazole (6), pyrazole
(7), and indazole (8), have been prepared as a further development of anticancer drugs with the general formula
[RuCl4(azole)2]- (A). These compounds were characterized by elemental analysis, IR spectroscopy, electronic
spectra, electrospray mass spectrometry, and X-ray crystallography. The electrochemical behavior has been studied
in detail in DMF, DMSO, and aqueous media using cyclic voltammetry, square wave voltammetry, and controlled
potential electrolysis. Compounds B and a number of C complexes exhibit one RuIII/RuII reduction, followed, at a
sufficiently long time scale, by metal dechlorination on solvolysis. The redox potential values in organic media
agree with those predicted by Lever's parametrization method, and the yet unknown EL parameters were estimated
for 1 (EL = 0.06 V), 3 (EL = 0.10 V), 4 (EL = 0.17 V), and 5 (EL = 0.18 V). The EL values for the azole ligands
1−8 correlate linearly with their basicity (pKa value of the corresponding azolium acid H2L+). In addition, a logarithmic
dependence between the homogeneous rate constants for the reductively induced stepwise replacement of chloro
ligands by solvent molecules and the RuIII/RuII redox potentials was observed. Lower E1/2 values (higher net electron
donor character of the ligands) result in enhanced kinetic rate constants of solvolysis upon reduction. The effect
of the net charge on the RuIII/RuII redox potentials in water is tentatively explained by the application of the Born
equation. In addition, the pH-dependent electrochemical behavior of trans-[RuCl2(1,2,4-triazole)4]Cl is discussed.
