Tuning of Redox Potentials for the Design of Ruthenium Anticancer Drugs − an Electrochemical Study of [trans-RuCl₄L(DMSO)]^- and [trans-RuCl₄L₂]^- Complexes, where L = Imidazole, 1,2,4-Triazole, Indazole

Abstract

The electrochemical behavior of [trans-RuCl(4)L(DMSO)](-) (A) and [trans-RuCl(4)L(2)](-) (B) [L = imidazole (Him), 1,2,4-triazole (Htrz), and indazole (Hind)] complexes has been studied in DMF, DMSO, and aqueous media by cyclic voltammetry and controlled potential electrolysis. They exhibit one single-electron Ru(III)/Ru(II) reduction involving, at a sufficiently long time scale, metal dechlorination on solvolysis, as well as, in organic media, one single-electron reversible Ru(III)/Ru(IV) oxidation. The redox potential values are interpreted on the basis of the Lever's parametrization method, and particular forms of this linear expression (that relates the redox potential with the ligand E(L) parameter) are proposed, for the first time, for negatively (1-) charged complexes with the Ru(III/II) redox couple center in aqueous phosphate buffer (pH 7) medium and for complexes with the Ru(III/IV) couple in organic media. The E(L) parameter was estimated for indazole showing that this ligand behaves as a weaker net electron donor than imidazole or triazole. The kinetics of the reductively induced stepwise replacement of chloride by DMF were studied by digital simulation of the cyclic voltammograms, and the obtained rate constants were shown to increase with the net electron donor character (decrease of E(L)) of the neutral ligands (DMSO < indazole < triazole < imidazole) and with the basicity of the ligated azole, factors that destabilize the Ru(II) relative to the Ru(III) form of the complexes. The synthesis and characterization of some novel complexes of the A and B series are also reported, including the X-ray structural analyses of (Ph(3)PCH(2)Ph)[trans-RuCl(4)(Htrz)(DMSO)], [(Ph(3)P)(2)N][trans-RuCl(4)(Htrz)(DMSO)], (H(2)ind)[trans-RuCl(4)(Hind)(DMSO)], and [(Hind)(2)H][trans-RuCl(4)(Hind)(2)].

Molybdenum Complexes Bearing the Tris(1‐pyrazolyl)methanesulfonate Ligand: Synthesis, Characterization and Electrochemical Behaviour

“…[68] The first oxidation potential of the Mo 0 complex 1 (-0. 35 3 ] n , in which L is a tridentate N-donor ligand [Tp (n = -1), [70] Tpm Me (n = 0), [71] 1,4,7-trimethyl-1,4,7-triazacyclononane (n = 0), [72] or 1,4,7-tribenzyl-1,4,7-triazacyclononane (n = 0)], [70] thus reflecting [66][67][68][73][74][75] the relative donor/acceptor abilities of these different L ligands. The more negative value (-0.53 V vs Fc/Fc + ) is reported [70] 3 ], [71] whereas that of 1 is intermediate, in accord with the order of the net electron-donor ability of the corresponding tripodal ligands.…”

Characterization of Coordination Compounds by Electrochemical Parameters

“…Nevertheless, Equation (15) is valid for allenylidenes and alkynyls. [28,36,42] ( 15) E L values are already known for a wide variety of ligands, [13][14][15][16][28][29][30]36,41,57,64,[70][71][72][73][74][75] including an extensive list of recently estimated values by the current author [36] for many carbyne, carbene, vinylidene, allenylidene and alkynyl ligands. Examples are given in Table 1.…”

“…[13][14][15][16]36,56] ) have already been proposed for the following M n+1/n redox couples: M = Nb (n = 3, 4), [13] Ta (n = 4), [13] Cr (n = 0, 2), [13] Mo (n = 0, 1), [13] Tc (n = 1-3), [14] Re (n = 1-3), [14] Fe (n = 2, 3), [13,26,27] Ru (n = 2, 3), [13,71] Os (n = 2) [13] and Rh (n = 1). [28,64] Normally, the redox centres are six-coordinate, with the exception of the four-and five-coordinate Rh II/I , [28,64] and in particular the five-coordinate Fe III/II [13] and Mn II/III [13] cases.…”

“…[28,64] Normally, the redox centres are six-coordinate, with the exception of the four-and five-coordinate Rh II/I , [28,64] and in particular the five-coordinate Fe III/II [13] and Mn II/III [13] cases. The parameters usually have been obtained in organic media, but different values are observed in water where solvation effects and the complex charge can play a relevant role, as observed for Cr III/II , [13] Fe III/II , [13] Ru III/II (2+/1+), [13] Ru III/II (1-/2-) [71,75] and Os III/II [13] systems. The charge effect has been studied [75] particularly for the Ru III/II system.…”

New Chlorido(dimethyl sulfoxide)iridium(III) Complexes with N6‐Substituted Adenines – Kinetic N(7) versus Thermodynamic N(9) Coordinated Adenine Isomers

“…[16][17][18] Moreover, several Ir III -and Rh III -related compounds have proved to be potent in vitro cytotoxic agents, [19,20] although similar "NAMI-A"-Ir III or Rh III complexes have been found to be inactive, [11,12,21] which has been related to the lack of lability for ligand substitution and redox properties of the metal centre. In this way, the more inert Ir III compounds could be useful as trace systems to study the route of Ru III analogues or designed complexes to deliver an active ligand to a specific receptor.…”