Takeko Matsumura-Inoue

Microwave synthesis and electrospectrochemical study on ruthenium(II) polypyridine complexes

A microwave assisted simple method was developed to prepare various ruthenium(II) polypyridine complexes rapidly with a high yield. For example, [Ru(Hdpa)3](ClO4)2 was prepared from RuCl3·3H2O in a few minutes in more than 90% yield. The oxidation potentials were determined for over 50 Ru(II) polypyridine complexes in acetonitrile to estimate the electrochemical ligand (L) parameters, from which we calculated oxidation potentials of various polypyridine Ru complexes. A linear relation between calculated and observed values indicates the additivity of the ligand contribution to the Ru(III)/Ru(II) potential. Moreover, the linear relation between the average difference of 13C-NMR chemical shifts of 4,4′ carbon atoms of bipyridine ligands and oxidation potentials for the bis bipyridine complexes, [Ru(bpy)2L]2+, was found with respect to the π-donor/-acceptor properties of L. The relation can be explained by quantum mechanical calculation using gaussian-98.

Bromomalonic acid as a source of photochemically produced Br− ion in the Ru(bpy)32+-catalyzed Belousov-Zhabotinsky reaction

Abstract Experimental observation shows that bromomalonic acid (BrMA) is one of the sources of photo-induced Br− ion in the photosensitive Belousov-Zhabotinsky reaction. The rate of Br− production by visible light was measured using a Br−-ion-selective electrode in a solution containing BrMA, H2SO4 and Ru(bpy)3SO4 but no oxybromine species. The order of reaction was 1 for [BrMA] and [H+], and about 1 2 for the light intensity and [Ru(bpy)32+]. Two types of probable photocyclic mechanisms are proposed.

The electrochemical behavior of Os(II) complexes with α,α′-bipyridine and o-phenanthroline in non-aqueous solvents

Abstract The electrode reactions of Os(II) complexes with α,α′-bipyridine and o -phenanthroline have been studied in non aqueous solvents. Tris bipyridine and tris phenanthroline complexes of Os(II) give one-step oxidation waves and three-step reduction waves, while bis bipyridine complexes of Os(II) containing py 2 , en, CN 2 , Cl 2 and Br 2 as mixed ligands give one-step oxidation waves and two-step reduction waves. Most of these waves correspond to reversible single electron transfers. It is noticed that the half-wave potentials or the peak potentials of bis bipyridine complexes are shifted to more negative direction than those of the tris complex in both oxidation and reduction processes. This is attributable to less electron with drawing nature of substituted ligands than bipyridine. These potential data, the shifts of E 1/2 or E p from those of tris complexes, and δ E *, the potential difference between two consecutive single electron waves, are discussed in terms of molecular orbital scheme.

Comparative study on He(I) photoelectron spectroscopy and voltammetry of ferrocene derivatives

The gas-phase ionization energies of 11 ferrocene derivatives have been measured by He(I) photoelectron spectroscopy and compared with the electrode oxidation potentials in aprotic solvents. The first four ionization energies and the oxidation potentials of these compounds change linearly with the Hammett substitution constants. Linear correlations with slopes ca. 0.7 have been obtained between the first adiabatic ionization energies and the oxidation potentials in several aprotic solvents. This result indicates that the solvent effect on Fc/Fc+ couples changes proportionally with the gas-phase ionization energies.

Notes. Ligand additivity in the oxidation potentials of bidentate mixed-ligand ruthenium(II) complexes

Reversible oxidation half-wave potentials E½r have been found to be additive according to the number of ligands x by analysing the potential map of [Ru(bipy)3–xLx]n+ complexes (bipy = 2,2′-bipyridine; L = polypyridine or β-diketone). The slope of plots of E½rvs. x depends on the kind of ligand L and affords a measure of the π-donor/π-acceptor ability of the bidentate ligands. Ligand parameters, PL, for various bidentate ligands, are proposed.

Synthesis and proton transfer-linked redox tuning of ruthenium(II) complexes with tridentate 2,6-bis(benzimidazol-2-yl)pyridine ligands

New ruthenium complexes of two tridentate ligands 2,6-bis(benzimidazol-2-yl)pyridine (L7) and 2,6-bis(1-methylbenzimidazol-2-yl)pyridine (L8) have been synthesised. Proton and 13C NMR spectroscopy served well for their characterization, and the observed change. Proton chemical shift yields information about the electron distribution accompanying deprotonation of the ligands. The [RuL72]n+ chelate acta as a tetrabasic acid, with pKa ranging from 2.5 to 10.7, depending on the ruthenium oxidation state. The absorption spectra and oxidation potentials are consequently sensitive to solution pH and to solvent. The proton-coupled oxidative electron-transfer reactions of the complexes afford stable higher oxidation states such as RuIV. The properties of the complexes are discussed in comparison to those of previously reported bis(tridentate ligand)ruthenium compounds.

Comparative study of chemical waves and temporal oscillations in the Ru(bpy)32+-catalyzed photosensitive Belousov–Zhabotinsky reaction

Abstract Properties of the chemical waves emerging from the mask edge were investigated for the Ru(bpy) 3 2+ -catalyzed Belousov–Zhabotinsky reaction under steady illumination while varying the initial concentration of malonic acid ([MA] 0 ) systematically. The wave velocity, the wavelength and the thickness of the oxidized band were found to decrease monotonously with [MA] 0 . The obtained results were qualitatively interpreted based on the temporal oscillations measured in a batch reactor. A key effect caused by increasing [MA] 0 was identified to be the enhancement of the reduction rate of Ru(bpy) 3 3+ .