Electrochemistry of Tris(β-diketonato)ruthenium(III) Complexes at Platinum Electrodes in Nonaqueous Solutions and Substituent Effects on Their Reversible Half-Wave Potentials

The one-electron oxidation and reduction processes at platinum electrodes of a series of β-substituted and γ-substituted tris(β-diketonato)ruthenium(III) complexes are studied in acetonitrile, N,N-dimethylformamide, and nitromethane solutions, each containing 0.1 mol dm−3 (C2H5)4NClO4 at 25 °C. Syntheses of three new γ-substituted derivatives are described. Attempts to isolate the immediate product of the one-electron oxidation of [Ru(acac)3] in acetonitrile failed; bis(acetonitrile)bis(acetylacetonato)ruthenium(III) was obtained instead. Diffusion coefficients of the complexes in the acetonitrile medium are presented. The reversible half-wave potentials for the oxidation and the reduction in the acetonitrile medium depended linearly on the sum of the Hammett constants of the substituents (σp for the β-substituents and σm for the γ-substituents). Analysis of the dependence of the half-wave potentials on several kinds of substituent parameters suggests that the inductive effect is operative at both the β-positions and the γ-position, while the resonance effect is operative only at the β-positions.