Two-electron-transfer redox systems. Part 8. Proving the electron stoichiometry for the electrochemical two-electron oxidation of N,N′-bis(ferrocenoyl)-1,2-diaminoethane

N,N′-Bis(ferrocenoyl)-1,2-diaminoethane is electrochemically oxidized at Pt electrodes in non-aqueous solvents with NBu4PF6 or NBu4[Al(pftb)4] (pftb = OC(CF3)3) as supporting electrolytes. Cyclic voltammetry (CV) at macro and ultramicro disk electrodes in propylene carbonate (PC) in the presence of the former electrolyte shows a single signal from which the number of transferred electrons n (equal to 2) and the diffusion coefficient D are estimated and confirmed by simulation. In a series of other solvents (DMF, DMSO, CH3CN, THF, CH2Cl2) with the same electrolyte, similar behavior is observed. The latter supporting electrolyte, however, induces signal broadening as compared to NBu4PF6 in PC for cyclic and differential pulse voltammetry as well as peak splitting in the case of THF and CH2Cl2. This is attributed to interaction between the two ferrocene moieties in the molecule, which is not relayed through a conjugated bridge. Diffusion coefficients in DMF and DMSO were determined by pulse gradient spin echo NMR experiments and compared to electrochemical values. The solvent dependence of D follows the Stokes-Einstein relation. Comproportionation equilibrium constants as calculated from the difference of the formal potentials E0 range from below 10 (PC, NBu4PF6) to approximately 150 (THF and CH2Cl2, NBu4[Al(pftb)4]).