In an aprotic medium and at a Pt electrode, cis- and trans-[Re(NCR)2(Ph2PCH2CH2PPh2)2]+ (cis + and trans + , respectively; R = aryl or alkyl) undergo two successive single-electron oxidations to form the 17-electron (cis 2+ or trans 2+) and 16-electron (cis 3+ or trans 3+) derivatives. The cis 3+ complexes isomerize to the corresponding trans 3+ complexes which undergo a slower decomposition reaction, and the rate constants (k i 3+ and k dec, respectively) have been determined by kinetic analysis of the cyclic voltammetric behavior. For the aromatic nitrile complexes, both rate constants increase with the electron-withdrawing ability (Hammett's σp constant) of R. The ratios of the isomeric equilibrium constants (cis 3+ ⇄ trans 3+, cis 2+ ⇄ trans 2+, and cis + ⇄ trans +), for the aromatic nitrile complexes, also increase with σp, the thermodynamic gain in favor of the trans isomer is much higher upon the first oxidation than upon the second one, and it decreases with the increase of σp (higher sensitivity of the energy of the HOMO of the trans isomers to the electronic effect of R). For the alkyl cyanide complexes, steric effects play a dominant role on their thermodynamic and kinetic behaviors, by shifting anodically the oxidation potential and enhancing the isomerization rate. The significance of those systems in terms of developing a “molecular hysteresis” behavior is also discussed.

No abstract