Solvent Dynamical Effects in Electron Transfer: Comparisons of Self-Exchange Kinetics for Cobaltocenium-Cobaltocene and Related Redox Couples with Theoretical Predictions

摘要

Rate constants, kex, and activation parameters for the self exchange of cobaltocenium-cobaltocene, Cp2Co, and the decamethyl derivative, Cp2Co, in thirteen organic solvents have been evaluated using the proton nmr line-broadening technique with the objective of probing the influence of solvent dynamics upon the electron-transfer kinetics. Together with some, corresponding measurements reported earlier for ferrocenium ferrocene, Cp2Fe, additional measurements for the decamethyl derivative, Cp2Fe, and with corresponding data for Cp2Co electrochemical exchange, these results enable a systematic comparative examination to be made of the effects of solvent dielectric relaxation on the barrier crossing frequency for such simple outer-sphere reactions. For the facile Cp2Co couple, the solvent dependence of the 'observed' frequency factors, extracted from the kex values by correcting for the solvent dependent barrier height, is an approximate accordance with the relative frequency factors, predicted from the continuum model of overdamped solvent relaxation.