Kinetic Control in Two-Electron Homogeneous Redox Electrocatalysis. Reduction of Monohalobiphenyls

Article abstract of DOI:10.1021/j100296a053

Kinetic control of the two-electron electrocatalytic dehalogenation of monohalobiphenyls to biphenyl was elucidated by analyzing voltammetric data with expanded-grid digital simulation/nonlinear regression.The method involves comparing goodness of fit of limited and mixed kinetic simulation models to the data and is applicable to second-order conditions.The rate-determining step in the dehalogenations was confirmed as electron transfer between the electrochemically generated phenanthridine anion radical and 4-chloro- (4-CB) and 4-bromobiphenyl (4-BB), rather than decomposition of the halobiphenyl anion radical.Rate constants for this step of (1.42 +/- 0.12) * 10³ M^-1 s^-1 for 4-CB and (5.1 +/- 1.8) * 10⁴ M^-1 s^-1 for 4-BB showed considerably improved precision (and accuracy in the latter case) over rate constants obtained under pseudo-first-order conditions, where the catalytic current had to be extracted from large currents for direct reduction of excess substrate.The simulation/regression method is general for two-electron homogeneous electrocatalytic reactions following similar mechanisms.Synthetic data were used to show that, for systems under mixed kinetic control, rate constants for both homogeneous electron transfer and decomposition of the haloaromatic anion radical can be estimated simultaneously.