Outer-Sphere One-Electron Reductions of Arenediazonium Salts

Article abstract of DOI:10.1021/ja00239a038

Arenediazonium tetrafluoroborate salts undergo facile reduction by both potassium ferrocyanide and decamethylferrocene.Their reaction rates are characteristically second order, and rate constants for the ferrocyanide reductions of substituted benzenediazonium ions ranging from p-nitro to p-methoxy span five orders of magnitude.Linear correlation between log(k_x/k_H) and Hammett ?-values is obtained with p=+4.7 for reactions with ferrocyanide and p=+3.3 for reactions with decamethylferrocene.Similar correlations are observed with the polarographic half-wave potentials of these diazonium salts.Marcus theory has been applied to these electron-transfer reactions to obtain estimates of the apparent self-exchange rate constants of arenediazonium ions.Their values are relatively low, and they exhibit a substantial unexpected substituent dependence (p=+6.4).Application of Marcus theory to known electron-transfer reactions of diazonium ions using these apparent self-exchange rate constants demonstrates their suitability for the prediction of reaction rate constants and their usefulness for mechanistic evaluations.