EPR investigation into the kinetics and mechanism of the one-electron reduction of benzenediazonium ions by FeII–EDTA and other iron(II) complexes

An EPR approach has been developed and applied to the determination of the rate constants for the decomposition of some arenediazonium ions by FeII complexes to give aryl radicals. In continuousflow experiments, steady-state concentrations have been measured both for the aryl radical-adducts to the fumarate anion and for ˙CH2CO2–(obtained by reaction of Ar˙ with the iodoacetate anion): analysis of the dependence of these upon [FeII] and [ArN2+] leads to values of the rate constants for electron transfer.For the reaction between FeII–EDTA and a series of diazonium ions, for which values of k are in the range 2 × 104–4 × 105 dm3 mol–1 s–1, it is shown that there is a good dual-parameter Hammett–Taft correlation (involving σI and σR+, and with ρ= 1.74), consistent with the occurrence of an outer-sphere electron-transfer process.