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

Abstract

An EPR approach has been developed and applied to the determination of the rate constants for the decomposition of some arenediazonium ions by Fe^II 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 [Fe^II] and [ArN₂⁺] leads to values of the rate constants for electron transfer.

For the reaction between Fe^II–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 σ_I and σ_R⁺, and with ρ= 1.74), consistent with the occurrence of an outer-sphere electron-transfer process.