Mechanistic studies on oxidation of hydrogen peroxide by an oxo-bridged diiron complex in aqueous acidic media

Abstract

A novel Raman spectroscopic model for the dinuclear iron site in ribonucleotide reductase and met-hemerythrin, [Fe₂(μ-O)(phen)₄(H₂O)₂]⁴⁺, 1, (phen = 1,10-phenanthroline) quantitatively oxidizes hydrogen peroxide to dioxygenvia an inner-sphere electron transfer pathway. Although 1 deprotonates to form [Fe₂(μ-O)(phen)₄(H₂O)(OH)]³⁺ (2) and [Fe₂(μ-O)(phen)₄(OH)₂]²⁺ (3) in aqueous media, neither 2 nor 3 is reactive in oxidising H₂O₂. In the presence of excess phen, no phen-releasing equilibria from 1, 2 and 3 exist. Kinetic evidence of the generation of a (μ-1,2 peroxo)diiron(III,III) intermediate, prior to electron transfer, were obtained. Significant rate retardation in D₂O media suggests proton coupled electron transfer (PCET) in the rate determining step of the title redox reaction.