Beneficial Effect of Acetic Acid on the Formation of Fe^III(OOH) Species and on the Catalytic Activity of Bioinspired Nonheme Fe^II Complexes.

Three new amine/pyridine Fe(II )complexes bearing pentadentate ligand with one, two or three electron enriched 4-methoxy-3,5-dimethylpyridine were used as catalysts for the oxidation of small organic molecules by hydrogen peroxide. The distribution of products formed suggests that these ligands are not enough electron donating to promote the O-O heterolytic cleavage of the oxidant in order to generate selective Fe-V(O) species. Using acetic acid in the reaction mixtures results in a significant increase of the efficiency of these catalytic systems. Our investigations show that the use of AcOH leads to the protonation/dissociation of a pyridyl moiety and the formation of (N-4)Fe-II(OAc)(OH) species. These complexes readily react with excess hydrogen peroxide to yield (N-4)Fe-III(OAc)(OOH) intermediates. These latter intermediates are proposed to evolve into (N-4)Fe-IV(OAc)(O), which are more efficient than the usual (N-4)Fe-IV(O) and (N-5)Fe-IV(O).