Efficient hydroxylation of aromatic compounds catalyzed by an iron(II) complex with H2O2

Abstract

A mononuclear iron(II) complex, Et4N[Fe(C10H6NO2)3], coordinated by three 1‐nitroso‐2‐naphtholate ligands in a fac‐N3O3 geometry, was initiated to catalyze the direct hydroxylation of aromatic compounds to phenols in the presence of H2O2 under mild conditions. Various reaction parameters, including the catalyst dosage, temperature, mole ratio of H2O2 to benzene, reaction time and solvents which could affect the hydroxylation activity of the catalyst, were investigated systematically for benzene hydroxylation to obtain ideal benzene conversion and high phenol distribution. Under the optimum conditions, the benzene conversion was 10.2% and only phenol was detected. The catalyst was also found to be active towards hydroxylation of other aromatic compounds with high substrate conversions. The hydroxyl radical formed due to the reaction of the catalyst and H2O2 was determined to be the crucial active intermediate in the hydroxylation. A rational pathway for the formation of the hydroxyl radical was proposed and justified by the density functional theory calculations. Copyright © 2014 John Wiley & Sons, Ltd.