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New mononuclear non‐heme FeII complexes derived from a well‐known pentadentate amine/pyridine ligand were synthesized. The new ligand bears an additional OH group on one pyridyl aimed at developing second sphere hydrogen bonds. Two binding modes of the ligand were observed that can be selectively obtained through the choice of the counterion: the OH group develops an intramolecular H‐bond with the 6th exogenous ligand in the classical mode, or an intermolecular one with the unbound triflate counterion in the alternative mode. The complexes were studied by cyclic voltammetry in the reductive activation of O2. The addition of an H‐bond improves the O2 activation potential with a gain of 90 mV in the classical case and 220 mV in the alternative one. The difference is ascribed to the development of stabilizing H‐bonds within the FeIII‐peroxo intermediate with the proximal O atom of peroxo (classical mode) or the distal one (alternative mode). Ultimately, the complex in the alternative mode activates O2 at −0.5 V vs SCE (500 mV gain compared to free O2). We took advantage of this significantly reduced energetic cost to carry out and achieve the electroassisted oxidation of thioanisole by O2 at −0.5 V vs SCE. [ABSTRACT FROM AUTHOR]

Three new amine/pyridine FeII 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 FeV(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 (N4)FeII(OAc)(OH) species. These complexes readily react with excess hydrogen peroxide to yield (N4)FeIII(OAc)(OOH) intermediates. These latter intermediates are proposed to evolve into (N4)FeIV(OAc)(O), which are more efficient than the usual (N4)FeIV(O) and (N5)FeIV(O). [ABSTRACT FROM AUTHOR]