Mononuclear iron(II) complexes containing a tripodal and macrocyclic nitrogen ligand: synthesis, reactivity and application in cyclohexane oxidation catalysis
Abstract
Two novel tripodal ligands L1 and L2 based on a tris(methylpyridyl)amine (TPA) motif have been prepared and reacted with two different iron(II) salts. The ligand L1 contains a bis(amino-phenyl)-TPA group whereas the macrocyclic ligand L2 displays two different coordinating cores, namely TPA and pyridine-dicarboxamide. The resulting mononuclear complexes 1-4 have been characterized at solid state and in solution by spectroscopic and electrochemical methods. All complexes are high spin and mainly pentacoordinated. X-ray diffraction analyses of crystals of complexes 2 and 3 demonstrate that the coordination sphere of the iron(II) centre adopts either a distorted bipyramidal-trigonal or square pyramidal geometry.In absence of exogenous substrate, oxidation of complex 2 by H2O2 induces an intramolecular aromatic hydroxylation, as shown by X-Ray structure of the resulting dinuclear complex 2’. Catalytic studies in presence of substrate (cyclohexane) show that the reaction process is strongly impacted by the macrocyclic topology of the ligand as well as the nature of the counter-ion.
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