The Properties of Hydrotris(3‐mesitylpyrazol‐1‐yl) Borate Iron(II) Complexes with Aryl Carboxylate Co‐ligands – Stabilization of an Iron(III) Alkylperoxide

Abstract

Through the reaction of [TpMesFeCl] with different benzoic acids, namely salicylic acid (HOBzo−OH), m‐chloro benzoic acid (HOBzm−Cl), p‐dimethylamino benzoic acid (OBzp−N(Me)2) and benzoic acid itself, in the presence of triethylamine corresponding complexes [TpMesFeOBzR] with varying residues R could be isolated and fully characterized (including paramagnetic NMR spectroscopy, elemental analysis, IR, cyclic voltammetry). From acetonitrile solutions they crystallized as acetonitrile adducts [TpMesFe(NCMe)OBzR], which indicates, that a coordination and activation of an exogeneous substrate is principally possible. While no reactivity towards O2 could be observed, in contact with tBuOOH all complexes were found to form iron(III) tert‐butylperoxide complexes [TpMesFe(OBzR)(OOtBu)], as evidenced by UV‐vis, EPR and Raman spectroscopy. Through UV‐vis studies it was shown, that both the formation rate and the stability of [TpMesFe(OBzR)(OOtBu)] are influenced by the basicity of the benzoate co‐ligands, which is determined by the substituents. An extraordinarily high stability was observed for the salicylate representative, which, however, cannot be explained on basis of such electronic effects; other potential stabilizing factors that may play an important role are discussed.