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.