The Properties Of Hydrotris(3-Mesitylpyrazol-1-Yl) Borate Iron(Ii) Complexes With Aryl Carboxylate Co-Ligands - Stabilization Of An Iron(Iii) Alkylperoxide

Through the reaction of [Tp(Mes)FeCl] with different benzoic acids, namely salicylic acid (HOBz(o-OH)), m-chloro benzoic acid (HOBz(m-Cl)), p-dimethylamino benzoic acid (OBz(p-N(Me)2)) and benzoic acid itself, in the presence of triethylamine corresponding complexes [Tp(Mes)FeOBz(R)] 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 [Tp(Mes)Fe(NCMe)OBz(R)], which indicates, that a coordination and activation of an exogeneous substrate is principally possible. While no reactivity towards O-2 could be observed, in contact with (BuOOH)-Bu-t all complexes were found to form iron(III) tert-butylperoxide complexes [Tp(Mes)Fe(OBz(R))((OOBu)-Bu-t)], 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 [Tp(Mes)Fe(OBz(R))((OOBu)-Bu-t)] 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.