Magnetic and structural characterization of Fe(II) and (III) pyclen complexes

In nature, most enzymatic oxidative processes are carried out by high-valent iron compounds.1 The search for simple non-heme complexes as simpler synthetic models is crucial to the implementation of similar processes in laboratory and larger scales. Macrocyclic ligands play a leading role in this field, due to their ability to efficiently stabilize high oxidation states of iron-oxo compounds.2 Supporting ligands design, moreover, having a significant impact on the spin state of the nonheme iron (iv)-oxo and iron (v) complexes, exerts a huge influence on the outcome of oxygen atom transfer (OAT), hydrogen atom transfer (HAT), and electron transfer (ET) reactions.3 Hence, a small library of several complexes of the pyclen family was synthetized to elucidate the effect of both macrocycle substituents and anionic ligands. Both iron (ii) and iron (iii) precursors were employed (Figure 1), and their structural and magnetic behaviour was fully characterized by means of Mössbauer spectroscopy, magnetometry and Raman spectroscopy. The generation of their active iron (iv) and iron (v) species was attempted with hydrogen peroxide and the characterization of their transition state was carried out with Mössbauer spectroscopy. As expected, a strong correlation between their measured spin state and their reactivity in both C-H activation and alcohols oxidation reactions was discovered. This study was thus able to reveal the strong correlation between the structural and electronic features of this class of complexes and their observed reactivity.