Synthesis of an Iron(IV) Aqua-Oxido Complex Using Ozone as an Oxidant

The iron(IV) oxido complex [(tmc)Fe=O(OTf)]OTf with the macrocyclic ligand 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclo-tetradecane (tmc) has been synthesized using ozone as an oxidant. By adding water to this compound the complex [(H₂ O)(tmc)Fe=O)](OTf)₂ could be prepared. This complex is important in regard to a better understanding of the reactivity of Fe^IV oxido complexes. Mössbauer measurements using the solid compound showed an isomer shift of δ=0.19 mm s^-1 and a quadrupole splitting ΔE_Q =1.38 mm s^-1 , confirming the high-valent Fe^IV state. DFT calculations were performed and led to an assignment of triplet spin multiplicity. Crystallographic characterization of [(H₂ O)(tmc)Fe=O)](OTf)₂ as well as of starting materials [(tmc)Fe(CH₃ CN)](OTf)₂ and [(tmc)Fe(OTf)]OTf together with previous results strongly suggest that [(H₂ O)(tmc)Fe=O)](OTf)₂ was formed similar to the oxido-hydroxido tautomerism analogous to heme systems.