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 [(H2O)(tmc)Fe=O)](OTf)2 could be prepared. This complex is important in regard to a better understanding of the reactivity of FeIV oxido complexes. Mössbauer measurements using the solid compound showed an isomer shift of δ=0.19 mm s−1 and a quadrupole splitting ΔEQ=1.38 mm s−1, confirming the high‐valent FeIV state. DFT calculations were performed and led to an assignment of triplet spin multiplicity. Crystallographic characterization of [(H2O)(tmc)Fe=O)](OTf)2 as well as of starting materials [(tmc)Fe(CH3CN)](OTf)2 and [(tmc)Fe(OTf)]OTf together with previous results strongly suggest that [(H2O)(tmc)Fe=O)](OTf)2 was formed similar to the oxido–hydroxido tautomerism analogous to heme systems. Water does not always hurt: The iron(IV) oxido complex [(H2O)(tmc)Fe=O)](triflate)2 (1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane=tmc) has been synthesized and structurally characterized. This complex is quite unusual in regard to a coordinated water molecule as an additional axial ligand.