Iron(IV)-oxo intermediates in nature contain two unpaired electrons in the Fe-O antibonding orbitals,which are thought to contribute to their high reactivity.T ochallenge this hypothesis,w ed esigned and synthesized closed-shell singlet iron(IV) oxo complex [(quinisox)Fe(O)] + (1 + ; quinisox-H = (N-(2-(2-isoxazoline-3-yl)phenyl)quinoline-8-carboxamide). We identified the quinisoxl igand by DFT computational screening out of over 450 candidates.After the ligand synthesis, we detected 1 + in the gas phase and confirmed its spin state by visible and infrared photodissociation spectroscopy(IRPD). The Fe-O stretching frequency in 1 + is 960.5 cm À1 ,c onsistent with an Fe-O triple bond, which was also confirmed by multireference calculations.T he unprecedented bond strength is accompanied by high gas-phase reactivity of 1 + in oxygen atom transfer (OAT)a nd in proton-coupled electron transfer reactions.T his challenges the current view of the spin-state driven reactivity of the Fe-O complexes.

Iron(IV)-oxo intermediates in nature contain two unpaired electrons in the Fe-O antibonding orbitals,which are thought to contribute to their high reactivity.T ochallenge this hypothesis,w ed esigned and synthesized closed-shell singlet iron(IV) oxo complex [(quinisox)Fe(O)] + (1 + ; quinisox-H = (N-(2-(2-isoxazoline-3-yl)phenyl)quinoline-8-carboxamide). We identified the quinisoxl igand by DFT computational screening out of over 450 candidates.After the ligand synthesis, we detected 1 + in the gas phase and confirmed its spin state by visible and infrared photodissociation spectroscopy(IRPD). The Fe-O stretching frequency in 1 + is 960.5 cm À1 ,c onsistent with an Fe-O triple bond, which was also confirmed by multireference calculations.T he unprecedented bond strength is accompanied by high gas-phase reactivity of 1 + in oxygen atom transfer (OAT)a nd in proton-coupled electron transfer reactions.T his challenges the current view of the spin-state driven reactivity of the Fe-O complexes.

Iron Complexes The design, synthesis, and reactivity of a closed shell iron(IV)–oxo complex with an Fe≡O triple bond is reported by E. Andris et al. in their Research Article on page 23137.

Eisenkomplexe Das Design, die Synthese und die Reaktivität eines geschlossenschaligen Eisen(IV)‐Oxo‐Komplexes mit einer Fe≡O‐Dreifachbindung wird von E. Andris et al. im Forschungsartikel auf S. 23337 vorgestellt.