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Redox‐Controlled Stabilization of an Open‐Shell Intermediate in a Bioinspired Enzyme Model

2018; Wiley; Volume: 2018; Issue: 31 Linguagem: Inglês

10.1002/ejic.201800570

1099-0682

Kristina Hanauer, Christoph Förster, Katja Heinze,

Electrocatalysts for Energy Conversion

Bis(ferrocenyl)‐appended dioxido molybdenum(VI) complexes perform oxygen‐atom transfer (OAT) reactions similar to sulfite oxidases. Positively charged ferrocenium ions accelerate the nucleophilic attack of the substrate. The fate of the intermediate species formed after the OAT depends on the initial redox states of the iron centers. In the all‐iron(II) state of the ferrocenyl moieties, a simple OAT from the Fe II Fe II Mo VI O 2 unit to a PMe 3 substrate occurs yielding Fe II Fe II Mo IV O and OPMe 3 without participation of the iron(II) centers. In the all‐iron(III) state, the ferrocenium intermediates are susceptible to decomposition initiated by the nucleophilic substrate. However, in the mixed Fe II /Fe III state, OAT to PMe 3 is rapidly followed by an intramolecular electron transfer (IET) within the initially formed Fe II Fe III Mo IV O(OPMe 3 ) species to give the Fe II Fe II Mo V O(OPMe 3 ) electromer. The absence of ferrocenium species, the presence of molybdenum(V) and the coordinated OPMe 3 in the quite persistent Fe II Fe II Mo V O(OPMe 3 ) electromer is demonstrated by EPR spectroscopy in combination with Density Functional Theory calculations. The IET‐coupled OAT reaction stabilizes this molybdenum(V) intermediate compared to the conventional molybdenum(IV) OAT reaction intermediate. This stabilization enables its characterization by spectroscopic means before the OPMe 3 product dissociates. This study presents a concept for redox‐controlled stabilization of a catalytically relevant intermediate.