Tuning the H‐Atom Transfer Reactivity of Iron(IV)‐Oxo Complexes as Probed by Infrared Photodissociation Spectroscopy

Guilherme L Tripodi,Magda M J Dekker,Jana Roithová,Lawrence Que

doi:10.1002/ange.202016695

Guilherme L Tripodi, Magda M J Dekker + Show 2 more

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https://doi.org/10.1002/ange.202016695

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Abstract

AbstractReactivities of non‐heme iron(IV)‐oxo complexes are mostly controlled by the ligands. Complexes with tetradentate ligands such as [(TPA)FeO]2+ (TPA=tris(2‐pyridylmethyl)amine) belong to the most reactive ones. Here, we show a fine‐tuning of the reactivity of [(TPA)FeO]2+ by an additional ligand X (X=CH3CN, CF3SO3−, ArI, and ArIO; ArI=2‐(tBuSO2)C6H4I) attached in solution and reveal a thus far unknown role of the ArIO oxidant. The HAT reactivity of [(TPA)FeO(X)]+/2+ decreases in the order of X: ArIO > MeCN > ArI ≈ TfO−. Hence, ArIO is not just a mere oxidant of the iron(II) complex, but it can also increase the reactivity of the iron(IV)‐oxo complex as a labile ligand. The detected HAT reactivities of the [(TPA)FeO(X)]+/2+ complexes correlate with the Fe=O and FeO−H stretching vibrations of the reactants and the respective products as determined by infrared photodissociation spectroscopy. Hence, the most reactive [(TPA)FeO(ArIO)]2+ adduct in the series has the weakest Fe=O bond and forms the strongest FeO−H bond in the HAT reaction.

Highlights

The development of non-heme iron(IV)-oxo complexes has been inspired by enzymatic oxidations.[1]
We demonstrate that infrared photodissociation spectroscopy can carry out direct experimental measurements of the bonds of interest and shed light on a critical question in this field.[20]
We have investigated the formation and hydrogen-atom transfer (HAT) reactivity of [(TPA)FeIV(O)(X)]+/2+ (X = MeCN, TfOÀ, ArI, ArIO) complexes in a flow setup with electrospray ionization mass spectrometry (ESI-MS) detection

Summary

Introduction

The development of non-heme iron(IV)-oxo complexes has been inspired by enzymatic oxidations.[1]. The common feature of the [(L)FeIV(O)]2+ complexes (L = tetradentate tripodal ligand) is that a solvent molecule or another 2 eÀ donor ligand is often attached as the sixth ligand (unless the supporting ligand is sterically hindered).[7] This labile ligand offers another opportunity to tune the reactivity of this type of iron(IV)-oxo complexes, this aspect has far not been investigated in that much detail.[7]. We focus on a family of iron(IV)-oxo complexes [(TPA)FeIVO(X)]2+ (X = labile ligand, Scheme 1). This family of analogous complexes offer an ideal platform to evaluate how the properties of the Fe=O bond and the newly formed FeOÀH bond affect the reactivities of these complexes in HAT reactions.

Results and Discussion

Conclusion

Conflict of interest