Exploring the Reactivity of High Valent Iron Intermediates in Water

The exceptional reactivity observed in non-heme iron enzymes can be attributed to their capability to access high-valent iron oxygen species in their active site. Numerous inorganic model complexes have been reported to date, providing insights into the intricate structural and spectroscopic features of many iron-containing enzymes and advancing our understanding of their enzymatic reaction pathways. While the reactivities of synthetic iron complexes have been evaluated using various oxidants, the investigation into the formation of reactive intermediates has primarily focused on acetonitrile. However, water, which serves as the medium in biological systems, has been less frequently employed in these studies. Motivated by this, we conducted a comprehensive study on the generation of key reactive species using various oxidants with a model complex, [(BnTPEN)Fe(II)(OTf)]⁺ (1) (where BnTPEN=N-benzyl-N,N,N-tris(2-pyridylmethyl)-1,2-diaminoethane) in water, which yielded important findings. In water, a quantitative yield of Fe(IV)=O species was achieved with the oxidant NaIO₄. Additionally, we observed an equilibrium between side-on Fe(III)−OO and Fe(III)−OOH, with the latter eventually converting to Fe(IV)=O. The insights gained from this study are likely to be relevant in the chemistry of other Fe(II) complexes with polypyridyl pentadentate ligands.