Characterization of the Fe<sup>V</sup>=O Complex in the Pathway of Water Oxidation
Roman Ezhov, Alireza Karbakhsh Ravari, Yulia Pushkar
Abstract
Abstract Hypervalent Fe V =O species are implicated in a multitude of oxidative reactions of organic substrates, as well as in catalytic water oxidation, a reaction crucial for artificial photosynthesis. Spectroscopically characterized Fe V species are exceedingly rare and, so far, were produced by the oxidation of Fe complexes with peroxy acids or H 2 O 2 : reactions that entail breaking of the O−O bond to form a Fe V =O fragment. The key Fe V =O species proposed to initiate the O−O bond formation in water oxidation reactions remained undetected, presumably due to their high reactivity. Here, we achieved freeze quench trapping of six coordinated [Fe V =O,(OH)(Pytacn)] 2+ (Pytacn=1‐(2′‐pyridylmethyl)‐4,7‐dimethyl‐1,4,7‐triazacyclononane) ( 2 ) generated during catalytic water oxidation. X‐ray absorption spectroscopy (XAS) confirmed the Fe V oxidation state and the presence of a Fe V =O bond at ≈1.60 Å. Combined EPR and DFT methods indicate that 2 contains a S =3/2 Fe V center. 2 is the first spectroscopically characterized high spin oxo‐Fe V complex and constitutes a paradigmatic example of the Fe V =O(OH) species proposed to be responsible for catalytic water oxidation reactions.