Characterization of the FeV=O Complex in the Pathway of Water Oxidation. (27th May 2020)

• Record Type: Journal Article
• Authors: Ezhov, Roman; Ravari, Alireza Karbakhsh; Pushkar, Yulia
• Is Part Of: Angewandte Chemie. Volume 132:Number 32(2020)
• Page Start: 13604
• Page End: 13607
• Publication Date: 2020-05-27
• Subjects: artificial photosynthesis -- Fe-based catalysts -- highly oxidized species -- water oxidation -- X-ray spectroscopy; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.202003278
• Languages: English
• ISSNs: 0044-8249

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 H2 O2 : 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. Abstract : Development of artificial photosynthesis requires efficient water splitting catalysts. The short lived, six coordinated reactive intermediate [Fe V =O, (OH)(Pytacn)] 2+ competent in O−O bond formation was trapped. X‐ray absorption spectroscopy (XAS) confirmed Fe V oxidation state and Fe V =O bond at ≈1.60 Å. EPR and DFT revealed that this is the high spin Fe V complex reacting via water nucleophilic attack to form the O−O bond.