Ezhov Roman, Ravari Alireza Karbakhsh, Pushkar Yulia
Department of Physics and Astronomy, Purdue University, 525 Northwestern avenue, West Lafayette, IN, 47906, USA.
Angew Chem Int Ed Engl. 2020 Aug 3;59(32):13502-13505. doi: 10.1002/anie.202003278. Epub 2020 May 27.
Hypervalent Fe =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 species are exceedingly rare and, so far, were produced by the oxidation of Fe complexes with peroxy acids or H O : reactions that entail breaking of the O-O bond to form a Fe =O fragment. The key Fe =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 =O,(OH)(Pytacn)] (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 oxidation state and the presence of a Fe =O bond at ≈1.60 Å. Combined EPR and DFT methods indicate that 2 contains a S=3/2 Fe center. 2 is the first spectroscopically characterized high spin oxo-Fe complex and constitutes a paradigmatic example of the Fe =O(OH) species proposed to be responsible for catalytic water oxidation reactions.
高价铁氧（Fe=O）物种参与了多种有机底物的氧化反应，以及催化水氧化反应，后者是人工光合作用的关键反应。经光谱表征的铁物种极为罕见，到目前为止，它们是通过用过氧酸或过氧化氢氧化铁配合物产生的：这些反应需要断裂O-O键以形成Fe=O片段。据推测，在水氧化反应中引发O-O键形成的关键铁氧物种尚未被检测到，可能是由于它们的高反应活性。在此，我们实现了对催化水氧化过程中生成的六配位[Fe=O(OH)(Pytacn)]（Pytacn=1-(2'-吡啶甲基)-4,7-二甲基-1,4,7-三氮杂环壬烷）（2）进行冷冻淬灭捕获。X射线吸收光谱（XAS）证实了铁的氧化态以及在约1.60 Å处存在Fe=O键。电子顺磁共振（EPR）和密度泛函理论（DFT）相结合的方法表明2含有一个S=3/2的铁中心。2是首个经光谱表征的高自旋氧合铁配合物，并且构成了被认为是催化水氧化反应原因的Fe=O(OH)物种的一个典型例子。
