Sizing up a supercharged ferryl

Terminal transition metal-oxo (oxo = O2−) intermediates enjoy storied status in inorganic chemistry. The elucidation of the vanadyl (VO2+) electronic structure by Ballhausen and Gray (1) helped usher in the era of molecular orbital depictions of bonding in transition metal chemistry. Since then, metal-oxo species have been implicated in vital roles throughout biological catalysis, with key examples including the ferryl-porphyrin radical intermediate, compound I (2) used by cytochrome P450 enzymes to hydroxylate C–H bonds and high-valent Mn-oxo species postulated to participate in O–O bond formation by the oxygen-evolving complex of photosystem II (3, 4). These natural examples have inspired considerable synthetic efforts: The past few decades have witnessed the syntheses of numerous examples of terminal metal-oxo complexes capable of activating moderately strong bonds (5⇓–7). The ubiquity of reactive terminal metal-oxos has also reached the field of heterogeneous catalysis. Recently, Solomon and coworkers (8) characterized a potent zeolite-supported ferryl (FeO2+) species capable of hydroxylating methane at room temperature. Now, in PNAS, Synder et al. (9) extend characterization of this species, using synchrotron-based spectroscopies to access valuable bonding parameters essential to defining the electronic structure underpinning the reactivity of this ferryl.The capacity for Fe-doped zeolites to effect methane hydroxylation under mild conditions has been known for decades (10). However, identifying the “active ingredient” in materials with low ( ca. 0.3 … [↵][1]1Email: kml236{at}cornell.edu. [1]: #xref-corresp-1-1