We discuss the structure, dynamics, and reactivity of Fe(II) centers in Metal Organic Frameworks (MOFs) that facilitate the selective oxidation of methane to methanol. Combining X-ray absorption, Mössbauer, and infrared spectroscopy we report this reactivity in Fe-based MOFs is engendered by the transformation of Fe(II) sites reacting with oxidants to form Fe(IV)=O, and these Fe(IV)=O species subsequently reacting in radical-rebound type pathways to enable alkane oxyfunctionalization. A combination of DFT cluster calculations and experimental kinetic measurements reveal the kinetically-relevant step to involve formation of the metal oxyl species, Fe(IV)=O, as well as a critical role of adjacent Fe(III) atoms in the node in coupling anti-ferromagnetically to confer high spin states on all Fe species in the active site. Selectivity determining steps transpire after the kinetically-relevant step; high selectivity to methanol results from steps beyond the radical-rebound mechanism involving gas phase transport of CH<sub>3</sub>OH and its stabilization as surface-bound OCH<sub>3</sub>* groups. These results, acquired by a multi-investigator team as part of the Inorganometallic Center for Catalyst Design (ICDC), as well as utility of Fe(IV)=O species in selectively oxidizing other organic substrates will be discussed.

Methane oxidation to methanol catalyzed by iron species in metal-organic framework nodes

ACS Spring 2022

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