Elucidation of the Active Mn-Species Responsible for Alkane Fluorination Catalyzed by Mn Porphyrins

The catalytic conversion of C–H to C–F bonds is a critical synthetic transformation of relevance to the pharmaceutical, agrochemical, and medicinal chemical industries. When coupled with an oxidant and a fluorine donor, biomimetic Mn-porphyrins have been shown to be capable of achieving this reaction. However, the definition of the active forms of these fluorinating Mn-porphyrins remains an unsolved challenge, which limits mechanistic understanding of the process and makes it challenging to systematically design better catalytic materials. Herein, we present a combination of kinetic, spectroscopic, and theoretical studies focused on alkane fluorination over Mn-containing porphyrins. Specifically, by correlating kinetic studies with resonance Raman, UV–vis, and high-energy resolution fluorescence detected X-ray absorption spectroscopic analysis of the various states of the catalyst, we provide evidence that a 6-coordinated Mn(IV) complex with −F and −OI(F)Ar axial ligands is the active species responsible for selective fluorination via Hydrogen Atom Transfer. This active state is distinct from the Mn═O species previously proposed to be the active intermediates for alkane fluorination and oxidation.