Characterization of Iron(IV)-oxo intermediate reactive pathway using 1s3p Resonant Inelastic X-ray Scattering (RIXS)

High-valent iron(IV)-oxo species are central to enzymatic C-H activation, where spin states strongly influence reactivity. Enzymes typically feature high-spin Fe(IV)=O, while most synthetic analogues are low-spin yet still oxidize strong C-H bonds. EPR studies show distinct intermediates and reaction pathways: [L^NHC Fe^IV(O)(MeCN)]²⁺ reacts via a π pathway through the triplet state, [Fe^IV(O)(TMC-py)]²⁺ follows a σ pathway consistent with quintet character, and [L^TMC Fe^IV(O)(MeCN)]²⁺ shows mixed spin signals. We will use 1s3p RIXS, to distinguish π and σ contributions via selective α/β spin-channel excitation, and to probe these paths in the presence of 1,4-cyclohexadien. The combined spectroscopic and computational analysis can test the two pathways in Fe(IV)-oxo and their intermediates.