Experimental Definition of the = 1 π vs = 2 σ Reactivity and = 2 Character in the Ground State of an = 1 FeO Complex.

Iron(IV)-oxo intermediates found in iron enzymes and artificial catalysts are competent for H atom abstraction in catalytic cycles. For = 2 intermediates, both axial and equatorial approaches are well-established. The mechanism for = 1 sites is not as well understood: an equatorial approach is more energetically favorable, and an axial approach requires crossing from the = 1 to the = 2 surface. In this study, we use 1s2p resonant inelastic X-ray scattering (RIXS) and Fe L-edge X-ray absorption spectroscopy on the = 1 [FeO(TMC)(CHCN)] and observe both = 2 and = 1 final states, which enables the experimental evaluation of the energetics of the axial and equatorial reactivity of an = 1 FeO center on its = 2 vs = 1 surface. The observation of = 2 final states in the RIXS spectrum demonstrates significant = 2 character spin-orbit mixed into the = 1 ground state.