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

• Published in: Journal of the American Chemical Society 2024-12, Vol.146 (51), p.35139-35145
• Main Authors: Braun, Augustin, Gee, Leland B., Waters, Max D. J., Baker, Michael L., Mara, Michael W., Zhou, Ang, Kroll, Thomas, Nordlund, Dennis, Sokaras, Dimosthenis, Hedman, Britt, Hodgson, Keith O., Que, Lawrence, Solomon, Edward I.
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126; 1520-5126
• DOI: 10.1021/jacs.4c11034

Iron­(IV)-oxo intermediates found in iron enzymes and artificial catalysts are competent for H atom abstraction in catalytic cycles. For S = 2 intermediates, both axial and equatorial approaches are well-established. The mechanism for S = 1 sites is not as well understood: an equatorial approach is more energetically favorable, and an axial approach requires crossing from the S = 1 to the S = 2 surface. In this study, we use 1s2p resonant inelastic X-ray scattering (RIXS) and Fe L-edge X-ray absorption spectroscopy on the S = 1 [FeIVO­(TMC)­(CH3CN)]2+ and observe both S = 2 and S = 1 final states, which enables the experimental evaluation of the energetics of the axial and equatorial reactivity of an S = 1 FeIVO center on its S = 2 vs S = 1 surface. The observation of S = 2 final states in the RIXS spectrum demonstrates significant S = 2 character spin–orbit mixed into the S = 1 ground state.