Motivating and constructing correlation diagrams for molecular transformations using X-Ray spectroscopic signatures : “Think Orbitals”

Kimika Teorikoa Seminar

Learning and understanding of chemistry is largely built around the concepts of molecular orbitals. Molecular reactivity is often studied using correlation diagrams which show the evolution of the molecular orbitals and corresponding interactions along a reaction coordinate. However, the fundamentals of many-bond theories describe molecular orbitals as not quantum mechanical observables [1]. Thus, these descriptors of chemical reactivity are often left on ambiguous grounds. Using X-Ray spectroscopic techniques, X-ray Absorption Spectroscopy (XAS) and Resonant Inelastic X-ray Scattering (RIXS) in particular, we demonstrate that, by probing the local electronic structure around a specific atom in a molecule, we can assign spectroscopic observables to certain orbital interactions. This is a unique way of motivating and constructing correlation diagrams and to uncover new descriptors of chemical reactivity. We show in particular, using the case of photo-initiated C-H activation by CpRh(CO)2,[2,3] that a correlation diagram for the oxidative addition of the C-H bond to transition metal center can be motivated from X-ray spectroscopic observables. Using time-resolved 4d metal L-edge XAS spectra obtained at an X-ray free electron laser (XFEL) and a synchrotron, we confirm the theoretically predicted RIXS signatures associated with the orbital interactions present in photolytic C- H activation process [4].

References:
[1] Orbitals: Some Fiction and Some Facts, J Autschbach, J. Chem. Educ. 2012, 89, 8, 1032–1040.
[2] Tracking C-H activation with orbital resolution. Raphael M. Jay1,*,† Ambar Banerjee1,*,†, et. al. Science, 2023, 380, 955–960
[3] Accessing Metal-Specific Orbital Interactions in C-H Activation using Resonant Inelastic X-ray Scattering, A Banerjee* et. al., Chemical
Science, 15(7), pp.2398-2409