Metal-ligand covalency of C-H activating iridium complexes from L-edge valence-to-core resonant inelastic X-ray...

The electronic structure of iridium carbonyl complexes is known to be fundamental to their ability to activate alkane C-H bonds following UV photolysis. Here, we investigate three prototypical iridium complexes with different ancillary ligands using valence-to-core resonant inelastic X-ray scattering measurements at the Ir L₃-edge in combination with optical absorption spectroscopy and calculations based on time-dependent density functional theory. We characterize experimentally how the nature and degree of metal-ligand hybridization impact valence-excited state energetics as well as how changes in ionic vs. covalent metal-ligand interactions for different ancillary ligands modulate charge densities at the central metal atom. The selectivity of our methods to the valence-excited state manifold allows us to observe and quantify shifts in the d-d and charge-transfer manifold of excited-states, which are both thought to influence the yield of photochemical C-H bond activation. Our combined experimental and theoretical study of this series of iridium complexes reveals the interplay of ligand structure, metal-ligand bonding or covalency and valence-excited state landscape, which allows to deduce a general understanding of how these properties impact photochemical pathways and reactivity in C-H activation and other photocatalytic applications.