Metal-Ligand Covalency of C-H Activating Iridium Complexes from L-edge Valence-to-Core Resonant Inelastic X-ray Scattering

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 such 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 the nature and degree of metal-ligand hybridization as well as how changes in ionic vs. covalent metal-ligand interactions for different ancillary ligands impact valence-excited state energetics. 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 approach reveals the interplay of ligand structure, metal-ligand bonding or covalency and valence-excited state landscape with implications for our understanding of how these properties impact photochemical pathways in C-H activation and other photocatalytic applications.