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

## TL;DR

This study uses advanced X-ray techniques to explore how metal-ligand bonding affects the electronic structure and reactivity of iridium complexes in C–H bond activation.

## Contribution

The paper introduces a novel approach using valence-to-core resonant inelastic X-ray scattering to quantify metal-ligand covalency and its impact on excited-state properties.

## Key findings

- Valence-to-core X-ray scattering reveals shifts in d–d and charge-transfer excited states influenced by ligand structure.
- Ionic and covalent bonding differences modulate metal charge densities and excited-state landscapes in iridium complexes.
- The study connects ligand structure and bonding to photochemical reactivity in C–H activation.

## Abstract

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.

Valence-to-core resonant inelastic X-ray scattering at the metal L3-edge reveals how differences in ionic versus covalent metal–ligand bonding modulates local metal charge densities and excited-state landscapes in a series of iridium complexes.