C-H activation has the potential to transform modern synthetic chemistry. Selectively cleaving C-H bonds and introducing new functional groups in molecules has been the holy grail of modern organic chemistry for many years. Even though these possibilities sound very promising, they do not come without major obstacles. One of the most fundamental ones is the chemical inertness of the C-H bond, which limits its reactivity. It can be overcome by using transition metalcomplexes, which upon dissociation of one ligand (either thermally or photochemically) generate highly reactive 16-valence-electron species. These intermediates can bind to C-H bonds from the solvent, forming so-called σ-complexes and subsequently break the C-H bond. The stability and reactivity of these σ-complexes plays a decisive role in whether the activation step can occur. In this thesis, I investigate intermediates of such C-H activation reactions using (time-resolved) X-ray spectroscopic techniques, which enable the characterization of the valence electronicstructure of these intermediates. Studying these intermediates allows a detailed understanding of ligand bonding at the orbital level. In particular, analyzing the charge-transfer interactions between the metal and the coordinating C-H bond in σ-complexes provides insight into reactivity differences among these intermediates. This understanding is of great importance for optimizing C-H activation reactions.
Timo Dederichs (2025) studied this question.