CHAktivierungsreaktionen

CHAktivierungs, commonly referred to as C–H activation, denotes a family of reactions in organometallic catalysis in which a carbon-hydrogen bond is cleaved and a new bond to a transition metal is formed. This enables direct functionalization of otherwise unreactive hydrocarbons into a variety of products, often with high atom economy and reduced need for prefunctionalized substrates.

Most C–H activation reactions proceed via a metal-centered process that forms a metal–carbon bond. Common mechanistic pathways include concerted metalation-deprotonation (CMD), oxidative addition, and sigma-bond metathesis. The exact route depends on the substrate, metal, ligands, and reaction conditions.

Directing groups are widely used to achieve site selectivity, coordinating to the metal and guiding activation to nearby C–H bonds. In nondirected C–H activation, selectivity arises from catalyst design, substrate electronics, or inherent C–H acidity. Catalysts frequently involve late-transition metals such as palladium, rhodium, ruthenium, and iridium, though cobalt and nickel are active in some systems. Reactions span arylation, alkylation, borylation, amination, and oxygenation, enabling rapid diversification and late-stage functionalization of complex molecules.

Challenges include achieving high site and chemoselectivity, expanding substrate scope, and tolerating sensitive functional groups. Sustainability and milder conditions remain priorities, as does extending C–H activation to more diverse substrates, including aliphatic and heteroatom-rich systems, and integrating it with cascade or photochemical strategies.