Palladium-Catalyzed C-H Arylation Reactions

Palladium-catalyzed C–H arylation reactions enable the direct formation of carbon–carbon bonds by activation of typically unreactive C–H bonds and coupling with aryl halides or pseudohalides. This atom-economical approach circumvents prefunctionalisation steps required in classical cross-coupling methods, delivering improved step efficiency and reduced waste. Mechanistically, the process often proceeds via a concerted metalation–deprotonation (CMD) pathway in which a palladium complex bearing suitably designed ligands cleaves the C–H bond, forms a palladacycle and subsequently undergoes transmetallation and reductive elimination to furnish the arylated product. Ligand design (for example phosphine or N-heterocyclic carbene frameworks) is critical to tuning regioselectivity, chemoselectivity and reaction rate. Both homogeneous systems and heterogeneous catalysts have been developed, the latter offering advantages in recyclability and green solvent compatibility. Applications span the synthesis of heterocyclic scaffolds in pharmaceutical targets, functional materials and agrochemicals. Recent efforts have focused on enhancing site selectivity in complex molecules, lowering catalyst loadings and integrating sustainable reaction media to meet growing demands for efficient and environmentally benign synthetic routes.

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Palladium-Catalyzed C-H Arylation Reactions publication trend

The graph below shows the total number of articles in palladium-catalyzed c-h arylation reactions across all publications each year (not limited to Nature Index journals).

Technical terms

C–H Activation: The process by which a metal catalyst cleaves a carbon–hydrogen bond to form a metal–carbon intermediate.

Arylation: Introduction of an aryl group into an organic molecule, commonly via metal-catalysed coupling.

Concerted Metalation–Deprotonation (CMD): A mechanism in which metallation and proton removal occur simultaneously in a single transition state.

Regioselectivity: Preference for bond formation at one location over others within a substrate.

Heterogeneous Catalyst: A solid catalyst that operates in a different phase from the reactants, facilitating recovery and reuse.

References

1. Regio‐ and Chemoselective Palladium‐Catalyzed Additive‐Free Direct C─H Functionalization of Heterocycles with Chloroaryl Triflates Using Pyrazole‐Alkyl Phosphine Ligands. Advanced Science (2024).
2. Room-Temperature Direct β‑Arylation of Thiophenes and Benzo[b]thiophenes and Kinetic Evidence for a Heck-type Pathway. Journal of the American Chemical Society (2016).
3. C–H arylations of 1,2,3-triazoles by reusable heterogeneous palladium catalysts in biomass-derived γ-valerolactone. Chemical Communications (2016).