Development of Structurally Diverse N-Heterocyclic Carbene Ligands via Palladium-Copper-Catalyzed Decarboxylative Arylation of Pyrazolo[1,5-a]pyridine-3-carboxylic Acid

A series of fused non‐classical normal N‐heterocyclic carbenes, Pyrpy‐NHC precursors derived from pyrazolo[1,5‐a]pyridines, has been prepared using palladium‐copper‐catalyzed decarboxylative arylation of pyrazolo[1,5‐a]pyridine‐3‐carboxylic acid. Air‐stable palladium and rhodium complexes of these ligands have been synthesized via mild transmetallation of Ag‐Pyrpy‐NHC. The structural properties of Rh(Pyrpy‐NHC)(COD)Cl complexes were determined via X‐ray analysis. The measurement of the CO stretching frequencies of dicarbonyl Rh‐Pyrpy‐NHC complexes revealed that the electron donating strength of Pyrpy‐NHC could be tuned by varying the substituents of the aryl group. A catalytic study of the Pd‐Pyrpy‐NHC complexes revealed promising activity in the Suzuki–Miyaura reaction under ambient atmospheric conditions.