5‐Sulfurated Imidazo[1,5‐ a ]Pyridin‐3‐ylidenes: Ligands for π‐Acidic Catalysts

A series of 5‐sulfurated imidazo[1,5‐ a ]pyridin‐3‐ylidenes (Imidazo[1,5‐ a ]pyridine carbenes: IPCs) and their Cu and Pd complexes were synthesized. Theoretical investigations of the free carbenes and Cu complexes implied that the IPCs were good π‐acceptors. Particularly, Cu complexes of 5‐arylsulfonyl IPC were strong π‐acids. These complexes were tested as π‐acidic catalysts in the Cu‐catalyzed hydroboration of an internal alkyne with diboron and the Mizoroki‐Heck reaction. As a result, the trend in reactivity corresponded with the theoretical considerations.