Imidazo[1,5-a]pyridine-3-ylidenes—pyridine derived N-heterocyclic carbene ligands

The ready synthesis of differently substituted 2H-imidazo1,5-a]pyridin-4-ium bromides is reported. These salts are precursors for a new class of N-heterocyclic carbene ligands. As a consequence of their bicyclic geometry, these ligands are capable of influencing the coordination sphere of a carbene bound metal. The usefulness of these ligands was demonstrated in the palladium-catalyzed Suzuki-Miyaura cross-coupling of sterically hindered aryl chlorides.