Oxime-Derived Palladacycles as Versatile Catalysts in Cross-Coupling Reactions

Recently, metallacycles, which are derivatives of carbocyclic compounds wherein a metal has replaced at least one carbon center, have attracted attention for their high catalytic reactivity. Palladacyles 1 and 2, developed by Nájera et al., are among such metallacycles, and have been used as catalysts for carbon-carbon bond formation. They are thermally stable and not sensitive to air or moisture.^1a) According to their result, 1 and 2 exhibit high catalytic activity in organic solvents as well as in aqueous solvents. For example, in the Sonogashira-type coupling reaction using 1, the desired acetylenes are obtained in good yields with no addition of copper and amines.^1b) On the other hand, in the Hiyama-type coupling reaction using 2, the desired styrene derivatives are obtained without using fluorides.^1c)

Furthermore, there are also several reports on applications to other cross-coupling reactions, such as the Suzuki-Miyaura^1d) and Heck^1e) reactions.