Palladium Complexes Bearing Mesoionic Carbene Ligands: Applications in -Arylation, -Methylation and Suzuki-Miyaura Coupling Reactions

Complexes of mesoionic carbene (MIC) ligands are gaining immense popularity in organometallic chemistry and homogeneous catalysis. We present here a series of palladium(II) complexes that are comprised of MIC donor ligands, and we demonstrate their applications in -arylation, -methylation, and Suzuki-Miyaura coupling reactions. All the complexes have been structurally characterized by X-ray crystallographic analysis. These palladium(II) complexes are potent precatalysts and they deliver good to excellent yields for both -arylation and Suzuki-Miyaura coupling reactions. A palladium(II) complex bearing two MIC units in a trans fashion is used for chemoselective Suzuki-Miyaura coupling reaction. This complex delivers lower yields in -arylation reactions compared with PEPPSI-type complexes, however, it gives an -methylated product when the reaction is conducted in N,N-dimethylformamide. Mercury poisoning experiments suggest that the Suzuki-Miyaura coupling reaction likely proceeds via Pd nanoparticles. However, the -arylation reaction proceeds homogeneously, as shown by the negative mercury poison test. The present results thus open up new avenues for MIC ligands in catalytic -arylation and -methylation reactions.