Palladium (II) Complexes with Pyrimidine NHC (C*Npyr) Ligands in the Suzuki-Miyaura Cross Coupling Reaction

• Catalytically highly active palladium (II) complexes with C*N pyr ligands synthesized from an imidazolium precursor with pyrimidine and mesityl ligands • Suzuki-Miyaura cross coupling of various aryl bromides and boronic acids in excellent yields • Mild reaction conditions in an environmentally friendly solvent mixture of water and ethanol (1: 1) We report the high catalytic activity of palladium (II) complexes with C*N pyr ligands synthesized from an imidazolium precursor with pyrimidine and mesityl ligands. We show that the pyrimidine nitrogen atom of the hemilabile pyrimidine carbene ligand can coordinate and dissociate reversibly to the palladium atom in dependence on the ligand environment at the palladium atom. We found that the carbene increases the catalytic activity while the pyrimidine nitrogen atom stabilizes the catalytically active species and increases its lifetime. Even at lower catalyst concentrations leading to turnover numbers of up to 760′000 the complexes were extraordinarily active. With the most active catalyst we demonstrate a large substrate scope and successfully coupled various aryl bromides and boronic acids in excellent yields under mild reaction conditions in an environmentally friendly and inexpensive solvent mixture of water and ethanol (1: 1) without the need for protective gases.