Invisible Chelating Effect Exhibited between Carbodicarbene and Phosphine through π-π Interaction and Implication in the Cross-Coupling Reaction

Palladium complexes supported with the mixed ligands carbodicarbene (CDC) and different phosphine ligands (PPh₃, PTol₃, and PCy₃) were prepared, and their molecular structures were characterized. Examination of the structures of 2-PPh₃ and 2-PTol₃ with cis configuration discloses the existence of an unexpected π-π interaction between one phenyl group of the phosphine and the benzimidazole ring of a CDC. The palladium complex 2-PPh₃ is an active Suzuki-Miyaura catalyst with a wide scope of substrates containing various functional groups and steric demands. In contrast to electron-withdrawing aryl bromide, the yield of product for electron-rich substrates was improved by adding a catalytic amount of DMSO under aerobic conditions. The solution NMR and structural analysis has revealed that the intramolecular π-π interaction between CDC and phosphine ligands has a positive influence on the activity of the reaction, which is further supported by quantum chemical calculations.