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.