N-heterocyclic olefin (NHO) is known as a highly electron-donative ligand, but its application to metal catalysts has rarely been studied. In this study, a well-defined NHO ligated-Pd catalyst was developed. N-substituents on NHO ligand affected the catalytic performance, and the addition of a phosphine co-ligand, in particular [2-(MeO)C₆H₄]₃P was effective to enhance the activity.

Abstract

N-heterocyclic olefin (NHO) is known as a highly electron-donative ligand, but its application to metal catalysts has rarely been studied. In this study, we synthesized 2-methyleneimidazolidine ligands equipped with a bicyclic frameworks with the goal of developing a NHO-ligated Pd catalyst. These synthesized [(NHO)PdCl(μ-Cl)]₂ complexes had a phosphine co-ligand that proved effective as a catalyst for Suzuki-Miyaura coupling at ambient temperature. By optimizing the N-substituents of NHO ligands and a phosphine co-ligand, we developed a [(NHO)Pd{[2-(CH₃O)C₆H₄]₃P}Cl₂] complex as a catalyst that shows good catalytic activity.