Bulky N-heterocyclic Carbene Palladium Catalytic C-N And C-O Coupling Reaction

The Pd-catalyzed Buchwald-Hartiwg coupling reaction is one of the powerful methodologies for the construction of C-N bonds.The ligands bound to palladium played key roles,while the phosphine ligand was the primary choice.However,most of the phosphines were sensitive to air and water.Moreover,the cross coupling often suffered from harsh reaction conditions,such as strict air and moisture-free conditions,in the presence of high palladium loading and long reaction time.With the demanding of the high efficient and environment-friendly phosphine-free ligands,the N-heterocarbenes have been received much attention in recently years.Nevertheless,the amination between the electron-rich aryl halides with?hetero?cyclic amimines,as well as the coupling of five-membered heterocyclic aryl halides with the?hetero?anilines were still significant challenge.In this thesis,the effort has devoted to explore a new type of NHCs,which is high air-stable and exhibited high efficiency.1.A type of rigid Pd-PEPPSI complexes?C1-C4?for C-N cross-coupling reaction was developed,and their structures were characterized by nuclear magnetic resonance.The structures of C1 and C3were further deterimined by X-ray single crystal diffraction.On the evaluating the electronic and steirc effects of these palladium complexes,it was found that the introduction of electron?-donated substituents on the N-aryl moiety and the large steric environment were essential for Buchwald-Hartwig cross-coupling.Under optimal reaction conditions,a wide range aminations and five-and six-membered?hetero?aryl chlorides were smoothly coupled in the presence of 0.1-2 mol%of the palladium loading.The established precatalysts provided valuable guidance for catalyst design and advancement of arylation amine synthesis under aerobic conditions.2.Based on the excellent performance of the rigid Pd-NHCs complexes,the deactivated nitro derivatives were selected as electrophilic substrates for their easily accessible.It was found that the Pd-PEPPSI complexes with rigid steric hindrance showed excellent activites toward the?hetero?arylphenol compounds to construct C-O bonds.It was found that the NHCs ligands played crucial roles on the stabilization of palladium intermediates and C3 gave the highest efficiency.The optimum conditions were established as:K₃PO₄ as the base,DMSO was used as the solvent and H₂O was used as the additive,in the air under a reaction temperature of100°C.A variey of?hetero?aromatic phenolic compounds with electron-withdrawing and large hindrance were tolerant,which affording the desired products in good to excellent yields.