Preparation Of Bulky N-heterocyclic NHC-Pd Catalyst With High Dispersibility And Its Catalysis To Suzuki-miyaura Reaction

Suzuki-Miyaura coupling reaction has been widely employed as one of the most important methods to form C-C bond since it was discovered by Suzuki-Miyaura,palladium catalyst is the most common catalyst in Suzuki-Miyaura coupling reaction.Although the structure of phosphorus ligand has been developed,the activity of the catalyst has been increased,but the palladium catalyst containing bulky N-Heterocyclic Carbene has attracted much attention due to its high catalytic activity,stability and adaptability for different substrates.However,the dispersibility of the palladium catalyst is also deteriorated because of the bulky structure,which just resulted in the decrease of the catalytic efficiency.Furthermore,most palladium catalysts containing bulky NHC ligand could not show good catalytic activity for aryl chloride.Therefore,the NHC-Pd(acac)Cl catalyst with good dispersibility was synthesized by modifying the long chain alkoxy group with good flexibility on the N-Heterocyclic Carbene ligand.Then,its catalytic performance in Suzuki-Miyaura reaction was carefully investigated.The main contents of this paper are as follows:(1)We synthesized a new bulky NHC ligand contiang a long alkyl chain.Based on this new ligand,alkoxylated N-heterocyclic NHC-Pd(acac)Cl catalyst with good dispersibility was prepared with palladium acetylacetonate and the palladium content reached to 0.94 mmol/g.(2)In this paper,the optimization for catalytic conditions in the Suzuki-Miyaura coupling reaction was carried out when bromine substrate and chlorobenzene substrate were selected as reaction substrate.It was found the catalytic efficiency reached 100% when the reaction was carried at 70?for 4 h and the solvent was selected 50% water and 50% ethanol.The TON value even reached 9.1�107.When the reaction substrate was selected as chlorobenzene substrate,the optimum conditions were as followed: the solvent was isopropanol,the base was selected as KOtBu,the temperature was about 80? and the reaction time was about 8 h.(3)The substrate adaptability of the catalyst was also discussed.It was found that the catalysts exhibited higher activity and stability in the coupling reaction of aryl bromides,aryl chlorides with aryl boronic acids.It has good substrate adaptability to aryl halides,especially for the catalytic effect of chlorinated aromatic compounds.