Study On The Coupling Reactions Catalyzed By SBA-15 Supported Palladium Catalyst In Supercritical Carbon Dioxide

Palladium catalyzed Suzuki and Heck coupling reactions are important routes for the construction of C-C bonds,which are widely used in the synthesis of natural products, pharmaceutical intermediates and fine chemicals,so they attract more attention from scientific workers.However,there are some drawbacks in traditional homogeneous reaction systems, such as,non-recyclable catalysts,environmental pollution caused by organic solvents,etc.To solve the problems above,the palladium catalyst was located in the channels by the multi-coordination of functional groups of modified SBA-15,and the substrates and bases were brought into the channels by supercritical carbon dioxide based on its low viscosity and high diffusivity.When the reaction was over,the coupling products were brought out of the channels by supercritical carbon dioxide.1.The phosphine ligand(MeO)₃Si(CH₂)₃CH₂C₆H₄PPh₂ that can be graft on the inner surface of mesoporous silicate SBA-15 was designed and synthesized.Its structure was characterized by ¹H NMR,¹³C NMR,³¹p NMR,HRMS,etc.The external and internal surfaces of mesoporous silicate SBA-15 were modified by trimethoxyphenylsilane and phosphine ligand respectively,and then the Ph-SBA-15-PPh₃-Pd catalyst was obtained by the treatment of the Ph-SBA-15-PPh₃ in a CH₂Cl₂ solution of Pd₂(dba)₃.The obtained catalyst was characterized by UV,XRD,BET,SEM,TEM,etc.The results indicated that the modified mosoporous sieve and the catalyst both maintained a two-dimensional hexagonal structure,only aperture,surface area and pore volume lowered slightly.2.The SBA-15 supported palladium catalyst was applied to catalyze Suzuki and Heck coupling reactions in supercritical carbon dioxide.The results of the study on the coupling reactions of different substrates and the characterization of the catalyst after reaction showed that the catalyst has high activity and good stability.3.There are some advantages of the SBA-15 supported palladium catalyst,First,it can be reused several times without any decrease in activity;Second,the phosphine ligand within the channels of SBA-15 can efficiently prevent the leaching of the palladium species;Third, the catalyst is almost completely unaffected by supercritical carbon dioxide and maintains the two-dimensional hexagonal structure;Fourth,the coupling product can be purified by simple recrystallization;Fifth,the three-phase test results show that the catalyst is heterogeneous.