Preparation And Application Of SBA-15-Supported Palladium Catalysts For Suzuki Coupling Reactions In Supercritical Carbon Dioxide

Palladium-catalyzed Suzuki cross-coupling reaction is one of the most efficient methods for the construction of C_aryl-C_aryl bonds,which is widely used in synthesis of natural products, polymers,liquid crystals,and advanced materials.High yields have been obtained with many substrates containing a wide range of functional groups on either coupling partner by homogeneous process in organic solvent.However,the use of organic solvent leads to the waste of energies and times to separate the desired product from reaction mixture,and which also leads to the environmental pollution.In this thesis,two kinds of SBA-15-supported palladium catalysts(PE-SBA-15-SH-Pd and PE-SBA-15-PPh₃-Pd) were designed and prepared for Suzuki cross-coupling reaction in the supercritical carbon dioxide(scCO₂).The catalytic activities of the above mentioned two catalysts were investigated using the coupling of 1-bromo-4-nitrobenzene with phenylboronic acid as a model reaction.1.The external and internal surfaces of mesoporous silicate SBA-15 were modified by trimethoxyphenylsilane and mercaptopropyl trimethoxysilane respectively,and then the PE-SBA-15-SH-Pd catalyst was obtained by treatment of the PE-SBA-15 in a THF solution of Pd(AcO)₂.The best result was obtained from the coupling reaction of 1-bromo-4-nitrobenzene with phenylboronic acid in the presence of PE-SBA-15-SH-Pd catalyst when(n-Bu)₄NOAc was employed as a base.2.Like described above,the external and internal surfaces of mesoporous silicate SBA-15 were modified by trimethoxyphenylsilane and(MeO)₃SiCH₂CH₂CH₂SCH₂C₆H₄PPh₂ containing triphenylphosphine moiety respectively,and then the PE-SBA-15-PPh₃-Pd catalyst was obatined by treatment of the PE-SBA-15-PPh3 in a CH₂Cl₂ solution of Pd₂(dba)₃.The best result was obtained from the coupling reaction of 1-bromo-4-nitrobenzene with phenylboronic acid in the presence of PE-SBA-15-PPh₃-Pd catalyst when DIPEA was employed as a base.It was found that the catalyst PE-SBA-15-PPh₃-Pd was very stable with high catalytic activity,can be reused for the coupling reaction of 1-bromo-4-nitrobenzene with phenylboronic acid more than ten times without lost activity.3.The structures of the modified materials were characterized by XRD,BET,FT-IR, SEM,TEM,etc.The palladium content of the SBA-15-supported palladium catalysts were mensurated by ICP.The results indicated that the structure of the modified SBA-15 was similar to that of unmodified one,only a little decreased diameter and volume of the pore of modified SBA-15 were observed.