Study On Pd@MOFs As A Heterogeneous Single-site Catalyst For Suzuki Reaction

Single-site catalysts have attracted great interest from researchers due to their uniform structure and unique catalytic performance.Among various porous supports,metal organic framework materials（MOFs）are expected to become an ideal support for single-site catalysts with their large specific surface area,good stability,clear structure and easy adjustment.The Suzuki-Miyaura coupling（SMC）reaction is one of the most common and effective methods for constructing C-C bonds.Highly active homogeneous catalytic systems often require the addition of organic phosphine ligands that are harmful to the environment.The product is not easy to separate and the catalyst is difficult to recycle and reuse;However,for the recyclable traditional heterogeneous catalysts,they often exhibited poor ability to catalyze the reaction of inert substrates.In this paper,combined with the nanopore confinement effect of MOFs,two single-site catalysts were designed and synthesized based on the frameworks with excellent thermal and chemical stability,and exhibited great performance in terms of stability,catalytic activity and recyclability.The main contents are as follows:（1）Study on the preparation,Characterization and catalyst properties of Pd@MOF-808（cat.1）for the SMC reaction:MOF-808 was synthesized with Zr OCl₂·8H₂O and1,3,5-benzenetricarboxylic acid through a“green water-based”method,and it was selected to synthesize cat.1 as s support.All of cat.1 and MOF-808 were characterized by PXRD,BET,SEM,TEM,TGA,XPS;the catalytic activity of cat.1 was confirmed with p-methoxy iodobenzene and phenylboronic acid,and the best reaction conditions were screened out:3mol%cat.1,Me OH,40°C,and 2 eq.K₂CO₃.A variety of substrates were expanded under optimal conditions to confirm the substrate adaptability of the system.The experiment shows that cat.1 can be recycled 5 times.（2）Study on the preparation,Characterization and catalyst properties of Pd@MOF-905（cat.2）for the SMC reaction:Firstly,acrylic acid ligand a2 was synthesized through Heck coupling and Hydrolysis reaction.Subsequently,MOF-905 was synthesized by self-assembly of zinc nitrate hexahydrate,terephthalic acid and a2,then Pd was introduced into MOF-905 to synthesize cat.2.Under certain conditions,cat.2 was characterized by PXRD,TGA,XPS,etc.;The catalytic activity of cat.2 was confirmed by the Suzuki reaction of p-methoxy iodobenzene and phenylboronic acid.The optimal conditions were screened out:3 mol%cat.2,Et OH,T=50℃,and 2 eq.Cs₂CO₃.Various of substrates were expanded under optimal conditions to confirm the substrate adaptability of the system.The experiment shows that cat.2 ould be recycled 5 times.The above experimental results showed that the two heterogeneous single-site catalysts（Pd@MOF-808 and Pd@MOF-905）had stable structures and excellent performance in the application of catalyzing the Suzuki-Miyaura reaction.Due to the excellent catalytic activity and recyclability of the catalysts we synthesized,it could be used as effective reference for studying the Suzuki-Miyaura coupling reaction.