| Due to the existence of various types of C-H bonds in organic molecules,these C-H bonds are less polar and require a higher activation energy barrier for the C-H bonds when participating in the reaction,which makes the activation of the C-H bonds more difficult.It is difficult to achieve the effectiveness of the C-H bonds in the reaction Conversion,so selective C-H bond functionalization becomes a difficult problem.A large number of studies have proved that some precious metals(Pd,Pt,Ru,etc.)can react with the C-H bonds in the molecule to form C-M bonds,and the resulting C-M bonds are much more reactive than their C-H bonds.At the same time,the use of heterogeneous catalysts can change the natural advantages of the reaction substrate adsorption,and can provide a reference method for solving this problem.Based on the above assumptions,it is proposed to modify the carbon properties of Pd nanoparticles during the synthesis of mesoporous carbon-based Pd catalysts,so as to control the electronic properties of Pd nanoparticles and achieve the purpose of selective functionalization of inert C-H bonds.In this paper,a C-modified Pd catalyst was prepared and the effect of selective hydroxylation of aryl-substituted pyridine compounds using this catalyst was investigated.The full text is divided into four chapters.The first chapter is a review of related literature,mainly introducing the research progress of C-H bond functionalization of pyridine and its derivatives.The second chapter introduces the synthesis method of carbon-modified Pd catalyst,the catalytic reaction conditions and the reagents and instruments involved in the experiment.The third chapter mainly introduces the use of solvent volatilization-induced self-assembly method,using the strong coordination of mercapto and palladium ions to synthesize highly dispersed,uniform Pd nanoparticles(2.7 nm)mesoporous carbon supported Pd catalyst.Through the thermal reduction process at a high temperature of 600 oC,palladium ions are reduced in situ.C species may be deposited and may preferentially deposit on low-coordinate atoms such as the corners of smaller nano-Pd particles to form C-Pd interstitial solid solution nanoparticles.,To achieve the modification of Pd catalyst with non-metallic atom C.The characterization of Pd 3d XPS,Pd K-edge XANES,etc.proves that through the modification of surface carbon or subsurface carbon in the thermal reduction catalyst,C-Pd bonds appear in Pd nanoparticles,which reduces the electron cloud density of Pd nanoparticles around C The proportion of palladium species in Pd nanoparticles was changed,which resulted in changes in the electronic structure of Pd nanoparticles.The CO-DRIFT characterization showed that there was only one obvious characteristic peak near 2050 cm-1 related to the adsorption sites of nanoparticles on the Pd catalyst.The deposition of substance C mainly affected the CO vibration peak near 1930 cm-1,resulting in CO There is only linear adsorption,which proves that carbon doping can change the active phase structure of Pd nanoparticles.Using TEM,XRD,etc.proved that the carbon-modified catalyst can effectively remove the surface carbon or subsurface carbon species in Pd nanoparticles under 200 oC air,and the catalyst structure and Pd nanoparticle size did not change significantly.Pd nanoparticles modified with surface carbon or subsurface carbon catalyze the hydroxylation reaction of aryl substituted pyridine compounds,which can change the selectivity of hydroxylated products.The experiment proves that oxygen can be used as a green oxidant.Under the catalysis of C-modified Pd catalyst,the hydroxylation of the C-H bond of 2-arylpyridine occurs on the pyridine group at 100 oC,and the selectivity of the hydroxylation product is 99%.This is due to the presence of surface carbon or subsurface carbon in the Pd nanoparticles,which affects the active sites such as the corners and corners of the Pd nanoparticles,resulting in the C-modified Pd catalyst can catalyze the reaction of 2-phenylpyridine to regenerate hydroxylation in pyridine Partial formation of 4-hydroxy-2-phenylpyridine is also the first example of the selective activation of C-H bonds by this method of regulating Pd nanoparticles.The system is suitable for a wide range of substrates.The Pd catalyst is recycled 6 times in the reaction of 2-phenylpyridine hydroxylation.There is still no decrease in the activity of the conversion reaction of 2-phenylpyridine and the agglomeration and loss of Pd nanoparticles in the catalyst..Hot filtration experiments and thiol material capture experiments further prove that the catalytic center is a non-leaching soluble Pd species in the solution phase.Compared with commercial Pd/C catalysts,our synthesized Pd nanoparticle catalysts have higher catalytic activity and stability.Chapter 4 summarizes the full text... |
PDF Full Text Request