Preparation Of Metal-carbon Covalent Bonds Stabilized Palladium And Osnium Nanoparticles And Their Catalytic Properties In Oxidation

Metal nanoparticles have become a hot research field and attracted extensive attention,due to their unique characters such as surface area effect,Kubo effect,small size effect,macroscopic quantum tunneling.They have been applied to various reactions successfully,including hydrogenations,oxidations and carbon-carbon bond coupling reactions and so on.The metal nanoparticles,most often stabilized through coordination bond or steric effect,is involved in catalytic mechanisms with a "semi-homogeneous" manner.The leaching of metal nanoparticles as homogeneous catalysts,however,remains to be a problem.Moreover,the nano-catalyzed asymmetric organic reactions are still limited.The induction process is easily disturbed by molecular complexes when "leaching" metal complexes exists due to the reversibility of coordinate bonds.In recent years,metal carbon covalent stabilization of metal nanoparticles obtained considerable attention.The strong metal-carbon covalent bond prevents the leaching of metal leading to a truely heterogeneous catalytic process.Our group has previously studied its performance on hydrogenation of N-heterocyclic compounds.However,this type of catalyst has not been applied to oxidation reaction,and a new type of asymmetric oxidation reaction system will be realized if combining with chiral ligands.Therefore,in this thesis,the covalent bonds stabilized palladium and osmium metal nanoparticles were prepared through a "one-phase"approach,with which dehydrogenation of N-heterocycles and asymmetric dihydroxylation of olefins were carried out,respectively.Two parts are included in the thesis as follows:Part ?:The palladium-carbon covalent bonds stabilized nanoparticles were prepared from binapthyl diazonium salts in homogeneous system through in-situ reduction and the Pd nanoparticles were characterized by TEM,ICP and FT-IR.The catalytic activity of dehydrogenation in 1,2,3,4-tetrahydroquinolines and their derivatives in water at room temperature was studied systematically.The recycling of palladium nanoparticles catalyst was achieved for 5 times,with relatively high catalytic activity remained.Part ?:The osmium-carbon covalent bonds stabilized nanoparticles were prepared from binapthyl diazonium salts in homogeneous system through in-situ reduction.The osmium nanoparticles were characterized by TEM,ICP,XPS,and applied in the asymmetric dihydroxylation of olefins.Remarkable size effect of osmium nanoparticles on the reactivity and enantioselecticity of dihydroxylation were revealed resulting from the density of organic shells with different ratios between the Os precursor and binapthyl diazonium salts.When external chiral source was added,both high stereoselectivity and catalytic activity was obtained with the osmium-carbon covalent bonds stabilized nanopartiles.