Application Of New Ligand Modified Supported Metal Catalysts In Organic Transformation

With the continuous innovation of nanotechnology and material science,the design and application of supported metal catalysts have made great progress through the efforts of researchers and the development of modern characterization technology.Supported metal catalysts can be prepared in a variety of ways,and the materials that can be used as carriers or grafted metal particles are endless.Different sizes of metal components(nanoclusters and nanoparticles)have different catalytic behaviors for various heterogeneous catalytic reactions.Existing literatures have shown that a number of factors,including the size and morphology of active metal components,chemical composition,metal-supported interaction,metal-reactant/solvent interaction,different ligands and modifiers,and the acid base of the carrier,have significant influence on the catalytic performance of supported metal catalysts.Recent development in synthetic control methods and advanced characterization techniques has made it possible to correlate the relationship between material structure and catalytic performance at the molecular level.Therefore,we synthesized two kinds of supported metal catalyst nanomaterials and explored their application in organic catalytic transformation.In chapter 2,we have designed and synthesized a novel and bifunctional nanoreactor by integrating metallic Pd(0)and[CpPd(?)Cl]2 capping ligands and self-assemblies(namely Pd(0)-[CpPd(?)Cl]2),which is obtained by a simple redox and in-situ transmetalation reaction between palladium ions and titanium ions of titanocene monochloride ligands.Due to restriction effect of the micelle carriers,the ultrasmall Pd monodisperse nanoparticles(2.7 nm)are mbedded in organic ligand skeletons.The self-assemblies can not only serve as a support providing physical barriers against aggregation of ultrasmall Pd nanoparticles,while keeping Pd nanoparticle core highly accessible,but also maintain the stability and high catalytic activity of Pd nanoparticles.In addition,the selective hydrogenation of ?,?-unsaturated aldehydes and acid-free acid-free acetalization cascade reaction was realized for the first time due to the combination of the two functions of metallic Pd(0)nanoparticles and Lewis acid Pd(?)ions in the[CpPd(?)Cl]2 ligands.Without any additive or even acid,using alcohols as the green solvent and reaction partner,the desired acetals are produced in moderate to excellent yields(up to 66%-98%yield).Not only unsaturated aromatic aldehydes,but also unsaturated aliphatic and heterocyclic aldehydes can be applied in this cascade.The results of hydrogenation/acetalization reactions reveal that Pd(0)-[CpPd(?)Cl]2 show high catalytic activity as well as selectivity towards acyclic/cyclic acetals.Due to its high potential,this nanocatalyst could be considered as a competitive and replaceable catalyst to conventional catalysts such as protonic,Lewis and solid acids for the synthesis of acetals.Our work has successfully engineered metal-ligand ensemble to obtain an attractive bifunctional heterogeneous catalyst for cascade organic transformations,presenting a significant step toward the attainment of green and sustainable chemical reactions.In chapter 3,the supported metal-organic ligand superstructures catalyst(namely Cu NCs@Cp2Ti(?)ClAc)was successfully prepared for the first time using copper acetate and titanocene monochloride as the basic material through rapid redox reaction and bottom-up self-assembly.The monodisperse copper nanoclusters were well embedded into the organic ligand framework formed by Cp2Ti(VI)ClAc ligands.Titanocene monochloride is a single electron transfer system and has a redox potential,which indeed can provide a favorable driving force,promoting self-assembly to form NCs which are ideal for catalysis.In addition,the organic micelle acts as a good carrier providing physical barriers against aggregation of copper nanoclusters and does not hinder the contact between the surface of copper nanoclusters and the reactants.Compared with various unstable and homogeneous Cu(?)complex compound catalysts,the cycloaddition reaction between the alkyne and azide catalyzed by the supported metal-organic ligand superstructures(Cu NCs@Cp2Ti(?)ClAc)exhibits excellent catalytic performance(99%)with the elevated reaction temperature(80?)and prolonged reaction time(12h).More importantly,the catalyst is easy to be separated and recovered,and its activity does not decrease obviously in the following reaction cycles,showing good stability.These principles of nanocatalyst design should be extended to various other very efficient mono-and polymetallic nanocatalysts in the close future.