Research On The New Catalytic Systems For Suzuki And Heck Coupling Reactions Of Aryl Halides

The palladium catalyzed coupling of bromo- and iodoarenes by Heck and Suzuki reactions is a well-established methodology in modem organic synthesis.The coupling products find good applications as intermediates in the preparation of materials,natural products and bioactive compounds.It is highly desirable to develop a phosphine-free new recyclable heterogeneous catalytic system to dispense the use of expensive and air-sensitive basic phosphines for palladium catalyzed coupling reactions of haloarenes.Four types of novel ligandless Pd or non-palladium catalysts for Heck and Suzuki reactions were developed in the current dissertation.Layered double hydroxides(LDHs),an important family of inorganic layered materials,have been found wide applications as catalysts,catalyst precursors or supports,adsorption,nanocomposite and drug delivery.Herein,surfactant (DS')-intercalated LDHs(MgAl-LDH-DS)were prepared via ions exchange method. Further exchange of DS^- with PdCl₄^2-resulted in LDHs intercalated by both DS" and PdCl₄^2-(PdCl₄^2-/MgAl-LDH-DS).Pd⁰/MgAl-LDH-DS were further obtained via the reduction of PdCl₄^2-/MgAl-LDH-DS with Vc.The Pd⁰ clusters were intercalated between the LDHs layers;hence the growth of Pd⁰ clusters would be effectively hindered by the limited space of the inter-layers created by the pre-intercalation of DS^-.The micro-space between LDH layers created by surfactant was hydrophobic,so the organic reactants could enter freely into these micro-reactors and interact with the pre-implanted Pd⁰ cluster,resulted in effective catalysis toward Suzuki reaction.Delaminating layered materials is of tremendous practical importance in applications due to the largely enhanced accessibility of their inner surface.Layered double hydroxides are layered materials constituted by a stacking of positive hydroxylated layers[M²⁺_1-xM^3+x_x(OH)₂]^x+separated by interlayered anionic species and water molecules[A_x/n^n-·m H₂O]^x-.As a consequence of its structure,the delaminated LDH phase would reach a theoretical specific surface area of 1,000 m²/g. Actually,applications of delaminated layered materials rather than LDHs have been developed previously.However,the practical application of delaminated LDH is still in its infancy,despite that the strategies for delaminations of LDHs have been relatively well-documented and well-established since the first case of the LDH delamination by use of surfactant was reported in 2000.In the present work,A novel ligand-free catalyst,Pd(â…¡)-doped colloidal layered double hydroxide(LDH),has been prepared from delamination of glycinate intercalated ternary-component MgPdAI-LDH([Mg_0.95Pd_0.05Al_1/3(OH)₂][Gly_1/3·mH₂O])in formamide.Subsequently, the catalytic performance of these mono-dispersed ultrathin nanosheets of LDH for Heck reaction was evaluated.Owing to the largely enhanced accessibility for reactant molecules resulting from the nature of high inner surface area of LDHs,these palladium-bearing nanosheets showed excellent efficiency for Heck reactions to a wide range of substrate molecules.The Pd sites and basic sites on the brucite-like nanosheets are combined at a molecular level and interact with each other closely because of the co-precipitation method employed;so the basic sites on the LDH monolayers might function as basic ligands.The electron-rich environment derived from basic sites of LDH layers would provide the requisite electron density on palladium to undergo oxidative addition of in situ formed Pd(0)with haloarene, accounting for the highly catalytic efficiency.This method of combination of catalytically active sites with LDHs might be extended to transition metals other than Pd(â…¡).The present work also developed a simple way to combine Pd⁰ with Fe₃O₄ nanoparticles(NPs),PdCl₄^2-was immobilized directly on the cationic Fe₃O₄ colloids through electrostatic interaction.Further reduction of these PdCl₄^2-/ Fe₃O₄ NPs resulted in Pd⁰/Fe₃O₄ NPs.These magnetic NPs-supported Pd⁰ clusters showed high efficiency toward Suzuki reactions.After reactions,the Pd⁰/ Fe₃O₄ NPs could be simply recycled by permanent magnet.This catalyst could be re-used for 5 times without significant loss in catalytic activity.Phthalocyanines(Pcs)are one of the most extensively studied functional materials. As functional materials,the immobilization of Pcs on some supports(e.g.,metal oxides)is essential for fully exploiting their functionalities.Both Fe₃O₄ nanoparticles (NPs)and Pcs are important functional materials,they are complementary in both properties and functions.The effective combinations of these two kinds of materials have potential application in catalysis,photo-catalysis and anticancer therapy.In the present work,SCFD-derived Fe₃O₄ nanoparticles were chose as substrate to react with phthalic nitrile(Ph(CN)₂)superficially to form FePc monolayer on the surface of Fe₃O₄ NPs.Using these two simple starting materials,Fe₃O₄ NPs chemically coated with FePc monolayer were obtained just in one step.To our best of knowledge,it is a totally new strategy to functionalize iron oxides with FePc.Also this method may be extended to other metal oxide(e.g.,TiO₂ and Fe₂O₃)nanoparticles and other phthalic nitrile derivatives.More interestingly,this in situ formed FePc@Fe₃O₄ nano-composite also exhibited catalytic activity toward Heck reaction;it is a non-palladium-catalyzed Heck reaction.This finding will lay a foundation to understand more accurately the mechanism of Heck reactions.