Theoretical And Experimental Study On Metal Nanoparticles Catalyzing Suzuki Cross Coupling And Hashmi Phenol Synthesis Reaction

Transition metal catalyzed Suzuki cross coupling reaction and Hashmi phenol synthesis reaction play important roles in drug development and synthesis,which has attracted extensively attention of many researchers.The wide application of transition metal catalysts promote the development of drug synthesis.In recent years,with the development of the concept of green chemistry,organic synthesis is developing towards green,economic and environmental protection.It is required that the catalyst has the advantages of high activity,low cost and easy circulation.Environmental protection and economic high active metal nano-catalyst came into being under the urgent demand.It is crucial to reveal the structure activity relationship（SAR）of catalysts for design of highly active nano-catalysts.These problems are expected to be solved through experiments and theoretical calculations.In this paper,the synthesis and characterization of dendrimer encapsulated nanoparticals（DENs）as well as their catalytic properties for Suzuki coupling reaction were introduced.In addition,the Hashmi phenol synthesis catalyzed by single walled nanotubes of Au（6,m）（m=0,1,2,3）were also studied.The concrete research result is as follows:Firstly,a series of Pd_xM_147-x（M=Cu,Pt,Au,Rh,Ru）DENs were synthesized.The experimental data showed that the diameter of Pd_x M_147-x（M=Cu,Pt,Au,Rh,Ru）DENs were in the range of 1.47².27 nm,and the particle size was the same as that of the closed-shell octahedron theoretical structure model which composed of 147 atoms.The results of Suzuki coupling catalyzed by Pd_xM_147-x（M=Cu,Pt,Au,Rh,Ru）DENs showed that the catalytic activity of alloy nanoparticles was significantly different.Among them,the catalytic activities of Pd₇₄Pt₇₃,Pd₇₄Au₇₃,Pd₇₄Rh₇₃ and Pd₇₄Ru₇₃ DENs were lower.Pd₇₄Cu₇₃ DENs had the similarity catalytic activity with the Pd₁₄₇ DENs.The results showed that the activity of Pd_xCu_147-x DENs was enhanced with the increase of Pd atom content.When the ratio of Pd:Cu=1:1,the activity tended to be stable.In addition,Pd₇₄Cu₇₃ DENs could catalyze a variety of reaction substrates with good substrate adaptability.The results showed that Cu is an ideal dopant for the synthesis of high activity and low-cost nano-catalyst.Based on the DFT theory,the mechanism of Suzuki coupling catalyzed by Pd₁₄₇ and Pd₇₄Cu₇₃ DENs was discussed,and the role of Cu atom in this catalytic cycle was revealed.The calculation results showed that the energy barrier of transmetalation process was effectively reduced by Cu atom,and the reaction rate determination step was changed,too.The reaction rate determination step of Suzuki coupling reaction catalyzed by Pd₁₄₇ DENs was transmetalation step,while the reaction rate determination step of Pd₇₄Cu₇₃ DENs in the catalytic process was reduction elimination step.The reaction energy barriers of the two determination steps were basically the same.It can be explained that Pd₁₄₇ DENS and Pd₇₄Cu₇₃DENs presented the similarity catalytic activity.Besides,the local electron density and differential electron density showed that the introduction of Cu reduced the Fermi energy levels at the top and edge sites of the nanocatalyst,weakening the interaction between the reactant intermediate and the atomic orbitals near the Pd₇₄Cu₇₃ DENs,reducing the adsorption energy of the product.This paper provides a valuable reference for the design of novel catalysts with high activity and low palladium content to catalyze Suzuki cross-coupling reaction.Moreover,the mechanism and charge effect of cycloisomerization ofω-alkynylfuran（Hashmi phenol synthesis）catalyzed by single-walled helical gold nanotubes（Au SWNTs）have been systematically investigated by density functional theory.Cycloisomerization ofω-alkynylfuran occurs by the 5-exo Friedel–Crafts-type（FCT）mechanism.Namely,5-exo cyclization,furan ring-opening,and ring-closing of the dienone carbene–gold intermediate.The reactions with Au（6,0）,Au（6,1）,Au（6,2）and Au（6,3）SWNTs showed low energy barriers along the 5-exo FCT path in acetonitrile solvent.However,the rate-determining steps catalyzed by the Au（6,m）SWNTs were different.From an energy perspective,the rate-determining step of the reaction catalyzed by Au（6,0）and Au（6,3）was the formation of the ring-closing dienone carbene–gold intermediate,but that of the reaction catalyzed by Au（6,1）and Au（6,2）was the furan ring-opening step,which can be attributed to the diversity of the d-band centers of the Au（6,m）SWNTs.The charge effects of the Au SWNTs in the catalytic activity was also investigated.Cationic Au（6,m）SWNTs were more suitable for cycloisomerization ofω-alkynylfuran than anionic Au（6,m）SWNTs,cationic Au（6,m）SWNTs significantly reduced the substrate adsorption energy on the catalyst surface,the energy barrier during the cyclization as well ring-closing step were reduced,too.Theoretical analysis showed that the structure of the Au（6,m）SWNTs could obviously affects the catalytic properties,cationic Au（6,m）SWNTs were beneficial for this reaction.This work provides insight into cycloisomerization ofω-alkynylfuran and valuable information for the application of Au SWNTs in catalysis.