The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
Fang Zhang - One of the best experts on this subject based on the ideXlab platform.
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multifunctional mesoporous silica supported palladium nanoparticles as efficient and reusable catalyst for water medium Ullmann Reaction
New Journal of Chemistry, 2012Co-Authors: Jianlin Huang, Wei Chai, Chao Liang, Jian Shen, Fang ZhangAbstract:Multifunctional mesoporous material (NH2&Ph-SBA-15) was synthesized by co-condensation of tetraethyl orthosilicate, amine-silane and phenyl-silane in the presence of triblock copolymer P123. The Pd nanoparticles immobilized on the NH2&Ph-SBA-15 support were fabricated by the impregnation and subsequent reduction method. The XRD, TEM, N2 sorption, IR and solid NMR measurements revealed that this novel mesoporous Pd catalyst (Pd/NH2&Ph-SBA-15) not only maintained ordered hexagonal mesopores, but also possessed characteristics of the two organic functional groups on the mesopore surface. Compared with Pd nanoparticles supported on the parent SBA-15 or monofunctionalized mesoporous materials, it displayed much higher catalytic reactivity and selectivity in the water-medium Ullmann Reaction. This could be attributed to the synergic promoting effect derived from binary organic functional groups since the NH2-groups led to the uniform dispersion of Pd nanoparticles inside the pore channels while the Ph-groups decreased the diffusion limitation of organic molecules in water. Furthermore, it could be conveniently recovered and recycled six times without significant loss of activity and selectivity.
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CO2‐promoted Water‐medium Ullmann Reaction over a Pd/Phenyl‐SBA‐15 Mesoporous Catalyst
Chinese Journal of Chemistry, 2008Co-Authors: Fang Zhang, Qin Chai, He-xing LiAbstract:Water-medium Ullmann Reaction was carried out in CO2 atmosphere over the mesoporous Pd/Ph-SBA-15 catalyst exhibiting high activity and selectivity owing to the uniform dispersion of Pd particles and hydrophobilic mesoporous channels which facilitate the diffusion and adsorption of organic molecules, especially in an aqueous medium. The CO2 also shows promoting effect on activity and selectivity, which could be understood by considering the role of H+ in the mechanism of Ullmann Reaction. The optimum Ph-Ph yield (84.0%) was obtained at p=0.8 MPa and V=6.0 mL and could remain almost unchanged even after the catalyst has been used repetitively for 5 times.
Qing Xu - One of the best experts on this subject based on the ideXlab platform.
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probing the support effect at the molecular level in the polyaniline supported palladium nanoparticle catalyzed Ullmann Reaction of aryl iodides
Journal of Catalysis, 2018Co-Authors: Daliang Tang, Lei Yu, Qing XuAbstract:Abstract A series of polyaniline (PANI)-supported palladium nanoparticles (Pd@PANIs) were fabricated from electron-deficient and -enriched substituted anilines and palladium chloride. PANIs’ support effect in the Pd@PANIs-catalyzed Ullmann Reaction of aryl iodides for generation of biaryls was then studied. The results revealed that, though having similar Pd content and morphology, these Pd@PANI catalysts behaved quite differently in catalytic activities in the Ullmann Reaction of aryl iodides, with the electron-enriched PANI supports having obviously enhanced activities for the Reaction. Mechanistic studies revealed this is due to the stronger coordination of the nitrogen ligands on the electron-enriched PANI support with the Pd centers, higher adsorption rates of the reactant on the electron-enriched Pd@PANI catalysts, especially those promoted by the Pd loading, and easier generation and higher ratio of the Pd(0) species in the catalyst, which is the active catalysts in the Ullmann Reaction responsible for the products’ yields and the TONs of the Reactions. In contrast, the specific surface area of the Pd@PANI catalyst is found to have little influence on the catalytic activity and adsorption capacity of the catalysts, and thus its influence may be omitted in the present Pd@PANIs-catalyzed Ullmann Reaction of aryl iodides. Therefore, a simple fine tuning of the PANI support’s electronic property by introducing electron-donating groups can be an effective protocol for enhancing the catalyst’s activity. This work may be the first example of a support effect study in PANI-supported metal nanoparticle-catalyzed Reactions.
Jianlin Huang - One of the best experts on this subject based on the ideXlab platform.
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multifunctional mesoporous silica supported palladium nanoparticles as efficient and reusable catalyst for water medium Ullmann Reaction
New Journal of Chemistry, 2012Co-Authors: Jianlin Huang, Wei Chai, Chao Liang, Jian Shen, Fang ZhangAbstract:Multifunctional mesoporous material (NH2&Ph-SBA-15) was synthesized by co-condensation of tetraethyl orthosilicate, amine-silane and phenyl-silane in the presence of triblock copolymer P123. The Pd nanoparticles immobilized on the NH2&Ph-SBA-15 support were fabricated by the impregnation and subsequent reduction method. The XRD, TEM, N2 sorption, IR and solid NMR measurements revealed that this novel mesoporous Pd catalyst (Pd/NH2&Ph-SBA-15) not only maintained ordered hexagonal mesopores, but also possessed characteristics of the two organic functional groups on the mesopore surface. Compared with Pd nanoparticles supported on the parent SBA-15 or monofunctionalized mesoporous materials, it displayed much higher catalytic reactivity and selectivity in the water-medium Ullmann Reaction. This could be attributed to the synergic promoting effect derived from binary organic functional groups since the NH2-groups led to the uniform dispersion of Pd nanoparticles inside the pore channels while the Ph-groups decreased the diffusion limitation of organic molecules in water. Furthermore, it could be conveniently recovered and recycled six times without significant loss of activity and selectivity.
Henry N C Wong - One of the best experts on this subject based on the ideXlab platform.
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palladium catalyzed double Ullmann Reaction an approach towards tetraphenylenes
Asian Journal of Organic Chemistry, 2016Co-Authors: Xin Li, Henry N C WongAbstract:A palladium-catalyzed double Ullmann coupling Reaction for the preparation of tetraphenylenes has been developed. With this protocol, twelve tetraphenylene derivatives were synthesized from the corresponding 2,2′-diiodobiaryls directly with the yields ranging from 13–51 %. Insights into the mechanism of these palladium-catalyzed double coupling Reactions are discussed, and the findings are expected to increase the level of understanding of palladium-catalyzed formation of carbon–carbon bonds within rigid molecular frameworks.
Emily A Lewis - One of the best experts on this subject based on the ideXlab platform.
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controlling selectivity in the Ullmann Reaction on cu 111
Chemical Communications, 2017Co-Authors: Emily A Lewis, Colin J Murphy, Melissa L Liriano, Matthew D Marcinkowski, Andrew J Therrien, Alex Pronschinske, E C H SykesAbstract:Using a surface science approach, the selectivity in the Ullmann cross-coupling of aryl halides on Cu(111) has been understood and controlled. The binding strength of the reactants and repulsion between them dictates which organometallic intermediates form, and hence the product distribution. Cross coupling can be maximized at low reactant concentrations.
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atomic scale insight into the formation mobility and Reaction of Ullmann coupling intermediates
Chemical Communications, 2014Co-Authors: Emily A Lewis, Colin J Murphy, Melissa L Liriano, Charles E H SykesAbstract:The Ullmann Reaction of bromobenzene, the simplest coupling reagent, to form biphenyl on a Cu surface proceeds via a highly mobile organometallic intermediate in which two phenyl groups extract and bind a single surface Cu atom.