title: Dendrimer-templated Pd nanoparticles and Pd nanoparticles synthesized by reverse microemulsions as efficient nanocatalysts for the Heck reaction: A comparative study.
abstract: Palladium nanoparticles (NPs) were prepared using a dendrimer-templated method using G4, G5 and G6 PAMAM-OH dendrimers as well as a reverse microemulsion method using the water/dioctyl sulfosuccinate sodium salt (aerosol-OT, AOT) surfactant/isooctane system with water to surfactant ratios (ω0) of 5, 10 and 13. These 6 catalysts were characterized by UV-Vis spectroscopy, TEM, EDX, and XRD. TEM micrographs showed that the average sizes of 2.74-3.32nm with narrower size distribution were achieved by using dendrimer-templated synthetic methods, whereas the reverse microemulsion method resulted in broad size distribution with an average size of 3.87-5.06nm. The influence of various reaction parameters such as base, catalyst dosing, alkene, aryl halide and temperature on the Heck C-C coupling reaction was evaluated. The activation parameters were derived from the reaction rate of each catalyst obtained at various temperatures. A correlation of catalytic activity, enthalpy of activation and particle size is discussed. Particle size changes of each catalyst were investigated after the catalytic reaction. Overall results indicated that dendrimer-templated Pd NP catalysts showed superior activity as compared to the Pd NPs synthesized by reverse microemulsions, with the dendrimer-templated G5-OH(Pd80) showing the best activity. These catalysts were also reusable for 3 cycles, retaining high yield and showing excellent yields under mild conditions. Therefore, the dendrimer-templated Pd NPs are efficient catalyst systems for the ligand-free Heck C-C coupling reaction.
authors.affiliation: Research Centre for Synthesis and Catalysis, Department of Chemistry, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa.
authors.forename: Ji-Hyang
authors.initials: JH
authors.lastname: Noh
authors.forename: Reinout
authors.initials: R
authors.lastname: Meijboom
mesh_terms: D000179:Acrylates / Q000737:chemistry*; D002384:Catalysis; D050091:Dendrimers / Q000737:chemistry*; D004143:Dioctyl Sulfosuccinic Acid / Q000737:chemistry; D004655:Emulsions; D017743:Equipment Reuse; D007462:Iodobenzenes / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D009795:Octanes / Q000737:chemistry; D010165:Palladium / Q000737:chemistry*; D010316:Particle Size; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D000179:Acrylates; D050091:Dendrimers; D004655:Emulsions; D007462:Iodobenzenes; D009795:Octanes; C104700:PAMAM Starburst; D013501:Surface-Active Agents; D014867:Water; D004143:Dioctyl Sulfosuccinic Acid; D010165:Palladium; C032490:n-butyl acrylate; C031905:iodobenzene; C045798:2,2,4-trimethylpentane
keywords: Activation energy; Dendrimer-templated; Enthalpy of activation; Heck C–C coupling; PAMAM-OH dendrimer; Pd nanoparticles; Reverse microemulsion