1,721,135 research outputs found
Catalizzatori "eterogenei" di coupling C-C
No full textThis article is a critical review on the use of heterogeneous catalysts in C-C coupling reactions (Heck reactions, cross-coupling reactions), with particular reference to the mechanism of catalysis, which appears to involve leaching into solution of the catalytically active species
Functionalised microgels: novel stabilisers for catalytically active metal colloids
No full textMicrogel stabilised palladium colloids have been prepared by a novel strategy based on the synthesis of microgels upon radical solution copolymerisation of suitable functional monomers containing sulfonic acid groups. These microgels can be conveniently loaded with Pd2+ ions which are subsequently reduced. The resulting metal colloids (10-20 nm diameter) can be precipitated from the reaction mixture and redispersed in suitable solvents. Preliminary tests indicate that microgel stabilised palladium colloids are active catalysts for the vinylation of aryl iodides and bromides (Heck reaction)
Room temperature preparation of highly crosslinked microgels
No full textA series of highly crosslinked microgels has been prepared at room temperature via photoinitiated polymerisation in dilute solution using methyl methacrylate (MMA) and ethylene dimethacrylate (EDMA), respectively as non-functional monomer and crosslinker in N,N-dimethylformamide (DMF) as a solvent. The effect of monomer concentration and EDMA/MMA ratio on the yield, molecular weight and microgel size was studied and the data were compared to those previously obtained for microgels of similar composition prepared by thermal initiation. This mild polymerisation method yields better results compared to the more conventional thermal method, since it allows higher monomer concentrations to be employed as well as a better microgel size control. Consequently, the method can be advantageously used for the preparation of highly crosslinked microgels with improved properties, particularly useful, e.g. for molecular imprinting applications
Efficient aerobic oxidation of alcohols in water catalysed by microgel-stabilised metal nanoclusters
No full textNoble metal nanoclusters stabilised by N,N-dimethylacrylamide-based soluble cross-linked polymers (microgels) have been prepared and tested as catalysts in the selective oxidation of secondary alcohols to the corresponding carbonyl compounds with molecular oxygen in water. Pd nanoclusters turned out to be superior catalysts compared with nanoclusters of other noble metals, such as Pt or An, they are efficient (TOF up to 70 h(-1)) and easily recoverable by simple extraction of the reaction product from the aqueous phase
Catalysis by metal nanoparticles supported on functional organic polymers
No full textThe preparation and catalytic applications of dispersed metal catalysts supported on organic functional polymers are presented. The advantages of these catalysts, such as the easy tailoring with respect to the nature of the used support, the "nanoscale" size control of metal crystallites by the polymer framework, the high accessibility and consequent catalytic activity in a proper liquid or liquid-vapor reaction systems are stressed. Various proposed catalytic processes making use of these materials are presented and evaluated, including multifunctional catalysis, e.g. redox-acid. Interesting peculiar aspects such as the enhancement of the hydrogenation rate by nitrogen containing moieties anchored to the polymer backbone are emphasised. When suitable, a comparison with catalysts based on inorganic supports is given
Macromolecule-palladium complexes as catalysts for the synthesis of hydrogen peroxide
No full textCommercial resin supports containing aromatic nitrogen bases as functional groups have been used as macromolecular ligands for palladium(II), thus yielding insoluble macromolecule-metal complexes. Preliminary tests were run with these materials as catalysts for the preparation of hydrogen peroxide from carbon monoxide, oxygen, and water. Pretreatment of the catalyst with an organic solvent was found to be necessary in order to achieve catalytic activity. The best results (turnover number = 6) were obtained with pretreatment in dioxane
Molecular Design of Novel Transition State Analogues for Molecular Imprinting
No full textThe synthesis and characterisation of novel polymerisable heterocycles containing boron is described. The compounds were designed to serve as transition state analogues of the enantioselective borane reduction of prochiral ketones with oxazaborolidine catalysts (CBS reduction). Preliminary results show that the heterocycles can be conveniently used as template monomers in the synthesis of molecularly imprinted polymers
Microgel-stabilised metal nanoclusters: improved solid-state stability and catalytic activity in Suzuki couplings
No full textMicrogel-stabilised nanoclusters of Pd and Pt have been prepared starting from microgels based on N,N-dimethylacrylamide. The size of the resulting nanoclusters is controlled by the nanomorphology of the microgel stabiliser. The microgel-stabilised nanoclusters are stable over long periods of time in the solid state as well as in solution. Microgel-stabilised Pd nanoclusters, as well as microgel-anchored palladium(II) acetate, are active catalysts for the Suzuki coupling of aryl bromides with phenylboronic acid
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