Search results for "Acetylene"

Palladium-ADC complexes as efficient catalysts in copper-free and room temperature Sonogashira coupling

2014

Abstract The metal-mediated coupling between cis-[PdCl2(CNR1)2] [R1 = cyclohexyl (Cy) 1, t-Bu 2, 2,6-Me2C6H3 (Xyl) 3, 2-Cl-6-MeC6H3 4] and hydrazones H2NN CR2R3 [R2, R3 = Ph 5; R2, R3 = C6H4(OMe-4) 6; R2/R3 = 9-fluorenyl 7; R2 = H, R3 = C6H4(OH-2) 8] provided carbene complexes cis-[PdCl2{C(N(H)N CR2R3) N(H)R1}(CNR1)] (9–24) in good (80–85%) yields. Complexes 9–24 showed high activity [yields up to 99%, and turnover numbers (TONs) up to 3.7 × 104] in the Sonogashira coupling of various aryl iodides with a range of substituted aromatic alkynes without the need of copper co-catalyst. The catalytic procedure runs at 80 °C for 1 h in EtOH using K2CO3 as a base. No formation of homocoupling or ac…

Shape-Dependence of Pd Nanocrystal Carburization during Acetylene Hydrogenation

2015

This interdisciplinary work combines the use of shape- and size-defined Pd nanocrystals (cubes of 10 and 18 nm, and octahedra of 37 nm) with in situ techniques and DFT calculations to unravel the dynamic phenomena with respect to Pd reconstruction taking place during acetylene hydrogenation. Notably, it was found that the reacting Pd surface evolved at a different pace depending on the shape of the Pd nanocrystals, due to their specific propensity to form carbides under reaction conditions. Indeed, Pd cubes (Pd(100)) reacted with acetylene to form a PdC0.13 phase at a rate roughly 6-fold higher than that of octahedra (Pd(111)), resulting in nanocrystals with different degrees of carburizati…

Selective hydrogenation of acetylene in ethylene feedstocks on Pd catalysts

1996

Abstract Pumice supported palladium catalysts were compared with Pd SiO 2 and Pd Al 2 O 3 in the hydrogenation of acetylene using typical industrial ethylene feedstocks: front-end and tail-end cuts. Pd/pumice catalysts exhibit good activity and excellent selectivity and stability in the title reaction. Their activity/selectivity pattern is controlled by the composition of the reaction mixture. The turnover frequency (TOF) increases, and the apparent activation energy (Ea) decreases, with the H 2 C 2 H 2 ratio, but they are not affected by the C 2 H 2 C 2 H 4 ratio. The selectivity to ethane (SE) does not change with acetylene conversion at low H 2 C 2 H 2 ratio (tail-end cut) and increases …

Hydrogenation of acetylene in ethylene rich feedstocks: Comparison between palladium catalysts supported on pumice and alumina

1998

Abstract The activity–selectivity patterns of Pd/pumice catalysts are compared with industrial and home prepared Pd/Al2O3 catalysts in the hydrogenation of acetylene in ethylene rich feedstocks (front-end and tail-end cuts). The iso-kinetic relationship (IKR) approach and a new mathematical model, surface site evolution model (SSEM), are employed in this comparison. Pumice and alumina supported Pd catalysts show different metal redox properties. A similar reaction mechanism is adequate to describe the reaction pathway independently by the catalysts and the gas mixtures considered. This mechanism involves the formation of surface polymers during the catalytic reactions and different catalyti…

cis-bromination of alkynes without cationic intermediates

2005

Heterogeneous Sonogashira Coupling over Nanostructured SiliaCat Pd(0)

2012

Sol–gel entrapped catalyst SiliaCat Pd(0) heterogeneously mediates the Sonogoashira coupling of different aryl halides and phenylacetylene either under thermal conditions or, much more efficiently, under microwave irradiation, affording good conversions of coupled products. Leaching of valued Pd is limited, and the catalyst can be reused.

CCDC 2107391: Experimental Crystal Structure Determination

2022

Related Article: Rossella Greco, Estefania Tiburcio-Fortes, Antonio Fernandez, Carlo Marini, Alejandro Vidal-Moya, Judit Oliver-Meseguer, Donatella Armentano, Emilio Pardo, Jesús Ferrando-Soria, Antonio Leyva-Pérez|2022|Chem.-Eur.J.|28||doi:10.1002/chem.202103781

Bulky Surface Ligands Promote Surface Reactivities of [Ag141X12(S-Adm)40]3+ (X = Cl, Br, I) Nanoclusters: Models for Multiple-Twinned Nanoparticles

2017

Surface ligands play important roles in controlling the size and shape of metal nanoparticles and their surface properties. In this work, we demonstrate that the use of bulky thiolate ligands, along with halides, as the surface capping agent promotes the formation of plasmonic multiple-twinned Ag nanoparticles with high surface reactivities. The title nanocluster [Ag141X12(S-Adm)40]3+ (where X = Cl, Br, I; S-Adm = 1-adamantanethiolate) has a multiple-shell structure with an Ag71 core protected by a shell of Ag70X12(S-Adm)40. The Ag71 core can be considered as 20 frequency-two Ag10 tetrahedra fused together with a dislocation that resembles multiple-twinning in nanoparticles. The nanocluster…

Hydrogenation of acetylene-ethylene mixtures on Pd catalysts: study of the surface mechanism by computational approaches. Metal dispersion and cataly…

2000

The hydrogenation mechanism of acetylene–ethylene mixtures on Pd catalysts under different experimental conditions was studied by employing a time-dependent Monte Carlo approach set to use a fixed series of event probabilities. The dependence of the catalyst activity and selectivity on the sizes of the metal particles was simulated at microscopic level and the results, also refined by fitting procedures, suggested proper explanations for the apparent nonuniformity of the related experimental findings. The use of the steric hindrance parameter of the surface species and the available surface energy on the metallic catalyst sites was decisive for reproducing the experimental results.

Cu(I) complexes with diethoxyphosphoryl-1,10-phenanthrolines in catalysis of C–C and C–heteroatom bonds formation

2015

Abstract Diethoxyphosphoryl substituted 1,10-phenanthroline copper(I) complexes were tested as catalysts in the Sonogashira-type reaction, α-arylation of phosphoryl-stabilized C–H acids, C–N, C–P bond forming reactions (substitution reactions) and in the reaction of phenylacetylene and bis(pinacolato)diboron (addition reaction). The complexes demonstrate fairly high catalytic activity and in some cases their efficiency is superior to that of the parent Cu(phen)(PPh 3 )Br (phen = phenanthroline).