Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
59,010
result(s) for
"Palladium"
Sort by:
Enhanced Selectivity in 4-Quinolone Formation: A Dual-Base System for Palladium-Catalyzed Carbonylative Cyclization with Fesub.5
The use of gaseous CO in Pd-catalyzed carbonylative quinolone synthesis presents challenges related to safety and precise pressure control. In response, a streamlined non-gaseous synthesis of 4-quinolone compounds has been developed. This study introduces a tunable CO-releasing system utilizing Fe(CO)[sub.5] activated by a dual-base system of piperazine and triethylamine. This alternative liquid CO resource facilitates the palladium-catalyzed carbonylative C-C coupling and subsequent intramolecular cyclization. By tuning the tandem kinetics of carbonylation and cyclization, this non-gaseous method achieves the successful synthesis of 22 distinct 4-quinolones with excellent yields. This is achieved through the three-component condensation of sub-stoichiometric amounts of Fe(CO)[sub.5] with 2-iodoaniline and terminal alkynes. Operando mechanistic studies have revealed a novel CO transfer mechanism that facilitates homogeneous carbonylative cyclization, distinguishing this method from traditional techniques. In addition to addressing safety concerns, this approach also provides precise control over selectivity, with significant implications for pharmaceutical research and the efficient synthesis of pharmaceutical and bioactive compounds.
Journal Article
Palladium-Catalyzed Direct
Palladium-catalyzed direct (het)arylation reactions of strongly electron-withdrawing tricyclic benzo[1,2-d:4,5-d′]bis([1,2,3]thiadiazole) and its 4,8-dibromo derivative were studied; the conditions for the selective formation of mono- and bis-aryl derivatives were found. The reaction of 4,8-dibromobenzo[1,2-d:4,5-d′]bis([1,2,3]thiadiazole) with thiophenes in the presence of palladium acetate as a catalyst and potassium pivalate as a base, depending on the conditions used, selectively gave both mono- and bis-thienylated benzo-bis-thiadiazoles in low to moderate yields; arenes were found to be inactive in these reactions. It was discovered that direct C-H arylation of benzo[1,2-d:4,5-d′]bis([1,2,3]thiadiazole with bromo(iodo)arenes and -thiophenes in the presence of Pd(OAc)2 and di-tert-butyl(methyl)phosphonium tetrafluoroborate salt is a powerful tool for the selective formation of 4-mono- and 4,8-di(het)arylated benzo-bis-thiadiazoles. Oxidative double C-H hetarylation of benzo[1,2-d:4,5-d′]bis([1,2,3]thiadiazole with thiophenes in the presence of Pd(OAc)[sub.2] and silver (I) oxide in DMSO was successfully employed to prepare bis-thienylbenzo-bis-thiadiazoles in moderate yields.
Journal Article
Impact of Rh, Ru, and Pd Leads and Contact Topologies on Performance of WSesub.2 FETs: A First Comparative Ab Initio Study
2D field-effect transistors (FETs) fabricated with transition metal dichalcogenide (TMD) materials are a potential replacement for the silicon-based CMOS. However, the lack of advancement in p-type contact is also a key factor hindering TMD-based CMOS applications. The less investigated path towards improving electrical characteristics based on contact geometries with low contact resistance (R [sub.C]) has also been established. Moreover, finding contact metals to reduce the R [sub.C] is indeed one of the significant challenges in achieving the above goal. Our research provides the first comparative analysis of the three contact configurations for a WSe[sub.2] monolayer with different noble metals (Rh, Ru, and Pd) by employing ab initio density functional theory (DFT) and non-equilibrium Green’s function (NEGF) methods. From the perspective of the contact topologies, the R [sub.C] and minimum subthreshold slope (SS [sub.MIN]) of all the conventional edge contacts are outperformed by the novel non-van der Waals (vdW) sandwich contacts. These non-vdW sandwich contacts reveal that their R [sub.C] values are below 50 Ω∙μm, attributed to the narrow Schottky barrier widths (SBWs) and low Schottky barrier heights (SBHs). Not only are the R [sub.C] values dramatically reduced by such novel contacts, but the SS [sub.MIN] values are lower than 68 mV/dec. The new proposal offers the lowest R [sub.C] and SS [sub.MIN], irrespective of the contact metals. Further considering the metal leads, the WSe[sub.2]/Rh FETs based on the non-vdW sandwich contacts show a meager R [sub.C] value of 33 Ω∙μm and an exceptional SS [sub.MIN] of 63 mV/dec. The two calculated results present the smallest-ever values reported in our study, indicating that the non-vdW sandwich contacts with Rh leads can attain the best-case scenario. In contrast, the symmetric convex edge contacts with Pd leads cause the worst-case degradation, yielding an R [sub.C] value of 213 Ω∙μm and an SS [sub.MIN] value of 95 mV/dec. While all the WSe[sub.2]/Ru FETs exhibit medium performances, the minimal shift in the transfer curves is interestingly advantageous to the circuit operation. Conclusively, the low-R [sub.C] performances and the desirable SS [sub.MIN] values are a combination of the contact geometries and metal leads. This innovation, achieved through noble metal leads in conjunction with the novel contact configurations, paves the way for a TMD-based CMOS with ultra-low R [sub.C] and rapid switching speeds.
Journal Article
Nasub.2SOsub.3-Promoted Heck Coupling and Homo-Coupling of Arylhydrazines at Room Temperature
A novel protocol facilitated by Na[sub.2]SO[sub.3] that enhances the efficiency of palladium-catalyzed Heck coupling and the homo-coupling reactions of arylhydrazines. This innovative method enables the effective construction of a diverse array of cinnamate derivatives and biphenyl compounds. Notably, these transformative reactions proceed smoothly at room temperature, leveraging the activation of C-N bonds. This technique not only streamlines the synthesis process but also expands our understanding and expertise in the realm of coupling reactions.
Journal Article
Optimizing Pt/Pd Ratios for Enhanced Low-Temperature Catalytic Oxidation of CO and C.sub.3H.sub.6 on Al.sub.2O.sub.3 Support
This study investigated the impact of diverse Pt-Pd ratios on the activity and performance of DOC. A range of Pt-Pd catalysts with different Pt-Pd ratios and monometallic Pd and Pt catalysts on Al.sub.2O.sub.3 support were evaluated systematically. 0.5%wt PGM was used to avoid the high catalyst costs. The light-off temperatures and conversion efficiencies of CO, NO, and C.sub.3H.sub.6 were investigated under simulated diesel exhaust conditions. Several scientific techniques were used to characterize the catalysts, such as XRD, XPS, H.sub.2-TPR, and CO.sub.2 TPD. The results demonstrated that using bimetallic Pt-Pd catalysts on Al.sub.2O.sub.3 support significantly improved light-off temperatures and conversion efficiency than monometallic Pt and Pd catalysts. The order of light-off temperatures and CO and C.sub.3H.sub.6 conversions was: 0.4Pt0.1Pd < 0.3Pt0.2Pd < 0.2Pt0.3Pd < 0.1Pt0.4Pd < 0.5Pd < 0.5Pt. The synergistic enhancement of catalytic activity can be ascribed to the coexistence of active sites for Pt and Pd. 0.4Pt0.1Pd bimetallic catalyst showed best activity and stability in conversion of CO and C.sub.3H.sub.6 among all catalysts. As a result of the competitive adsorption of C.sub.3H.sub.6 and CO on Pt surface, which restricts the availability of adsorbed oxygen, the monometallic Pt/Al.sub.2O.sub.3 catalyst demonstrated high light-off temperatures and slow CO and C.sub.3H.sub.6 conversion rates. However, the Pd/Al.sub.2O.sub.3 catalyst showed very stable conversion efficiency, demonstrating metallic Pd's higher stability than Pt/Al.sub.2O.sub.3. Results demonstrated that Pt can be prudently incorporated into Pd-catalysts to improve their catalytic activity. It is noteworthy that the optimal Pt to Pd ratio plays a vital role in balancing activity and stability. The careful use of Pt-modified Pt-Pd bimetallic catalysts holds promise for achieving desired emissions conversion conditions. For instance, the 0.4Pt0.1Pd bimetallic catalysts exhibited superior activity and stability in the conversion of CO and C.sub.3H.sub.6 compared to other bimetallic catalysts. Pt loading above a specific amount may reduce activity due to Pt and Pd active site overlap and saturation.
Journal Article
Lattice Oxygen and Feed Oxygen Exchange for the High Rate of H.sub.2 + O.sub.2 Recombination on Ti.sub.1-xPd.sub.xO.sub.2-x Catalyst at Room Temperature
The Pd ion substituted TiO.sub.2, synthesized by solution combustion method crystallizes in anatase structure with stable composition Ti.sub.1-xPd.sub.xO.sub.2-x (x = 0.01-0.03) creating an oxide ion vacancy per Pd.sup.2+ ion substitution. Over 1.35 mol of H.sub.2 per mole of bulk Pd ions, in 5 nm nanocrystalline catalyst Ti.sub.1-xPd.sub.xO.sub.2-x (x = 0.03) is adsorbed at 300 K. On exposure of only hydrogen to Ti.sub.0.98Pd.sub.0.02O.sub.1.98 at 300 K, water is formed making the catalyst wet. On heating in a vacuum, mass loss due to water is 0.026 mol /mole of catalyst meaning 1.3 mol of hydrogen per mole of Pd ion in the catalyst. Pd ion substitution in TiO.sub.2 anatase activates lattice oxygen leading to the formation of H.sub.2O on exposure to H.sub.2 gas at 300 K utilizing lattice oxygen. On heating in air at 650 K the reduced catalyst is regenerated. The catalyst produces a high rate of H.sub.2 + O.sub.2 recombination up to 9 [micro]moles.sup.-1 g.sup.-1 at 300 K, and over 230 [micro]moles.sup.-1 g.sup.-1 at 330 K with a TOF of 2000 h.sup.-1. The catalyst is coated on cordierite honeycomb avoiding handling of powder catalyst. The rates are highest compared to any catalyst for H.sub.2 + O.sub.2 recombination known so far. Extensive DFT calculation on (101) surface in Ti.sub.31Pd.sub.1O.sub.63 slab confirmed (a) one oxygen out of 4 bonded to Pd ion in nearly square geometry is fully activated to form water molecule creating an oxide ion vacancy; (b) dissociative adsorption of H.sub.2 on one of the Pd as well as oxide ion and not both on Pd ion; (c) exchange of feed oxygen with lattice oxygen during 2H.sub.2 + O.sub.2 recombination; (d) 2H.sub.2 + O.sub.2 [right arrow] 2H.sub.2O molecules form per Pd ion in one cycle regenerating the catalyst, Ti.sub.0.97Pd.sub.0.03O.sub.1.97 surface explaining high rates of recombination and (e) Pd ion undergoes redox cycle with Ti and oxide ions acting as charge reservoirs.
Journal Article
Correction: Kornet, M.M.; Müller, T.J.J. Recent Advances in Sequentially Pd-Catalyzed One-Pot Syntheses of Heterocycles. Molecules 2024, 29, 5265
In the original publication [...]
Journal Article
Solubility of Metal Precursors in Supercritical COsub.2: Measurements and Correlations
Knowledge of the solubility of metal precursors in supercritical (sc) CO[sub.2] is a key factor for determining the best operation conditions for the synthesis of supported metallic nanoparticles. In this paper, new experimental solubility data of Cu(acac)[sub.2], Pd(acac)[sub.2], and Pt(acac)[sub.2] in scCO[sub.2] for temperatures from 313 to 353 K and pressures from 10 to 40 MPa are presented and compared with the literature data and correlated with semi-empirical density-based models (Chrastil, extended Kumar and Johnston, extended Bartle, and the original and modified Méndez–Santiago–Teja). In addition, literature data for the solubility of Cu(tmhd)[sub.2], Pd(tmhd)[sub.2], and Pt(cod)me[sub.2] in scCO[sub.2] were also correlated with the above-mentioned models. The best result, i.e., the best agreement between the experimental and calculated solubility datasets, was observed for the Chrastil model. Applying the Chrastil and extended Bartle models, the dissolution, sublimation, and solvation enthalpies were estimated. Furthermore, these correlation results were compared with the results from Ushiki et al., who correlated the solubilities of metal acetylacetonates in scCO[sub.2] from the literature using the PC-SAFT equation of state. This comparison showed that the original Méndez–Santiago–Teja model enabled a better description of the experimental data by a factor of three.
Journal Article
Mechanochemical Synthesis of PdOsub.2 Nanoparticles Immobilized over Silica Gel for Catalytic Suzuki–Miyaura Cross-Coupling Reactions Leading to the C-3 Modification of 1IH/I-Indazole with Phenylboronic Acids
The C-3 modification of 1H-indazole has produced active pharmaceuticals for the treatment of cancer and HIV. But, so far, this transformation has seemed less available, due to the lack of efficient C-C bond formation at the less reactive C-3 position. In this work, a series of silica gel-supported PdO[sub.2] nanoparticles of 25–66 nm size were prepared by ball milling silica gel with divalent palladium precursors, and then employed as catalysts for the Suzuki–Miyaura cross-coupling of 1H-indazole derivative with phenylboronic acid. All the synthesized catalysts showed much higher cross-coupling yields than their palladium precursors, and could also be reused three times without losing high activity and selectivity in a toluene/water/ethanol mixed solvent. Although the palladium precursors showed an order of activity of PdCl[sub.2](dppf, 1,1′-bis(diphenylphosphino)ferrocene) > PdCl[sub.2](dtbpf, 1,1′-bis(di-tert-butylphosphino)ferrocene) > Pd(OAc, acetate)[sub.2], the synthesized catalysts showed an order of C1 (from Pd(OAc)[sub.2]) > C3 (from PdCl[sub.2](dtbpf)) > C2 (from PdCl[sub.2](dppf)), which conformed to the orders of BET (Brunauer–Emmett–Teller) surface areas and acidities of these catalysts. Notably, the most inexpensive Pd(OAc)[sub.2] can be used as a palladium precursor for the synthesis of the best catalyst through simple ball milling. This work provides a highly active and inexpensive series of catalysts for C-3 modification of 1H-indazole, which are significant for the large-scale production of 1H-indazole-based pharmaceuticals.
Journal Article