Palladium Precursor Research Articles

Synthesis Method for Cellulose Nanofiber Biotemplated Palladium Composite Aerogels.

Here, a method to synthesize cellulose nanofiber biotemplated palladium composite aerogels is presented. Noble metal aerogel synthesis methods often result in fragile aerogels with poor shape control. The use of carboxymethylated cellulose nanofibers (CNFs) to form a covalently bonded hydrogel allows for the reduction of metal ions such as palladium on the CNFs with control over both nanostructure and macroscopic aerogel monolith shape after supercritical drying. Crosslinking the carboxymethylated cellulose nanofibers is achieved using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) in the presence of ethylenediamine. The CNF hydrogels maintain their shape throughout synthesis steps including covalent crosslinking, equilibration with precursor ions, metal reduction with high concentration reducing agent, rinsing in water, ethanol solvent exchange, and CO2 supercritical drying. Varying the precursor palladium ion concentration allows for control over the metal content in the final aerogel composite through a direct ion chemical reduction rather than relying on the relatively slow coalescence of pre-formed nanoparticles used in other sol-gel techniques. With diffusion as the basis to introduce and remove chemical species into and out of the hydrogel, this method is suitable for smaller bulk geometries and thin films. Characterization of the cellulose nanofiber-palladium composite aerogels with scanning electron microscopy, X-ray diffractometry, thermal gravimetric analysis, nitrogen gas adsorption, electrochemical impedance spectroscopy, and cyclic voltammetry indicates a high surface area, metallized palladium porous structure.

Palladium enriched tungsten oxide thin films: an efficient gas sensor for hazardous gases

Palladium enriched tungsten trioxide thin films were prepared by spraying solution of ammonium tungstate as a precursor on glass substrates using spray pyrolysis deposition technique. Palladium chloride as a precursor for palladium was introduced in the precursor solution during refluxing process before deposition. The catalyst Pd with different concentrations was introduced on series of WO3 films. X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy were applied to analyze structure and morphology of the deposited thin films. The effect of Pd enrichment on the microstructure, electrical and gas sensing properties of the as-synthesized WO3 thin films was studied. Variation in the electrical conductivity of pure and Pd supplemented WO3 films was measured in air and in the presence of hazardous gases such as NO2, SO2 and NH3. The addition of 3 w/o Pd in WO3 raised the gas response of the film to 1.1 towards NO2 at lowest operating temperature of 100 °C. The film shows adequate response towards SO2 (0.32) and NH3 (0.27) at 200 °C and 225 °C, respectively. The response and recovery time ranged in 0.5–1.25 s and 1–6.7 s respectively even for high gas concentrations upto 750 ppm.

Amido-functionalized N-Heterocyclic carbene ligands and corresponding PalladiumComplexes: Synthesis, characterization and catalytic activity

Thirteen amido functionalized N-heterocyclic carbene ligands were synthesized via a simple synthetic procedure. The synthesized ligands were characterized by NMR, FAB-MS and single crystal X-ray analysis, unanimously confirming the proposed structures. Subsequent complexation with a palladium precursor allowed the synthesis of four new complexes. The molecules structures of all four complexes were confirmed by single crystal X-ray diffraction. The catalytic activity of the synthesized ligands and complexes was tested for the Heck alkenylation of aryl iodide readily allowing the synthesis of cinnamic acids esterin yields ranging from 67 to 93% for ligands and 69–95% for complexes while turn-over-numbers of up to 75000 was observed for the complexes.

Towards Selective Syntheses of Octadienylethers from the Butadiene Palladium‐catalyzed Telomerization with Polyols in Aqueous Biphasic Medium

AbstractThe palladium catalyzed telomerization of butadiene with polyols has been efficiently performed under aqueous and biphasic medium leading to the corresponding octadienylethers. Depending on the choice of the organic co‐solvent and nature of the catalyst employed to promote the reaction, mono‐ to fully substituted ethers could be obtained with high selectivities and yields. Particularly, pentaerythritol was telomerized for the first time allowing the selective synthesis of the corresponding monotelomers by using methylethylketone as organic co‐solvent and the water soluble ligand TPPTS associated to a simple palladium precursor. Polyethers of sorbitol could be efficiently obtained by using a mixture of TPPTS and PPh3 ligands.

Single-Step Fabrication of Nanostructured Palladium Thin Films via Aerosol-Assisted Chemical Vapor Deposition (AACVD) for the Electrochemical Detection of Hydrazine

Aerosol-assisted chemical vapor deposition (AACVD) is successfully implemented for the fabrication of nanostructured palladium (Pd) thin films on FTO substrate. The Pd films are produced using a commercially available precursor palladium acetylacetonate (Pd(C5H7O2)2) under the flow of N2 gas without incorporating hydrogen gas or any other reducing agent. This synthetic strategy can effectively confront the previous problems related with conventional CVD approach while depositing palladium thin films such as reduced volatility and thermal instability of precursors. The palladium thin films were characterized by powder X-ray diffraction (pXRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) analysis. Hydrazine is a colorless and flammable chemical routinely used in rocket fuel, agro-chemicals, textile dyes, and as corrosion inhibitors in various industries. However, hydrazine is a toxic and highly carcinogenic chemical. The newly fabricated palladium nanostructured films were tested for electrochemical sensing of hydrazine in this study. A highly stable and reproducible amperometric response for hydrazine oxidation was obtained with a superior limit of detection (LOD) of 10 nM, and limit of quantification (LOQ) of 33 nM while the sensitivity value calculated was 2.94 μA μM−1 cm−2. A linear concentration range of 1–325 μM was achieved by chronoamperometry.

Oxime palladacycle in PEG as a highly efficient and recyclable catalytic system for phenoxycarbonylation of aryl iodides with phenols

In this report, we have developed a sustainable protocol for the synthesis of aromatic esters by a carbonylative method using di‐μ‐chlorobis [5‐hydroxy‐2‐[1‐(hydroxyimino‐ĸN) ethyl] phenyl‐ĸC] palladium (II) dimer (1) catalyst in PEG‐400 as a greener and recyclable solvent. The reaction is carried out at room temperature using CO in a balloon. Good to excellent yield of various esters can be synthesize using this protocol. Direct insertion of CO moiety leads to the high atom and step economy. Compared to previous protocol this phosphine free approach for the synthesis of aromatic esters provides high Turnover Number (TON) and Turnover Frequency (TOF). Developed approach has an alternative route for use of conventional palladium precursor with high conversion and selectivity. The catalyst system and product can easily be separated using diethyl ether as a solvent. The Pd/PEG‐400 system could be reused up to a fifth consecutive cycle without any loss of its activity and selectivity.

Catalytic Performance of Supported Pd Catalyst Prepared with Different Palladium Precursors for Catalytic Combustion of BTH.

Catalytic combustion of benzene, toluene, and hexane (BTH) was carried out to investigate in this study the effect of palladium precursor on the property and performance of 1 wt.% Pd/γ-Al₂O₃. Properties were characterized by X-ray diffraction (XRD), Brunauer Emmett Teller (BET) surface area, temperature programmed reduction (TPR), Transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analyses. When palladium precursor was used to prepare the catalyst, it had a great effect on the property and performance of the supported palladium catalyst. Total acidity, size of palladium particle, and oxidation state of palladium were associated with catalytic activity of the catalyst. Higher total acidity of the catalyst and larger particle size of palladium favorably affected the catalytic activity. In addition, palladium species with high oxidation state might be useful to increase catalytic activity in BTH combustion.

Синтез катализаторов Pd/C: подходы к регулированию структуры активных центров для достижения высокой селективности в реакциях гидрирования органических соединений

В работе проведено обобщение способов регулирования физико-химических и каталитических свойств композиций Pd/C при варьировании условий их синтеза. На примере результатов, полученных авторами, продемонстрировано влияние природы углеродного носителя, состава предшественника палладия и условий его восстановления, добавления второго активного металла на формирование палладиевых центров, их дисперсность, электронное состояние и каталитические свойства в практически важных реакциях гидрирования. Приведенные данные могут быть полезны для создания катализаторов Pd/C, обладающих высокими активностью и селективностью в реакциях гидрирования полифункциональных органических соединений.

Transformation of Alumina-Supported Palladium Precursors during Reductive Activation

The transformation of alumina-supported palladium salts during isothermal treatment in a reducing atmosphere has been studied to determine the optimum reduction temperature for the Pd/Al2O3 catalyst. It has been found that the interaction of palladium acetylacetonate with alumina surface sites is stronger than the interaction of the acetate complex. Owing to this factor, the diameter of the resulting active-ingredient particles is smaller in the case of the former precursor in the entire temperature range of reductive treatments. The optimum reduction temperature for the supported palladium salts is 500°С; this temperature provides the formation of palladium particles characterized by the maximum conversion of methylacetylene and propadiene at a high selectivity for conversion to propylene. The systems activated at temperatures of up to 400°C exhibit low activity in the hydrogenation of methylacetylene and propadiene; this behavior is attributed to an incomplete reduction of palladium from Pd salts to form oxidized and coordinatively unsaturated species of the active ingredient.

Aminophosphine Palladium Pincer-Catalyzed Carbonylative Sonogashira and Suzuki-Miyaura Cross-Coupling with High Catalytic Turnovers.

This work documents the first palladium pincer complex-catalyzed carbonylative Sonogashira (CS) and carbonylative Suzuki–Miyaura (CSM) cross-coupling. Compared to previous protocols, which employ hazardous and toxic solvents, the aminophosphine pincer complex {[C6H3-2,6-(NHP{piperidinyl}2)2]Pd(Cl)} (III) catalyzes both the cross-coupling reactions in propylene carbonate, an eco-friendly and sustainable polar aprotic solvent. Advantageously, employing III allows the CS cross-coupling to be carried out at a palladium loading of 10–4 mol % and the CSM cross-coupling to be carried out at 10–6 mol %, thus resulting in catalytic turnovers of 105 and 107, respectively. Relative comparison of the pincer complex with conventional palladium precursors Pd(OAc)2 and PdCl2(PPh3)2 shows the efficiency and robustness of the pincer complex in effecting higher catalytic activity at low palladium loadings.

Agmatine attenuated sensorimotor gating deficit in schizophrenia model in rats: Combination of neonatal MK-801 and isolation rearing

An interesting aspect of palladium chemistry includes quite a large number of species, often invoked to explain the fascinating catalytic processes, reactive intermediates involved in chemical transformations as these palladium precursors are very stable and innocent in nature. These complexes have found extensive applications as catalytic materials with tremendous potential in areas such as photonics to biochemistry, as shown by recent articles 1, 2. One such class of palladium precursors that are inert toward moisture, air, and having high thermal stability are the “(C,N)Pd” palladacycles. The formation of cyclopalladated complexes is a widely investigated topic from the structural as well as catalytic point of view 3, 4. In this regard, many researchers individually and in groups are actively pursuing the quest for the next generation of palladacycle in order to explore it as a catalyst for organic transformations and as a possible biologically active drug ingredient (5). The present contribution aims to provide investigations of some of the most significant achievements accomplished toward the generalizations of palladacycles during the last decade (6). The aim of this chapter is therefore to document the luminescent, sensing and biological properties of cyclopalladated complexes.

The partial dehydrogenation of aluminium dihydrides.

The reactions of a series of β-diketiminate stabilised aluminium dihydrides with ruthenium bis(phosphine), palladium bis(phosphine) and palladium cyclopentadienyl complexes is reported. In the case of ruthenium, alane coordination occurs with no evidence for hydrogen loss resulting in the formation of ruthenium complexes with a pseudo-octahedral geometry and cis-relation of phosphine ligands. These new ruthenium complexes have been characterised by multinuclear and variable temperature NMR spectroscopy, IR spectroscopy and single crystal X-ray diffraction. In the case of palladium, a series of structural snapshots of alane dehydrogenation have been isolated and crystallographically characterised. Variation of the palladium precursor and ligand on aluminium allows kinetic control over reactivity and isolation of intermetallic complexes that contain new Pd-Al and Pd-Pd interactions. These complexes differ by the ratio of H : Al (2 : 1, 1.5 : 1 and 1 : 1) with lower hydride content species forming with dihydrogen loss. A combination of X-ray and neutron diffraction studies have been used to interrogate the structures and provide confidence in the assignment of the number and position of hydride ligands. 27Al MAS NMR spectroscopy and calculations (DFT, QTAIM) have been used to gain an understanding of the dehydrogenation processes. The latter provide evidence for dehydrogenation being accompanied by metal-metal bond formation and an increased negative charge on Al due to the covalency of the new metal-metal bonds. To the best of our knowledge, we present the first structural information for intermediate species in alane dehydrogenation including a rare neutron diffraction study of a palladium-aluminium hydride complex. Furthermore, as part of these studies we have obtained the first SS 27Al NMR data on an aluminium(i) complex. Our findings are relevant to hydrogen storage, materials chemistry and catalysis.

The liquid phase catalytic hydrogenation of furfural to furfuryl alcohol

We report the hydrogenation of furfural (FF) to furfuryl alcohol (FA) with Pd-containing catalysts stabilized by hypercrosslinked polystyrene (HPS). FF is one of the major ingredients of biooil produced by biomass pyrolysis, while FA is a source of value-added chemicals, thus, creating an effective path from biomass to important compounds. Different palladium precursors (PdCl2(CH3CN)2, Pd(CH3COO)2) were used for the catalysts synthesis. The nature of the precursor influences the size of palladium nanoparticles. The TEM and SAXS data showed that when using PdCl2(CH3CN)2, a monomodal distribution of particles size with mean diameter 5.4 ± 1.2 nm was observed, whereas for Pd(CH3COO)2, multimodal particle size distribution with the mean particle sizes up to 13.8 ± 5.4 nm was observed. The comparison of the catalytic activities of Pd-containing catalysts indicated that the more disperse sample of palladium showed higher values of FF conversion and selectivity to FA because of small particles.

Pd/DNA as Highly Active and Recyclable Catalyst of Suzuki–Miyaura Coupling

Pd/DNA catalysts were prepared in a mixed H2O/EtOH solvent using palladium precursors, Pd(OAc)2 and PdCl2, in different dosages and salmon fish sperm DNA. As prepared, the Pd/DNA contained Pd(II) and Pd(0) nanoparticles of various sizes and morphologies, depending on the preparation method. Pd/DNA efficiently catalyzed the Suzuki–Miyaura cross-coupling of various aryl bromides with phenylboronic acids. The catalyst was recovered by simple phase separation and then reused in seven consecutive cycles with a high activity.

Pd nanoparticles at N-heterocyclic carbene at ZIF-8 as an ultrafine, robust and sustainable heterogeneous system for Suzuki-Miyaura cross coupling processes

Producing nanoparticles with controlled size without any aggregation is an important challenge for enhancing the catalytic activities of the metal nanoparticles (MNPs) supported on metal–organic frameworks (MOFs). In this work, a new hybrid nanoporous material, Pd nanoparticles at N-heterocyclic carbene at zeolitic imidazolate framework (Pd NPs at NHC at ZIF-8), with a high internal surface area was successfully prepared by immobilizing anionic sulfonated N-heterocyclic carbene–palladium(II) precursor inside the cavities of ZIF-8 using “impregnation approach” followed by reduction with Sodium borohydride (NaBH4). The as-prepared new Pd NPs at NHC at ZIF-8 composite proved to be highly active and showed excellent stability as a heterogeneous catalyst for Suzuki-Miyaura cross-coupling reaction.

An efficient Pd/C catalyst design based on sequential ligand exchange method for the direct synthesis of H2O2

A new catalyst preparation method involving the sequential ligand exchange of anionic palladium complexes to cationic complexes via the formation of palladium hydroxide intermediates is proposed. The novel method enables the electrostatic adsorption of an anionic palladium complex on the negatively charged carbon surface, and therefore makes it possible to obtain small and highly dispersed Pd nanoparticles. The H2O2 productivity and H2 selectivity of the ligand-exchanged catalyst were 16 and 3.6 times higher than those of the Pd/C catalyst prepared by using the same anionic palladium precursor. The strikingly different activities mainly attributed to the difference in the nanoparticle size and the oxidation state of Pd, which clearly indicates that the activity of Pd/C catalyst for the direct synthesis of H2O2 can be greatly improved by the sequential ligand exchange method.

Palladium nanoparticles synthesis, characterization using glucosamine as the reductant and stabilizing agent to explore their antibacterial & catalytic applications

Low cost and an easy technique for the synthesis of palladium nanoparticles (PdNPs) was developed. Glucosamine was used to stabilize palladium precursor (PdCl2) into palladium nanoparticles. Several analytical techniques were used for the determination of morphology, crystalline structure; size, capping, and composition of synthesize palladium nanoparticles. The UV-visible spectroscopy SPR peak (Surface Plasmon Resonance) at 284 nm revealed synthesis of PdNPs. Energy dispersive X-ray (EDX) and X-ray diffraction (XRD) studies proved the elemental composition and crystalline structure of the synthesized palladium nanoparticles respectively. The average particle sizes (5.5 nm) were obtained by using the 1 M glucosamine solution, with a fixed amount of PdCl2 (4 mM). Moreover, the as synthesized PdNPs was evaluated against Gram negative bacterial E. which shows tremendous antibacterial activity as compare to tobramycin standard antibiotics. It's mechanistically found that PdNPs damage cell membrane and caused imbalance of metabolism system of the cell as a result production of reactive oxygen species (ROS). Thus, these finding revealed that cells become leaky and all organelles come out from cells, finally caused death of the E. coli. Addition, the as prepared PdNPs also showed excellent catalytic activities toward reduction of methylene blue and 4-nitrophenol.Thus, glucosamine mediated PdNPs having dual functions biomedical as well as intoxicating catalyst for industries.

Heck Transformations of Biological Compounds Catalyzed by Phosphine-Free Palladium.

The development and optimization of synthetic methods leading to functionalized biologically active compounds is described. Two alternative pathways based on Heck-type reactions, employing iodobenzene or phenylboronic acid, were elaborated for the arylation of eugenol and estragole. Cinnamyl alcohol was efficiently transformed to saturated arylated aldehydes in reaction with iodobenzene using the tandem arylation/isomerization sequential process. The arylation of cinnamyl alcohol with phenylboronic acid mainly gave unsaturated alcohol, while the yield of saturated aldehyde was much lower. Catalytic reactions were carried out using simple, phosphine-free palladium precursors and water as a cosolvent, following green chemistry rules as much as possible.

Exceptional Catalytic Activities and Sensing Performance of Palladium Decorated Anisotropic Gold Nanoparticles

AbstractThe present perspective explores the effect of composition and morphology on the catalytic and surface enhanced Raman scattering (SERS) sensing applications of anisotropic bimetallic gold‐palladium (Au−Pd) nanoparticles. The morphology of the nanoparticles was controlled by a ‘soft’ templating approach by using a hexagonal lyotropic liquid crystalline phase. The mesophases comprised of toluene‐swollen surfactant cylinders, doped with the gold (Au) and palladium (Pd) precursors, stabilized by a monolayer of surfactant and co‐surfactant molecules, arranged in a hexagonal lattice in water as continuous medium. Anisotropic nanostructures of Au having very small Pd nanoparticles deposited on their surface were produced when hexagonal mesophases containing Au and Pd precursors were subjected to gamma irradiation. The synthesized nanomaterials were thoroughly characterized using X‐ray diffraction (XRD), transmission electron microscopy (TEM) and X‐ray photoemission spectroscopy (XPS). These nanomaterials showed exceptionally high catalytic activities for the reduction of 4‐nitrophenol with the normalized rate constant of the bimetallic Au−Pd catalyst being 1.5 times higher than the best catalyst that is reported in the literature. These bimetallic Au−Pd nanostructures also demonstrated very good enhancement for Raman signals of methylene blue by demonstrating an enhancement factor of the order of 106 and a detection limit as low as 0.1 nM.

Activity and selectivity of carbon supported palladium catalysts prepared from bis(η3-allyl)palladium complexes in phenylacetylene hydrogenation

Liquid phase hydrogenation of phenylacetylene was investigated on a series of 9.1 wt% Pd/C catalysts prepared from bis(η3-allyl)palladium complexes, as well as commercial Russian Pd/C catalyst (GIPKH-108). Pd/C catalysts were characterized by oxygen absorption and SEM. All prepared Pd/C catalysts demonstrated very high selectivity to styrene. The reduction temperature of palladium precursor has a significant effect on the palladium dispersity, but the substituent near terminal carbon atom of allyl ligand affects the dispersity more essentially than reduction temperature. Pd/C catalyst prepared from bis[(η3-allyl)palladium acetate] showed highest metal dispersity, activity and selectivity in the hydrogenation of phenylacetylene to styrene.