Heterogeneous Palladium Catalyst Research Articles

ReaxFF Simulations of Lignin Fragmentation on a Palladium-Based Heterogeneous Catalyst in Methanol-Water Solution.

The interaction of fragments derived from lignin depolymerization with a heterogeneous palladium catalyst in methanol-water solution is studied by means of experimental and theoretical methodologies. Quantum chemistry calculations and molecular dynamics simulations based on the ReaxFF approach are combined effectively to obtain an atomic level characterization of the crucial steps of the adsorption of the molecules on the catalyst, their fragmentation, reactions, and desorption. The main products are identified, and the most important routes to obtain them are explained through extensive computational procedures. The simulation results are in excellent agreement with the experiments and suggest that the mechanisms comprise a fast chemisorption of identified fragments from lignin on the metal interface accompanied by bond breaking, release of some of their hydrogens and oxygens to the support, and eventual desorption depending on the local environment. The strongest connections are those involving the aromatic rings, as confirmed by the binding energies of selected representative structures, estimated at the quantum chemistry level. The satisfactory agreement with the literature, quantum chemistry data, and experiments confirms the reliability of the multilevel computational procedure to study complex reaction mixtures and its potential application in the design of high-performance catalytic devices.

N-heterocyclic carbene-Pd(II) complex based on theophylline supported on Fe3O4@SiO2 nanoparticles: Highly active, durable and magnetically separable catalyst for green Suzuki-Miyaura and Sonogashira-Hagihara coupling reactions

In this paper, a novel heterogeneous palladium catalyst was synthesized by anchoring N-heterocyclic carbene-Pd(II) complex based on theophylline on magnetic Fe3O4@SiO2 nanoparticles. The synthesized magnetic composite was characterized by fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray analysis (EDX), thermogravimetric analysis (TGA), vibration sample magnetometry (VSM), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), dynamic light scattering (DLS), N2 adsorption-desorption isotherm analysis (BET), UV–vis spectroscopy and elemental analysis. Also, loading content of palladium on the catalyst was measured by inductive coupled plasma (ICP) analysis. The synthesized catalyst was used successfully for the Suzuki cross-coupling reactions of various aryl halides (I, Br, Cl) with phenylboronic acids. This reaction was best performed in water as a green solvent in the presence of just 0.37–0.5 mol% of the catalyst at 60 °C. Also, we have reported this recyclable catalytic system as a stable phosphine-free Pd catalyst for the Sonogashira cross-coupling of aryl halides (I, Br, Cl) with terminal aromatic and aliphatic alkynes under solvent-free conditions. All coupling reactions proceeded with good to excellent yields. The catalyst showed good stability and was recovered and reused for eight reaction cycles without a significant loss in its catalytic activity. Also, the leaching of the catalyst has been examined by a hot filtration test and ICP-AES analysis.

Synthesis of poly(ether ketone amide)s by a heterogeneous palladium-catalyzed polycondensation of aromatic diiodides, diamines, and carbon monoxide

A series of novel aromatic poly(ether ketone amide)s (PEKAs) were synthesized by the heterogeneous palladium-catalyzed carbonylative polycondensation of aromatic diiodides with ether ketone units, aromatic diamines, and carbon monoxide in N, N-dimethylacetamide (DMAc) at 120°C using 6 mol% of a magnetic nanoparticles–supported bidentate phosphine palladium complex (Fe3O4@SiO2-2P-PdCl2) as catalyst and 1,8-diazabicyclo[5,4,0]-7-undecene as base. The PEKAs had inherent viscosities ranging from 0.61 dl g−1 to 0.75 dl g−1. All the PEKAs were soluble in strong dipolar organic solvents. These PEKAs showed glass transition temperatures between 178°C and 232°C and 10% weight loss temperatures ranging from 443°C to 496°C in nitrogen. These PEKAs could be cast into transparent, flexible, and strong films from DMAc solutions with tensile strengths of 72.8–82.6 MPa, tensile moduli of 2.19–2.84 GPa, and elongations at break of 5.4–7.5%. Importantly, the heterogeneous palladium catalyst can be conveniently recovered from the reaction mixture by simply applying an external magnet and recycled up to eight times without significant loss of activity.

Synthesis of poly(ether ketone amide)s containing 4‐aryl‐2,6‐ diphenylpyridine moieties by a heterogeneous palladium‐catalyzed polycondensation of aromatic diiodides, aromatic diamines, and carbon monoxide

New aromatic poly(ether ketone amide)s containing 4‐aryl‐2,6‐diphenylpyridine units were prepared by the heterogeneous palladium‐catalyzed carbonylative polymerization of aromatic diiodides with ether ketone units, aromatic diamines bearing pyridine groups, and carbon monoxide. Polymerizations were performed in N,N‐dimethyl‐ acetamide (DMAc) at 120°C in the presence of a magnetic nanoparticles‐supported bidentate phosphine palladium complex [Fe3O4@SiO2‐2P‐PdCl2] as catalyst with 1,8‐diazabicycle[5,4,0]‐7‐undecene (DBU) as base and generated poly(ether ketone amide)s with inherent viscosities up to 0.79 dL/g. All the polymers were soluble in many organic solvents. These polymers showed glass transition temperatures between 219°C and 257°C and 10% weight loss temperatures ranging from 467°C to 508°C in nitrogen. These polyamides could be cast into transparent, flexible, and strong films from DMAc solution with tensile strengths of 86.4 to 113.7 MPa, tensile moduli of 2.34 to 3.19 GPa, and elongations at break of 5.2% to 6.9%. These polymers also exhibited good optical transparency with an ultraviolet‐visible absorption cut‐off wavelength in the 371 to 384‐nm range. Importantly, the new heterogeneous palladium catalyst can easily be recovered from the reaction mixture by simply applying an external magnet and recycled at least 8 times without significant loss of activity. Our catalytic system not only avoids the use of an excess of PPh3 and prevents the formation of palladium black, but also solves the basic problems of palladium catalyst recovery and reuse.

A covalently anchored Pd(II)-Schiff base complex over a modified surface of mesoporous silica SBA-16: An efficient and reusable catalyst for the Heck-Mizoroki coupling reaction in water

A new heterogeneous palladium catalyst was prepared by covalent anchoring of a palladium- (II)-Schiff base complex onto the mesoporous cage-like material SBA-16. Several instrumental techniques such as Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), inductively coupled plasma optical emission spectroscopy (ICP-OES), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray analysis (EDX), powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption isotherms, UV–vis spectroscopy, and elemental analysis were carried out to characterize the structure and composition of the catalyst. This catalyst displayed excellent activity for the Heck-Mizoroki reaction of various aryl halides and alkenes in water as a green solvent. It was found that the solid catalyst could be easily recovered by simple filtration and reused six times without a significant loss of catalytic activity. In addition, Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (PXRD), N2 adsorption-desorption isotherms, and high resolution transmission electron microscopy (HRTEM) techniques were used to prove the stability of the reused catalyst.

Recycable complex catalysts immobilized on mercaptan-functionalized glass-polymer supports

The use of the mercaptan-functionalized bisphenol A diglycidyl ether epoxy (base material) encapsulated on glass core as matrices for metal catalysts was investigated. Here, the acquiring knowledge of recyclable palladium catalysts for organic reaction which can be mechanically separated from the reaction media and next use as a heterogeneous catalyst in large-scale industries was the most important goal. Homogeneous Pd precursor [PdCl2(PhCN)2] has been heterogenized by attaching to prepared glass-polymeric supports via ligand exchange process. Collected research results indicate that mercaptans used to cure epoxy resin can greatly affect the catalytic properties of the epoxy resin with supported palladium catalyst. The epoxy system modified with mercaptans has a few possible catalytic coordination centers especially oxygen and sulfur to which the palladium ion can be bound. It should be noted that although various concentrations of palladium complex were used, the amount of metal attached to epoxide supports remained the same, that is below the sorption capacity of the polymers. Presented new type of glass-polymer supports comparing to other used corresponding organic carriers offers several practical advantages such as morphological and chemical structure of the matrix, which affect the properties of the heterogenized catalyst in the selected organic reactions: Heck reaction and hydrogenation reaction were investigated. The catalytic activity of all formulated systems was similar to homogeneous palladium precursor PdCl2(PhCN)2. The resulting glass-polymeric matrices and heterogenized palladium catalysts were characterized by varied research techniques such as surface analysis technique (ToF–SIMS) and scanning electron microscopy with energy-dispersive X-ray analyzer (SEM-EDX). We used likewise the atomic absorption spectroscopy (AAS) method to quantify the amount of palladium loaded in the recyclable support and also the BET method to determine specific pore size distribution parameters. Furthermore, XPS spectroscopy showed information about surface structure and chemical states in the palladium-supported catalysts.

A practical synthesis of unsymmetrical triarylphosphines by heterogeneous palladium(0)-catalyzed cross-coupling of aryl iodides with diphenylphosphine

The heterogeneous cross-coupling reaction of aryl iodides with diphenylphosphine was achieved in DMAc at 130 °C in the presence of 1.0 mol% of MCM-41-supported tridentate nitrogen palladium(0) complex [MCM-41-3N-Pd(0)] with KOAc as base, yielding a variety of unsymmetrical triarylphosphines in good to excellent yields. The turnover frequency (TOF) of the catalyst can reach 30.67 h−1. This new heterogeneous palladium(0) catalyst could easily be prepared by a simple procedure from commercially readily available reagents, and exhibited the same catalytic activity as homogeneous Pd(OAc)2 or Pd(PPh3)4, and could be recovered by filtration of the reaction solution and recycled at least seven times without significant loss of catalytic activity.

Designed heterogeneous palladium catalysts for reversible light-controlled bioorthogonal catalysis in living cells

As a powerful tool for chemical biology, bioorthogonal chemistry broadens the ways to explore the mystery of life. In this field, transition metal catalysts (TMCs) have received much attention because TMCs can rapidly catalyze chemical transformations that cannot be accomplished by bio-enzymes. However, fine controlling chemical reactions in living systems like bio-enzymes is still a great challenge. Herein, we construct a versatile light-controlled bioorthogonal catalyst by modifying macroporous silica-Pd0 with supramolecular complex of azobenzene (Azo) and β-cyclodextrin (CD). Its catalytic activity can be regulated by light-induced structural changes, mimicking allosteric regulation mechanism of bio-enzymes. The light-gated heterogeneous TMCs are important for in situ controlling bioorthogonal reactions and have been successfully used to synthesize a fluorescent probe for cell imaging and mitochondria-specific targeting agent by Suzuki–Miyaura cross-coupling reaction. Endowing the bioorthogonal catalyst with new functions is highly valuable for realizing more complex researches in biochemistry.

A sustainable heterogenized palladium catalyst for Suzuki-Miyaura cross coupling reaction of azaheteroaryl halides in aqueous media

A unique recyclable Pd catalyst (‘SiO2’-NH2-Pd) for Suzuki-Miyaura coupling reaction of azaheteroaryl halides is developed. The catalytic system is working under mild aqueous condition with low Pd loading and without the use of phosphine ligand. The plausible mechanism is proposed based on the formation of undesired symmetrical biaryl from the coupling reaction of azaheteroaryl chlorides due to the oxidative homocoupling of nucleophilic arylboronic acid. This catalytic system represents an attractive and promising approach for the synthesis of azaheterobiaryls with high product yields. The catalyst has demonstrated an excellent recyclability.

A practical method for heterogeneously-catalyzed Mizoroki–Heck reaction: Flow system with adjustment of microwave resonance as an energy source

The microwave-assisted and continuous-flow Mizoroki–Heck reaction using a heterogeneous palladium catalyst supported on the anion-exchange resin DIAION WA30 (7% Pd/WA30) is described. The microwave resonance is finely adjusted to 2.4 GHz according to the electric permittivity of the reaction medium for efficient heating. Organic solvents, such as acetonitrile, N,N-dimethylacetamide, and toluene, can be sufficiently heated even with a low intensity of microwave irradiation in a 7% Pd/WA30-packed, glass tube-shaped catalyst cartridge, which was designed based on the electric permittivity of the solvents. The catalyst cartridge can be continuously reused at least 5 runs without exchange.

Palladium nanoparticles immobilized on EDTA‐modified Fe3O4@SiO2 nanospheres as an efficient and magnetically separable catalyst for Suzuki and Sonogashira cross‐coupling reactions

In this study, a novel heterogeneous palladium catalyst was synthesized by anchoring palladium onto ethylenediaminetetraacetic acid (EDTA)‐coated Fe3O4@SiO2 magnetic nanocomposite and used for the Suzuki and Sonogashira cross‐coupling reactions. The properties of the magnetic catalyst were characterized by FT‐IR, XRD, TEM, FE‐SEM, DLS EDX, XPS, N2 adsorption‐desorption isotherm analysis, TGA, VSM, elemental analysis and the loading level of Pd in catalyst was measured to be 0.51 mmol/g by ICP. The catalyst was used in Suzuki cross‐coupling reactions of various aryl halides, including less reactive chlorobenzenes with phenylboronic acid without any additive or ligand under green conditions. Furthermore, we have reported this recyclable catalytic system for Sonogashira cross‐coupling reactions of various aryl halides (I, Br, Cl) under copper and ligand‐free conditions in the presence of DMF/H2O (1:2/v:v) as a solvent. The magnetic catalyst could also be separated by an external magnet and reused six times without any significant loss of activity.

Preparation, structural characterization, and catalytic performance of Pd(II) and Pt(II) complexes derived from cellulose Schiff base

In this study, we reported production, characterization, and catalytic behavior of two novel heterogeneous palladium(II) and platinum(II) catalysts derived from cellulose biopolymer. In order to eliminate the use of toxic organic or inorganic solvents and to reduce the use of excess energy in the coupling reactions, we have developed a very simple, rapid, and eco-friendly microwave irradiation protocol. The developed microwave-assisted method of Suzuki cross coupling reactions produced excellent reaction yields in the presence of cellulose supported palladium and platinum (II) catalysts. Moreover, the catalysts easily regenerated after simple filtration, and they gave good reusability. This study revealed that the designed catalysts and method provide clean, simple, rapid, and impressive catalytic performance for Suzuki coupling reactions.

Versatile Heterogeneous Palladium Catalysts for Diverse Carbonylation Reactions under Atmospheric Carbon Monoxide Pressure

AbstractHerein, we report a versatile carbonylation protocol using heterogeneous Pd0 nanoparticles supported on the metal–organic frameworks (MOFs) MIL‐88B‐NH2 (Fe/Cr). The synthesis of a vast array of carbonyls, which includes amides, esters, carboxylic acids, and α‐ketoamides, was achieved through mono‐ and dicarbonylation reactions. The selectivity could be controlled simply by tuning the reaction conditions. Superior activity and selectivity were recorded in some cases compared to that achieved with commercial Pd/C. However, the utility of an elaborate catalyst support is questionable and important reactivity and recyclability issues are discussed.

Pronounced effect of pore dimension of silica support on Pd-catalyzed Suzuki coupling reaction under ambient conditions

The pore size of the mesoporous silica support affects the reactivity of heterogeneous palladium catalysts in the Suzuki reaction under ambient conditions, which is leveled at higher temperature.

Synthesis of N-Lauroyl Sarcosine by Amidocarbonylation: Comparing Homogeneous and Heterogeneous Palladium Catalysts

An improved system for the synthesis of N-acyl amino acids via Pd-catalyzed amidocarbonylation is reported. Utilizing inexpensive Pd black gives the industrially important surfactant N-lauroyl sarcosine in excellent yields (95%) on a multi-gram scale. Advantages of the new system include reusability, decreased process temperature, and, importantly, drastically decreased co-catalyst loading.

Pd immobilized on polyamide based on melamine and terephalic acid as an efficient and recyclable catalyst for Suzuki‐Miyaura coupling reaction

A simple synthetic strategy of polyamide was described from melamine and terephalic acid via one‐step polycondensation. PdCl2 was then immobilized on the polyamide (denoted as Pd/MPA). Melamine and terephalic acid not only acted as monomers but also provided the ligand sites to help the polyamide to coordinate with Pd(II). The Pd/MPA catalyst was characterized by FT‐IR, TGA, SEM, TEM, XPS, N2 adsorption‐desorption and atomic absorption spectroscopy. The catalyst was used in Suzuki‐Miyaura coupling reaction of various aryl halides, including less reactive chlorobenzene and benzyl chloride, to give the coupling products in moderate to excellent yields. High turnover frequencies (TOF) up to 29400 h‐1 can be also obtained. In addition, it behaved truly as a heterogeneous catalyst with high reusability after being recycled 6 times and palladium leaching was negligible during the process. This work provides a practical polyamide support to develop heterogeneous palladium catalysts with simple synthetic procedure and low cost.

One-step synthesis of Pd-NPs@Cu2(BDC)2DABCO as efficient heterogeneous catalyst for the Suzuki–Miyaura cross-coupling reaction

A new heterogeneous palladium catalyst has been synthesized by one-step encapsulation in nanoporous metal-organic framework Cu2(BDC)2(DABCO) (BDC = 1,4-benzenedicarboxylate, DABCO = 1,4-diazabicyclo[2.2.2]octane) under a temperature control program. Supported Pd nanoparticles (Pd-NPs@Cu2(BDC)2(DABCO)) were characterized by X-ray diffraction, BET analysis, field emission scanning electron microscopy, transmission electron microscopy, inductively coupled plasma atomic emission and X-ray photoelectron spectroscopy (XPS). The Highly dispersed Pd particles (Pd-NPs@Cu2(BDC)2(DABCO)) offered a very efficient catalytic activity towards the Suzuki–Miyaura cross-coupling reaction.

A phosphine-free, atom-efficient cross-coupling of aryl iodides with triarylindiums or trialkynylindiums catalyzed by immobilization of palladium(0) in MCM-41

The first phosphine-free heterogeneous atom-efficient cross-coupling reaction of aryl iodides with triarylindiums or trialkynylindiums was achieved in THF at 68 °C by using 1 mol% of MCM-41-immobilized palladium(0)-Schiff base complex [MCM-41-N,N-Pd(0)] as catalyst, yielding a variety of unsymmetrical biaryls and arylalkynes in good to excellent yields. The heterogeneous palladium(0) catalyst could easily be prepared via a simple procedure from commercially readily available reagents, and recovered by filtration of the reaction solution and recycled at least 10 times without significant loss of activity.

Glycerol Isopropyl Ethers: Direct Synthesis from Alcohols and Synthesis by the Reduction of Solketal

AbstractThe catalytic reduction of solketal ((2,2‐dimethyl‐1,3‐dioxolan‐4‐yl)methanol) over bifunctional heterogeneous palladium catalysts is proposed as an alternative to the synthesis of glycerol isopropyl ethers by the etherification of glycerol. The direct synthesis of glycerol isopropyl ethers from isopropanol and glycerol requires severe conditions (T=130–150 °C, p(H2)=20–35 bar) and a large excess of isopropanol to reach a considerable yield. The main reaction products in the catalytic reduction of solketal are glycerol mono‐ and di‐isopropyl ethers and solketal isopropyl ether. Solketal conversion over Al‐HMS‐supported palladium catalysts (T=120 °C and p(H2)=20 bar) affords a mixture of ethers with a high degree of conversion (87 %), 78 % selectivity, and excellent regioselectivity between isomeric ethers. Zeolite‐BEA‐supported palladium catalysts also exhibit high activity but much lower selectivity because of intense acetone aldol condensation. The effects of Si/Al ratios in BEA zeolites and Al‐HMS aluminosilicates and the amounts of supported palladium (1 and 2 wt %) on the properties of the catalysts at different reaction temperatures and hydrogen pressures are considered.

Development of a Unique Heterogeneous Palladium Catalyst for the Suzuki–Miyaura Reaction using (Hetero)aryl Chlorides and Chemoselective Hydrogenation

AbstractA unique heterogeneous palladium catalyst (7% Pd/WA30) supported on an anion exchange resin, which contains N,N‐dimethylaminoalkyl functionalities on the polymer backbone, was developed. 7% Pd/WA30 could smoothly catalyze Suzuki–Miyaura reactions of even less reactive heteroaryl chlorides and heteroarylboronic acids to afford various (hetero)biaryls due to the electron‐donating effect of the tert‐amines on WA30 to Pd species. It was also applicable as a chemoselective hydrogenation catalyst, showing inactivity for the hydrogenolysis of tert‐butyldimethylsilyl (TBS) ethers, alkyl benzyl ethers, and benzyl alcohols. The tert‐amines on WA30 acted as moderate catalyst poisons for Pd, resulting in chemoselective hydrogenation. 7% Pd/WA30 was reused for at least five times without any loss of the hydrogenation catalytic activity.magnified image