A versatile supported silver for heterogeneously catalysed processes: Synthesis of 3‐Acyloxylindolines solvent‐free conditions

We have found that fibrous nanosilica (KCC‐1) can used as a excellent support for the synthesis of highly sparse nanoparticles and has high surface area that was functionalized with Tetrathia‐azacyclopentadecane (TTACP) groups acting as the strong performers so that the Ag nanoparticles were well‐dispersed without aggregation on the fibers of the KCC‐1 microspheres (KCC‐1/TTACP/Ag). We enthusiasm to report one‐pot synthesis of 3‐Acyloxylindolines for first time from N‐tosyl‐2‐vinylaniline, and benzoic acid in the presence of KCC‐1/TTACP/Ag as a catalyst.     

Ni@Pd nanoparticles supported on ionic liquid‐functionalized KCC‐1 as robust and recyclable nanocatalysts for cycloaddition of propargylic amines and CO2

Novel heterogeneous catalyst systems comprised of a fibrous nanosilica‐supported nano‐Ni@Pd‐based ionic liquid (KCC‐1/IL/Ni@Pd) are described for the cyclization of propargylic amines with CO₂ to provide 2‐oxazolidinones. KCC‐1 with high surface area was functionalized with IL acting as a robust anchor so that the nano‐Ni@Pd was well dispersed on the fibres of the KCC‐1 microspheres, without aggregation. Because of the amplification effect of IL, high loading capacities of the nanocatalysts were achieved. The reported synthesis includes several advantages like solvent‐free conditions, operational simplicity, short reaction times, environmentally benign reaction conditions, cost effectiveness, high atom economy and excellent yields, making it a genuinely green protocol.     

Engineered mesoporous ionic‐modified γ‐Fe2O3@hydroxyapatite decorated with palladium nanoparticles and its catalytic properties in water

A new mesoporous organic–inorganic nanocomposite was formulated and then used as stabilizer and support for the preparation of palladium nanoparticles (Pd NPs). The properties and structure of Pd NPs immobilized on prepared 1,4‐diazabicyclo[2.2.2]octane (DABCO) chemically tagged on mesoporous γ‐Fe₂O₃@hydroxyapatite (ionic modified (IM)‐MHA) were investigated using various techniques. The synergistic effects of the combined properties of MHA, DABCO and Pd NPs, and catalytic activity of γ‐Fe₂O₃@hydroxyapatite‐DABCO‐Pd (IM‐MHA‐Pd) were investigated for the Heck cross‐coupling reaction in aqueous media. The appropriate surface area and pore size of mesoporous IM‐MHA nanocomposite can provide a favourable hard template for immobilization of Pd NPs. The loading level of Pd in the nanocatalyst was 0.51 mmol g^?1. DABCO bonded to the MHA surface acts as a Pd NP stabilizer and can also lead to colloidal stability of the nanocomposite in aqueous solution. The results reveal that IM‐MHA‐Pd is highly efficient for coupling reactions of a wide range of aryl halides with olefins under green conditions. The superparamagnetic nature of the nanocomposite means that the catalyst to be easily separated from solution through magnetic decantation, and the catalytic activity of the recycled IM‐MHA‐Pd showed almost no appreciable loss even after six consecutive runs.     

Green chemical synthesis of Pd nanoparticles for use as efficient catalyst in Suzuki‐Miyaura cross‐coupling reaction

Herein, we report the synthesis of tiny spherical Pd nanoparticles (NPs) by green chemical method under ambient conditions using flower extract of Lantana camara plant. The size of the Pd NPs is tunable from 4.7 to 6.3 nm by systematically controlling the concentration of either metal ions or plant extract. The synthesized Pd NPs were well characterized by different spectroscopic, microscopic and diffractometric techniques. The Pd NPs offered good size‐dependent catalytic activity in the Suzuki‐Miyaura C‐C coupling reaction under mild reaction conditions in (1: 1) water‐ethanol mixture. The catalyst is stable and exhibited excellent reusability up to three cycles of coupling reaction after which the catalytic activity decreases.     

Influence of the Base on Pd@MIL‐101‐NH2(Cr) as Catalyst for the Suzuki–Miyaura Cross‐Coupling Reaction

The chemical stability of metal–organic frameworks (MOFs) is a major factor preventing their use in industrial processes. Herein, it is shown that judicious choice of the base for the Suzuki–Miyaura cross‐coupling reaction can avoid decomposition of the MOF catalyst Pd@MIL‐101‐NH₂(Cr). Four bases were compared for the reaction: K₂CO₃, KF, Cs₂CO₃ and CsF. The carbonates were the most active and achieved excellent yields in shorter reaction times than the fluorides. However, powder XRD and N₂ sorption measurements showed that the MOF catalyst was degraded when carbonates were used but remained crystalline and porous with the fluorides. XANES measurements revealed that the trimeric chromium cluster of Pd@MIL‐101‐NH₂(Cr) is still present in the degraded MOF. In addition, the different countercations of the base significantly affected the catalytic activity of the material. TEM revealed that after several catalytic runs many of the Pd nanoparticles (NPs) had migrated to the external surface of the MOF particles and formed larger aggregates. The Pd NPs were larger after catalysis with caesium bases compared to potassium bases.     

Microenvironment Effects in Electrocatalysis: Ionic‐Liquid‐Like Coating on Carbon Nanotubes Enhances the Pd‐Electrocatalytic Alcohol Oxidation

A new catalyst consisting of ionic liquid (IL)‐functionalized carbon nanotubes (CNTs) obtained through 1,3‐dipolar cycloaddition support‐enhanced electrocatalytic Pd nanoparticles (Pd@IL(Cl^?)‐CNTs) was successfully fabricated and applied in direct ethanol alkaline fuel cells. The morphology, structure, component and stability of Pd@IL(Cl^?)‐CNTs were systematic characterized by transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM), Raman spectra, thermogravimetric analysis (TGA) and X‐ray diffraction (XRD). The new catalyst exhibited higher electrocatalytic activity, better tolerance and electrochemical stability than the Pd nanoparticles (NPs) immobilized on CNTs (Pd@CNTs), which was ascribed to the effects of the IL, larger electrochemically active surface area (ECSA), and greater processing performance. Cyclic voltammograms (CVs) at various scan rates illustrated that the oxidation behaviors of ethanol at all electrodes were controlled by diffusion processes. The investigation of the different counteranions demonstrated that the performance of the IL‐CNTs hybrid material was profoundly influenced by the subtly varied structures of the IL moiety. All the results indicated that the Pd@IL(Cl^?)‐CNTs catalyst is an efficient anode catalyst, which has potential applications in direct ethanol fuel cells and the strategy of IL functionalization of CNTs could be available to prepare other carbonaceous carrier supports to enhance the dispersivity, stability, and catalytic performance of metal NPs as well.     

Pd‐Cu alloy nanoparticle supported on amine‐terminated ionic liquid functional 3D graphene and its application on Suzuki cross‐coupling reaction

Well distributed Pd‐Cu bimetallic alloy nanoparticles supported on amine‐terminated ionic liquid functional three‐dimensional graphene (3D IL‐rGO/Pd‐Cu) as an efficient catalyst for Suzuki cross‐coupling reaction has been prepared via a facile synthetic method. The introduction of IL‐NH₂ cations on the surface of graphene sheets can effectively avoid the re‐deposition of graphene sheets, allowing the catalyst to be reused up to 10 cycles. The addition of Cu not only saves cost but also ensures high catalytic efficiency. It is worthy to note that the catalyst 3D IL‐rGO/Pd_2.5Cu_2.5 can efficiently catalyze the Suzuki cross‐coupling reaction with the yield up to 100% in 0.25 h, almost one‐fold higher than that by the pristine IL‐rGO/Pd_2.5 catalyst (52%). The Powder X‐Ray Diffraction (XRD), combining energy dispersive X‐ray spectroscopy (EDS) mapping results confirm the existence and distribution of Pd and Cu in the bimetallic nanoparticles. The transmission electron microscopy (TEM) reveals the nanoparticle size with an average diameter of 3.0 ± 0.5 nm. X‐ray photoelectron spectroscopy (XPS) analysis proved the presence of electron transfer from Cu to Pd upon alloying. Such alloying‐induced electronic modification of Pd‐Cu alloy and 3D ionic liquid functional graphene with large specific surface area both accounted for the catalytic enhancement.     

Copper‐Free Sonogashira Coupling of Acid Chlorides with Terminal Alkynes in the Presence of a Reusable Palladium Catalyst: An Improved Synthesis of 3‐Iodochromenones (=3‐Iodo‐4H‐1‐benzopyran‐4‐ones)

Pd/C is used as an efficient catalyst for the copper‐free Sonogashira coupling of acid chlorides and terminal alkynes to afford ynones in high yields (Tables 1 and 3). Cyclization of (2‐methoxyaryl)‐substituted ynones induced by I₂/ammonium cerium(IV) nitrate (CAN) at room temperature gave 3‐iodochromenones (=3‐iodo‐4H‐1‐benzopyran‐4‐ones) in excellent yield (Table 4).     

Magnetite tethered mesoionic carbene‐palladium (II): An efficient and reusable nanomagnetic catalyst for Suzuki‐Miyaura and Mizoroki‐Heck cross‐coupling reactions in aqueous medium

In this paper, a highly active, air‐ and moisture‐stable and easily recoverable magnetic nanoparticles tethered mesoionic carbene palladium (II) complex (MNPs‐MIC‐Pd) as nanomagnetic catalyst was successfully synthesized by a simplistic multistep synthesis under aerobic conditions using commercially available inexpensive chemicals for the first time. The synthesized MNPs‐MIC‐Pd nanomagnetic catalyst was in‐depth characterized by numerous physicochemical techniques such as FT‐IR, ICP‐AES, FESEM, EDS, TEM, p‐XRD, XPS, TGA and BET surface area analysis. The prepared MNPs‐MIC‐Pd nanomagnetic catalyst was used to catalyze the Suzuki–Miyaura and Mizoroki–Heck cross‐coupling reactions and exhibited excellent catalytic activity for various substrates under mild reaction conditions. Moreover, MNPs‐MIC‐Pd nanomagnetic catalyst could be easily and rapidly recovered by applying an external magnet. The recovered MNPs‐MIC‐Pd nanomagnetic catalyst exhibited very good catalytic activity up to ten times in Suzuki–Miyaura and five times in Mizoroki–Heck cross‐coupling reactions without considerable loss of its catalytic activity. However, MNPs‐MIC‐Pd nanomagnetic catalyst shows notable advantages such as heterogeneous nature, efficient catalytic activity, mild reaction conditions, easy magnetic work up and recyclability.     

Effect of Hydrohalogenation of Metal/Zeolite Catalysts for Cyclohexene Hydroconversion ‐Part 3‐ Pd/H‐ZSM‐5 Catalysts

Cyclohexene (CHE) hydroconversion was performed in a flow reactor at atmospheric pressure and temperatures of 50–400 °C using: Pd/H‐ZSM‐5, Pd/H‐ZSM‐5(HCl), and Pd/H‐ZSM‐5(HF) catalysts. These catalysts were characterized for acid site strength distribution via NH₃ TPD, Pd dispersion via H₂ chemisorption, TPR via reduction of the metal oxide in the catalysts and XRD for tracing crystallinity The hydroconversion steps proceeded as follows: CHE → Cyclohexane (CHA); CHE → Methylcyclopentenes (MCPEs) → Methylcyclopentane (MCPA); CHE → Cyclohexadienes (CHDEs) → Benzene → Alkylbenzenes; CHE and others → Hydrocrackedproducts. The overall hydroconversion of CHE was achieved in the catalyst order: Pd/H‐ZSM‐5 > Pd/H‐ZSM‐5(HF) > Pd/H‐ZSM‐5(HCl). CHE hydrogenation step was the major reaction at low temperatures which significantly inhibited via HCl treatment, but slightly enhanced via HF treatment. At medium temperatures, on all catalysts, isomerisation to MCPEs and MCPA increase to a maximum then a decline with a further increase of temperature. The overall isomerisation of CHE was highest on the untreated catalyst. During the higher temperature range, dehydrogenation, alkylation and hydrocracking were increased with temperature. Dehydrogenation of CHE always yielded larger amounts of 1,3‐CHDE than 1,4‐CHDE. These cyclohexadienes were produced in the catalyst order: Pd/H‐ZSM‐5(HF) > Pd/H‐ZSM‐5(HCl) > Pd/H‐ZSM‐5. In general, benzene alkylation to toluene exceeded that of xylenes, indicating that the second methylation is more difficult than the first. However, the catalytic activities for benzene and toluene production were in the order: Pd/H‐ZSM‐5 » Pd/H‐ZSM‐5(HCl) > Pd/H‐ZSM‐5(HF), whereas for xylenes production, Pd/H‐ZSM‐5 » Pd/H‐ZSM‐5(HF) > Pd/H‐ZSM‐5(HCl). Intrapore diffusion plays an important role during the dehydrogenation reactions as well as during the interconversion of individual aromatic hydrocarbons.     

Synthesis of multi‐functionalized carbonyl compounds by palladium–catalysed γ‐substitution of MBH adducts with activated amides

Catalytic allylic γ‐substitution with Morita‐Baylis‐Hillman (MBH) adducts for creating a new family of unsymmetrical dicarbonyl compounds was presented in this work, in which a variety of allylated amide products were achieved in good yields and high regioselectivity with excellent linear‐to‐branched ratios. Especially, it was found that the Pd/HZNU‐Phos complex exhibited remarkably high activity (with a TON up to 16800) in this transformation between dicarbonyl amides and MBH adducts. In addition, the possibly multisite interaction between multifunctional Pd/HZNU‐Phos catalyst system and substrates might responsible for its exceptionally high efficiency in this reaction.     

Biosynthesis of Pd/MnO2 nanocomposite using Solanum melongena plant extract and its application for the one‐pot synthesis of 5‐substituted 1H‐tetrazoles from aryl halides

In this work, for the first time, Solanum melongena plant extract was used for the green synthesis of Pd/MnO₂ nanocomposite via reduction osf Pd(II) ions to Pd(0) and their immobilization on the surface of manganese dioxide (MnO₂) nanoparticles (NPs) as an effective support. The synthesized nanocomposite were characterized by various analytical techniques such as Fourier transform infrared (FT‐IR), X‐ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive X‐ray spectroscopy (EDS) and UV–Vis spectroscopy. The catalytic activity of Pd/MnO₂ nanocomposite was used as a heterogeneous catalyst for the one‐pot synthesis of 5‐substituted 1H‐tetrazoles from aryl halides containing various electron‐donating or electron‐withdrawing groups in the presence of K ₄ [Fe (CN) ₆ ] as non‐toxic cyanide source and sodium azide. The products were obtained in good yields via a simple methodology and easy work‐up. The nanocatalyst can be recycled and reused several times with no remarkable loss of activity.     

CuI/Fe3O4 NPs@Biimidazole IL‐KCC‐1 as a leach proof nanocatalyst for the synthesis of imidazo[1,2‐a]pyridines in aqueous medium

In the present work, an innovative leach proof nanocatalyst based on dendritic fibrous nanosilica (DFNS) modified with ionic liquid loaded Fe₃O₄ NPs and CuI salts was designed and applied for the rapid synthesis of imidazo[1,2‐a]pyridines from the reaction of phenyl acetylene, 2‐aminopyridine, and aldehydes in aqueous medium. The structure of the synthesized nanocatalyst was studied by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared (FT‐IR), flame atomic absorption spectroscopy (FAAS), energy‐dispersive X‐ray (EDX), and X‐ray diffraction (XRD), vapor–liquid–solid (VLS), and adsorption/desorption analysis (Brunauer–Emmett–Teller [BET] equation) instrumental techniques. CuI/Fe₃O₄NPs@IL‐KCC‐1 with high surface area (225 m² g^?1) and porous structure not only exhibited excellent catalytic activity in aqueous media but also, with its good stability, simply recovered by an external magnet and recycled for eight cycles without significant loss in its intrinsic activity. Higher catalytic activity of CuI/Fe₃O₄NPs@IL‐KCC‐1 is due to exceptional dendritic fibrous structure of KCC‐1 and the ionic liquid groups that perform as strong anchors to the loaded magnetic nanoparticles (MNPs) and avoid leaching them from the pore of the nanocatalyst. Green reaction media, shorter reaction times, higher yields (71–97%), easy workup, and no need to use the chromatographic column are the advantages of the reported synthetic method.     

Highly efficient polymer‐stabilized palladium heterogeneous catalyst: Synthesis,characterization and application for Suzuki–Miyaura and Mizoroki–Heck coupling reactions

A suitable approach to stabilize palladium nanoparticles (Pd NPs), with an average diameter of 3–4 nm, on magnetic polymer is described. A new magnetic polymer containing 4′‐(4‐hydroxyphenyl)‐2,2′:6′,2″‐terpyridine (HPTPy) ligand was prepared by the polymerization of itaconic acid (ITC) as a monomer and trimethylolpropane triacrylate (TMPTA) as a cross‐linker and fully characterized. Pd NPs embedded on the magnetic polymer were successfully applied in Suzuki–Miyaura and Mizoroki–Heck coupling reactions under low palladium loading conditions, and provided the corresponding products with excellent yields (up to 98%) and high catalytic activities (TOF up to 257 hr^?1). Also, the catalyst can be easily separated and reused for at least consecutive five times with a small drop in catalytic activity.     

Pd@Pt Core–Shell Nanoparticles with Branched Dandelion‐like Morphology as Highly Efficient Catalysts for Olefin Reduction

A facile synthesis based on the addition of ascorbic acid to a mixture of Na₂PdCl₄, K₂PtCl₆, and Pluronic P123 results in highly branched core–shell nanoparticles (NPs) with a micro–mesoporous dandelion‐like morphology comprising Pd core and Pt shell. The slow reduction kinetics associated with the use of ascorbic acid as a weak reductant and suitable Pd/Pt atomic ratio (1:1) play a principal role in the formation mechanism of such branched Pd@Pt core–shell NPs, which differs from the traditional seed‐mediated growth. The catalyst efficiently achieves the reduction of a variety of olefins in good to excellent yields. Importantly, higher catalytic efficiency of dandelion‐like Pd@Pt core–shell NPs was observed for the olefin reduction than commercially available Pt black, Pd NPs, and physically admixed Pt black and Pd NPs. This superior catalytic behavior is not only due to larger surface area and synergistic effects but also to the unique micro–mesoporous structure with significant contribution of mesopores with sizes of several tens of nanometers.     

Convenient Synthesis of 1H‐Indol‐1‐yl Boronates via Palladium(0)‐Catalyzed Borylation of Bromo‐1H‐indoles with ‘Pinacolborane’

An atom‐economic Pd⁰‐catalyzed synthesis of a series of pinacol‐type indolylboronates 3 from the corresponding bromoindole substrates 2 and pinacolborane (pinBH) as borylating agent was elaborated. The optimal catalyst system consisted of a 1 : 2 mixture of [Pd(OAc)₂] and the ortho‐substituted biphenylphosphine ligand L‐3 (Scheme 4, Table). Our synthetic protocol was applied to the fast, preparative‐scale synthesis of 1‐substituted indolylboronates 3a – h in the presence of different functional groups, and at a catalyst load of only 1 mol‐% of Pd.     

Synthesis,characterization and catalytic performance of core‐shell structure magnetic Fe3O4/P(GMA‐EGDMA)‐NH2/HPG‐COOH‐Pd catalyst

A strategy has been developed for the synthesis, characterization and catalysis of magnetic Fe₃O₄/P(GMA‐EGDMA)‐NH₂/HPG‐COOH‐Pd core‐shell structure supported catalyst. The P(GMA‐EGDMA) polymer layer was coated on the surface of hollow magnetic Fe₃O₄ microspheres through the effect of KH570. The core‐shell magnetic Fe₃O₄/P(GMA‐EGDMA) modified by ‐NH₂ could be grafted with HPG. Then, the hyperbranched glycidyl (HPG) with terminal ‐OH were modified by ‐COOH and adsorbed Pd nanoparticles. The hyperbranched polymer layer not only protected the Fe₃O₄ magnetic core from acid–base substrate corrosion, but also provided a number of functional groups as binding sites for Pd nanoparticles. The prepared catalyst was characterized by UV–vis, TEM, SEM, FTIR, TGA, ICP‐OES, BET, XRD, DLS and VSM. The catalytic tests showed that the magnetic Fe₃O₄/P(GMA‐EGDMA)‐NH₂/HPG‐COOH‐Pd catalyst had excellent catalytic performance and retained 86% catalytic efficiency after 8 consecutive cycles.     

Enhanced catalytic performance of Pd‐Ga bimetallic catalysts for 2‐ethylanthraquinone hydrogenation

A series of Pd and Pd‐Ga bimetallic catalysts were prepared by a co‐impregnation method for 2‐ethylanthraquinone (EAQ) hydrogenation to produce hydrogen peroxide. Compared with 0.6Pd catalyst, the hydrogenation efficiency of 0.6Pd1.2Ga catalyst (11.9 g L^?1) increases by 32.2%, and the stability of 0.6Pd1.2Ga catalyst is also higher than that of 0.6Pd catalyst. The structures of the samples were determined by N₂ adsorption–desorption, ICP, XRD, CO chemisorption, TEM, H₂‐TPR, in situ CO‐DRIFTS and XPS. The results suggest that incorporation of Ga species improves Pd dispersion and generates a strong interaction between Ga₂O₃ and Pd interface or between Pd and support. DFT calculation results indicate that the strong adsorption of carbonyl group on Ga₂O₃/Pd interface facilitates the activation of EAQ and promotes the hydrogenation efficiency.     

Trans‐3,5‐dihydroperoxy‐3,5‐dimethyl‐1,2‐dioxalane/HBr System as New,Effective, Mild and Non‐toxic Reagent for Synthesis of 2‐Aryl‐1H‐benzothiazoles and 2‐Aryl‐1‐arylmethyl‐1H‐benzimidazoles

Ttrans‐3,5‐dihydroperoxy‐3,5‐dimethyl‐1,2‐dioxalane has been used as new, effective, solid, inexpensive and nontoxic oxidant for in situ generation of Br⁺ from HBr. This system has been applied as catalyst for synthesis of 2‐aryl‐1H‐benzothiazoles and 2‐aryl‐1‐arylmethyl‐1H‐benzimidazoles at room temperature in excellent yields and high purity.