Catalytic activity and facile recovery of a cyclometalated N‐heterocyclic carbene palladium(II) complex immobilized by non‐covalent interactions on reduced graphene oxide

The growing concern about the potentially adverse effects of the production of chemical compounds on the sustainable development of the environment has led to a great deal of efforts to search for low‐cost and environmentally friendly catalytic systems. A pyrene‐tagged N‐heterocyclic carbene palladacycle complex ([Pd{(C,N)C₆H₄CH₂NH(Et)}(Imd‐P)Br]) was prepared by reacting imidazolium salt with dimer ([Pd₂{(C,N)C₆H₄CH₂NH(Et)}₂(μ‐OAc)₂]). Then, it was immobilized onto the surface of reduced graphene oxide (rGO) via π–π stacking forces. The hybrid compound ((NHC)Pd‐rGO) was made in a one‐step process. Various techniques were employed to characterize the compound. In addition, computational studies were used to verify the interaction between the Pd complex and rGO. The catalytic activity of the molecular complex and hybrid material was evaluated in both Suzuki–Miyaura cross‐coupling reactions and reduction of p‐nitrophenol to p‐aminophenol. The catalytic activity of the hybrid material was enhanced in comparison with the corresponding homogeneous analogue. Thus, rGO seems to play a significant role in catalytic activity. Hot filtration experiments show the heterogeneous nature of the catalyst resulting from the strong interaction between pyrene and graphene. The hybrid (NHC)Pd‐rGO material could be recycled up to six times with no decrease in catalytic activity.     

Easy conversion of nitrogen‐rich silk cocoon biomass to magnetic nitrogen‐doped carbon nanomaterial for supporting of Palladium and its application

In this study, magnetic nitrogen‐doped carbon (MNC) was fabricated through facile carbonization and activation of natural silk cocoons containing nitrogen and then combined with Fe₃O₄ nanoparticles to create a good support material for palladium. Palladium immobilization on the support resulted in the formation of magnetic nitrogen‐doped carbon‐Pd (MNC‐Pd). The prepared heterogeneous catalyst was well characterized using FT‐IR, TGA, EDX, FE‐SEM, XRD, VSM, and ICP‐OES techniques. Thereafter, the synthesis of biaryl compounds was conducted to investigate the catalyst performance via the reaction of aryl halides and phenylboronic acid. Further, the catalyst could be used and recycled for six consecutive runs without any significant loss in its activity.     

18‐Crown‐6 promoting Pd/C‐catalyzed cross‐coupling reaction of aryl bromides and arylboronic acids in aqueous media

Pd/C‐catalyzed Suzuki–Miyaura cross‐coupling between aryl bromides and arylboronic acids in 50% methanol aqueous solution proceeded smoothly in the presence of 18‐crown‐6. Various aryl bromides bearing electron‐withdrawing groups and electron‐donating groups coupled with arylboronic acid in high yields. In addition, the catalyst could be recycled five times without loss of activity. Copyright © 2012 John Wiley & Sons, Ltd.     

Pd nanoparticles immobilized on PNIPAM–halloysite: highly active and reusable catalyst for Suzuki–Miyaura coupling reactions in water

Poly(N‐isopropylacrylamide)–halloysite (PNIPAM‐HNT) nanocomposites exhibited inverse temperature solubility with a lower critical solution temperature (LCST) in water. Palladium (Pd) nanoparticles were anchored on PNIPAM‐HNT nanocomposites with various amounts of HNT from 5 to 30 wt%. These Pd catalysts exhibited excellent reactivities for Suzuki–Miyaura coupling reactions at 50–70 °C in water. In particular, Pd anchored PNIPAM/HNT (95:5 w/w ratio) nanocomposites showed excellent recyclability up to 10 times in 96% average yield by simple filtration. Copyright © 2014 John Wiley & Sons, Ltd.     

Palladium nanoparticles deposited on a graphene–benzimidazole support as an efficient and recyclable catalyst for aqueous‐phase Suzuki–Miyaura coupling reaction

Graphene oxide was functionalized with benzimidazole for palladium immobilization. The resultant graphene–benzimidazole‐supported palladium composite (G‐BI‐Pd) was characterized using infrared and Raman spectroscopies, transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. G‐BI‐Pd showed excellent catalytic activity and fast reaction kinetics in the aqueous‐phase Suzuki–Miyaura reaction of aryl iodides and bromides with phenylboronic acid under relatively mild conditions (5–25 min, 80 °C). The catalyst can be used several times without any significant loss of its catalytic activity.     

Acid‐treated g‐C3N4‐Cu2O composite catalyst with enhanced photocatalytic activity under visible‐light irradiation

Acid‐treated g‐C₃N₄‐Cu₂O was prepared by hydrothermal reduction followed by high temperature calcination and acid exfoliation. The structures and properties of as‐synthesized samples were characterized using a range of techniques, such as X‐ray photoelectron spectroscopy, scanning electron microscopy, Photoluminescence Spectroscopy and the Brunauer–Emmett–Teller (BET) theory. The photocatalytic activity was evaluated by measuring the photodegradation of methyl orange under visible‐light irradiation. Based on the results of TEM, XPS, EPR and other techniques, it was verified that a heterojunction was formed. The acid treatment process can increase the specific surface area to form abundant heterojunction interfaces as channels for photo‐generated carrier separation, thereby enhancing its light utilization and quantum efficiency. Results indicate that acid‐treated g‐C₃N₄‐Cu₂O possesses a large specific surface area, which provides plentiful activated sites for heterojunctions to form; in addition, it showed a high visible light effect and the minimum charge‐transfer resistance. Furthermore, the g‐C₃N₄‐Cu₂O material exhibits high levels of effectiveness and stability. Electron paramagnetic resonance and a series of radical trapping experiments demonstrate that the holes and ?O₂^? could be the main active species in methyl orange photodegradation. This work could provide new insights into the fabrication of composite materials as high‐performance photocatalysts, and facilitate their application in addressing environmental protection issues.     

Highly efficient Pd‐PEPPSI‐IPr catalyst for N‐(4‐pyridazinyl)‐bridged bicyclic sulfonamides via Suzuki–Miyaura coupling reaction

A protocol for the Suzuki–Miyaura coupling of novel 2‐(6‐chloropyridazin‐3‐yl)‐5‐(aryl/heteroarylsulfonyl)‐2,5‐diazabicyclo[2.2.1]heptanes and heteroarylboronic acids to afford variety of coupled products was realized. Pd‐PEPPSI‐IPr catalyst was found to be a powerful and reusable catalyst under relatively mild reaction conditions.     

Palladium immobilized on amidoxime‐functionalized magnetic Fe3O4 nanoparticles: a highly stable and efficient magnetically recoverable nanocatalyst for sonogashira coupling reaction

We describe the synthesis of a novel Fe₃O₄/amidoxime (AO)/Pd nanocatalyst by grafting of AO groups on Fe₃O₄ nanoparticles and subsequent deposition of Pd nanoparticles. Prior to grafting of AO, the 2‐cyanoethyl‐functionalized Fe₃O₄ nanoparticles prepared through combining 2‐cyanoethyltriethoxysilane and Fe₃O₄ were treated with hydroxylamine. The AO‐grafted Fe₃O₄ nanoparticles were then used as a platform for the deposition of Pd nanoparticles. The catalyst was characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, scanning and transmission electron microscopies, vibrating sample magnetometry, wavelength‐ and energy‐dispersive X‐ray spectroscopies and inductively coupled plasma analysis. Fe₃O₄/AO/Pd is novel phosphine‐free recyclable heterogeneous catalyst for Sonogashira reactions. Interestingly, the novel catalyst could be recovered in a facile manner from the reaction mixture by applying an external magnet device and recycled seven times without any significant loss in activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Templating effect of carbon nanoforms on highly cross‐linked imidazolium network: Catalytic activity of the resulting hybrids with Pd nanoparticles

Two different carbon nanoforms (CNFs), namely multi‐walled carbon nanotubes (MWCNTs) and carbon nanohorns (CNHs), have been chosen as support for the direct polymerization of a bis‐vinylimidazolium salt. Transmission electron microscopy analyses revealed a templating effect of the CNFs on the growth of the polymeric network, which perfectly covers their whole surfaces creating a cylindrical or spherical coating for MWCNTs and CNHs, respectively. Subsequently, the CNFs‐polyimidazolium have been used as stabilizers for Pd nanoparticles (Pd NPs), and the obtained materials have been characterized by means of analytical and spectroscopic techniques and then employed as easily recoverable and recyclable catalysts for Suzuki and Heck reactions. Quantitative conversions have been obtained in almost all the explored reactions, even employing low loading of catalyst (down to 0.007 mol%). Suzuki reactions were carried out in pure water under aerobic conditions. Both materials showed excellent activity and recyclability for the investigated C‐C coupling reactions, with the CNHs‐based material resulting slightly more active than the MWCNTs‐based one due to a higher superficial exposure of Pd NPs.     

Palladium on magnetic Irish moss: A new nano‐biocatalyst for suzuki type cross‐coupling reactions

A novel heterogeneous magnetic palladium nano‐biocatalyst was designed by utilizing Irish moss, a family of sulfated polysaccharides extracted from algae, as a natural biopolymer. This magnetic Irish moss decorated with palladium (Pd–Fe₃O₄@IM) to form a biomagnetic catalytic system was synthesized and well characterized by FT–IR analysis, X‐ray powder diffraction, field emission scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, atomic absorption spectroscopy and transmission electron microscopy. The catalyst was stable to air and moisture and displayed high catalytic activity in ligand‐free Suzuki–Miyaura cross‐coupling reactions conducted under green chemistry reaction conditions. The aromatic ketones are produced by the cross‐coupling reaction between acid chlorides and aryl boronic acid derivatives in high yields.     

A rapid and efficient catalysis system for the synthesis of 4‐vinylbiphenyl derivatives

A series of 4‐vinylbiphenyl derivatives were synthesized by Pd(OAc)₂/PCy₃‐catalyzed Suzuki–Miyaura reaction in the presence of K₃PO₄.3H₂O as base in toluene at 80°C for only 10–30 min, and the corresponding products achieved 65–98% yields. According to this efficient C―C bond‐forming method, the obtained yields of 4‐vinylbiphenyl liquid crystal compounds were up to 92–96%. Copyright © 2013 John Wiley & Sons, Ltd.     

Pd(l‐proline)2 complex: an efficient catalyst for Suzuki–Miyaura coupling reaction in neat water

An efficient catalytic system for Suzuki–Miyaura coupling reactions in neat water has been developed by using a water‐soluble Pd(l ‐proline)₂ catalyst. Under the optimized conditions, various biaryl compounds were obtained in good to excellent yields and a wide range of functional groups on the tested substrates were well tolerated. The catalytic system could be reused at least six times with no significant loss in its activity. Copyright © 2014 John Wiley & Sons, Ltd.     

Palladium nanoparticles immobilized on amphiphilic and hyperbranched polymer‐functionalized magnetic nanoparticles: An efficient semi‐heterogeneous catalyst for Heck reaction

To address the obstacles facing the use of palladium‐based homogeneous and heterogeneous catalysts in C─C cross‐coupling reactions, a novel semi‐heterogeneous support was developed based on hyperbranched poly(ethylene glycol)‐block ‐poly(citric acid)‐functionalized Fe₃O₄ magnetic nanoparticles (Fe₃O₄@PCA‐b ‐PEG). Because of the surface modification of the Fe₃O₄ nanoparticles with amphiphilic and hyperbranched polymers (PCA‐b ‐PEG), these hybrid materials are not only soluble in a wide range of solvents (e.g. water, ethanol and dimethylformamide) but also are able to trap Pd²⁺ ions via complex formation of free carboxyl groups of the PCA dendrimer with metal ions. The reduction of trapped palladium ions in the dendritic shell of Fe₃O₄@PCA‐b ‐PEG leads to immobilized palladium nanoparticles. The morphology and structural features of the catalyst were characterized using various microscopic and spectroscopic techniques. The catalyst was effectively used in the palladium‐catalysed Mizoroki–Heck coupling reaction in water as a green solvent. In addition, the catalyst can be easily recovered from the reaction mixture by applying an external magnetic field and reused for more than ten consecutive cycles without much loss in activity, exhibiting an example of a sustainable and green methodology.     

Palladium supported on modified magnetic nanoparticles: a phosphine‐free and heterogeneous catalyst for Suzuki and Stille reactions

An efficient magnetic nanoparticle‐supported palladium (Fe₃O₄/SiO₂‐PAP‐Pd) catalyst is reported for the Suzuki cross‐coupling and Stille reactions. This method provides a novel and much improved modification of the Suzuki and Stille coupling reactions in terms of phosphine‐free catalyst, short reaction time, clean reaction and small quantity of catalyst. Another important feature of this method is that the catalyst can be easily recovered from the reaction mixture and reused with no loss of its catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Well‐dispersed N‐heterocyclic carbene–palladium complex anchored onto poly(acrylic acid)/poly(vinyl alcohol) nanofibers: Novel,superior and ecofriendly nanocatalyst for the Suzuki–Miyaura cross‐coupling reaction

Polymeric nanocomposite@Pd is one of the crown jewels for the catalysis of cross‐coupling reactions. This Pd nanocomposite on various polymeric supports has been well established to catalyze cross‐coupling reactions, but its preparation supported on the surface of nanofibers has been largely overlooked. Herein, we report the preparation of a poly(acrylic acid) (PAA)/poly(vinyl alcohol) (PVA) nanofiber‐supported N‐heterocyclic carbene–Pd complex. The first step involves the preparation of PAA/PVA nanofibers using the electrospinning process. The second step comprises the reaction of water‐soluble poly(ethylene glycol)‐imidazole with modified PAA/PVA nanofibers followed by introduction of PdCl₂ to achieve successfully the desired nanocomposite. The catalytic activity of this nanocomposite was examined in the expeditious synthesis of biaryl compounds using the Suzuki–Miyaura cross‐coupling reaction under mild reaction conditions. The composite offers multiple features such as good hydrophilic properties, high surface area, admirable potential in repeatability tests and being recyclable for several runs without significant loss in its activity under the optimum reaction conditions. Our results showed the superior applicability of this novel nanocatalyst in terms of conversion reaction, yields and turnover frequencies. The structure of the catalyst was characterized using a variety of techniques.     

Magnetic iron oxide nanoparticles–N‐heterocyclic carbene–palladium(II): a new,efficient and robust recyclable catalyst for Mizoroki–Heck and Suzuki–Miyaura coupling reactions

A new and efficient nanoparticle–N‐heterocyclic carbene–palladium complex was synthesized and characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy, energy‐dispersive X‐ray analysis, X‐ray diffraction, transmission electron microscopy, elemental analysis, inductively coupled plasma analysis and vibrating sample magnetometry. This catalytic system was found to be a highly active catalyst in the Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions. These reactions were best performed in dimethylformamide and water, respectively, in the presence of only 0.054 mol% of palladium under mild conditions. Moreover, the catalyst could be recovered easily and reused at least ten times without any considerable loss of its catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

Pd(OAc)2@SBA‐15/PrEn nanoreactor: a highly active,reusable and selective phosphine‐free catalyst for Suzuki–Miyaura cross‐coupling reaction in aqueous media

A series of ordered mesoporous organic–inorganic hybrid material was designed by using the amine‐functionalized SBA‐15 (PdX₂@SBA‐15/N_Y, Y = 1, 2) as solid support for palladium complexes. Among them, the Pd(OAc)₂/ethylenediamine complex encapsulated into SBA‐15 (Pd(OAc)₂@SBA‐15/PrEn or Pd(OAc)₂@SBA‐15/PrNHEtNH₂) exhibits higher activity and selectivity toward Suzuki cross‐coupling reaction under aerobic conditions and water solvent mixture. The SBA‐15/PrEn supported palladium pre‐catalyst could be separated easily from reaction products and used repetitively several times, showing its superiority over homogeneous catalysts for industrial and chemical applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Degradation of carbon tetrachloride using ultrasound‐assisted nanoscaled zero‐valent iron particles@sulfur/nitrogen dual‐doped reduced graphene oxide composite: Kinetics,activation energy,effects of reaction conditions and degradation mechanism

We report a study of the synthesis of nanoscale zero‐valent iron particles stabilized by sulfur/nitrogen dual‐doped reduced graphene oxide (i.e. nZVI@SN‐rGO) and their applications as major reactants for the dechlorination of carbon tetrachloride (CT) by combining sonolysis with consideration of several operation parameters such as pH, temperature, catalyst dosage, as well as in the presence of common inorganic anions. The experimental results showed that the modified technology could remain effective for up to 180 min of reaction time under optimal conditions. Especially, there was no significant reduction in the removal efficiency toward CT even after five cycles, which was indicative of good stability. A study of the effects of common inorganic anions revealed that the presence of Clˉ and HCO₃ˉ exhibited different positive effects in the following order: Clˉ > HCO₃ˉ; NO₃ˉ and SO₄²ˉ showed inhibition effects on CT removal. The structure and properties of nZVI@SN‐rGO were characterized using X‐ray diffraction, scanning electron microscopy, surface area analysis, Raman spectroscopy and X‐ray photoelectron spectroscopy. Additionally, the corresponding activation energy was approximately 31.04 kJ mol^?1, suggesting that the surface chemical reaction rather than diffusion was the rate‐limiting step in the CT decomposition process. More importantly, the possible reaction mechanism and dechlorination pathway of CT using the ultrasound‐assisted nZVI@SN‐rGO system were also investigated.     

Novel palladium nanoparticles supported on β‐cyclodextrin@graphene oxide as magnetically recyclable catalyst for Suzuki–Miyaura cross‐coupling reaction with two different approaches in bio‐based solvents

A novel nanocatalyst was designed and prepared. Initially, the surface of magnetic graphene oxide (M‐GO) was modified using thionyl chloride, tris(hydroxymethyl)aminomethane and acryloyl chloride as linkers which provide reactive C═C bonds for the polymerization of vinylic monomers. Separately, β‐cyclodextrin (β‐CD) was treated with acryloyl chloride to provide a modified β‐CD. Then, in the presence methylenebisacrylamide as a cross‐linker, monomers of modified β‐CD and acrylamide were polymerized on the surface of the pre‐prepared M‐GO. Finally, palladium acetate and sodium borohydride were added to this composite to afford supported palladium nanoparticles. This fabricated nanocomposite was fully characterized using various techniques. The efficiency of this easily separable and reusable heterogeneous catalyst was successfully examined in Suzuki–Miyaura cross‐coupling reactions of aryl halides and boronic acid as well as in modified Suzuki–Miyaura cross‐coupling reactions of N‐acylsuccinimides and boronic acid in green media. The results showed that the nanocatalyst was efficient in coupling reactions for direct formation of the corresponding biphenyl as well as benzophenone derivatives in green media based on bio‐based solvents. In addition, the nanocatalyst was easily separable, using an external magnet, and could be reused several times without significant loss of activity under the optimum reaction conditions.     

In situ green synthesis of Cu‐Ni bimetallic nanoparticles supported on reduced graphene oxide as an effective and recyclable catalyst for the synthesis of N‐benzyl‐N‐aryl‐5‐amino‐1H‐tetrazoles

In the present work, for the first time we have designed a novel approach for the synthesis of N‐benzyl‐N‐aryl‐5‐amino‐1H‐tetrazoles using reduced graphene oxide (rGO) decorated with Cu‐Ni bimetallic nanoparticles (NPs). In situ synthesis of Cu/Ni/rGO nanocomposite was performed by a cost efficient, surfactant‐free and environmentally benign method using Crataegus azarolus var. aronia L. leaf extract as a stabilizing and reducing agent. Phytochemicals present in the extract can be used to reduce Cu²⁺ and Ni²⁺ ions and GO to Cu NPs, Ni NPs and rGO, respectively. Analyses by means of FT‐IR, UV–Vis, EDS, TEM, FESEM, XRD and elemental mapping confirmed the Cu/Ni/rGO formation and also FT‐IR, NMR, and mass spectroscopy as well as elemental analysis were used to characterize the tetrazoles. The Cu/Ni/rGO nanocomposite showed the superior catalytic activity for the synthesis of N‐benzyl‐N‐aryl‐5‐amino‐1H‐tetrazoles within a short reaction time and high yields. Furthermore, this protocol eliminates the need to handle HN₃.