Green and effective route for the synthesis of monodispersed palladium nanoparticles using herbal tea extract (Stachys lavandulifolia) as reductant,stabilizer and capping agent,and their application as homogeneous and reusable catalyst in Suzuki coupling reactions in water

A simple and eco‐friendly procedure has been devised for the green synthesis of palladium nanoparticles, using the aqueous extract of herbal tea (Stachys lavandulifolia), a renewable and nontoxic natural phyto‐exudate. The water‐soluble components of the extract act as reducing agent and stabilizer. This green route does not require a surfactant or capping agent for the growth of palladium nanoparticles. The generated nanoparticles were analysed using UV–visible spectroscopy, transmission electron microscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X‐ray analysis and inductively coupled plasma. The palladium nanoparticles having spherical shape and dimensions of between 5 and 7 nm were employed as a homogeneous catalyst for Suzuki coupling reactions conducted in water under mild conditions. Good yields of products, a facile work‐up, no evidence of leached palladium from the catalyst surface and smooth recovery of the catalysis by adding ethyl acetate, which could be reused at least eight times, confirm the very good efficiency of the catalytic reaction. Copyright © 2014 John Wiley & Sons, Ltd.     

Biochar as heterogeneous support for immobilization of Pd as efficient and reusable biocatalyst in C–C coupling reactions

Biochar is a stable and carbon‐rich solid which has a high density of carbonyl, hydroxyl and carboxylic acid functional groups on its surface. In this work, the surface of biochar nanoparticles (BNPs) was modified with 3‐choloropropyltrimtoxysilane and further 2‐(thiophen‐2‐yl)‐1H‐benzo[d]imidazole was anchored on its surface. Then, palladium nanoparticles were fabricated on the surface of the modified BNPs and further the catalytic application was studied as recyclable biocatalyst in carbon–carbon coupling reactions such as Suzuki–Miyaura and Heck–Mizoroki cross‐coupling reactions. The structure of the catalyst was characterized using scanning electron microscopy, transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, thermogravimetric analysis, X‐ray diffraction and atomic absorption spectroscopy. The catalyst can be reused several times without a decrease in its catalytic efficiency. In addition to the several advantages reported, application of biochar as catalyst support for the first time is a major novelty of the present work.     

Biosynthesis of palladium nanoparticles using Rosa canina fruit extract and their use as a heterogeneous and recyclable catalyst for Suzuki–Miyaura coupling reactions in water

A facile and green route for the synthesis of palladium nanoparticles was developed utilizing non‐toxic and renewable natural Rosa canina fruit extract as the reducing, stabilizing and capping agent, and they were applied as a heterogeneous catalyst for Suzuki coupling reactions between phenylboronic acid and a range of aryl halides containing iodo, bromo and chloro moieties in water under moderate reaction conditions. The structural investigation of the generated nanoparticles was performed with UV–visible spectroscopy, transmission electron microscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and energy‐dispersive X‐ray analysis. The method has some advantages such as high yields, efficiency, elimination of surfactant, chemical reductants, ligand and organic solvent, economic, cleaner reaction profiles, heterogeneous catalysis, simple methodology and easy workup. The catalyst can be recovered and reused seven times without any significant decrease in catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

A green synthesis of palladium nanoparticles by Sapindus mukorossi seed extract and use in efficient room temperature Suzuki–Miyaura cross‐coupling reaction

A simple and green method for the synthesis of palladium nanoparticles using an aqueous extract of Sapindus mukorossi seed has been demonstrated. The synthesized nanoparticles were characterized using UV–visible spectroscopy, powxder X‐ray diffraction, energy‐dispersive X‐ray analysis and transmission electron microscopy. The nanocatalyst was successfully utilized in an efficient Suzuki–Miyaura cross‐coupling reaction at room temperature.     

Green,cost‐effective and efficient procedure for Heck and Sonogashira coupling reactions using palladium nanoparticles supported on functionalized Fe3O4@SiO2 by polyvinyl alcohol as a highly active,durable and reusable catalyst

A novel heterogenized organometallic catalyst was synthesized by coordinating palladium with polyvinyl alcohol‐functionalized Fe₃O₄@SiO₂ nanospheres. This novel catalyst was characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, transmission electron microscope, field emission scanning electron microscope, dynamic light scattering, UV–vis spectroscopy, X‐ray photoelectron spectroscopy, energy dispersive X‐ray analysis, thermogravimetric analysis and inductively coupled plasma analysis. The prepared palladium nanoparticles supported on polyvinyl alcohol functionalized Fe₃O₄@SiO₂ nanoparticles were successfully applied as a magnetically recyclable catalyst in Heck and Sonogashira coupling reactions in water. They showed remarkable activity toward aryl halides (I, Br, Cl) using very low palladium loading in excellent yields and demonstrated high TONs (mmol of product per mmol of catalyst). Also, the catalyst could be magnetically separated and reused seven times without any appreciable loss of catalytic activity.     

Green synthesis of palladium nanoparticles using Pistacia atlantica kurdica gum and their catalytic performance in Mizoroki–Heck and Suzuki–Miyaura coupling reactions in aqueous solutions

A one‐pot green method for the synthesis of palladium nanoparticles (Pd‐NPs) supported on Pistacia atlantica kurdica (P. a. kurdica) gum is described. This natural gum is used as a reducing and stabilising agent. The formation of the Pd‐NPs/P. a. kurdica gum catalyst was verified using several techniques, such as Fourier transform infrared spectroscopy, ultraviolet–visible spectrophotometry, scanning and transmission electron microscopies, X‐ray diffraction, energy‐dispersive X‐ray spectroscopy, dynamic light scattering and wavelength‐dispersive X‐ray spectroscopy. The Pd‐NPs stabilised by P. a. kurdica gum were employed as a heterogeneous catalyst in Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions at low palladium loading (0.1 mol%) under aerobic, phosphine‐free and ligand‐free conditions in water. Product yields of up to 98%, a facile work‐up, no evidence of leached palladium from the catalyst surface and smooth recovery of the catalyst, which can be reused at least eight times, confirm the efficiency of the catalysts in the reactions investigated. Copyright © 2015 John Wiley & Sons, Ltd.     

Efficient synthesis of 5‐substituted tetrazoles catalysed by palladium–S‐methylisothiourea complex supported on boehmite nanoparticles

An efficient and general method is reported for the synthesis of 5‐substituted 1H ‐tetrazole derivatives in the presence of S ‐methylisothiourea complex of palladium immobilized on boehmite nanoparticles (Pd‐SMTU@boehmite) as an efficient and recyclable nanocatalyst. Boehmite nanoparticles were not sensitive to air or moisture and were prepared without inert atmosphere in water at room temperature. Then a novel type of phosphine‐free palladium complex was immobilized on these nanoparticles. This catalyst was characterized using Fourier transform infrared, thermogravimetric, Brunauer–Emmett–Teller, transmission and scanning electron microscopic, energy‐dispersive X‐ray spectroscopic, X‐ray diffraction and inductively coupled plasma optical emission spectroscopic techniques. The catalyst was reused several times without palladium leaching or change in its structure.     

Palladium–S‐propyl‐2‐aminobenzothioate immobilized on Fe3O4 magnetic nanoparticles as catalyst for Suzuki and Heck reactions in water or poly(ethylene glycol)

A moisture‐ and air‐stable heterogenized palladium catalyst was synthesized by coordination of palladium with S‐propyl‐2‐aminothiobenzamide supported on Fe₃O₄ magnetic nanoparticles. The prepared nanocatalyst was characterized using Fourier transform infrared, energy‐dispersive X‐ray and inductively coupled plasma atomic emission spectroscopies, X‐ray diffraction, vibrating sample magnetometry, transmission and scanning electron microscopies, dynamic laser scattering and thermogravimetric analysis. This catalyst could be dispersed homogeneously in water or poly(ethylene glycol) and further applied as an excellent nano‐organometal catalyst for Suzuki and Heck reactions. The catalyst was easily separated with the assistance of an external magnet from the reaction mixture and reused for several consecutive runs without significant loss of its catalytic efficiency or palladium leaching. The leaching of catalyst was examined using hot filtration and inductively coupled plasma atomic emission spectroscopy. Also, the effects of various reaction parameters on the Suzuki and Heck reactions are discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Magnetic nanoparticle‐tethered Schiff base–palladium(II): Highly active and reusable heterogeneous catalyst for Suzuki–Miyaura cross‐coupling and reduction of nitroarenes in aqueous medium at room temperature

As a continuation of our efforts to develop new heterogeneous nanomagnetic catalysts for greener reactions, we identified a Schiff base–palladium(II) complex anchored on magnetic nanoparticles (SB‐Pd@MNPs) as a highly active nanomagnetic catalyst for Suzuki–Miyaura cross‐coupling reactions between phenylboronic acid and aryl halides and for the reduction of nitroarenes using sodium borohydride in an aqueous medium at room temperature. The SB‐Pd@MNPs nanomagnetic catalyst shows notable advantages such as simplicity of operation, excellent yields, short reaction times, heterogeneous nature, easy magnetic work up and recyclability. Characterization of the synthesized SB‐Pd@MNPs nanomagnetic catalyst was performed with various physicochemical methods such as attenuated total reflectance infrared spectroscopy, UV–visible spectroscopy, inductively coupled plasma atomic emission spectroscopy, energy‐dispersive X‐ray spectroscopy, field‐emission scanning electron microscopy, transmission electron microscopy, powder X‐ray powder diffraction, thermogravimetric analysis and Brunauer–Emmett–Teller surface area analysis.     

Biosynthesis of palladium nanoparticles as a heterogeneous and reusable nanocatalyst for reduction of nitroarenes and Suzuki coupling reactions

A facile and green route for the synthesis of palladium nanoparticles (Pd‐NPs) was developed utilizing non‐toxic and renewable natural green tea extract as the reducing, stabilizing and capping agent. The as‐prepared Pd‐NPs@Oak Gum catalyst was characterized using UV–visible spectroscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy and energy dispersive X‐ray spectroscopy. The Pd‐NPs@Oak Gum catalyst could be used as an efficient and heterogeneous catalyst for Suzuki coupling reactions between phenylboronic acid and a range of aryl halides containing iodo, bromo and chloro moieties and also for the reduction of nitroarenes using sodium borohydride in an environmental friendly medium. Excellent yields of products were obtained with a wide range of substrates and the catalyst was recycled multiple times without any significant loss of its catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

Finely dispersed palladium on silk‐fibroin as an efficient and ligand‐free catalyst for Heck cross‐coupling reaction

A palladium–fibroin complex (Pd/Fib.) was prepared by the addition of sonicated fibroin fiber in water to palladium acetate solution. Pd (OAc)₂ was absorbed by fibroin and reduced with NaBH₄ at room temperature to the Pd(0) nanoparticles. Powder‐X‐ray diffraction, scanning electron microscopy–energy‐dispersive X‐ray spectroscopy, Fourier transform‐infrared, CHN elemental analysis and inductively coupled plasma‐atomic emission spectroscopy were carried out to characterize the Pd/Fib. catalyst. Catalytic activity of this finely dispersed palladium was examined in the Heck coupling reaction. The catalytic coupling of aryl halides (‐Cl, ‐Br, ‐I) and olefins led to the formation of the corresponding coupled products in moderate to high yields under air atmosphere. A variety of substrates, including electron‐rich and electron‐poor aryl halides, were converted smoothly to the targeted products in simple procedure. Heterogeneous supported Pd catalyst can be recycled and reused several times.     

Synthesis of dendrimers terminated by DABCO ligands and applications of its palladium nanoparticles for catalyzing Suzuki–Miyaura and Mizoroki–Heck couplings

A new kind of silica‐supported third‐generation dendrimers capped by 1,4‐diaza‐bicyclo[2.2.2]octane (DABCO) group‐stabilized palladium(0) nanoparticles, and their enhanced catalytic activity in Suzuki–Miyaura and Mizoroki–Heck reactions in excellent yield under mild conditions, was reported. The resulting silica‐supported dendrimer‐stabilized palladium(0) nanoparticles with a particle size of 10–20 nm were prepared in situ by treatment with PdCl₂ and hydrazine in ethanol at 60 °C for 24 h. The catalyst as prepared was characterized by FT‐IR, X‐ray diffraction, thermal analysis, elementary analysis (EA), scanning electron microscopy and transmission electron microscopy. Recycling experiments showed that the catalyst could be easily recovered by simple filtration and reused for up to five cycles without losing its activity. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and characterization of bromine source supported on magnetic Fe3O4 nanoparticles: A new,versatile and efficient magnetically separable catalyst for organic synthesis

Tribenzylammonium tribromide supported onto magnetic nanoparticles (Br₃‐TBA‐Fe₃O₄) as a bromine source was successfully synthesized and characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy and vibrating sample magnetometry. The synthesized catalyst is shown to be a versatile and highly efficient heterogeneous catalyst for the Knoevenagel condensation and synthesis of 2,3‐dihydroquinazolin‐4(1H )‐one and polyhydroquinoline derivatives. To the best of the authors' knowledge, this is the first report of the use of a bromine source immobilized on Fe₃O₄ nanoparticles as a magnetically separable catalyst for these reactions. The nanosolid catalyst can be magnetically recovered and reused readily several times without significant loss in catalytic efficiency.     

Sustainable Catalysis: Rational Pd Loading on MIL‐101Cr‐NH2 for More Efficient and Recyclable Suzuki–Miyaura Reactions

Palladium nanoparticles have been immobilized into an amino‐functionalized metal–organic framework (MOF), MIL‐101Cr‐NH₂, to form Pd@MIL‐101Cr‐NH₂. Four materials with different loadings of palladium have been prepared (denoted as 4‐, 8‐, 12‐, and 16 wt %Pd@MIL‐101Cr‐NH₂). The effects of catalyst loading and the size and distribution of the Pd nanoparticles on the catalytic performance have been studied. The catalysts were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier‐transform infrared (FTIR) spectroscopy, powder X‐ray diffraction (PXRD), N₂‐sorption isotherms, elemental analysis, and thermogravimetric analysis (TGA). To better characterize the palladium nanoparticles and their distribution in MIL‐101Cr‐NH₂, electron tomography was employed to reconstruct the 3D volume of 8 wt %Pd@MIL‐101Cr‐NH₂ particles. The pair distribution functions (PDFs) of the samples were extracted from total scattering experiments using high‐energy X‐rays (60 keV). The catalytic activity of the four MOF materials with different loadings of palladium nanoparticles was studied in the Suzuki–Miyaura cross‐coupling reaction. The best catalytic performance was obtained with the MOF that contained 8 wt % palladium nanoparticles. The metallic palladium nanoparticles were homogeneously distributed, with an average size of 2.6 nm. Excellent yields were obtained for a wide scope of substrates under remarkably mild conditions (water, aerobic conditions, room temperature, catalyst loading as low as 0.15 mol %). The material can be recycled at least 10 times without alteration of its catalytic properties.     

First report of the direct supporting of palladium–arginine complex on boehmite nanoparticles and application in the synthesis of 5‐substituted tetrazoles

Boehmite nanoparticles are aluminium oxide hydroxide (γ‐AlOOH) particles, which were prepared using a simple and inexpensive procedure in water at room temperature and further modified using arginine. Subsequently palladium particles were immobilized on their surface to prepare Pd‐Arg@boehmite. This novel nanostructured compound was fully characterized using thermogravimetric analysis, X‐ray diffraction, inductively coupled plasma optical emission (ICP‐OES) and energy‐dispersive X‐ray spectroscopies, and scanning and transmission electron microscopies. Finally, this catalyst was applied as a moisture‐ and air‐stable heterogeneous material for the synthesis of 5‐substituted 1H –tetrazole derivatives. The leaching of palladium and heterogeneity of the catalyst were studied using hot filtration and ICP‐OES. This catalyst demonstrated remarkable recyclability. The novelty of this work is that it represents the first time an amino acid has been grafted on boehmite nanoparticles.     

Greener approach for synthesis of monodispersed palladium nanoparticles using aqueous extract of green tea and their catalytic activity for the Suzuki–Miyaura coupling reaction and the reduction of nitroarenes

A facile and green route for the synthesis of palladium nanoparticles (NPs) was developed utilizing non‐toxic and renewable natural green tea extract as the reducing, stabilizing and capping agent. The as‐prepared Pd‐NPs@G.Tea extract was characterized using UV–visible spectroscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, field‐emission scanning electron microscopy, transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. The Pd‐NPs@G.Tea extract could be used as an efficient and heterogeneous catalyst for Suzuki coupling reactions between phenylboronic acid and a range of aryl halides containing iodo, bromo and chloro moieties, and also for the reduction of nitroarenes using sodium borohydride in an environmentally friendly medium. Excellent yields of products were obtained with a wide range of substrates and the catalyst was recycled multiple times without any significant loss of its catalytic activity.     

Synthesis of magnetically recyclable Fe3O4@[(EtO)3Si–L1H]/Pd(II) nanocatalyst and application in Suzuki and Heck coupling reactions

A Pd(II) Schiff base complex as an efficient and highly heterogeneous catalyst was developed by immobilization of a palladium complex on the surface of modified Fe₃O₄ magnetite nanoparticles. These surface‐modified nanoparticles were characterized using various techniques such as transmission electron microscopy, X‐ray diffraction, thermogravimetric analysis, vibrating sample magnetometry, elemental analysis and Fourier transform infrared spectroscopy. The palladium catalyst exhibited efficient catalytic activity in Suzuki and Heck coupling reactions. This method has notable advantages such as excellent chemoselectivity, mild reaction conditions, short reaction times and excellent yields. The yields of the products were in the range 85–100%. Also, the nanocatalyst can be easily recovered with a permanent magnet and reused at least five times without noticeable leaching or loss of its catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.     

CoFe2O4@SiO2‐CPTES‐Guanidine‐Cu(II): A novel and reusable nanocatalyst for the synthesis of 2,3‐dihydroquinazolin‐4(1H)‐ones and polyhydroquinolines and oxidation of sulfides

CoFe₂O₄@SiO₂‐CPTES‐Guanidine‐Cu(II) magnetic nanoparticles were synthesized and used as a new, inexpensive and efficient heterogeneous catalyst for the synthesis of polyhydroquinolines and 2,3‐dihydroquinazoline‐4(1H)‐ones and for the oxidation of sulfides. The structure of this nanocatalyst was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, vibrating sample magnetometry, thermogravimetric analysis, X‐ray diffraction and inductively coupled plasma optical emission spectrometry. Simple preparation, high catalytic activity, simple operation, high yields, use of green solvents, easy magnetic separation and reusability of the catalyst are some of the advantages of this protocol.     

Fullerene–Ionic‐Liquid Conjugates: A New Class of Hybrid Materials with Unprecedented Properties

A modular approach has been followed for the synthesis of a series of fullerene–ionic‐liquid (IL) hybrids in which the number of IL moieties (two or twelve), anion, and cation have been varied. The combination of C₆₀ and IL give rise to new unique properties in the conjugates such as solubility in water, which was higher than 800 mg mL^?1 in several cases. In addition, one of the C₆₀–IL hybrids has been employed for the immobilization of palladium nanoparticles through ion exchange followed by reduction with sodium borohydride. Surprisingly, during the reduction several carbon nanostructures were formed that comprised nano‐onions and nanocages with few‐layer graphene sidewalls, which have been characterized by means of thermogravimetric analysis (TGA), X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), scanning electron microscopy/energy‐dispersive X‐ray analysis (SEM‐EDAX), and high‐resolution transmission electron microscopy (HRTEM). Finally, the material thus obtained was successfully applied as catalyst in Suzuki and Mizoroki–Heck reactions in a concentration of just 0.2 mol %. In the former process it was recyclable for five runs with no loss in activity.     

Fe3O4@SiO2@l‐arginine@Pd(0): a new magnetically retrievable heterogeneous nanocatalyst with high efficiency for C–C bond formation

The surface of Fe₃O₄@SiO₂ nanoparticles was modified using l ‐arginine as a green and available amino acid to trap palladium nanoparticles through a strong interaction between the metal nanoparticles and functional groups of the amino acid. The proposed green synthetic method takes advantage of nontoxic reagents through a simple procedure. Characterization of Fe₃O₄@SiO₂@l ‐arginine@Pd(0) was done using Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, X‐ray diffraction, vibrating sample magnetometry and inductively coupled plasma analysis. The catalytic activity of Fe₃O₄@SiO₂@l ‐arginine@Pd(0) as a new nanocatalyst was investigated in C – C coupling reactions. Waste‐free, use of green medium, efficient synthesis leading to high yield of products, eco‐friendly and economic catalyst, excellent reusability of the nanocatalyst and short reaction time are the main advantages of the method presented. Copyright © 2016 John Wiley & Sons, Ltd.