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.     

Synergistic Activities in the Ullmann Coupling of Chloroarenes at Ambient Temperature by Pd‐Supported Calcined Ferrocenated La2O3

Novel palladium‐doped nanoparticles have been explored to serve as the first metal oxide‐derived heterogeneous catalyst for Ullmann reaction of chloroarenes under mild condition (34 °C). This heterogeneous catalyst exhibited high catalytic activity towards the Ullmann homocoupling of chloroarenes into a series of useful symmetrically biaryl products with good to excellent yields in the presence of ethanol and NaOH, thereby leading to green and economical Ullmann reaction. The produced nanoparticles were successfully characterized by various techniques including PXRD, XPS, HRTEM, SEM‐EDS, BET, TGA techniques, elemental mapping analysis and ICP‐OES. Interestingly, based on characterization and experimental data, a reasonable mechanism has been proposed. Also, the formation of aryl methyl ketone as a by‐product has been further confirmed by isotopic labelling experiments that the acetyl moiety is derived from ethanol. Moreover, the catalyst was stable and could be easily reused up to 5 times under atmospheric air without suffering significant loss in catalytic activity.     

An efficient,mild and selective Ullmann‐type N‐arylation of indoles catalysed by Pd immobilized on amidoxime‐functionalized mesoporous SBA‐15 as heterogeneous and recyclable nanocatalyst

A wide range of N‐arylated indoles were selectively synthesized through intermolecular C(aryl)? N bond formation from the corresponding aryl iodides and indoles through Ullmann‐type coupling reactions in the presence of a catalytic amount of Pd immobilized on amidoxime‐functionalized mesoporous SBA‐15 (SBA‐15/AO/Pd(0)) under mild reaction conditions. These cross‐coupled products were obtained in excellent yields under mild conditions at extremely low palladium loading (ca 0.3 mol%), and the heterogeneous catalyst can be readily recovered by simple filtration and reused seven times with loss in its activity. Copyright © 2015 John Wiley & Sons, Ltd.     

A highly active multi‐usable palladium pyridylfluorene film‐based catalyst for C–C cross‐coupling reactions

The two terminal pyridyl nitrogen atoms of 2,7‐bis(4‐pyridyl)fluorene ( 1 ) were coordinated to Pd(II) ions to give self‐assembled, multilayer films using the layer‐by‐layer (LbL) method. The films were prepared by alternately dipping the substrate, pre‐coated with a polyethyleneimine layer, in aqueous solutions of PdCl₂ and ethanol solutions of 1 . The resulting films were characterized using UV–visible absorption spectroscopy, atomic force microscopy (AFM), X‐ray photoelectron spectroscopy, scanning electron microscopy (SEM) and inductively coupled plasma atomic emission spectroscopy (ICP‐AES). UV–visible spectra and SEM images show almost uniform growth of the film in a near ideal LbL manner. AFM images show that nanostructured aggregates of Pd(II) complexes form on the surface. With an increase in the number of Pd(II)/ 1 bilayers, more particulate aggregates are distributed on the surface. When released from the substrate, the Pd(II) complex nanostructure shows high catalytic activity for Suzuki–Miyaura and Mizoroki–Heck cross‐coupling reactions. The catalyst loading is as low as 9.1 × 10^?3 mol% Pd, as measured using ICP‐AES, and high turnover numbers of up to 1.08 × 10⁴ are obtained. Copyright © 2015 John Wiley & Sons, Ltd.     

Modification of the Solution Behavior of Pd12L24 Metal–Organic Nanocages via PEGylation

The dilute solutions behaviors of Pd₁₂L₂₄ metal–organic nanocage and its two PEGylated derivatives are explored. The basic nanocages can self‐assemble into vesicle‐like blackberry structures in polar solvents via counterion‐mediated attraction, whereas the PEGylated nanocages always stay as discrete ions under the same conditions, demonstrating that the PEGylation can improve the stability of the single nanocages. In addition, larger nanocages are found to self‐assemble in less polar solvents.     

Pd(0)-guanidine@MCM-41: a very effective catalyst for rapid production of bis (pyrazolyl)methanes

In this research, a rapid, green and efficient protocol for synthesis of bis (pyrazolyl)methane derivatives in the presence of Pd(0)-guanidine@MCM-41 catalysts under solvent-free conditions by the following two methods has been reported: (i) via the one-pot pseudo five-component reaction among phenylhydrazine (2 equivalents), ethyl acetoacetate (2 equivalents) and aromatic aldehydes (1 equivalent); and (ii) the one-pot pseudo three-component reaction between 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one (2 equivalents) and aromatic aldehydes (1 equivalent). Some advantages of this protocol include: green conditions, extremely short times, high efficiency, proper one-pot operation, generality of method, easy work-up and recyclability, and reusability of the catalyst up to five times without significant loss in catalytic activity.     

CeO2/Pd Nanoparticles Incorporated Fly Ash Zeolite: An Efficient and Recyclable Catalyst for Csp2-Csp2 Bond Formation Reactions

The catalytic activity of CeO₂ and palladium nanoparticles supported fly ash zeolite (CeO₂/Pd@FAZ) for C_sp²-C_sp² bond formation was studied. CeO₂/Pd@FAZ was characterized by FTIR, XRD, EDAX and TEM studies. In the Suzuki-Miyauracross-coupling reaction, biphenyl derivatives with excellent yields were obtained, and the reaction conditions were optimized. The catalytic activity was explored using a wide variety of diversely substituted aryl bromides and chlorides with aryl boronic acid under optimized reaction conditions. The recyclability of the catalyst was established for three cycles, with the conversion rate from 99 to 40%, which gained the advantage of heterogeneous catalysis.     

Direct synthesis of hyperbranched ethene oligomers and ethene-MA co-oligomers using iminopyridyl systems with weak neighboring group interactions

The synthesis of hyper-branched ethene oligomers through catalytic insertion reactions with late transition metal catalysts is unique in its synthetic and practical scope. In this study, a series of iminopyridyl Ni(II) and Pd(II) complexes with electron-rich distal aryl motifs were synthesized and characterized. These complexes were very efficient in ethene oligomerization and co-oligomerization with methyl acrylate (MA). Hyperbranched ethene oligomers with different microstructures were generated using different metal species in ethene oligomerization. More importantly, hyperbranched ethene-MA co-oligomers with varying incorporation ratios were generated via ethene and MA co-oligomerization using the Pd(II) complexes. Most notably, weak neighboring group interactions of distal aryl motifs in the nickel system are more effective in influencing the microstructure of ethene oligomers than the corresponding palladium system.     

Key Role of a-Top CO on Terrace Sites of Metallic Pd Clusters for CO Oxidation

Pd-based catalysts are the most widely used for CO oxidation because of their outstanding catalytic activity and thermal stability. However, fundamental understanding of the detailed catalytic processes occurring on Pd-based catalysts under realistic conditions is still lacking. In this study, we investigated CO oxidation on metallic Pd clusters supported on Al₂O₃ and SiO₂. High-angle annular dark-field scanning transmission electron microscopy revealed the formation of similar-sized Pd clusters on Al₂O₃ and SiO₂. In contrast, CO chemisorption analysis indicated a gradual change in the dispersion of Pd (from 0.79 to 0.2) on Pd/Al₂O₃ and a marginal change in the dispersion (from 0.4 to 0.24) on Pd/SiO₂ as the Pd loading increased from 0.27 to 5.5 wt %; these changes were attributed to differences in the metal-support interactions. Diffuse reflectance infrared Fourier-transform spectroscopy revealed that fewer a-top CO species were present in Pd supported on Al₂O₃ than those in Pd supported on SiO₂, which is related to the morphological differences in the metallic Pd clusters on these two supports. Despite the different dispersion profiles and surface characteristics of Pd, O₂ titration demonstrated that linearly bound CO (with an infrared signal at 2090 cm⁻¹) reacted first with oxygen in the case of CO-saturated Pd on Al₂O₃ and SiO₂, which suggests that a-top CO on the terrace site plays an important role in CO oxidation. The experimental observations were corroborated by periodic density functional calculations, which confirmed that CO oxidation on the (111) terrace sites is most plausible, both kinetically and thermodynamically, compared to that on the edge or corner sites. This study will deepen the fundamental understanding of the effect of Pd clusters on CO oxidation under reaction conditions.     

Pd‐catalyzed desulfitative Hiyama coupling with sulfonyl chlorides

Palladium‐catalyzed desulfitative Hiyama cross‐coupling reactions of various arylsulfonyl chlorides with aryltriethoxysilane have been achieved in good yields. The reported cross‐coupling reactions are tolerant to the common functional groups regardless of electron‐withdrawing or electron‐donating, making these transformations attractive alternatives to the traditional cross‐coupling approaches. Copyright © 2014 John Wiley & Sons, Ltd.