Microstructure and catalytic performances of chitosan intercalated montmorillonite supported palladium (0) and copper (II) catalysts for Sonogashira reactions

Pd@HKUST-1@Cu(II)/CMC composite bead as an efficient synergistic bimetallic catalyst for Sonogashira cross-coupling reactions

We fabricated an efficient Pd@HKUST-1@Cu(II)/CMC composite bead catalyst through an innovative strategy based on the unique properties of metal-organic frameworks (MOFs) and carboxymethylcellulose (CMC). In this strategy, HKUST-1 MOFs were grown in-situ on the surface of micrometer-sized Cu-based CMC beads (Cu(II)/CMC), then Pd(II) ions were incorporated into the pores of the MOF and further be partially reduced to Pd(0) NPs, which is an active species for oxidative addition with aryl halides in Sonogashira reactions. The micron-sized Cu(II)/CMC beads were formed through inter/intramolecularly crosslinking facilitated by Cu(II) ions, which was achieved by the metathesis of Cu(II) with numerous carboxylic groups of CMC. Such Cu(II)/CMC bead offers many Cu(II) ions as interaction sites for in-situ nucleation and growth of HKUST-1 MOFs. The architecture and composition of the prepared Pd@HKUST-1@Cu(II)/CMC composite were fully verified by various techniques such as FTIR, XRD, TGA, BET, XPS, SEM, TEM, EDX, and elemental mapping analysis. This novel composite bead was applied as an efficient and reusable heterogeneous Pd/Cu bimetallic catalyst for Sonogashira reactions, decarbonylative Sonogashira reaction, and Sonogashira cyclization tandem reactions. The catalyst is readily isolated by simple filtration, and can be reused for five consecutive runs with retaining its activity and structural integrity.

TiO2-Modified Montmorillonite-Supported Porous Carbon-Immobilized Pd Species Nanocomposite as an Efficient Catalyst for Sonogashira Reactions

In this study, a combination of the porous carbon (PCN), montmorillonite (MMT), and TiO₂ was synthesized into a composite immobilized Pd metal catalyst (TiO₂-MMT/PCN@Pd) with effective synergism improvements in catalytic performance. The successful TiO₂-pillaring modification for MMT, derivation of carbon from the biopolymer of chitosan, and immobilization of Pd species for the prepared TiO₂-MMT/PCN@Pd⁰ nanocomposites were confirmed using a combined characterization with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N₂ adsorption-desorption isotherms, high-resolution transition electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. It was shown that the combination of PCN, MMT, and TiO₂ as a composite support for the stabilization of the Pd catalysts could synergistically improve the adsorption and catalytic properties. The resultant TiO₂-MMT₈₀/PCN₂₀@Pd⁰ showed a high surface area of 108.9 m²/g. Furthermore, it exhibited moderate to excellent activity (59-99% yield) and high stability (recyclable 19 times) in the liquid-solid catalytic reactions, such as the Sonogashira reactions of aryl halides (I, Br) with terminal alkynes in organic solutions. The positron annihilation lifetime spectroscopy (PALS) characterization sensitively detected the development of sub-nanoscale microdefects in the catalyst after long-term recycling service. This study provided direct evidence for the formation of some larger-sized microdefects during sequential recycling, which would act as leaching channels for loaded molecules, including active Pd species.

Novel lignin-supported copper complex as a highly efficient and recyclable nanocatalyst for Ullmann reaction

In this work, we prepared polyhydroxylated lignin by demethylation and hydroxylation of lignin, and grafted phosphorus-containing groups by nucleophilic substitution reaction, the resulting material could be used as a carrier for the preparation of heterogeneous Cu-based catalysts (PHL-CuI-OPR₂). The optimal PHL-CuI-OP^tBu₂ catalyst was characterized by FT-IR, TGA, BET, XRD, SEM-EDS, ICP-OES, XPS. The catalytic performance of PHL-CuI-OP^tBu₂ in the Ullmann CN coupling reaction was evaluated using iodobenzene and nitroindole as model substrates under nitrogen atmosphere with DME and H₂O as cosolvent at 95 °C for 24 h. The applicability of modified lignin-supported copper catalyst was investigated of various aryl/heteroaryl halides with indoles under optimal conditions, the corresponding products were obtained with high yield. Additionally, it could be easily recovered from the reaction medium by an easy centrifugation and washing.

Palladium Supported on Bioinspired Materials as Catalysts for C–C Coupling Reactions

In recent years, the immobilization of palladium nanoparticles on solid supports to prepare active and stable catalytic systems has been deeply investigated. Compared to inorganic materials, naturally occurring organic solids are inexpensive, available and abundant. Moreover, the surface of these solids is fully covered by chelating groups which can stabilize the metal nanoparticles. In the present review, we have focused our attention on natural biomaterials-supported metal catalysts applied to the formation of C–C bonds by Mizoroki–Heck, Suzuki–Miyaura and Sonogashira reactions. A systematic approach based on the nature of the organic matrix will be followed: (i) metal catalysts supported on cellulose; (ii) metal catalysts supported on starch; (iii) metal catalysts supported on pectin; (iv) metal catalysts supported on agarose; (v) metal catalysts supported on chitosan; (vi) metal catalysts supported on proteins and enzymes. We will emphasize the effective heterogeneity and recyclability of each catalyst, specifying which studies were carried out to evaluate these aspects.

Antibacterial Activity and Mechanism of ZnO/Cu2+-Chitosan/Montmorillonite

A new composite antibacterial material ZnO/Cu²⁺-Chitosan/Montmorillonite (ZCCM) was prepared with montmorillonite as carrier, Zn(Ac)₂•2H₂O, Cu(NO₃)₂•3H₂O and chitosan as raw materials. ZCCM was characterized by X-ray diffraction, nitrogen physical adsorption, scanning electron microscopy and energy dispersion spectrometry. The antibacterial activity of ZCCM against Escherichia coli, Salmonella typhimurium, and Staphylococcus aureus was evaluated by minimal inhibitory concentration, minimum bactericidal concentration and the influence of growth curves. ZCCM displays excellent antibacterial activity which is higher than ZnO-Montmorillonite, Cu²⁺-Montmorillonite and ZnO/Cu²⁺-Montmorillonite. In addition, the antibacterial mechanism of ZCCM was investigated by analyzing bacterial morphology, integrity of cell membrane, lipid peroxidation and the effect of histidine on antibacterial activity of materials. It is found that cell morphologies of bacteria are damaged and bacterial cells are shrunken. With the increase of cell membrane permeability, the intracellular dissolved matters leak continuously. What's more, the reactive oxygen species are generated and biomacromolecules are oxidized.

Applications of bimetallic PdCu catalysts

Bimetallic PdCu nanoparticles can be applied as catalysts in a wide range of chemical and electrochemical reactions.

Novel bio-inspired three-dimensional nanocomposites based on montmorillonite and chitosan

In this study, inspired by nacre-like structural natural shells, novel three-dimensional (3D) nanocomposites based on natural nanoplatelets of montmorillonite (MMT) and polysaccharide of chitosan (CS) were prepared with solution intercalation and self-assembly process. The CS-intercalated-MMT nanoplatelets units acted as "bricks" and CS molecules acted as "mortar", arranging in fairly well-ordered layered structure. With addition of glutaraldehyde (GA) and Pd²⁺ cations, synergistic toughening and strengthening effects of covalent and ionic bonds could be achieved. The best mechanical properties of the prepared 3D nanocomposites were observed as 5.6 KJ/m² (impact strength), 3.3 GPa (flexural modulus), and 65.8 MPa (flexural strength), respectively, which showed higher toughness but lower flexural properties than natural pearl mussel shells. Nevertheless, both the impact and flexural properties of the prepared 3D nanocomposite were much higher than the other natural shell, i.e. green grab shell. Besides conventional methods characterizations, the nacre-like structure of the artificial 3D nanocomposite was further evidenced with positron annihilation lifetime spectroscopy characterizations. This work might facilitate a versatile platform for developing green 3D bionanocomposites with fairly good mechanical properties.

Phosphorylation triggered growth of metal phosphate on halloysite and sepiolite nanoparticles: preparation, entrapment in chitosan hydrogels and application as recyclable scavengers

Surprising growth of crystalline metal phosphate during clay phosphorylation. When entangled in chitosan beads, good adsorption performance could be reached.

Catalytic farming: reaction rotation extends catalyst performance

The use of heterogeneous catalysis has key advantages compared to its homogeneous counterpart, such as easy catalyst separation and reusability. However, one of the main challenges is to ensure good performance after the first catalytic cycles. Active catalytic species can be inactivated during the catalytic process leading to reduced catalytic efficiency, and with that loss of the advantages of heterogeneous catalysis. Here we present an innovative approach in order to extend the catalyst lifetime based on the crop rotation system used in agriculture. The catalyst of choice to illustrate this strategy, Pd@TiO₂, is used in alternating different catalytic reactions, which reactivate the catalyst surface, thus extending the reusability of the material, and preserving its selectivity and efficiency. As a proof of concept, different organic reactions were selected and catalyzed by the same catalytic material during target molecule rotation.

Porous organic polymer with in situ generated palladium nanoparticles as a phase-transfer catalyst for Sonogashira cross-coupling reaction in water

A new Pd nanoparticle loaded and imidazolium-ionic liquid decorated organic polymer of Pd@PTC-POP was readily fabricated via a Pd(PPh₃)₄ catalysed in situ one-pot Suzuki cross-coupling reaction between imidazolium attached dibromobenzene and 1,3,5-tri(4-pinacholatoborolanephenyl)benzene. Besides the high thermal and chemical stability, the obtained Pd@PTC-POP can be used as a highly active and reusable phase-transfer solid catalyst to promote the Sonogashira coupling reaction in water. The obtained results indicate that the Pd@PTC-POP herein could create a versatile family of solid phase transfer catalysts for promoting a broad scope of reactions carried out in water.

A Pd nanoparticle loaded and imidazolium-ionic liquid decorated organic polymer, which can be used as a highly active phase-transfer solid catalyst to promote the Sonogashira reaction in water, was reported.