Catalysts Based Upon Organoclay with Tunable Polarity and Dispersion Behavior: New Catalysts for Hydrogenation, C–C Coupling Reactions and Fluorous Biphase Catalysis

Montmorillonite-catalysed coupling reactions: a green overview

Coupling reactions are widely significant in organic synthesis, and within the green chemistry perspective the utilization of montmorillonite clay as a catalyst offers a viable alternative to traditional coupling protocols. Montmorillonite clay is an effective, eco-friendly, economic and recyclable catalyst, and its heterogeneous nature facilitates easy isolation and reusability. The majority of coupling reactions executed with montmorillonite catalysts offer notable advantages over their homogeneous counterparts, including enhanced efficiency, selectivity, operational simplicity, elimination of toxic solvents and ligands, maintenance of mild reaction conditions, and cost-effectiveness. This review gives a comprehensive summary of the literature to date on coupling reactions catalysed by montmorillonite clay, while also outlining future prospects in this area.

Nanoparticles Supported on Sub-Nanometer Oxide Films: Scaling Model Systems to Bulk Materials

Ultrathin layers of oxides deposited on atomically flat metal surfaces have been shown to significantly influence the electronic structure of the underlying metal, which in turn alters the catalytic performance. Upscaling of the specifically designed architectures as required for technical utilization of the effect has yet not been achieved. Here, we apply liquid crystalline phases of fluorohectorite nanosheets to fabricate such architectures in bulk. Synthetic sodium fluorohectorite, a layered silicate, when immersed into water spontaneously and repulsively swells to produce nematic suspensions of individual negatively charged nanosheets separated to more than 60 nm, while retaining parallel orientation. Into these galleries oppositely charged palladium nanoparticles were intercalated whereupon the galleries collapse. Individual and separated Pd nanoparticles were thus captured and sandwiched between nanosheets. As suggested by the model systems, the resulting catalyst performed better in the oxidation of carbon monoxide than the same Pd nanoparticles supported on external surfaces of hectorite or on a conventional Al2 O3 support. XPS confirmed a shift of Pd 3d electrons to higher energies upon coverage of Pd nanoparticles with nanosheets to which we attribute the improved catalytic performance. DFT calculations showed increasing positive charge on Pd weakened CO adsorption and this way damped CO poisoning.

Nanopartikel auf subnanometer dünnen oxidischen Filmen: Skalierung von Modellsystemen

Durch die Abscheidung von ultradünnen Oxidschichten auf atomar‐flachen Metalloberflächen konnte die elektronische Struktur des Metalls und hierdurch dessen katalytische Aktivität beeinflusst werden. Die Skalierung dieser Architekturen für eine technische Nutzbarkeit war bisher aber kaum möglich. Durch die Verwendung einer flüssigkristallinen Phase aus Fluorhectorit‐Nanoschichten, können wir solche Architekturen in skalierbarem Maßstab imitieren. Synthetischer Natriumfluorhectorit (NaHec) quillt spontan und repulsiv in Wasser zu einer nematischen flüssigkristallinen Phase aus individuellen Nanoschichten. Diese tragen eine permanente negative Schichtladung, sodass selbst bei einer Separation von über 60 nm eine parallele Anordnung der Schichten behalten wird. Zwischen diesen Nanoschichten können Palladium‐Nanopartikel mit entgegengesetzter Ladung eingelagert werden, wodurch die nematische Phase kollabiert und separierte Nanopartikel zwischen den Schichten fixiert werden. Die Aktivität zur CO‐Oxidation des so entstandenen Katalysators war höher als z. B. die der gleichen Nanopartikel auf konventionellem Al2O3 oder der externen Oberfläche von NaHec. Durch Röntgenphotoelektronenspektroskopie konnte eine Verschiebung der Pd‐3d‐Elektronen zu höheren Bindungsenergien beobachtet werden, womit die erhöhte Aktivität erklärt werden kann. Berechnungen zeigten, dass mit erhöhter positiver Ladung des Pd die Adsorptionsstärke von CO erniedrigt und damit auch die Vergiftung durch CO vermindert wird.

Hierarchical Assembly of Atomically Precise Metal Clusters as a Luminescent Strain Sensor

We demonstrate the formation of a versatile luminescent organo-inorganic layered hybrid material, composed of bovine serum albumin (BSA)-protected Au₃₀ clusters and aminoclay sheets. X-ray diffraction revealed the intercalation of Au₃₀@BSA in the layered superstructure of aminoclay sheets. Coulombic attraction of the clusters and the clay initiates the interaction, and the appropriate size of the clusters allowed them to intercalate within the lamellar aminoclay galleries. Electron microscopy measurements confirmed the hierarchical structure of the material and also showed the cluster-attached clay sheets. Zeta potential measurement and dynamic light scattering probed the gradual formation of the ordered aggregates in solution. The hybrid material could be stretched up to 300% without fracture. The emergence of a new peak in the luminescence spectrum was observed during the course of mechanical stretching. This peak increased in intensity gradually with the degree of elongation or strain of the material. A mechanochromic luminescence response was further demonstrated with a writing experiment on a luminescent mat of the material, made by electrospinning.

A Non-innocent Magnesium Organoclay-Based Drug Vehicle for Improving the Cancer Therapy Effect of Methotrexate

A synthetic, dispersible magnesium aminoclay (MgAC) was synthesized in the present study. Besides, structural and spectroscopic detections were conducted to investigate the MgAC nanoclay. With a poor aqueous solubility, methotrexate (MTX) has been applied as a valid antitumor agent in recent years. In our research, an unobtrusive sol-gel process was carried out to manufacture the MgAC-MTX nanohybrids through entrapment of MTX over MgAC in situ. The final product was capable of desquamating and thus dispersed in water, equably. In comparison with rough MTX, the MgAC-MTX nanocomposite with a preferable treatment efficacy against MCF-7 cells was mainly attributed to the preeminent enhanced aqueous solubility, controlled release and the increased cellular uptake capacity. Moreover, with excellent anticancer function and hypotoxicity as vindicated in vivo, the MgAC-MTX nanohybrid was supposed to own the potency in the application of malignant tumors cure as a valid nanomedicine. It turned out that, by virtue of its high bioavailability, the MgAC-MTX nanohybrids with high bioavailability is deserving of further study for the treatment of cancers.

Recent advances in noble metal nanocatalysts for Suzuki and Heck cross-coupling reactions

Since metal nanoparticles have a high surface-to-volume ratio and very active surface atoms, they are very attractive catalysts for a wide variety of organic and inorganic reactions, compared to bulk catalysts. Metal nanoparticles suspended in colloidal solutions and those adsorbed onto bulk supports have been used as catalysts for a wide variety of carbon-carbon bond formation reactions such as the Suzuki and Heck cross-coupling reactions. This review article highlights some of the latest advances in the application of noble metal nanoparticles as catalysts for these two industrially important classes of cross-coupling reactions. We will discuss several important advances in using metal nanocatalysts in Suzuki and Heck cross-coupling reactions such as investigations on the nanoparticle shape dependence on the catalytic activity, novel types of supported metal nanoparticles as nanocatalysts, and the use of bi-metallic, tri-metallic and multi-metallic nanoparticles as catalysts for the Suzuki and Heck cross-coupling reactions.