Palladium nanoparticles embedded on mesoporous TiO2 material (Pd@MTiO2) as an efficient heterogeneous catalyst for Suzuki-Coupling reactions in water medium

Reduced Tiara-like Palladium Complex for Suzuki Cross-Coupling Reactions

The design of highly active and structurally well-defined catalysts has become a crucial issue for heterogeneous catalysed reactions while reducing the amount of catalyst employed. Beside conventional synthetic routes, the employment of polynuclear transition metal complexes as catalysts or catalyst precursors has progressively intercepted a growing interest. These well-defined species promise to deliver catalytic systems where a strict control on the nuclearity allows to improve the catalytic performance while reducing the active phase loading. This study describes the development of a highly active and reusable palladium-based catalyst on alumina (Pd8 /Al2 O3 ) for Suzuki cross-coupling reactions. An octanuclear tiara-like palladium complex was selected as active phase precursor to give isolated Pd-clusters of ca. 1 nm in size on Al2 O3 . The catalyst was thoroughly characterised by several complementary techniques to assess its structural and chemical nature. The high specific activity of the catalyst has allowed to carry out the cross-coupling reaction in 30 min using only 0.12 mol % of Pd loading under very mild and green reaction conditions. Screening of various substrates and selectivity tests, combined with recycling and benchmarking experiments, have been used to highlight the great potentialities of this new Pd8 /Al2 O3 catalyst.

Recent Progress of Metal Nanoparticle Catalysts for C–C Bond Forming Reactions

Over the past few decades, the use of transition metal nanoparticles (NPs) in catalysis has attracted much attention and their use in C–C bond forming reactions constitutes one of their most important applications. A huge variety of metal NPs, which have showed high catalytic activity for C–C bond forming reactions, have been developed up to now. Many kinds of stabilizers, such as inorganic materials, magnetically recoverable materials, porous materials, organic–inorganic composites, carbon materials, polymers, and surfactants have been utilized to develop metal NPs catalysts. This review classified and outlined the categories of metal NPs by the type of support.

Photocatalytic demulsification of oil/water emulsions containing nonionic surfactant

Separation of oil-water (OW) emulsions is investigated using a photocatalytic demulsification approach. Experiments were conducted using two types of photocatalysts, namely, ZnO and TiO₂. The emulsion samples were prepared with oil to water ratios of 1:3, 1:1, and 3:1 and using nonionic surfactant Tween 20 as an emulsifier. The demulsification efficiency was determined using a direct time varying phase separation measurement, while dynamic light scattering (DLS) and microscope imaging (MI) were used to determine the change in emulsion droplets size. The investigation results showed that all the emulsions were destabilized and separated within 30-90 min with demulsification efficiency that ranged from 38 to 90%. On the other hand, untreated control samples remained stable with no phase separation for more than 24 h. For most of the studied experimental conditions, TiO₂ nanoparticles gave better demulsification results than ZnO. Modeling of the batch demulsification kinetics for both systems agreed satisfactorily with the experimental measurements. This could allow its further extension towards design of continuous processes for potential implementation in treatment of industrial oily wastewaters.

Decorated palladium nanoparticles on chitosan/δ-FeOOH microspheres: A highly active and recyclable catalyst for Suzuki coupling reaction and cyanation of aryl halides

In this study, an eco-friendly and low cost magnetic nanocomposite consisting of chitosan/δ-FeOOH microspheres (CS/δ-FeOOH) was fabricated as a stabilizer by using a simple method. Pd nanoparticles (Pd NPs) were decorated on the designed CS/δ-FeOOH, and the resulting Pd NPs@CS/δ-FeOOH microspheres were employed as a heterogeneous catalyst in the construction of biaryl and benzonitriles. Pd NPs@CS/δ-FeOOH microspheres efficiently catalyzed the conversion of aryl iodides and bromides to the desired biaryls within 3 h. Moreover, Pd NPs@CS/δ-FeOOH microspheres showed high catalytic potential against synthesis of benzonitriles by providing yields up to of 99% within 4 h. More importantly, it was proved that Pd NPs@CS/δ-FeOOH microspheres were able to be easily recycled and reused up to eight runs for both reactions. This study reveals that Pd NPs@CS/δ-FeOOH microspheres are useful and recyclable nanocatalysts, which catalyze the synthesis of biaryl and benzonitriles with good reaction yields.

Noticeable improvement in the toxic gas-sensing activity of the Zn-doped TiO2 films for sensing devices

Sensing element view, sening mechanism, stability, response and recovery time of the Zn-doped TiO₂ films.

Pd/APN-Mn(BTC) as novel, highly efficient, and recyclable catalyst for Suzuki–Miyaura cross coupling reaction

A novel, heterogeneous, and bifunctional metal organic framework containing palladium and manganese, Pd/APN-Mn(BTC), has been prepared and completely characterized using FTIR, XRD, SEM-EDS, N2 adsorption–desorption, TG-DTG, NH3-TPD, and ICP analytical techniques. The APN-Mn(BTC) framework has been shown to be a useful platform for the stabilization and support of palladium nanoparticles (Pd NPs). Very effective catalytic activity has been exhibited by the highly dispersed Pd particles, Pd-NPs/APN-Mn(BTC), in the Suzuki–Miyaura cross-coupling reaction with reasonable to excellent reaction yields under mild conditions in H2O–ethanol solvent.

Green Synthesis of Oxide-Supported Pd Nanocatalysts by Laser Methods for Room-Temperature Carbon-Carbon Cross-Coupling Reactions

This work reports the design and development of a new class of highly active Pd nanocatalysts supported on substoichiometric oxides. These novel catalysts are generated by green laser synthesis methods to generate high-surface-area substoichiometric oxide nanoparticles followed by photoreduction in aqueous solutions to deposit highly active Pd nanocatalysts within the surface defects of the oxides. The laser methods eliminate the use of toxic chemicals, including hazardous solvents and chemical reducing agents, and allow efficient reduction of the Pd ions in aqueous solutions aided by the photogenerated electrons from the semiconductor support. The Pd catalysts incorporated within these oxides exhibit high activity for carbon-carbon bond-forming reactions. The Pd/TiO₂ catalyst with 0.3 mol % Pd achieves 100% conversion in the reaction between bromobenzene and benzeneboronic acid to the biphenyl product within 240 minutes at room temperature without any external heating. With a catalyst loading of 0.3 mol % Pd in the microwave-assisted reaction between bromobenzene and benzeneboronic acid at 60 °C, 92 and 83% conversions to the biphenyl product are achieved within 5 min of reaction time using the Pd/TiO₂ and Pd/ZnO catalysts, respectively. The results demonstrate a remarkable catalytic activity of the substoichiometric oxide-supported Pd catalysts with turnover frequencies (TOF, h^-1) of 24 000, 10 000, and 3200 achieved under mirowave-assisted reactions at 60 °C for the 0.03 mol% Pd of the Pd/TiO₂, Pd/ZnO, and Pd/ZrO₂ catalysts, respectively. The high activity and good reusability of these nanocatalysts are attributed to the optimum catalyst-support interaction between the small Pd nanoparticles and the surface defects of the substoichiometric oxide support prepared by the laser vaporization-controlled condensation method.

Design of Carbon-carbon and Carbon-heteroatom Bond Formation Reactions under Green Conditions

:

The development of C-C and C-heteroatom (C-N, C-O and C-P) bond reactions is a field of significant interest and has received momentous attention in modern organic chemistry. These reactions have been exploited in the synthesis of pharmaceuticals, agrochemicals and molecules of interest in materials science. With the increasing awareness of global warming and the use of renewable energies, it is of paramount importance to reduce the usage of hazardous chemicals in both industrial and academic research and to achieve a healthier environment through green practices. Green chemistry is a rapidly emerging approach that shows us a path for the sustainable growth of future science and technologies. In the recent past, healthy growth has been recorded in a number of organic reactions in aqueous media, which are environment-friendly and energy conserving. This review documents the literature on the development of green methodologies involving the design of C-C, C-O, C-N and C-P bond formations of coupling and condensed reactions. It emphasizes the exceptional practices and important advances achieved using alternative green tools, such as microwave (MW), high-speed ball milling (HSBM) and ultrasound irradiation techniques, and a variety of reusable catalysts and green solvents, with attention to water.

Development of Titanium Dioxide-Supported Pd Catalysts for Ligand-Free Suzuki–Miyaura Coupling of Aryl Chlorides

The catalyst activities of various heterogeneous palladium catalysts supported by anatase-, rutile- and brookite-type titanium oxide for ligand-free Suzuki–Miyaura cross-coupling reactions of aryl chlorides were evaluated. Palladium acetate [Pd(OAc)2], supported on anatase-type titanium oxide (TiO2) via acetonitrile solution impregnation process without reduction [Pd/TiO2 (anatase-type)], demonstrated the highest catalyst activity in comparison to those of other titanium oxide (rutile- or brookite-type) supported Pd(OAc)2 without reduction and reduced Pd/TiO2 (anatase-type) [Pd(red)/TiO2 (anatase-type)]. Various aryl chloride and bromide derivatives were smoothly coupled with arylboronic acids including heteroarylboronic acids in the presence of 5–10 mol% Pd/TiO2 (anatase-type) without the addition of any ligands. Although the fresh Pd/TiO2 (anatase-type) catalyst was surprisingly comprised of ca. 1:2 mixture of palladium(II) and palladium(0) species according to X-ray photoelectron spectroscopy (XPS), in spite of no reduction process, significant further increment of palladium(0) species was observed during the Suzuki–Miyaura coupling reaction, and Pd/TiO2 (anatase-type) was converted into a catalyst, which contained palladium(0) species as the main component [ca. 1:5 mixture of palladium(II) and palladium(0) species]. Therefore, the reduction via the electron donation process to the palladium(II) species may have occurred during the reaction on anatase-type titanium oxide.

Lipidic Mesophase-Embedded Palladium Nanoparticles: Synthesis and Tunable Catalysts in Suzuki-Miyaura Cross-Coupling Reactions

Lipidic cubic phases (LCPs) can reduce Pd²⁺ salts to palladium nanoparticles (PdNPs) of ∼5 nm size in their confined water channels under mild conditions. The resulting PdNP-containing LCPs were used as nanoreactor scaffolds to catalyze Suzuki-Miyaura cross-coupling reactions in the aqueous channels of the mesophase. To turn on catalysis, PdNP-containing LCPs were activated by swelling the aqueous channels of the lipidic framework, thereby enabling diffusion of the water-soluble substrates to the catalysts. The mesophases play a threefold role: they act as reducing agents for Pd²⁺, as limiting templates for their growth, and as support. The system was characterized and investigated by small-angle X-ray scattering (SAXS), cryo-transmission electron microscopy, dynamic light scattering, and nuclear magnetic resonance. Bulk LCPs and three dispersed palladium/lipid hybrid nanoparticle types were applied in the catalysis. The latter-liposomes, hexosomes, and cubosomes-can be obtained by design through combination of lipids and additives. The Suzuki-Miyaura cross-coupling of 5-iodo-2'-deoxyuridine and phenylboronic acid was used as a model reaction to study these systems. Bulk Pd-LCPs deliver the Suzuki-Miyaura product in 24 h in conversions up to 98% at room temperature, whereas with palladium/lipid dispersions at 40 °C, 68% of the starting material was transformed to the product after 72 h.

Nickel-metalated porous organic polymer for Suzuki–Miyaura cross-coupling reaction

A new Ni(ii)-α-diimine-based porous organic polymer, namely Ni(ii)-α-diimine-POP, was constructed in high yield via the Sonogashira coupling reaction between the metallo-building block of Ni(ii)-α-diimine and 1,3,5-triethynylbenzene. Besides the high thermal and chemical stability, the obtained Ni(ii)-α-diimine-POP can be a highly active reusable heterogeneous catalyst to promote the Suzuki–Miyaura coupling reaction. The obtained results indicate that the Ni(ii)-α-diimine-POP herein is a promising sustainable alternative to the Pd-based catalysts for catalysing the C–C formation in a heterogeneous way.

A porous organic polymer with Ni(ii) α-diimine moiety, which can be a highly active reusable heterogeneous catalyst to promote the Suzuki–Miyaura coupling reaction, was reported.

Size-Dependent Catalytic Activity and Fate of Palladium Nanoparticles in Suzuki-Miyaura Coupling Reactions

Stable, catalytically active palladium nanoparticles of various average diameters (1.9-7.4 nm) have been synthesized and characterized by X-ray diffraction, spectroscopy, and microscopy techniques to demonstrate remarkable size-dependent and renewed catalytic activity toward the Suzuki-Miyaura coupling reaction in green protocol. The catalytic activity is found to depend on the amount of the reducing agent, stabilizer-precursor ratio, solvent composition, and aryl halides used. The product obtained by this reaction is characterized by ¹H NMR, ¹³C NMR, and IR spectroscopy analyses. A newly developed kinetic equation illustrates that while the catalyst particles of the lowest dimension are gradually exposed to the reactants and hence activated due to partial removal of capping polymer from the catalyst surface, others are deactivated due to agglomeration during the progress of the reaction, as conformed by the microscopic profiles of the used and unused catalysts.

Novel Magnetically-Recyclable, Nitrogen-Doped Fe3O4@Pd NPs for Suzuki–Miyaura Coupling and Their Application in the Synthesis of Crizotinib

Novel magnetically recyclable Fe3O4@Pd nanoparticles (NPs) were favorably synthesized by fixing palladium on the surface of nitrogen-doped magnetic nanocomposites. These catalysts were fully characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TG), and X-ray photoelectron spectroscopy (XPS). The prepared catalyst exhibited good catalytic activity for Suzuki–Miyaura coupling reactions of aryl or heteroaryl halides (I, Br, Cl) with arylboronic acids. These as-prepared catalysts could be readily isolated from the reaction liquid by an external magnet and reused at least ten times with excellent yields achieved. In addition, using this protocol, the marketed drug crizotinib (anti-tumor) could be easily synthesized.

Poly(tetrafluoroethylene)-Stabilized Metal Nanoparticles: Preparation and Evaluation of Catalytic Activity for Suzuki, Heck, and Arene Hydrogenation in Water

Poly(tetrafluoroethylene)-stabilized Pd nanoparticles (PTFE-PdNPs) were prepared in water with 4-methylphenylboronic acid as a reductant and characterized using powder X-ray diffraction, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy, and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Small PdNPs with a fairly uniform size were obtained in the presence of PTFE, whereas aggregation of palladium was observed in the absence of PTFE. PTFE-PdNPs showed high catalytic activity for the Suzuki coupling reaction in water and were reused without any loss of activity. No palladium species were observed by ICP-AES analysis in the reaction solution after the reaction, nor was any change in particle size observed after the recycle experiment. PTFE-PdNPs also exhibited excellent catalytic activity and reusability for the Heck reaction in water. Although palladium species were not detected in the reaction solution after the reaction, aggregates and smaller sizes of PdNPs were observed in the TEM image of the recovered catalyst. PTFE was also useful as the stabilizer of rhodium nanoparticles (RhNPs) prepared by reduction with NaBH4. PTFE-RhNPs showed high catalytic activity and reusability toward arene hydrogenation under mild conditions.