A facile synthesis of PEGylated Cu2O@SiO2/MnO2 nanocomposite as efficient photo−Fenton−like catalysts for methylene blue treatment

The removal of toxic organic dyes from wastewater has received much attention from the perspective of environmental protection. Metal oxides see wide use in pollutant degradation due to their chemical stability, low cost, and broader light absorption spectrum. In this work, a Cu2O−centered nanocomposite Cu2O@SiO2/MnO2−PEG with an average diameter of 52 nm was prepared for the first time via a wet chemical route. In addition, highly dispersed MnO2 particles and PEG modification were realized simultaneously in one step, meanwhile, Cu2O was successfully protected under a dense SiO2 shell against oxidation. The obtained Cu2O@SiO2/MnO2−PEG showed excellent and stable photo−Fenton−like catalytic activity, attributed to integration of visible light−responsive Cu2O and H2O2−responsive MnO2. A degradation rate of 92.5% and a rate constant of 0.086 min−1 were obtained for methylene blue (MB) degradation in the presence of H2O2 under visible light for 30 min. Additionally, large amounts of •OH and 1O2 species played active roles in MB degradation. Considering the enhanced degradation of MB, this stable composite provides an efficient catalytic system for the selective removal of organic contaminants in wastewater.

Functionalization of graphene oxide with a hybrid P, N ligand for immobilizing and stabilizing economical and non-toxic nanosized CuO: an efficient, robust and reusable catalyst for the C–O coupling reaction in O-arylation of phenol

A new graphene oxide based heterogeneous catalytic system holding CuO nanoparticles through P and N donor sites for the C–O coupling reaction.

Copper supported silica-based nanocatalysts for CuAAC and cross-coupling reactions

Recent advances in Cu/SiO2-based heterogeneous catalysts for click reaction, C–N, C–S, and C–O coupling reactions are reviewed and summarized.

Light-assisted Ullmann coupling of phenols and aryl halides: The synergetic effect between plasmonic copper nanoparticles and carbon nanotubes from various sources

Utilizing light and plastic wastes as resources to turn the wasted phenols and hazardous aryl halides into value added chemicals seems to be an attractive idea for alleviating the energy crisis and environmental problems. In this work, we loaded plasmonic copper nanoparticles (Cu NPs) onto carbon nanotubes (CNTs) from various sources including commercial CNTs and those derived from plastic wastes. Under visible-light irradiation, the catalyst could efficiently convert phenols and aryl halides to diaryl ethers. Similar with commercial CNTs, excellent activity is also achieved when utilizing CNTs derived from different kinds of plastic wastes as support for the system. Further investigation shows that the visible-light irradiation and light-excited plasmonic Cu NPs are necessary to inhibit the phenol degradation on CNTs and in turn promote the cross-coupling of phenol and aryl halides. Compared with metal oxides and other carbon materials, the excellent capability of CNTs to absorb light, to convert light to heat, and to adsorb both two reactants simultaneously are critical to enhance the activity of Cu NPs, achieving the high yield of diaryl ethers. We believe that this study could provide a novel strategy for catalyst design and generate a more economically-sustainable process.

Copper nanocatalysts applied in coupling reactions: a mechanistic insight

Copper-based nanocatalysts have seen great interest for use in synthetic applications since the early 20th century, as evidenced by the exponential number of contributions reported (since 2000, more than 48 000 works published out of about 81 300 since 1900; results from SciFinder using "copper nanocatalysts in organic synthesis" as keywords). These huge efforts are mainly based on two key aspects: (i) copper is an Earth-abundant metal with low toxicity, leading to inexpensive and eco-friendly catalytic materials; and (ii) copper can stabilize different oxidation states (0 to +3) for molecular and nanoparticle-based systems, which promotes different types of metal-reagent interactions. This chemical versatility allows different pathways, involving radical or ionic copper-based intermediates. Thus, copper-based nanoparticles have become convenient catalysts, in particular for couplings (both homo- and hetero-couplings), transformations that are involved in a remarkable number of processes affording organic compounds, which find interest in different fields (medicinal chemistry, natural products, drugs, materials, etc.). Clearly, this richness in reactivity makes understanding the mechanisms more complex. The present review focuses on the analysis of reported contributions using monometallic copper-based nanoparticles as catalytic precursors applied in coupling reactions, paying attention to those shedding light on the reaction mechanism.

Green Synthesis of Cu Nanoparticles in Modulating the Reactivity of Amine-Functionalized Composite Materials towards Cross-Coupling Reactions

Control over both dispersion and the particle size distribution of supported metal particles is of paramount importance for the catalytic activity of composite materials. We describe the synthesis of materials with Cu nanoparticles well-dispersed on different amine-functionalized supports, using the extract of Wallich Spurge as a green, reducing agent. Graphene oxide (GO), mesoporous silica (MCM-41), mesoporous zirconia, and reduced graphene oxide-mesoporous silica (RGO-MCM-41) were explored as supports. Cu nanoparticles were better stabilized on RGO-MCM-41 compared to other supports. The novel composite materials were characterized by X-ray diffraction (XRD), Raman spectra, Scanning electron microscope (SEM), Transmission electron microscopy analysis and HR-TEM. SEM and EDX techniques. High angle XRD confirmed the conversion of graphene oxide to reduced graphene oxide (RGO) with plant extract as a reducing agent. Both XRD and TEM techniques confirmed the Cu nanoparticle formation. The catalytic activity of all the prepared materials for the Ullmann coupling reactions of carbon-, oxygen-, and nitrogen-containing nucleophiles with iodobenzene was evaluated. From the results, 5 wt% Cu on amine-functionalized reduced graphene oxide/mesoporous silica nanocomposite (5 wt%Cu(0)-AAPTMS@RGO-MCM-41) exhibited excellent efficiency with 97% yield of the C-C coupling product in water at 80 °C in 5 h. The activity remained unaltered almost up to the fourth cycle. The Cu nanoparticles stabilized by organic amine group on RGO hybrid facilitated sustained activity.

Recent Advancement of Ullmann Condensation Coupling Reaction in the Formation of Aryl-Oxygen (C-O) Bonding by Copper-Mediated Catalyst

Transition metal-catalyzed chemical transformation of organic electrophiles and organometallic reagents belong to the most important cross coupling reaction in organic synthesis. The biaryl ether division is not only popular in natural products and synthetic pharmaceuticals but also widely found in many pesticides, polymers, and ligands. Copper catalyst has received great attention owing to the low toxicity and low cost. However, traditional Ullmann-type couplings suffer from limited substrate scopes and harsh reaction conditions. The introduction of homogeneous copper catalyst with presence of bidentate ligands over the past two decades has totally changed this situation as these ligands enable the reaction promoted in mild condition. The reaction scope has also been greatly expanded, rendering this copper-based cross-coupling attractive for both academia and industry. In this review, we will highlight the latest progress in the development of useful homogeneous copper catalyst with presence of ligand and heterogeneous copper catalyst in Ullmann type C-O cross-coupling reaction. Additionally, the application of Ullmann type C-O cross coupling reaction will be discussed.

Ligand and Cu free N-arylation of indoles, pyrroles and benzylamines with aryl halides catalyzed by a Pd nanocatalyst

Herein, the N-arylation of aromatic heterocycles like indoles and pyrroles is reported by a Pd nanocatalyst under ligand- and Cu-free conditions.

Copper(I)-USY as a Ligand-Free and Recyclable Catalyst for Ullmann-Type O-, N-, S-, and C-Arylation Reactions: Scope and Application to Total Synthesis

The copper(I)-doped zeolite Cu^I-USY proved to be a versatile, efficient, and recyclable catalyst for various Ullmann-type coupling reactions. Easy to prepare and cheap, this catalytic material enables the arylation and heteroarylation of diverse O-, N-, S-, and C-nucleophiles under ligand-free conditions while exhibiting large functional group compatibility. The facility of this catalyst to promote C-O bond formation was further demonstrated with the total synthesis of 3-methylobovatol, a naturally occurring diaryl ether of biological relevance. From a mechanistic viewpoint, two competitive pathways depending on the nature of the nucleophile and consistent with the obtained results have been proposed.

Diaryl ethers synthesis: nano-catalysts in carbon-oxygen cross-coupling reactions

The diaryl ether moiety is not only prevalent in a significant number of natural products and synthetic pharmaceuticals but also widely found in many pesticides, polymers, and ligands. Ullmann-type cross-coupling reactions between phenols and aryl halides are regarded as one of the most important methods for the synthesis of this important and versatile structural motif. In recent years, the use of nano-sized metal catalysts in this coupling reaction has attracted a lot of attention because of these catalysts with their high surface-to-volume ratio, high surface energy, and reactive morphology allows for rapid C-O bond formation under mild and ligand-free conditions. In this review we will highlight the power of these catalysts in Ullmann-type C-O cross-coupling reactions.

Highly Efficient Heterogeneous Copper-Catalysed O-Arylation of Phenols by Nitroarenes Leading to Diaryl Ethers

The heterogeneous O-arylation of phenols by nitroarenes was achieved in DMF at 100 °C by using an MCM-41-immobilised bidentate nitrogen copper(II) complex [MCM-41-2N-Cu(OAc)2] as catalyst, yielding a variety of unsymmetrical diaryl ethers in good to excellent yields. This heterogeneous copper catalyst can be easily prepared by a simple procedure from commercially readily available and inexpensive reagents, recovered by filtration of the reaction solution and recycled at least seven times without significant loss of activity.

Ni nanoparticles on RGO as reusable heterogeneous catalyst: effect of Ni particle size and intermediate composite structures in C-S cross-coupling reaction

The present work demonstrates the C–S cross-coupling reaction between aryl halides and thiols using nickel nanoparticles (Ni NPs) supported on reduced graphene oxide (Ni/RGO) as a heterogeneous catalyst. It is observed that the uniformly dispersed Ni NPs supported on RGO could exhibit excellent catalytic activity in C–S cross-coupling reactions and the catalytic application is generalized with diverse coupling partners. Although the electron-rich planar RGO surface helps in stabilizing the agglomeration-free Ni NPs, the catalytic process is found to occur involving Ni(II) species and the recovered catalyst containing both Ni(0)/Ni(II) species is equally efficient in recycle runs. A correlation of loading of Ni species, size of NPs and the intermediate Ni-related heterostructures formed during the catalytic process has been established for the first time, and found to be best in the C–S cross-coupling reaction for Ni(0) and Ni(II) NPs of the average sizes 11–12 nm and 4 nm, respectively.

Incorporation of CuO NPs into modified UiO-66-NH2 metal–organic frameworks (MOFs) with melamine for catalytic C–O coupling in the Ullmann condensation

The UiO-66-NH₂ is initially modified with melamine via a post-synthetic approach. CuO NPs are then anchored via the available functional groups on the surface of the modified MOF.

Precious metal-like oxide-free copper nanoparticles: high oxidation resistance and geometric structure

Precious metal-like oxide-free copper nanoparticles, which are desired for alternatives as precious metal nanoparticles, were synthesized by environmental-friendly photoreduction method.

An effective and environment-friendly system for Cu NPs@RGO-catalyzed C–C homocoupling of aryl halides or arylboronic acids in ionic liquids under microwave irradiation

Cu NPs@RGO can effectively catalyze Ullmann C–C homocoupling of aryl halides and arylboronic acids under microwave irradiation in green solvent ionic liquid..

Cu₂O Nanoparticles Anchored on Amine-Functionalized Graphite Nanosheet: A Potential Reusable Catalyst

Synthesis of Cu2O-amine-functionalized graphite nanosheet (AFGNS) composite has been accomplished at room temperature. In the first step, AFGNS is synthesized by wet chemical functionalization where the -NH2 groups formed on nanosheet surface help to anchor the Cu(2+) ions homogeneously through coordinate bonds. Reduction of Cu(2+) (3.4 × 10(-2) mmol) in the presence of NaBH4 (1.8 mmol) can be restricted to Cu(1+) on AFGNS surface at room temperature. This leads to the formation of uniform Cu2O nanoparticles (NP) on AFGNS. The role played by the -NH2 groups in anchoring Cu(2+) ions and followed by stabilizing the Cu2O NP on AFGNS was understood by controlled reactions in the absence of -NH2 groups and without any graphitic support, respectively. The prepared Cu2O-AFGNS composite shows excellent catalytic activity toward degradation of an azo dye, methyl orange, which is an environmental pollutant. The dye degradation proceeds with high rate constant value, and the composite shows high stability and excellent reuse capability.

Barberry fruit extract assisted in situ green synthesis of Cu nanoparticles supported on a reduced graphene oxide–Fe3O4 nanocomposite as a magnetically separable and reusable catalyst for the O-arylation of phenols with aryl halides under ligand-free conditions

In situ synthesis of copper nanoparticles (NPs) supported on a reduced graphene oxide (RGO)–Fe₃O₄ nanocomposite was carried out with barberry fruit extract as a reducing and stabilizing agent.