Copper Acetylides Research Articles

Preparation of Ni-Cu-C composite catalysts prepared from mixed nickel and copper hydroxides for selective hydrogenation of 4-nitrophenol

A high-performance Ni-Cu-C composite catalyst was prepared from mixed nickel hydroxide and copper hydroxide, which were obtained by coprecipitation, by thermal treatment with acetylene-containing gas at 120 °C followed by hydrogen reduction at 180 °C. The characterization results of XRD, TEM, XPS, and H2-TPR measurements confirmed the presence of nickel carbide (Ni3C), copper carbide (CuxC), Cu, and Ni in the matrix of amorphous carbon in the composite catalyst. The mild preparation temperature and the porous carbon shell layers prevented the nano-sized particles from aggregation. The formation of interstitial Ni3C and CuxC significantly enhanced the dissociation of molecular hydrogen, accelerating the selective hydrogenation of 4-nitrophenol (4-NP) to yield 4-aminophenol (4-AP) at relatively mild conditions (80 °C and 1.0 MPa hydrogen pressure). The catalytic performance of the composite catalysts depended strongly on the Ni/Cu molar ratio, with an optimal Ni/Cu molar ratio of 4. In addition, the composite catalyst showed high conversion and selectivity to the corresponding aniline in the selective hydrogenation of other nitroarenes, including nitrobenzene, 4-nitrotoluene, 4-nitrochlorobenzene, 4-nitrobenzaldehyde, 4-nitroacetophenone, and 2-nitroaniline. The catalyst offers a novel approach to rational design and preparation of high-performance abundant metal catalysts for selective hydrogenation of nitroarenes.

Synergistic performance evaluation of copper–WC-graphene composites: Microstructure, mechanical properties, corrosion, and wear behavior under microwave sintering

This study investigates the synergistic performance of copper–WC–graphene composites fabricated using microwave sintering. Optical Microstructure analysis demonstrated a uniform distribution of reinforcing elements (WC and graphene) within the copper matrix across various compositions (Cu - 5 wt % WC, Cu - 5 wt % WC – 2.5 wt % Graphene, Cu - 5 wt % WC – 5 wt % Graphene, Cu - 5 wt % WC – 7.5 wt % Graphene). The SEM images further revealed controlled porosity and crack-free surfaces. Interfacial bond strength among WC, graphene, and copper was evidenced through SEM and wettability results, affirming successful phase integration. Mechanical property assessments unveiled substantial improvements in compressive strength (31.76%) and hardness (67.21%) after incorporating 5 wt % WC and 7.5 wt % graphene. Corrosion resistance was affirmed through minimal weight loss (0.201 mg) in a 3.5 wt % NaCl solution over 120 h. Wear tests exhibited a noteworthy 81.25% reduction in wear rate for Cu - 5 wt % WC – 7.5 wt % Graphene, emphasizing enhanced wear resistance. The coefficient of friction is determined to be 0.265. XRD analysis validates the composite's composition, featuring copper, copper oxide, copper carbide, tungsten carbide, and carbon phases.

Numerical Modelling and Simulation for Sliding Wear Effect with Microstructural Evolution of Sputtered Titanium Carbide Thin Film on Metallic Materials

Titanium carbide materials are introduced into manufacturing industries for the reinforcement and surface protection of base materials due to their substantial ability to withstand severe environments, which include sliding wear, corrosion, and mechanical failures. A thin film of titanium carbide (TiC) is coated onto brass and copper substrates using the radio frequency magnetron sputtering (RFMS) deposition method. The coating process is carried out at constant processing parameters, which include a sputtering power of 200 W, a temperature of 80 °C, a deposition time of 180 min, and an argon (Ar) gas flow rate at 10 standard cubic centimetres per minute (SCCM). The coating, together with the base materials, is modelled and its behaviours are simulated using ANSYS Workbench R19.2 Academic, supported by Mechanical APDL solver for nonlinear finite element analysis (FEA). The deformation, equivalent stress–strain characteristics, and elastic–plastic properties of the coating are determined at applied loads of 60 N and 25 N and coefficients of friction (CoF) of 0.25 and 0.38 for the thin film deposition on brass and copper substrates. The sliding distance and the speed of the alloy steel ball used during the sliding wear operation are found to be 3 mm and 4 mm/s, respectively. The sliding wear modelling and simulation process are, however, designed for the ball-on-flat (BoF) wear technique with a dry sliding approach. Therefore, BoF wear simulations are also performed on titanium carbide–brass (TiC-Br) and titanium carbide–copper (TiC-Cu) conjugates for the evaluation of surface engineering applications such as cutting tools and in automotive, aerospace, thermomechanical, and biomedical fields. The ball used for the FEA wear simulation is made from alloy steel material (AISI 52100) with a radius of 3.175 mm.

Lewis acid-mediated transformations of 5-acyl-N-fluoroalkyl-1,2,3-triazoles to cyclopentenones, indenones, or oxazoles.

We present a transition metal-free approach to 2-N-substituted indenones, cyclopentenones, and 4-carbonyl oxazoles, based on the reaction of 5-acylated N-fluoroalkyl substituted 1,2,3-triazoles (prepared by a three-component click reaction of copper acetylides, fluoroalkyl azides, and acyl chlorides) with Lewis acids aluminium trichloride or boron trifluoride etherate, proceeding via the generation and cyclization of vinyl cations.

Synthetic Access to 1,3-Butadiynes via Electro-redox Cuprous-Catalyzed Dehydrogenative Csp–Csp Homocoupling of Terminal Acetylenes

AbstractHerein, we disclose the oxidative homocoupling of terminal alkynes under electrochemically generated cuprous catalysis. The scope of this protocol was established by preparing an array of structurally and electronically different 1,3-butadiyne derivatives. Good synthetic yields, functional group tolerance, oxidant-free conditions, and no cross-selectivity are some of the intrinsic advantages of this methodology. The developed chemistry features the electro-redox formation of copper acetylide, an intermediate appropriate for the Csp–Csp coupling step. The chemical state of copper in the acetylide intermediate was found to be Cu(I), as confirmed by click trapping experiments, cyclic voltammetry, EPR spectroscopy, and XPS. A competition reaction to determine the reactivity of electronically dissimilar acetylenes revealed that the product ratio is rather dependent on the electronic nature of the alkynyl substituents. To highlight the synthetic value of the products, selected diynes were subjected to chemical diversification.

Atomically precise ultrasmall copper cluster for room-temperature highly regioselective dehydrogenative coupling

Three-component dehydrogenative coupling reactions represent important and practical methodologies for forging new C–N bonds and C–C bonds. Achieving highly all-in-one dehydrogenative coupling functionalization by a single catalytic system remains a great challenge. Herein, we develop a rigid-flexible-coupled copper cluster [Cu3(NHC)3(PF6)3] (Cu3NC(NHC)) using a tridentate N-heterocyclic carbene ligand. The shell ligand endows Cu3NC(NHC) with dual attributes, including rigidity and flexibility, to improve activity and stability. The Cu3NC(NHC) is applied to catalyze both highly all-in-one dehydrogenative coupling transformations. Mechanistic studies and density functional theory illustrate that the improved regioselectivity is derived from the low energy of ion pair with copper acetylide and endo-iminium ions and the low transition state, which originates from the unique physicochemical properties of the Cu3NC(NHC) catalyst. This work highlights the importance of N-heterocyclic carbene in the modification of copper clusters, providing a new design rule to protect cluster catalytic centers and enhance catalysis.

Anaerobic photoinduced Cu(0/I)-mediated Glaser coupling in a radical pathway

The reaction mechanism of the historic copper-catalyzed Glaser coupling has been debated to be based on redox cycles of Cu ions in specific oxidation states or on a radical mechanism based on Cu(0)/Cu(I). Here, the authors demonstrate two coexisting Glaser coupling pathways which can be differentiated by anaerobic/irradiation or aerobic reaction conditions. Without O2, copper(I) acetylides undergo a photo-excited pathway to generate highly reactive alkynyl radicals, which combine together to form a homo-coupling product or individually react with diverse X-H (X = C, N, O, S and P) substrates via hydrogen atom transfer. With O2, copper(I) acetylides are oxidized to become a Cu-acetylide/Cu-O merged Cu(I/II) intermediate for further oxidative coupling. This work not only complements the radical mechanism for Glaser coupling, but also provides a mild way to access highly energetic alkynyl radicals for efficient organic transformations.

Synergistic effects of CuZnMg-based catalysts for enhanced catalysis in alkyne-aldehyde coupling reactions

The coupling of acetylene and formaldehyde provides an atomic economy and a green feasible strategy for the synthesis of high value-added chemicals, but the development of efficient catalysts remains a challenge. In this work, we present the construction of CuZnxMgyAl-LDO multicenter catalysts using layered double hydroxide derivatives. By optimizing the Zn/Mg ratio, the CuZn3Mg1Al-LDO catalyst has a 78.1% yield of 1,4-butynediol and a turnover frequency of 5.36 h−1. The characterization and density functional theory results demonstrated that the synergistic effects of CuO-(ZnMgAl)Ox multicenter structure can adjust the chemical environment of Cu species, change its electronic structure, allowing them to be rapidly converted into copper acetylide active species, as well as to a higher electrophilicity and better anti-reduction ability. Importantly, such extraordinary efficacy of the multicenters catalyst is attributed to the Cu species-MgO and ZnO units, which work synergistically to generate the active acetylene species and activate the carbonyl bonds of formaldehyde, respectively. The results reported herein provide a new strategy for constructing multicenter and offer insights into the structure–property relationship of catalysts.

Manipulating micro-electric field and coordination-saturated site configuration boosted activity and safety of frustrated single-atom Cu/O Lewis pair for acetylene hydrochlorination

Simultaneously boosting acetylene hydrochlorination activity and avoiding formation of explosive copper acetylide over Cu-based catalyst, which represented a promising alternative to Hg-based and noble metal catalysts, remained challenging. Herein, we fabricated a frustrated single-atom Cu/O Lewis pair catalyst (Cu/O-FLP) by coupling epoxide group (C–O–C) with atom-dispersed Cu-cis-N2C2Cl center to address this challenge. The basic epoxy site modulated the electron-deficient state of Lewis-acidic Cu center and paired with the Cu-cis-N2C2Cl moiety to preferentially break HCl into different electronegative Cu–Clδ− and C–O–Hδ+ intermediates, which further induced both an extra localized electric field to polarize acetylene and a upshift of the d-band center of catalyst, thereby promoting adsorption and enrichment of acetylene by enhancing the dipolar interaction between acetylene and active intermediates. Moreover, the generated Cu–Clδ− and C–O–Hδ+ drastically reduced the energy barrier of rate-limiting step and made vinyl chloride easier to desorb from the Lewis-basic oxygen-atom site rather than traditional Lewis-acidic Cu center. These superiorities ensured a higher activity of Cu/O-FLP compared with its counterparts. Meanwhile, preferential dissociation of HCl endowed single-atom Cu with the coordination-saturated configuration, which impeded formation of explosive copper acetylide by avoiding the direct interaction between Cu and acetylene, ensuring the intrinsic safety during catalysis.

The Effect of Rolling Temperature and Rolling Ratio on Hardness and TRS Boron Carbide 10% wt. B4C Reinforcement Copper Matrix Composite

In this study, the effect of adding boron carbide (B4C) 10% wt. and a grain size of 90 μm on the mechanical and physical properties, such as microstructure, hardness, and density, of cold pressed copper carbide (Cu-B4C) composites was investigated. To improve the mechanical properties of commercial copper powders with a particle size of 40 μm, B4C was added with a particle size of 90 μm, 10% wt. The (Cu-B4C) composites were sintered in argon gas at 850°C for 120 minutes. Some samples were hot-rolled at temperatures (600°C,700°C,800°C) and rolling pressures (10%,20%,30%,40%) and the values obtained before and after hot rolling were compared. Where a comparison was made between density, hardness, and bending resistance, the sintered products before and after hot rolling were studied by SEM-EDS analysis. In the obtained images, it was found that B4C was homogeneously dispersed in the (Cu) matrix. The hardness of the composites increased with the increase in B4C percentage, the decrease in density, and the increase in porosity of the original samples. The hardness values of the rolled samples increased with increasing rolling temperatures (600°C,700°C,800°C) and rolling pressure ratios (10%,20%,30%,40%) and bending strength decreased with increasing rolling temperatures and pressure ratios for all samples that have been subjected to these changes.

Computational Design of a Two-Dimensional Copper Carbide Monolayer as a Highly Efficient Catalyst for Carbon Monoxide Electroreduction to Ethanol.

Rationally designing stable and low-cost electrocatalysts with high efficiency is of great significance for the large-scale electrochemical reduction of carbon monoxide (eCOR) to high-value-added multicarbon products. Inspired by the tunable atomic structures, abundant active sites, and excellent properties of two-dimensional (2D) materials, in this work, we designed several novel 2D C-rich copper carbide materials as eCOR electrocatalysts by performing an extensive structural search and comprehensive first-principles computations. According to the computed phonon spectra, formation energies, and ab initio molecular dynamics simulations, we screened out two highly stable candidates, i.e., CuC2 and CuC5 monolayers with metallic features. Interestingly, the predicted 2D CuC5 monolayer exhibits superior eCOR performance for C2H5OH synthesis with high catalytic activity (low limiting potential of -0.29 V and small activation energy for C-C coupling of 0.35 eV) and high selectivity (significant suppressing effect on the side reactions). Thus, we predicted that the CuC5 monolayer holds great potential as an eligible electrocatalyst for CO conversion to multicarbon products, which could motivate more study to develop highly efficient electrocatalysts in similar binary noble-metal compounds.

Lewis-Acid-Mediated Intramolecular Cyclization of 4-Aryl-5-allyl-1,2,3-triazoles to Substituted Cyclopentene Derivatives.

4-Aryl-5-allyl-N-fluoroalkyl-1,2,3-triazoles available by a three-component reaction of fluoroalkyl azides, copper acetylides, and allyl halides underwent aluminum halide-mediated transformation to N-(4-halo-2-aryl-cyclopentenyl) imidoyl halides by cyclization of vinyl cation intermediates, followed by halide capture. Utilization of the cyclic products was demonstrated by the synthesis of N-alkenyl amides, amidines, isoquinolines, and tetrazoles or by the subsequent modification of the cyclopentene ring.

Metal-promoted synthesis of steroidal ethynyl selenides having anticancer activity

In this study, we have described simple and efficient methodology for the metal-promoted (Cu2I2) preparation of steroidal ethynyl selenides. The compounds were characterized using 1H, 13C and 77Se NMR, FT IR spectroscopy, and MS analysis. A proposed mechanism of the metal-promoted reaction involves the formation of a σ-bound copper acetylide. Due to the fact that organoselenium-based compounds possess a pleiotropic properties and associated with their promising biological activities, in the next step of the study biocompatibility and anticancer activity of the synthesized compounds was evaluated. Steroidal selenides were tested in vitro against estrogen-depend breast cancer cells MCF-7 using spectrophotometric, fluorometric and luminometric methods. Designed selenides showed high hemocompatibility, lack of toxicity against cardiomyocytes cell and great anti-cancer activity in vitro against estrogen-depend breast cancer cells upon 24 h of treatment. We revealed that selenides decrease the viability and proliferation ability of MCF-7 cells by induction of cell apoptosis. It has been noted that the overproduction of reactive oxygen species (ROS) and associated with its activation of Caspase 3/7 are a major mechanism that is responsible of selenides-caused cell death. These data indicate that organoselenium based compounds have great antineoplastic potential and might be developed as novel class of agents dedicated to the breast-cancer therapies.

Copper carbide composite catalyst for hydrogenolysis of glycerol to 1,2-propanediol

The hydrogenolysis of renewable glycerol towards 1,2-propanediol (abbreviate as 1,2-PDO) has been a promising approach. In this work, high-performance catalysts containing copper carbide (CuxC) were prepared by the following procedure: (1) synthesis of Cu(OH)2-Zn(OH)2 mixture via a microchannel reaction system, (2) thermal treatment at 100 °C in 0.50 vol% C2H2/Ar gas, and (3) reduction at 300 °C under H2 atmosphere. The continuous synthesis of Cu(OH)2-Zn(OH)2 mixture in a microchannel reaction system yielded highly dispersed precursors, and the addition of ZnO led to improved dispersion of copper species with enhanced acidity. The new crystal phase, copper carbide (CuxC), was generated through reacting Cu(OH)2 particles with C2H2/Ar and subsequent hydrogen reduction. CuxC exhibited significantly higher hydrogenation activity than Cu metal, and contributed to enhanced catalytic activity for continuous glycerol hydrogenolysis in the fixed-bed reactor. Copper carbide composite catalyst (Cu/Zn = 8) afforded 100 % glycerol conversion and high selectivity (92.3 %) towards 1,2-PDO at 240 °C, 2.0 MPa and WHSV 3 h−1.

Selective Synthesis of 5‐Alkynyl Trisubstituted 1,2,3‐triazoles from Azides and Alkynes via Photoexcited Copper(I)acetylides

AbstractVisible‐light‐initiated copper(I) catalyzed selective synthesis of 5‐alkynyl trisubstituted 1,2,3‐triazoles from azides and alkynes is reported. The reaction proceeded via photoexcited copper(I)acetylides with azides to in‐situ formation of cuprate‐triazole followed by oxidative C−C(sp) coupling with another alkynes. The UV‐Visible spectrum shows that in‐situ photoexcited copper(I)acetylides (λabs=425–485 nm) is most probably the key light absorbing species responsible for CuAAC reactions.

Recent advances in synthesis of ketenimines

Ketenimines are a kind of reactive species that can be used as synthetic intermediates. In the last two decades, there has been a surge of interest in this class of building blocks and their applications, which has led to extensive research on ketenimine derivatives such as fluorine ketenimine, metal complexes of ketenimines, and the various methods of their preparation. Ketenimines have been prepared by a variety of methods, including photolysis, elimination, or rearrangement reactions. As well as, ketenimines can be prepared using a variety of useful reagents, including isocyanates, copper acetylide, amides, organometallic compounds, and metal complexes. An overview of these achievements is presented here.

Highly efficient Cu-based catalysts for selective hydrogenation of furfural: A key role of copper carbide

Copper catalysts showed excellent CO hydrogenation selectivity, but poor ability of hydrogen dissociation. Herein, a strategy to improve the activity of a Cu-based catalyst is developed by thermal treatment of Cu(OH)2 at 100 °C with C2H2/Ar (0.5 vol%) followed by H2 reduction at 300 °C. By means of X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS), it was revealed that CuxC crystallites, in addition to Cu crystallites, were present in the prepared catalysts. In furfural hydrogenation at 60 °C and 1.0 MPa, the CuxC-containing catalyst showed significantly higher activity than the Cu counterpart prepared from the same precursor by H2 reduction at 300 °C. The introduction of ZnO improved the dispersion, and thus led to enhanced catalytic performance. The CuxC-Cu-ZnO catalyst with Zn/Cu molar ratio of 0.5 showed considerably high hydrothermal stability in a 70-h run, with furfural conversion of >99.0% and the furfuryl alcohol selectivity of 100%.

Synthesis of β-Polychlorinated Alkynes Enabled by Copper-Catalyzed Multicomponent Reaction.

Functional molecules bearing polychlorinated moieties usually play versatile roles in organic synthesis and biochemistry. A copper-catalyzed multicomponent polychloro-carboalkynylation of alkenes presents an efficient and operationally simple approach for the synthesis of β-polychlorinated alkynes. Mechanistic experiments were conducted demonstrating that an in situ generated copper acetylide complex was the real catalyst and reactive intermediate during the copper-catalytic cycle. And enantioselective exploration demonstrated potential application for the synthesis of chiral β-polychlorinated alkynes.

Copper‐Catalysed Synthesis of Propargyl Alcohol and Derivatives from Acetylene and other Terminal Alkynes

AbstractA copper(I)/phosphine system that homogeneously catalyses the alkynylation of formaldehyde with acetylene or terminal alkynes is reported. Using acetylene at atmospheric pressure, the catalyst consisting of <1 mol% copper(I) phenylacetylide and a trialkyl bisphosphine ligand shows a high selectivity towards the formation of propargyl alcohol rather than 1,4‐butynediol, which is not reported for common heterogeneous copper acetylide catalysts. The biphasic water/toluene reaction mixture allows the separation of targeted products with the aqueous layer and catalyst recycling via the organic layer.magnified image

Synthesis of Polydiynes via an Unexpected Dimerization/Polymerization Sequence of C3 Propargylic Electrophiles.

Here, we describe the unexpected discovery of a Cu-catalyzed condensation polymerization reaction of propargylic electrophiles (CPPE) that transforms simple C3 building blocks into polydiynes of C6 repeating units. This reaction was achieved by a simple system composed of a copper acetylide initiator and an electron-rich phosphine ligand. Alkyne polymers (up to 33.8 kg/mol) were produced in good yields and exclusive regioselectivity with high functional group compatibility. Hydrogenation of the product afforded a new polyolefin-type backbone, while base-mediated isomerization led to a new type of dienyne-based electron-deficient conjugated polymer. Mechanistic studies revealed a new α-α selective Cu-catalyzed dimerization pathway of the C3 unit, followed by in situ organocopper-mediated chain-growth propagation. These insights not only provide an important understanding of the Cu-catalyzed CPPE of C3, C4, and C6 monomers in general but also lead to a significantly improved synthesis of polydiynes from simpler starting materials with handles for the incorporation of an α-end functional group.