Search Results (9)

Enhancing the oxidation resistance of copper nanoparticles (CuNPs) is a crucial objective in plasmonic photocatalytic reactions. In this study, a series of Cu/X catalysts was synthesized using semiconductor nanomaterials (X = TiO₂, ZnO, BN, TiN, SiC, and C₃N₄) as supports for CuNPs. These catalysts were systematically evaluated in visible-light-driven photocatalytic oxidative homocoupling of phenylacetylene (OHA). Comprehensive characterization revealed distinct metal-support interactions and nanostructure evolution during repeated catalytic cycles. The photocatalytic performance, copper leaching, and structural stability of the catalysts were compared. Cu/TiO₂ achieved the highest 1,3-diyne yield (up to 93%) in the first two cycles. In contrast, Cu/ZnO showed minimal copper leaching and excellent recyclability, retaining high activity over three consecutive cycles without the need for reduction pretreatment. Comparative studies revealed that the combination of localized surface plasmon resonance (LSPR) and efficient electron transfer within the Cu⁰-Cu₂O-CuO composite was a key factor in enhancing the photocatalytic activity and stability. These findings provide new insights into the rational design of durable CuNP-based photocatalysts for visible-light-driven organic transformations. Full article

Due to the importance of biaryls as natural products, drugs, agrochemicals, dyes, or organic electronic materials, a green alternative biaryl synthesis has been developed based on easy-to-prepare and cheap copper(I)-exchanged zeolite catalysts. Cu^I-USY proved to efficiently catalyze the direct homocoupling of either phenols or aryl boronic acids under simple and practical conditions. The Cu^I-USY-catalyzed oxidative homocoupling of phenols could conveniently be performed under air either in warm methanol or water with good to high yields. In methanol, a small amount of Cs₂CO₃ was required, while none was necessary in water. The homocoupling of aryl boronic acids was best performed also in warm methanol, without an additive. These mild conditions showed good functional-group tolerance, leading to a variety of substituted (hetero)biaryls (28 examples). The heterogeneous Cu^I-USY catalyst could readily be recovered and reused. Interestingly, the homocoupling of vinyl boronic acids was successfully coupled to a Diels–Alder reaction, even in a one-pot process, allowing access to highly functionalized cyclohexenes. Full article

A novel catalytic system for homocoupling terminal acetylenes was elaborated based on CuCl as a catalyst (10 mol%), TMEDA as a base and CCl₄ as an oxidant. The influence of the solvent, base, amount of catalyst and CCl₄ on the reaction was investigated. Methanol was found to be the solvent of choice. The broad synthetic scope of the reaction was demonstrated. Diynes with various substituents were prepared in up to 92% yields. The possible reaction mechanism is discussed. Full article

Porous organic polymers incorporating nitrogen-rich functionalities have recently emerged as promising materials for efficient and highly selective CO₂ capture and separation. Herein, we report synthesis and characterization of new two-dimensional (2D) benzene- and triazine-based azo-bridged porous organic polymers. Different synthetic approaches towards the porous azo-bridged polymers were tested, including reductive homocoupling of aromatic nitro monomers, oxidative homocoupling of aromatic amino monomers and heterocoupling of aromatic nitro monomers and a series of aromatic diamines of different lengths and rigidity. IR spectroscopy, ¹³C CP/MAS NMR spectroscopy, powder X-ray diffraction, elemental analysis, thermogravimetric analysis, nitrogen adsorption–desorption experiments and computational study were used to characterize structures and properties of the resulting polymers. The synthesized azo-bridged polymers are all amorphous solids of good thermal stability, exhibiting various surface areas (up to 351 m² g⁻¹). The obtained results indicated that the synthetic methods and building units have a pronounced effect on the porosity of the final materials. Reductive and oxidative homocoupling of aromatic nitro and amino building units, respectively, lead to 2D azo-bridged polymers of substantially higher porosity when compared to those produced by heterocoupling reactions. Periodic DFT calculations and Grand-canonical Monte Carlo (GCMC) simulations suggested that, within the used approximations, linear linkers of different lengths do not significantly affect CO₂ adsorption properties of model azo-bridged polymers. Full article

The protocol, 3-methyldec-1-yn-3-ol (1a) was chosen to perform the dimerization process. The optimal conditions for synthesis of 8,13-dimethylicosa-9,11-diyne-8,13 (2a) with high efficiency when using copper-catalyzed, N,N,N′N′-tetramethylethylenediamine as a ligand and CCl₄ and methanol solvents in atmospheric pressure were determined. The structure of the obtained compound was proved by IR, ¹H-NMR and ¹³C-NMR spectroscopy. Full article

5,10,15,20-tetrakis-[4-(ethynyl)phenyl]porphyrin (TEP) was synthesized from the condensation of 4-(ethynyl)benzaldehyde and pyrrole catalyzed by boron trifluoride diethyl etherate in dichloromethane (DCM). After oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and purification, TEP was obtained in 34% yield. This porphyrin was metaled with Zn(II) acetate in DCM/methanol to produce the complex ZnTEP in 98% yield. A homocoupling reaction of terminal alkynes of ZnTEP to diynes was used to synthesize conjugated polymer organogel (ZnTEPP). The reaction was co-catalyzed by PdCl₂(PPh₃)₂ and CuI in tetrahydrofuran. The solvent was evaporated to obtain xerogel and the SEM images showed microporous structure. In addition, spectroscopic and photodynamic studies of ZnTEPP indicated that the porphyrin unit retains its properties as a photosensitizer. Thus, this polymer is an interesting material with potential applications in forming photoactive aseptic surfaces. Full article

An iron-catalyzed asymmetric oxidative homo-coupling of 2-naphthols for the synthesis of 1,1′-Bi-2-naphthol (BINOL) derivatives is reported. The coupling reaction provides enantioenriched BINOLs in good yields (up to 99%) and moderate enantioselectivities (up to 81:19 er) using an iron-complex generated in situ from Fe(ClO₄)₂ and a bisquinolyldiamine ligand [(1R,2R)-N¹,N²-di(quinolin-8-yl)cyclohexane-1,2-diamine, L1]. A number of ligands (L2–L8) and the analogs of L1, with various substituents and chiral backbones, were synthesized and examined in the oxidative coupling reactions. Full article

In this communication, we present studies of the oxidative homocoupling of arylboronic acids catalyzed by immobilised palladium nanoparticles in aqueous solution. This reaction is of significant interest because it shares a key transmetallation step with the well-known Suzuki-Miyaura cross-coupling reaction. Additives can have significant effects on catalysis, both in terms of reaction mechanism and recovery of catalytic species, and our aim was to study the effect of added halides on catalytic efficiency and catalyst recovery. Using kinetic studies, we have shown that added halides (added as NaCl and NaBr) can increase the catalytic activity of the palladium nanoparticles more than 10-fold, allowing reactions to be completed in less than half a day at 30 °C. However, this increased activity comes at the expense of catalyst recovery. The results are in agreement with a reaction mechanism in which, under conditions involving high concentrations of chloride or bromide, palladium leaching plays an important role. Considering the evidence for analogous reactions occurring on the surface of palladium nanoparticles under different reaction conditions, we conclude that additives can exert a significant effect on the mechanism of reactions catalyzed by nanoparticles, including switching from a surface reaction to a solution reaction. The possibility of this switch in mechanism may also be the cause for the disagreement on this topic in the literature. Full article

This present mini-review covers recently published results on Cu(I) and Cu(II) complexes immobilized on polystyrene carriers, which are used as heterogeneous, eco-friendly reusable catalysts applied for carbon–carbon and carbon–nitrogen forming reactions. Recent advances and trends in this area are demonstrated in the examples of oxidative homocoupling of terminal alkynes, the synthesis of propargylamines, nitroaldolization reactions, azide alkyne cycloaddition, N-arylation of nitrogen containing compounds, aza-Michael additions, asymmetric Friedel–Crafts reactions, asymmetric Mukaiyama aldol reactions, and asymmetric 1,3-dipolar cycloaddition of azomethine ylides. The type of polystyrene matrix used for the immobilization of complexes is discussed in this paper, and particularly, the efficiency of the catalysts from the point of view of the overall reaction yield, and possible enantioselectivity and potential reusing, is reviewed. Full article