Coupling Products Research Articles

Electrochemical CO2/CO reduction on Ag/Cu electrodes and exploring minor Fischer–Tropsch reaction pathways

Ag/Cu hybrids have emerged as highly efficient catalysts for electrochemical (EC) CO2 reduction, yielding impressive C–C coupling products. We investigate Ag/Cu electrodes prepared via sputter deposition to explore their potential in EC CO2 and CO reductions. Our study highlights the significant impact of Ag thickness on resulting gas and liquid products, emphasizing the vital role of the Ag/Cu interface. Under CO2-saturated conditions, CO, CH4, and C2H4 are produced with high Faradaic efficiencies, while CO2-saturated KHCO3 generates formate, ethanol, propanol, isopropanol, acetate, and acetone. Experiments in phosphate conditions reveal new pathways for long-chain hydrocarbons (CnH2n and CnH2n+2, n = 2–7), typical products of Fischer-Tropsch chemistry. We also demonstrate CO hydrogenation to CH4 and C2-7 hydrocarbons, with alkane/alkene ratios influenced by electrolyte nature, concentration, applied potential, and Ag-modified Cu. These insights have implications for energy, environmental applications, and the future of EC CO2 and CO reduction through C–C coupling.

Synthesis of COF-SO3H immobilized on manganese ferrite nanoparticles as an efficient nanocomposite in the preparation of spirooxindoles

The synthesis of sulfonamide-functionalized magnetic porous nanocomposites is highly significant in chemistry due to their exceptional properties and potential as catalysts. COFs are a new class of organic porous polymers and have significant advantages such as low density, high chemical and thermal stability, and mechanical strength. Therefore, we decided to synthesize COFs based on magnetic nanoparticles, by doing so, we can also prevent the agglomeration of MnFe2O4. MnFe2O4@COF–SO3H possesses a large specific surface area, supermagnetism, and is acidic, making it an optimal catalyst for organic reactions. This particular catalyst was effectively employed in the green and rapid synthesis of various spiro-pyrano chromenes, while several analytical techniques were utilized to analyze its structural integrity and functional groups. The role of a specific site of MnFe2O4@COF–SO3H was confirmed through different control experiments in a one-pot reaction mechanism. It was determined that MnFe2O4@COF–SO3H acts as a bifunctional acid–base catalyst in the one-pot preparation of spirooxindole derivatives. The formation of a spiro skeleton in the multicomponent reaction involved the construction of three new σ bonds (one C–O bond and two C–C bonds) within a single process. The efficiency of the MnFe2O4@COF–SO3H complex is investigated in the synthesis of spirooxindoles of malononitrile, and various isatins with 1,3‐dicarbonyles. The nanocatalyst demonstrated excellent catalytic activity that gave the corresponding coupling products good to excellent yields. Furthermore, the heterogeneous magnetic nanocatalyst used in this study demonstrated recoverability after five cycles with minimal loss of activity.

Activation of Aryl and Alkyl Halides Enabled by Strong Photoreduction Potentials of a Hantzsch Ester/Cs2CO3 System.

We disclose herein a light-induced Hantzsch ester-initiated aryl and alkyl radical generation protocol from aryl halides (Br and Cl) and alkyl iodides. This method provides access to a wide range of benzo-fused heterocycles and C(sp3)-C(sp3) coupling products. The reductive detosylation reaction has also been demonstrated using the same reaction conditions. Initial mechanism studies provide evidence of the formation of an alkyl radical.

Rhodium-Catalyzed Direct Vinylene Annulation of 2-Aryloxazolines and Cascade Ring-Opening Using a Vinyl Selenone

AbstractOver the past two decades, transition-metal-catalyzed C–H activation and the subsequent oxidative cyclization with alkynes or their surrogates has emerged as a powerful synthetic tool for fused heteroaromatics. We report a Rh(III)-catalyzed annulation and ring-opening cascade reaction with 2-aryloxazolines. By utilizing a vinyl selenone as an oxidizing acetylene surrogate, the target three-component coupling products were obtained in high yields without using a stoichiometric amount of external oxidant.

Synthesis of Axially Chiral Bibenzo[g]coumarin Derivatives by Rhodium-Catalyzed Oxidative Annulation of Thiocarbamates

AbstractPolyaromatic organic compounds have attracted significant attention because of their wide range of applications in various functional materials. Recently, transition-metal-catalyzed C–H bond activation and the subsequent oxidative cyclization with unsaturated compounds has emerged as a promising synthetic method for multiring systems. We report a two-step synthesis of binaphthyl-fused chiral bibenzo[g]coumarin derivatives by Rh-catalyzed annulative coupling reaction of BINOL-based thiocarbamates with alkynes. The optical properties of the coupling products were evaluated.

Pd-catalyzed synthesis, characterization, and biological evaluations of pyrazole derivatives: DFT, molecular modelling and antioxidant studies

Using Pd(PPh3)4 as a catalyst, a new series of coupling products (5a–5l) synthesized from pyrazole derivatives (4a-4c) and substituted boronic acids. Afterward, 1H, 13C-NMR, FT-IR, UV-visible, and LC-MS techniques were used to characterize the pyrazole derivatives. These pyrazole derivatives (4a-4c and 5a-5l) were assessed for their in-vitro antifungal activity, growth pattern evaluations, and hemolytic assays against the Candida strains. The antibacterial inhibitory potential of the lead compound 5c, with a panel of three Gram-positive bacterial strains and two Gram-negative bacterial strains, was employed to find out MIC, FICI, and toxicity. Results showed that the MIC values with all bacterial strains for compound 5c indicate substantial antimicrobial potential. Analog 5c was tested for its ability to interact with Ct-DNA using various techniques. Compound 5c showed binding constants (Kb) of 9.93 × 105 M−1 while the Gibbs free energy was -34.22 kJmol−1. The linear Stern-Volmer constant (KSV) for 5c was calculated to be 4.81 × 104. DFT calculation study has been investigated for the geometrical optimization and energy parameters calculation. Pyrazole derivative 5c was used for molecular modelling investigation with PDB: 1BNA, 2XCT, and 5FSA, which validated the manner of binding and supported in vitro DNA binding results. Utilizing the DPPH and H2O2 assay, derivative 5c was also tested for antioxidant activity.

Photocatalytic C-C coupling and H2 production with tunable selectivity based on ZnxCd1-xS solid solutions for benzyl alcohol conversions under visible light

Photocatalytic C-C coupling is a green and sustainable route to produce value-added chemicals. However, the product selectivity is generally non-tunable and there is a lack of an in-depth understanding of the dependence of product selectivity on the band structure of the semiconductor photocatalyst. Here, ZnxCd1-xS solid solutions have been explored for photocatalytic C-C coupling using benzyl alcohol as a typical reactant. The conversion rate of benzyl alcohol and selectivity of C-C coupling products is inherently linked to the solid solution level of ZnxCd1-xS which can be readily tuned. An optimal solid solution level has been found at Zn0.6Cd0.4S (x = 0.6) which delivers a conversion rate of 91.61% and a selectivity of 98.83% for C-C coupling products. These findings not only deepen the understanding on factors that affect product selectivity but also justify the usefulness of solid solutions in tuning the C-C coupling reactions.

Synergistic Merger of Ketone, Halogen Atom Transfer (XAT), and Nickel-Mediated C(sp3)-C(sp2) Cross-Electrophile Coupling Enabled by Light.

In the present manuscript, we have developed a unique catalytic system by merging photoexcited ketone catalysis, halogen atom transfer (XAT), and nickel catalysis to forge C(sp3)-C(sp2) cross-electrophile coupling products from unactivated iodoalkanes and (hetero)aryl bromides. The synergistic catalytic system works under mild reaction conditions and tolerates a variety of functional groups; moreover, this strategy allows the late-stage modification of medicinally relevant molecules. Preliminary mechanistic studies reveal the role of the α-aminoalkyl radical, which further participates in the XAT process with alkyl iodides to generate the desired alkyl radical, which eventually intercepts with the nickel catalytic cycle to liberate the products in good to excellent yields.

1,2,3‐Triazole‐Assisted Heck Cross‐Coupling for the Synthesis of Olefinated Benzosuberene Analogues from Cedrus deodara Oil

AbstractHerein, we have reported an effective semi‐synthetic strategy for the synthesis of a new class of triazole‐bearing alkenylated benzosuberene analogues from himachalenes, extracted from Cedrus deodara oil. A highly efficient 1,2,3‐triazole triggered Heck cross‐coupling has been developed under palladium catalyzed conditions. The 1,2,3‐triazole moiety helps significantly to activate the carbon‐halogen bond and thereby promotes the coupling product. The developed protocol endures an array of arylated as well as alkylated triazole‐substituted benzocycloheptene to achieve the corresponding products in moderate to good yields.

C-N Bond Formation at Discrete CuIII-Aryl Complexes.

Copper(III) aryl species are widely proposed as intermediates in Cu-catalyzed C-C and C-heteroatom bond formation reactions. Despite their wide utility, mechanistic aspects of C-heteroatom formation at CuIII centers as well as factors that lead to byproducts, e.g., Ar-H, Ar-Ar, remain elusive due to the rarity of discrete CuIII-Ar complexes. Herein, we report the synthesis and reactivity of a series of CuII and CuIII aryl complexes that closely mimic the intermediates in Cu-catalyzed C-N coupling reactions. Copper(II) aryl complexes [TBA][LCuII-ArR] were synthesized via the treatment of CuII with a range of aryl donors, such as ZnAr2R, TMS-ArR, and ArR-Bpin. Oxidation of [TBA][LCuII-ArR] produces formal copper(III) aryl complexes LCuIII-ArR. Treatment of copper(III) aryl complexes with neutral nitrogen nucleophiles produces the C-N coupling product in up to 64% yield, along with commonly observed byproducts, such as Ar-H and Ar-Ar. Hammett analysis of the C-N bond formation performed with various N-nucleophiles shows a ρ value of -1.66, consistent with the electrophilic character of LCuIII-ArR. We propose mechanisms for common side reactions in Cu-catalyzed coupling reactions that lead to the formation of Ar-Ar and Ar-H.

Cobalt-59 NMR relaxation times of symmetric tris(γ-substituted-acetylacetonato)cobalt(III) complexes in benzene

Cobalt-59 NMR relaxation times, T1(59Co), and chemical shifts, δ(59Co), of symmetric tris(γ-substituted-acetylacetonato)cobalt(III) complexes, [Co(acac-X)3], which have chloride, bromide, nitro, and phenyl groups at the methine carbon atoms in the chelate ligands, have been measured in benzene at four temperatures between 284 and 319 K. In view of the viscosity dependence of 1/T1(59Co), the 59Co relaxation is caused by the reorientation of the static electric field gradient at the nucleus in every complex. Assuming that the rotational volume is replaced by the van der Waals volume, the nuclear quadrupolar coupling products, {(1 + ηq2/3)(eQq/h)2}1/2, were obtained for the series of [Co(acac-X)3] complexes in benzene. The negative correlation between {(1 + ηq2/3)(eQq/h)2}1/2 and δ(59Co) was observed for the four complexes [Co(acac)3], [Co(acac-Cl)3], [Co(acac-Br)3], and [Co(acac-NO2)3] except for [Co(acac-Ph)3]. This discrepancy strongly suggests that the rotational volume of the propeller-like [Co(acac-Ph)3] complex with the protruding phenyl groups cannot be simply treated as the van der Waals volume, different from the other almost spherical complexes. Actually, the estimation of the rotational volumes from the distances between the central cobalt and g-substituents gave much better correlation between {(1 + ηq2/3)(eQq/h)2}1/2 and δ(59Co) for all the complexes including [Co(acac-Ph)3].

Unusual Ring Opening of Bicyclic Terpenes During Pd‐Catalyzed Coupling with Aromatic Halides

AbstractHerein we describe Pd‐catalyzed cross‐coupling reaction of α‐pinene derivative – pinacarvone O‐methyl oxime (1) with aryl halides (2). Surprisingly, the formation of the C−C coupling product was accompanied by an unexpected opening of the pinene bicyclic structure. The (Z)‐2‐aryl‐4,4,5‐trimethylcyclohexa‐2,5‐dien‐1‐one O‐methyl oxime (3) was formed as the resulting product. The reaction conditions of the developed synthetic procedure were carefully optimized and the reaction mechanism was supposed on the basis of data obtained by structural and computational methods.

Synthesis of palladium complexes containing benzimidazole core and their catalytic activities in direct C[sbnd]H functionalization of five-membered heterocyclic bioactive motifs

Herein, we reported the synthesis of nine new PEPPSI-Pd(II)–N-heterocyclic carbene (NHC) complexes 3a-h containing benzimidazole core and examined their catalytic activities in the direct arylation of heteroaromatic species with aryl bromides and arylchlorides. Nine new Pd benzimidazole complexes were synthesized and their structures were elucidated by 1H and 13C NMR spectroscopy, FT-IR spectroscopy, and elemental analysis methods. In the 13C NMR spectra, NCHN peaks of Pd(II) complexes were observed between 159.7–161.5 ppm. Further, direct arylation reaction, using KOAc as base and DMAc as solvent under inert conditions, were carried out with the synthesized complexes in the presence of various aryl bromides and chlorides, and 2-acetyl furan, and furfuryl acetate 2-acetylthiophene and N-methylpyrrole-2- carboxaldehyde. Moreover, moderate to hig yields were obtained in the direct arylation of heteroarenes and aryl bromides under 1 mol% catalyst loading at 150 °C for 2 h loading conditions. The results showed that electron-donating and electron-withdrawing substituents on the aryl halides might produce coupling products in good yields in the presence of complexes 2a-d. Taken together, our findings are expected to contribute to the synthesis and design of palladium complexes containing benzimidazole core structures.

Solvent-Selective Synthesis of Diaryl Disulfides and Arylthio Acetic Acids Using Thioglycolic Acid and Copper Catalysts

AbstractAn efficient Cu-catalytic protocol for the synthesis of diaryl disulfides from aryl iodides using thioglycolic acid as the sulfur source has been developed. This transformation was successful only in aqueous DMSO, and when the solvent system was switched to aqueous DMF, arylthio acetic acids, the immediate C–S coupling products, were obtained. Each synthetic protocol was optimized and applied to various aryl iodides to afford the corresponding products in good to excellent yields.

Synergistic performance of a new bimetallic complex supported on magnetic nanoparticles for Sonogashira and C–N coupling reactions

This paper describes the synthesis of a novel Cu–Ni bimetallic system comprising of magnetic nanoparticles, as the core, and 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole (4-ABPT), as a conjugated bridge, between nickel and copper species. With low Cu and Ni loading (0.06 mol% Ni, 0.08 mol% Cu), the resulting Fe3O4@SiO2@4-ABPT/Cu–Ni showed to be a highly efficient catalyst for the Sonogashira and C–N cross-coupling reactions. The developed catalyst was well characterized by FT-IR, XRD, EDX-mapping, FE-SEM, TEM, ICP, VSM, TGA/DTG/DTA, LSV, and XPS techniques. Fe3O4@SiO2@4-ABPT/Cu–Ni nanocatalyst was compatible with a wide range of amines and aryl halides in the Sonogashira and C–N cross-coupling reactions and offered desired coupling products in high to excellent yields under palladium- and solvent-free conditions. Based on the XPS results, the 4-ABPT ligand can adjust electron transfer between Ni and Cu in Fe3O4@SiO2@4-ABPT/Cu–Ni, promoting the formation and stabilization of Cu+ and Ni3+ species. Electronic interactions and the synergistic effect between these metals increased the selectivity and activity of Fe3O4@SiO2@4-ABPT/Cu–Ni catalyst in the Sonogashira and C–N cross-coupling reactions compared with its monometallic counterparts. Additionally, the magnetic properties of Fe3O4@SiO2@4-ABPT/Cu–Ni facilitated its separation from the reaction mixture, promoting its reuse for several times with no significant loss in its catalytic activity or performance.

Palladium-Catalyzed Cross-Coupling Reaction of Bis(cyclopentadienyl)diaryltitaniums with Terminal Alkynes

Organotitanium compounds find application in diverse reactions, including carbon–carbon bond formation and oxidation. While titanium (IV) compounds have been used in various applications, the potential of bis(cyclopentadienyl)diaryltitanium in cross-coupling reactions remains unexplored. This study focuses on Sonogashira-type cross-coupling reactions involving terminal alkynes and organotitanium compounds. Diaryltitanocenes were synthesized using titanocene dichloride with lithium intermediates derived from aryl iodide. Under open-flask conditions, reactions of diphenyltitanocenes with ethynylbenzene in the presence of 20 mol% Pd(OAc)2 in DMF produced coupling products in a remarkable 99% yield. Various diaryltitanocenes and alkynes under standard conditions yielded corresponding cross-coupling products with moderate to good yields. Notably, the Sonogashira-type alkynylation proceeds under mild conditions, including open-flask conditions, and without the need for a base. Furthermore, this cross-coupling is atom-economical and involves the active participation of both aryl groups of the diaryltitanocene. Remarkably, this study presents the first example of a Sonogashira-type cross-coupling using titanium compounds as pseudo-halides.

Palladium-Catalyzed Decarbonylative Coupling of (Hetero)Aryl Boronate Esters with Difluorobenzyl Glutarimides.

This report describes the Pd-catalyzed decarbonylative coupling of difluorobenzyl glutarimides with (hetero)aryl boronate esters to yield difluorobenzyl-substituted (hetero)arene products. The use of PAd2Bu as the phosphine ligand in combination with neopentylboronate ester nucleophiles proved critical for the selective formation of the decarbonylative coupling product versus analogous difluorobenzyl ketone. This transformation is effective for electronically diverse (hetero)aryl boronate esters and substituted difluorobenzyl glutarimides.

Biodegradable Water-Soluble Matrix for Immobilization of Biocidal 4-Hexylresorcinol.

Biocidal coatings have been used in biomedicine, cosmetology and the food industry. In this article, the coatings are described as being composed of non-stoichiometric polycomplexes, products of electrostatic coupling of two commercial biodegradable ionic polymers, anionic sodium alginate and cationic quaternized hydroxyethyl cellulose ethoxylate. Non-stoichiometric polycomplexes with a 5-fold excess of the cationic polymer were used for immobilizing hydrophobic biocidal 4-hexylresorcinol (HR). Being dispersed in water, the polycomplex particles were capable of absorbing a tenfold excess of HR in relation to the polycation. After deposition onto the plastic surface and drying, the aqueous polycomplex-HR composite formulation forms a transparent homogeneous coating, which swells slightly in water. The interpolyelectrolyte complex (IPEC) is substantially non-toxic. The incorporation of HR in the IPEC imparts antimicrobial activity to the resulting composite, in both aqueous solutions and coatings, against Gram-negative and Gram-positive bacteria and yeast. The polysaccharide-based polycomplexes with embedded HR are promising for the fabrication of biocidal films and coatings.

The acylation with aldehydes via dual C-H activations by combining photocatalysis and palladium catalysis

A method was presented for the acylation of arenes using various aldehydes through dual CH activation at room temperature. The Pd-catalyst is initially activated to a triple state by absorbing energy from blue light. Furthermore, the 3Pd(AcO)2 required lower activation free energy to transition state 3(TS-2) based on the DFT calculation to ensure the reaction being proceeded at room temperature. This aldehyde-derived acyl radical merged with Pd-catalyzed activation of arenes to afford the cross coupling products.

Photoredox Coupling of CO2 Reduction with Benzyl Alcohol Oxidation over Ternary Metal Chalcogenides (ZnmIn2S3+m, m = 1-5) with Regulable Products Selectivity.

Integrating photocatalytic CO2 reduction with selective benzyl alcohol (BA) oxidation in one photoredox reaction system is a promising way for the simultaneous utilization of photogenerated electrons and holes. Herein, ZnmIn2S3+m (m = 1-5) semiconductors (ZnIn2S4, Zn2In2S5, Zn3In2S6, Zn4In2S7, and Zn5In2S8) with various composition faults were synthesized via a simple hydrothermal method and used for effective selective dehydrocoupling of benzyl alcohol into high-value C-C coupling products and reduction of CO2 into syngas under visible light. The absorption edge of ZnmIn2S3+m samples shifted to shorter wavelengths as the atomic ratio of Zn/In was increased. The conduction band and valence band position can be adjusted by changing the Zn/In ratio, resulting in controllable photoredox ability for selective BA oxidation and CO2 reduction. For example, the selectivity of benzaldehyde (BAD) product was reduced from 76% (ZnIn2S4, ZIS1) to 27% (Zn4In2S7, ZIS4), while the selectivity of hydrobenzoin (HB) was increased from 22% to 56%. Additionally, the H2 formation rate on ZIS1 (1.6 mmol/g/h) was 1.6 times higher than that of ZIS4 (1.0 mmol/g/h), and the CO formation rate on ZIS4 (0.32 mmol/g/h) was three times higher than that of ZIS1 (0.13 mmol/g/h), demonstrating that syngas with different H2/CO ratios can be obtained by controlling the Zn/In ratio in ZnmIn2S3+m. This study provides new insights into unveiling the relationship of structure-property of ZnmIn2S3+m layered crystals, which are valuable for implementation in a wide range of environment and energy applications.