Mechanism Of Coupling Reaction Research Articles

Advances in Exploring Mechanisms of Oxidative Phenolic Coupling Reactions

Biphenolic compounds serve as important scaffolds for the development of biologically active molecules. Among the methods for the synthesis of biarenols, oxidative coupling, which directly forms a C–C bond, has been extensively explored in various metal‐catalyzed (V, Cr, Co, Fe, Cu, etc.) reactions, electrochemical reactions, and photochemical reactions over the decades. While the exact mechanisms remain elusive in many cases, numerous mechanistic studies have provided valuable insights. This review focuses on the mechanistic details of the oxidative coupling of phenols or naphthols, involving at least one radical at least one radical intermediate. Additionally, the factors governing chemoselectivity (homo‐ and cross‐coupling), regioselectivity (ortho‐, meta‐ and para‐), and enantioselectivity (R and S configuration) are discussed, with a particular emphasis on intermediates and transition states, encompassing various oxidation sites for phenols and potential coupling sites.

Air-Stable Cobalt(III) and Chromium(III) Complexes as Single-Component Catalysts for the Activation of Carbon Dioxide and Epoxides.

Cobalt(III) and chromium(III) salophen chloride complexes were synthesized and tested for the cycloaddition of carbon dioxide (CO2) with epoxides to obtain cyclic carbonates. The cat1, cat2, cat4, and cat5 complexes presented high catalytic activity without cocatalysts and are solvent-free at 100 °C, 8 bar, and 9 h. At these conditions, the terminal epoxides (1a-1k) were successfully converted into the corresponding cyclic carbonates with a maximum conversion of ∼99%. Moreover, cat5 was highlighted due to its capability of opening internal epoxides such as limonene oxide (1l) with a 36% conversion to limonene carbonate (2l), and from cyclohexene oxide (1m), cyclic trans-cyclohexene carbonate (2m) and poly(cyclohexene carbonate) were obtained with 15% and 85% selectivity, respectively. A study of the coupling reaction mechanism was proposed with the aid of electrospray ionization mass spectrometry (ESI-MS) analysis, confirming the single-component behavior of the complexes through their ionization due to epoxide coordination. In addition, crystallographic analysis of cat1 single crystals grown in a saturated solution of pyridine helped to demonstrate that the substitution of chloride ion by pyridine ligands to form an octahedral coordination occurs (Py-cat1), supporting the proposed mechanism. Also, a recyclability study was performed for cat5, and a total turnover number of 952 was obtained with only minor losses in catalytic activity after five cycles.

Dinuclear Cu(I) molecular electrocatalyst for CO2-to-C3 product conversion

Molecular metal complex catalysts are highly tunable in terms of their CO2 reduction performance by means of their flexible molecular design. However, metal complex catalysts have challenges in their structural stability and it has not been possible to synthesize high-value-added C3 products due to their inability to perform C–C coupling. Here we show a CO2 reduction reaction catalysed by a Br-bridged dinuclear Cu(I) complex that produces C3H7OH with high robustness during the reaction. The C–C coupling reaction mechanism was analysed by experimental operando surface-enhanced Raman scattering analysis, and theoretical quantum-chemical calculations proposed the formation of a C–C coupling intermediate species with substrate incorporation between the two Cu centres. Molecular design guidelines based on this discovery offer an approach to developing next-generation catalysts that generate multicarbon CO2 reduction products.

Substitution Effects in Aryl Halides and Amides into the Reaction Mechanism of Ullmann-Type Coupling Reactions.

In this article, we present a comprehensive computational investigation into the reaction mechanism of N-arylation of substituted aryl halides through Ullmann-type coupling reactions. Our computational findings, obtained through DFT ωB97X-D/6-311G(d,p) and ωB97X-D/LanL2DZ calculations, reveal a direct relation between the previously reported experimental reaction yields and the activation energy of haloarene activation, which constitutes the rate-limiting step in the overall coupling process. A detailed analysis of the reaction mechanism employing the Activation Strain Model indicates that the strain in the substituted iodoanilines is the primary contributor to the energy barrier, representing an average of 80% of the total strain energy. Additional analysis based on conceptual Density Functional Theory (DFT) suggests that the nucleophilicity of the nitrogen in the lactam is directly linked to the activation energies. These results provide valuable insights into the factors influencing energetic barriers and, consequently, reaction yields. These insights enable the rational modification of reactants to optimize the N-arylation process.

Carbon Dioxide and Nitrate Electrocatalytic C-N Coupling for Sustainable Production of Urea

Review Carbon Dioxide and Nitrate Electrocatalytic C-N Coupling for Sustainable Production of Urea Litao Jia, and Fanghua Li * School of Environment, Harbin Institute of Technology, Harbin 150090, China * Correspondence: fanghuahope01@hit.edu.cn Received: 15 December 2023; Revised: 17 January 2024; Accepted: 19 February 2024; Published: 5 March 2024 Abstract: The electrocatalytic co-reduction of carbon dioxide (CO2) and nitrate (NO3−) for urea synthesis under environmental conditions offers a promising solution for achieving sustainable environmental management. Besides, electrochemical urea synthesis is an alternative approach for cleaner production of urea compared to the conventional urea industrial production process with high energy consumption and pollution. However, lower urea yield, lower selectivity and unclear C-N coupling reaction mechanism are still the main challenges to its large-scale application. In this review, we focus on accurate and reliable detection methods and evaluation criteria for urea products, recent progress on CO2 and NO3− electrocatalytic co-reduction synthesis of urea, rational design of high-performance electrocatalysts, and C-N coupling reaction mechanism of urea electrochemical synthesis under atmospheric conditions. This review could contribute to the development of electrochemical urea synthesis via effective remediation of CO2 and NO3−.

Bulk bismuth anodes for wide-temperature sodium-ion batteries enabled by electrolyte chemistry modulation

Sodium ion batteries (SIBs) are considered reliable supplies for next-generation energy devices. However, there is a limited understanding of strategies to prevent the performance deterioration of SIBs under extreme temperature conditions. This study aimed to address this challenge by developing modified electrolyte chemistry to achieve stable wide-temperature SIBs. Weakly Na+-solvating solvent 2-methyltetrahydrofuran (MeTHF) was used to promote the kinetics of Na+ de-solvation. Moreover, 1,2-dimethoxyethane (DME) was introduced as a co-solvent because of the high solubility for Na salts and the coupling reaction mechanism with the Bi electrode. The formulated electrolyte not only endows an anion-dominated NaF-rich solid electrolyte interface (SEI) layer, but also reduces the energy required for the Na+ across the SEI layer (from 291.2 to 89.6 meV). Consequently, Na||Bi half batteries achieve stable cycles at 400 mA g−1 at −20, 20 and 60 °C, respectively. Meanwhile, the extreme operating temperature of the batteries can be extended to −40 and 80 °C, which exceeds those of most current lithium/sodium-based batteries. Furthermore, full batteries employing Na3V2(PO4)3 as the cathode material exhibit stable operation over a wide temperature range of −20 to 60 °C. This electrolyte design strategy presented in this study shows significant promise for enabling wide-temperature SIBs with improved performance.

Scope and Mechanism of the Ruthenium-Catalyzed Deaminative Coupling Reaction of Enones with Amines via Regioselective Cα–Cβ Bond Cleavage

Scope and Mechanism of the Ruthenium-Catalyzed Deaminative Coupling Reaction of Enones with Amines via Regioselective C_α–C_β Bond Cleavage

Salt-Mediated Coarsening in Conversion-Reaction-Synthesized Nanoporous Metals and Nanocomposites Resolved through In Situ Synchrotron Diffraction Studies

High-energy synchrotron X-rays were used to probe the structural and microstructural evolution in Fe, Co, and Cu nanoporous metals (NPMs) and metal/salt nanocomposites (NCs) produced by recently developed conversion reaction synthesis (CRS) methods. Microstructure analysis of as-synthesized samples via whole pattern fitting showed that the NPMs exhibit domain sizes that increase as Co < Fe < Cu, with both Fe and Co having crystallite sizes below 3.0 nm. The as-synthesized metal/salt NCs had similar metal sizes, and additionally, the salt in the composite had unusually large lattice microstrain whose origin is attributed to chemical substitution of metal ions into the salt (e.g., Li1–3xFexCl for Fe3+). When thermal annealing is used to modify crystallite size, pore collapse often occurs in NPMs but NCs can be effectively tuned without this problem. While the NC coarsening occurs slowly at low temperatures, it was found that there is a drastic acceleration of the reaction rate at a specific onset temperature that results in the crystallite size increasing by an order of magnitude in about a minute. Curiously, there was no evidence in the diffraction data for salt melting at this onset temperature. However, there was a sharp reduction in the salt chemical lattice strain at the onset temperature, indicating that rapid metal coarsening is facilitated by the salt. This behavior indicates an unexpectedly coupled reaction mechanism by which the metal ions needed for grain growth are supplied by the salt in a rate-limiting fashion.

Borrowing hydrogen and dehydrogenative/oxidative cyclization reactions catalyzed by a CCC-NHC pincer Re complex: An air stable catalyst for the synthesis of α-alkylated ketones and quinolines

Successful catalytic activity of the CCC-NHC pincer Re(I) complex was achieved for the borrowing hydrogen coupling reaction between primary and secondary benzylic alcohols. An expansive scope of 17 aromatic and 2 aliphatic substrates were investigated and isolated yields from 40% to 91% were collected. The aliphatic substrates yielded complex aldol self-condensation by-products. The catalytic activity of the CCC-NHC pincer Re(I) complex was also evaluated for the formation of quinolines via the dehydrogenative/oxidative cyclization of 2-aminobenzyl alcohols with benzylic ketones or secondary benzylic alcohols. Isolated yields from 68% to 87% were obtained for 12 examples. All products and by-products were fully characterized by 1H &13C NMR and mass spectroscopies. Control studies such as dehydrogenative and hydrogen transfer reaction were carried out, and the results from these experiments supported a proposed mechanism of a borrowing hydrogen coupling reaction catalyzed by the CCC-NHC pincer Re(I) complex.

Study on exothermic effect of surface modified porous aluminum

Aluminum powder is widely used in the field of energy materials due to its high energy density. However, the combustion of aluminum powder is limited by the dense oxide film on the surface. In this study, surface modified porous aluminum (TFA@Al) was prepared by a simple chemical method. The morphology and structure of the TFA@Al surface were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The thermal oxidation and thermal nitridation processes of TFA@Al were analyzed by thermal analyzer (TG-DSC). The results show that the etched holes on the surface of TFA@Al can effectively promote the oxidation of aluminum and improve the exothermic effect of aluminum. The coupling reaction mechanism between Al core and oxygen at the etched holes is proposed. The explosion heat and combustion of thermite composed of TFA@Al and CuO (TFA@Al/CuO) and thermite composed of Al and CuO (Al/CuO) were also studied. The results show that TFA@Al/CuO has higher explosion heat value and emission spectral intensity than Al/CuO. Surface modified porous aluminum is expected to be used in the field of aluminum-containing energy materials.

Preparation, characterization and electrocatalytic performance of a novel poly(2,5-di(thienyl)pyrrole) modified electrode bearing TEMPO

A novel monomer 2,5-di(thienyl)pyrrole bearing TEMPO, 4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)benzoyl-oxy-2,2,6,6-tetramethylpiperidin-1-yloxy (SNS-TEMPO) was synthesized. The corresponding polymer modified electrode (PSNS-TEMPO) was successfully prepared by cyclic voltammetry, and characterized by SEM, EDS, XPS and element mapping. For comparison, another novel monomer 4-​(1H-​pyrrol-​1-​yl)​benzoyl-oxy-2,2,6,6-tetramethylpiperidin-1-yloxy (N-TEMPO) was synthesized and the corresponding polymer modified electrode (PN-TEMPO) was prepared. Introduction of thiophene unit on each side of pyrrole unit to extend the conjugation chain length was propitious to make the electropolymerization of SNS-TEMPO easier. In addition, the electrocatalytic performance for electrooxidative self-coupling of benzylamine to N-benzylidenebenzylamine on PSNS-TEMPO was better than that on PN-TEMPO prepared under similar conditions. The possible reaction mechanism of benzylamine self-oxidation coupling reaction with PSNS-TEMPO was proposed.

Green synthesis of aluminum hydroxide from alumina–silica based solid hazardous waste

The collaborative detoxification and extraction of valuable resources from various industrial wastes are proposed based on the composition characteristics and toxic properties of different solid/hazardous wastes such as coal gangue, aluminum dross, red mud, spent cathode carbon blocks, and carbide slag. The coupling reaction mechanism of the valuable or toxic components of aluminum, sodium, silicon, calcium, iron, fluorine, and nitrogen in the industrial wastes was studied in order to explore the potential value of waste. The results show that the alumina and sodium components in the industrial wastes are efficiently extracted, and the reaction process is promoted by iron and carbonaceous substances. The hazardous solid waste aluminum dross and the spent cathode carbon block are detoxified during the reaction process. The optimal reaction temperature is 1150 °C, and the residence time is 45–75 min. The extraction rate of Al2O3 is 92.4–93.3%, and the extraction rate of Na2O is 93.5–94.4%. The extracted alumina and sodium components can be used to prepare a series of high quality alumina.

Review on Electrocatalytic Coreduction of Carbon Dioxide and Nitrogenous Species for Urea Synthesis.

The electrochemical coreduction of carbon dioxide (CO2) and nitrogenous species (such as NO3-, NO2-, N2, and NO) for urea synthesis under ambient conditions provides a promising solution to realize carbon/nitrogen neutrality and mitigate environmental pollution. Although an increasing number of studies have made some breakthroughs in electrochemical urea synthesis, the unsatisfactory Faradaic efficiency, low urea yield rate, and ambiguous C-N coupling reaction mechanisms remain the major obstacles to its large-scale applications. In this review, we present the recent progress on electrochemical urea synthesis based on CO2 and nitrogenous species in aqueous solutions under ambient conditions, providing useful guidance and discussion on the rational design of metal nanocatalyst, the understanding of the C-N coupling reaction mechanism, and existing challenges and prospects for electrochemical urea synthesis. We hope that this review can stimulate more insights and inspiration toward the development of electrocatalytic urea synthesis technology.

Mechanism of Carbon-Carbon Coupling Reactions Catalyzed by Imine-Ligand-Assisted N-Heterocyclic Carbene Palladium Complexes

Mechanism of Carbon-Carbon Coupling Reactions Catalyzed by Imine-Ligand-Assisted N-Heterocyclic Carbene Palladium Complexes

One‐pot synthesis of 1,3‐disubstituted imidazo[1,5‐a]pyridines via acceptorless dehydrogenative coupling of primary alcohols promoted by binuclear ruthenium(II) N^O‐chelating complexes

A simple, straightforward and atom economic strategy to the synthesis of 1,3‐disubstituted imidazo[1,5‐a]pyridines using binuclear ruthenium(II) catalyst through acceptorless dehydrogenative coupling of primary alcohols with 2‐benzoylpyridine has been presented. New binuclear arene Ru(II) N^O chelating complexes of common formula [(η6‐benzene)2Ru2Cl2(μ‐L)], L = bis (furoylhydrazone) derivatives (1–3) were synthesized and characterized by analytical and spectral (FT‐IR, NMR and HR‐MS) techniques. The solid‐state molecular structure of one of the complexes (complex 1) has been authorized by single‐crystal XRD method. Further, a wide range of 1,3‐disubstituted imidazo[1,5‐a]pyridine derivatives have been successfully attained in good to excellent yields using binuclear arene Ru(II) catalysts with 1.0 mol% of catalyst loading. Further, control experiments unveil that the dehydrogenative coupling reaction mechanism proceeds via the formation of aldehyde and imine intermediates. The overall catalytic system releases H2 and water as only valuable by‐products.

Process coupling of CO2 and glycerol comprehensive utilization based on anionic 2D nanomaterial

AbstractWe developed an approach to realize the comprehensive utilization of CO2 and glycerol by smartly design a nanocatalyst, which concerns the coupling of catalytic reactions and the separation or capture process. Specifically, MgFe‐CO32−‐LDHs with different thickness were fabricated by employing atmospheric CO2 as carbon source and an atomic‐level interface was constructed by introducing Pt single atoms to obtain series of Pt/MgFe‐LDHs nanocatalysts. During a catalytic assessment, the CO32− confined within interlayer was in situ converted when integrated with glycerol oxidation under irradiation. The optimal nanocatalyst exhibited a decent conversion efficiency of CO32−‐CO‐CH4 and near 100% selectivity of secondary hydroxy group in glycerol. DFT calculation, isotope‐labeled experiments and in situ spectrograph characterization revealed possible coupling reaction mechanism. More importantly, the nanocatalyst exhibited impressive reusability for at least six 6 runs. The developed multiple coupling process will be an alternative and promising procedure for the waste and low‐valued sources synergetic utilization.

Iron-Catalyzed Cross-Electrophile Coupling of Inert C–O Bonds with Alkyl Bromides

Iron-Catalyzed Cross-Electrophile Coupling of Inert C–O Bonds with Alkyl Bromides

Decomposition mechanism of ethanol molecule on the nano-boron surface: An experimental and DFT study

The boron/ethanol nanofluid fuel with a high-energy density has better ignition performance as compared to traditional liquid fuels, so it has broad application prospects in fuel injection systems. However, the actual reaction mechanism of ethanol molecule over the nano-sized boron surface is still unclear and needs to be further explored. Hence, the specific reaction behavior of ethanol molecule on the boron (001) surface was investigated by a density functional theory (DFT) calculation. The geometric configuration and the energy of intermediates involved in the decomposition process of ethanol were analyzed and the dissociation route was drawn to find the optimal reaction path. The reaction CH3CH2OH → CH3CH2O → CH2CH2O → CHCH2O → CHCHO(Ⅰ) → CHCO → CH + CO → C + CO is the most preferable path. In this reaction path, the rate-determining step is the dehydrogenation of CH to form C. It is also found that oxygen is dissociated easily on the boron (001) surface and the presence of oxidation sites effectively decreases the energy barriers of the β-dehydrogenation of CH3CH2O and CHCHO (Ⅰ) species as well as the α-dehydrogenation of CHCH2O. This work emphasizes the important catalytic effect of boron on the decomposition of ethanol and can provide a benchmark for future research on the two-phase coupling reaction mechanism of emerging nanofluid fuels.

Revisiting Reduction of CO2 to Oxalate with First-Row Transition Metals: Irreproducibility, Ambiguous Analysis, and Conflicting Reactivity.

Construction of higher C≥2 compounds from CO2 constitutes an attractive transformation inspired by nature’s strategy to build carbohydrates. However, controlled C–C bond formation from carbon dioxide using environmentally benign reductants remains a major challenge. In this respect, reductive dimerization of CO2 to oxalate represents an important model reaction enabling investigations on the mechanism of this simplest CO2 coupling reaction. Herein, we present common pitfalls encountered in CO2 reduction, especially its reductive coupling, based on established protocols for the conversion of CO2 into oxalate. Moreover, we provide an example to systematically assess these reactions. Based on our work, we highlight the importance of utilizing suitable orthogonal analytical methods and raise awareness of oxidative reactions that can likewise result in the formation of oxalate without incorporation of CO2. These results allow for the determination of key parameters, which can be used for tailoring of prospective catalytic systems and will promote the advancement of the entire field.

Insights into the promotion mechanism of ceria-zirconia solid solution to ethane combustion over Pt-based catalysts

Pt/Ce0.5Zr0.5O2 (denoted as Pt/CZ11) and Pt/Al2O3 with identical Pt loading and dispersion were prepared and evaluated for ethane catalytic combustion. Pt/CZ11 exhibited higher activity than Pt/γ-Al2O3 even with similar Pt dispersion. Combined with various characterizations, it was revealed that the enrichments of surface active oxygen and oxygen vacancy on Pt/CZ11 facilitated ethane combustion owing to the strong interaction between Pt and Ce-Zr solid solution. Moreover, in situ DRIFT results demonstrated that different reaction mechanisms were followed over Pt/CZ11 and Pt/Al2O3. The front followed the single-site Langmuir-Hinshelwood (L-H), in which C2H6 and O2 were absorbed and activated on Pt sites. While the coupled reaction mechanism involving L-H and Mars-van Krevelen (MvK) were illustrated over Pt/CZ11, on which ethane can be activated on Pt sites and CZ11 support. More mechanistic insights into ethane combustion provided the guidelines for the developments of catalysts with superior performance for light-carbon alkane volatile organic compounds.