Synthesis Of Imines Research Articles

Cu-UiO-66 Catalyzed Synthesis of Imines via Acceptorless Dehydrogenative Coupling of Alcohols and Amines.

Herein, the Cu-UiO-66 catalyst was developed for acceptorless dehydrogenative coupling (ADC) between alcohols and amines to produce imines. The Cu-UiO-66 catalyst was synthesized by installing Cu2+ onto Zr-oxo clusters in UiO-66, and the catalyst efficiently catalyzes the ADC reaction under mild and environmentally friendly conditions with excellent selectivity. Mechanistic studies reveal that the O2·- radicals and porosity of formed in Cu-UiO-66 participate cooperatively during the catalytic cycle. Meanwhile, the only by-product of the system is environmentally benign water. Cycling tests and hot filtration tests showed that the Cu-UiO-66 catalyst exhibited excellent stability and catalytic activity during the reaction. Importantly, the Cu-UiO-66 catalyst might provide a promising strategy for the ADC reaction between alcohols and amines to produce imines.

Highly selective electrosynthesis of imines via electroreduction coupling of nitroarenes with aryl aldehydes on Co9S8 with positively charged sulfur vacancies

The electrocatalytic synthesis of imines through the reductive imination of nitroarenes with aldehydes is a facile, environmentally friendly, and valuable process. In this study, high selectivity electrosynthesis of imines was realized through the electrocatalytic C-N coupling reaction between nitroarenes and aryl aldehydes on Co9S8 nanoflowers with rich sulfur vacancies (Co9S8-Vs). Comparative experiments revealed that positively charged sulfur vacancies play a pivotal role in boosting catalytic selectivity towards imines. Electron-deficient sulfur vacancies intensified the adsorption of negatively charged Ph-NO2, thereby enhancing the conversion rate of the electrochemical nitrobenzene-reduction reaction (eNB-RR). Simultaneously, sulfur vacancies augmented the adsorption capability of negatively charged Ph-CHO, enriching Ph-CHO species at the electrode interface and expediting the Schiff base condensation reaction rate. The experimental results show that the reaction conditions can satisfy the different nitroarenes and aryl aldehydes in the electrocatalytic aqueous-phase system under mild conditions to obtain the corresponding imine products in high selectivity. This study provides a facile and environmentally friendly pathway for future electrocatalytic synthesis of imine.

Continuous Synthesis and Processing of Covalent Organic Frameworks in a Flow Reactor.

Covalent organic frameworks (COFs) are typically prepared in the form of insoluble microcrystalline powders using batch solvothermal reactions that are energy-intensive and require long annealing periods (>120 °C, >72 h). Thus, their wide-scale adoption in a variety of potential applications is impeded by complications related to synthesis, upscaling, and processing, which also compromise their commercialization. Here we report a strategy to address both the need for scalable synthesis and processing approaches through the continuous, accelerated synthesis, and processing of imine- and hydrazone-linked COFs using a flow microreactor. The flow microreactor is capable of unprecedented COF productivities, up to 61,111 kg m-3 day-1, and provides control over key stages of COF formation, including nanoparticle growth, self-assembly, and precipitation. Additionally, the technique successfully yields highly crystalline and porous COFs in versatile macroscopic structures such as monoliths, membranes, prints, and packed beds. We also show that a COF synthesized using the flow microreactor acts as an excellent photocatalyst for the photocatalytic degradation of perfluorooctanoic acid (PFOA) outperforming the degradation efficiency of its batch analogue and other classical photocatalysts such as titanium dioxide (TiO2).

Design and One-pot Synthesis of Novel Carbazole-based Thiazolone Imines

Design and One-pot Synthesis of Novel Carbazole-based Thiazolone Imines

Novel synthesis of vanadium phosphorus/ cerium promoted manganese oxide (VPO/Ce-OMS-2) nanocomposite as an efficient and selective catalyst for the aerobic oxidative coupling of benzyl alcohol and aniline to imine in the liquid phase

In this investigation, the VPO/Ce-OMS-2 composite was synthesized via the mechanochemical method and it was employed for the synthesis of imine in the liquid phase through a two-step process of oxidation of benzyl alcohol and subsequent condensation with aniline using air as an oxidant. The composite was synthesized with different mass ratios of (1:1), (1.5:1), (2:1) and (2.5:1). The effect of the VPO/Ce-OMS-2 mass ratio on catalyst activity has been investigated. As the mass ratio increases from (1:1) to (2:1), the benzyl alcohol conversion gradually increases, reaching 93% at a (2:1) mass ratio. Among the synthesized samples, the VPO/Ce-OMS-2(2:1) composite exhibited the highest selectivity towards imine formation and conversion of benzyl alcohol. Various techniques, such as XRD, FT-IR, BET, FESEM, EDX, DRS, NH3-TPD, and HRTEM, were utilized to characterize the catalysts. Results indicated that the composite synthesized with a (2:1) mass ratio has a favorable surface area, a mixture of micro-meso structures, and a high number of acidic sites, as confirmed by BET-BJH and NH3-TPD techniques. The DRS analysis demonstrated that the interaction between the two catalysts, VPO and Ce-OMS-2, enhances the selectivity for the desired product. The results clearly show the synergism effect in the combination of components VPO and Ce-OMS-2 and improving the activity and selectivity of the synthesized nanocomposite. The effects of reaction temperature, reaction time, solvents, VPO/Ce-OMS-2 mass ratio, catalyst amount, and reusability were studied. Recycling results for the VPO/Ce-OMS-2(2:1) composite show that the benzyl alcohol conversion decreases slightly after five cycles of use, and its stability is almost maintained. Optimizing the reaction conditions (0.2 g catalyst, VPO/Ce-OMS-2 mass ratio (2:1), solvent toluene, reaction temperature 90°C, and t = 8 h) resulted in a 93% conversion of benzyl alcohol with complete selectivity for the imine.

Exploring the potential of metal tailored imine based covalent organic framework for asymmetric supercapacitor applications

Currently, a fascinating area of research involves the development of stable and efficient materials for energy storage systems. The current work describes the synthesis of imine linked covalent organic framework (COF) using 4,4′,4′',4′''-(ethene-1,1,2,2-tetrayl) tetraaniline and terephthalaldehyde (TAT-COF) as precursors through solvothermal method. In addition, cobalt has been integrated to the imine linkage of TAT-COF to generate CO@TAT-COF. The X-ray diffraction study reveals the formation of ordered and crystalline TAT-COF with eclipsed (AA) stacking configuration. Morphological characterization indicated the accumulation of metal species over stick like structured TAT-COF. Energy-dispersive X-ray (EDX) and Fourier Transform Infrared Spectroscopy results shows the successive intercalation of Co to the TAT-COF matrix. TAT-COF and Co@TAT-COF were examined towards electrochemical performance for supercapacitor applications. A two fold higher specific capacitance (Csp) was obtained in Co@TAT-COF (637 F/g) compared to TAT-COF (315 F/g) at 5 mV/s scan rate. The Co@TAT-COF showed an energy density (ED) of 58 Wh/kg at a power density of (PD) of 1500 W/kg. Enhanced electrochemical performance in Co@TAT-COF could be attributed to the structural confinement, conductivity, enhanced interlayer spacing and porosity. Co@TAT-COF has been used as positive electrode to fabricate an asymmetric device (ASD) in using Swagelok cell. The Csp of the fabricated ASD was found to be 95 F/g at 2 mV/s scan rate. ASD showed good stability with 73 % retention of Csp over 5000 charge/discharge cycles. The obtained results indicate the suitability of the engineered COFs towards energy storage devices.

Single-Atom Co-N4 Sites Mediate C=N Formation via Reductive Coupling of Nitroarenes with Alcohols.

It remains challenging to construct C=N bonds due to their facile hydrogenation. Herein, a single Co atom catalyst was discovered to be active for the selective construction of C=N bonds toward the synthesis of imines and N-heterocycles via reductive coupling of nitroarenes with various alcohols, including inert aliphatic ones. DFT calculations and experimental data revealed that the transfer hydrogenation proceeded via the intramolecular hydride transfer and the transfer of H from the α-Csp3-H bond to the nitro group was the rate-determining step. The single Co atoms served as a bridge to transfer the electrons from the catalyst to the adsorbed alcohol molecules, resulting in the activation of the α-Csp3-H bond. Unlike metal nanoparticles, the C=N bonds in imine products can be reserved due to the large steric hindrance from substituents on C and N. DFT calculation also confirmed that transfer hydrogenation of the C=N bonds in imines is thermodynamically unfavored with a much higher energy barrier compared with the transfer hydrogenation of the -NO2 group (1.47 vs 1.15 eV).

Advancing the design of heterogeneous catalyst: Copper-montmorillonite for regioselective alkyne hydroamination

Transition metal catalysts supported on natural materials offer promising avenues for sustainable organic synthesis. In this study, we present the synthesis, characterisation, and catalytic performance of copper nanoparticles supported on montmorillonite K10 (CuMK10) as a heterogeneous catalyst for hydroamination reactions. CuMK10, synthesised through a robust and established nanoparticle synthesis methodology, demonstrates remarkable catalytic efficiency and selectivity in the synthesis of imines via hydroamination of terminal alkynes. The catalyst exhibits exceptional regioselectivity, predominantly yielding Markovnikov products, demonstrating its potential as a versatile tool in organic synthesis. Moreover, CuMK10 shows favourable reusability, offering economic benefits and practical utility due to its ease of recovery and reuse. Comprehensive structural and mechanistic studies provide insights into the catalyst's performance, paving the way for the development of efficient and environmentally benign catalytic systems.

Modification Structure of Cinnamaldehyde with Primary Amines by Reflux and Sonication Methods in the Presence of Sulfuric Acid as a Catalyst

Cinnamon is one of the most valuable natural resources that sustains life and exists freely in nature. Cinnamaldehyde is the primary compound in cinnamon oil. It has a unique structure that contains a benzene ring, an aldehyde group, and an unsaturated double bond. Cinnamaldehyde has been structurally modified to improve biological activity. In this research, cinnamaldehyde and nitrophenyl amines were reacted with sulfuric acid as a catalyst by refluxing and sonication. UV-Vis Spectroscopy, FT-IR, 1H-NMR, and 13C-NMR were used to validate the chemical structures. Thin-layer chromatography (TLC) revealed a new single spot formed by the reaction of cinnamaldehyde and 4-amino-2-nitrophenol. By refluxing for 2 hours or sonicating for 30 minutes, a novel imine chemical, 4-nitro-2-((3-phenylallylidene)amino)phenol, was effectively synthesized with a yield of 75.21% or 83.71%, respectively. This imine was obtained as a dark red powder with a melting point of 237 °C. Meanwhile, only sonication produced a novel product from the reaction of cinnamaldehyde and 4-nitroaniline. However, the structural elucidation has not yet been performed because the yield was so low. Surprisingly, there was no reaction between cinnamaldehyde and 2,4-dinitroaniline. It was most likely owing to the amine’s bulky structure and the presence of two nitro groups in the amine as electron-withdrawing groups that reduced the nucleophilicity of the amine. We demonstrated that sonication is a suitable approach for imine synthesis, as it is commonly utilized in organic compound synthesis protocols.

Synthesis and characterization of Ru(II) complexes with polyfunctional amides and their application in catalytic oxidative coupling of amines

The synthesis and characterization of some new mononuclear Ru(II) complexes of the type [(Ru(L)2(DMSO)2] and [(Ru(L)2] (L = O,O-donor bidentate or N,O,O-donor tridentate or O,O,O-donor tridentate amide ligands) is described. These metal complexes were characterized by Elemental analysis (EA), IR, 1H NMR, and mass spectral data and their structures have been proposed. Next, these complexes were investigated as catalysts in the oxidative coupling of amines by tert-butyl hydroperoxide (TBHP) oxidant to produce selectively the corresponding imines in high yields in CH3CN. The influence of various reaction parameters such as selection of oxidant and solvent during the benzyl amine oxidative coupling was systematically monitored to optimize the catalytic conditions. The utility of optimized reaction conditions was further extended to investigate the amine substrate scope. Based on the experimental results and previous reports, a plausible mechanism was also deduced for the selective synthesis of imines.

Mild and selective synthesis of imines and N-Heterocyclic compounds via formic acid-mediated reductive coupling strategy over Nitrogen-Coordinated cobalt Single-Atom catalysts

The selective formation of C = N bonds through the formic acid-mediated reductive coupling of nitro groups with carbonyl groups over heterogeneous catalysts poses challenges due to the corrosion of metal catalysts by formic acid and the rapid further hydrogenation of C = N into C-N bonds. In this study, we demonstrate that nitrogen-coordinated cobalt single-atom catalysts exhibit robust activity in this transformation. Various imines and N-heterocyclic compounds, including benzimidazoles, quinazolines, and pyrroles, can be synthesized at a modest temperature of only 70 °C. The high catalytic activity is attributed to the synergistic roles of nitrogen and cobalt atoms, serving as basic and active sites, respectively. Experimental data, complemented by density functional theory (DFT) calculations, clearly indicate that the transfer hydrogenation of nitrobenzene preferentially proceeds via the “direct” pathway rather than the “condensation” pathway. Moreover, the reduction of C = N bonds into C-N bonds demands much higher energy than the reduction of nitro groups, thereby enabling high selectivity towards C = N bonds. The findings of this study are expected to provide a novel approach for selective C = N bond formation and contribute to a deeper understanding of the mechanism underlying the reductive amination process.

Synthesis, structural characterization and antitrypanosomal activity of ferrocenyl-based imines with (2 or 4)-nitrophenyl-2-furan group

Two new metallocene complexes with formulation [Fe(η5-C5H5){(η5-C5H4)-NCH-2-C4H2O-(5-C6H4-2-NO2)}] (3) and [Fe(η5-C5H5){(η5-C5H4)-NCH-2-C4H2O-(5-C6H4-4-NO2)}] (4) have been synthesized and their antitrypanosomal activity has been evaluated. Complexes 3 and 4 were obtained by condensation reaction of ferrocenylamine (1) with respective 5-(2-nitrophenyl)-2-furancarboxaldehyde (2a) or 5-(4-nitrophenyl)-2-furancarboxaldehyde (2b). The complexes were fully characterized by spectroscopic techniques (FT-IR, 1H and 13C{1H} NMR, and HRMS), which confirm their correct obtainment. The crystal structures of 3 and 4 were also determined by single crystal X-ray diffraction. Furthermore, UV–visible studies revealed that compounds 3 and 4 exhibited suitable stability in DMSO:HEPES buffer solution (80:20) throughout 24 h. The in vitro antiparasitic activities of ferrocenyl imine derivatives 3 and 4 were assessed against two species of parasites, Trypanosoma cruzi (T. cruzi) and Trypanosoma brucei (T. brucei). The obtained results revealed that compound 3 (EC50 = 0.44 μM) exhibited nearly a 40-fold greater efficacy as an anti-T. brucei agent compared to derivative 4 (EC50 = 16.0 μM). Moreover, compound 3 demonstrated superior potency when compared with its organometallic analogs (EC50 = 2.42–13.3 μM), which were previously reported by our research group. Interestingly, the EC50 value of 3 was found to be 8 times greater than that of nifurtimox (EC50 = 3.56 μM). The cytotoxicity of the ferrocenyl imines was also evaluated on the L6 rat skeletal myoblast cell line.

One pot, two-step synthesis of 2-(subs.)-1H-benzimidazoles using wet copper slag as magnetically separable and recyclable catalyst

This work describes the first-ever use of Wet copper slag for 2-(subs.)-1H-benzimidazoles synthesis. It is a by-product of the copper refining and smelting processes utilized as a basic catalyst in the present work. Wet copper slag is prepared by immersing a natural copper slag in water to improve the hydroxyl group and, hence, basicity. Iron oxide content in the copper slag helps provide the basic environment and uses surrounding air for the successful oxidative condensation of imines and o-phenylenediamine. Various aldehydes reacted well with p-anisidine for imine synthesis. Further reaction with substituted o-phenylenediamine and o-phenylenediamine gives desired 2-(subs.)-1H-benzimidazoles in environmental-friendly ethanol: water (9:1) as solvent at 85 °C within 40 to 60 min. The present method showed critical advantages of mild reaction conditions, wide availability, recyclability, and magnetic separability of a Copper-slag with moderate to excellent product yields. Overall, the present approach offers a promising route for the efficient and sustainable synthesis of 2-(subs.)-1H-benzimidazoles, which have a wide range of applications in various fields, including pharmaceuticals, agrochemicals, and materials science.

Efficient Asymmetric Syntheses of Chiral Imines with Multi-Stereocenters

Efficient Asymmetric Syntheses of Chiral Imines with Multi-Stereocenters

A Phosphine-Oxide Cobalt(II) Complex and Its Catalytic Activity Studies toward Alcohol Dehydrogenation Triggered Direct Synthesis of Imines and Quinolines.

Herein, a new pincer-like amino phosphine donor ligand, H2L1, and its phosphine-oxide analog, H2L2, were synthesized. Subsequently, cobalt(II) complexes 1 and 2 were synthesized by the reaction of anhydrous Co(II)Cl2 with ligands H2L1 and H2L2, respectively. The ligands and complexes were fully characterized by various physicochemical and spectroscopic characterization techniques. Finally, the identity of the complexes 1 and 2 was confirmed by single crystal X-ray structure determination. The phosphine ligand containing complex 1 was converted to the phosphine oxide ligand containing complex 2 in air in acetonitrile solution. Both complexes 1 and 2 were investigated as precatalysts for alcohol dehydrogenation-triggered synthesis of imines in air. The phosphine-oxide complex 2 was more efficient than the phosphine complex 1. A wide array of alcohols and amines were successfully reacted in a mild condition to result in imines in good to excellent yields. Precatalyst 2 was also highly efficient for the synthesis of varieties of quinolines in air. As H2L2 in 2 has side arms that can be deprotonated, we investigated complex 2 for its base (KOtBu) promoted deprotonation events by various spectroscopic studies and DFT calculations. These studies have shown that mono deprotonation of the amine side arm attached to the pyridine is quite feasible, and deprotonation of complex 2 leads to a dearomatized pyridyl ring containing complex 2a. The mechanistic investigations of the catalytic reaction, by a combination of experimental and computational studies, have suggested that the dearomatized complex, 2a acted as an active catalyst. The reaction proceeded through the hydride transfer pathway. The activation barrier of this step was calculated to be 26.5 kcal/mol, which is quite consistent with the experimental reaction temperature under aerobic conditions. Although various pincer-like complexes are explored for such reactions, phosphine oxide ligand-containing complexes are still unexplored.

Copper Phenylacetylide and TiO2 Modification for an Efficient Visible-Light-Driven Oxidative Coupling of Amines.

The selective oxidation of amines to imines under mild conditions has attracted much attention. Our study reveals that copper phenylacetylide (PhC2Cu) could serve as an efficient photocatalyst for imine synthesis under visible-light irradiation (>400 nm). Utilizing benzylamine as a model reactant, PhC2Cu achieves an imine yield of 50.4%, which is 5 times higher than that of P25 under the same conditions and comparable to the yield obtained by the 3 wt % Au/P25 photocatalyst (55.4%). Further loading 3.9 nm TiO2 onto PhC2Cu through tetrabutyl titanate hydrolysis increases the imine yield to 84.7%, with a Ti:Cu atomic ratio of 3.65%. Control experiments, photoluminescence (PL) spectra, optical pump terahertz probe (OPTP) spectra, and electron spin resonance (ESR) tests confirm that the optimized TiO2 modification promotes the separation of excited carriers and electron transfer in PhC2Cu and facilitates the activation of surface oxygen, thereby enhancing the formation of superoxide radicals, a key active oxygen species in the reaction system. This work presents a promising strategy for efficient imine synthesis via amine coupling and expands the application field of PhC2Cu-based photocatalysts.

Synthesis of α,α-Difluoro-β-amino Ketones from N-Boc-α-Amidosulfones and Pentafluoro-gem-diols.

To circumvent the synthesis and isolation of imines, a method was devised to construct α,α-difluoro-β-amino ketones from N-Boc-α-amidosulfones. The reactive nucleophiles, difluoroenolates, are generated in situ from the pentafluoro-gem-diols using cesium fluoride in pyridine. NMR studies confirm the role of the α-amidosulfones in this process. Incubation of the α,α-difluoro-β-amino ketones in rat serum demonstrates the relative stability of this structure as well as its value as a chemical probe or lead.

Thiophene-Based Covalent Triazine Frameworks as Visible-Light-Driven Heterogeneous Photocatalysts for the Oxidative Coupling of Amines.

This study reports on a metal-free Covalent Triazine Framework (CTF) incorporating bithiophene structural units (TP-CTF) with a semicrystalline structure as an efficient heterogeneous photocatalyst under visible light irradiation. The physico-chemical properties and composition of this material was confirmed via different characterization solid-state techniques, such as XRD, TGA, CO2 adsorption and FT-IR, NMR and UV-Vis spectroscopies. The compound was synthesized through a solvothermal process and was explored as a heterogeneous photocatalyst for the oxidative coupling of amines to imines under visible light irradiation. TP-CTF demonstrated outstanding photocatalytic activity, with high conversion rates and selectivity. Importantly, the material exhibited exceptional stability and recyclability, making it a strong candidate for sustainable and efficient imine synthesis. The low bandgap of TP-CTF enabled the efficient absorption of visible light, which is a notable advantage for visible-light-driven photocatalysis.

Constructing 2D/2D g-C3N4/BiOCl Z-scheme heterojunction for synthesis of imines via photocatalytic coupling of benzylamine

Here, 2D/2D Z-scheme heterojunctions, BiOCl/g-C3N4 (CN-B), are successfully prepared for the photocatalytic coupling of benzylamine (BA) to N-benzylidenebenzylamine (NBA) in air atmosphere under visible light. The high conversion (96.1 %) of BA can be achieved over the optimal catalyst (CN-B-1.6), with a selectivity of NBA (95.2 %). The interface charges are redistributed on CN-B because of the strong interaction between BiOCl and g-C3N4, benefiting to the activation of substrates. The results of In situ diffuse reflectance infrared Fourier-transform spectroscopy (in situ DRIFTS), Electron paramagnetic resonance (EPR) and X-ray photoelectron spectra (XPS) reveal that O2 and BA molecules can be activated via coordinating on the interface of CN-B, thus improving the photocatalytic performance. The migrated pathway of photogenerated carriers follows the mechanism of Z-scheme heterojunction, improving the utilization of electrons-holes. Finally, we put forward a possible mechanism at a molecular scale to explain the photocatalytic pathway. This work emphasizes how to create an effective heterojunction photocatalyst for the photocatalytic organic synthesis.

An Insight into Fluorinated Imines and Hydrazones as Antibacterial Agents.

Fluorinated imines (Schiff bases) and fluorinated hydrazones are of particular interest in medicinal chemistry due to their potential usefulness in treating opportunistic strains of bacteria that are resistant to commonly used antibacterial agents. The present review paper is focused on these fluorinated molecules revealing strong, moderate or weak in vitro antibacterial activities, which have been reported in the scientific papers during the last fifteen years. Fluorinated building blocks and reaction conditions used for the synthesis of imines and hydrazones are mentioned. The structural modifications, which have an influence on the antibacterial activity in all the reported classes of fluorinated small molecules, are highlighted, focusing mainly on the importance of specific substitutions. Advanced research techniques and innovations for the synthesis, design and development of fluorinated imines and hydrazones are also summarized.