Imine Functionality Research Articles

Iminium-Bridged Resorcinol-Silane Networks and Their Pyrolyzed Derivatives as Electrode Materials for the Electrocatalytic Oxygen Reduction Reaction and Supercapacitors.

We report the synthesis of iminium-bridged resorcinol-silane (I-R-S) gel networks through the reaction of resorcinol with 3-aminopropyl triethoxysilane (APTES) in the presence of acetone under ambient conditions. Ambient pressure drying leads to monolithic gels with minimal shrinkage and cracks, eliminating the use of conventional supercritical drying. The gels were found to have bulk and skeletal densities of 0.90 and 1.23 g/cm3, respectively. Interestingly, it was found that acetone plays the dual role of solvent (solubilizing the precursors, APTES, and resorcinol) and reactant by reacting with amine present in APTES to form imine functionalities. Furthermore, the imine was found to react with resorcinol to form I-R-S gel networks. The I-R-S gel was found to be hydrophobic with a contact angle of between 99 and 103°. Upon pyrolysis at higher temperatures (600, 800, and 1000 °C), the I-R-S gels transformed to silica containing N-doped carbon as confirmed by X-ray photoelectron spectroscopy (XPS). Further removal of silica by hydrofluoric acid (HF) treatment lead to porous N-doped carbon which was found to effectively electrocatalyze the oxygen reduction reaction (ORR) by mixed 3e- pathway. Note that the sample pyrolyzed at 600 °C followed by treatment with HF displayed an ∼2e- pathway with a higher peroxide yield of 91%. Due to the high specific surface area and increased microporosity, the pyrolyzed samples treated with HF were found to exhibit a specific capacitance of 213 F/g with capacity retention of 90% for up to 2100 cycles.

Dinuclear Copper(I) Complexes Supported by Bis‐Tridentate N‐Donor‐Ligands: Turning‐On Tyrosinase Activity

AbstractFour structurally related bis‐tridentate N‐donor ligands with either two secondary amine or two imine functions were synthesized, and the corresponding dicopper(I) complexes were investigated as catalysts for the tyrosinase‐like conversion of 2,4‐di‐tert‐butylphenol (DTBP‐H) to 3,5‐di‐tert‐butylquinone (DTBQ). Notably, the imine systems show evidence for both a μ‐η2 : η2‐peroxo‐dicopper(II) species and catalytic conversion of DTBP‐H to DTBQ. Moreover, kinetic studies indicate that a dinuclear copper‐oxygen species is involved in the monooxygenation of DTBP‐H. In contrast, the amine systems do not show monooxygenase activity. Comparison of the experimentally determined catalytic activities with DFT‐optimized geometries of μ‐η2 : η2‐peroxo‐dicopper(II) intermediates suggests that the ligand rigidity of the imine systems allows equatorial attack of the substrate and, thus, subsequent monooxygenation whereas this is not possible in the amine systems due to the fact that no free equatorial positions are available in the μ‐peroxo intermediate.

Atmospheric Oxidation of Imine Derivative of Piperazine Initiated by OH Radical

The cyclic imine 1,2,3,6-tetrahydropyrazine (THPyz) has been observed to be the major atmospheric photo-oxidation product of piperazine, a widely used solvent in carbon-capture technology, yet little is known about its own fate. Very few studies have focused on the atmospheric chemistry of imines in general, despite consistently appearing as major products of amine oxidation. In this work, we explore the reaction mechanism of THPyz oxidation initiated by OH radicals, as well as the fate of the first-generation C-centered (alkyl) and N-centered (aminyl) radical products, with quantum chemistry and theoretical kinetics methods. We predict that the major initial reaction steps involve H-abstraction from a carbon adjacent to the amine nitrogen, leading to subsequent formation of a second imine function via the O2-addition/HO2-elimination pathway. Calculated yields of potentially hazardous products are low but non-negligible. Typically carcinogenic compounds, nitrosamines and nitramines, are expected to have a maximum yield of ∼7% and ∼11%, respectively, under high NOx regimes, considering the uncertainties in the obtained rates. Low yield (1–14%) of an isocyanate is also predicted, formed in a channel following initial H-abstraction from the imine carbon. The aminyl radical formed from OH radical addition to the imine carbon undergoes fast C–C bond scission, leading to an imidic acid. These pathways are minor for OH radical oxidation of THPyz but could be more competitive for other Schiff bases.

Photocurable extended vanillin-based resin for mechanically and chemically recyclable, self-healable and digital light processing 3D printable thermosets

A vanillin-based photocurable resin was designed for circularity by incorporation of imine functionalities through a Schiff-base reaction between the aldehyde function of vanillin and amino group of ethylene diamine. Sufficient flexibility was provided by a short aliphatic segment introduced by reaction of vanillin with ethylene carbonate, while photocurability was obtained by subsequent methacrylation. The cured thermoset had good solvent resistance, relatively high glass transition temperature (∼75 °C) and good thermal stability with an onset of degradation above 300 °C. Due to the crosslinked structure and imine linkages, the thermoset expressed malleability, self-healing and thermal reprocessability. Furthermore, it could be chemically recycled by immersing in ethylene diamine, which activated transimination. The obtained oligomeric product with amine-terminal groups could be utilized for production of new thermoset films. Tensile testing illustrated similar elastic modulus for mechanically and chemically recycled thermosets, while a slight increase was observed for the self-healed samples, ascribable to a completion of the curing during the post-processing. At the same time elongation and stress at break slightly decreased. Finally, the suitability of the resin for the production of 3D objects by means of digital light processing (DLP) 3D printing was demonstrated.

Enantioselective Reductive N-Cyclization–Alkylation Reaction of Alkene-Tethered Oxime Esters and Alkyl Iodides by Nickel Catalysis

Asymmetric cross-electrophile difunctionalization of tethered alkenes has become a powerful tool for the production of chiral cyclic scaffolds; however, the current studies all focus on carbocyclization reactions. Herein, we report an N-cyclization-alkylation reaction and thus showcase the potential of heterocyclization for accessing new enantioenriched cyclic architectures. This work establishes a new approach for enantioselective aza-Heck cyclization/cross-coupling sequence, which remains a long-standing unsolved challenge for the synthetic community. The reaction proceeds with primary, secondary, and a few tertiary alkyl iodides, and the use of newly defined ligands gave highly enantioenriched pyrrolines with improved molecular diversity under mild conditions. The presence of imine functionality allows for further structural variations.

Strong proton transfer from phenolic ring to imine functionality in 1D azido and dicyanamido bridged Mn(II) coordination polymers: Synthesis, crystal structure and magnetic studies

In this research, two new 1D coordination polymers of Mn(II), [Mn(LH)2(µ1,5-dca)2]n (1) and [Mn(LH)2(µ1,3-N3)(CH3OH)(N3)]n (2) were synthesized and characterized by elemental analysis, spectroscopic methods, single crystal X-ray analysis and magnetic measurements (LH = Schiff base ligand obtained from the reaction of 2-hydroxy-1-naphthaldehyde and 2-amino-5-chloropyridine). These compounds were synthesized by the reaction of LH, MnCl2·4H2O and NaN(CN)2 (for compound 1) or NaN3 (for compound 2) in 1:1:2 M ratio in methanol. The spectroscopic and structural studies indicated that strong intramolecular proton transfer from naphtholic oxygen to the imine nitrogen is occurred in the ligand and due to this; the nitrogen atom of imine functionality is not coordinated to the metal core. As a result, the ligand is coordinated to the metal core as monodentate neutral ligand. The proton transfer process was attributed to the strong electron withdrawing properties of 5-chloropyridine ring. In the structure of compound 1 and 2, the manganese ions are connected to each other through µ1,5-dca and µ1,3-azide bridges, respectively to form 1D coordination polymers. The magnetic measurements showed the presence of antiferromagnetic interactions between Mn∙∙∙Mn cores in both of the obtained 1D coordination polymers, whereat the exchange interaction is an order of magnitude stronger in azido compared to dicyanamido bridged compound (–3.7 cm−1 vs. –0.30 cm−1).

Metal-Ligand Cooperativity in Iron Dinitrogen Complexes: Proton-Coupled Electron Transfer Disproportionation and an Anionic Fe(0)N2 Hydride.

Metal-ligand cooperativity and redox-active ligands enable the use of open-shell first-row transition metals in catalysis. However, the fleeting nature of the reactive intermediates prevents direct inspection of the relevant catalytic species. By employing phosphine α-iminopyridine (PNN)-based complexes, we show that chemical and redox metal-ligand cooperativity can be combined in the coordination sphere of iron dinitrogen complexes. These systems show dual activation modes either through deprotonation, which triggers reversible core dearomatization, or through reversibly accepting one electron by reducing the imine functionality. (PNN)Fe(N2) fragments can be obtained under mildly reducing conditions. Deprotonation of such complexes induces dearomatization of the pyridine core while retaining a terminally coordinated N2 ligand. This species is nevertheless stable in solution only below -30 °C and undergoes unusual ligand-assisted redox disproportionation through proton-coupled electron transfer at room temperature. The origin of this phenomenon is the significant lability of the α-imine C-H bonds in the dearomatized species, where the calculated bond dissociation free energy is 48.7 kcal mol-1. The dispropotionation reaction yields an overreduced iron compound, demonstrating that the formation of such species can be triggered by mild bases, and does not require harsh reducing agents. Reaction of the dearomatized species with dihydrogen yields a rare anionic Fe hydride that binds dinitrogen and features a rearomatized core.

Unstability of cinnabarinic acid, an endogenous metabolite of tryptophan, under situations mimicking physiological conditions

The kynurenine pathway of l-tryptophan metabolism produces several compounds of high physiological importance in the central nervous system and the immune response. Among them, cinnabarinic acid (CA) which results from the condensation of two molecules of 3-hydroxy-anthranilic acid has been identified as an activator of the metabotropic glutamate receptor (mGluR4) and the aryl hydrocarbon receptor (AhR). However, very few information was available about its stability under physiological conditions. This article shows that CA is unstable even under very soft conditions mimicking physiological conditions. Incubations in phosphate buffer pH 7.4 lead to several products coming from various reactions such as addition of H2O on its quinone imine function, decarboxylation, and deamination. Moreover, CA rapidly reacts with glutathione (GSH), leading to adducts that result from the Michael type addition of this physiological nucleophile on the quinone imine function of CA. These preliminary results indicate that the great reactivity of CA and the nature of its various products should be considered when studying its activity towards any biological target.

C-Methylation Of Organic Substrates. A Comprehensive Overview. Part IVa. Methylating Agents Other Than Methane, Methanol, and Methyl Metals

: C-Methylation of organic substrates was accomplished with a number of methylating agents other than methane, methanol, and methyl metals. They include methyl halides (MeX, X = I, Br, Cl, F), methyl-containing halogenated reagents, methyl peroxides, dimethyl carbonate (DMC), dimethylsulfoxide (DMSO), N,N-dimethyl formamide (DMF), diazomethane, formate salts, trioxane, CO/H2, CO2/H2, and dimethyl ether (DME). Under particular conditions, some methyl- containing molecules such as polymethylbenzenes, methylhydrazine, tris(diethylamino) sulfonium difluorotrimethylsilicate, methyl tosylate, long-chain alkyl alcohols, and acetic acid unexpectedly C-methylated a variety of organic substrates. A few cases of C-methylation were only reported to occur in the absence of catalysts. Otherwise, transition metal complexes as catalysts in conjunction with specific ligands and bases were ubiquitously present in most C-methylation reactions. Of the reactions, Suzuki-Miyaura-type cross-coupling remained of paramount importance in making 11CH3-bearing positron emission tomography tracers (PETs), one of the best applications of such methylation. Methylation proceeded at C(aromatic)-X, C(sp3)-X C(sp2)-X, and C(sp)-X of substrates (X = H, halogen). Ortho-methylation was regioselectively observed with aromatic substrates when they bear moieties such as pyridyl, pyrimidyl, amide, and imine functionalities, which were accordingly coined ‘ortho-directing groups’.

Green, economical synthesis of nitrogen enriched carbon nanoparticles from seaweed extract and their application as invisible ink and fluorescent film

In this article, we synthesized fluorescent nitrogen-enriched carbon nanoparticles (N-CNPs), which were prepared via the hydrothermal treatment of pyrolyzed seaweed extract and ethylene diamine at 160 °C for 12.0 h. These N-CNPs demonstrated a 12 nm average diameter with carbonyl, hydroxyl, and imine functionality on their surface. The zeta potential value was found to be negative which further confirms the presence of acid/imine groups on the surface of N-CNPs. The prepared N-CNPs showed strong blue fluorescence with 24% quantum yield under UV light illumination. Here, we introduced metal-free water dispersed N-CNPs as invisible ink for security purposes. The information was written by the N-CNPs in TLC plate and N-CNPs/PVA flexible composite film is invisible in daylight and can be readable in UV light illumination.

Transition Metal Complex Catalyzed Photo- and Electrochemical (De)hydrogenations Involving C=O and C=N Bonds

AbstractHerein, we summarize the photo- and electrochemical protocols for dehydrogenation and hydrogenations involving carbonyl and imine functions. The three basic principles that have been explored to interconvert such moieties with transition metal complexes are discussed in detail and the substrate scope is evaluated. Furthermore, we describe some general thermodynamic and kinetic aspects of such electro- and photochemically driven reactions.1 Introduction2 Dehydrogenation Reactions2.1 Electrochemical Dehydrogenations Using High-Valent Metal Species2.2 Electrochemical Dehydrogenations Involving Metal Hydride species2.3 Photochemically Driven Dehydrogenation3 Hydrogenation Reactions3.1 Electrochemical Protocols3.2 Photochemical Protocols4 Conclusion5 Abbreviations

Palladium complex of sulphated schiff base with ortho-vanillin as catalyst for O-arylation of phenol

Organochalcogen compounds due to their hassle-free synthesis and air and moisture insensitive nature have attracted substantial attention in scientific world. They have profound applications in the development of catalytic systems that have emerged as efficient catalysts in various chemical transformations. Organochalcogen ligands have contributed to the backbone of several catalytic systems used for O-arylation reaction which is an effective tool for the synthesis of diaryl ether substituents. Synthesis of several bioactive compounds rely on this method. A thioether ligand L1 has been prepared by reaction of 3-(chloropropyl)amine hydrochloride with the insitu generated PhSNa. The L1 has been condensed with o-vanillin to synthesize ligand L2 having imine functionality. The structure of ligand L2 has been authenticated using proton and carbon-13 NMR techniques. The synthesis of an efficient N, S coordinated bidentate novel palladium complex 1 ([Pd(L2)Cl2]), by the reaction of ligand L2 with [PdCl2(CH3CN)2] in chloroform-hexane system has been carried out. The structure of 1 has also been corroborated by 1H ,13C{1H} NMR and mass spectroscopic techniques. Its catalytic potential has been tested for etherication of various aryl bromides with phenol. Cheaply available aryl chlorides have also been coupled to determine the efficiency of Pd(II) complex 1. The complex 1 gave good yields while exhibiting excellent tolerance towards electronically diverse aryl halides with 0.5 mol% catalyst loading. The nature of catalysis has been found to be purely homogeneous on conducting mercury and triphenylphosphine poisoning tests.

2-((E)-1-((E)-(2-methoxybenzylidene)hydrazono)ethyl)phenol based cost-effective sensor for the selective detection of Eu3+ ions

The detection of lanthanides has emerged as an attractive field of research due to potential applications in biomedical sciences. Here we design a simple and cost-effective ligand 2-((E)-1-((E)-(2-methoxybenzylidene)hydrazono)ethyl)phenol (MHEP) that acts as a rapid selective sensor for Eu3+ ions with a blue shift in UV–visible, ratiometric enhancement in fluorescence intensity and significant redox potential changes in cyclic voltammetric graph among various metal ions in the CH3OH:H2O (1:1, v/v) solvent system. The UV–visible titrations are used to determine the limit of detection 1.2 × 10−7 M, the limit of quantitation 41 × 10−7 M and linear range 22 × 10−6 M−1 to 124 × 10−6 M−1 are determined. The binding stoichiometry is determined by Job’s plot, mole ratio method and Benesi-Hildebrand plot that is found 1:1 (MHEP:Eu3+) with association constant 2.360 × 105 M−1. The IR spectroscopy reveals the role of imine functionalities for the Eu3+ ions detection.

Topology-Controlled AIEE of Iminocoumarin Luminophores.

Aggregation-induced emission enhancement (AIEE) is an unusual phenomenon where luminophores show a higher photoluminescence efficiency in the aggregated and solid state. We report the design and synthesis of a series of luminophores 1-4 with imine functionality at 6 position of coumarin and studied their AIE propensities on self-assembly. The effect of the topology of the phenolic hydroxyl group on the emission behaviour of the luminophores has been investigated. The imines show significant solvatochromism with high emission in non-polar solvents, whereas the emission gets quenched in the polar solvent. The fluorescence in the toluene-hexane mixture arises due to the aggregation of fluorophores and falls under the category of AIEE. Not only the solution state emission of the isomeric iminocoumarin luminophores is notably varied, but also their solid-state emission found to be significantly different from each other. Moreover, the iminocoumarin 1 selectively recognizes Fe(III) over Fe(II) with a prominent color change. In situ oxidation of Fe(II) with H2 O2 exhibits the same effect like Fe(III) and developed a chemical combinational logic gate.

Design, synthesis, DFT calculations, molecular docking and antimicrobial activities of novel cobalt, chromium metal complexes of heterocyclic moiety-based 1,3,4-oxadiazole derivatives

A Schiff base, 5-(4-methylphenyl)-4-[(pyridin-2-ylmethylidene)amino]-4H-1,2,4-oxadiazole as a bidentate ligand has been synthesized by the reaction between the 4-amino-5-(4-methylphenyl)-4H-1,3,4-oxadiazole and aromatic aldehyde. The Schiff base reacted with CoCl3·6H2O and CrCl3·6H2O in ethanol to yield 1,3,4-oxadiazole complexes. The structures of synthesized ligand and their complexes have been established on the basis of their IR, Mass and 1H-NMR spectra. Electronic and geometric structures of both cobalt and chromium complexes were investigated by density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM) calculations. DFT-based reactivity calculations estimated the studied system as strong electrophile and/or strong nucleophile in polar organic reactions. Moreover, most reactive sites were predicted theoretically based on the delocalized and localized indexes. The nature of Ligand-Metal chemical bonding is discussed in terms of the natural bond orbital (NBO) and QTAIM analysis. Accordingly, the metal ions such as cobalt and chromium are bidentate coordinated with the Schiff base by nitrogen atoms of imine function and pyridine, to form stable complexes. Furthermore, the chromium ions have an affinity superior to the cobalt ions towards Schiff base ligand. In addition, the results of the antibacterial activity in-vitro show that the metal complexation confers an increase in the antibacterial activity of the complexed ligand compared to the free ligand against both Gram-positive and Gram-negative bacteria with broad spectrum activity. In silico molecular docking studies of the ligands and their complexes were applied to describe the probable binding modes into the active site of Escherichia coli (E. coli) FabH and Salmonella typhimurium LT2 neuraminidase (STNA) receptors. The increase in biological activity could be attributed to the high stability of the complexes and strong affinities to bacterial enzyme receptors. Communicated by Ramaswamy H. Sarma

Synthesis, characterization, DFT study and antioxidant activity of (2-hydroxynaphthalen-1-yl) methyl 2-hydroxyphenyl amino phosphonic acid

New molecule α-aminophosphonate namely (2-hydroxynaphthalen-1-yl) methyl 2-hydroxyphenyl amino phosphonic acid (HMHP) was synthesized by condensation based on 2-amino phenol and 2-hydroxy naphthaldehyde. During the reaction, imine intermediate namely 2-hydroxyphenyl imino naphthalen-2-ol (HIN) was formed before adding acid phosphorous to the reaction mixture. It can be confirmed the concept of Kabachinik-Fields reaction, which it's perform the attachment of phosphorus atom to the carbon atom of imine function. Both compounds were identified using IR, 1H, 13C and 31P NMR spectroscopic techniques. The evaluation of the antioxidant activity of HMHP and HIN was investigated by utilizing several in vitro assays: scavenging activity against DPPH radical and H2O2 non radical, β-carotene/linoleic acid against linoleic peroxidation, reducing power against ferric oxidation and phosphomolybdate (TAC) against molybdate ion oxidation. Results indicate that HMHP reflects greater antioxidant potency compared to HIN in most tests, where it is apt to offer the hydrogen radical very well at IC50 (37.64 ± 1.43) in DPPH test. For the other tests the inhibition percent at 50 % are relatively closed between them. Except the H2O2 scavenging, while HIN exhibited excellent activity at IC50 (24.7306 ± 0.71785). The quantum chemical calculations were performed using density functional theory (DFT) to study the effects of the transfer electronic and proton transfer on the antioxidant activities of the synthesized compounds. Also, theoretical FT-IR was calculated. The experimental results are in comfort with those calculated theoretically.

Design of Stimuli-Responsive Dynamic Covalent Delivery Systems for Volatile Compounds (Part 1): Controlled Hydrolysis of Micellar Amphiphilic Imines in Water.

Despite their intrinsic hydrolysable character, imine bonds can become remarkably stable in water when self-assembled in amphiphilic micellar structures. In this work, we systematically studied some of these structures and the influence of various parameters that can be used to take control of their hydrolysis, including pH, concentration, the position of the imine function in the amphiphilic structure, relative lengths of the linked hydrophilic and hydrophobic moieties. Thermodynamic and kinetic data led us to the rational design of stable imines in water, partly based on the location of the imine function within the hydrophobic part of the amphiphile and on a predictable quantitative term that we define as the total hydrophilic-lipophilic balance (HLB). In addition, we show that such stable systems are also stimuli-responsive and therefore, of potential interest in trapping and releasing micellar components on demand.

Neutral Unsymmetrical Coordinated Cyclophane Polymerization Catalysts.

Cyclophane structures can control steric pressure in the otherwise open spaces of square‐planar d8‐metal catalysts. This elegant concept was so far limited to symmetrical coordinated metals. We report how a cyclophane motif can be generated in ligands that chelate via two different donors. An ancillary second imine in the versatile κ2‐N,O‐salicylaldiminato catalyst type enables ring closure via olefin metathesis and selective double bond hydrogenation to yield a 30‐membered ring efficiently. Experimental and theoretical analyses show the ancillary imine is directed away from the active site and inert for catalysis. In ethylene polymerization the cyclophane catalyst is more active and temperature stable vs. an open structure reference, notably also in polar solvents. Increased molecular weights and decreased degrees of branching can be traced to an increased energy of sterically demanding transition states by the encircling cyclophane while chain propagation remains highly efficient.

Access to Polycyclic Indol(en)ines viaBase‐Catalyzed Intramolecular Dearomatizing 3‐Alkenylation of Alkynyl Indoles

Main observation and conclusionPolycyclic indolines and indolenines were synthesized via base‐catalyzed intramolecular dearomatizing 3‐alkenylation reactions of alkynyl indoles 1 at room temperature. The base enhanced the nucleophilicity of the carbon at the 3‐position of the indole moiety, facilitating an exclusive 5‐exo‐dig cyclization reaction with the alkyne to form spiroindolenines 2. The imine functionality of 2 could undergo in situ nucleophilic addition to form spiroindolines 3 when R was a carbamoyl group or reduction to form spiroindolines 4 when R was H.

Synthesis of Stannylated Aryl Imines and Amines via Aryne Insertion Reactions into Sn-N Bonds.

The reaction of in situ generated arynes with stannylated imines to provide ortho-stannyl-aniline derivatives is reported. The readily prepared trimethylstannyl benzophenone imine is introduced as an efficient reagent to realize the aryne σ-insertion reaction. The imine functionality is an established N-protecting group and insertions proceed with good yields and good to excellent regioselectivities. The product anilines are valuable starting materials for follow-up chemistry thanks to the rich chemistry offered by the trimethylstannyl moiety.