Imine Functionality Research Articles

Polymeric nanoassembly of imine functionalized magnetite for loading copper salts to catalyze Henry and A3-coupling reactions

Poly(ethylenimine) was grafted on the magnetite (Fe3O4) nanoparticles, and subsequently reacted with different aldehydes to form the imine functionalities (Fe3O4-Imine NPs). Thus formed Fe3O4-Imine NPs could host copper salts generally used as the homogeneous catalyst in organic reactions with the stability prerequisite for the recycling. The expected chemical structures of Fe3O4-Imine NPs were ascertained by the FTIR and CHNS analyses. The physical structure of Fe3O4-Imine NPs was found to be corn-like assemblies from the images obtained by FESEM and HRTEM. The Fe3O4-Imine NPs assemblies possessed the superparamagnetic properties which made possible to withdraw these particles from the reaction solution efficiently. The copper salt loading capacity of the Fe3O4-Imine was lower than that of the Fe3O4-PEI, but the water content in the Fe3O4-Imine was higher (10 wt%) than that of the Fe3O4-PEI (2.5 wt%). Among different aldehydes and copper salts used, the Fe3O4-Imine formed by benzaldehyde and loaded with copper acetate salt exhibited better catalytic activity in the Henry reactions using water as the solvent. Also, the Fe3O4-Imine showed better catalytic activity than that obtained using the Fe3O4-PEI in both Henry reactions and A3-coupling of aldehyde, pyrrolidine, and phenyl acetylene reactants. The several representative examples of these coupling reactions were studied to understand the different parameters affecting the catalytic efficacy of copper acetate loaded Fe3O4-Imine.

Preparation of new enforcement polyamide nanocomposite filled by ternary layer double hydroxide and investigation of electrochemical activity, optical and thermal properties

Herein, we report synthesis and manipulation of new reinforced polyamide nanocomposites filled by modified ternary (Mg, Zn, Al) layered double hydroxide by a solution intercalation technique. First, a new optically and electrochemically active polyamide 5 containing a new combination of azobenzene unit, imine function, triphenylamine segment and pyridine moiety in the main chain was prepared by reaction of a newly dicarboxylic acid 3 and 2,6-diaminopyridine 4. Then, two resulting nanocomposites containing 3 and 6% of DLDH were prepared and structures, morphology, electrochemical activity, thermal and optically properties of them were investigated. Also, dye-modified ternary layered double hydroxide was obtained by a co-precipitation method. The π–π* transition related to trans azobenzene chromosphere showed a single absorption between 290 and 350 nm. The electrochemically active behavior of resulting films onto glassy carbon exhibited cyclic voltammetry peak at 0.5–0.9 V, which was enhanced by filling polymer matrix with modified DLDH. On the other hand, significant improvements at T5, T10 and char yields of resulting nanocomposites were observed as compared to the polymer.

Phosphasalalen Rare-Earth Complexes for the Polymerization of rac-Lactide and rac-β-Butyrolactone.

A series of new phosphasalalen pro-ligands, analogues of salalen but with an iminophosphorane replacing the imine functionality, and their corresponding rare-earth alkoxide and siloxide complexes were synthesized. The multinuclear NMR spectra and X-ray diffraction analyses revealed that, for the tert-butoxide and ethoxide complexes, the resulting phosphasalalen rare-earth product was composed of a mononuclear alkoxide and a binuclear complex containing bridged alkoxo and hydroxo groups, while an analogous binuclear complex was isolated as the sole product for the siloxide complex. All the complexes could catalyze the heteroselective ring-opening polymerization (ROP) of rac-lactide (Pr up to 0.77) with high catalytic activities and a controlled polydispersity. Remarkably, the yttrium and lutetium phosphasalalen complexes could also efficiently catalyze the ROP of rac-β-butyrolactone to produce syndiotactic polymers (Pr up to 0.73) while their salalen analogues were inert, revealing the special effects of the iminophosphorane moiety. Detailed end-group analyses and kinetic investigations suggested that the alkoxo-hydroxo-bridged complexes maintained their binuclear structures in the polymerization.

Facile One‐Pot Assembly of Push–Pull Imines by a Selective C–F Substitution Process in Aryl Fluorides

Herein, we report the synthesis of a series of push–pull imines by considering cyclic diamino substituent at the C‐centre and fluoroaryl substituent at the N‐centre. This has been achieved by a selective aromatic nucleophilic substitution of different fluoroarenes by N‐H‐substituted N‐heterocyclic imines (NHIs) at ambient conditions without any additional reagent. Solid‐state molecular structure analysis reveals the elongation of the central C–N bond of the imine functionality, which is consistent with the push–pull nature of these imines. The push–pull nature of these imines is further validated by computational studies.

Platinum nanoparticles embedded into polyaniline on carbon cloth: improvement of oxygen reduction at cathode of microbial fuel cell used for conversion of medicinal plant wastes into bio-energy

ABSTRACT A microbial fuel cell is a biological electrochemical system that extracts electrons stored in organic matter by oxidation using catalytic properties of microorganisms at bioanode. The major problem in such device, is however limited power production due to slow kinetic of oxygen reduction at cathode. It is worthwhile to develop new materials that fulfil these requirements. The polymerization of aniline onto carbon cloth for effective electrodeposition of platinum nanoparticles has been carried out by chronoamperometry and cyclic voltammetry. Three materials were thus elaborated, namely pristine carbon cloth, carbon cloth modified with platinum and carbon cloth modified by polymerization of aniline for immobilization of Pt-nanoparticles. The FTIR spectroscopy analysis revealed characteristic band located in 1720–1650 cm−1, attributed to imine function, main component in skeleton of polymer PANI chain. The modified materials have been utilized as cathode in cell inoculated with medicinal plant wastes for improvement of oxygen reduction. Modified cathode with CC-PANI-Pt proved higher performances in all respects: increase of cell voltage from 338 to 765 mV and power density from 862 to 1510 mW/m2 and abatement of COD of microbial inoculum leachate to 88%. Another feature of cell with modified cathode CC-PANI-Pt, was the enormous electric charge density harvested upon oxidation of 1 mL of acetate 7.62 C/cm2 compared to that of cell with pristine CC cathode 0.54 C/cm2. Nevertheless, coulombic efficiency for conversion of medicinal plant wastes into bioenergy was relatively lower 9%, making in evidence that elaborated electrochemical device was rather efficient and benificial environmentally than energetically.

Amino-Functionalized Porphyrin-Based Porous Organic Polymers for CO2 Capture and Hg2+ Removal

Functionalized porous organic polymers (POPs) with high Brunauer–Emmett–Teller (BET) surface area (SBET) and unique porosity are promising for CO2 capture and Hg2+ removal, although their facile synthesis remains a challenge. Herein, a kind of novel amino-functionalized porphyrin-based POPs was developed based on the Friedel–Craft acylation reaction and Schiff-base reaction, and melamine was adopted as both the rigid cross-linking bridges and the amino-functionalized agent for the construction of the polymers. The resultant polymers exhibited high SBET (587 m2/g) and pore volume (0.46 cm3/g) with abundant amino, imine, and triazine functionalities (42.08 wt %). The CO2 uptake reached 172 mg/g at 273 K and 1.0 bar and the maximum Hg2+ capacity reached 328.1 mg/g. In particular, the characteristic hierarchical micro/mesoporosity of the polymers was beneficial for the kinetic adsorption due to the fast diffusion of Hg2+ in the pore channels. This study offers a facile postfunctionalization strategy to fabricate the functionalized POPs with high surface area and unique hierarchical porosity.

Synthesis of 1,5‐Ring‐Fused Imidazoles from Cyclic Imines and TosMIC – Identification of in situ Generated N‐Methyleneformamide as a Catalyst in the van Leusen Imidazole Synthesis

Imidazoles fused with a cyclic system in 1,5‐position were synthesized via the van Leusen imidazole synthesis employing saturated aliphatic tricycles including an imine function in the base catalyzed cycloaddition reaction with p‐toluenesulfonyl‐methyl isocyanide (TosMIC). Thereby, N‐(tosylmethyl)formamide, a decomposition product of TosMIC, was found to act as a promoter of this reaction leading to considerably reduced reaction times and improved yields. Mechanistic studies revealed that N‐(tosylmethyl)formamide is transformed into N‐methyleneformamide acting as a catalyst in this reaction under the applied basic conditions. Being a Michael acceptor, the employed imines add to this compound, thus being transformed into iminium ions. The so formed intermediates facilitate the first step of the van Leusen imidazole synthesis, which is the addition of deprotonated TosMIC to the iminium subunit. N‐methyleneformamide is finally reformed during the overall reaction and can thus be considered as an organocatalyst of the studied cycloaddition reaction.

Density Functional Theory Investigation of the Binding of ThioTEPA to Purine Bases: Thermodynamics and Bond Evolution Theory Analysis.

Density functional theory with the ωB97X-D exchange-correlation functional together with implicit as well as explicit solvation is used to describe the reactions of the adenine and guanine purine bases on N,N',N″-triethylenethiophosphoramide (thioTEPA), an alkylating agent used as an anticancer drug. This reaction is decomposed into (i) a nucleophilic addition and (ii) a proton "migration" that is mediated by the solvent molecules. The calculations reveal that the first step is rate determining and that the presence of an explicit water molecule to mediate the proton migration has a negligible role on the kinetics of the first step, so that the focus is set on the first step of the reaction. ωB97X-D calculations highlight (i) the activation energy (Gibbs free enthalpy) is smaller for imine nitrogens than amine nitrogens, (ii) for the imine functions, the activation energy is slightly smaller for adenine than for guanine together with a larger exergonicity for the alkylation by adenine, and (iii) among the amine nitrogens, the presence of stabilizing H-bonds in the case of exocyclic amines leads to smaller activation energy than for the endocyclic ones. The reaction mechanisms are unraveled by employing the bond evolution theory, combining the use of electronic localization functions, and their evolution along the intrinsic reaction coordinate, with Thom's catastrophe theory. These analyses, suitable for highlighting the populations of the major monosynaptic and disynaptic basins, show (i) the reaction with imine nitrogens begins by the cleavage of the C-N aziridine bond and is followed by the simultaneous formation of the new C-N bond and the disappearance of the nitrogen lone pair, (ii) the reaction with the nitrogen atom of an endocyclic or exocyclic amine proceeds first by the formation of the cross-linking C-N bond and then by the cleavage of the C-N aziridine bond and the disappearance of the nitrogen lone pair, and (iii) in case ii, this bond breaking and forming occur before the transition state, which has been correlated to the increased Gibbs enthalpy of activation with respect to the reaction with the nitrogen atom of imine functions.

Fabrication of nanoscale covalent porous organic polymer: An efficacious catalyst for Knoevenagel condensation

Abstract Porous organic polymer (POP) plays an important role as a catalyst for their unique properties like high porosity, excellent thermal stability and persistence towards various solvents (polar/nonpolar). In this work, a nanoscale spherical POP is fabricated by simple polymerization between triformylphloroglucinol and triaminobenzene at room temperature following Schiff-base condensation. The micro-porosity, morphology, surface charge and functionality of the synthesized POP are thoroughly characterized using the relevant techniques. The POP demonstrates efficient catalysis for Knoevenagel condensation at room temperature with higher % of conversion (~98%). The presence of imine functionality with high negative potential attracts H+ ions to facilitate the catalysis. Available active sites of the material favour to coordinate the loosed water molecule for the formation of the product. Here almost complete product formation (almost 98%) is observed within 2 h at room temperature for Knoevenagel condensation between benzaldehyde and malononitrile. The synthesized catalyst also exhibits efficient reusability with retaining good catalytic stability.

Bis(imino)pyrazine-Supported Iron Complexes: Ligand-Based Redox Chemistry, Dearomatization, and Reversible C-C Bond Formation.

Iron complexes supported by novel π-acidic bis(imino)pyrazine (PPzDI) ligands can be functionalized at the nonligated nitrogen atom, and this has a marked effect on the redox properties of the resulting complexes. Dearomatization is observed in the presence of cobaltocene, which reversibly reduces the pyrazine core and not the imine functionality, as observed in the case of the pyridinediimine-ligated iron analogues. The resulting ligand-based radical is prone to dimerization through the formation of a long carbon-carbon bond, which can be subsequently cleaved under mild oxidative conditions.

Four-Component Fusion Protocol with NiO/ZrO2 as a Robust Recyclable Catalyst for Novel 1,4-Dihydropyridines.

Nickel oxide loaded on zirconia (NiO/ZrO2) as an expedient catalyst is reported for the synthesis of 18 unsymmetrical 1,4-dihydropyridine derivatives. The Lewis acidic nature of the catalyst proved an excellent choice for the one-pot, four-component fusion reaction with excellent yields of 89–98% and a completion time of 20–45 min. Mechanistic studies show that enamine and imine functionalities are the two possible pathways for the formation of 1,4-dihydropyridines with high selectivity. Crystal structures of two novel compounds (5a, 5c) were reported. The catalyst demonstrated reusability up to six cycles. The reaction at room temperature and ethanol as a solvent make this protocol green and economical.

Synthesis and molecular docking studies of imines as α-glucosidase and α-amylase inhibitors.

Imine functionality is found in many compounds with important biological activity. Thus, the development of novel synthetic approaches for imines is important. In this work, it is propose an easy, eco-friendly and straightforward synthesis pathway of aryl imines under microwave irradiation catalyzed by Alumina-sulfuric acid. In addition, the in vitro enzymatic inhibition, antioxidant activity and molecular docking studies were performed. The aryl imines were isolated with yields in the range of 37-94%. All aryl imines synthesized were evaluated for in vitro inhibitory potential against α-glucosidase and α-amylase enzymes and the results exhibited that the most of the compounds displayed inhibitory activity against both enzymes. The (E)-1-(4-nitrophenyl)-N-(pyridin-2-yl)methanimine (3d) was 1.15-fold more active than acarbose against α-amylase whilst the (E)-1-phenyl-N-(pyridin-2-yl)methanimine (3c) displayed similar activity that acarbose against α-glucosidase. The molecular docking studies in α-glucosidase and α-amylase reveal that aryl imines mainly establish an H-bond with the R2-subtituent and hydrophobic interactions with the R1-subtituent. The docking analysis reveals these synthetic aryl imines 3d-i interact in same active site than acarbose drug in both enzymes.

Mechanism of the Iron(0)-Catalyzed Hydrosilylation of Aldehydes: A Combined DFT and Experimental Investigation

Hydrosilylation is a fundamental organometallic transformation for the reduction of alkene, carbonyl, and imine functionalities. Herein, we use density functional theory (DFT) calculations, supplem...

Dehydroalkylative Activation of CNN- and PNN-Pincer Ruthenium Catalysts for Ester Hydrogenation.

Ruthenium-pincer complexes bearing CNN- and PNN-pincer ligands with diethyl- or diisopropylamino side groups, which have previously been reported to be active precatalysts for ester hydrogenation, undergo dehydroalkylation on heating in the presence of tricyclohexylphosphine to release ethane or propane, giving five-coordinate ruthenium(0) complexes containing a nascent imine functional group. Ethane or propane is also released under the conditions of catalytic ester hydrogenation, and time-course studies show that this release is concomitant with the onset of catalysis. A new PNN-pincer ruthenium(0)-imine complex is a highly active catalyst for ester hydrogenation at room temperature, giving up to 15 500 turnovers with no added base. This complex was shown to react reversibly at room temperature with two equivalents of hydrogen to give a ruthenium(II)-dihydride complex, where the imine functionality has been hydrogenated to give a protic amine side group. These observations have potentially broad implications for the identities of catalytic intermediates in ester hydrogenation and related transformations.

Chalcogen (S/Se) Ligated Palladium(II) Complexes of Bulky Ligands: Application in O‐Arylation of Phenol

AbstractTwo N‐pyrene based ligands L1 (1‐pyrene‐CH=N(CH2)2‐SPh) and L2 (1‐pyrene‐CH=N(CH2)2‐SePh) with an imine functionality and a chalcogen donor have been synthesized and characterized using 1H as well as 13C NMR spectral techniques. Palladium(II) complexes (1; PdCl2−ĸ2−L1 and 2; PdCl2−ĸ2−L2) of L1 and L2 have been prepared, isolated and characterized using NMR and single crystal X‐ray diffraction studies. The geometry around Pd is nearly square planar in these complexes and ligands are coordinated to the metal centre in a bidentate (S/Se, N) mode. The molecular complexes 1 and 2 have been explored as potential catalysts in O−arylation reaction between substituted aryl halides and phenol. Both the complexes showed excellent efficiency towards this coupling and a TON of 990 (maximum TOF 310) has been achieved using 0.1 mol% of catalyst 2. The effect of the nature of chalcogen donor atom (S/Se) on catalytic efficiency of the complexes has been observed as selenium congener was more efficient than sulphur counterpart.

Efficient Cobalt Catalyst for Ambient-Temperature Nitrile Dihydroboration, the Elucidation of a Chelate-Assisted Borylation Mechanism, and a New Synthetic Route to Amides.

N,N-Diborylamines have emerged as promising reagents in organic synthesis; however, their efficient preparation and full synthetic utility have yet to be realized. To address both shortcomings, an effective catalyst for nitrile dihydroboration was sought. Heating CoCl2 in the presence of PyEtPDI afforded the six-coordinate Co(II) salt, [(PyEtPDI)CoCl][Cl]. Upon adding 2 equiv of NaEt3BH, hydride transfer to one chelate imine functionality was observed, resulting in the formation of (κ4-N,N,N,N-PyEtIPCHMeNEtPy)Co. Single-crystal X-ray diffraction and density functional theory calculations revealed that this compound possesses a low-spin Co(II) ground state featuring antiferromagnetic coupling to a singly reduced imino(pyridine) moiety. Importantly, (κ4-N,N,N,N-PyEtIPCHMeNEtPy)Co was found to catalyze the dihydroboration of nitriles using HBPin with turnover frequencies of up to 380 h-1 at ambient temperature. Stoichiometric addition experiments revealed that HBPin adds across the Co-Namide bond to generate a hydride intermediate that can react with additional HBPin or nitriles. Computational evaluation of the reaction coordinate revealed that the B-H addition and nitrile insertion steps occur on the antiferromagnetically coupled triplet spin manifold. Interestingly, formation of the borylimine intermediate was found to occur following BPin transfer from the borylated chelate arm to regenerate (κ4-N,N,N,N-PyEtIPCHMeNEtPy)Co. Borylimine reduction is in turn facile and follows the same ligand-assisted borylation pathway. The independent hydroboration of alkyl and aryl imines was also demonstrated at 25 °C. With a series of N,N-diborylamines in hand, their addition to carboxylic acids allowed for the direct synthesis of amides at 120 °C, without the need for an exogenous coupling reagent.

Synthesis, characterization, structure and redox property of azo-amido and orthometallated azo-imine platinum(II) complexes

The reaction of the ligands bis-2,2′-(N-alkylamino)azobenzene, 1a–c, with K2[PtCl4] in a 1:1 ratio in methanol afforded two types of Pt(II) complexes, 2a–b and 2c. Ligands 1a–b give new Pt(II) amido azo complexes, whereas 1c forms an unexpected orthoplatinated azo imine complex through the unusual oxidative dehydrogenation of one secondary amine (–CH2–NH–) group of the ligand into an imine (–CHN–) function. All three complexes were characterized by 1H NMR and IR spectroscopy, together with elemental analysis. Furthermore, the solid-state structures of two complexes (2a and 2c) were determined using single crystal X-ray diffraction analysis. The diffraction analysis revealed that the ligand 1a binds with the Pt(II) ion in a monoanionic terdentate (N,N,N) fashion, offering a distorted square planar geometry where the fourth coordination site is satisfied by one chloride ligand. In contrast, the 1c ligand binds with the Pt(II) ion in a bi-anionic tetradentate (C,N,N,N) fashion, offering a distorted square planar geometry. Several weaker non-covalent forces are responsible for altering the molecular packing in the lattice. The redox properties of the new complexes were also examined.

Synthesis, Molecular Properties Prediction and Antimicrobial Activity of Imidazolyl Schiff Bases, Triazoles and Azetidinones.

Benzylidenehydrazinyl imidazoles (3) are prepared from 2-hydrazinyl imidazoles (2) on treatment with hydrazine. The imine functionality in 3 is utilized to develop 5'-aryl-N-(4-aryl-1H-imidazol-2-yl)-1H-1,2,3-triazol-1-amines (5) by 1,3-dipolar cycloaddition of diazomethane followed by aromatization with I2 in DMSO. Compounds 3 are also explored to prepare 4'-aryl-1-(4-aryl-1H-imidazol-2-ylamino)-3-chloroazetidin-2-ones (6) on treatment with chloroacetyl chloride. The Molinspiration calculations predicted that 3, 5 and 6 have molecular hydrophobicity, conformational flexibility, good intestinal absorption and bioactivity scores. The chloro, bromo and nitro substituted imidazolyl azetidinones (6c, 6d, 6f) and nitro substituted imidazolyl triazole (5f) exhibited excellent antibacterial activity on B. subtilis, whereas chloro and nitro substituted imidazolyl triazoles (5c, 5f) showed prominent antifungal activity on A. niger.

Pd(II)-immobilized on a nanoporous triazine-based covalent imine framework for facile cyanation of haloarenes with K4Fe(CN)6

A porous covalent organic framework incorporated with both imine and triazine functionalities (TPA-TCIF) was synthesized by Schiff-base condensation of 2,4,6-tris(4-aminophenyl)triazine and tris(4-formylphenyl)amine under the solvothermal condition of a 1-butanol:1,2-dichlorobenzene mixture. The resulting TPA-TCIF was a highly ordered crystalline network with surface area of 2938 m2 g−1, which was among the highest reported imine-based porous covalent organic frameworks. TPA-TCIF was also stable in water and other organic solvents. Pd(II) was immobilized into TPA-TCIF network and the resultant Pd/TPA-TCIF was tested as a catalyst for the additive-free cyanation of haloarenes with non-toxic K4[Fe(CN)6]. The catalyst showed excellent catalytic activity, and both electron-donating / -withdrawing groups attached to the para- and meta-positions of bromoarenes produced the respective nitriles with good to excellent yields. The catalyst could be reused up to five times without noticeable loss of activity or catalyst poisoning by cyanide ions during the reaction.

Dioxygen Activation with Molybdenum Complexes Bearing Amide-Functionalized Iminophenolate Ligands.

Two novel iminophenolate ligands with amidopropyl side chains (HL2 and HL3) on the imine functionality have been synthesized in order to prepare dioxidomolybdenum(VI) complexes of the general structure [MoO2L2] featuring pendant internal hydrogen bond donors. For reasons of comparison, a previously published complex featuring n-butyl side chains (L1) was included in the investigation. Three complexes (1–3) obtained using these ligands (HL1–HL3) were able to activate dioxygen in an in situ approach: The intermediate molybdenum(IV) species [MoO(PMe3)L2] is first generated by treatment with an excess of PMe3. Subsequent reaction with dioxygen leads to oxido peroxido complexes of the structure [MoO(O2)L2]. For the complex employing the ligand with the n-butyl side chain, the isolation of the oxidomolybdenum(IV) phosphino complex [MoO(PMe3)(L1)2] (4) was successful, whereas the respective Mo(IV) species employing the ligands with the amidopropyl side chains were found to be not stable enough to be isolated. The three oxido peroxido complexes of the structure [MoO(O2)L2] (9–11) were systematically compared to assess the influence of internal hydrogen bonds on the geometry as well as the catalytic activity in aerobic oxidation. All complexes were characterized by spectroscopic means. Furthermore, molecular structures were determined by single-crystal X-ray diffraction analyses of HL3, 1–3, 9–11 together with three polynuclear products {[MoO(L2)2]2(µ-O)} (7), {[MoO(L2)]4(µ-O)6} (8) and [C9H13N2O]4[Mo8O26]·6OPMe3 (12) which were obtained during the synthesis of reduced complexes of the type [MoO(PMe3)L2] (4–6).