Imine Condensation Reactions Research Articles

Synthesis of a Scalable Two-Dimensional Covalent Organic Framework by the Photon-Assisted Imine Condensation Reaction on the Water Surface.

An atomically thin two-dimensional (2D) covalent organic framework (COF) was successfully synthesized via the photon-assisted imine condensation reaction within 1 h from the highly uniform and homogeneous precursor solution layer floating on the water surface. The polarity optimization of the precursor solution was the key step for the successful formation of the high-quality 2D COF because only the precursor solution consisting of polarity-controlled solvents allows ideal floating on the water surface. The polarity-controlled solution not only prohibits the agglomeration of the organic precursors on the water surface but also facilitates the wafer scale and layer number-controllable synthesis of the 2D COF. The resulting 2D COF has a uniform porous structure and highly oriented layered structure along the out-of-plane direction as observed by microscopy analysis and X-ray diffraction, respectively. In addition, we successfully fabricated field effect transistor type polyimine-based COF (pi-COF) electronic devices to demonstrate the prompt electrical responses to photo-exposure and water vapor exposure, suggesting the potential applications of the pi-COF in electrical photodetector or moisture-detector devices.

A Zn-salen based covalent triazine framework as a promising candidate for CO2 capture

A Zn-salen based covalent triazine framework (Zn@CTF) was prepared through ZnCl2 promoted one-pot procedure under ionothermal conditions using salen type precursor N,N′-Bis(5-cyano-salicylidene)-1,2-benzendiamine derived from imine condensation reaction of 3-formyl-4-hydroxybenzonitrile and 1,2-diaminebenzene. The chemical structure of the obtained polymer was characterized by solid-state 13C nuclear magnetic resonance (NMR), fourier transform infrared (FT-IR), energy dispersive spectrometer (EDS) and element analysis. Powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA) showed that the prepared polymer possessed amorphous structure and good thermal stability. The porous property of the polymer material was also characterized by N2 adsorption/desorption isotherm and the Zn@CTF material exhibited excellent porosity with a Brunauer-Emmett-Teller (BET) surface area of up to 598.2 m2 g−1. The surface microstructure property was evaculated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The CO2 adsorption performance of the Zn@CTF was further investigated and it was found that the CO2 uptake capacity was 43.9 cm3 g−1 at 273 K.

Novel n-channel organic semiconductor based on pyrene-phenazine fused monoimide and bisimides

Large π-conjugated pyrene-phenazine monoimide and bisimides were synthesized by imine condensation reaction. These imides form well ordered 1D nanotapes upon self-assembly in solution. Electrochemical and electric conductivity measurement reveal it can be served as an n-channel semiconductor with large charge carrier mobility up to 4.1cm2V−1s−1. Both alkylated imides are highly luminescent, and can be quenched via protonization using trifluoroacetic acid, which could be served as potential colorimetric acid sensors.

Synthesis, characterization, cytotoxicity and antimicrobial activity of copper complexes of N-imine pendant derivatives of 2-(methylthio)aniline

NS-containing ligands with the 2-thioaniline motif and imine functional group linked phenyl, 2-pyridyl and 2-thienyl pendants were synthesized by imine condensation reactions with corresponding aldehydes. 2-(methylthio)-N-(2-thienylmethylene)-benzenamine is a new compound characterized by NMR, FTIR and UV–vis. Single crystal X-ray crystallographic data was obtained for all three ligands. The corresponding Cu(I) complexes were obtained by addition of CuBr in toluene/acetonitrile solutions affording the bis-bidentate NS- and SNS-complexes. Aerobic oxidation of one compound, the Cu(I) complex of 2-(methylthio)-N-(2-pyridylmethylene)-benzenamine, afforded the corresponding Cu(II) complex which was characterized by single crystal X-ray crystallography and presented a pentacoordinated CuBr2 adduct of 2-(methylthio)-N-(2-pyridylmethylene)-benzenamine with a distorted square pyramidal coordination environment. Free ligands and the Cu complexes were screened for antimicrobial activity and 2-(methylthio)-N-(2-pyridylmethylene)-benzenamine copper(II) dibromide showed activity against B. cereus and S. aureus. The cytotoxicity of ligands and Cu complexes on mammalian cell cultures was assessed by the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide) assay on mouse macrophages cell line (J774.A1) and human breast cancer cell line (MCF7). The free NS-ligands showed good biocompatibility with both cell lines. Cu(I) and Cu(II) complexes showed significant effects on cell viability with dose-response dependency.

3D Porphyrin-Based Covalent Organic Frameworks.

The design and synthesis of three-dimensional covalent organic frameworks (3D COFs) bearing photoelectric units have been considered as a big challenge. Herein, for the first time, we reported the targeted synthesis of two 3D porphyrin-based COFs (3D-Por-COF and 3D-CuPor-COF), starting from tetrahedral (3D-Td) and square (2D-C4) building blocks connected through [4 + 4] imine condensation reactions. On the basis of structural characterizations, 3D-Por-COF and 3D-CuPor-COF are microporous materials with high surface areas, and are proposed to adopt a 2-fold interpenetrated pts topology with Pmc21 space group. Interestingly, both 3D COFs are photosensitive and can be used as heterogeneous catalyst for generating singlet oxygen under photoirradiation. However, 3D-Por-COF shows enhanced photocatalytic activity compared with 3D-CuPor-COF, indicating the properties of 3D porphyrin-based COFs can be tuned by metalation of porphyrin rings. The results reported here will greatly inspire us to design and synthesize 3D COFs bearing other metalloporphyrins for interesting applications (e.g., catalysis) in the future.

Sequential amine functionalization inducing structural transition in an aldehyde-containing zeolitic imidazolate framework: application to gas separation membranes

A modification in the gas separation performance of zeolitic imidazolate framework (ZIF)-supported hollow fiber (HF) membranes by means of an imine-condensation functionalization reaction carried out by microfluidics is reported. The accommodation of voluminous amine molecules in the SIM-1, Zn(4-methyl-5-imidazolecarboxaldehyde)2, also known as ZIF-94, sod structure during the functionalization reaction caused the ZIF atoms to be rearranged in a less dense rho structure, with a wider pore diameter and a diminished CO2 affinity. These changes had effects on the membrane performance, resulting in an enhanced CO2 permeance while maintaining a good permeance–selectivity balance. ZIF aldehyde-containing SIM-1 membranes were earlier prepared on the inner side of polymeric P84® HF using a microfluidic approach. The SIM-1 membranes displayed very interesting results in the separation of gas mixtures of great relevance to the natural gas field. High selectivities in the separation of He/CH4 (160), H2/CH4 (136) and CO2/CH4 (38) mixtures were achieved, and these are the first SIM-1 membranes with such a high separation performance to the best of our knowledge. These SIM-1 membranes were in situ stepwise functionalized with long-chain amine solutions, namely, hexyl- and nonylamine. Microfluidics allowed the easy sequential implementation of this post-reaction step in the membrane fabrication procedure. An imine-condensation reaction took place between the aldehyde groups in the 4-methyl-5-imidazolecarboxaldehyde ligand forming SIM-1 and the corresponding amines. The extent of the reaction was analyzed by FTIR, TGA and XRD, together with the changes in the textural properties and the adsorption capacities.

Charge Transport in 4 nm Molecular Wires with Interrupted Conjugation: Combined Experimental and Computational Evidence for Thermally Assisted Polaron Tunneling.

We report the synthesis, transport measurements, and electronic structure of conjugation-broken oligophenyleneimine (CB-OPI 6) molecular wires with lengths of ∼4 nm. The wires were grown from Au surfaces using stepwise aryl imine condensation reactions between 1,4-diaminobenzene and terephthalaldehyde (1,4-benzenedicarbaldehyde). Saturated spacers (conjugation breakers) were introduced into the molecular backbone by replacing the aromatic diamine with trans-1,4-diaminocyclohexane at specific steps during the growth processes. FT-IR and ellipsometry were used to follow the imination reactions on Au surfaces. Surface coverages (∼4 molecules/nm(2)) and electronic structures of the wires were determined by cyclic voltammetry and UV-vis spectroscopy, respectively. The current-voltage (I-V) characteristics of the wires were acquired using conducting probe atomic force microscopy (CP-AFM) in which an Au-coated AFM probe was brought into contact with the wires to form metal-molecule-metal junctions with contact areas of ∼50 nm(2). The low bias resistance increased with the number of saturated spacers, but was not sensitive to the position of the spacer within the wire. Temperature dependent measurements of resistance were consistent with a localized charge (polaron) hopping mechanism in all of the wires. Activation energies were in the range of 0.18-0.26 eV (4.2-6.0 kcal/mol) with the highest belonging to the fully conjugated OPI 6 wire and the lowest to the CB3,5-OPI 6 wire (the wire with two saturated spacers). For the two other wires with a single conjugation breaker, CB3-OPI 6 and CB5-OPI 6, activation energies of 0.20 eV (4.6 kcal/mol) and 0.21 eV (4.8 kcal/mol) were found, respectively. Computational studies using density functional theory confirmed the polaronic nature of charge carriers but predicted that the semiclassical activation energy of hopping should be higher for CB-OPI molecular wires than for the OPI 6 wire. To reconcile the experimental and computational results, we propose that the transport mechanism is thermally assisted polaron tunneling in the case of CB-OPI wires, which is consistent with their increased resistance.

A Titanium-Organic Framework as an Exemplar of Combining the Chemistry of Metal- and Covalent-Organic Frameworks.

A crystalline material with a two-dimensional structure, termed metal-organic framework-901 (MOF-901), was prepared using a strategy that combines the chemistry of MOFs and covalent-organic frameworks (COFs). This strategy involves in situ generation of an amine-functionalized titanium oxo cluster, Ti6O6(OCH3)6(AB)6 (AB = 4-aminobenzoate), which was linked with benzene-1,4-dialdehyde using imine condensation reactions, typical of COFs. The crystal structure of MOF-901 is composed of hexagonal porous layers that are likely stacked in staggered conformation (hxl topology). This MOF represents the first example of combining metal cluster chemistry with dynamic organic covalent bond formation to give a new crystalline, extended framework of titanium metal, which is rarely used in MOFs. The incorporation of Ti(IV) units made MOF-901 useful in the photocatalyzed polymerization of methyl methacrylate (MMA). The resulting polyMMA product was obtained with a high-number-average molar mass (26 850 g mol(-1)) and low polydispersity index (1.6), which in many respects are better than those achieved by the commercially available photocatalyst (P-25 TiO2). Additionally, the catalyst can be isolated, reused, and recycled with no loss in performance.

Weaving of organic threads into a crystalline covalent organic framework.

A three-dimensional covalent organic framework (COF-505) constructed from helical organic threads, designed to be mutually weaving at regular intervals, has been synthesized by imine condensation reactions of aldehyde functionalized copper(I)-bisphenanthroline tetrafluoroborate, Cu(PDB)2(BF4), and benzidine (BZ). The copper centers are topologically independent of the weaving within the COF structure and serve as templates for bringing the threads into a woven pattern rather than the more commonly observed parallel arrangement. The copper(I) ions can be reversibly removed and added without loss of the COF structure, for which a tenfold increase in elasticity accompanies its demetalation. The threads in COF-505 have many degrees of freedom for enormous deviations to take place between them, throughout the material, without undoing the weaving of the overall structure.

Controllable Synthesis of Covalent Porphyrinic Cages with Varying Sizes via Template-Directed Imine Condensation Reactions.

Covalent porphyrinic cages (CPCs) have been a target of interest for years. In this paper, we report the design and synthesis of two CPCs in which the cofacial porphyrins have a distance of 7.66 and 11.96 Å via template-directed imine condensation reactions and through the selective choice of templating linker and diamine length.

Targeted synthesis of a large triazine-based [4+6] organic molecular cage: structure, porosity and gas separation.

Herein, we report the targeted synthesis and solid state assembly of a novel triazine-based [4+6] organic molecular cage. The tetrahedral cage features a large cavity (∼2070 Å(3)), and after desolvation, the resultant material exhibits a high Brunauer-Emmett-Teller surface area of 1181 m(2) g(-1) and also features selective adsorption of CO2 over N2.

Highly-efficient synthesis of covalent porphyrinic cages via DABCO-templated imine condensation reactions.

We report a new approach to construct covalent porphyrinic cages with different spacer lengths, in which the cage compounds have been conveniently synthesized in quantitative yields, via DABCO-templated imine condensation reactions.

Tetratopic pyrimidine–hydrazone ligands modified with terminal hydroxymethyl and acryloyl arms and their Pb(ii), Zn(ii), Cu(ii) and Ag(i) complexes

The first tetratopic pyrimidine-hydrazone (pym-hyz) molecular strands containing terminal hydroxymethyl (L1) and acryloyl (L2) functional groups have been synthesised. L1 was produced by step-wise imine condensation reactions, starting with 6-hydroxymethyl-2-pyridinecarboxaldehyde. L2 was then synthesised through the treatment of L1 with acryloyl chloride. NMR spectroscopy and X-ray crystallography showed that the ligands adopted a helical shape, comprised of 1 and 1/3 helical turns. Both L1 and L2 uncoiled upon reaction with an excess amount of Pb(II), Zn(II) and Cu(II) ions, resulting in linear M4LA8 complexes (where M = Pb(II), Zn(II), or Cu(II); L = L1 or L2; and A = ClO4(-), SO3CF3(-) or BF4(-)). Horse-shoe shaped Pb2LA4 complexes were also formed by reacting Pb(II) ions with either L1 or L2 in a 2 : 1 metal to ligand ratio. The addition of Ag(I) ions to either L1 or L2 resulted in Ag2L2A2 double helicates, which were stable in the presence of excess Ag(I). The Pb(II), Zn(II) and Ag(I) complexes were characterised by NMR spectroscopy, while UV-Vis spectroscopy was used to probe the Cu(II) complexes. In addition, X-ray crystallography was used to analyse the linear Pb4L1A8, horse-shoe shaped Pb2L1(ClO4)4, twisted Cu3L2(SO3CF3)6, and double helicate Ag2L12(SO3CF3)2 complexes yielding the structures [Pb4L1(ClO4)7(H2O)]ClO4·4CH3NO2 (1), [Pb4L1(SO3CF3)8]2·6CH3CN·H2O (2), [Pb2L1(ClO4)2(CH3CN)(H2O)](ClO4)2·2CH3CN·C4H10O·H2O (3), [Cu3L2(SO3CF3)3(CH3CN)2(H2O)](SO3CF3)3·2CH3CN·H2O (4) and [Ag2L12](SO3CF3)2·CH3CN·H2O (5), respectively.

Organosilica functionalized zeolitic imidazolate framework ZIF-90 membrane for CO2/CH4 separation

The separation of CO2/CH4 is reported by using 3-aminopropyltriethoxysilane (APTES) modified zeolitic imidazolate framework ZIF-90 membrane. The as-prepared ZIF-90 membrane was modified by APTES based on an imine condensation reaction between the free aldehyde groups of the ZIF-90 frameworks and the amino groups of APTES. After APTES modification, the morphology, purity and crystallinity of the ZIF-90 membrane keep unchanged. Attributing to both pore mouth narrowing and sealing of invisible intercrystalline defects of the polycrystalline ZIF-90 layer, the separation performances of the APTES-modified ZIF-90 membrane are remarkably enhanced. For the separation of equimolar CO2/CH4 mixture at 225°C and 1bar, a CO2 permeance of 1.26×10−8 molm−2s−1Pa−1 and a CO2/CH4 selectivity of 4.7 are obtained, which is of promising in the potential application of CO2 separation and removal.

Exo‐Functionalized Shape‐Persistent [2+3] Cage Compounds: Influence of Molecular Rigidity on Formation and Permanent Porosity

The bigger the better? Rigidity is more important than size for the construction of permanent porous crystals from organic cage compounds. Two [2+3] cage compounds have been synthesized by an imine condensation reaction. The one consisting of rigid subunits (figure left) has an accessible BET surface area of 744 m2 g−1, whereas the cage compound with flexible subunits is basically nonporous (BET surface area: 30 m2 g−1) although the shape-persistent cavity is larger (9.8 vs. 7.8 Å).

Thermodynamic, kinetic, and structural factors in the synthesis of imine-linked dynamic covalent frameworks

The formation of imine-linked dynamic covalent frameworks (DCFs) has been systematically studied to determine how different factors such as reaction solvent and composition, reaction kinetics and thermodynamics, and structure of the building units influence the yield, degree of condensation, and homogeneity of the resulting products. Using molecular tetraimine analogs, we first investigated the kinetics and thermodynamics of imine condensation reactions under a variety of conditions, as well as the structures of the basic tetraimine units by X-ray crystallography. These model systems allowed us to identify conditions that favored both high reversibility and fast reaction kinetics for the imine condensation, leading in the end to the development of effective synthetic routes toward imine-linked DCFs with high degrees of cross-linking and homogeneity.

Large Self‐Assembled Chiral Organic Cages: Synthesis, Structure, and Shape Persistence

Keep the cage filled: Two large organic cages (see example) with void diameters of 1.2 nm were synthesized through [8+12] imine condensation reactions. The materials become amorphous upon solvent removal and show little permanent porosity. Molecular dynamics simulations give an insight into the mechanism of these processes, suggesting strategies for synthesizing larger shape-persistent organic cages in the future. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Highly CO2-Selective Organic Molecular Cages: What Determines the CO2 Selectivity

A series of novel organic cage compounds 1-4 were successfully synthesized from readily available starting materials in one-pot in decent to excellent yields (46-90%) through a dynamic covalent chemistry approach (imine condensation reaction). Covalently cross-linked cage framework 14 was obtained through the cage-to-framework strategy via the Sonogashira coupling of cage 4 with the 1,4-diethynylbenzene linker molecule. Cage compounds 1-4 and framework 14 exhibited exceptional high ideal selectivity (36/1-138/1) in adsorption of CO(2) over N(2) under the standard temperature and pressure (STP, 20 °C, 1 bar). Gas adsorption studies indicate that the high selectivity is provided not only by the amino group density (mol/g), but also by the intrinsic pore size of the cage structure (distance between the top and bottom panels), which can be tuned by judiciously choosing building blocks of different size. The systematic studies on the structure-property relationship of this novel class of organic cages are reported herein for the first time; they provide critical knowledge on the rational design principle of these cage-based porous materials that have shown great potential in gas separation and carbon capture applications.

A miniemulsion polymerization technique for encapsulation of silicon quantum dots in polymer nanoparticles

Miniemulsion polymerization techniques were used to encapsulate luminescent alkylated silicon quantum dots (Si-QDs) within polymer nanoparticles composed of styrene and 4-vinylbenzaldehyde monomers. The polymer nanoparticles had mean diameters in the range 90-150 nm depending on the reaction conditions, however all samples showed narrow particle size distributions, as determined by dynamic light scattering and atomic force microscopy. The Si-QDs were found to have a small, but beneficial effect on the polymerization process by reducing the polydispersity of the final polymer particles, which we attribute to co-surfactant action of the undecene used to form the alkyl capping layer on the Si-QDs. Confocal microspectroscopy was used to confirm that the luminescent alkylated Si-QDs were encapsulated within the polymer nanoparticles and also provided luminescence and Raman spectra which show peaks corresponding to both alkylated Si-QDs and the polymer nanoparticles. Treatment of the polymer nanoparticles with dilute aqueous sodium hydroxide solution, which is known to corrode Si and extinguish the luminescence of alkylated Si-QDs, results in only a partial reduction in luminescence suggesting that the majority of the alkylated Si-QDs are encapsulated sufficiently deep within the polymer matrix to protect them from alkaline attack. Miniemulsion polymerization of the monomers styrene and 4-vinylbenzaldehyde affords polymer nanoparticles displaying reactive aldehyde groups upon their surfaces, which could then be decorated with a selection of molecules through imine, oxime or hydrazone condensation reactions. We speculate that polymer-SiQD composite nanoparticles whose surfaces can be further decorated will increase the utility of luminescent Si-QDs in applications such as anti-counterfeiting and as probes of biological processes.

Preparation of an Ester-Substituted Triscatechol Ligand and Characterization of the Corresponding M4L4 Titanium(IV) Complex

The ester-substituted triscatechol ligand L-H6 can be easily prepared in a triple imine condensation reaction. The required trisamine is prepared starting from diphenylamine and 2-bromobenzoic acid methylester. Upon coordination of titanium(IV) ions the tetrahedral M4L4 coordination compound is obtained, which due to the symmetry breaking substituent exists as a mixture of isomers. However, the complex can be unambiguously characterized by ESI-MS.