Current Trends in Metal–Organic and Covalent Organic Framework Membrane Materials

Metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) have been thoroughly investigated with regards to applications in gas separation membranes in the past years. More recently, new preparation methods for MOFs and COFs as particles and thin‐film membranes, as well as for mixed‐matrix membranes (MMMs) have been developed. We will highlight novel processes and highly functional materials: Zeolitic imidazolate frameworks (ZIFs) can be transformed into glasses and we will give an insight into their use for membranes. In addition, liquids with permanent porosity offer solution processability for the manufacture of extremely potent MMMs. Also, MOF materials influenced by external stimuli give new directions for the enhancement of performance by in situ techniques. Presently, COFs with their large pores are useful in quantum sieving applications, and by exploiting the stacking behavior also molecular sieving COF membranes are possible. Similarly, porous polymers can be constructed using MOF templates, which then find use in gas separation membranes

Arenediazonium salts transformations in water media: Coming round to origins

Aromatic diazonium salts belong to an important class of organic compounds. The chemistry of these compounds has been originally developed in aqueous media, but then chemists focused on new synthetic methods that utilize reactions of diazonium salts in organic solvents. However, according to the principles of green chemistry and resource-efficient technologies, the use of organic solvents should be avoided. This review summarizes new trends of diazonium chemistry in aqueous media that satisfy requirements of green chemistry and sustainable technology. © 2016 Tomsk Polytechnic University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license

Direct Synthesis of ZIF-8 on Transmission Electron Microscopy Grids Allows Insights into the Growth Process

Metal-organic frameworks (MOFs) have received increased attention in recent years due to their exceptional properties and versatility. MOFs consist of metal nodes connected by organic linkers. Particularly interesting are surface-anchored films (SURMOFs), which are grown on bulk substrates. Transmission electron microscopy (TEM) is a key technique for the analysis of the structural and chemical properties of SURMOFs on the nanoscale. For TEM sample preparation, however, the SURMOF film must be detached from the bulk substrate and transferred to an electron-transparent support. This detachment process is a severe source of damage for the SURMOF film. The preparation of SURMOFs for TEM studies is thus an obstacle that has not yet been solved satisfactorily

Direct Synthesis of ZIF-8 on Transmission Electron Microscopy Grids Allows Structure Analysis and 3D Reconstruction

The first example of layer‐by‐layer growth of a metal–organic framework (MOF) directly on transmission electron microscopy (TEM) grids is described. ZIF‐8 is deposited on thin amorphous carbon films and subjected to a structure analysis by (scanning) TEM ((S)TEM). This method serves as a two‐in‐one synthesis and TEM sample‐preparation technique and allows straightforward analysis of ZIF‐8 crystallites. Artifacts resulting from sample preparation are completely avoided by this approach. The morphological properties, crystal structure, and the chemical composition of the material are investigated with high spatial resolution by a variety of methods of (analytical) electron microscopy. Furthermore, the incorporation of metallic nanoparticles in ZIF‐8 by integrating a corresponding step into the layer‐by‐layer deposition process is examined. The formation of ZIF‐8 crystals on the film proceeds as under the absence of nanoparticle‐forming synthesis steps. However, the nanoparticles rather cover the supporting amorphous carbon film than being incorporated in the ZIF‐8 material. This information cannot be obtained from standard characterization techniques but requires the application of analytical (S)TEM techniques

Star-shaped triarylamines - One-step metal-free synthesis and optoelectronic properties

Triarylamine derivatives are often implemented in organic optoelectronic devices due to their excellent hole-transport properties and their versatile structural tuneability. Common synthetic routes to obtain functionalized triarylamines follow multi-step procedures utilizing transition metal catalysts. Here, we investigate the synthesis of a series of star-shaped tris(biphenylamines) by a one-step base-promoted homolytic aromatic substitution (BHAS), simultaneously attaching three peripheral arenes to the triarylamine core. We demonstrate the versatility of this synthetic route by coupling four different functionalized arenes to the core and study their influence on the optoelectronic properties. BHAS as a metal-free synthetic route produces pure organic semiconductors without transition metal residues.Peer reviewe

Disulfide‐Bridged Dynamic Covalent Triazine Polymer Thin Films by Interface Polymerization: High Refractive Index with Excellent Optical Transparency

Exploring innovative strategies for molecular structuring of dynamic materials that combine self-correcting intrinsic reversibility with the robustness of covalent bonds, has been a long-standing objective from applications perspective in fields ranging from molecular engineering to nanotechnology and interfacial science. To establish dynamic covalent chemistry approaches combined with interfacial polymerization, herein, a distinct synthetic approach is reported to develop disulfide-bridged 2D polymeric C$_3$N$_3$S$_3$ triazine thin-films by interfacial thiol-disulfide dynamic exchange process crosslinking tritopic planar 1,3,5-triazine-2,4,6-trithiol molecular tectons via intermolecular disulfide formation in the presence of I$_2$ vapors at the air/water interface under redox condition. The resulting centimeter-scale polymeric thin-films are covalently cross-linked, dynamic in nature, featuring tunable thickness (6–200 nm) and significant morphological variations are realized under the influence of varying reaction time, concentration and types of reducing agents. Notably, C$_3$N$_3$S$_3$ polymer thin films exhibit a transflectance of around 99.5% in the range from 430 to 1800 nm, show high refractive indices (1.730–1.488) and optical anisotropy with uniaxial negative birefringence. The C$_3$N$_3$S$_3$ free-standing polymer thin-films can be easily transferred to different substrates or possibly into application-relevant forms for device fabrications, making this useful from materials application perspective

Cerebellar dysfunction in multiple sclerosis

International audienceThe optimization of a palladium-catalyzed Heck Matsuda reaction using an optimization algorithm is presented. We modified and implemented the Nelder-Mead method in order to perform constrained optimizations in a multidimensional space. We illustrated the power of our modified algorithm through the optimization of a multivariable reaction involving the arylation of a deactivated olefin with an arenediazonium salt. The great flexibility of our optimization method allows to fine-tune experimental conditions according to three different objective functions: maximum yield, highest throughput, and lowest production cost. The beneficial properties of flow reactors associated with the power of intelligent algorithms for the fine-tuning of experimental parameters allowed the reaction to proceed in astonishingly simple conditions unable to promote the coupling through traditional batch chemistry

Matsuda–Heck reaction with arenediazonium tosylates in water

An environmentally friendly Matsuda–Heck reaction with arenediazonium tosylates has been developed for the first time. A range of alkenes was arylated in good to quantitative yields in water. The reaction is significantly accelerated when carried out under microwave heating. The arylation of haloalkylacrylates with diazonium salts has been implemented for the first time

Expanded Cyclotetrabenzoins

Cyclobenzoins are stable and shape-persistent macrocycles which offer promise as components of optoelectronic and porous materials. We report three new cyclotetrabenzoins, derived from biphenyl, naphthalene, and tolane skeletons. Their synthesis relied on the N-heterocyclic carbene-catalyzed benzoin condensation. Isolated as their acetic esters, these compounds are characterized by structures similar in shape, but larger in size than the parent cyclotetrabenzoin. Alkyne groups of the tolane-based cyclotetrabenzoin were post-synthetically functionalized with Co2(CO)6 moieties under mild reaction conditions.<br /

Ultra-fast Suzuki and Heck reactions for the synthesis of styrenes and stilbenes using arenediazonium salts as super-electrophiles

International audienceThe super-electrophilic properties of arenediazonium salts have been exploited for achieving ultra-fast palladium-catalyzed coupling reactions with turnover frequencies up to 16 200 h(-1). These ultra-fast coupling reactions have been exemplified with the synthesis of prone-to-polymerization styrenes within seconds through Suzuki cross-couplings with potassium vinyltrifluoroborate. Heterocycles and functional groups such as halides were well tolerated. The ambivalent properties of potassium vinyltrifluoroborate also allowed the development of ultra-fast sequential Suzuki-Heck reactions for the preparation of symmetrical and unsymmetrical stilbenes within minutes