Bottom-Up Synthesis of Covalent Organic Frameworks with Quasi-Three-Dimensional Integrated Architecture via Interlayer Cross-Linking.

Developing strategies to enhance the structural robustness of covalent organic frameworks (COFs) is of great importance. Here, we rationally design and synthesize a class of cross-linked COFs (CCOFs), in which the two-dimensional (2D) COF layers are anchored and connected by polyethylene glycol (PEG) or alkyl chains through covalent bonds. The bottom-up fabrication of these CCOFs is achieved by the condensation of cross-linked aldehyde monomers and tritopic amino monomers. All the synthesized CCOFs possess high crystallinity and porosity, and enhanced structural robustness surpassing the typical 2D COFs, which means that they cannot be exfoliated under ultrasonication and grinding due to the cross-linking effect. Furthermore, the cross-linked patterns of PEG units are uncovered by experimental results and Monte Carlo molecular dynamics simulations. It is found that all CCOFs are dominated by vertical cross-layer (interlayer) connections (clearly observed in high-resolution transmission electron microscopy images), allowing them to form quasi-three-dimensional (quasi-3D) structures. This work bridges the gap between 2D COFs and 3D COFs and provides an efficient way to improve the interlayered stability of COFs.

Solvent-Free Synthesis of C=N Linked Two-Dimensional Covalent Organic Frameworks.

Covalent organic frameworks (COFs) are an emerging class of porous crystalline polymers with well-defined structures and tunable functionalities, which have fascinating applications in a wide range of fields. However, the synthetic procedures of COFs are mainly confined to the solvothermal synthesis method which usually requires harsh experimental conditions. In this work, an effective solvent-free synthesis method to construct a series of two-dimensional (2D) COFs including imine-linked, azine-linked, ß-ketoenamine-linked, which avoids the complicated solvent screening process and most of the disadvantages of solvothermal methods is developed. The crystallinity and porosity of these COFs are comparable to those prepared by traditional solvothermal routes. What's more, the advantages of the solvent-free method enable the production of gram-scale of those 2D COFs through a one-pot reaction, demonstrating high industrial application potentials.

Bottom-Up Synthesis of 8-Connected Three-Dimensional Covalent Organic Frameworks for Highly Efficient Ethylene/Ethane Separation.

Developing cost-/energy-efficient separation techniques for purifying ethylene from an ethylene/ethane mixture is highly important but very challenging in the industrial process. Herein, using a bottom-up [8 + 2] construction approach, we rationally designed and synthesized three three-dimensional covalent organic frameworks (COFs) with 8-connected bcu networks, which can selectively remove ethane from an ethylene/ethane mixture with high efficiency. These COF materials, which are fabricated by the condensation reaction of a customer-designed octatopic aldehyde monomer with linear diamino linkers, possess high crystallinity, good structural robustness, and high porosity. Attributed to the well-organized micro-sized pores with a nonpolar/inert pore environment, these COFs display high ethane adsorption capacity and good selectivity over ethylene, making them among the best ethane-selective adsorbents for ethylene purification. Their excellent ethylene/ethane separation performance is validated by dynamic breakthrough experiments with high-purity ethylene (>99.99%) produced through a single adsorption process. The separation performance surpasses all reported C2H6-selective COFs and even some benchmark metal-organic frameworks. This work provides important guidance for the design of new adsorbents for value-added gas purification.

Construction of Covalent Organic Frameworks via Three-Component One-Pot Strecker and Povarov Reactions.

Postsynthetic modification (PSM) has been demonstrated to be a powerful method for achieving new covalent organic frameworks (COFs) via single-step or multistep organic functional group transformations on established COF frameworks. PSM, however, might sometimes lead to collapse of the COF framework, decreases in crystallinity, or low postsynthetic yield due to the inherent limit of solid-state synthesis. Herein we report, for the first time, a new synthetic strategy that can generate new COFs via multicomponent one-pot in situ reactions. In total, 12 α-aminonitrile- and quinoline-linked COFs with high crystallinity and permanent porosity are successfully achieved by three-component one-pot in situ Strecker and Povarov reactions under solvothermal conditions in high yields. The obtained COFs feature the same structures as those obtained from the stepwise PSM approach on an established imine-linked COF. This in situ multicomponent assembly strategy, as a synthetic methodology parallel to PSM, might open a new route for constructing COFs that is not possible under PSM conditions.

Cu-catalyzed C-H amination/Ullmann N-arylation domino reaction: a straightforward synthesis of 9,14-diaryl-9,14-dihydrodibenzo[a,c]phenazine.

A Cu-catalyzed C-H amination/Ullmann N-arylation domino reaction of phenanthrene-9,10-diamines with aryl iodides has been developed, which provides a straightforward and facile access to 9,14-diaryl-9,14-dihydrodibenzo[a,c]phenazine. This reaction features readily available starting materials and simple experimental operation.