Binaphthyl-based chiral covalent organic frameworks for chiral drug separation.

Separation of racemic drugs is of great importance and interest in chemistry and pharmacology. Here, we report the bottom-up synthesis of the binaphthyl-based chiral covalent organic frameworks (CCOFs), (R)-BHTP-COF. Then, high-performance liquid chromatography (HPLC) columns were prepared using (R)-BHTP-COF as a chiral stationary phase (CSP). Racemic ibuprofen was successfully baseline-separated on (R)-BHTP-COF-based CSP, and achieved excellent selectivity (α = 2.32) and chromatographic resolution (Rs = 3.39) factors. Meanwhile, the separation of six racemic drugs by the (R)-BHTP-COF-packed column exhibited high resolution, selectivity, and durability. The successful applications indicate the great potential of CCOFs as a novel stationary phase for efficient HPLC separation.

A BINOL-phosphoric acid and metalloporphyrin derived chiral covalent organic framework for enantioselective α-benzylation of aldehydes.

The catalytic asymmetric α-benzylation of aldehydes represents a highly valuable reaction for organic synthesis. For example, the generated α-heteroarylmethyl aldehydes, such as (R)-2-methyl-3-(pyridin-4-yl)propanal ((R)-MPP), are an important class of synthons to access bioactive drugs and natural products. We report herein a new and facile synthetic approach for the asymmetric intermolecular α-benzylation of aldehydes with less sterically hindered alkyl halides using a multifunctional chiral covalent framework (CCOF) catalyst in a heterogeneous way. The integration of chiral BINOL-phosphoric acid and Cu(ii)-porphyrin modules into a single COF framework endows the obtained (R)-CuTAPBP-COF with concomitant Brønsted and Lewis acidic sites, robust chiral confinement space, and visible-light induced photothermal conversion. These features allow it to highly promote the intermolecular asymmetric α-benzylation of aldehydes via visible-light induced photothermal conversion. Notably, this light-induced thermally driven reaction can effectively proceed under natural sunlight irradiation. In addition, this reaction can be easily extended to a gram-scale level, and its generality is ascertained by asymmetric α-benzylation reactions on various substituted aldehydes and alkyl bromides.

Construction of acid-base bifunctional covalent organic frameworks via Doebner reaction for catalysing cascade reaction.

We report herein a series of quinoline-4-carboxylic acid linked COFs via the multicomponent one-pot in situ Doebner reaction. The obtained acid-base bifunctional COFs are chemically stable and can highly promote one-pot cascade deacetalization-Knoevenagel condensation reaction in a heterogeneous way under solvent-free conditions.

Homochiral Covalent Organic Framework for Catalytic Asymmetric Synthesis of a Drug Intermediate.

(S)-2-(2-Chlorophenyl)-2-(6,7-dihydrothieno[3,2-c]pyridin-5(4H)-yl)acetonitrile ((S)-CIK) is a key intermediate in the synthesis of (S)-clopidogrel, which is one of the most saleable worldwide antiplatelet and antithrombotic drugs. We show herein a facile method for the direct synthesis of (S)-CIK via Strecker reaction using a homochiral covalent framework catalyst in a heterogeneous way. The asymmetric synthesis involves a photothermal-conversion-triggered, thermally driven reaction which affords (S)-CIK in 98% yield with 94% enantiomeric excess under visible-light irradiation. Furthermore, the above approach is readily extended to a gram-scale level on a fixed-bed continuous-flow model reactor. The potential utility of this strategy is highlighted by the preparation of many more other types of chiral drugs and drug intermediates in a green and facile way.

Homochiral Covalent Organic Frameworks for Asymmetric Catalysis.

Owing to their permanent porosity, highly ordered and extended structure, good chemical stability, and tunability, covalent organic frameworks (COFs) have emerged as a new type of organic materials that can offer various applications in different fields. Benefiting from the huge database of organic reactions, the required functionality of COFs can be readily achieved by modification of the corresponding organic functional groups on either polymerizable monomers or established COF frameworks. This striking feature allows homochiral covalent organic frameworks (HCCOFs) to be reasonably designed and synthesized, as well as their use as a unique platform to fabricate asymmetric catalysts. This contribution provides an overview of new progress in HCCOF-based asymmetric catalysis, including design, synthesis, and their application in asymmetric organic synthesis. Moreover, major challenges and developing trends in this field are also discussed. It is anticipated that this review article will provide some new insights into HCCOFs for heterogeneous asymmetric catalysis and help to encourage further contributions in this young but promising field.

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.

Photothermal conversion triggered thermal asymmetric catalysis within metal nanoparticles loaded homochiral covalent organic framework.

For seeking high enantiopurity, the previously reported thermal asymmetric catalysis is usually carried out at low temperature sometimes with limited yield, that is, the high enantiomeric excess (ee) usually at the cost of high yield. Thus, the achieving both high stereoselectivity and yield is an enormous challenge. We report herein two metal nanoparticle (M NP)-loaded and porphyrin-containing homochiral covalent organic framework (CCOF)-based composite catalysts, and their application in the thermally-driven asymmetric one-pot Henry and A3-coupling reactions. All the reactions are conducted at elevated temperatures with both excellent stereoselectivity and yield which resulted from the synergy of CCOF confinement effect and M NP catalytic activation. Notably, the needed thermal energy for the asymmetric reactions herein is derived from the photothermal conversion via porphyrin-based CCOF upon irradiation with visible light. Remarkably, the CCOF confinement effect can be effectively maintained up to 100 °C for the asymmetric one-pot Henry and A3-coupling reactions herein.

Homochiral BINAPDA-Zr-MOF for Heterogeneous Asymmetric Cyanosilylation of Aldehydes.

A new homochiral BINAPDA-Zr-MOF was prepared by a new chiral organic linker of (R)-4,4'-(6,6'-dichloro-2,2'-diethoxyl-[1,1'-binaphthalene]-4,4'-diyl)dibenzoic acid (R-L) and ZrCl4 under solvothermal conditions. Its structure was determined by Pawley refinement on the basis of the measured PXRD pattern determined for BINAPDA-Zr-MOF, and it showed that the obtained chiral MOF crystallized in the F23 space group with the same topological structure as that of UiO-66. The obtained BINAPDA-Zr-MOF can be a very active catalyst to catalyze aldehyde cyanosilylation. In addition, the chiral BINAPDA-Zr-MOF was a typical solid catalyst, which was proved by a hot leaching test; moreover, it could be reused at least five times without loss of its catalytic activity and enantioselectivity.

Visible-light triggered selective reduction of nitroarenes to azo compounds catalysed by Ag@organic molecular cages.

Herein, a new Ag nanoparticle (Ag NP) loaded organic molecular cage is reported. The obtained Ag@1 can act as a highly efficient heterogeneous catalyst for the selective reduction of nitroarenes to azo compounds under visible-light irradiation.

Cu3L2 metal-organic cages for A3-coupling reactions: reversible coordination interaction triggered homogeneous catalysis and heterogeneous recovery.

The reported Cu(ii) metal-organic cage (Cu3L2, 1) can be a highly active reusable catalyst to homogeneously catalyze the A3-coupling reaction in CHCl3 and can be heterogeneously recovered by simply adding 1,4-dioxane via formation of the insoluble metal-organic framework (Cu3L2(1,4-dioxane)1.5, 2).

Ru Nanoparticles-Loaded Covalent Organic Framework for Solvent-Free One-Pot Tandem Reactions in Air.

Condensation of benzene-1,3,5-tricarbohydrazide with benzene-1,4-dicarboxaldehyde generated a new covalent organic framework, COF-ASB (1), in which the organic units are held together via hydrazone linkage to form porous frameworks. COF-ASB (1) is highly crystalline and displays good chemical and thermal stability and is permanently porous. In addition, 1 can be an ideal support to load Ru nanoparticles (Ru NPs) to generate Ru@COF-ASB (2). The obtained composite material is able to highly promote one-pot tandem synthesis of imine products from benzyl alcohols and corresponding amines under solvent-free conditions in air.

Dual Heterogeneous Catalyst Pd-Au@Mn(II)-MOF for One-Pot Tandem Synthesis of Imines from Alcohols and Amines.

A new Mn(II) metal-organic framework (MOF) 1 was synthesized by the combination of 4,4,4-trifluoro-1-(4-(pyridin-4-yl)phenyl)butane-1,3-dione (L) and Mn(OAc)2 in solution. 1 features a threefold-interpenetrating NbO net containing honeycomb-like channels, in which the opposite Mn(II)···Mn(II) distance is 23.5075(10) Å. Furthermore, 1 can be an ideal platform to support Pd-Au bimetallic alloy nanoparticles to generate a composite catalytic system of Pd-Au@Mn(II)-MOF (2). 2 can be a highly active bifunctional heterogeneous catalyst for the one-pot tandem synthesis of imines from benzyl alcohols and anilines and from benzyl alcohols and benzylamines.

Cu(ii)/Cu(0)@UiO-66-NH2: base metal@MOFs as heterogeneous catalysts for olefin oxidation and reduction.

Two copper-loaded MOF materials, namely Cu(ii)@Ui-O-66-NH2 (1) and Cu(0)@UiO-66-NH2 (2), are reported. They can, respectively, serve as highly efficient heterogeneous catalysts for olefin oxidation and hydrogenation under mild conditions. Complete styrene hydrogenation occurs in 15 min at ambient temperature with quantitative yield.

A drug-loaded nanoscale metal-organic framework with a tumor targeting agent for highly effective hepatoma therapy.

Drug delivery systems with targeting agents for precise drug release in cancer therapy are very significant and important. Herein, we report the rational design and synthesis of a DOX (doxorubicin) loaded UiO-68-type of nanoscale metal-organic framework (NMOF) with a tumor targeting agent (folic acid, FA), DOX@UiO-68-FA (3), as a multifunctional drug delivery system for hepatoma (Hep G2) therapy via tail-vein injection. Compared to free DOX, FA-unloaded DOX@Mi-UiO-68 (2), 3 exhibits a much higher antitumor efficacy, which was confirmed by cell imaging, standard 3-(4,5-dimethylthiahiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) proliferation and in vivo experiments.

A MOF-membrane based on the covalent bonding driven assembly of a NMOF with an organic oligomer and its application in membrane reactors.

A UiO-66-MOF-based membrane UiO-66-TEM (1) was prepared by the assembly of methacrylamide-decorated UiO-66-NH-Met with a thiol side chain-attached polysiloxane (PSI-SH) via a photoinduced thiol-ene click reaction. The obtained membrane 1 can be a platform to support Au nanoparticles (Au NPs) to generate an Au-MOF-polymer composite membrane Au@UiO-66-TEM (2). 1 and 2 can be used to build highly efficient continuous flow-through membrane reactors for Knoevenagel condensation of 4-nitrobenzaldehyde with malononitrile and 4-nitrophenol (4-NP) reduction at ambient temperature, respectively.

Au@Cu(II)-MOF: Highly Efficient Bifunctional Heterogeneous Catalyst for Successive Oxidation-Condensation Reactions.

A new composite Au@Cu(II)-MOF catalyst has been synthesized via solution impregnation and full characterized by HRTEM, SEM-EDS, XRD, gas adsorption-desorption, XPS, and ICP analysis. It has been shown here that the Cu(II)-framework can be a useful platform to stabilize and support gold nanoparticles (Au NPs). The obtained Au@Cu(II)-MOF exhibits a bifunctional catalytic behavior and is able to promote selective aerobic benzyl alcohol oxidation-Knoevenagel condensation in a stepwise way.

Pd(0)@UiO-68-AP: chelation-directed bifunctional heterogeneous catalyst for stepwise organic transformations.

A bifunctional heterogeneous catalyst Pd(0)@UiO-68-AP based on a chelation-directed post-synthetic approach is reported. It exhibits typical heterogeneous catalytic behaviour and can promote benzyl alcohol oxidiation-Knoevenagel condensation in a stepwise way.

Pd@Cu(II)-MOF-Catalyzed Aerobic Oxidation of Benzylic Alcohols in Air with High Conversion and Selectivity.

A new 3D porous Cu(II)-MOF (1) was synthesized based on a ditopic pyridyl substituted diketonate ligand and Cu(OAc)2 in solution, and it features a 3D NbO motif which is determined by the X-ray crystallography. Furthermore, the Pd NPs-loaded hybrid material Pd@Cu(II)-MOF (2) was prepared based on 1 via solution impregnation, and its structure was confirmed by HRTEM, SEM, XRPD, gas adsorption-desorption, and ICP measurement. 2 exhibits excellent catalytic activity (conversion, 93% to >99%) and selectivity (>99% to benzaldehydes) for various benzyl alcohol substrates (benzyl alcohol and its derivatives with electron-withdrawing and electron-donating groups) oxidation reactions in air. In addition, 2 is a typical heterogeneous catalyst, which was confirmed by hot solution leaching experiment, and it can be recycled at least six times without significant loss of its catalytic activity and selectivity.

Nanoscale UiO-MOF-based luminescent sensors for highly selective detection of cysteine and glutathione and their application in bioimaging.

We report a practical approach, the first of its kind, to construct nanoscale UiO-type metal-organic framework (Mi-UiO-66 and Mi-UiO-67) fluorescent probes for the detection of Cys and GSH. They showed high sensitivity (10(-11) M) and selectivity for Cys and GSH, and their fluorescence imaging of Cys and GSH in living cells was well demonstrated.

Fabrication of Cd(II)-MOF-based ternary photocatalytic composite materials for H2 production via a gel-to-crystal approach.

Cd(II)-MOF-based ternary composite materials of CdS@Cd(II)-MOF@TiO2 were prepared by a unique TiO2 induced gel-to-crystal approach. CdS@Cd(II)-MOF@TiO2 was demonstrated to be a highly active photocatalyst for hydrogen production under visible light based on water photolysis.