Postsynthetic Metalation of Bipyridyl-Containing Metal–Organic Frameworks for Highly Efficient Catalytic Organic Transformations

In-situ activation of biomimetic single-site bioorthogonal nanozyme for tumor-specific combination therapy

Copper-catalyzed click chemistry offers creative strategies for activation of therapeutics without disrupting biological processes. Despite tremendous efforts, current copper catalysts face fundamental challenges in achieving high efficiency, atom economy, and tissue-specific selectivity. Herein, we develop a facile "mix-and-match synthetic strategy" to fabricate a biomimetic single-site copper-bipyridine-based cerium metal-organic framework (Cu/Ce-MOF@M) for efficient and tumor cell-specific bioorthogonal catalysis. This elegant methodology achieves isolated single-Cu-site within the MOF architecture, resulting in exceptionally high catalytic performance. Cu/Ce-MOF@M favors a 32.1-fold higher catalytic activity than the widely used MOF-supported copper nanoparticles at single-particle level, as first evidenced by single-molecule fluorescence microscopy. Furthermore, with cancer cell-membrane camouflage, Cu/Ce-MOF@M demonstrates preferential tropism for its parent cells. Simultaneously, the single-site CuII species within Cu/Ce-MOF@M are reduced by upregulated glutathione in cancerous cells to CuI for catalyzing the click reaction, enabling homotypic cancer cell-activated in situ drug synthesis. Additionally, Cu/Ce-MOF@M exhibits oxidase and peroxidase mimicking activities, further enhancing catalytic cancer therapy. This study guides the reasonable design of highly active heterogeneous transition-metal catalysts for targeted bioorthogonal reactions.

Optimizing post-synthetic metal incorporation in mixed-linker MOFs: insights from metalation studies on bipyridine-containing UiO-67 single crystals

The postsynthetic metalation (PSM) of metal-organic frameworks (MOFs) with intrinsic metal binding sites is an intriguing strategy to introduce catalytic function into MOFs. The spatial distribution of the catalytic sites within the MOF crystal will affect the efficiency of the material, but the factors that govern depth distribution of the introduced metal sites are often not well understood. Herein, we employ Rutherford backscattering spectrometry (RBS) to investigate the metal distribution in a series of post-synthetically metalated mixed linker bpdc/BPY UiO-67 (UiO = Universitet i Oslo, bpdc = biphenyl-dicarboxylate, BPY = 2,2'-bipyridine-5,5'-dicarboxylate) single crystals as a function of linker ratio and metalation time. The RBS spectra reveal large differences in the depth distribution of inserted Ni2+ ions, and core/shell architectures are observed in high BPY materials at shorter incubation times. The incubation times to achieve uniform metal incorporation increases with increasing BPY ratios in the materials, suggesting that the presence of the BPY linkers slow down metal uptake. We propose a combination of ionic interactions and pore clogging, where coordinated ions reduce the available pore space for further ions to diffuse deeper into the framework as reasons for the observed trends. The observations are likely relevant for other mixed-linker MOF systems, and understanding the effect that linker ratios have on PSM and cation distribution will aid in future optimizations of catalytic MOFs.

Colorimetric detection of Fe2+ and Cr2O72- in environmental water samples based on dual-emitting RhB-embedded Zr-MOFs

Three dye-loaded tunable dual-emission colorimetric fluorescent probes RhB@UiO-66-Ph (R@U-P) were prepared by in-situ encapsulation method under solvothermal conditions. The resonance energy transfer between UiO-66-Ph and RhB made the dual emission of R@U-P easily tunable with the embedded dye content changing. The R@U-P composites achieved emission from purple light to red light, and served as probes to realize comparative detection of Fe3+, Fe2+ and Cr2O72- in water through colorimetric or quenching detection mode. Mechanism study indicates that the resonance energy transfer or electron transfer interactions between R@U-P composites and inorganic ions resulted in the relative changes of the two emission peaks and realized the selective detection of analytes. The preparation and application of R@U-P probes provide a promising strategy for the in-situ encapsulation dye to obtain two dual-emission composites for the comparative detection of Fe3+, Fe2+ and Cr2O72- in water samples.

Self-Supported Chiral Dirhodium Organic Frameworks Enables Efficient Asymmetric Cyclopropanation

The development of heterogeneous chiral dirhodium catalysts for fabricating important bioactive substances and reducing the loss of noble metals has long been of significant interest. However, there still remains formidable synthetic challenges since it requires multiple steps of the synthetic process, and rhodium is easily leached from solid materials during the reaction. Here, we demonstrated a self-supported strategy based on the Suzuki-Miyaura coupling reaction to construct two chiral dirhodium organic frameworks for heterogeneous asymmetric catalysis. The synthetic approach is simple and efficient since it requires only a small number of preparation steps and does not require any catalyst supporting materials. The obtained chiral dirhodium materials can be highly efficient and recyclable heterogeneous catalysts for asymmetric cyclopropanation between diazooxindole and alkenes. Importantly, Rh2-MOCP-2 exhibited almost similar catalytic performance compared to homogeneous catalyst Rh2(S-Br-NTTL)4. The afforded catalytic performance (93.9% yield with 80.9% ee) highly surpasses previous heterogeneous dirhodium catalysts reported to date.

Low-Valent Metals in Metal-Organic Frameworks Via Post-Synthetic Modification

Metal-organic frameworks (MOFs) provide uniquely tunable, periodic platforms for site-isolation of reactive low-valent metal complexes of relevance in modern catalysis, adsorptive applications, and fundamental structural studies. Strategies for integrating such species in MOFs include post-synthetic metalation, encapsulation and direct synthesis using low-valent organometallic complexes as building blocks. These approaches have each proven effective in enhancing catalytic activity, modulating product distributions (i.e., by improving catalytic selectivity), and providing valuable mechanistic insights. In this minireview, we explore these different strategies, as applied to isolate low-valent species within MOFs, with a particular focus on examples that leverage the unique crystallinity, permanent porosity and chemical mutability of MOFs to achieve deep structural insights that lead to new paradigms in the field of hybrid catalysis.

Bioinspired Cu(II) Defect Sites in ZIF-8 for Selective Methane Oxidation

Activating the C-H bonds of alkanes without further oxidation to more thermodynamically stable products, CO and CO2, is a long-sought goal of catalytic chemistry. Inspired by the monocopper active site of methane monooxygenase, we synthesized a Cu-doped ZIF-8 metal-organic framework with 25% Cu and 75% Zn in the nodes and activated it by heating to 200 °C and dosing in a stepwise fashion with O2, methane, and steam. We found that it does oxidize methane to methanol and formaldehyde. The catalysis persists through at least five cycles, and beyond the third cycle, the selectivity improves to the extent that no CO2 can be detected. Experimental characterization and analysis were carried out by PXRD, DRUV-vis, SEM, and XAS (XANES and EXAFS). The reaction is postulated to proceed at open-coordination copper sites generated by defects, and the mechanism of methanol production was explicated by density functional calculations with the revMO6-L exchange-correlation functional. The calculations reveal a catalytic cycle of oxygen-activated CuI involving the conversion of two molecules of CH4 to two molecules of CH3OH by a sequence of hydrogen atom transfer reactions and rebound steps. For most steps in the cycle, the reaction is more favored by singlet species than by triplets.

Sheltering Mono-P-Ligated Metal Complexes in Porous Polystyrene Monolith: Effect of Aryl Pendant Stabilizers on Catalytic Durability

Metal centers that can generate coordinatively unsaturated metals in accessible and stable states have been developed using synthetic polymers with sophisticated ligand and scaffold designs, which required synthetic efforts. Herein, we report a simple and direct strategy for producing polymer-supported phosphine-metal complexes, which stabilizes mono-P-ligated metals by modulating the electronic properties of the aryl pendant groups in the polymer platform. A three-fold vinylated PPh3 was copolymerized with a styrene derivative and a cross-linker to produce a porous polystyrene-phosphine hybrid monolith. Based on the Hammett substituent constants, the electronic properties of styrene derivatives were modulated and incorporated into the polystyrene backbone to stabilize the mono-P-ligated Pd complex via Pd-arene interactions. Through NMR, TEM, and comparative catalytic studies, the polystyrene-phosphine hybrid, which induces selective mono-P-ligation and moderate Pd-arene interactions, demonstrated high catalytic durability for the cross-coupling of chloroarenes under continuous-flow conditions.

Selective Methane Oxidation to Acetic Acid Using Molecular Oxygen over a Mono-Copper Hydroxyl Catalyst

Acetic acid is an industrially important chemical, produced mainly via carbonylation of methanol using precious metal-based homogeneous catalysts. As a low-cost feedstock, methane is commercially transformed to acetic acid via a multistep process involving energy-intensive methane steam reforming, methanol synthesis, and, subsequently, methanol carbonylation. Here, we report a direct single-step conversion of methane to acetic acid using molecular oxygen (O₂) as the oxidant under mild conditions over a mono-copper hydroxyl site confined in a porous cerium metal-organic framework (MOF), Ce-UiO-Cu(OH). The Ce-UiO MOF-supported single-site copper hydroxyl catalyst gave exceptionally high acetic acid productivity of 335 mmolg_cat^-1 in 96% selectivity with a Cu TON up to 400 at 115 °C in water. Our spectroscopic and theoretical studies and controlled experiments reveal that the conversion of methane to acetic acid occurs via oxidative carbonylation, where methane is first activated at the copper hydroxyl site via σ-bond metathesis to afford Cu-methyl species, followed by carbonylation with in situ-generated carbon monoxide and subsequent hydrolysis by water. This work may guide the rational design of heterogeneous abundant metal catalysts for the activation and conversion of methane to acetic acid and other valuable chemicals under mild and environmentally friendly reaction conditions.

Ratiometric fluorescence detection of artemisinin based on photoluminescent Zn-MOF combined with hemin as catalyst

Artemisinin (ART) is a type of frontline drug to treat drug-resistant falciparum malaria. Simple, accurate and selective determination of ART is significant to monitor its clinical pharmaceutical efficacy. Herein, a new ratiometric fluorescence method has been designed for the determination of ART with Zn-MOF as fluorescence reference and hemin as catalyst, respectively. Zn-MOF possesses intrinsic fluorescence at 443 nm owing to 2-aminoterephthalic acid ligand. When o-phenylenediamine (OPD) is mixed with hemin, a weak fluorescent signal at 570 nm ascribed to oxidized product of OPD (oxOPD) is observed. In the presence of ART, hemin can catalyze ART to break its peroxide bridge and release a large number of reactive oxygen species, which effectively oxidize OPD into luminescent oxOPD. Therefore, the fluorescence at 570 nm is enhanced significantly while the fluorescence of Zn-MOF remains basically unchanged. Thus, a ratiometric fluorescence sensing platform has been constructed for the detection of ART. This method exhibits wider linear range (0.15 μM-150 μM) with detection limit of 50 nM. This novel and selective method has been used to detect ART in compound naphthoquinone phosphate tablets.

Photoexcitation of Fe3 O Nodes in MOF Drives Water Oxidation at pH=1 When Ru Catalyst Is Present

Artificial photosynthesis strives to convert the energy of sunlight into sustainable, eco-friendly solar fuels. However, systems with light-driven water oxidation reaction (WOR) at pH=1 are rare. Broadly used [Ru(bpy)₃ ]²⁺ (bpy=2,2'-bipyridine) photosensitizer has a fixed +1.23 V potential which is insufficient to drive most water oxidation catalysts (WOCs) in acid, while Fe₂ O₃ , featuring the highly oxidizing holes, is not stable at low pH. Here, the key examples of Fe-based metal-organic framework (MOF) water oxidation photoelectrocatalysts active at pH=1 are presented. Fe-MIL-126 and Fe MOF-dcbpy structures were formed with 4,4'-biphenyl dicarboxylate (bpdc), 2,2'-bipyridine-5,5'-dicarboxylate (dcbpy) linkers and their mixtures. Presence of dcbpy linkers allows integration of metal-based catalysts via coordination to 2,2'-bipyridine fragments. Fe-based MOFs were doped with Ru-based precursors to achieve highly active MOFs bearing [Ru(bpy)(dcbpy)(H₂ O)₂ ]²⁺ WOC. Materials were analyzed with X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infra-red (FTIR) spectroscopy, resonance Raman, X-ray absorption spectroscopy, fs optical pump-probe, electron paramagnetic resonance (EPR), diffuse reflectance and electric conductivity measurements and were modeled by band structure calculations. It is shown that under reaction conditions, Fe^III and Ru^III oxidation states are present, indicating rate-limiting electron transfer in MOF. Fe₃ O nodes emerge as photosensitizers able to drive prolonged O₂ evolution in acid. Further developments are possible via MOF's linker modification for enhanced light absorption, electrical conductivity, reduced MOF solubility in acid, Ru-WOC modification for faster WOC catalysis, or Ru-WOC substitution to 3d metal-based systems. The findings give further insight for development of light-driven water splitting systems based on Earth-abundant metals.

Rational design of mesoporous chiral MOFs as reactive pockets in nanochannels for enzyme-free identification of monosaccharide enantiomers

Monosaccharides play significant roles in daily metabolism in living organisms. Although various devices have been constructed for monosaccharide identification, most rely on the specificity of the natural enzyme. Herein, inspired by natural ionic channels, an asymmetrical MOF-in-nanochannel architecture is developed to discriminate monosaccharide enantiomers based on cascade reactions by combining oxidase-mimicking and Fenton-like catalysis in homochiral mesoporous CuMOF pockets. The identification performance is remarkably enhanced by the increased oxidase-mimicking activity of Au nanoparticles under a local surface plasmon resonance (LSPR) excitation. The apparent steady-state kinetic parameters and nano-fluidic simulation indicate that the different affinities induced by Au-LSPR excitation and the confinement effect from MOF pockets precipitate the high chiral sensitivity. This study offers a promising strategy for designing an enantiomer discrimination device and helps to gain insight into the origin of stereoselectivity in a natural enzyme.

Synthesis of 3D Cadmium(II)-Carboxylate Framework Having Potential for Co-Catalyst Free CO2 Fixation to Cyclic Carbonates

Metal-organic frameworks (MOFs) are porous coordination polymers with interesting structural frameworks, properties, and a wide range of applications. A novel 3D cadmium(II)-carboxylate framework, CdMOF ([Cd2(L)(DMF)(H2O)2]n), was synthesized by the solvothermal method using a tetracarboxylic bridging linker having amide functional moieties. The CdMOF crystal structure exists in the form of a 3D layer structure. Based on the single-crystal X-ray diffraction studies, the supramolecular assembly of CdMOF is explored by Hirshfeld surface analysis. The voids and cavities analysis is performed to check the strength of the crystal packing in CdMOF. The CdMOF followed a multistage thermal degradation pattern in which the solvent molecules escaped around 200 °C and the structural framework remained stable till 230 °C. The main structural framework collapsed (>60 wt.%) into organic volatiles between 400–550 °C. The SEM morphology analyses revealed uniform wedge-shaped rectangular blocks with dimensions of 25–100 μm. The catalytic activity of CdMOF for the solvent and cocatalyst-free cycloaddition of CO2 into epichlorohydrin was successful with 100% selectivity. The current results revealed that this 3D CdMOF is more active than the previously reported CdMOFs and, more interestingly, without using a co-catalyst. The catalyst was easily recovered and reused, having the same performance.

Ionic encapsulation of a methanol carbonylation catalyst in a microporous metal-organic framework

The anionic rhodium complex cis-[Rh(CO)₂I₂]^-, active in the Monsanto process for acetic acid production, has been heterogenised via Coulombic interactions in the pores of a UiO-66-type metal-organic framework (MOF). The MOF-supported catalyst is active for the carbonylation of methanol and is recyclable, retaining its framework crystallinity following catalysis. Intermediates in the catalytic cycle observed by IR spectroscopy confirm the same mechanism as the established homogeneous process.

Multifunctional Lanthanide-Based Metal-Organic Frameworks Derived from 3-Amino-4-hydroxybenzoate: Single-Molecule Magnet Behavior, Luminescent Properties for Thermometry, and CO2 Adsorptive Capacity

Herein, we describe and study a new family of isostructural multifunctional metal–organic frameworks (MOFs) with the formula {[Ln₅L₆(OH)₃(DMF)₃]·5H₂O}_n (where (H₂L) is 3-amino-4-hydroxybenzoic acid ligand) for magnetism and photoluminescence. Interestingly, three of the materials (Dy-, Er-, and Yb-based MOFs) present single-molecule magnet (SMM) behavior derived from the magnetic anisotropy of the lanthanide ions as a consequence of the adequate electronic distribution of the coordination environment. Additionally, photoluminescence properties of the ligand in combination with Eu and Tb counterparts were studied, including the heterometallic Eu–Tb mixed MOF that shows potential as ratiometric luminescent thermometers. Finally, the porous nature of the framework allowed showing the CO₂ sorption capacity.

A new family of isostructural multifunctional metal−organic frameworks has been described and studied for magnetism and photoluminescence. Interestingly, some materials present single-molecule magnet behavior, and photoluminescence properties of the ligand in combination with Eu and Tb counterparts were studied, including the heterometallic Eu−Tb mixed MOF that shows potential as ratiometric luminescent thermometers. Finally, the porous nature of the framework allowed showing the CO₂ sorption capacity.

Emerging single atom catalysts in gas sensors

Single atom catalysts (SACs) offer unprecedented opportunities for high-efficiency reactions taking place in many important fields of catalytic processes, electrochemistry, and photoreactions. Due to their maximized atomic utilization and unique electronic and chemical properties, SACs can provide high activity and excellent selectivity for gas adsorption and electron transport, leveraging SACs that enhance the detection sensitivity and selectivity to target gases. In the past few years, SACs including both noble (Pt, Pd, Au, etc.) and non-noble (Mn, Ni, Zn etc.) metals have been demonstrated to be very useful in optimizing sensing performances. However, a comprehensive review on this topic is still missing. Herein, we summarize the synthesis technologies of SACs that are applicable to gas sensors. The electronic and chemical interactions between SACs and host sensing materials, which are crucial to sensor functions, are discussed. Then, we highlight the application progress of various SACs in gas sensors. Prospects in the creation of new sensing materials with emerging SACs and versatile supports are also present. Finally, the challenges and prospects of SACs in the future development of sensors are analyzed.

Photo-Induced Preparation of Ag@MOF-801 Composite Based Heterogeneous Nanocatalyst for the Production of Biodiesel

Hybrid materials based on metal-organic frameworks (MOFs) and nanoparticles (NPs) have gained considerable popularity in a variety of applications. Particularly, these types of materials have demonstrated excellent efficiency in heterogeneous catalysis due to the synergistic effect between the components. Herein, we report a simple, eco-friendly, photocatalytic method for the fabrication of Zr containing MOF-801 and a silver (Ag) NPs-based hybrid (Ag@MOF-801). In this method, the photocatalytic property of the central metal ion (Zr) of MOF was exploited to promote the formation and deposition of Ag NPs on the surface of the MOF-801 under the irradiation of visible light. The successful incorporation of Ag NPs was ascertained by powder X-ray diffraction (XRD) and UV-Vis analysis, while the morphology and surface area of the sample was determined by N2 adsorption–desorption and scanning electron microscopy (SEM), respectively. The resulting Ag@MOF-801 hybrid served as a highly efficient catalyst for the transesterification of used vegetable oil (UVO) for the production of biodiesel. The Ag@MOF-801 catalyst exhibited superior catalytic activity compared to its pristine MOF-801 counterpart due to the enhanced surface area of the material.

Supported Lanthanum Borohydride Catalyzes CH Borylation Inside Zeolite Micropores

The zeolite‐supported lanthanide La(BH₄)_x‐HY₃₀ catalyzes C−H borylation of benzene with pinacolborane (HBpin), providing a complementary approach to precious, late transition metal‐catalyzed borylations. The reactive catalytic species are generated from La grafted at the Brønsted acid sites (BAS) in micropores of the zeolite, whereas silanoate‐ and aluminoate‐grafted sites are inactive under the reaction conditions. During typical catalytic borylations, conversion to phenyl pinacolborane (PhBpin) is zero‐order in HBpin concentration. A turnover number (TON) of 167 is accessed by capping external silanols, selectively grafting at BAS sites, and adding HBpin slowly to the reaction.

Catalytic Performance and Electrophoretic Behavior of an Yttrium-Organic Framework Based on a Tricarboxylic Asymmetric Alkyne

A new Y-based metal-organic framework (MOF) GR-MOF-6 with a chemical formula of {[YL(DMF)₂]·(DMF)}_n {H₃L = 5-[(4-carboxyphenyl)ethynyl] isophthalic acid; DMF = N,N-dimethylformamide} has been prepared by a solvothermal route. Structural characterization reveals that this novel material is a three-dimensional MOF in which the coordination of the tritopic ligand to Y(III) metal ions leads to an intercrossing channel system extending over three dimensions. This material has proven to be a very efficient catalyst in the cyanosilylation of carbonyls, ranking second in catalytic activity among the reported rare earth metal-based MOFs described so far but with the lowest required catalyst loading. In addition, its electrophoretic behavior has been studied in depth, providing a zero-charge point between pH 4 and 5, a peak electrophoretic mobility of -1.553 μm cm V^-1 s^-1, and a ζ potential of -19.8 mV at pH 10.

MOF-enabled confinement and related effects for chemical catalyst presentation and utilization

A defining characteristic of nearly all catalytically functional MOFs is uniform, molecular-scale porosity. MOF pores, linkers and nodes that define them, help regulate reactant and product transport, catalyst siting, catalyst accessibility, catalyst stability, catalyst activity, co-catalyst proximity, composition of the chemical environment at and beyond the catalytic active site, chemical intermediate and transition-state conformations, thermodynamic affinity of molecular guests for MOF interior sites, framework charge and density of charge-compensating ions, pore hydrophobicity/hydrophilicity, pore and channel rigidity vs. flexibility, and other features and properties. Collectively and individually, these properties help define overall catalyst functional behaviour. This review focuses on how porous, catalyst-containing MOFs capitalize on molecular-scale confinement, containment, isolation, environment modulation, energy delivery, and mobility to accomplish desired chemical transformations with potentially superior selectivity or other efficacy, especially in comparison to catalysts in homogeneous solution environments.

Single Atom Sites Catalysts based on High Specific Surface Area Supports

Catalysis is the heart of modern chemical industry. Supports with high specific surface area are crucial for the fabrication of efficient catalysts with elevated metal dispersion. Single atom sites catalysts...

Fecht's acid revisited: a spirocyclic dicarboxylate for non-aromatic MOFs

The first of a new class of spiroalkane-derived MOF linkers shows aromaticity is not a prerequisite for ligand design in porous materials.

Introducing Postmetalation Metal-Organic Framework to Control Perovskite Crystal Growth for Efficient Perovskite Solar Cells

A novel lead-containing metal-organic framework (Pb-MOF) is synthesized through postmetalation of MOF-525. Postmetalation renders lead ions bound with the organic linker of MOF-525, which can serve as nucleation points to promote perovskite crystallization. The introduction of lead postmetalated MOF-525 (Pb-MOF) as a scaffold layer between compact TiO₂ (c-TiO₂) layer and perovskite layer promotes perovskite crystal growth in enlarging crystal grain size with better crystallinity, hence decreasing defect sites in the perovskite layer. Postmetalation of MOF-525 with lead ions allows MAPbI₃ to form a solid crystal structure to facilitate the charge separation between electron transport layer (ETL) and light-harvesting layer so as to resolve the issue of possible vacancies present in MOFs. As a result, the champion perovskite solar cell (PSC) with the introduction of Pb-MOF exhibits a power conversion efficiency (PCE) of 20.87% and better stability (86% PCE retention after 40 days), outperforming the pristine PSC (16.85% PCE, with 52% retention after 40 days) and MOF-525-introduced PSC (18.61% PCE, with 76% retention after 40 days).

A hydrostable Zn2+ coordination polymer for multifunctional detection of inorganic and organic contaminants in water

From the perspective of human health and environmental safety, the development of hydrostable fluorescent sensors for the detection of heavy metal ions and nitroaromatics is an important but a challenging issue. To this end, a water-stable Zn²⁺ coordination polymer formulated as {[Zn(H₂L)]·2DMF·3H₂O}_n (ZnCP) was prepared elaborately by a solvothermal method using a multidentate ligand (H₄L) with 2,6-pyridine-dicarboxylic acid spaced by para-substituted benzene. Single-crystal analysis shows that the new ZnCP exhibits one-dimensional chain structural features, which further promoted to afford a wrinkled two-dimensional network structure via inter-chain hydrogen bonding. Powder X-ray diffraction and fluorescence measurements show that it can maintain crystallinity and structural integrity under harsh acidic and alkaline conditions with the pH ranging from 4 to 11. Notably, the bright blue-emissive ZnCP showed selective fluorescence quenching effects for Fe³⁺ and picric acid (PA), which makes it an excellent chemical sensor for Fe³⁺ and picric acid (PA) with low detection limits of 0.41 and 0.26 μM in water. The recognition mechanism of Fe³⁺ could be attributed to UV absorption competition and resonance energy transfer in the aid of weak electrostatic interactions, while the recognition mechanism of PA is considered to be a multi-quenching mechanism dominated by absorption competition and PET effects with the assistance of hydrogen bonding. In addition, poly(methyl methacrylate) (PMMA) films doped with ZnCP (ZnCP@PMMA) were developed to provide better sensing performance and portability for practical applications.

A novel yttrium-based metal-organic framework for the efficient solvent-free catalytic synthesis of cyanohydrin silyl ethers

A new porous metal-organic framework (MOF) with the chemical formula [Y₅L₆(OH)₃(DMF)₃]·5H₂O (1) (where L = 3-amino-4-hydroxybenzoate) has been prepared by a solvothermal procedure. The structural characterization reveals that this material consists of a robust three-dimensional metal-organic framework (MOF) grown with clusters formed by Y(iii) and hydroxide anions joined to one another by the ligand, giving rise to an open structure with interconnected microchannels with variable dimensions. This assembled set has shown to possess a fascinating catalytic activity for the cyanosilylation of a broad range of aldehydes and ketones with exceptional recyclability, a solvent-free medium, and one order of magnitude lower catalyst loading compared to all related lanthanide-based MOFs described so far in the literature.

Single-Crystal-to-Single-Crystal Transformations of Metal-Organic-Framework-Supported, Site-Isolated Trigonal-Planar Cu(I) Complexes with Labile Ligands

Transition-metal complexes bearing labile ligands can be difficult to isolate and study in solution because of unwanted dinucleation or ligand substitution reactions. Metal-organic frameworks (MOFs) provide a unique matrix that allows site isolation and stabilization of well-defined transition-metal complexes that may be of importance as moieties for gas adsorption or catalysis. Herein we report the development of an in situ anion metathesis strategy that facilitates the postsynthetic modification of Cu(I) complexes appended to a porous, crystalline MOF. By exchange of coordinated chloride for weakly coordinating anions in the presence of carbon monoxide (CO) or ethylene, a series of labile MOF-appended Cu(I) complexes featuring CO or ethylene ligands are prepared and structurally characterized using X-ray crystallography. These complexes have an uncommon trigonal planar geometry because of the absence of coordinating solvents. The porous host framework allows small and moderately sized molecules to access the isolated Cu(I) sites and displace the "place-holder" CO ligand, mirroring the ligand-exchange processes involved in Cu-centered catalysis.

Construction of Peroxidase-like Metal-Organic Frameworks in TiO2 Nanochannels: Robust Free-Standing Membranes for Diverse Target Sensing

The high cost and easy denaturation of natural enzymes under environmental conditions hinder their practical usefulness in sensing devices. In this study, peroxidase (POD)-like metal-organic frameworks (MOFs) were in situ grown in the nanochannels of an anodized TiO₂ membrane (TiO₂NM) as an electrochemical platform for multitarget sensing. By directly using a nanochannel wall as the precursor of metal nodes, Ti-MOFs were in situ derived on the nanochannel wall. Benefitting from the presence of bipyridine groups on the ligands, the MOFs in the nanochannels provide plenty of sites for Fe³⁺ anchoring, thus endowing the resulting membrane (named as Fe³⁺:MOFs/TiO₂NM) with remarkable POD-like activity. Such Fe³⁺-induced POD-like activity is very sensitive to thiol-containing molecules owing to the strong coordination effect of thiols on Fe³⁺. Most importantly, the POD-like activity of nanochannels can be in situ characterized by the current-potential (I-V) properties via catalyzing the oxidation of 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) substrate to the corresponding positively charged product ABTS^•+. As a proof-of-concept application, the free-standing POD-like membranes were applied as a label-free assay in sensing cysteine, as well as monitoring acetylcholinesterase (AChE) activity through the generated thiol-containing product. Furthermore, based on the toxicity effect of organophosphorus (OP) compounds on AChE, the robust membranes were successfully utilized to evaluate the toxicity of diverse OP compounds. The POD-like nanochannels open up an innovative way to expand the application of nanochannel-based electrochemical sensing platforms in drug inspection, food safety, and environmental pollution.

Merging N-Hydroxyphthalimide into Metal-Organic Frameworks for Highly Efficient and Environmentally Benign Aerobic Oxidation

Two highly efficient metal-organic framework catalysts TJU-68-NHPI and TJU-68-NDHPI have been successfully synthesized through solvothermal reactions of which the frameworks are merged with N-hydroxyphthalimide (NHPI) units, resulting in the decoration of pore surfaces with highly active nitroxyl catalytic sites. When t-butyl nitrite (TBN) is used as co-catalyst, the as-synthesized MOFs are demonstrated to be highly efficient and recyclable catalysts for a novel three-phase heterogeneous oxidation of activated C-H bond of primary and secondary alcohols, and benzyl compounds under mild conditions. Based on the high efficiency and selectivity, an environmentally benign system with good sustainability, mild conditions, simple work-up procedure has been established for practical oxidation of a wide range of substrates.

Amino Acid-Functionalized Metal-Organic Frameworks for Asymmetric Base-Metal Catalysis

We report a strategy to develop heterogeneous single-site enantioselective catalysts based on naturally occurring amino acids and earth-abundant metals for eco-friendly asymmetric catalysis. The grafting of amino acids within the pores of a metal-organic framework (MOF), followed by post-synthetic metalation with iron precursor, affords highly active and enantioselective (>99 % ee for 10 examples) catalysts for hydrosilylation and hydroboration of carbonyl compounds. Impressively, the MOF-Fe catalyst displayed high turnover numbers of up to 10 000 and was recycled and reused more than 15 times without diminishing the enantioselectivity. MOF-Fe displayed much higher activity and enantioselectivity than its homogeneous control catalyst, likely due to the formation of robust single-site catalyst in the MOF through site-isolation.

Recent Advances in Heterogeneous Ir Complex Catalysts for Aromatic C–H Borylation

Aromatic C–H borylation catalyzed by an Ir complex is among the most powerful methods for activating inert bonds. The products, i.e., arylboronic acids and their esters, are usable chemicals for the Suzuki–Miyaura cross-coupling reaction, and significant effort has been directed toward the development of homogeneous catalysis chemistry. In this short review, we present a recent overview of current heterogeneous Ir-complex catalyst developments for aromatic C–H borylation. Not only have Ir complexes been immobilized on support surfaces with phosphine and bipyridine ligands, but Ir complexes incorporated within solid materials have also been developed as highly active and reusable heterogeneous Ir catalysts. Their catalytic activities and stabilities strongly depend on their surface structures, including linker length and ligand structure.

1 Introduction and Homogeneous Ir Catalysis

2 Heterogeneous Ir Complex Catalysts for C–H Borylation Reactions

3 Other Heterogeneous Metal Complex Catalysts for C–H Borylation Reactions

4 Summary and Outlook

Structure evolution of single-site Pt in a metal-organic framework

Heterogeneous single-metal-site catalyst or single-atom catalyst research has grown rapidly due to the accessibility of modern characterization techniques that can provide invaluable information at the atomic-scale. Herein, we study the structural evolution of isolated single Pt sites incorporated in a metal-organic framework containing bipyridine functional groups using in situ diffuse reflectance infrared Fourier transform spectroscopy with CO as the probe molecule. The structure and electronic properties of the isolated Pt sites are further corroborated by x-ray photoelectron spectroscopy and aberration-corrected scanning transmission electron microscopy. We find the prerequisite of high temperature He treatment for Pt activation and CO insertion and inquire into the structural transformation of Pt site process by dynamic nuclear polarization-enhanced solid-state nuclear magnetic resonance spectroscopy.

Dumbbell-Shaped 2,2'-Bipyridines: Controlled Metal Monochelation and Application to Ni-Catalyzed Cross-Couplings

2,2'-Bipyridine ligands (dsbpys) with dumbbell-like shapes and differently substituted triarylmethyl groups at the C5 and C5' positions showed high ligand performance in the Ni-catalyzed cross-electrophile coupling and the Ni/photoredox-synergistically catalyzed decarboxylative coupling reactions. The superior ligand effects of dsbpys compared to the conventional bpy ligands were attributed to the monochelating nature of dsbpys.

Recyclable Transition Metal Catalysis using Bipyridine-Functionalized SBA-15 by Co-condensation of Methallylsilane with TEOS

Well-defined recyclable Pd- and Rh-bipyridyl group-impregnated SBA-15 catalysts were prepared for C-C bond coupling reaction and selective hydrogenation reactions, respectively. These SBA-15 derived ligands for the catalysts were prepared by direct and indirect co-condensation method using bipyridyl-linked methallylsilane. This indirect method, involving methoxysilane generated from methallylsilane shows higher loading efficiency of transition metal catalysts on SBA-15 than the direct use of methallylsilane.