Bifunctional iridium-(2-aminoterephthalate)–Zr-MOF chemoselective catalyst for the synthesis of secondary amines by one-pot three-step cascade reaction

Immobilization of Silver(I) Ions on Amino-Functionalized Chromium(III) Terephthalate with Organophosphine and its C-H Carboxylation of a Heteroaromatic Compound

A newly designed heterogenized catalyst that incorporates silver(I) ions with 2-(dicyclohexylphosphaneyl)acetaldehyde (PCy2 aldehyde) into amino-functionalized chromium(III) terephthalate is developed. Silver(I) ions were robustly immobilized on the amino-functionalized chromium(III) terephthalate, which contains an imine bond formed by the reaction with PCy2 aldehyde. The Ag(I) ion is coordinated with the phosphine in the imine group to create MIL-101-AP(Ag). Characterizations were carefully carried out according to the synthetic steps. The catalytic performance of MIL-101-AP(Ag) was evaluated through the C-H carboxylation of thiophene-2-carbonitrile, achieving a 10 % yield with a turnover number of 1.0. The recyclability of the MIL-101-AP(Ag) catalyst was successfully demonstrated with five cycle, with no loss in activity and selectivity observed. This approach, which involves the formation of an imine bond to facilitate silver loading with phosphine on amino-functionalized MIL-101(Cr), exhibits significant potential for both CO2 fixation and C-H carboxylation, thereby highlighting the modified material's promise as a sustainable catalyst.

One-pot reductive amination of carbonyl compounds and nitro compounds via Ir-catalyzed transfer hydrogenation

The formation of C-N bond is a vital synthetic tool for establishing molecular diversity, which is highly sought after in a wide range of biologically active natural products and drugs. Herein, we present a new strategy for the synthesis of secondary amines via iridium-catalyzed one-pot reductive amination of carbonyl compounds with nitro compounds. This method is demonstrated for a variety of carbonyl compounds, including miscellaneous aldehydes and ketones, which are compatible with this catalytic system, and deliver the desired products in good yields under mild conditions. In this protocol, the reduction of nitro compounds occurs in situ first, followed by reductive amination to form amine products, providing a new one-pot procedure for amine synthesis.

Fabrication and characterization of a novel catalyst based on modified zirconium metal-organic-framework for synthesis of polyhydroquinolines

A novel catalyst was fabricated in this study based on zirconium MOF modified with pyridine carboxaldehyde in a solvothermal reaction, embedded with cerium. In order to confirm the catalyst structure, various characterization techniques, including FTIR, Far IR, EDX, XRD, TGA, FE-SEM, ICP, and BET analyses, were employed. The results indicated that the UiO-66-Pyca-Ce (III) catalyst had a Langmuir surface area of 501.63 m2/g, a pore volume of 0.28 cm3/g, and a pore size of 2.27 nm. To study catalytic activity, a sequential approach of Knoevenagel condensation and Michael addition was used to synthesize various polyhydroquinoline derivatives. The reaction took place at ambient temperature. The UiO-66-Pyca-Ce (III) catalyst demonstrated high efficacy (90%) and reusability in asymmetric synthesis of polyhydroquinoline derivatives for several reasons, including the possession of three Lewis acid activation functions.

Multifunctional Lanthanide Metal-Organic Frameworks Based on -NH2 Modified Ligand: Fluorescent Ratio Probe, CrO42- Ions Adsorption, and Photocatalytic Property

In response to the growing concern for environmental pollution, two lanthanide compounds {[Ln(L)(H2O)]·4H2O}n (where Ln = Tb and Gd, H3L = 1-amino-2,4,6-benzene tricarboxylic acid) were synthesized using a -NH2 modified ligand and systematically characterized. Both compounds exhibit remarkable fluorescence response, adsorption of CrO42- ions, and photocatalytic degradation properties, as well as exceptional acid-base and thermal stability. Remarkably, the pH-dependent 1-Tb exhibits exceptional performance as a fluorescent probe for detecting Fe3+ and CrO42-/Cr2O72- ions in aqueous solutions, while also serving as a ratiometric fluorescent probe for the detection of Cr3+, offering rapid response, high sensitivity, selectivity, and recoverability advantages in application. Moreover, 1-Tb exhibits excellent detection capabilities and displays effective adsorption of CrO42- ions, with a maximum adsorption capacity of 230.71 mg/g. On the other hand, 1-Gd exhibits superior performance compared to 1-Tb in the photocatalytic degradation of antibiotics. The degradation mechanism is further elucidated by conducting experiments with DFT theoretical calculations.

Facile and efficient preparation of amino bearing metal-organic frameworks-coated cotton fibers for solid-phase extraction of non-steroidal anti-inflammatory drugs in human plasma

The determination of blood concentration of non-steroidal anti-inflammatory drugs (NSAIDs) is highly desired in clinical practice. In this work, three amino bearing metal-organic frameworks (amino-MOFs) coated cotton fibers were prepared using a facile cysteine-triggered in situ growth strategy and proposed as in-tip solid-phase microextraction (in-SPME) adsorbents for efficient extraction of non-steroidal anti-inflammatory drugs from human plasma. The self-made adsorbents exhibited satisfactory extraction performance toward three NSAIDs including diclofenac sodium, ketoprofen and flurbiprofen. Under the optimized conditions, the established method exhibited satisfactory enrichment performance, low limits of detection and excellent extraction efficiency. Good reproducibility, wide linear range, excellent linearity and satisfactory sensitivity were obtained in the experiment. The method was also used for the enrichment and determination of NSAIDs in human plasma samples. Good recoveries were obtained, ranging from 66.5% to 98.9% with relative standard deviations less than 6.62%. The good performance of amino-MOFs was due to the synergistic effects arising from grafted charged amino groups within ordered pores of suitable size, leading to strong affinity towards guest molecules. Electrostatic interaction, hydrogen bond and π-π interaction played a vital role in the extraction of NSAIDs. This report indicated the potential of amino-MOFs as efficient adsorbents for the determination of NSAIDs from human plasma.

Ruthenium-catalyzed reductive amination of ketones with nitroarenes and nitriles

The Ru(dppbsa)-catalyzed reductive amination of ketones with nitroarenes and nitriles using H₂ as the environmentally benign hydrogen surrogate is developed in this study. Cross-experiments demonstrated that both reactions are initiated by the reduction of nitroarenes or nitriles to the corresponding amines, followed by condensation with ketones to give imines and thereafter hydrogenation. However, the route to the formation of an amino-ligated Ru complex during the reduction of nitroarenes or nitriles, followed by in situ nucleophilic C-N coupling, cannot be completely excluded. This newly developed versatile method features good functional group tolerance, which provides a novel design platform for homogeneous catalysts in constructing motifs of secondary amines.

Two pillared-layer metal-organic frameworks based on the pinwheel trinuclear carboxylate-clusters of Zn(II) and Co(II): synthesis, crystal structures, magnetic study, and Lewis acid catalysis

Using a dicarboxylic acid, [1,1'-biphenyl]-4,4'-dicarboxylic acid (H₂L1) and an exobidentate ligand, (1E,1'E)-N,N'-(1,4-phenylene)bis(1-(pyridin-4-yl)methanimine) (L2), two 3D interpenetrated networks, {[Zn₃(L1)₃(L2)]·9H₂O}_n (Zn-MOF) and {[Co₃(L1)₃(L2)(DMF)]·0.5DMF}_n (Co-MOF), have been prepared in good yields. The crystal structure analysis of Zn-MOF and Co-MOF revealed that both have a 3D pillared-layer structure based on pinwheel trinuclear metal-carboxylate clusters as secondary building units (SBUs). Furthermore, the structures also exhibited three-fold interpenetration. Although the overall networks in Zn-MOF and Co-MOF showed significant resemblances, there are marked differences in their crystal structures, which are associated with the coordination environment of the metal centre and the binding modes of the carboxylates. Gas adsorption studies (N₂ at 77 K and 1 bar) indicated that Co-MOF is more porous than Zn-MOF. Magnetic measurements on Co-MOF indicate a significant antiferromagnetic interaction (45 K to 303 K) between trimeric Co(II) S = 3/2 spins through syn-syn carboxylato bridges. Both MOFs were studied for the Lewis acid catalyzed Knoevenagel condensation reactions between benzaldehydes and malononitrile with an active methylene group, where Zn-MOF was found to be a better catalyst than Co-MOF. This was supported by the Monte Carlo simulations indicating the better substrate binding ability of Zn-MOF than Co-MOF.

Hierarchical-pore UiO-66-NH2 xerogel with turned mesopore size for highly efficient organic pollutants removal

Persistent organic pollutants in water are not only a potential threat to human health, but also cause damage to the ecological environment. Hence, the removal of large organic pollutants from wastewater is of great importance for environmental protection. Herein, hierarchical-pore UiO-66-NH₂ xerogels (H-UiO-66-NH₂ xerogels) with different mesopore size, H-UiO-66-NH₂-11.6 nm and H-UiO-66-NH₂-3.7 nm, were successfully synthesized by combining sol-gel-based method and acid modulator, featuring the characteristics of simple operation, rapid and scalable process, low cost, and the high space-time yield (STY). N₂ adsorption-desorption isotherms reveal that the obtained H-UiO-66-NH₂ xerogels possess high surface area, hierarchical-pore structures, large pore volume, and turntable mesopore size. Batch adsorption experiments demonstrate that H-UiO-66-NH₂-11.6 nm has excellent adsorption performance for reactive red 195 (RR 195) dye removal. The maximum adsorption capacity of H-UiO-66-NH₂-11.6 nm is 884.96 mg g^-1, which is 4.7 times of the microporous UiO-66-NH₂ (185.15 mg g^-1). Moreover, the removal efficiency of H-UiO-66-NH₂-11.6 nm for RR 195 can exceed 99 %. The adsorption mechanism reveals that the excellent RR 195 capture stems from the large mesoporous structure and abundant adsorption sites provided by the Zr cluster and -NH₂ groups in H-UiO-66-NH₂-11.6 nm. Besides, H-UiO-66-NH₂-11.6 nm also exhibits a much larger adsorption capacity for some other organic pollutants, such as tetracycline, reactive black 5, and amoxicillin, demonstrating that the H-UiO-66-NH₂ xerogel has great potential for organic pollutant removal.

Confined-based catalyst investigation through the comparative functionalization and defunctionalization of Zr-MOF

In metal–organic frameworks, confined space as a chemical nanoreactor is as important as organocatalysis or coordinatively unsaturated metal site catalysis. In the present study, a set of mixed-ligand structures with UiO-66 architecture have been prepared. To the best of our knowledge, for the first time, structures derived by the solvothermal mixing ligand method and ultrasonic-assisted linker exchange approaches have been compared. Additionally, the relationship between the preparation method, structural properties, and catalytic efficiency of the prepared materials in the Knoevenagel condensation of aldehydes has been investigated. The prepared catalyst is very stable and can be recovered and reused for at least ten periods.

In metal–organic frameworks, confined space as a chemical nanoreactor is as important as organocatalysis or coordinatively unsaturated metal site catalysis.

High-yield halide-assisted synthesis of metal-organic framework UiO-based nanocarriers

The synthesis of nanosized metal-organic frameworks (NMOFs) is requisite for their application as injectable drug delivery systems (DDSs) and other biorelevant purposes. Herein, we have critically examined the role of different synthetic parameters leading to the production of UiO-66 crystals smaller than 100 nm. Of note, we demonstrate the co-modulator role conferred by halide ions, not only to produce NMOFs with precise morphology and size, but also to significantly improve the reaction yield. The resulting NMOFs are highly crystalline and exhibit sustained colloidal stability in different biologically relevant media. As a proof of concept, these NMOFs were loaded with Rhodamine 6G (R6G), which remained trapped in most common biologically relevant media. When incubated with living mammalian cells, the R6G-loaded NMOFs were efficiently internalized and did not impair cell viability even at relatively high doses.

Strategies for the application of metal-organic frameworks in catalytic reactions

Efficient catalysts play crucial roles in various organic reactions and polymerization. Metal–organic frameworks (MOFs) have the merits of ultrahigh porosity, large surface area, dispersed polymetallic sites and modifiable linkers, which make them promising candidates for catalyzation. This review primarily summarizes the recent research progress on diverse strategies for tailoring MOFs that are endowed with excellent catalytic behavior. These strategies include utilizing MOFs as nanosized reaction channels, metal nodes decorated as catalytic active sites and the modification of ligands or linkers. All these make them highly attractive to various applications, especially in catalyzing organic reactions or polymerizations and they have proven to be effective catalysts for a wide variety of reactions. MOFs are still an evolving field with tremendous prospects; therefore, through the research and development of more modification and regulation strategies, MOFs will realize their wider practical application in the future.

Metal–organic frameworks (MOFs) are promising candidates for catalyzation. This review primarily summarized the recent research progress in diverse strategies for tailoring MOFs which are endowed with more excellent catalytic behavior.

High-Temperature Synthesis of Carbon-Supported Bimetallic Nanocluster Catalysts by Enlarging the Interparticle Distance

Supported bimetallic nanoparticle catalysts with small size have attracted wide research attention in catalysis but are difficult to synthesize because high-temperature annealing required for alloying inevitably accelerates metal sintering and leads to larger particles. Here, we report a simple and scalable "critical interparticle distance" method for the synthesis of a family of bimetallic nanocluster catalysts with an average particle size of only 1.5 nm by using large-surface-area carbon black supports at high temperatures, which consist of 12 diverse combinations of 3 noble metals (Pt, Ru, and Rh) and 4 other metals (Cr, Fe, Zr, and Sn). In this strategy, high-temperature treatments ensure the formation of alloyed bimetallic nanoparticles and enlargement of the interparticle distance on high-surface-area supports significantly suppresses metal sintering. The prepared ultrafine Pt₂Sn and RuSn nanocluster catalysts exhibited enhanced performance in catalyzing the synthesis of aromatic secondary amines and the selective hydrogenation of furfural, respectively.

A new type of heterogeneous catalysis strategy for organic reactions: Ugi-3CR catalyzed by highly stable MOFs with exposed carboxyl groups

A mild and highly efficient Ugi-3CR using a novel Cu-COOH@MOF-6 as the catalyst has been developed, which provides facile access to α-amino amides. The recycling test and XRD images showed that the catalytic system has good stability and recyclability.

Spatial intimacy of binary active-sites for selective sequential hydrogenation-condensation of nitriles into secondary imines

Precisely controlling the spatial intimacy of multiple active sites at sub-nanoscale in heterogeneous catalysts can improve their selectivity and activity. Herein, we realize a highly selective nitrile-to-secondary imine transformation through a cascaded hydrogenation and condensation process by Pt₁/CoBO_x comprising the binary active sites of the single-dispersed Pt and interfacial Lewis acidic B. Atomic Pt sites with large inter-distances (>nanometers) only activate hydrogen for nitrile hydrogenation, but inhibit condensation. Both adjacent B…B on CoBO_x and neighbouring Pt…B pairs with close intimacy of ~0.45 nm can satisfy the spatial prerequisites for condensation. Mechanism investigations demonstrate the energetically favorable pathway occurred on adjacent Lewis acidic B sites through the nitrile adsorption (acid-base interaction), hydrogenation via hydrogen spillover from Pt to B sites and sequential condensation. Strong intermolecular tension and steric hindrance of secondary imines on active sites lead to their effective desorption and thereby a high chemoselectivity of secondary imines.

Precisely controlling the spatial intimacy of multiple active sites in heterogeneous catalysts can significantly affect the selectivity and activity. Here the authors show a binary active site of single atom Pt and Lewis acidic B with spatial intimacy enables a highly selective nitrile-to-secondary imine transformation.

Prototype Atomically Dispersed Supported Metal Catalysts: Iridium and Platinum

When metal nanoparticles on supports are made smaller and smaller-to the limit of atomic dispersion-they become cationic and take on new catalytic properties that are only recently being discovered. The synthesis of these materials is reviewed, including their structure characterization-especially by atomic-resolution electron microscopy and X-ray absorption and infrared spectroscopies-and relationships between structure and catalyst performance, for reactions including hydrogenations, oxidations, and the water gas shift. Structure determination is challenging because of the intrinsic nonuniformity of the support surfaces-and therefore the structures on them-but fundamental understanding has advanced rapidly, benefiting from nearly uniform catalysts consisting of metals on well-defined-crystalline-supports and their characterization by spectroscopy and microscopy. Recent advances in atomic-resolution electron microscopy have spurred the field, providing stunning images and deep insights into structure. The iridium catalysts have typically been made from organoiridium precursors, opening the way to understanding and control of the metal-support bonding and ligands on the metal, including catalytic reaction intermediates. Platinum catalysts are usually made with less precision, from salt precursors, but they catalyze a wider array of reactions than the iridium, typically being stable at higher temperatures and seemingly offering rich prospect for discovery of new catalysts.

Metal-based Heterogeneous Catalysts for One-Pot Synthesis of Secondary Anilines from Nitroarenes and Aldehydes

Recently, N-substituted anilines have been the object of increasing research interest in the field of organic chemistry due to their role as key intermediates for the synthesis of important compounds such as polymers, dyes, drugs, agrochemicals and pharmaceutical products. Among the various methods reported in literature for the formation of C-N bonds to access secondary anilines, the one-pot reductive amination of aldehydes with nitroarenes is the most interesting procedure, because it allows to obtain diverse N-substituted aryl amines by simple reduction of nitro compounds followed by condensation with aldehydes and subsequent reduction of the imine intermediates. These kinds of tandem reactions are generally catalyzed by transition metal-based catalysts, mainly potentially reusable metal nanoparticles. The rapid growth in the last years in the field of metal-based heterogeneous catalysts for the one-pot reductive amination of aldehydes with nitroarenes demands for a review on the state of the art with a special emphasis on the different kinds of metals used as catalysts and their recyclability features.

The role of metal–organic porous frameworks in dual catalysis

Metal–organic frameworks (MOFs) are a valuable group of porous crystalline solids with inorganic and organic parts that can be used in dual catalysis.

Transition-Metal-Catalyzed Reductive Amination Employing Hydrogen

The reductive amination, the reaction of an aldehyde or a ketone with ammonia or an amine in the presence of a reducing agent and often a catalyst, is an important amine synthesis and has been intensively investigated in academia and industry for a century. Besides aldehydes, ketones, or amines, starting materials have been used that can be converted into an aldehyde or ketone (for instance, carboxylic acids or organic carbonate or nitriles) or into an amine (for instance, a nitro compound) in the presence of the same reducing agent and catalyst. Mechanistically, the reaction starts with a condensation step during which the carbonyl compound reacts with ammonia or an amine, forming the corresponding imine followed by the reduction of the imine to the alkyl amine product. Many of these reduction steps require the presence of a catalyst to activate the reducing agent. The reductive amination is impressive with regard to the product scope since primary, secondary, and tertiary alkyl amines are accessible and hydrogen is the most attractive reducing agent, especially if large-scale product formation is an issue, since hydrogen is inexpensive and abundantly available. Alkyl amines are intensively produced and use fine and bulk chemicals. They are key functional groups in many pharmaceuticals, agro chemicals, or materials. In this review, we summarize the work published on reductive amination employing hydrogen as the reducing agent. No comprehensive review focusing on this subject has been published since 1948, albeit many interesting summaries dealing with one or the other aspect of reductive amination have appeared. Impressive progress in using catalysts based on earth-abundant metals, especially nanostructured heterogeneous catalysts, has been made during the early development of the field and in recent years.

Co-Fe-layered double hydroxide decorated amino-functionalized zirconium terephthalate metal-organic framework for removal of organic dyes from water samples

In this study, a new efficient adsorbent of Co-Fe-layered double hydroxides@metal-organic framework (Co-Fe-LDH@UiO-66-NH₂) was synthesized and used for extraction of methylene blue (MB) and methylene red (MR) from water samples prior to their determination by UV-Vis spectrophotometer. The adsorbent was characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDX), X-ray Diffraction (XRD), and Brunauer-Emmett-Teller (BET) analyses. The impact of various parameters such as pH of the aqueous phase, extraction time, amount of adsorbent, type and volume of eluent solvent, desorption time, and sample volume were studied. The maximum extraction recovery was obtained at an optimized pH 8.0 and extraction time 10.0 min. The adsorption process was fitted by the Langmuir model with a maximum adsorption capacity of 555.62 mg/g and 588.2 mg/g, respectively, for MB and MR. Under optimum conditions, the limit of detection (LOD) for MB was 0.7 μgL^-1 and 0.9 μgL^-1 for MR. Furthermore, the Co-Fe-LDH@UiO-66-NH₂ composite showed high efficiency for the removal of the analytes from environmental water samples.

A Pyridyltriazol Functionalized Zirconium Metal-Organic Framework for Selective and Highly Efficient Adsorption of Palladium

This work reports the synthesis of pyridyltriazol-functionalized UiO-66 (UiO stands for University of Oslo), namely, UiO-66-Pyta, from UiO-66-NH₂ through three postsynthetic modification (PSM) steps. The good performance of the material derives from the observation that partial formylation (∼21% of -NHCHO groups) of H₂BDC-NH₂ by DMF, as persistent impurity, takes place during the synthesis of the UiO-66-NH₂. Thus, to enhance material performance, first, the as-synthesized UiO-66-NH₂ was deformylated to give pure UiO-66-NH₂. Subsequently, the pure UiO-66-NH₂ was converted to UiO-66-N₃ with a nearly complete conversion (∼95%). Finally, the azide-alkyne[3+2]-cycloaddition reaction of 2-ethynylpyridine with the UiO-66-N₃ gave the UiO-66-Pyta. The porous MOF was then applied for the solid-phase extraction of palladium ions from an aqueous medium. Affecting parameters on extraction efficiency of Pd(II) ions were also investigated and optimized. Interestingly, UiO-66-Pyta exhibited selective and superior adsorption capacity for Pd(II) with a maximum sorption capacity of 294.1 mg g^-1 at acidic pH (4.5). The limit of detection (LOD) was found to be 1.9 μg L^-1. The estimated intra- and interday precisions are 3.6 and 1.7%, respectively. Moreover, the adsorbent was regenerated and reused for five cycles without any significant change in the capacity and repeatability. The adsorption mechanism was described based on various techniques such as FT-IR, PXRD, SEM/EDS, ICP-AES, and XPS analyses as well as density functional theory (DFT) calculations. Notably, as a case study, the obtained UiO-66-Pyta after palladium adsorption, UiO-66-Pyta-Pd, was used as an efficient catalyst for the Suzuki-Miyaura cross-coupling reaction.

Poly(lauryl methacrylate)-Grafted Amino-Functionalized Zirconium-Terephthalate Metal-Organic Framework: Efficient Adsorbent for Extraction of Polycyclic Aromatic Hydrocarbons from Water Samples

In this study, a novel porous hybrid material, poly(lauryl methacrylate) polymer-grafted UiO-66-NH2 (UiO = University of Oslo), was synthesized for efficient extraction of polycyclic aromatic hydrocarbons (PAHs) from aqueous samples. The polymer end-tethered covalently to the MOF's surface was synthesized by surface-initiated atom transfer radical polymerization, revealing a distinct type of morphology. The adsorbent was characterized by scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy, powder X-ray diffraction, N2 adsorption-desorption analysis, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The analyses were carried out by gas chromatography-mass spectrometry. Parameters including the type and volume of the eluent, the amount of the adsorbent, and adsorption and desorption times were investigated and optimized. Under optimal conditions, the limit of detection, intraday precision, and interday precision were in the range of 3-8 ng L-1, 1.4-3.1, and 4.1-6.5%, respectively. The procedure was used for analysis of PAHs from natural water samples.

Catalytic Reductive Amination of Aldehydes and Ketones With Nitro Compounds: New Light on an Old Reaction

Reductive amination of carbonyl compounds with primary amines is a well-established synthetic methodology for the selective production of unsymmetrically substituted secondary and tertiary amines. From the industrial and green chemistry perspective, it is attractive to combine reductive amination with the synthesis of primary amines in a single one-pot catalytic process. In this regard, nitro compounds, which are readily available and inexpensive feedstocks, received much attention as convenient precursors to primary amines in such processes. Although the direct reductive coupling of nitro compounds with aldehydes/ketones to give secondary and tertiary amines has been known since the 1940's, due to the development of highly efficient and selective non-noble metal-based catalysts a breakthrough in this area was made in the last decade. In this short overview, recent progress in the methodology of the reductive amination with nitro compounds is summarized together with applications to the synthesis of bioactive amines and heterocycles. Remaining challenges in this field are also analyzed.

Catalytic reductive aminations using molecular hydrogen for synthesis of different kinds of amines

Catalytic reductive aminations using molecular hydrogen represent an essential and widely used methodology for the synthesis of different kinds of amines.

Engineering Metal-Organic Framework Catalysts for C-C and C-X Coupling Reactions: Advances in Reticular Approaches from 2014-2018

Metal-organic frameworks (MOFs) are a class of crystalline porous materials that have been actively used for several industrial and synthetic applications. MOFs are spatially and geometrically extrapolated coordination polymers with intriguing properties such as tunable porosity and dimensionality. In terms of their catalytic efficiency, MOFs combine the easy recoverability of heterogeneous catalysts with the increased selectivity of biological catalysts. It is therefore not surprising that a lot of work on optimizing MOF catalysts for organic transformations has been carried out over the past decade. In this review, recent developments in MOF catalysis are summarized, with special attention being paid to C-C, C-N, and C-O coupling reactions. The influence of pore size, pore environment, and load on catalytic activity is described. Post-synthetic stabilization techniques and host-guest interactions in caged MOF scaffolds are detailed. Mechanistic aspects pertaining to the use of MOFs in asymmetric heterogeneous catalysis are highlighted and categorized.

Post Synthetic Defect Engineering of UiO-66 Metal–Organic Framework with An Iridium(III)-HEDTA Complex and Application in Water Oxidation Catalysis

Clean production of renewable fuels is a great challenge of our scientific community. Iridium complexes have demonstrated a superior catalytic activity in the water oxidation (WO) reaction, which is a crucial step in water splitting process. Herein, we have used a defective zirconium metal–organic framework (MOF) with UiO-66 structure as support of a highly active Ir complex based on EDTA with the formula [Ir(HEDTA)Cl]Na. The defects are induced by the partial substitution of terephthalic acid with smaller formate groups. Anchoring of the complex occurs through a post-synthetic exchange of formate anions, coordinated at the zirconium clusters of the MOF, with the free carboxylate group of the [Ir(HEDTA)Cl]− complex. The modified material was tested as a heterogeneous catalyst for the WO reaction by using cerium ammonium nitrate (CAN) as the sacrificial agent. Although turnover frequency (TOF) and turnover number (TON) values are comparable to those of other iridium heterogenized catalysts, the MOF exhibits iridium leaching not limited at the first catalytic run, as usually observed, suggesting a lack of stability of the hybrid system under strong oxidative conditions.

Post-functionalization of UiO-66-NH2 by 2,5-Dimercapto-1,3,4-thiadiazole for the high efficient removal of Hg(II) in water

A new MOFs adsorbent was prepared by post-functionalization of UiO-66-NH₂ with 2,5-Dimercapto-1,3,4-thiadiazole and utilized to remove the Hg(II) in water selectively. The UiO-66-types were detected by Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscope (FESEM), Brunauer-Emmett-Teller (BET) and zeta potential instruments. The adsorption properties of the new MOFs adsorbent were investigated by batch experiments. The actual maximum adsorption amount was 670.5 mg/g at the optimal pH of 3. Adsorption kinetic and isotherm models were exceedingly fitted to pseudo-second-order and Langmuir/Dubinin-Radushkevich, respectively. The adsorption process and mode were geared to monolayer and chemisorption, the removal rate was directly proportional to the square of mercury ions concentration. The UiO-66-DMTD adsorbent was easy to be regenerated and the removal rate decreased by only 13.5% after ten consecutive cycles. The results of FTIR, XRD and XPS suggested that the adsorption mechanism lay on the complexation reaction between Hg(II) and thiol/nitrogen-containing groups. Moreover, compared with other competitive metal ions, viz., Zn(II), Co(IV), Ni(II), Cd(II), Mg(II), Fe(III), Ca(II) and Cu(II), the UiO-66-DMTD demonstrated an outstanding selective adsorption for Hg(II). These results manifested that the UiO-66-DMTD was a latent adsorbent for the efficient and selective removal of Hg(II) in wastewater.

Different functional group modified zirconium frameworks for the photocatalytic reduction of carbon dioxide

UiO-68-PSMs of UiO-68-F, UiO-68-CH₃ and UiO-68-OCH₃ achieved by post-synthetic modification were found to show different activity for photocatalytic CO₂ reduction.

A step forward in solvent knitting strategies: ruthenium and gold phosphine complex polymerization results in effective heterogenized catalysts

A knitting strategy has been applied to obtain metal–phosphine porous organic polymers (Kphos(M)), resulting in effective heterogenized catalysts for different reactions.

Insights into Functionalization of Metal-Organic Frameworks Using In Situ NMR Spectroscopy

Postsynthetic reactions of metal-organic frameworks (MOFs) are versatile tools for producing functional materials, but the methods of evaluating these reactions are cumbersome and destructive. Here we demonstrate and validate the use of in situ NMR spectroscopy of species in the liquid state to examine solvent-assisted ligand exchange (SALE) and postsynthetic modification (PSM) reactions of metal-organic frameworks. This technique allows functionalization to be monitored over time without decomposing the product for analysis, which simplifies reaction screening. In the case of SALE, both the added ligand and the ligand leaving the framework can be observed. We demonstrate this in situ method by examining SALE and PSM reactions of the robust zirconium MOF UiO-67 as well as SALE with the aluminum MOF DUT-5. In situ NMR spectroscopy provided insights into the reactions studied, and we expect that future studies using this method will permit the examination of a variety of MOF–solute reactions.