A metal-organic framework immobilised iridium pincer complex

Continuous-Flow Catalysis Using Phosphine-Metal Complexes on Porous Polymers: Designing Ligands, Pores, and Reactors

Continuous-flow syntheses using immobilized catalysts can offer efficient chemical processes with easy separation and purification. Porous polymers have gained significant interests for their applications to catalytic systems in the field of organic chemistry. The porous polymers are recognized for their large surface area, high chemical stability, facile modulation of surface chemistry, and cost-effectiveness. It is crucial to immobilize transition-metal catalysts due to their difficult separation and high toxicity. Supported phosphine ligands represent a noteworthy system for the effective immobilization of metal catalysts and modulation of catalytic properties. Researchers have been actively pursuing strategies involving phosphine-metal complexes supported on porous polymers, aiming for high activities, durabilities, selectivities, and applicability to continuous-flow systems. This review provides a concise overview of phosphine-metal complexes supported on porous polymers for continuous-flow catalytic reactions. Polymer catalysts are categorized based on pore sizes, including micro-, meso-, and macroporous polymers. The characteristics of these porous polymers are explored concerning their efficiency in immobilized catalysis and continuous-flow systems.

New insights for valorization of polyolefins/light alkanes: catalytic dehydrogenation of n-alkanes by immobilized pincer-iridium complexes

This scientific review delves into the innovative realm of polyolefins/light alkanes valorization through their catalytic dehydrogenation employing pincer-ligated iridium organometallic complexes. These widely studied catalysts exhibit outstanding properties, although the intrinsic characteristics of homogeneous catalysis (such as challenging product-catalyst separation, poor applicability to continuous-flow processes and low recyclability) limit their activity and industrial application, as well as their thermal stability. Through the immobilization of complexes on inorganic supports, these downsides have been bypassed, harnessing the true potential of these catalysts, affording more selective and stable catalysts in addition to facilitating their implementation in industrial processes. The findings described herein contribute to the advancement in the understanding of catalytic processes in hydrocarbon transformations, offering promising avenues for sustainable and selective production of valuable chemical intermediates from readily available feedstocks.

Conceptual and Practical Aspects of Metal-Organic Frameworks for Solid-Gas Reactions

The presence of site-isolated and well-defined metal sites has enabled the use of metal-organic frameworks (MOFs) as catalysts that can be rationally modulated. Because MOFs can be addressed and manipulated through molecular synthetic pathways, they are chemically similar to molecular catalysts. They are, nevertheless, solid-state materials and therefore can be thought of as privileged solid molecular catalysts that excel in applications involving gas-phase reactions. This contrasts with homogeneous catalysts, which are overwhelmingly used in the solution phase. Herein, we review theories dictating gas phase reactivity within porous solids and discuss key catalytic gas-solid reactions. We further treat theoretical aspects of diffusion within confined pores, the enrichment of adsorbates, the types of solvation spheres that a MOF might impart on adsorbates, definitions of acidity/basicity in the absence of solvent, the stabilization of reactive intermediates, and the generation and characterization of defect sites. The key catalytic reactions we discuss broadly include reductive reactions (olefin hydrogenation, semihydrogenation, and selective catalytic reduction), oxidative reactions (oxygenation of hydrocarbons, oxidative dehydrogenation, and carbon monoxide oxidation), and C-C bond forming reactions (olefin dimerization/polymerization, isomerization, and carbonylation reactions).

Synthesis of Phenol-Tagged Ruthenium Alkylidene Olefin Metathesis Catalysts for Robust Immobilisation Inside Metal–Organic Framework Support

Two new unsymmetrical N-heterocyclic carbene ligand (uNHC)-based ruthenium complexes featuring phenolic OH function were obtained and fully characterised. The more active one was then immobilised on the metal–organic framework (MOF) solid support (Al)MIL-101-NH2. The catalytic activity of such a heterogeneous system was tested, showing that, while the heterogeneous catalyst is less active than the corresponding homogeneous catalyst in solution, it can catalyse selected olefin metathesis reactions, serving as the proof-of-concept for the immobilisation of catalytically active complexes in MOFs using a phenolic tag.

Engineering Single-Atom Sites into Pore-Confined Nanospaces of Porphyrinic Metal-Organic Frameworks for the Highly Efficient Photocatalytic Hydrogen Evolution Reaction

As a type of heterogeneous catalyst expected for the maximum atom efficiency, a series of single-atom catalysts (SACs) containing spatially isolated metal single atoms (M-SAs) have been successfully prepared by confining M-SAs in the pore-nanospaces of porphyrinic metal-organic frameworks (MOFs). The prepared MOF composites of M-SAs@Pd-PCN-222-NH₂ (M = Pt, Ir, Au, and Ru) display exceptionally high and persistent efficiency in the photocatalytic hydrogen evolution reaction with a turnover number (TON) of up to 21713 in 32 h and a beginning/lasting turnover frequency (TOF) larger than 1200/600 h^-1 based on M-SAs under visible light irradiation (λ ≥ 420 nm). The photo-/electrochemical property studies and density functional theory calculations disclose that the close proximity of the catalytically active Pt-SAs to the Pd-porphyrin photosensitizers with the confinement and stabilization effect by chemical binding could accelerate electron-hole separation and charge transfer in pore-nanospaces, thus promoting the catalytic H₂ evolution reaction with lasting effectiveness.

Iridium-Catalyzed Dehydrogenation in a Continuous Flow Reactor for Practical On-Board Hydrogen Generation From Liquid Organic Hydrogen Carriers

To enable the large-scale use of hydrogen fuel cells for mobility applications, convenient methods for on-board hydrogen storage and release are required. A promising approach is liquid organic hydrogen carriers (LOHCs), since these are safe, available on a large scale, and compatible with existing refueling infrastructure. Usually, LOHC dehydrogenation is carried out in batch-type reactors by transition metals and their complexes and suffers from slow H2 release kinetics and/or inability to reach high energy density by weight, owing to low conversion or the need to dilute the reaction mixture. In this study, a continuous flow reactor is used in combination with a heterogenized iridium pincer complex, which enables a tremendous increase in LOHC dehydrogenation rates. Thus, dehydrogenation of isopropanol is performed in a regime that, in terms of gravimetric energy density, hydrogen generation rate, and precious metal content, is potentially compatible with applications in a fuel-cell powered car.

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.

The modulation effect of an electron-rich guest on the luminescence of naphthalene diimide-based metal–organic frameworks

A series of host–guest MOF materials were successfully fabricated by virtue of donor–acceptor interactions, which exhibit color-tunable emissions in a wide wavelength range by rational selection of guest molecules.

Green synthesis of AgNP-ligand complexes and their toxicological effects on Nilaparvata lugens

BACKGROUND

Despite developments in nanotechnology for use in the pharmaceutical field, there is still a need for implementation of this technology in agrochemistry. In this study, silver nanoparticles (AgNPs) were successfully prepared by a facile and an eco-friendly route using two different ligands, 2'-amino-1,1':4',1″-terphenyl-3,3″,5,5″-tetracarboxylic acid (H4L) and 1,3,6,8-tetrakis (p-benzoic acid)-pyrene (TBAPy), as reducing agents. The physiochemical properties of the as-obtained AgNPs were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The toxicity of H4L-AgNP and TBAPy-AgNP against the brown planthopper (BPH, Nilaparvata lugens) was also measured.

RESULTS

SEM and TEM analyses demonstrated the formation of quasi-spherical AgNP structures in the presence of H4L and TBAPy. Insecticidal assays showed that TBAPy is less effective against N. lugens, with a median lethal concentration (LC50) of 810 mg/L, while the toxicity of H4L increased and their LC50 reached 786 mg/L 168 h posttreatment at a high concentration of 2000 mg/L. H4L-AgNPs were also highly toxic at a low concentration of 20 mg/L, with LC50 =  ~ 3.9 mg/L 168 h posttreatment, while TBAPy-AgNPs exhibited less toxicity at the same concentration, with LC50 =  ~ 4.6 mg/L.

CONCLUSIONS

These results suggest that the synthesized AgNPs using the two ligands may be a safe and cheaper method compared with chemical insecticides for protection of rice plants from pests and has potential as an effective insecticide in the N. lugens pest management program.

Using Postsynthetic X-Type Ligand Exchange to Enhance CO2 Adsorption in Metal-Organic Frameworks with Kuratowski-Type Building Units

Postsynthetic modification methods have emerged as indispensable tools for tuning the properties and reactivity of metal-organic frameworks (MOFs). In particular, postsynthetic X-type ligand exchange (PXLE) at metal building units has gained increasing attention as a means of immobilizing guest species, modulating the reactivity of framework metal ions, and introducing new functional groups. The reaction of a Zn-OH functionalized analogue of CFA-1 (1-OH, Zn(ZnOH)₄(bibta)₃, where bibta^2- = 5,5'-bibenzotriazolate) with organic substrates containing mildly acidic E-H groups (E = C, O, N) results in the formation of Zn-E species and water as a byproduct. This Brønsted acid-base PXLE reaction is compatible with substrates with pK_a(DMSO) values as high as 30 and offers a rapid and convenient means of introducing new functional groups at Kuratwoski-type metal nodes. Gas adsorption and diffuse reflectance infrared Fourier transform spectroscopy experiments reveal that the anilide-exchanged MOFs 1-NHPh_0.9 and 1-NHPh_2.5 exhibit enhanced low-pressure CO₂ adsorption compared to 1-OH as a result of a Zn-NHPh + CO₂ ⇌ Zn-O₂CNHPh chemisorption mechanism. The MFU-4l analogue 2-NHPh ([Zn₅(OH)_2.1(NHPh)_1.9(btdd)₃], where btdd^2- = bis(1,2,3-triazolo)dibenzodioxin), shows a similar improvement in CO₂ adsorption in comparison to the parent MOF containing only Zn-OH groups.

Pyrene-based metal organic frameworks: from synthesis to applications

Pyrene is one of the most widely investigated aromatic hydrocarbons given to its unique optical and electronic properties. Hence, pyrene-based ligands have been attractive for the synthesis of metal-organic frameworks (MOFs) in the last few years. In this review, we will focus on the most important characteristics of pyrene, in addition to the development and synthesis of pyrene-based molecules as bridging ligands to be used in MOF structures. We will summarize the synthesis attempts, as well as the post-synthetic modifications of pyrene-based MOFs by the incorporation of metals or ligands in the structure. The discussion of promising results of such MOFs in several applications; including luminescence, photocatalysis, adsorption and separation, heterogeneous catalysis, electrochemical applications and bio-medical applications will be highlighted. Finally, some insights and future prospects will be given based on the studies discussed in the review. This review will pave the way for the researchers in the field for the design and development of novel pyrene-based structures and their utilization for different applications.

Synthesis and reactivity of iridium complexes of a macrocyclic PNP pincer ligand

Having recently reported on the synthesis and rhodium complexes of the novel macrocyclic pincer ligand PNP-14, which is derived from lutidine and features terminal phosphine donors trans-substituted with a tetradecamethylene linker (Dalton Trans., 2020, 49, 2077-2086 and Dalton Trans., 2020, 49, 16649-16652), we herein describe our findings critically examining the chemistry of iridium homologues. The five-coordinate iridium(i) and iridium(iii) complexes [Ir(PNP-14)(η2:η2-cyclooctadiene)][BArF4] and [Ir(PNP-14)(2,2'-biphenyl)][BArF4] are readily prepared and shown to be effective precursors for the generation of iridium(iii) dihydride dihydrogen, iridium(i) bis(ethylene), and iridium(i) carbonyl derivatives that highlight important periodic trends by comparison to rhodium counterparts. Reaction of [Ir(PNP-14)H2(H2)][BArF4] with 3,3-dimethylbutene induced triple C-H bond activation of the methylene chain, yielding an iridium(iii) allyl hydride derivative [Ir(PNP-14*)H][BArF4], whilst catalytic homocoupling of 3,3-dimethylbutyne into Z-tBuC[triple bond, length as m-dash]CCHCHtBu could be promoted at RT by [Ir(PNP-14)(η2:η2-cyclooctadiene)][BArF4] (TOFinitial = 28 h-1). The mechanism of the latter is proposed to involve formation and direct reaction of a vinylidene derivative with HC[triple bond, length as m-dash]CtBu outside of the macrocyclic ring and this suggestion is supported experimentally by isolation and crystallographic characterisation of a catalyst deactivation product.

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.

Regioselective Functionalization of the Mesoporous Metal-Organic Framework, NU-1000, with Photo-Active Tris-(2,2'-bipyridine)ruthenium(II)

Solvent-assisted ligand incorporation is an excellent method for the post-synthetic functionalization of Zr-based metal-organic frameworks (MOFs), as carboxylate-derivative functionalities readily coordinate to the Zr6 nodes by displacing node-based aqua and terminal hydroxo ligands. In this study, a photocatalytically active ruthenium complex RuII(bpy)2(dcbpy), that is, bis-(2,2'-bipyridine)-(4,4'-dicarboxy-2,2'-bipyridine)ruthenium, was installed in the mono-protonated (carboxylic acid) form within NU-1000 via SALI. Crystallographic information regarding the siting of the ruthenium complex within the MOF pores is obtained by difference envelope density analysis. The ruthenium-functionalized MOF, termed Ru-NU-1000, shows excellent heterogeneous photocatalytic activity for an oxidative amine coupling reaction.

Immobilization of an Iridium Pincer Complex in a Microporous Polymer for Application in Room-Temperature Gas Phase Catalysis

An iridium dihydride pincer complex [IrH2 (POCOP)] is immobilized in a hydroxy-functionalized microporous polymer network using the concepts of surface organometallic chemistry. The introduction of this novel, truly innocent support with remote OH-groups enables the formation of isolated active metal sites embedded in a chemically robust and highly inert environment. The catalyst maintained high porosity and without prior activation exhibited efficacy in the gas phase hydrogenation of ethene and propene at room temperature and low pressure. The catalyst can be recycled for at least four times.

Metal-Organic Framework-Based Catalysts with Single Metal Sites

Metal-organic frameworks (MOFs) are a class of distinctive porous crystalline materials constructed by metal ions/clusters and organic linkers. Owing to their structural diversity, functional adjustability, and high surface area, different types of MOF-based single metal sites are well exploited, including coordinately unsaturated metal sites from metal nodes and metallolinkers, as well as active metal species immobilized to MOFs. Furthermore, controllable thermal transformation of MOFs can upgrade them to nanomaterials functionalized with active single-atom catalysts (SACs). These unique features of MOFs and their derivatives enable them to serve as a highly versatile platform for catalysis, which has actually been becoming a rapidly developing interdisciplinary research area. In this review, we overview the recent developments of catalysis at single metal sites in MOF-based materials with emphasis on their structures and applications for thermocatalysis, electrocatalysis, and photocatalysis. We also compare the results and summarize the major insights gained from the works in this review, providing the challenges and prospects in this emerging field.

Alterations to secondary building units of metal–organic frameworks for the development of new functions

Post-synthetic modification methods for the secondary building units in MOFs facilitate unique structures and properties that are impossible to access via direct syntheses, which can be classified as four categories.

Spectroscopy, microscopy, diffraction and scattering of archetypal MOFs: formation, metal sites in catalysis and thin films

A comprehensive overview of characterization tools for the analysis of well-known metal–organic frameworks and physico-chemical phenomena associated to their applications.

Hollow porous organic nanospheres for anchoring Pd(PPh3)4 through a co-hyper-crosslinking mediated self-assembly strategy

A facile synthesis of Pd(PPh₃)₄-functionalized hollow porous organic nanospheres with excellent catalytic activity is reported for the first time.

Fighting Deactivation: Classical and Emerging Strategies for Efficient Stabilization of Molecular Electrocatalysts

Development of highly active molecular electrocatalysts for fuel-forming reactions has relied heavily on understanding mechanistic aspects of the electrochemical transformations. Careful fine-tuning of the ligand environment oriented mechanistic pathways towards higher activity and optimal product distribution for several catalysts. Unfortunately, many catalysts deactivate in bulk electrolysis conditions, diminishing the impact of the plethora of highly tuned molecular electrocatalytic systems. This Minireview covers classical and emerging methods developed to circumvent catalyst deactivation and degradation, with an emphasis on successes with molecular electrocatalysts.

Cyclometalated Ir-Zr Metal-Organic Frameworks as Recyclable Visible-Light Photocatalysts for Sulfide Oxidation into Sulfoxide in Water

Aerobic photo-oxidation of sulfide into sulfoxide in water is of great interest in green chemistry. In this study, three highly stable Ir(III)-Zr(IV) metal-organic frameworks (Ir-Zr MOFs), namely Zr₆-Irbpy (bpy is 2,2'-bipyridine), Zr₆-IrbpyOMe (bpyOMe is 4,4'-dimethoxy-2,2'-bipyridine), and Zr₆-Irphen (phen is 1,10-phenanthroline), are constructed by using [Ir(pqc)₂(L)₂]Cl complexes (where pqc is 2-phenylquinoline-4-carboxylic acid and L is an ancillary ligand bpy, bpyOMe, or phen) as linkers and Zr₆ cluster as nodes. The constructed Ir-Zr MOFs present high catalytic activity on aerobic photo-oxidation of sulfide into sulfoxide under visible light irradiation in water at room temperature. Moreover, the reaction is high chemoselectivity and functional group tolerance. The catalyst can be readily recycled and reused at least 10 times without loss of catalytic activity. Mechanism studies demonstrate that superoxide radical is the reactive oxygen species in the sulfoxidation, which is generated by electron transfer from the excited triplet photosensitizer ³[Ir-Zr-MOF]* to O₂. The high activity of photocatalytic sulfoxidation in water may be attributed to the stabilization of the persulfoxide intermediate by hydrogen bond formation with water solvent, which accelerates the conversion of persulfoxide into sulfoxide and prevents further oxidation of sulfoxide into sulfone. This work provides a new strategy for the green synthesis of sulfoxides under ambient conditions.

Inter-molecular hydrogen bonding in isostructural pincer complexes [OH-( t-BuPOCOP t-Bu)MCl] (M = Pd and Pt)

In the crystal structure of the isostructural title compounds, namely {2,6-bis-[(di-tert-butyl-phosphan-yl)-oxy]-4-hy-droxy-phen-yl}chlorido-palladium(II), [Pd(C22H39O3P2)Cl], 1, and {2,6-bis-[(di-tert-butyl-phosphan-yl)-oxy]-4-hy-droxy-phen-yl}chlorido-platinum(II), [Pt(C22H39O3P2)Cl], 2, the metal centres are coordinated in a distorted square-planar fashion by the POCOP pincer fragment and the chloride ligand. Both complexes form strong hydrogen-bonded chain structures through an inter-action of the OH group in the 4-position of the aromatic POCOP backbone with the halide ligand.

A mesoporous NNN-pincer-based metal–organic framework scaffold for the preparation of noble-metal-free catalysts

A terpyridine-based mesoporous 3D MOF was synthesized as a general scaffold for catalyst preparation.

Single-Site Ruthenium Pincer Complex Knitted into Porous Organic Polymers for Dehydrogenation of Formic Acid

Owing to its capacity for reversible hydrogen storage, formic acid (FA) holds great promise as an alternative energy carrier to conventional fossil fuel systems. Whereas the decomposition of FA to hydrogen (H₂ ) and carbon dioxide (CO₂ ) through homogeneous catalysis is well established, the selective and efficient dehydrogenation of FA by a robust heterogeneous catalyst remains a challenge. A new heterogeneous ruthenium pincer framework with single-atomic sites was prepared in one step by the direct knitting of a phosphorus-nitrogen PN³ P-pincer ruthenium complex in a porous organic polymer. The heterogeneous ruthenium complex efficiently dehydrogenates formic acid in both organic and aqueous media with remarkably enhanced stability. Notably, no detectable CO was generated and a turnover number (TON) of 145 300 was attained in a continuous experiment with no significant decline in catalytic activity (in sharp contrast, a total TON of only 5600 was obtained with the homogeneous analog under the same conditions). The single-atomic sites in the porous framework combined the desirable attributes of high reactivity and selectivity of a homogeneous catalyst with the significantly enhanced catalyst stability and reusability benefits of heterogeneous catalysis.

Probing the Evolution of Palladium Species in Pd@MOF Catalysts during the Heck Coupling Reaction: An Operando X-ray Absorption Spectroscopy Study

The mechanism of the Heck C-C coupling reaction catalyzed by Pd@MOFs has been investigated using operando X-ray absorption spectroscopy (XAS) and powder X-ray diffraction (PXRD) combined with transmission electron microscopy (TEM) analysis and nuclear magnetic resonance (¹H NMR) kinetic studies. A custom-made reaction cell was used, allowing operando PXRD and XAS data collection using high-energy synchrotron radiation. By analyzing the XAS data in combination with ex situ studies, the evolution of the palladium species is followed from the as-synthesized to its deactivated form. An adaptive reaction mechanism is proposed. Mononuclear Pd(II) complexes are found to be the dominant active species at the beginning of the reaction, which then gradually transform into Pd nanoclusters with 13-20 Pd atoms on average in later catalytic turnovers. Consumption of available reagent and substrate leads to coordination of Cl^- ions to their surfaces, which causes the poisoning of the active sites. By understanding the deactivation process, it was possible to tune the reaction conditions and prolong the lifetime of the catalyst.

Electroactive Ferrocene at or near the Surface of Metal-Organic Framework UiO-66

Here, we describe the installation of a ferrocene derivative on and within the archetypal metal-organic framework (MOF), UiO-66, by solvent-assisted ligand incorporation. Thin films of the resulting material show a redox peak characteristic of the Fc/Fc⁺ couple, as measured by cyclic voltammetry. Consistent with restriction of redox reactivity solely to Fc molecules sited at or near the external surfaces of MOF crystallites, chronoamperometry measurements indicate that less than 20% of the installed Fc molecules are electrochemically active. Charge-transport diffusion coefficients, D_CT, of 6.1 ± 0.8 × 10^-11 and 2.6 ± 0.2 × 10^-9 cm²/s were determined from potential step measurements, stepping oxidatively and reductively, respectively. The 40-fold difference in D_CT values contrasts with the expectation, for simple systems, of identical values for oxidation-driven versus reduction-driven charge transport. The findings have implications for the design of MOFs suitable for delivery of redox equivalents to framework-immobilized electrocatalysts and/or delivery of charges from a chromophoric MOF film to an underlying electrode, processes that may be central to MOF-facilitated conversion of solar energy to chemical or electrical energy.

Encapsulation of Crabtree's Catalyst in Sulfonated MIL-101(Cr): Enhancement of Stability and Selectivity between Competing Reaction Pathways by the MOF Chemical Microenvironment

Crabtree's catalyst was encapsulated inside the pores of the sulfonated MIL-101(Cr) metal-organic framework (MOF) by cation exchange. This hybrid catalyst is active for the heterogeneous hydrogenation of non-functionalized alkenes either in solution or in the gas phase. Moreover, encapsulation inside a well-defined hydrophilic microenvironment enhances catalyst stability and selectivity to hydrogenation over isomerization for substrates bearing ligating functionalities. Accordingly, the encapsulated catalyst significantly outperforms its homogeneous counterpart in the hydrogenation of olefinic alcohols in terms of overall conversion and selectivity, with the chemical microenvironment of the MOF host favouring one out of two competing reaction pathways.

Rational design of a flu-type heterometallic cluster-based Zr-MOF

Following the HSAB principle, the cooperative assembly of tetrahedral [Cu₄I₄(Ina)₄]^4- metalloligands and 8-connecting [Zr₆(μ₃-OH)₈(OH)₈]⁸⁺ building units leads to the first heterometallic cluster-based Zr-MOF (1). The results provide a successful strategy for rational design of heterometallic cluster-based Zr-MOFs.

Computational Design of Functionalized Metal-Organic Framework Nodes for Catalysis

Recent progress in the synthesis and characterization of metal-organic frameworks (MOFs) has opened the door to an increasing number of possible catalytic applications. The great versatility of MOFs creates a large chemical space, whose thorough experimental examination becomes practically impossible. Therefore, computational modeling is a key tool to support, rationalize, and guide experimental efforts. In this outlook we survey the main methodologies employed to model MOFs for catalysis, and we review selected recent studies on the functionalization of their nodes. We pay special attention to catalytic applications involving natural gas conversion.

A polystyrene supported [PdCl–(SeCSe)] complex: a novel, reusable and robust heterogeneous catalyst for the Sonogashira synthesis of 1,2-disubstituted alkynes and 1,3-enynes

PS-[PdCl–(SeCSe)] has been introduced as a novel and heterogeneous catalyst, which exhibits outstanding catalytic activity in the Sonogashira cross-coupling reactions.

Stable metal–organic frameworks as a host platform for catalysis and biomimetics

Recent years have witnessed the exploration and synthesis of an increasing number of metal–organic frameworks (MOFs). The utilization of stable MOFs as a platform for catalysis and biomimetics is discussed.

Role of a Modulator in the Synthesis of Phase-Pure NU-1000

NU-1000 is a robust, mesoporous metal-organic framework (MOF) with hexazirconium nodes ([Zr₆O₁₆H₁₆]⁸⁺, referred to as oxo-Zr₆ nodes) that can be synthesized by combining a solution of ZrOCl₂·8H₂O and a benzoic acid modulator in N,N-dimethylformamide with a solution of linker (1,3,6,8-tetrakis(p-benzoic acid)pyrene, referred to as H₄TBAPy) and by aging at an elevated temperature. Typically, the resulting crystals are primarily composed of NU-1000 domains that crystallize with a more dense phase that shares structural similarity with NU-901, which is an MOF composed of the same linker molecules and nodes. Density differences between the two polymorphs arise from the differences in the node orientation: in NU-1000, the oxo-Zr₆ nodes rotate 120° from node to node, whereas in NU-901, all nodes are aligned in parallel. Considering this structural difference leads to the hypothesis that changing the modulator from benzoic acid to a larger and more rigid biphenyl-4-carboxylic acid might lead to a stronger steric interaction between the modulator coordinating on the oxo-Zr₆ node and misaligned nodes or linkers in the large pore and inhibit the growth of the more dense NU-901-like material, resulting in phase-pure NU-1000. Side-by-side reactions comparing the products of synthesis using benzoic acid or biphenyl-4-carboxylic acid as a modulator produce structurally heterogeneous crystals and phase-pure NU-1000 crystals. It can be concluded that the larger and more rigid biphenyl-4-carboxylate inhibits the incorporation of nodes with an alignment parallel to the neighboring nodes already residing in the crystal.

Sonochemical synthesis and structural characterization of a new nanostructured Co(II) supramolecular coordination polymer with Lewis base sites as a new catalyst for Knoevenagel condensation

A new Co(II) mixed-ligand coordination supramolecular polymer with composition [Co₂(ppda)(4-bpdh)₂(NO₃)₂]_n (1) (where, ppda=p-phenylenediacrylic acid, 4-bpdh=2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene) was synthesized using solvothermal, mechanochemical and sonochemical methods. Compound 1 and the new nanostructure have been characterized by single-crystal X-ray, infrared spectroscopy (IR), powder X-ray diffraction (PXRD) analysis and scanning electron microscopy (SEM). The thermal stability of compound 1 was also studied by thermal gravimetric analysis (TGA). The surface area of these compounds was determined by BET. The single-crystal X-ray data shows a new interesting two-dimensional coordination polymer (CP). In addition, the effect of various sonication concentrations of initial reagents, power of ultrasound irradiation and also the time on the size and morphology of nano-structured coordination polymer 1 were evaluated. Moreover, it has been demonstrated that the nanostructure of the CP1 can be used as a catalyst in Knoevenagel condensation reaction.