Reversible Metalation and Catalysis with a Scorpionate-like Metallo-ligand in a Metal–Organic Framework

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.

Core-shell inorganic NP@MOF nanostructures for targeted drug delivery and multimodal imaging-guided combination tumor treatment

It is well known that metal-organic framework (MOF) nanostructures have unique characteristics such as high porosity, large surface areas and adjustable functionalities, so they are ideal candidates for developing drug delivery systems (DDSs) as well as theranostic platforms in cancer treatment. Despite the large number of MOF nanostructures that have been discovered, conventional MOF-derived nanosystems only have a single biofunctional MOF source with poor colloidal stability. Accordingly, developing core-shell MOF nanostructures with good colloidal stability is a useful method for generating efficient drug delivery, multimodal imaging and synergistic therapeutic systems. The preparation of core-shell MOF nanostructures has been done with a variety of materials, but inorganic nanoparticles (NPs) are highly effective for drug delivery and imaging-guided tumor treatment. Herein, we aimed to overview the synthesis of core-shell inorganic NP@MOF nanostructures followed by the application of core-shell MOFs derived from magnetic, quantum dots (QDs), gold (Au), and gadolinium (Gd) NPs in drug delivery and imaging-guided tumor treatment. Afterward, we surveyed different factors affecting prolonged drug delivery and cancer therapy, cellular uptake, biocompatibility, biodegradability, and enhanced permeation and retention (EPR) effect of core-shell MOFs. Last but not least, we discussed the challenges and the prospects of the field. We envision this article may hold great promise in providing valuable insights regarding the application of hybrid nanostructures as promising and potential candidates for multimodal imaging-guided combination cancer therapy.

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.

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).

Inhibition, Binding of Organometallics, and Thermally Induced CO Release in an MFU-4-Type Metal-Organic Framework Scaffold with Open Bidentate Bibenzimidazole Coordination Sites

Triazolate-based MFU-4-type metal-organic frameworks are promising candidates for various applications, of which heterogeneous catalysis has emerged as a hot topic owing to the facile post-synthetic metal and ligand exchange in Kuratowski secondary building units (SBUs). Herein, we present the largest non-interpenetrated isoreticular MFU-4-type framework CFA-19 ([Co₅^IICl₄(H₂-bibt)₃]; H₄-bibt = 1,1',5,5'-tetrahydro-6,6'-biimidazo[4,5-f]benzotriazole; CFA-19 = Coordination Framework Augsburg University-19) and the CFA-19-Tp derivative featuring trispyrazolylborate inhibited SBUs as a scaffold with open bibenzimidazole coordination sites at the backbone of the H₄-bibt linker. The proof-of-principle incorporation of accessible M^IBr(CO)₃ (M = Re, Mn) sites in CFA-19-Tp was revealed by single-crystal X-ray diffraction, and a thermally induced CO release was observed for MnBr(CO)₃. Deprotonation of bibenzimidazole was also achieved by the reaction with ZnEt₂.

Site Isolation in Metal-Organic Layers Enhances Photoredox Gold Catalysis

Herein, we report the synthesis of a metal-organic layer, Hf-Ru-Au, containing Ru(bipyridine)₃²⁺-type photosensitizers and (phosphine)-AuCl catalysts for photoredox Au-catalyzed cross-coupling of allenoates, alkenes, or alkynes with aryldiazonium salts to afford furanone, tetrahydrofuran, or aryl alkyne derivatives, respectively. Site isolation of (phosphine)-AuCl complexes in Hf-Ru-Au prevents Au catalyst deactivation via ligand redistribution, Au(I) disproportionation, and aryl-phosphine reductive elimination, while the proximity between the Ru photosensitizers and Au catalysts enhances catalytic efficiency, with 14-200 times higher activity over those of the homogeneous controls in the cross-coupling reactions.

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.

Chemoselective and Tandem Reduction of Arenes Using a Metal-Organic Framework-Supported Single-Site Cobalt Catalyst

The development of heterogeneous, chemoselective, and tandem catalytic systems using abundant metals is vital for the sustainable synthesis of fine and commodity chemicals. We report a robust and recyclable single-site cobalt-hydride catalyst based on a porous aluminum metal-organic framework (DUT-5 MOF) for chemoselective hydrogenation of arenes. The DUT-5 node-supported cobalt(II) hydride (DUT-5-CoH) is a versatile solid catalyst for chemoselective hydrogenation of a range of nonpolar and polar arenes, including heteroarenes such as pyridines, quinolines, isoquinolines, indoles, and furans to afford cycloalkanes and saturated heterocycles in excellent yields. DUT-5-CoH exhibited excellent functional group tolerance and could be reusable at least five times without decreased activity. The same MOF-Co catalyst was also efficient for tandem hydrogenation-hydrodeoxygenation of aryl carbonyl compounds, including biomass-derived platform molecules such as furfural and hydroxymethylfurfural to cycloalkanes. In the case of hydrogenation of cumene, our spectroscopic, kinetic, and density functional theory (DFT) studies suggest the insertion of a trisubstituted alkene intermediate into the Co-H bond occurring in the turnover limiting step. Our work highlights the potential of MOF-supported single-site base-metal catalysts for sustainable and environment-friendly industrial production of chemicals and biofuels.

Templated synthesis of zirconium(IV)-based metal-organic layers (MOLs) with accessible chelating sites

Metal-organic layers (MOLs) are of great interest in heterogeneous catalysis, particularly materials that can accommodate extraneous metal centres. Here, we demonstrate a two-step preorganisation/delamination synthetic strategy using CuI as a template to prepare Zr-based MOLs with accessible 'syn' bis-pyrazolyl chelating sites (named UAM-2·ns) that are poised for quantitative post-synthetic metalation with late transition metals.

Complexes of Platinum Group Metals with a Conformationally Locked Scorpionate in a Metal-Organic Framework: An Unusually Close Apical Interaction of Palladium(II)

We report synthetic strategies for installing platinum group metals (PGMs: Pd, Rh, Ir, and Pt) on a scorpionate-derived linker (TpmC*) within a metal-organic framework (MOF), both by room-temperature postsynthetic metalation and by direct solvothermal synthesis, with a wide range of metal loadings relevant for fundamental studies and catalysis. In-depth studies for the palladium adduct Pd(II)@Zr-TpmC* by density-functional-theory-assisted extended X-ray absorption fine structure spectroscopy reveals that the rigid MOF lattice enforces a close Pd(II)-N_apical interaction between the bidentate palladium complex and the third uncoordinated pyrazole arm of the TpmC* ligand (Pd-N_apical = 2.501 ± 0.067 Å), an interaction that is wholly avoided in molecular palladium scorpionates.

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.

Metal-Organic Framework-Confined Single-Site Base-Metal Catalyst for Chemoselective Hydrodeoxygenation of Carbonyls and Alcohols

Chemoselective deoxygenation of carbonyls and alcohols using hydrogen by heterogeneous base-metal catalysts is crucial for the sustainable production of fine chemicals and biofuels. We report an aluminum metal-organic framework (DUT-5) node support cobalt(II) hydride, which is a highly chemoselective and recyclable heterogeneous catalyst for deoxygenation of a range of aromatic and aliphatic ketones, aldehydes, and primary and secondary alcohols, including biomass-derived substrates under 1 bar H₂. The single-site cobalt catalyst (DUT-5-CoH) was easily prepared by postsynthetic metalation of the secondary building units (SBUs) of DUT-5 with CoCl₂ followed by the reaction of NaEt₃BH. X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy (XANES) indicated the presence of Co^II and Al^III centers in DUT-5-CoH and DUT-5-Co after catalysis. The coordination environment of the cobalt center of DUT-5-Co before and after catalysis was established by extended X-ray fine structure spectroscopy (EXAFS) and density functional theory. The kinetic and computational data suggest reversible carbonyl coordination to cobalt preceding the turnover-limiting step, which involves 1,2-insertion of the coordinated carbonyl into the cobalt-hydride bond. The unique coordination environment of the cobalt ion ligated by oxo-nodes within the porous framework and the rate independency on the pressure of H₂ allow the deoxygenation reactions chemoselectively under ambient hydrogen pressure.

HKUST-1 Metal Organic Framework as an Efficient Dual-Function Catalyst: Aziridination and One-Pot Ring-Opening Transformation for Formation of β-Aryl Sulfonamides with C-C, C-N, C-S, and C-O Bonds

Metal-organic frameworks (MOFs) are extensively used in catalysis due to their robust structure, well-defined periodic reaction centers, and high porosity. We report Cu₃(BTC)₂·(H₂O)₃ (HKUST-1) as an efficient heterogeneous catalyst for aziridination of alkene and ring-opening reaction of activated aziridines. Furthermore, we demonstrate that the transfer of a nitrogen group from PhINTs to olefins and its analogue to give aziridines takes place at the coordinatively unsaturated Cu(II) site of Cu₃(BTC)₂-MOF; however, the ring opening of activated aziridines is controlled by the Cu(II) Lewis acid site, and generation of coordinative unsaturation by thermal activation of the MOF is not necessarily important. The key advantage of this catalytic approach is the direct formation of C-C, C-N, C-O, and C-S bonds yielding β-aryl sulfonamide derivatives through a simultaneous aziridination ring-opening reaction of the alkene in one pot using a single catalyst.

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.

Invisible Silver Guests Boost Order in a Framework That Cyclizes and Deposits Ag3Sb Nanodots

The infusion of metal guests into (i.e., metalating) the porous medium of metal-organic frameworks (MOFs) is a topical approach to wide-ranging functionalization purposes. We report the notable interactions of AgSbF₆ guests with the designer MOF host ZrL1 [Zr₆O₄(OH)₇(L1)_4.5(H₂O)₄]. (1) The heavy-atom guests of AgSbF₆ induce order in the MOF host to allow the movable alkyne side arm to be fully located by X-ray diffraction, but they themselves curiously remain highly disordered and absent in the strucutral model. The enhanced order of the framework can be generally ascribed to interaction of the silver guests with the host alkyne and thioether functions, while the invisible heavy-atom guest represents a new phenomenon in the metalation of open framework materials. (2) The AgSbF₆ guests also participate in the thermocyclization of the vicinal alkyne units of the L1 linker (at 450 °C) and form the rare nanoparticle of Ag₃Sb supported on the concomitantly formed nanographene network. The resulted composite exhibits high electrical conductivity (1.0 S/cm) as well as useful, mitigated catalytic activity for selectively converting nitroarenes into the industrially important azo compounds, i.e., without overshooting to form the amine side products. The heterogeneous/cyclable catalysis entails only the cheap reducing reagents of NaBH₄, ethanol, and water, with yields being generally close to 90%.

Spectroscopic Evidence of Hyponitrite Radical Intermediate in NO Disproportionation at a MOF-Supported Mononuclear Copper Site

Dianionic hyponitrite (N₂ O₂ ^2- ) is often proposed, based on model complexes, as the key intermediate in reductive coupling of nitric oxide to nitrous oxide at the bimetallic active sites of heme-copper oxidases and nitric oxide reductases. In this work, we examine the gas-solid reaction of nitric oxide with the metal-organic framework Cu^I -ZrTpmC* with a suite of in situ spectroscopies and density functional theory simulations, and identify an unusual chelating N₂ O₂ ^.- intermediate. These results highlight the advantage provided by site-isolation in metal-organic frameworks (MOFs) for studying important reaction intermediates, and provide a mechanistic scenario compatible with the proposed one-electron couple in these enzymes.

Architectural and catalytic aspects of designer materials built using metalloligands of pyridine-2,6-dicarboxamide based ligands

This perspective presents the design, synthesis and crystal structures of a large number of architectures constructed using assorted metalloligands of pyridine-2,6-dicarboxamide based ligands. The metalloligands offered various appended functional groups, whereas design strategies included varying both their position and number. A combination of these parameters resulted in the development of assorted architectures including discrete trinuclear and tetranuclear complexes as well as 1D/2D/3D coordination polymers. The metalloligand strategy not only assisted in the construction of ordered crystalline materials with varied dimensionalities but also judiciously allowed the incorporation of Lewis acidic and redox-active secondary metals in the resultant architectures. As a result, such designer architectures illustrated their noteworthy role both as homogenous and heterogeneous catalysts in different organic transformation reactions.

Defect Engineering of Copper Paddlewheel-Based Metal-Organic Frameworks of Type NOTT-100: Implementing Truncated Linkers and Its Effect on Catalytic Properties

A series of new defect-engineered metal-organic frameworks (DEMOFs) were synthesized by framework doping with truncated linkers employing the mixed-linker approach. Two tritopic defective (truncated) linkers, biphenyl-3,3',5-tricarboxylates (L_H) lacking a ligating group and 5-(5-carboxypyridin-3-yl)isophthalates (L_Py) bearing a weaker interacting ligator site, were integrated into the framework of Cu₂(BPTC) (NOTT-100, BPTC = biphenyl-3,3',5,5'-tetracarboxylates). Incorporating L_H into the framework mainly generates missing metal node defects, thereby obtaining dangling COOH groups in the framework. However, introducing L_Py forms more modified metal nodes featuring reduced and more accessible Cu sites. In comparison with the pristine NOTT-100, the defect-engineered NOTT-100 (DE-NOTT-100) samples show two unique features: (i) functional groups (the protonated carboxylate groups as the Brønsted acid sites or the pyridyl N atoms as the Lewis basic sites), which can act as second active sites, are incorporated into the MOF frameworks, and (ii) more modified paddlewheels, which provided extra coordinatively unsaturated sites, are generated. The cooperative functioning of the above characteristics enhances the catalytic performance of certain types of reactions. For a proof of concept, two exemplary reactions, namely, the cycloaddition of CO₂ with propylene oxide to propylene carbonate and the cyclopropanation of styrene, were carried out to evaluate the catalytic activities of those DE-NOTT-100 materials depending on the defect structure.

Using nature's blueprint to expand catalysis with Earth-abundant metals

Numerous redox transformations that are essential to life are catalyzed by metalloenzymes that feature Earth-abundant metals. In contrast, platinum-group metals have been the cornerstone of many industrial catalytic reactions for decades, providing high activity, thermal stability, and tolerance to chemical poisons. We assert that nature's blueprint provides the fundamental principles for vastly expanding the use of abundant metals in catalysis. We highlight the key physical properties of abundant metals that distinguish them from precious metals, and we look to nature to understand how the inherent attributes of abundant metals can be embraced to produce highly efficient catalysts for reactions crucial to the sustainable production and transformation of fuels and chemicals.

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.

Isolating reactive metal-based species in Metal-Organic Frameworks - viable strategies and opportunities

Structural insight into reactive species can be achieved via strategies such as matrix isolation in frozen glasses, whereby species are kinetically trapped, or by confinement within the cavities of host molecules. More recently, Metal-Organic Frameworks (MOFs) have been used as molecular scaffolds to isolate reactive metal-based species within their ordered pore networks. These studies have uncovered new reactivity, allowed observation of novel metal-based complexes and clusters, and elucidated the nature of metal-centred reactions responsible for catalysis. This perspective considers strategies by which metal species can be introduced into MOFs and highlights some of the advantages and limitations of each approach. Furthermore, the growing body of work whereby reactive species can be isolated and structurally characterised within a MOF matrix will be reviewed, including discussion of salient examples and the provision of useful guidelines for the design of new systems. Novel approaches that facilitate detailed structural analysis of reactive chemical moieties are of considerable interest as the knowledge garnered underpins our understanding of reactivity and thus guides the synthesis of materials with unprecedented functionality.

Metal-Organic Layers for Synergistic Lewis Acid and Photoredox Catalysis

We report the design of a new multifunctional metal-organic layer (MOL), Hf₁₂-Ir-OTf, comprising triflate (OTf)-capped Hf₁₂ secondary building units (SBUs) and photosensitizing Ir(DBB)[dF(CF₃)ppy]₂⁺ [DBB-Ir-F, DBB = 4,4'-di(4-benzoato)-2,2'-bipyridine; dF(CF₃)ppy = 2-(2,4-difluorophenyl)-5-(trifluoromethyl)pyridine] bridging ligands. Hf₁₂-Ir-OTf effectively catalyzed dehydrogenative cross-couplings of heteroarenes with ethers, amines, and unactivated alkanes with turnover numbers of 930, 790, and 950, respectively. Hf₁₂-Ir-OTf also competently catalyzed late-stage functionalization of bioactive and drug molecules such as caffeine, Fasudil, and Metyrapone. The superior catalytic performance of Hf₁₂-Ir-OTf over a mixture of photoredox catalyst and stoichiometric amounts of Brønsted acids or substoichiometric amounts (20 mol %) of Lewis acids is attributed to the close proximity (1.2 nm) between photoredox and Lewis acid catalysts in Hf₁₂-Ir-OTf, which not only facilitates the reaction between the carbon radical and the activated heteroarene but also accelerates the electron transfer from the nitrogen radical intermediate to the Ir(IV) species in the catalytic cycle.

Electron transfer in the confined environments of metal–organic coordination supramolecular systems

In this review, we overview regulatory factors and diverse applications of electron transfer in confined environments of supramolecular host–guest systems.

Metal-Organic-Framework-Supported and -Isolated Ceria Clusters with Mixed Oxidation States

The formation of oxygen vacancies via reversible transitions between Ce(IV) and Ce(III) plays a crucial role in the propensity of cerium oxide to act as a supporting promoter in oxidative heterogeneous catalysis. An open challenge is, however, preparation of high-porosity, supported arrays of isolated ceria(IV, III) clusters with high porosity. Herein, we report two examples of oxy-Ce(IV, III) clusters supported and spatially isolated on an oxy-zirconium MOF, NU-1000. The clusters are introduced using either of two Ce complexes (precursors): Ce^IV(tmhd)₄ (tmhd = 2,2,6,6-tetramethyl-3,5-heptanedionate) or Ce^III(iPrCp)₃ (iPrCp = tris(isopropyl-cyclopenta-dienyl), via SIM (solvothermal installation in MOFs). The prepared materials are named Ce-l-SIM-NU-1000 and Ce-n-SIM-NU-1000, respectively. X-ray photoelectron spectroscopy characterization shows that the ratio of Ce(III) to Ce(IV) oxidation states can be modulated. Difference envelope density analyses of X-ray scattering show that Ce_xO_yH_z clusters in Ce-n-SIM-NU-1000 are located between pairs of Zr₆ nodes, whereas in Ce-l-SIM-NU-1000, they are sited on MOF linkers throughout the micropores of NU-1000. Cluster size differences were further evaluated by pair function distribution (PDF) analyses of total X-ray scattering reveal that the node sited clusters contain of only a few cerium ions, whereas the linker-sited clusters each contain ∼90 cerium ions. The observed size appears to be defined by the size of NU-1000s triangular pores, that is, cluster formation appears to be pore templated. The Ce-SIM functionalized materials are catalytically active for hydrolysis of DMNP (dimethyl 4-nitrophenyl phosphate), a nerve-agent simulant. Conversion of a small fraction of the Ce(IV) ions in which the presence of small fractions of the cerium(IV) ions in Ce-l-SIM-NU-1000 to cerium(III) significantly enhances catalytic activity-perhaps by labilizing aqua ligands and facilitating simulant binding to the clusters Lewis-basic metal ions. While not explored here, the larger clusters, when partially reduced, are, we believe, candidate catalysts for O₂ activation and subsequent selective oxidation of organic substrates.

Chaperone-like chiral cages for catalyzing enantio-selective supramolecular polymerization

Chiral organic cages can assist enantio-selective supramolecular polymerization through a catalyzed assembly (catassembly) strategy, like chaperones assist the assembly of biomolecules.

Cage catalysis has emerged as an important approach for mimicking enzymatic reactions by increasing the reaction rate and/or product selectivity of various types of covalent reactions. Here, we extend the catalytic application of cage compounds to the field of non-covalent molecular assembly. Acid-stable chiral imine cages are found to catalyze the supramolecular polymerization of porphyrins with an accelerated assembling rate and increased product enantioselectivity. Because the imine cages have a stronger interaction with porphyrin monomers and a weaker interaction with porphyrin assemblies, they can fully automatically detach from the assembled products without being consumed during the catalytic process. We reveal the kinetics of the auto-detachment of cages and the chirality growth of the assemblies using spectroscopic characterization studies. We find that the passivation groups attached to the cages are important for maintaining the structural stability of the cages during catalyzed assembly, and that the steric geometries of the cages can profoundly affect the efficiency of chiral regulation. This strategy demonstrates a new type of catalytic application of cage compounds in the field of molecular assembly, and paves the way to controlling supramolecular polymerization through a catalytic pathway.

Reversible Structural Transformations of Metal-Organic Frameworks as Artificial Switchable Catalysts for Dynamic Control of Selectively Cyanation Reaction

The synthesis of molecular-level artificial switchable catalysts, of which activity in different chemical processes can be switched by controlling different stimuli, has provided a new paradigm to perform mechanical tasks and measurable work. In this work, to obtain highly effective and regioselective artificial switchable catalysts, a hierarchical anion-pillared framework {(H₃ O)[Cu(CPCDC)(4,4'-bpy)]}_n (1; H₃ CPCDC=9-(4-carboxyphenyl)-9H-carbazole-3,6-dicarboxylic acid, 4,4'-bpy=4,4'-bipyridine), including free [H₃ O]⁺ ions as guest molecules, was constructed. Upon dissolve-exchange-crystallization behavior, fascinating reversible structural transformations proceeded between anion framework 1 and neutral 2D stair-stepping framework {[Cu(CPCDC)(4,4'-bpe)]}_n (2; 4,4'-bpe=4,4'-vinylenedipyridine). Moreover, frameworks 1 and 2 can act as heterogeneous artificial switchable catalysts to selectively promote the direct cyanation reaction of terminal alkynes and azobisisobutyronitrile. The results indicated that 1 and 2 exhibited excellent selectivity to generate vinyl isobutyronitrile skeletons or propiolonitrile frameworks, respectively, as unique products. Furthermore, indicating paper, GC-MS, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy analysis demonstrated that the reversible structural transformations endowed 1 and 2 with well-defined platforms to stabilize the isobutyronitrile and CN sources through the different catalytic pathways.

Group 11 tris(pyrazolyl)methane complexes: structural features and catalytic applications

Tris(pyrazolyl)methane ligands (Tpm^x) have been for years a step behind their highly popular boron-anionic analogues, the tris(pyrazolyl)borate ligands (Tp^x).

Janus triple tripods build up a microporous manifold for HgCl2 and I2 uptake

Three tripods for a versatile molecular scaffold: combining the Janus core for supramolecular recognition and the planar carboxyl tripod for framework construction enables metal uptake and iodine removal applications.