Biomimetic Chiral Nanomaterials with Selective Catalysis Activity

Chiral nanomaterials with unique chiral configurations and biocompatible ligands have been booming over the past decade for their interesting chiroptical effect, unique catalytical activity, and related bioapplications. The catalytic activity and selectivity of chiral nanomaterials have emerged as important topics, that can be potentially controlled and optimized by the rational biochemical design of nanomaterials. In this review, chiral nanomaterials synthesis, composition, and catalytic performances of different biohybrid chiral nanomaterials are discussed. The construction of chiral nanomaterials with multiscale chiral geometries along with the underlying principles for enhancing chiroptical responses are highlighted. Various biochemical approaches to regulate the selectivity and catalytic activity of chiral nanomaterials for biocatalysis are also summarized. Furthermore, attention is paid to specific chiral ligands, materials compositions, structure characteristics, and so on for introducing selective catalytic activities of representative chiral nanomaterials, with emphasis on substrates including small molecules, biological macromolecule, and in-site catalysis in living systems. Promising progress has also been emphasized in chiral nanomaterials featuring structural versatility and improved chiral responses that gave rise to unprecedented chances to utilize light for biocatalytic applications. In summary, the challenges, future trends, and prospects associated with chiral nanomaterials for catalysis are comprehensively proposed.

Design and Advanced Manufacturing of NU-1000 Metal-Organic Frameworks with Future Perspectives for Environmental and Renewable Energy Applications

Metal-organic frameworks (MOFs) represent a relatively new family of materials that attract lots of attention thanks to their unique features such as hierarchical porosity, active metal centers, versatility of linkers/metal nodes, and large surface area. Among the extended list of MOFs, Zr-based-MOFs demonstrate comparably superior chemical and thermal stabilities, making them ideal candidates for energy and environmental applications. As a Zr-MOF, NU-1000 is first synthesized at Northwestern University. A comprehensive review of various approaches to the synthesis of NU-1000 MOFs for obtaining unique surface properties (e.g., diverse surface morphologies, large surface area, and particular pore size distribution) and their applications in the catalysis (electro-, and photo-catalysis), CO2 reduction, batteries, hydrogen storage, gas storage/separation, and other environmental fields are presented. The review further outlines the current challenges in the development of NU-1000 MOFs and their derivatives in practical applications, revealing areas for future investigation.

Repair of missing linker defects in UiO-66 by a "molecular patch" boosting the 1-hexene hydroformylation reaction

Fabrication of MOFs with missing linker defects has become a common means to improve catalytic performances. However, the stability of the defects deserves to be investigated first. In this work, we found that 3-phenylpropionaldehyde (3-PPA) could coordinate with the missing linker defects of UiO-66, which highlighted the instability of the missing linker defects. 3-PPA acted as a molecular patch for the modification of the Rh/UiO-66 catalyst, which repaired the open Zr₆ sites and resulted in a remarkable improvement of aldehyde selectivity (from 50.0% to 89.6%) in 1-hexene hydroformylation.

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.

Recent progress in the design, synthesis and applications of chiral metal-organic frameworks

Chiral Metal-Organic Frameworks (CMOFs) are unique crystalline and porous class of materials which is composed of organic linkers and metal ions. CMOFs surpass traditional organic and inorganic porous materials because of their tunable shape, size, functional diversity, and selectivity. Specific applications of CMOFs may be exploited by introducing desired functional groups. CMOFs have chiral recognition abilities, making them unique for chiral compound synthesis and separation. The CMOFs can be synthesized through different approaches. Two main approaches have been discussed, i.e., direct and indirect synthesis. Synthetic strategies play an essential role in getting desired properties in MOFs. CMOFs find potential applications in adsorption, asymmetric catalysis, luminescence, degradation, and enantioselective separation. The MOFs’ porosity, stability, and reusability make them an attractive material for these applications. The plethora of applications of CMOFs have motivated chemists to synthesize novel MOFs and number of MOFs have been ever-escalating. Herein, the synthetic methods of CMOFs and their various applications have been discussed.

Lanthanum-1,2,3-Triazole-Based 2D Coordination Polymer is an Efficient Catalyst for the Oxidation of Olefins

A new two-dimensional (2D) coordination polymer (CP) [La(C₁₈H₁₄N₃O₆)₂(H₂O)(OH)]_n has been prepared from a 1,2,3-triazole linker and lanthanum nitrate hexahydrate in DMF. The La-CP was characterized by single-crystal X-ray crystallography, highlighting the binding motif at La ions and the fact that the material contains channels with entrapped solvent. The CP showed good catalytic activity for the oxidation of a wide variety of olefins (linear, cyclic, aromatic, and functionalized alkenes) to aldehydes. Mechanistic studies show that the oxidation reaction proceeds via a non-free-radical mechanism. The catalyst could be recovered and reused five times without major changes in activity for the oxidation of styrene to benzaldehyde.

Chiral Metal-Organic Frameworks

In the past two decades, metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) assembled from metal ions or clusters and organic linkers via metal-ligand coordination bonds have captivated significant scientific interest on account of their high crystallinity, exceptional porosity, and tunable pore size, high modularity, and diverse functionality. The opportunity to achieve functional porous materials by design with promising properties, unattainable for solid-state materials in general, distinguishes MOFs from other classes of materials, in particular, traditional porous materials such as activated carbon, silica, and zeolites, thereby leading to complementary properties. Scientists have conducted intense research in the production of chiral MOF (CMOF) materials for specific applications including but not limited to chiral recognition, separation, and catalysis since the discovery of the first functional CMOF (i.e., d- or l-POST-1). At present, CMOFs have become interdisciplinary between chirality chemistry, coordination chemistry, and material chemistry, which involve in many subjects including chemistry, physics, optics, medicine, pharmacology, biology, crystal engineering, environmental science, etc. In this review, we will systematically summarize the recent progress of CMOFs regarding design strategies, synthetic approaches, and cutting-edge applications. In particular, we will highlight the successful implementation of CMOFs in asymmetric catalysis, enantioselective separation, enantioselective recognition, and sensing. We envision that this review will provide readers a good understanding of CMOF chemistry and, more importantly, facilitate research endeavors for the rational design of multifunctional CMOFs and their industrial implementation.

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.

Metal Organic Frameworks as Heterogeneous Catalysts in Olefin Epoxidation and Carbon Dioxide Cycloaddition

Metal–organic frameworks (MOFs) are a family of porous crystalline materials that serve in some cases as versatile platforms for catalysis. In this review, we overview the recent developments about the use of these species as heterogeneous catalysts in olefin epoxidation and carbon dioxide cycloaddition. We report the most important results obtained in this field relating them to the presence of specific organic linkers, metal nodes or clusters and mixed-metal species. Recent advances obtained with MOF nanocomposites were also described. Finally we compare the results and summarize the major insights in specific Tables, outlining the major challenges for this emerging field. This work could promote new research aimed at producing coordination polymers and MOFs able to catalyse a broader range of CO2 consuming reactions.

Chirality Remote Control in Nanoporous Materials by Circularly Polarized Light

The ability to dynamically control chirality remains a grand challenge in chemistry. Although many molecules possess chiral isomers, lacking their isolation, for instance during photoisomerization, results in racemic mixtures with suppressed enantiospecific chiral properties. Here, we present a nanoporous solid in which chirality and enantioselective enrichment is induced by circularly polarized light (CPL). The material is based on photoswitchable fluorinated azobenzenes attached to the scaffold of a crystalline metal-organic framework (MOF). The azobenzene undergoes trans-to-cis-photoisomerization upon irradiation with green light and reverts back to trans upon violet light. While each moiety in cis conformation is chiral, we show the trans isomer also possesses a nonplanar, chiral conformation. During photoisomerization with unpolarized light, no enantiomeric enrichment is observed and both isomers, R- and S-cis as well as R- and S-trans, respectively, are formed in identical quantities. In contrast, CPL causes chiral photoresolution, resulting in an optically active material. Right-CPL selectively excites R-cis and R-trans enantiomers, producing a MOF with enriched S-enantiomers, and vice versa. The induction of optical activity is reversible and only depends on the light-handedness. As shown by first-principle DFT calculations, while both, trans and cis, are stabilized in nonplanar, chiral conformations in the MOF, the trans isomer adopts a planar, achiral form in solution, as verified experimentally. This shows that the chiral photoresolution is enabled by the linker reticulation in the MOF. Our study demonstrates the induction of chirality and optical activity in solid materials by CPL and opens new opportunities for chiral resolution and information storage with CPL.

High performance of ultrasonic-assisted synthesis of two spherical polymers for enantioselective catalysis

Chiral polymers have aroused great attention in among chiral supramolecular materials based on their features. Herein, for the first time, the synthesis of chiral polymeric composites (CMNPs/1,4-Zbtb & 1,3-Zbtb) have been reported with entrapment through three strategies: ultrasonic irradiation, solvothermal, and mechanical stirring. According to the obtained results, it is found that ultrasound-assisted synthesis can be considered as an inexpensive and efficient method than the others, from the point ofviewof energy and time consuming. In this strategy, encapsulation of chiral magnetic nanoparticles (CMNPs) by using tetrazole-based polymers (Zbtbs) happens, in-situly. These chiral sphere-like inorganic-organic polymers can be considered as core and shell composites with catalytic activity due to their acidic (semi unsaturated Zn: open metal sites) and basic (abundant basic nitrogens) centers. In these structures, the unprecedented chirality induction can happen from the core to shell by non-covalent interaction, easily. They could catalyze symmetric oxidation and asymmetric henry condensation to give chiral β-nitroalkanol. Circular dichroism and chiral gas chromatography were used to characterize the produced enantiomers. These chiral polymeric materials can be considered as unique acid-base bifunctional catalysts with efficient properties such as high stability, enantiomeric excess, enantioselectivity to the main product, and protecting from CMNPs leaching.

Anion and solvent controlled growth of crystalline and amorphous zinc(ii) coordination polymers and a molecular complex

Controlled bottom-up synthesis of amorphous coordination polymers with tailored metal coordination is a research field in its infancy. In this study, synthesis control was achieved to selectively prepare one-dimensional (1D) crystalline and amorphous zinc(ii)-based coordination polymers and a dimeric molecular compound, all with similar coordination geometry as evidenced by X-ray diffraction and total scattering studies. The compounds were obtained by bottom up self-assembly of Zn(ii) with terephthalate (tph^2-) as linker and the enantiopure chelating ligand S-(1,2)-bis(1H-benzimidazol-2-yl)ethanol (L). The solvent and the coordination ability of the precursor zinc salt anion control the crystalline products formed by slow diffusion at room temperature: perchlorate allows isolation of the phase pure crystalline 1D polymer {[Zn(tph)(L)]·H₂O·3DMF}_n (1·H₂O·3DMF, DMF = N,N-dimethylformamide). In contrast, zinc chloride leads to the formation of either a mixture of polymeric 1·H₂O·3DMF and a dimeric molecular species [Zn₂Cl₂(tph)(L)₂]·4DMF (2·4DMF), or to the phase pure dimer 2·4DMF, depending on the Zn(ii) : tphH₂ stoichiometry. A modified synthesis using zinc nitrate and fast precipitation by base addition results in an amorphous analogue of the 1D polymer (3). Chains of 1·H₂O·3DMF pack into a non-porous crystalline material with a surface area of just 6 m² g^-1, while the outer surface area of amorphous polymer 3 is a factor of eight larger. Hence, the amorphous compound provides larger metal site accessibility for potential surface chemical reactions, while maintaining the coordination geometry of the metal sites. The temperature response of crystalline polymer 1·H₂O·3DMF was studied using multi-temperature single crystal X-ray diffraction (100-300 K). The a = b axes display normal positive thermal expansion, while the c axis remains constant with increasing temperature due to partial relaxation of the terephthalate linkers and slightly changed geometry within the individual polymer chains.

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.

Construction of an Asymmetric Porphyrinic Zirconium Metal-Organic Framework through Ionic Postchiral Modification

Herein, one kind of neutral chiral zirconium metal-organic framework (Zr-MOF) was reported from the porphyrinic MOF (PMOF) family with a metallolinker (Mn^III-porphyrin) as the achiral polytopic linker [free base tetrakis(4-carboxyphenyl)porphyrin] and chiral anions. Achiral Zr-MOF was chiralized through the exchange of primitive anions with new chiral organic anions (postsynthetic exchange). This chiral functional porphyrinic MOF (CPMOF) was characterized by several techniques such as powder X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, ¹H NMR, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and Brunauer-Emmett-Teller measurements. In the resulting structure, there are two active metal sites as Lewis acid centers (Zr and Mn) and chiral species as Brønsted acid sites along with their cooperation as nucleophiles. This CPMOF shows considerable bimodal porosity with high surface area and stability. Additionally, its ability was investigated in asymmetric catalyses of prochiral substrates. Interactions between framework chiral species and prochiral substrates have large impacts on the catalytic ability and chirality induction. This chiral catalyst proceeded asymmetric epoxidation and CO₂ fixation reactions at lower pressure with high enantioselectivity due to Lewis acids and chiral auxiliary nucleophiles without significant loss of activity up to the sixth step of consecutive cycles of reusability. Observations revealed that chiralization of Zr-MOF could happen by a succinct strategy that can be a convenient method to design chiral MOFs.

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.

A Highly Efficient Heterogeneous Catalyst of Bimetal-Organic Frameworks for the Epoxidation of Olefin with H2O2

A series of bimetel organic framework Mn_xCu_1-x-MOF were prepared. The MOFs was characterized and analyzed by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The catalytic activity of the developed catalyst was tested on various olefins by H₂O₂ as oxidant. The MOFs catalyst exhibits excellent catalytic activity for the epoxidations of various aromatic and cyclic olefins. Particularly, Mn_0.1Cu_0.9-MOF can achieve 90.2% conversion of styrene with 94.3% selectivity of styrene oxide at 0 °C after reaction 6 h. The MOF exhibited the catalytic activity of inverse temperature effect on epoxidation of styrene. The introduction of copper component can stabilize H₂O₂ and inhibit its decomposition to a certain extent. The catalyst can be reused at least five cycles without significant loss in activity towards epoxidation.

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.

Hybrid nanomaterials for asymmetric purposes: green enantioselective C–C bond formation by chiralization and multi-functionalization approaches

We present a simple and novel strategy for synthesis of a MOF-based chiral multi-functional hybrid nanomaterial through chiralization and multi-functionalization approaches for asymmetric purposes.

Melting point–solubility–structure correlations in chiral and racemic model cocrystals

Comparison of chiral and racemic binary cocrystals showed that the chiral building block limits the formation of certain intermolecular interactions, decreases the packing efficiency, lowers the melting point and increases aqueous solubility.