A Porous Metal-Organic Framework Assembled by [Cu30] Nanocages: Serving as Recyclable Catalysts for CO2 Fixation with Aziridines

Effective Reduction of CO2 with Aromatic Amines into N-Formamides Triggered by Noble-Free Metal-Organic Framework Catalysts Under Mild Conditions

The reductive transformation of carbon dioxide (CO2) into high-valued N‑formamides matches well with the atom economy and the sustainable development intention. Nevertheless, developing a noble-free metal catalyst under mild reaction conditions is desirable and challenging. Herein, a caged metal-organic framework (MOFs) [H2N(CH3)2]2{[Ni3(µ3-O)(XN)(BDC)3]·6DMF}n (1) (XN = 6″-(pyridin-4-yl)-4,2″:4″,4″'-terpyridine), H2BDC = terephthalic acid) is harvested, presenting high thermal and chemical stabilities. Catalytic investigation reveals that 1 as a renewable noble-free MOFs catalyst can catalyze the CO2 reduction conversion with aromatic amines tolerated by broad functional groups at least ten times, resulting in various formamides in excellent yields and selectivity under the mildest reaction system (room temperature and 1 bar CO2). Density functional theory (DFT) theoretical studies disclose the applicable reaction path, in which the CO2 hydrosilylation process is initiated by the [Ni3] cluster interaction with CO2 via η2-C, O coordination mode. This work may open up an avenue to seek high-efficiency noble-free catalysts in CO2 chemical reduction into high value-added chemicals.

Metal Hydrogen-Bonded Organic Frameworks as Open Lewis Acid Catalysts for Two Types of CO2 Transformations

Efficient and multiple CO2 utilization into high-value-added chemicals holds significant importance in carbon neutrality and industry production. However, most catalysis systems generally exhibit only one type of CO2 transformation with the efficiency to be improved. The restricted abundance of active catalytic sites or an inefficient utilization rate of these sites results in the constraint. Consequently, we designed and constructed two metal hydrogen-bonded organic frameworks (M-HOFs) {[M3(L3-)2(H2O)10]·2H2O}n (M = Co (1), Ni (2); L = 1-(4-carboxyphenyl)-1H-pyrazole-3,5-dicarboxylic acid) in this research. 1 and 2 are well-characterized, and both show excellent stability. The networks connected by multiple hydrogen bonds enhance the structural flexibility and create accessible Lewis acidic sites, promoting interactions between the substrates and catalytic centers. This enhancement facilitates efficient catalysis for two types of CO2 transformations, encompassing both cycloaddition reactions with epoxides and aziridines to afford cyclic carbonates and oxazolidinones. The catalytic activities (TON/TOF) are superior compared with those of most other catalysts. These heterogeneous catalysts still exhibited high performance after being reused several times. Mechanistic studies indicated intense interactions between the metal sites and substrates, demonstrating the reason for efficient catalysis. This marks the first instance on M-HOFs efficiently catalyzing two types of CO2 conversions, finding important significance for catalyst design and CO2 utilization.

Highly Stable 72-Nuclearity Nanocages for Efficient Synthesis of Aryl Nitriles via Ni/Cu Synergistic Catalysis

Seeking noble-metal-free catalysts for efficient synthesis of aryl nitriles under mild conditions poses a significant challenge due to the use of hypertoxic cyanides or high-pressure/temperature NH3/O2 in conventional synthesis processes. Herein, we developed a novel framework 1 assembled by [Ni72] nanocages with excellent solvents/pH stability. To investigate the structure-activity relationship of catalytic performance, several isostructural MOFs with different molar ratios of Ni/Cu by doping Cu2+ into framework 1 (Ni0.59Cu0.41 (2), Ni0.81Cu0.19 (3), Ni0.88Cu0.12 (4), and Ni0.92Cu0.08 (5)) were prepared. Catalytic studies revealed that catalyst 3 exhibited remarkable performance in the synthesis of aryl nitriles, utilizing a formamide alternative to hypertoxic NaCN/KCN. Notably, catalyst 3 achieved an excellent TOF value of 9.8 h-1. Furthermore, catalyst 3 demonstrated its applicability in a gram-scale experiment and maintained its catalytic performance even after six recycling cycles, owing to its high stability resulting from significant electrostatic and orbital interactions between the Ni center and ligands as well as a large SOMO-LUMO energy gap supported by DFT calculations. Control experiments and DFT calculations further revealed that the excellent catalytic performance of catalyst 3 originated from the synergistic effect of Ni/Cu. Importantly, this work not only provides a highly feasible method to construct highly stable MOFs containing multinuclear nanocages with exceptional catalytic performance but also represents the first example of a heterogeneous catalyst for the synthesis of aryl nitriles using formamide as the cyanide source.

Reticular Synthesis of Flexible Rare-Earth Metal-Organic Frameworks: Control of Structural Dynamics and Sorption Properties Through Ligand Functionalization

An exciting direction in metal-organic frameworks involves the design and synthesis of flexible structures which can reversibly adapt their structure when triggered by external stimuli. Controlling the extent and nature of response in such solids is critical in order to develop custom dynamic materials for advanced applications. Towards this, it is highly important to expand the diversity of existing flexible MOFs, generating novel materials and gain an in-depth understanding of the associated dynamic phenomena, eventually unlocking key structure-property relationships. In the present work, we successfully utilized reticular chemistry for the construction of two novel series of highly crystalline, flexible rare-earth MOFs, RE-thc-MOF-2 and RE-teb-MOF-1. Extensive single-crystal to single-crystal structural analyses coupled with detailed gas and vapor sorption studies, shed light onto the unique responsive behavior. The development of these series is related to the reported RE-thc-MOF-1 solids which were found to display a unique continuous breathing and gas-trapping property. The synthesis of RE-thc-MOF-2 and RE-teb-MOF-1 materials represents an important milestone as they provide important insights into the key factors that control the responsive properties of this fascinating family of flexible materials and demonstrates that it is possible to control their dynamic behavior and the associated gas and vapor sorption properties.

Hierarchical 2D honeycomb-like network from barium-seamed nanocapsules

We report on a two-dimensional hexagonal "honeycomb" network comprising barium-seamed metal-organic nanocapsules involving a hexameric assembly of pyrogallol[4]arene ligands. The incorporated barium ions act as spacers to generate a solvent-accessible void, hierarchical self-assembly having an individual void volume near 13 000 Å3. This work illustrates the surprising chemistry that remains to be discovered by integrating large or classically non-reactive metal ions within supramolecular assemblies, networks, and organic nanocapsules.

CO2 Cycloaddition under Ambient Conditions over Cu-Fe Bimetallic Metal-Organic Frameworks

Carbon dioxide cycloaddition into fine chemicals is prospective technology to solve energy crisis and environmental issues. However, high temperature and pressure are usually required in the conventional cycloaddition reactions of CO2 with epoxides. Moreover, metal active sites play a vital role in the CO2 cycloaddition, but it is still unclear. Herein, we select the isostructural MOF-919-Cu-Fe and MOF-919-Cu-Al as models to promote the performance and clarify the effects of metal type on the CO2 cycloaddition. The MOF-919-Cu-Fe with exposed Fe and Cu Lewis acid sites reaches the CO2 cycloaddition with over 99.9% conversion and over 99.9% selectivity at room temperature and a 1 bar CO2 atmosphere, 3.0- and 52.6-fold higher than those of the MOF-919-Cu-Al with Al and Cu sites (33.8%) and the 1H-pyrazole-4-carboxylic acid, Fe, and Cu mixed system (1.9%), respectively. The proposed mechanism demonstrated that the exposed Fe3+ sites facilitate the ring opening of epoxide and CO2 activation to boost the CO2 cycloaddition reaction. This work provides a new insight to tune the catalytic sites of MOFs to achieve high performance for CO2 fixation.

Thermocatalytic Conversion of CO2 to Valuable Products Activated by Noble-Metal-Free Metal-Organic Frameworks

Thermocatalysis of CO2 into high valuable products is an efficient and green method for mitigating global warming and other environmental problems, of which Noble-metal-free metal-organic frameworks (MOFs) are one of the most promising heterogeneous catalysts for CO2 thermocatalysis, and many excellent researches have been published. Hence, this review focuses on the valuable products obtained from various CO2 conversion reactions catalyzed by noble-metal-free MOFs, such as cyclic carbonates, oxazolidinones, carboxylic acids, N-phenylformamide, methanol, ethanol, and methane. We classified these published references according to the types of products, and analyzed the methods for improving the catalytic efficiency of MOFs in CO2 reaction. The advantages of using noble-metal-free MOF catalysts for CO2 conversion were also discussed along the text. This review concludes with future perspectives on the challenges to be addressed and potential research directions. We believe that this review will be helpful to readers and attract more scientists to join the topic of CO2 conversion.

Incorporating Catalytic Units into Nanomaterials: Rational Design of Multipurpose Catalysts for CO2 Valorization

ConspectusCO2 conversion to valuable chemicals is effective at reducing CO2 emissions. We previously proposed valorization strategies and developed efficient catalysts to address thermodynamic stability and kinetic inertness issues related to CO2 conversion. Earlier, we developed molecular capture reagents and catalysts to integrate CO2 capture and conversion, i.e., in situ transformation. Based on the mechanistic understanding of CO2 capture, activation, and transformation at a molecular level, we set out to develop heterogeneous catalysts by incorporating catalytic units into nanomaterials via the immobilization of active molecular catalysts onto nanomaterials and designing nanomaterials with intrinsic catalytic sites.In thermocatalytic CO2 conversion, carbonaceous and metal-organic framework (MOF)-based catalysts were developed for nonreductive and reductive CO2 conversion. Novel Cu- and Zn-based MOFs and carbon-supported Cu catalysts were prepared and successfully applied to the cycloaddition, carboxylation, and carboxylative cyclization reactions with CO2, generating cyclic carbonates, carboxyl acids, and oxazolidinones as respective target products. Reductive conversion of CO2, especially reductive functionalization with CO2, is a promising transformation strategy to produce valuable chemicals, alleviating chemical production that relies on petrochemistry. We explored the hierarchical reductive functionalization of CO2 using organocatalysts and proposed strategies to regulate the CO2 reduction level, triggering heterogeneous catalyst investigation. Introducing multiple active sites into nanomaterials opens possibilities to develop novel CO2 transformation strategies. CO2 capture and in situ conversion were realized with an N-doped carbon-supported Zn complex and MOF materials as CO2 adsorbents and catalysts. These nanomaterial-based catalysts feature high stability and excellent efficiency and act as shape-selective catalysts in some cases due to their unique pore structure.Nanomaterial-based catalysts are also appealing candidates for photocatalytic CO2 reduction (PCO2RR) and electrocatalytic CO2 reduction (ECO2RR), so we developed a series of hybrid photo-/electrocatalysts by incorporating active metal complexes into different matrixes such as porous organic polymers (POPs), metal-organic layers (MOLs), micelles, and conducting polymers. By introducing Re-bipyridine and Fe-porphyrin complexes into POPs and regulating the structure of the polymer chain, catalyst stability and efficiency increased in PCO2RR. PCO2RR in aqueous solution was realized by designing the Re-bipyridine-containing amphiphilic polymer to form micelles in aqueous solution and act as nanoreactors. We prepared MOLs with two different metallic centers, i.e., the Ni-bipyridine site and Ni-O node, to improve the efficiency for PCO2RR due to the synergistic effect of these metal centers. Sulfylphenoxy-decorated cobalt phthalocyanine (CoPc) cross-linked polypyrrole was prepared and used as a cathode, achieving the electrocatalytic transformation of diluted CO2 benefiting from the CO2 adsorption capability of polypyrrole. We fabricated immobilized 4-(t-butyl)-phenoxy cobalt phthalocyanine and Bi-MOF as cathodes to promote the paired electrolysis of CO2 and 5-hydroxymethylfurfural (HMF) and obtained CO2 reductive products and 2,5-furandicarboxylic acid (FDCA) efficiently.

Two novel Ln8 clusters bridged by CO32- effectively convert CO2 into oxazolidinones and cyclic carbonates

It is difficult and challenging to design and construct high-nuclearity Ln(III)-based clusters due to the high coordination numbers and versatile coordination geometries of Ln(III) ions. Herein, two novel octanuclear Ln(III)-based clusters [Ln₈(H₂L^-)₄(HL^2-)₄(NO₃)₆ (CO₃)₂](NO₃)₂·2CH₃CN (Ln = Nd (1) and Sm (2)) have been synthesized under solvothermal conditions. The X-ray single analysis reveals that both 1 and 2 are octanuclear structures and the eight central Ln(III) ions are bridged by two CO₃^2- anions. Catalytic study revealed that 1 and 2 can effectively catalyze the cycloaddition reaction of CO₂ and aziridines or epoxides simultaneously under mild conditions. What is more, cluster 1, as a heterogeneous catalyst, can be reused at least three times without obvious loss in catalytic activity for coupling of CO₂ and epoxides. To our knowledge, cluster 1 is the first Ln(III)-based cluster catalyst used for the conversion of CO₂ with aziridines or epoxides simultaneously. This work provides a successful strategy to integrate high-nuclear Ln(III)-based clusters for CO₂ conversion, which may open a new space for the construction of multifunctional high-nuclear Ln(III)-based clusters as efficient catalysts for CO₂ conversion.

Direct Conversion of CO2 in Lime Kiln Waste Gas Catalyzed by a Copper-Based N-heterocyclic Carbene Porous Polymer

Industrial waste gas is one of the major sources of atmospheric CO₂ , yet the direct conversion of the low concentrations of CO₂ in waste gases into high value-added chemicals have been a great challenge. Herein, a copper-based N-heterocyclic carbene porous polymer catalyst (Cu@NHC-1) for the direct conversion of low concentration CO₂ into oxazolidinones was successfully fabricated via a facile copolymerization process followed by the complexation with Cu(OAc)₂ . A continuous flow device was designed to deliver a continuous and stable carbon source for the reaction. Due to the triple synergistic effect of its porous structure, nitrogen activation sites and catalytic Cu center, Cu@NHC-1 shows highly efficient and selective adsorption, activation, and conversion of the low concentration CO₂ (30 vol%). Its practical application potential is demonstrated by the ability to successfully convert the CO₂ in lime kiln waste gas into oxazolidinones in satisfactory yields under mild conditions.

Highly Efficient Conversion of Aziridines and CO2 Catalyzed by Microporous [Cu12] Nanocages

The conversion of CO₂ as a C1 source into value-added products is an attractive alternative in view of the green synthesis. Among the reported approaches, the cyclization reaction of aziridines with CO₂ is of great significance since the generated N-containing cyclic skeletons are extensively found in pharmaceutical chemistry and industrial production. However, a low turnover number (TON) and homogeneous catalysts are often involved in this catalytic system. Herein, one novel copper-organic framework {[Cu₂(L^4-)(H₂O)₂]·3DMF·2H₂O}_n (1) (H₄L = 2'-fluoro-[1,1':4',1″-Terphenyl]-3,3″,5,5″-tetracarboxylic acid) assembled by nanosized [Cu₁₂] cages was successfully synthesized and structurally characterized, which exhibits high CO₂/N₂ selectivity due to the strong interactions between CO₂ and open Cu(II) sites and ligands in the framework. Catalytic investigations suggest that 1 as a heterogeneous catalyst can effectively catalyze the cyclization of aziridines with CO₂, and the TON can reach a record value of 90.5. Importantly, 1 displays excellent chemical stability, which can be recycled at least five times. The combination explorations of nuclear magnetic resonance (NMR), ¹³C-isotope labeling experiments, and density functional theory (DFT) clearly uncover the mechanism of this aziridine/CO₂ coupling reaction system, in which 1 and tetrabutylammonium bromide (TBAB) can highly activate the substrate molecule, and the synergistic catalytic effect between them can greatly reduce the reaction energy barrier from 51.7 to 36.2 kcal/mol.

Highly Efficient Visible-Light-Driven CO2-to-CO Conversion by Coordinatively Unsaturated Co-Salen Complexes in a Water-Containing System

The development of cost-effective catalysts for CO₂ reduction is highly desired but remains a significant challenge. The unsaturated coordination metal center in a catalyst is favorable for the process of catalytic CO₂ reduction. In this paper, two asymmetric salen ligands were used to synthesize two coordinatively unsaturated Co-salen complexes. The two Co-salen complexes exhibit an unsaturated coordination pattern and display high activity and CO selectivity for visible-light-driven CO₂ reduction in a water-containing system. The photocatalytic performance of 2 is higher than that of 1 because the reduction potential of the catalytic Co^II center and the energy barrier of the catalytic transition states of 2 are lower than those of 1, with turnover numbers (TON_CO), turnover frequencies (TOF), and CO selectivity values of 8640, 0.24 s^-1, and 97% for 2, respectively. The photocatalytic reduction of CO₂ to CO for 2 is well supported by control experiments and density functional theory (DFT) calculations.

Advancements and Challenges in Reductive Conversion of Carbon Dioxide via Thermo-/Photocatalysis

Carbon dioxide (CO₂) is the major greenhouse gas and also an abundant and renewable carbon resource. Therefore, its chemical conversion and utilization are of great attraction for sustainable development. Especially, reductive conversion of CO₂ with energy input has become a current hotspot due to its ability to access fuels and various important chemicals. Nowadays, the controllable CO₂ hydrogenation to formic acid and alcohols using sustainable H₂ resources has been regarded as an appealing solution to hydrogen storage and CO₂ accumulation. In addition, photocatalytic CO₂ reduction to CO also provides a potential way to utilize this greenhouse gas efficiently. Besides direct CO₂ hydrogenation, CO₂ reductive functionalization integrates CO₂ reduction with subsequent C-X (X = N, S, C, O) bond formation and indirect transformation strategies, enlarging the diverse products derived from CO₂ and promoting CO₂ reductive conversion into a new stage. In this Perspective, the progress and challenges of CO₂ reductive conversion, including hydrogenation, reductive functionalization, photocatalytic reduction, and photocatalytic reductive functionalization are summarized and discussed along with the key issues and future trends/directions in this field. We hope this Perspective can evoke intense interest and inspire much innovation in the promise of CO₂ valorization.

Metal phosphonates as heterogeneous catalysts for highly efficient chemical fixation of CO2 under mild conditions

Two new compounds with novel structures were prepared, one of which displays excellent catalytic activity to transform CO2 gas to cyclic carbonates under mild conditions and free of solvent.

Efficient Cycloaddition of CO2 and Aziridines Activated by a Quadruple-Interpenetrated Indium-Organic Framework as a Recyclable Catalyst

On the basis of the global warming effect, it is of great significance to convert CO₂ into the high value-added products oxazolidinones, but investigations on main-group-based metal-organic frameworks (MOFs) as heterogeneous catalysts still have not been reported so far. In this work, a quadruple-interpenetrated porous indium-based MOF, {[NH₂(CH₃)₂][In(CPT)₂]·3CH₃CN·3DMA}_n (1), is constructed from the organic ligand 3,5-bis(4'-carboxyphenyl)-1,2,4-triazole through solvothermal reactions, and N₂ adsorption proves that the framework has a high Brunauer-Emmett-Teller surface areas with 2024 m²/g. The catalytic research on CO₂ conversion reveals that compound 1 has high reactivity for the cycloaddition of CO₂ with aziridines, and the product 3-ethyl-5-phenyloxazolidin-2-one can be obtained with a yield of 99% under mild conditions. In addition, 1 exhibits excellent activity for different kinds of substrates and can be reused at least five cycles without any significant deactivation, suggesting that 1 is a potential candidate for the chemical conversion of CO₂ and aziridines. Mechanistic explorations indicate that the high efficiency of 1 is attributed to the indium center in the framework as a Lewis acid site, and the large porosity can enrich substrates. Importantly, 1 behaved as the first main-group MOF-based catalyst in the reported coupling reaction of CO₂ with aziridines.

An uncommon multicentered ZnI-ZnI bond-based MOF for CO2 fixation with aziridines/epoxides

A novel cluster-based MOF with uncommon multicentered Zn^I-Zn^I bonds {[K_1.2Na_2.8Zn^I₈(HL)₁₂]·4H₂O}_n (HL = tetrazole monoanion) (1) was synthesized, which showed higher stability than the reported Zn^I-Zn^I bonded compounds. Moreover, 1 can effectively and circularly catalyze the cyclization of CO₂ and aziridines or epoxides with five substituent groups. Importantly, this is the first time that the catalytic properties of MOFs with multicentered metal-metal bonded clusters as the catalyst have been studied.

Green Conversion of CO2 and Propargylamines Triggered by Triply Synergistic Catalytic Effects in Metal-Organic Frameworks

Cyclization of propargylamines with CO₂ to obtain 2-oxazolidone heterocyclic compounds is an essential reaction in industry but it is usually catalyzed by noble-metal catalysts with organic bases as co-catalysts under harsh conditions. We have synthesized a unique Cu^I /Cu^II mixed valence copper-based framework {[(Cu^I ₆ I₅ )Cu₃ ^II L₆ (DMA)₃ ](NO₃ )⋅9DMA}_n (1) with good solvent and thermal stability, as well as a high density of uncoordinated amino groups evenly distributed in the large nanoscopic channels. Catalytic experiments show that 1 can effectively catalyze the reaction of propargylamines with CO₂ , and the yield can reach 99 %. The turnover frequency (TOF) reaches a record value of 230 h^-1 , which is much higher than that of reported noble-metal catalysts. Importantly, this is the first report of heterogeneously catalyzed green conversion of propargylamines with CO₂ without solvents and co-catalysts under low temperature and atmospheric pressure. A mechanistic study reveals that a triply synergistic catalytic effect between Cu^I /Cu^II and uncoordinated amino groups promotes highly efficient and green conversion of CO₂ . Furthermore, 1 directly catalyzes this reaction with high efficiency when using simulated flue gas as a CO₂ source.

A more effective catalysis of the CO2 fixation with aziridines: computational screening of metal-substituted HKUST-1

A vital issue for the fixation and conversion of CO2 into useful chemical products is to find effective catalysts. In this work, in order to develop more effective and diverse catalysts, we implemented the first computational screening study (at M06-2X//B3LYP level) on the cycloaddition of CO2 with aziridines under eighteen metal-substituted HKUST-1 MOFs and tetrabutylammonium bromide (TBAB) as a co-catalyst. For all considered catalytic systems, the ring-opening of aziridine is calculated to be the rate-determining step. Up to 11 M-HKUST-1 systems, i.e., Rh (31.87 kcal mol-1), Y (31.02), Sc (30.50), V (30.02), Tc (29.90), Cd (29.80), Ti (29.32), Mn (29.05), Zn (28.29), Fe (27.85) and Zr (25.09), possess lower ring-opening barrier heights than the original Cu-HKUST-1 (32.90), indicative of their superior catalytic ability to the original Cu-HKUST-1 in theory. With the lowest ring-opening barrier, Zr-HKUST-1 is strongly advocated for future synthetic and catalytic studies.

Three Mn(ii) metal–organic frameworks with the same chemical composition, but different topological structures and properties

Solvothermal reactions of a novel multidentate ligand, 2,5-bis-(1,2,4-triazol-1-yl)-terephthalic acid (H₂TTPA), with MnCl₂ afforded three structurally distinct coordination polymers with the same formula, [Mn(TTPA)·H₂O]_n (Mn-(1–3)).

Solvent-controlled metal coordination polymers of Co(ii) with different topological structures and properties

Three multidimensional Co-polymers were obtained. Co-1 exhibits as a 2D layer. Co-2 displays as a tetranodal (4,4,5,6)-connected 3D MOFs. Co-3 is a binodal (4,6)-connected 3D framework.

Solvent-Dependent Assembly and Magnetic Relaxation Behaviors of [Cu4I3] Cluster-Based Lanthanide MOFs: Acting as Efficient Catalysts for Carbon Dioxide Conversion with Propargylic Alcohols

Two structurally similar metal-organic frameworks (MOFs) [Dy₂Cu₄I₃(IN)₇(DMF)₂]·DMF (1) and [Dy₂Cu₄I₃(IN)₇(DMA)₂]·DMA (2) (HIN = isonicotinic acid) feathering different coordinated solvent molecules were successfully isolated by tuning the types of solvents in the reaction system. Structural tests indicate that 1 and 2 are both built from 1D Dy(III) chains and copper iodide clusters [Cu₄I₃], generating into three-dimensional frameworks with an open 1D channel along the a axis. 1 and 2 display extensive and excellent solvent stability. Magnetic studies of 1 and 2 indicate that they exhibit interesting solvent-dependent magnetization dynamics. Importantly, 1 and 2 can act as highly effective catalysts for the carboxylic cyclization of propargyl alcohols with carbon dioxide (CO₂) under ambient operating conditions. Additionally, the substrate scope was further explored over compound 1 based on the optimal conditions, and it exhibits efficient cyclic carboxylation of various terminal propargylic alcohols with CO₂. This research offers an effective approach for the solvent-guided synthesis of MOFs materials and also presents the great application value of MOFs in CO₂ chemical conversion.

Secondary Sphere Effects on Porous Polymeric Organocatalysts for CO2 Transformations: Subtle Modifications Resulting in Superior Performance

Albeit harnessing secondary sphere interactions to exert control over the reaction outcomes has primarily been applied to enzymatic and organometallic catalysis, there are seldom any studies that introduce outer-sphere modifiers into organocatalysts. This is even less in the corresponding heterogeneous catalytic system. In this contribution, we experimentally and computationally investigate the role of secondary effects in the reactivity of bromide anions toward CO₂ transformations. Six pyridinium cationic porous frameworks have been synthesized and fully characterized. Structure-activity relationships and kinetics show that the type and the location of the substituents on the cationic framework have a significant impact on the nucleophilic reactivity of their bromide counter anion. Specifically, the attachment of amine substituent to the ortho position relative to a pyridinium motif produces a remarkably efficient catalyst for CO₂ transformation, by a factor of six times greater in comparison to the pristine pyridinium-based polymer. The hydrogen-bond-interaction-promoted reagent activation and enhanced delocalization ability of bromide counter anion are believed to be the key to driving the reaction toward CO₂ utilization. These observations, therefore, champion the leverage of secondary interaction for optimizing the reactivity of organocatalysts.

Dual hydrogen-bond donor group-containing Zn-MOF for the highly effective coupling of CO2 and epoxides under mild and solvent-free conditions

A novel 3D Zn₃(L)₃(H₂L) MOF with dual hydrogen-bond donor (HBD) groups exhibited an efficient catalytic performance for the CO₂ cycloaddition with epoxides under 80 °C, 1.0 MPa and solvent-free conditions.

Formation of CX Bonds in CO2 Chemical Fixation Catalyzed by Metal-Organic Frameworks

Transformation of CO₂ based on metal-organic framework (MOF) catalysts is becoming a hot research topic, not only because it will help to reduce greenhouse gas emission, but also because it will allow for the production of valuable chemicals. In addition, a large number of impressive products have been synthesized by utilizing CO₂ . In fact, it is the formation of new covalent bonds between CO₂ and substrate molecules that successfully result in CO₂ solidly inserting into the products, and only four types of new CX bonds, including CH, CC, CN, and CO bonds, are observed in this exploration. An overview of recent progress in constructing CX bonds for CO₂ conversion catalyzed by various MOF catalysts is provided. The catalytic mechanism of generating different CX bonds is further discussed according to both structural features of MOFs and the interactions among CO₂ , substrates, as well as MOFs. The future opportunities and challenges in this field are also tentatively covered.

Defect-engineering a metal–organic framework for CO2 fixation in the synthesis of bioactive oxazolidinones

Three-component, solvent-free cycloaddition of epoxides with aromatic amines and CO₂.

Highly efficient synergistic CO2 conversion with epoxide using copper polyhedron-based MOFs with Lewis acid and base sites

The catalytic performances and effect of LASs and LBSs of four isomorphous Cu-PMOFs in CO₂ cycloaddition reaction were systematically studied. JLU-Liu21 exhibited significant catalytic efficiency, remarkable recyclability and catalytic stability.

Synthesis of Oxazolidinones by using Carbon Dioxide as a C1 Building Block and an Aluminium-Based Catalyst

Oxazolidinone synthesis through the coupling of carbon dioxide and aziridines was catalysed by an aluminium(salphen) complex at 50-100 °C and 1-10 bar pressure under solvent-free conditions. The process was applicable to a variety of substituted aziridines, giving products with high regioselectivity. It involved the use of a sustainable and reusable aluminium-based catalyst, used carbon dioxide as a C₁ source and provided access to pharmaceutically important oxazolidinones as illustrated by a total synthesis of toloxatone. This protocol was scalable, and the catalyst could be recovered and reused. A catalytic cycle was proposed based on stereochemical, kinetic and Hammett studies.

Application of Metal–Organic Frameworks in CO2 Capture and Conversion

Metal–organic frameworks (MOFs) are promising candidates for CO2 capture and conversion as they possess remarkable properties, including large surface area, open channels and permanent porosity. Through the judicious selection of metal clusters and organic linkers, a framework with a desired topology can be realized. Furthermore, the study of the noncovalent interactions in MOFs provides significant insights into the relationship between the catalytic performance and the framework structure, which will also further promote the development of MOFs as heterogeneous catalysts for CO2 capture and conversion. This chapter is divided into four sections. The first section gives a brief introduction to the structures and chemical features of MOFs. The second section concentrates on MOFs as heterogeneous catalysts for the chemical fixation of CO2 with organic compounds. The third section presents MOFs as photocatalysts for CO2 reduction. The last section covers the application of MOFs in the electrocatalytic reduction of CO2. Particular challenges in the rational design and application of MOF catalysts and research opportunities for further development are highlighted. It is hoped that this chapter will not only serve as a starting point to gain insights into this challenging field but will also stimulate more intensive research on the development of creative MOFs as heterogeneous catalysts towards CO2 capture and conversion.

Carbon capture and conversion using metal–organic frameworks and MOF-based materials

This review summarizes recent advances and highlights the structure–property relationship on metal–organic framework-based materials for carbon dioxide capture and conversion.

A nested Cu24@Cu72-based copper–organic polyhedral framework for selective adsorption of cationic dyes

A double-walled Cu₂₄@Cu₇₂ caged-within-cage copper–organic framework contains a cuboctahedral Cu₂₄-cage, truncated face-centered cubic Cu₆₀-cage and truncated octahedral Cu₇₂-cage.