In Situ Formation of Frustrated Lewis Pairs in a Water-Tolerant Metal-Organic Framework for the Transformation of CO2

Homogeneous and Heterogeneous Frustrated Lewis Pairs for the Activation and Transformation of CO2

Due to the serious ecological problems caused by the high CO2 content in the atmosphere, reducing atmospheric CO2 has attracted widespread attention from academia and governments. Among the many ways to mitigate CO2 concentration, the capture and comprehensive utilization of CO2 through chemical methods have obvious advantages, whose key is to develop suitable adsorbents and catalysts. Frustrated Lewis pairs (FLPs) are known to bind CO2 through the interaction between unquenched Lewis acid sites/Lewis base sites with the O/C of CO2, simultaneously achieving CO2 capture and activation, which render FLP better potential for CO2 utilization. However, how to construct efficient FLP targeted for CO2 utilization and the mechanism of CO2 activation have not been systematically reported. This review firstly provides a comprehensive summary of the recent advances in the field of CO2 capture, activation, and transformation with the help of FLP, including the construction of homogeneous and heterogeneous FLPs, their interaction with CO2, reaction activity, and mechanism study. We also illustrated the challenges and opportunities faced in this field to shed light on the prospective research.

Engineering Frustrated Lewis Pair Active Sites in Porous Organic Scaffolds for Catalytic CO2 Hydrogenation

Frustrated Lewis pairs (FLPs), featuring reactive combinations of Lewis acids and Lewis bases, have been utilized for myriad metal-free homogeneous catalytic processes. Immobilizing the active Lewis sites to a solid support, especially to porous scaffolds, has shown great potential to ameliorate FLP catalysis by circumventing some of its inherent drawbacks, such as poor product separation and catalyst recyclability. Nevertheless, designing immobilized Lewis pair active sites (LPASs) is challenging due to the requirement of placing the donor and acceptor centers in appropriate geometric arrangements while maintaining the necessary chemical environment to perform catalysis, and clear design rules have not yet been established. In this work, we formulate simple guidelines to build highly active LPASs for direct catalytic hydrogenation of CO2 through a large-scale screening of a diverse library of 25,000 immobilized FLPs. The library is built by introducing boron-containing acidic sites in the vicinity of the existing basic nitrogen sites of the organic linkers of metal-organic frameworks collected in a "top-down" fashion from the CoRE MOF 2019 database. The chemical and geometrical appropriateness of these LPASs for CO2 hydrogenation is determined by evaluating a series of simple descriptors representing the intrinsic strength (acidity and basicity) of the components and their spatial arrangement in the active sites. Analysis of the leading candidates enables the formulation of pragmatic and experimentally relevant design principles which constitute the starting point for further exploration of FLP-based catalysts for the reduction of CO2.

Finding Natural, Dense, and Stable Frustrated Lewis Pairs on Wurtzite Crystal Surfaces for Small-Molecule Activation

The surface frustrated Lewis pairs (SFLPs) open up new opportunities for substituting noble metals in the activation and conversion of stable molecules. However, the applications of SFLPs on a larger scale are impeded by the complex construction process, low surface density, and sensitivity to the reaction environment. Herein, wurtzite-structured crystals such as GaN, ZnO, and AlP are found for developing natural, dense, and stable SFLPs. It is revealed that the SFLPs can naturally exist on the (100) and (110) surfaces of wurtzite-structured crystals. All the surface cations and anions serve as the Lewis acid and Lewis base in SFLPs, respectively, contributing to the surface density of SFLPs as high as 7.26×1014 cm-2. Ab initio molecular dynamics simulations indicate that the SFLPs can keep stable under high temperatures and the reaction atmospheres of CO and H2O. Moreover, outstanding performance for activating the given small molecules is achieved on these natural SFLPs, which originates from the optimal orbital overlap between SFLPs and small molecules. Overall, these findings not only provide a simple method to obtain dense and stable SFLPs but also unfold the nature of SFLPs toward the facile activation of small molecules.

Precise Distance Control and Functionality Adjustment of Frustrated Lewis Pairs in Metal-Organic Frameworks

We report the construction of frustrated Lewis pairs (FLPs) in a metal-organic framework (MOF), where both Lewis acid (LA) and Lewis base (LB) are fixed to the backbone. The anchoring of a tritopic organoboron linker as LA and a monotopic linker as LB to separate metal oxide clusters in a tetrahedron geometry allows for the precise control of distance between them. As the type of monotopic LB linker varies, pyridine, phenol, aniline, and benzyl alcohol, a series of 11 FLPs were constructed to give fixed distances of 7.1, 5.5, 5.4, and 4.8 Å, respectively, revealed by 11B-1H solid-state nuclear magnetic resonance spectroscopy. Keeping LA and LB apart by a fixed distance makes it possible to investigate the electrostatic effect by changing the functional groups in the monotopic LB linker, while the LA counterpart remains unaffected. This approach offers new chemical environments of the active site for FLP-induced catalysis.

Magnetically Recyclable Borane Lewis Acid Catalyst for Hydrosilylation of Imines and Reductive Amination of Carbonyls

Fluorinated arylborane-based Lewis acid catalysts have shown remarkable activity and serve as ideal examples of transition metal-free catalysts for diverse organic transformations. However, their homogeneous nature poses challenges in terms of recyclability and separation from reaction mixtures. This work presents an efficient technique for the heterogenization of boron Lewis acid catalysts by anchoring Piers' borane to allyl-functionalized iron oxide. This catalyst demonstrates excellent activity in the hydrosilylation of imines and the reductive amination of carbonyls using various silanes as reducing agents under mild reaction conditions. The catalyst exhibits broad tolerance towards a wide range of functional substrates. Furthermore, it exhibits good recyclability and can be easily separated from the products using an external magnetic field. This work represents a significant advance in the development of sustainable heterogenous metal-free catalysts for organic transformations.

Defect-Induced All-Solid-State Frustrated Lewis Pair on Metal-Organic Monolayer Accelerating Photocatalytic CO2 Reduction with H2O Vapor

Understanding the structure-performance relationships of a frustrated Lewis pair (FLP) at the atomic level is key to yielding high efficiency in activating chemically "inert" molecules into value-added products. A sound strategy was developed herein through incorporating oxygen defects into a Zr-based metal-organic layer (Zr-MOL-D) and employing Lewis basic proximal surface hydroxyls for the in situ formation of solid heterogeneous FLP (Zr4-δ-VO-Zr-OH). Zr-MOL-D exhibits a superior CO2 to CO conversion rate of 49.4 μmol g-1 h-1 in water vapor without any sacrificing agent or photosensitizer, which is about 12 times higher than that of pure MOL (Zr-MOL-P), with extreme stability even after being placed for half a year. Theoretical and experimental results reveal that the introduction of FLP converts the process of the crucial intermediate COOH* from an endothermic reaction to an exothermic spontaneous reaction. This work is expected to provide new prospects for developing efficient MOL-based photocatalysts in FLP chemistry through a sound defect-engineering strategy.

DFT mechanistic study of the chemical fixation of CO2 by aziridine derivatives

Using density functional theory (DFT), we treat the reaction of coupling of CO2 with aziridine in gas phase, in the presence of water and of a green catalyst (NaBr). Computations show that, in gas phase, this ring-opening conversions to oxazolidinones initiates by coordinating a CO2 molecule to the nitrogen atom of the aziridine. Then, a nucleophilic interaction between one oxygen atom of the coordinated CO2 and the carbon atom of the aziridine occurs. For methyl substituted aziridine, two pathways are proposed leading either to 4-oxazolidinone or to 5-oxazolidinone. Besides, we show that the activation energy of this reaction reduces in aqueous solution, in the presence of a water molecule explicitly or NaBr catalyst. In addition, the corresponding reaction mechanisms and regioselectivity associated with this ring-opening conversions to oxazolidinones, in the presence of carbon dioxide are found to be influenced by solvent and catalyst. The present findings should allow better designing regioisomer oxazolidinones relevant for organic chemistry, medicinal and pharmacological applications.

Water Activation Triggered by Cu-Co Double-Atom Catalyst for Silane Oxidation

High-performance catalysts sufficient to significantly reduce the energy barrier of water activation are crucial in facilitating reactions that are restricted by water dissociation. Herein we present a Cu-Co double-atom catalyst (CuCo-DAC), which possesses a uniform and well-defined CuCoN6 (OH) structure, and works together to promote water activation in silane oxidation. The catalyst achieves superior catalytic performance far exceeding that of single-atom catalysts (SACs). Various functional silanes are converted into silanols with up to 98 % yield and 99 % selectivity. Kinetic studies show that the activation energy of silane oxidation by CuCo-DAC is significantly lower than that of Cu single-atom catalyst (Cu-SAC) and Co single-atom catalyst (Co-SAC). Theoretical calculations demonstrate two different reaction pathways where water splitting is the rate-determining step and it is accelerated by CuCo-DAC, whereas H2 formation is key for its single-atom counterpart.

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.

Activation of Ethanol via Conjunction of a Photocatalyst and a HAT Reagent for the Synthesis of Benzimidazoles

The transformation of ethanol to value-added chemicals has tremendous potential. However, generally, harsh reaction conditions are needed for the functionalization of ethanol due to its high dehydrogenation energy. Herein, a metal-free photo-mediated activation of challenging ethanol and higher aliphatic alcohols for the synthesis of differently functionalized benzimidazoles under mild conditions is disclosed. The interplay of a photocatalyst and a HAT reagent facilitated the activation of aliphatic alcohols. A wide array of diamines with different functional groups were well tolerated, and the protocol was also extended to N-substituted diamines for the synthesis of industrially important benzimidazoles. A probable catalytic cycle was proposed based on various mechanistic studies.

Introducing Frustrated Lewis Pairs to Metal-Organic Framework for Selective Hydrogenation of N-Heterocycles

Hydrogenated nitrogen heterocyclic compounds play a critical role in the pharmaceutical, polymer, and agrochemical industries. Recent studies on partial hydrogenation of nitrogen heterocyclic compounds have focused on costly and toxic precious metal catalysts. As an important class of main-group catalysts, frustrated Lewis pairs (FLPs) have been widely applied in catalytic hydrogenation reactions. In principle, the combination of FLPs and metal-organic framework (MOF) is anticipated to efficiently enhance the recyclability performance of FLPs; however, the previously studied MOF-FLPs showed low reactivity in the hydrogenation of N-heterocycles compounds. Herein, we offer a novel P/B type MOF-FLP catalyst that was achieved via a solvent-assisted linker incorporation approach to boost catalytic hydrogenation reactions. Using hydrogen gas under moderate pressure, the proposed P/B type MOF-FLP can serve as a highly efficient heterogeneous catalyst for selective hydrogenation of quinoline and indole to tetrahydroquinoline and indoline-type drug compounds in high yield and excellent recyclability.

Aminoguanidine-Catalyzed Reductive Cyclization of o-Phenylenediamines with CO2 in the Presence of Triethoxysilane

An inexpensive and efficient aminoguanidine-catalyzed reductive cyclization of o-phenylenediamines with CO₂ in the presence of triethoxysilane is described. Various functionalized benzimidazoles, benzoxazole, and benzothiazole were synthesized in high yields. Mechanistic studies indicate that formic acid as a cocatalyst promotes the cyclization reaction.

Synthesis of triarylborane-centered N-heterocyclic carbene cages with tunable photophysical properties

Triarylborane-based discrete metal-carbene supramolecular cages [M₃(1)₂](PF₆)₃ (M = Ag, Au) were synthesized and characterized. The new hexacarbene assemblies show a significant solvatochromic effect in solvents of different polarity. Furthermore, the reversible fluoride binding property of [Au₃(1)₂](PF₆)₃ was investigated by UV-vis absorption and fluorescence titrations. This work holds promise for future developments in the area of highly emissive and stimulus-responsive NHC-metal assemblies.

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).

Chiral Frustrated Lewis Pair@Metal-Organic Framework as a New Platform for Heterogeneous Asymmetric Hydrogenation

Asymmetric hydrogenation, a seminal strategy for the synthesis of chiral molecules, remains largely unmet in terms of activation by non-metal sites of heterogeneous catalysts. Herein, as demonstrated by combined computational and experimental studies, we present a general strategy for integrating rationally designed molecular chiral frustrated Lewis pair (CFLP) with porous metal-organic framework (MOF) to construct the catalyst CFLP@MOF that can efficiently promote the asymmetric hydrogenation in a heterogeneous manner, which for the first time extends the concept of chiral frustrated Lewis pair from homogeneous system to heterogeneous catalysis. Significantly, the developed CFLP@MOF, inherits the merits of both homogeneous and heterogeneous catalysts, with high activity/enantio-selectivity and excellent recyclability/regenerability. Our work not only advances CFLP@MOF as a new platform for heterogeneous asymmetric hydrogenation, but also opens a new avenue for the design and preparation of advanced catalysts for asymmetric catalysis.

Sustainable and Chemoselective Synthesis of α-Aminonitriles Using Lewis and Brønsted Acid-Functionalized Nanoconfined Spaces

α-Aminonitriles are significant components in the synthesis of biological compounds and complex drugs. Although efficient, procedures for synthesizing α-aminonitriles suffer from high loadings of expensive catalysts, long reaction times, energy-intensive conditions, and expensive, toxic solvents. Herein, we report the use of metal-organic framework Cr-MIL-101-SO3H as a catalyst for the facile synthesis of eight α-aminonitriles, five of which are reported as new molecules. We found that the presence of both open Cr3+ Lewis and -SO3H Brønsted acids in the MIL-101 pores is vital for the one-pot synthesis of α-aminonitriles. The catalytic reaction is conducted under solvent-free conditions at room temperature and a Cr-MIL-101-SO3H loading of 1% by the total mass, which is considered a sustainable synthetic pathway of α-aminonitriles. Additionally, we demonstrated for the first time that Cr-MIL-101-SO3H exhibits a high degree of catalytic chemoselectivity, differing substrates with sterically hindered and electronically withdrawn functional groups. Our study expands the existing family of α-aminonitriles and provides an intelligent strategy for the development of catalysts that can be used to synthesize functional α-aminonitriles with potential in therapeutics and health applications.

Mapping Active Site Geometry to Activity in Immobilized Frustrated Lewis Pair Catalysts

The immobilization of molecular catalysts imposes spatial constraints on their active site. We reveal that in bifunctional catalysis such constraints can also be utilized as an appealing handle to boost intrinsic activity through judicious control of the active site geometry. To demonstrate this, we develop a pragmatic approach, based on nonlinear scaling relationships, to map the spatial arrangements of the acid–base components of frustrated Lewis pairs (FLPs) to their performance in the catalytic hydrogenation of CO₂. The resulting activity map shows that fixing the donor–acceptor centers at specific distances and locking them into appropriate orientations leads to an unforeseen many‐fold increase in the catalytic activity of FLPs compared to their unconstrained counterparts.

Visible-Light-Responsive UiO-66(Zr) with Defects Efficiently Promoting Photocatalytic CO2 Reduction

It is of great importance to understand the relationship between the structure and properties at the atomic level, which provides a solid platform for the design of efficient heterogeneous catalysts. However, it remains a challenge to elucidate the roles of the structure of reaction sites in the catalytic activity of active sites due to the lack of understanding of the structure of specific active site species. Herein, taking the metal-organic framework (MOF) UiO-66(Zr) as a prototype, MOF catalysts with all-solid-state frustrated Lewis pairs (FLPs) Zr³⁺-OH were synthesized in situ by adding acetic acid (HAc) as a modulator. By introducing missing linkers, UiO-66(Zr) first becomes a visible-light-responsive photocatalyst for CO₂ reduction. The in situ Fourier transform infrared (FTIR) spectrum reveals that b-CO₃^2- is the key intermediate for the activation of CO₂ molecules through FLPs Zr³⁺-OH. Moreover, defective UiO-66(Zr) could "self-breath" by surface hydroxyls. This finding not only provides a new avenue for utilizing UV-responsive MOFs by defect engineering but also sheds light on its catalytic activity at the atomic level.

Frustrated Lewis Pairs in Heterogeneous Catalysis: Theoretical Insights

Frustrated Lewis pair (FLP) catalysts have attracted much recent interest because of their exceptional ability to activate small molecules in homogeneous catalysis. In the past ten years, this unique catalysis concept has been extended to heterogeneous catalysis, with much success. Herein, we review the recent theoretical advances in understanding FLP-based heterogeneous catalysis in several applications, including metal oxides, functionalized surfaces, and two-dimensional materials. A better understanding of the details of the catalytic mechanism can help in the experimental design of novel heterogeneous FLP catalysts.

Highly Efficient Conversion of Propargylic Alcohols and Propargylic Amines with CO2 Activated by Noble-Metal-Free Catalyst Cu2 O@ZIF-8

The cyclization reactions of propargylic alcohols and propargylic amines with CO₂ are important in industrial applications, but it was a great challenge that non-noble-metal catalysts catalyzed both reactions under mild conditions. Herein, the catalyst Cu₂ O@ZIF-8 was prepared by encapsulating Cu₂ O nanoparticles into robust ZIF-8, and it can effectively catalyze the cyclization of both propargylic alcohols and propargylic amines with CO₂ into valuable α-alkylidene cyclic carbonates and oxazolidinones with turnover numbers (TONs) of 12.1 and 19.6, which can be recycled at least five times. The mechanisms were further uncovered by NMR, FTIR, ¹³ C isotope-labeling experiments and DFT calculations, in which Cu₂ O and DBU can synergistically activate the C≡C bond and the hydroxy/amino group of substrates. Importantly, it is the first example of a noble-metal-free catalyst that can catalyze both propargylic alcohols and propargylic amines with CO₂ simultaneously.

In situ activation of COOH-functionalized ZIF-90-enabled reductive CO2N-formylation

A heterogeneous COOH-functionalized ZIF-90 porous catalyst (ZIF-90-C) was prepared for enhanced CO2 adsorption/activation, and the in situ generated –COO− species can efficiently promote the N-formylation reaction.

Synthesis of Highly Functionalizable Symmetrically and Unsymmetrically Substituted Triarylboranes from Bench-Stable Boron Precursors

A novel and convenient methodology for the one-pot synthesis of sterically congested triarylboranes by using bench-stable aryltrifluoroborates as the boron source is reported. This procedure gives systematic access to symmetrically and unsymmetrically substituted triarylboranes of the types BAr2 Ar' and BArAr'Ar'', respectively. Three unsymmetrically substituted triarylboranes as well as their iridium-catalyzed C-H borylation products are reported. These borylated triarylboranes contain one to three positions that can subsequently be orthogonally functionalized in follow-up reactions, such as Suzuki-Miyaura cross-couplings or Sonogashira couplings.

An air-stable, reusable Ni@Ni(OH)2 nanocatalyst for CO2/bicarbonate hydrogenation to formate

Production of formate via CO2/bicarbonate hydrogenation using cheap metal-based heterogeneous catalysts is attractive. Herein, we report the organometallic synthesis of a foam-like Ni@Ni(OH)2 composite nanomaterial which exhibited remarkable air stability and over 2 times higher catalytic activity than commercial RANEY® Ni catalyst in formate synthesis. Formate generation was achieved with an optimal rate of 6.0 mmol gcat-1 h-1 at 100 °C, a significantly lower operation temperature compared to the 200-260 °C reported in the literature. Deep characterization evidenced that this nanomaterial was made of an amorphous Ni(OH)2 phase covering metallic Ni sites; a core-shell structure which is crucial for the stability of the catalyst. The adsorption of bicarbonates onto the Ni@Ni(OH)2 catalyst was found to be a kinetically relevant step in the reaction, and the Ni-Ni(OH)2 interface was found to be beneficial for both CO2 and H2 activation thanks to a cooperative effect. Our findings emphasize the underestimated potential of Ni-based catalysts in CO2 hydrogenation to formate, indicating a viable strategy to develop stable, cheap metal catalysts for greener catalytic applications.

Controlling the Lewis Acidity and Polymerizing Effectively Prevent Frustrated Lewis Pairs from Deactivation in the Hydrogenation of Terminal Alkynes

Two strategies were reported to prevent the deactivation of Frustrated Lewis pairs (FLPs) in the hydrogenation of terminal alkynes: reducing the Lewis acidity and polymerizing the Lewis acid. A polymeric Lewis acid (P-BPh₃) with high stability was designed and synthesized. Excellent conversion (up to 99%) and selectivity can be achieved in the hydrogenation of terminal alkynes catalyzed by P-BPh₃. This catalytic system works quite well for different substrates. In addition, the P-BPh₃ can be easily recycled.

Simple and green synthesis of benzimidazoles and pyrrolo[1,2-a]quinoxalines via Mamedov heterocycle rearrangement

This method is metal and catalyst-free and only solvent (HOAc) is required with H₂O as the sole byproduct.

CO2 -Folded Single-Chain Nanoparticles as Recyclable, Improved Carboxylase Mimics

Emulating the function of natural carboxylases to convert CO₂ under atmospheric condition is a great challenge. Herein we report a class of CO₂ -folded single-chain nanoparticles (SCNPs) that can function as recyclable, function-intensified carboxylase mimics. Lewis pair polymers containing bulky Lewis acidic and basic groups as the precursor, can bind CO₂ to drive an intramolecular folding into SCNPs, in which CO₂ as the folded nodes can form gas-bridged bonds. Such bridging linkages highly activate CO₂ , which endows the SCNPs with extraordinary catalytic ability that can not only catalyze CO₂ -insertion of C(sp³ )-H for imitating the natural enzyme's function, it can also act on non-natural carboxylation pathways for C(sp² and sp)-H substrates. The nanocatalysts are of highly catalytic efficiency and recyclability, and can work at room temperature and near ambient CO₂ condition, inspiring a new approach to sustainable C₁ utilization.

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.

CO2 Methanation via Amino Alcohol Relay Molecules Employing a Ruthenium Nanoparticle/Metal Organic Framework Catalyst

Methanation of carbon dioxide (CO2 ) is attractive within the context of a renewable energy refinery. Herein, we report an indirect methanation method that harnesses amino alcohols as relay molecules in combination with a catalyst comprising ruthenium nanoparticles (NPs) immobilized on a Lewis acidic and robust metal-organic framework (MOF). The Ru NPs are well dispersed on the surface of the MOF crystals and have a narrow size distribution. The catalyst efficiently transforms amino alcohols to oxazolidinones (upon reaction with CO2 ) and then to methane (upon reaction with hydrogen), simultaneously regenerating the amino alcohol relay molecule. This protocol provides a sustainable, indirect way for CO2 methanation as the process can be repeated multiple times.

ROMP-Boranes as Moisture-Tolerant and Recyclable Lewis Acid Organocatalysts

Although widely used in catalysis, the multistep syntheses and high loadings typically employed are limiting broader implementation of highly active tailor-made arylborane Lewis acids and Lewis pairs. Attempts at developing recyclable systems have thus far met with limited success, as general and versatile platforms are yet to be developed. We demonstrate a novel approach that is based on the excellent control and functional group tolerance of ring-opening metathesis polymerization (ROMP). The ROMP of highly Lewis acidic borane-functionalized phenylnorbornenes afforded both a soluble linear copolymer and a cross-linked organogel. The polymers proved highly efficient as recyclable catalysts in the reductive N-alkylation of arylamines under mild conditions and at exceptionally low catalyst loadings. The modular design presented herein can be readily adapted to other finely tuned triarylboranes, enabling wide applications of ROMP-borane polymers as well-defined supported organocatalysts.

Facile access to N-formyl imide as an N-formylating agent for the direct synthesis of N-formamides, benzimidazoles and quinazolinones

N-Formamide synthesis using N-formyl imide with primary and secondary amines with catalytic amounts of p-toluenesulfonic acid monohydrate (TsOH·H₂O) is described. This reaction is performed in water without the use of surfactants. Moreover, N-formyl imide is efficiently synthesized using acylamidines with TsOH·H₂O in water. In addition, N-formyl imide was successfully used as a carbonyl source in the synthesis of benzimidazole and quinazolinone derivatives. Notable features of N-formylation of amines by using N-formyl imide include operational simplicity, oxidant- and metal-free conditions, structurally diverse products, and easy applicability to gram-scale operation.

N-heterocyclic carbene-functionalized metal-organic frameworks for the chemical fixation of CO2

N-heterocyclic carbenes (NHCs) are a class of molecules with a lone pair of carbene electrons and thus, they have the ability to activate CO2 to form imidazolium carboxylates. The incorporation of activated, metal-free NHC moieties into metal-organic frameworks (MOFs) without the decomposition of metal-carboxylate coordination motifs is highly desired owing to the high CO2 affinity and versatile chemical functionalities in MOFs. Herein, we have summarized the recent in situ generation approaches to form metal-free NHC-functionalized MOFs, which are a unique class of CO2-conversion catalysts with high catalytic activity, selectivity and stability, superior to those of homogenous and other heterogeneous NHC analogues. The NHC-functionalized MOFs for catalytic CO2 reduction include reactions such as the hydroboration of CO2, hydrosilylation of CO2, N-methylation using CO2 and hydrogenation of CO2 to formic acid. Overall, the synthetic strategy of metal-free NHC-functionalized MOFs, the unique catalytic pathways of NHC-functionalized MOFs, and potentially new research directions of NHC-functionalized MOFs are discussed, which will guide researchers to attempt to design new NHC-MOFs and extend their catalytic applications in the chemical fixation of CO2.

Alternative Pathway of CO2 Hydrogenation by Lewis-Pair-Functionalized UiO-66 MOF Revealed by Metadynamics Simulations

The reaction between H₂ and CO₂ catalyzed by an intramolecular frustrated Lewis pair, which is covalently bonded to a UiO-66 metal-organic framework (MOF), is considered in this work. Free energy surfaces (FESs) for this reaction are generated throughout finite-temperature density functional theory (DFT) metadynamics (MD) simulations. The simulated FESs indicate an alternative stepwise pathway for the hydrogenation of CO₂. Furthermore, indications of weaker binding of CO₂ than H₂ to the Lewis pair centers have been observed via metadynamics simulations. These findings were unknown from the results of static-DFT calculations, which proposed a concerted reduction of CO₂. The results of the present work may influence the design of new efficient heterogeneous Lewis pair (LP)-functionalized MOFs to catalyze capture and conversion of CO₂ to high-value chemicals.