N-Heterocyclic Carbene-Like Catalysis by a Metal–Organic Framework Material

MOF-Incorporated Binuclear N-Heterocyclic Carbene-Cobalt Catalyst for Efficient Conversion of CO2 to Formamides

Environmental problem caused by carbon emission is of widespread concern. Involving CO₂ as C₁ resource into chemical synthesis is one of the most attractive ways for carbon recycling. Herein, the first example of host-guest composites featuring metal-organic framework (MOF)-encapsulated binuclear N-heterocyclic carbene (NHC) complex, Co₂ @MIL101, was developed with the molecularly dispersed [Co(IPr)Br]₂ (μ-Br)₂ (Co₂ ) loading in the cage of MIL-101(Cr) via a "ligand-in-dimer-trap" strategy, which was comprehensively investigated through various techniques including synchrotron X-ray absorption, electron microscopy, X-ray diffraction, solid-state nuclear magnetic resonance spectroscopy, and others. The noble-metal-free double-sites catalyst Co₂ @MIL101 exhibited promising stability, activity, efficiency, reusability, and substrate adaptability for converting CO₂ into various formamides with amines and hydrosilanes and achieved the best performance for one of the most useful formamides, N-methyl-N-phenylformamide (MFA), among the recyclable catalysts at ambient conditions, providing a reliable approach to successfully unify the advantages of both homo- and heterogeneous catalysts. Density functional theory calculations were applied to illustrate the superior activity of the binuclear NHC complex center as double-sites catalyst toward the activation of CO₂ .

Construction of Stable Metal-Organic Framework Platforms Embedding N-Heterocyclic Carbene Metal Complexes for Selective Catalysis

We report a bottom-up approach to immobilize catalysts into MOFs, including copper halides and gold chloride in a predictable manner. Interestingly, the structures of MOFs bearing NHC metal complexes maintained a similar 4-fold interpenetrated cube. They exhibited exceptionally high porosity despite the interpenetrated structure and showed good stability in various solvents. Moreover, these MOFs possess high size activity depending on the size of the substrates in various reactions, compared to homogeneous catalysis. Also, the high catalytic activity of MOFs can be preserved 4 times without significant loss of crystallinity. Incorporation of the various metal complexes into MOFs allows for the preparation of functional MOFs for practical applications.

Triplet Carbene with Highly Enhanced Thermal Stability in the Nanospace of a Metal-Organic Framework

Triplet carbenes (TCs) are of great interest due to their magnetic properties and reactivity, which descend from TCs' unique electronic state. However, the reactivity and stability of TCs are usually a trade-off, and it is difficult to achieve both at the same time. In this work, we were able to enhance the thermal stability of a TC species while maintaining its reactivity by confining them in the nanospace of a metal-organic framework (MOF). We synthesized a new MOF using a TC precursor; subsequently, TCs were generated by photostimulation. The TCs generated in the MOF nanospace were detectable up to 170 K, whereas their non-MOF-confined counterparts (bare ligand) could not be detected above 100 K. In addition, the reactivity of TC generated in MOF with O₂ was drastically improved compared to that of bare ligand. Our approach is generally applicable to the stabilization of highly reactive species, whose reactivity needs to be preserved.

N-Heterocyclic Carbene Functionalized Covalent Organic Framework for Transesterification of Glycerol with Dialkyl Carbonates

The development of a heterogeneous catalyst through the combination of novel carrier and powerful catalytic active sites is of particular interest. Herein, the successful integration of an N-Heterocyclic carbene (NHC) moiety into a covalent organic framework (COF) was achieved by coupling 4,4′,4′′,4′′′-(pyrene-1,3,6,8-tetrayl) tetraaniline (PyTTA) and equimolar 4,7-bis(4-formylphenyl)-1-methyl-1H-benzimidazole (IM) and 2′3′5′6′-tetrafluoro-[1,1′:4′,1′′-terphenyl]-4,4′-dicarbaldehyde (4F) followed by ionization with 1-bromobutane (C4H9Br) and then deprotonation upon addition of a base. The resulting material exhibited promising heterogeneous catalytic activity towards transesterification reaction of glycerol with dialkyl carbonate. Moreover, good recyclability granted no substantial loss of activity upon five cycles. Combination of COFs and NHCs might synergize their characteristics, thus providing more possibilities for creating new patterns of catalytic reactivity.

Recent progress in the development of MOF-based optical sensors for Fe3

Fe(iii) is a common pollutant released into our ecosystem from various industrial and anthropogenic activities which when in excess interferes with human health. A plethora of sensors based on various designs and working principles are being continuously synthesized and improvised for its facile detection. In the present review, we have provided a brief overview of the developments made in the field of metal organic framework (MOF) based optical sensors for Fe3+. MOFs have exponentially emerged in the field of research due to their high porosity, modular construction and easy tunability. These inorganic-organic hybrid porous materials are being essentially promoted as optical sensors because of their unique photophysical properties and potential sensing applications.

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.

N-Heterocyclic Carbenes in Materials Chemistry

N-Heterocyclic carbenes (NHCs) have become one of the most widely studied class of ligands in molecular chemistry and have found applications in fields as varied as catalysis, the stabilization of reactive molecular fragments, and biochemistry. More recently, NHCs have found applications in materials chemistry and have allowed for the functionalization of surfaces, polymers, nanoparticles, and discrete, well-defined clusters. In this review, we provide an in-depth look at recent advances in the use of NHCs for the development of functional materials.

SuFEx in Metal-Organic Frameworks: Versatile Postsynthetic Modification Tool

A new type of click reaction, sulfur(VI) fluoride exchange (SuFEx), has been utilized to prepare five postsynthetically modified UiO-67 series metal-organic frameworks (MOFs). The postsynthetic modification (PSM) via SuFEx can be achieved selectively for the sulfonyl fluoride (R-SO₂F) without degrading the MOF structure as confirmed by X-ray crystallographic analysis. The present SuFEx method provides a straightforward tool for introducing new functionality inside MOFs. Introduction of an imidazolium group into the MOF afforded a heterogeneous catalyst for the benzoin condensation reaction.

Structure, sensing and photocatalytic properties of two multifunctional 3D luminescent coordination polymers based on an N-heterocyclic carboxylic acid

Two novel luminescent coordination polymers, {[Zn(tmlb)(H₂tmlb)]·H₂O}_n (1) and [Zn(tmlb)(bbibp)]_n (2) ((bbibp = bis(benzoimidazo-1-ly)biphenyl), H₂tmlb = (1H-1,2,4-triazol-1-yl)methylenebis(benzoic acid)), have been rationally designed and successfully solvothermally synthesized.

Post-synthetically modified MOF for the A3-coupling reaction of aldehyde, amine, and alkyne

A new heterogeneous NHC catalyst (Ag-NHC-MOF) was synthesized by the post-synthetic modification of an azolium-containing metal–organic framework.

Three metalloporphyrin frameworks containing imidazole groups: synthesis, characterization and properties

Three metalloporphyrin frameworks containing imidazole groups were structurally characterized, revealing the moderate CO₂ adsorption capacity and high catalytic activity for ethylbenzene oxidation.

NIR emission and luminescent sensing of a lanthanide–organic framework with Lewis basic imidazole and pyridyl sites

Three luminescent lanthanide–organic frameworks, [Ln(Himdc)(ina)(H₂O)]_n, consist of a 3D microporous lanthanide carboxylate ([Eu(COO)₃]_n) framework and imidazole and pyridyl sites for the luminescent sensor.

Syntheses, structures, luminescent and photocatalytic properties of various polymers based on a “V”-shaped dicarboxylic acid

Four novel luminescent coordination polymers were synthesized under solvothermal conditions, and compounds2–4can serve as a Fe³⁺/Cu²⁺fluorescent sensor through quenching the luminescence, respectively.

Coordination frameworks containing compounds as catalysts

This article describes a collection of MOF containing compounds as catalysts in a diverse range of organic transformation reactions.

Enhanced product selectivity promoted by remote metal coordination in acceptor-free alcohol dehydrogenation catalysis

A bimetallic [Ir³⁺]₂ complex was synthesized based on a bridging 1,2,3-triazole ligand that coordinates to one Cp*Ir unit as N,N-bidentate chelate, and to the other as a C,C-bidentate ligand.

Catalytically active lead(ii)–imidazolium coordination assemblies with diversified lead(ii) coordination geometries

Five new catalytically active lead(ii)–imidazolium coordination assemblies with diversified lead(ii) coordination geometries were successfully synthesized and used as catalysts for benzoin condensation reactions.

Synthesis, structure, and properties of a 3D porous Zn(ii) MOF constructed from a terpyridine-based ligand

A new Zn MOF has been synthesized based on a terpyridine-based ligand, which exhibits selective fluorescent sensing properties for metal ions and nitroaromatic compounds, especially Fe³⁺, 4-NPH and 4-NP.

Crystal structures, topological analysis and luminescence properties of three coordination polymers based on a semi-rigid ligand and N-donor ligand linkers

Three new mixed-ligand coordination polymers have been synthesized based on 3,3′-(anthracene-9,10-diyl)diacrylate acid and different N-donor ligands. Complex 2 displays rapid and selective sensing of Fe³⁺.

Topology-guided design of an anionic bor-network for photocatalytic [Ru(bpy)3]2+ encapsulation

An anionic metal–organic framework, PCN-99, has been synthesized through a topology-guided strategy; its underlying bor-net is realized by the use of a tetrahedral [In(COO)₄]⁻ node and a judiciously designed trigonal planar linker.