Supramolecular polymer network constructed by a functionalized polyimidazolium salt derived from metal-carbene template approach

In this study,we present a supramolecular templating approach for constructing polyimidazolium salt containing crown ether and cyclobutane moieties.This strategy involves the formation of metal-carbene templates,photochemical cycloaddition,and subsequent demetallation of metal ions.Driven by the host-guest chemistry between crown ether units and ammonium salts,we successfully fabricated a supramolecular polymer SPN1,which features imidazolium receptors and cyclobutane units.The obtained SPN1 demonstrates outstanding reversible stimulus-response,antibacterial behavior and conductivity.

NHC-derived carbon-centered luminescent radicals with shortwavelength emission via suppression of Kasha's rule

Luminescent organic radicals have garnered increasing attention owing to their versatile applications in sensing, imaging, and organic light-emitting diodes(OLEDs), attributed to their unique emission properties originating from the doublet spin state.However, the natural narrow bandgap of organic free radicals typically limits their emission to the long-wavelength region.Designing luminescent organic radicals with short-wavelength emission remains a significant challenge. Herein, a series of carbon-centered radicals with short-wavelength emission(383–476 nm) by combining N-heterocyclic carbenes with various polycyclic aromatic hydrocarbons(PAHs)(2-naphthyl, 2a~Ⅰ and 2b~Ⅰ;2-phenanthryl, 2a~Ⅱand 2b~Ⅱ;2-anthryl, 2a~Ⅲand 2b~Ⅲ;3-phenanthryl, 2a~Ⅳand 2b~Ⅳ). Theoretical calculations reveal that the introduction of PAHs significantly increases the ΔE_(D2-D1) in 2a^(Ⅰ–Ⅲ)and 2b^(Ⅰ–Ⅲ)compared to that in phenyl-derived radical congeners. Consequently, the internal transition from D2 to D1 is impeded, leading to a high yield of D2 emission and a suppressed Kasha's rule, thereby overcoming the limitations imposed by their narrow bandgap. For 2a~Ⅳ and 2b~Ⅳ, despite a moderately large ΔED2-D1value, the ΔED3-D1value exceeds 1 e V, indicating that their emission likely originates from the D3 state. Furthermore, we utilized 2a~Ⅲand 2b~Ⅲ as emissive materials in OLEDs,resulting in blue emissions with external quantum efficiencies of 7.5% and 6.5%, respectively.

Enhancement on Hemilabile Phosphine-Amide Palladium and Nickel Catalysts for Ethylene(Co)Polymerization with Polar Monomers Using a Cyclizing Strategy

To address the issue of hemilabile catalyst in olefin polymerization catalysis, a cyclizing strategy was used to construct novel N-bridged phosphine-carbonyl palladium and nickel catalysts, resulting in improvements on ethylene(co)polymerizations. The N-bridged phosphinecarbonyl Pd catalysts(Pd1-Pd5) and Ni catalysts(Ni1-Ni5) bearing five-to eight-membered-ring structures were designed and synthesized.Catalytic performance for ethylene(co)polymerization became better as the size of N-containing bridge increased. The seven-membered-ring bridged catalysts Pd4 and Ni4 exhibited the best performance in terms of catalytic activity, polymer molecular weight and incorporation of acrylates and acrylic acid. The better performance of these catalysts bearing larger-size bridges was tentatively attributed to the methyleneinduced higher electron density around nitrogen, which strenghtens the coordination of carbonyl group to metal center, and also to the steric effect offered by this cyclization. This work provides a new strategy to enhance hemilabile polymerization catalysts.

An Ultralong Low-Temperature Phosphorescent Pentagonal-Prismatic Organometallic Cylinder Featuring Pentaphenylpyrrole-N-Heterocyclic Carbenes

A pentagonal-prismatic cylinder[Ag5(L)2](PF6)5 obtained from the pentaphenylpyrrole-bridged pentaimidazolium salt H5-L(PF6)5 and AgI ions was determined by X-ray diffraction analyses.The target organometallic cylinder not only exhibited enhanced fluorescence emission in dilute solution at room temperature but also showed an improved phosphorescence ratio compared with the free precursor and maintained a long lifetime(1.39 s)in the solid state at 77 K.Furthermore,the experimental results and DFT calculations confirmed that the formation of the organometallic cylinder promoted intersystem crossing.Meanwhile,the frontier orbitals of[Ag5(L)2](PF6)5 showed the main contribution of building block PPP as the luminescence source of[Ag5(L)2](PF6)5 by a modest heavy-atom effect.These results provide a strategy for constructing enhanced phosphorescent emission and long lifetime organometallic supramolecular phosphorescent materials.

Radical organometallic nanocages with redox switchable poly-NHC ligands

Developing discrete radical organometallic nanocages is essential for fabricating functional materials.In this study,we construct a series of poly-NHC-based(NHC=N-heterocyclic carbene)organometallic nanocages 3a-3c with different sizes by employing redox-active bis(triarylamine)derivatives with differentπ-conjugated spacers as building blocks.The varied sizes of nanocages 3a-3c modulate the distance of the redox-active centers and reversibly convert them to radical nanocages 3a^(2+)-3c^(2+)through chemical and electrochemical oxidation.Radical nanocages 3a^(2+)-3c^(2+)display clear bond and angle alteration and retention of their three-dimensional topologies.This work not only merely proves that these nanocages are excellent stimulus-responsive materials but also opens a door to the rational design of novel radical organometallic nanocages.

N-Heterocyclic carbene-stabilized platinum nanoparticles within a porphyrinic nanocage for selective photooxidation

The successful construction of highly stable and active platinum nanoparticles(Pt NPs) within the confined cavity of a threedimensional porphyrinic nanocage is presented in this study. The flexible porphyrinic nanocage containing eight N-heterocyclic carbene(NHC) precursors was prepared using a metal-carbene-templated ring-closing metathesis(RCM) approach as new capping materials for the fabrication/stabilization of Pt NPs. Notably, the NHC-stabilized Pt NPs within the porphyrinic nanocage exhibited high catalytic activity for selective oxidation of 2-chloroethyl ethyl sulfide to nontoxic 2-chloroethyl ethyl sulfoxide with excellent stability and recyclability.

Supramolecular Template-Assisted Catalytic[2+2]Photocycloaddition in Homogeneous Solution

Supramolecular interactions can help recognize and organize substrates around an enzyme’s active sites and subsequently assemble a new molecule in a certain way.Inspired by nature’s control of reactions,in this work we designed a template catalyst equipped with ditopic Au(I)–N-heterocyclic carbene(NHC)functional sites that direct olefin substrates into reactive geometries via collaboration of coordination-driven interactions.Notably,this catalyst enables the realization of catalytic[2+2]photocycloadditions with as low as 2 mol%catalyst loading in homogeneous solution and the delivery of a series of cyclobutane derivatives with excellent conversions and stereoselectivities.The success of gram-scale reactions further demonstrates the feasibility of this strategy,which lays a solid foundation for the large-scale preparation of cyclobutane derivatives in the future.

Single-Crystalline Organoiridium Complex for Gas-Triggered Chromogenic Switches and Its Applications on CO Detection and Reversible Scavenging

Summary of main observation and conclusion Nonporous molecular single crystals of coordinatively unsaturated 16-electron metallacycle are found to undergo highly selective-yet reversible-binding of CO over CH4,H2,N2,CO2,various volatile organic compounds and water,through binding of the molecule to its metal centers.Carbon monoxide is taken up by black crystals and subsequently liberated from the corresponding orange CO adduct by reversible metal coordination,the structural evidence obtained from in situ X-ray diffraction.The single-crystallinity of the metallacycle is retained even after several cycles.The material,when adsorbed on silica,shows remarkable sensitivity and selectivity for CO,allowing visual CO sensing in the solid state.The metallacycle offer the possibility of serving as readily regenerable scavenger for removing trace CO from gas mixtures with N2.

Chiral Coordination Metallacycles/Metallacages for Enantioselec-tive Recognition and Separation

In recent years,chiral discrete supramolecular coordination complexes have attracted increasing interest as simple enzyme mimetics owing to their aesthetic architectures and potential applications in chiral science.This review summarizes the recent advances on chiral coordination metallacy-cles/metallacages with inherent cavities for enanti on selective recog nition and separation,including their design principles and synthesis,the in troduc-tion of chirality and functionality,structural adaptability,and host-guest bonding in enantioselective process.Finally,the perspectives on the remain-ing challenges and future opportunities are presented.

Metal-Carbene-TempIated Photochemistry in Solution: A Universal Route towards Cyclobutane Derivatives

Background and Originality Content Cyclobutane moieties are an important class of motifs since they are frequently found in the medicinally relevant compounds such as alkaloids and pharmaceuticals.[1] Therefore,the develop­ment of efficient synthetic strategies for the construction of cy­clobutanes and their derivatives has always been a focus of inter-est.[2a] Photochemical reactions are powerful tools for synthesiz­ing compounds with high complexity and diversity.[2b-h] Among them,photochemical[2+2]cycloaddition is a widely used proto­col for the preparation of such compounds.[2h]However,this kind of reaction always suffers from the challenges of controlling the resulting products of the intermolecular[2+2]photodimerization.In principle,to achieve cyclobutanes via[2+2]cycloaddition,the two olefins should be oriented in a parallel fashion keeping the distance less than 4.2 A apart from each other.

Recent Advances in the Chemistry of N-Heterocyclic-Carbene-Functionalized Metal-Nanoparticles and Their Applications

Metal-nanoparticles (M-NPs)have been widely applied in catalysis,imaging,sensing and medicine.One particularly active area of this research is the modification of the surface of the nanoparticles to prevent aggregation through the coordination of ligands.N-Heterocyclic carbenes (NHCs)have emerged as suitable ligands for this purpose due to their affinity to the metals and their strongly electron donating nature.

Template Synthesis of Metal Nanoparticles within Organic Cages

Background Metal nanoparticles(M-NPs)have attracted tremendous interest in recent years due to their unique physical and chemical properties resulting from their size reduction and shape variation.[1]In particular,the use of ultra-small M-NPs as efficient catalysts in various reactions is a rapidly growing area of research as a consequence of their synthetic accessibility and superior catalytic efficiency.[2]However,due to their high surface energy,small M-NPs are prone to aggregation during reactions and associated loss of their catalytic activities.To deal with this difficulty,various stabilizers and/or supports have been developed,for instance,small organic ligands,dendritic architectures,and polymers.Unfortunately,these materials all have limitations,such as low stability,constant leaching,irregular distribution or regrowth and combinations of these.Therefore,it is highly desirable to develop superior support materials that can overcome these issues.

Strategies for the construction of supramolecular assemblies from poly-NHC ligand precursors

The field of supramolecular assemblies has developed rapidly in the last few decades,thanks in a large part to their diverse applications.These assemblies have been mostly based on Werner-type coordination motifs in which metal centres are coordinated by nitrogen or oxygen donors.Recently,N-heterocyclic carbene(NHC)ligands have been employed as carbon donors not only because of their appealing structures but also due to the extensive applications in catalysis,biomedicine and material science of the resulting assemblies.During the last decade,NHC-based supramolecular assemblies have witnessed rapid growth and extensive application in molecular recognition,luminescent materials and catalysis.For different topological systems,a diverse selection of poly-NHC precursors and synthetic strategies is crucial to precisely control the synthesis of supramolecular architectures.Several synthetic strategies have been developed to synthesise two-dimensional(2D)molecular metallacycles and three-dimensional(3D)metallacages from a wide range of poly-NHC precursors,including a straightforward one-pot strategy,supramolecular transmetalation,stepwise synthesis,an improved one-pot strategy involving self-sorting behaviour of 3D metallacages and a subtle variation strategy of poly-NHC ligand precursors.This review offers a summary of the synthetic strategies applied for the construction of different poly-NHC-based supramolecular assemblies,particularly emphasizes recent progress in the synthesis of large and complex supramolecular assemblies from poly-NHC precursors,and further attention is given to their application in postsynthetic modifications(PSMs),host-guest chemistry,luminescent properties and biomedical applications.

Formation of Functional Cyclooctadiene Derivatives by Supramolecularly- Controlled Topochemical Reactions and Their Use as Highly Selective Fluorescent Biomolecule Probes

Summary of main observation and conclusion Controlling the regio-and stereochemistry of the photoproducts in solution is far more challenging for polvenes than for monoalkenes.Herein,a supramolecularly-controlled topochemical reaction of conjugated dienes in homogeneous system is developed,ultimately providing two cyclooctadiene-cored tetraimidazolium molecular receptors exclusively.These cyclooctadiene derivatives exhibited highly sensi-tive and selective fluorescence sensing for thymine relative to other biologically relevant species in aqueous solution at physiological pH.Both the cycloo-ctadiene moieties and imidazolium units play important roles in the selective recognition observed.The presented supramolecularly-controlled method allows the simple yet rare selective photoconversion of flexible cyclooctadiene derivatives in solution.This study offers a new synthetic strategy for the preparation of functional molecules with potential for use in biological applic ations.

Phase-mediated controllable intramolecular and intermolecular photocycloadditions assisted by supramolecular templates

Understanding and controlling supramolecular template effect assembly via a photochemical reaction in different solid and solution phases is one of the main topics in photochemistry. Here, an interesting case of phase-mediated controllable intramolecular/intermolecular photochemical [2+2] cycloadditions assisted by supramolecular templates was demonstrated. Direct irradiation of the complexes in solution yields intramolecular photoproducts exclusively, whereas exposure of the solid powder sample under the same conditions yields intermolecular dinuclear species quantitatively. The nature of the phase and supramolecular interaction affects the geometrical arrangements of the metallacycles, leading to different cycloaddition products under photoirradiation. The crystal structures of different products were investigated by single-crystal X-ray diffraction, nuclear magnetic resonance(NMR) spectrometry, and electrospray ionization mass spectrometry(ESI-MS).

Multistimuli-Responsive Fluorescent Organometallic Assemblies Based on Mesoionic Carbene-Decorated Tetraphenylethene Ligands and Their Applications in Cell Imaging

The controllable construction of light-emitting organometallic supramolecular materials integrating stimulus responses and biological applications is still a major challenge today.In this work,emissive organometallic assemblies based on AgI/AuI and mesoionic carbene-decorated tetraphenylethene(MIC-TPE)ligands have been synthesized and characterized.Photophysical studies showed that these organometallic assemblies[M_(4)(2)_(2)](OTf)_(4) not only fluoresce in various dilute solutions,resulting from the rigidification of MIC-TPE ligands upon complexation,but also show tunable fluorescence wavelengths and intensity behaviors in mixed solvent systems and at varying temperatures while in solution,and mechanical pressure stimulus-responsive fluorescent features in the solid state.Furthermore,the organometallic cages[M_(4)(2)_(2)](OTf)_(4)(M=Ag and Au)were successfully employed for cell imaging and showed the potential of anticancer activity,making them promising candidates for cancer theranostics.This work provides a simple and efficient method to prepare highly emissive and stimulus-responsive organometallic materials and paves the way for related biological applications such as cancer cell imaging and targeted therapy.

Bottom-up construction of mesoporous supramolecular isomers based on a Pd_(3)L_(6) triangular prism as templates for shape specific aggregation of polyiodide

Bottom-up construction of highly complex architecture from simple components remains one of the long-standing challenges in chemistry.Herein two supramolecular isomers based on large trigonal prismatic Pd_(3)L^(1)_(6)building block are reported.Significantly,they can be controllably obtained by adjusting the solute concentration during crystal growth.Specifically,the square shape crystals,α-[Pd_(3)L^(1)_(6)](PF_(6))_(12)in the cubic system with I143 m space group,can be isolated from a high-concentration solution of Pd_(3)L^(1)_(6).Interestingly,a mesoporous cage assembled from eight Pd_(3)L^(1)_(6)units with a diameter of 24Åis observed in the crystal structure.For the low-concentration solution of Pd_(3)L^(1)_(6),the rectangular shape crystalsβ-[Pd_(3)L^(1)_(6)](PF_(6))_(12)are obtained,which crystallize in the hexagonal system with P 63/m space group,and display two-dimension packing pattern and one-dimension mesoporous channels(diameter ca.22Å)along the c axis.Moreover,the two supramolecular isomers were used as nanoporous reactors to induce the specific formation of polyiodides with different compositions and shapes as evidenced from single crystal X-ray diffraction studies.These findings provide a reference in targeting functional crystalline mesoporous supramolecular materials from a single complex building unit.

Photoinduced E to Z isomerization of tetraphenylethylene derivatives within organometallic supramolecular assemblies

Isolation of E-1,2-bis(4-bromophenyl)-1,2-diphenyl-ethylene from the E/Z isomer mixture obtained by a Mc Murry coupling reaction and reaction of this isomer with imidazole followed by N-alkylation with n Bu Br and anion exchange yielded the bisimidazolium tetraphenylethylene(TPE)derivative H_(2)-E-1(PF_(6))_(2).The reaction of H_(2)-E-1(PF_(6))_(2) with Ag_(2)O yielded the dinuclear metallarectangle[Ag_(2)(E-1)2](PF_(6))_(2) where the two bis-NHC donors E-1 bridge two silver atoms.Irradiation of[Ag_(2)(E-1)2](PF_(6))_(2) leads to E/Z isomerization of the di-NHC ligand and formation of Z-1 in the mononuclear complex[Ag(Z-1)]PF_(6).Demetallation of the di-NHC ligand with NH_(4)Cl/NH_(4)PF_(6) yielded bisimidazolium salt H_(2)-Z-1(PF_(6))_(2).The unique isomerization of the E-TPE derivative into its Z-isomer via metal complex formation/irradiation/demetallation cannot be achieved by irradiation of the individual imidazolium salt.The emissive properties of the TPE complexes[Ag_(2)(E-1)2](PF_(6))_(2) and[Ag(Z-1)]PF_(6) have been investigated.

A trefoil-shaped macrocycle with [12]-imidazolium cations

A trefoil-like two-dimensional(2D)C_(3v) symmetric organic[12]-imidazolium cation H_(12)-2(PF_(6))_(12) featuring three[4]-imidazolium macrocycles was synthesized in three steps.The reaction of a dodecakis H_(12)-1(PF_(6))_(12) imidazolium salt with Ag_(2)O resulted in the formation of a hexanuclear AgI dodecacarbene assembly[Ag_(6)(1)](PF_(6))_(6).Upon UV irradiation,the photodimerization of the cinnamic ester pendants of[Ag_(6)(1)](PF_(6))_(6) led to the generation of a trefoil-like complex[Ag_(6)(2)](PF_(6))_(6) containing three closed metallacycles.Removal of metal ions allowed for the synthesis of the target molecule.All complexes were fully characterized by NMR spectroscopy(^(1)H,^(13)C{^(1)H}and 2D NMR)and high-resolution electrospray ionization mass spectrometry(HR-ESI-MS).

Hierarchical self-assembly of crown ether based metal-carbene cages into multiple stimuli-responsive cross-linked supramolecular metallogel

The hierarchical self-assembly(HSA) strategy widely utilized in biological systems has been applied in artificial systems to orchestrate small building blocks into complex functional architectures. The non-interfering interactions glue various building blocks together and produce new species with attractive properties. Herein, we functionalized NHC-based assemblies with orthogonal host–guest interaction to fabricate metal-carbene based supramolecular polymer gel. A series of unique crown etherappended cylinder-like trinuclear AuIhexacarbene assemblies [Au_(3)(L)_(2)](PF_(6))_(3)(L=D1–D4, A1–A4) were synthesized from the corresponding trisimidazolium salts H_(3)-L(PF_(6))_(3)(L=D1–D4, A1–A4) in which the N-wingtip of the imidazole moieties were substituted with three identical crown ether groups of different sizes(B15C5, B18C6, B21C7, DB24C8). The gold carbene assembly is able to complex six ammonium salts without disrupting the underlying metal-carbene cylinders. In addition, the supramolecular polymer metallogel featuring a multiple-responsiveness can be formed by using [Au_(3)(A_(4))_(2)](PF_(6))_(3) appended with DB24C8 as the core and bisammonium salt as the cross-linker. The case of introducing orthogonal interaction to NHC moiety by N-wingtip substitution demonstrates the feasibility and the power of such strategy to expand the NHC-based supramolecular system and endow them with novel properties.