Synthesis And Post-assembly Modification Of Poly-NHC Macrocycles And Cages

Since the isolation and crystal structure characterization of the first stable N-heterocyclic carbenes（NHCs）by Arduengo et al in 1991,N-heterocyclic carbene ligands have attracted considerable attention.Metal-NHC complexes derived from imidazolium salts and transition metals have found multiple applications in catalysis,photoelectric material,and metallodrugs.The properties of NHCs largely resemble the typical phosphines.NHC ligands have been proven to have additional advantages to the widely utilized phosphine ligands.NHCs can form stronger bonds with metal ions than phosphine ligands.Metal-NHC complexes tend to be stable toward oxygen,moisture,and heat.Therefore,NHCs have been considered to be attractive ancillary ligands and alternative reagents of phosphines.In recent years,the synthesis of poly-NHC ligands（NHC=N-heterocyclic carbene）and the preparation of metallosupramolecular assemblies from such ligands have become a burgeoning area of research.The combination of appropriate metal ions with multitopic NHC ligands has been used for the self-assembly of various metallosupramolecular structures.However,the majority of these structures are homoleptic assemblies featuring only one type of poly-NHC ligand.The preparation of heteroleptic assemblies from at least two different poly-NHC ligands remains very rare.In addition,very few post-assembly modification（PAM）reactions have been used to modify poly-NHC assemblies under solution conditions.Therefore,in this paper,the synthesis and PAM of polycarbene architectures were described.The specific content of each part is as follows:Part 1:Features of Metal-NHC complexes and crown ether were combined in the same molecule,and the synthesis and molecular structures of NHC-bridged mononuclear Ag（I）and Au（I）cationic metallacrown ethers were described.A suitable olefin-bridged dicarbene ligand has been introduced into the metallacycles.Their application as template molecules for photochemical[2+2]cycloaddition reaction is achieved,and the final thioketone derivatives were expected to be used as promising mercury receptors or chemosensors in sewage treatment.Part 2:An alternative synthetic strategy for the preparation of pure organic macrocycles is described.[Ag₂（dicarbene）₂]²⁺metallacycles were employed as templates for the ring-closing metathesis of olefinic C=C double bonds in solution.Subsequent removal of the template silver ions from the RCM product results in polyimidazolium macrocycles.The size of the pure organic macrocycles can be easily tuned by adjusting the length of the bridging units of the dicarbene precursors.Preliminary investigation shows the potential of the macrocycle as iodide sensors.Part 3:Two trisimidazolium salts with identical size,shape and electronically different central backbones were designed and prepared.The formation of the heteroligand assembly is driven by a donor-acceptor interaction between the central six-membered rings present in the two tris-NHC ligands.The study expands to concepts of narcissistic and social self-sorting from classical Werner-type ligands to organometallic NHC chemistry thereby opening new routes for the construction of poly-NHC metal assemblies with increasing complexity.Part 4:The design and fabrication of a series of hexazido-terminated M^I-C_NHC cages were demonstrated.An ESI-MS-based process-tracing study was conducted on the copper-catalyzed‘‘click’’（Cu AAC）reactions without disrupting the integrity of the threedimensional structure,allowing all of the possible intermediates of the PAM process to be observed.The TPE-functionalised cages were found to have aggregation-induced emission,highlighting the excellent versatility of functionalised poly-NHC compounds as a new type of molecular platform for novel applications.Part 5:Some polycarbene cages with large aromaticπ-systems units are inert to photochemical[2+2]cycloaddition.In order to overcome this challange,we demonstrate the highly efficient synthesis of tri-or tetranuclear polycarbene cages in which N-tethered terminal olefins substituents were designed for the subsequent post-synthetic ring-closing olefin metathesis（RCM）reaction.The obtained polyimidazolium organic cages allow in-situ-generated Pt nanoparticles to be encapsulated in the cavity.The photocatalytically driven selective aerobic oxidation of mustard-gas simulant was studied using the as-prepared poly-NHC shell-encapsulated Pt NPs.