Multivalency-Directed Magic-Ring [2](3)Catenane by Olefin Metathesis

Mechanically interlocked molecular handcuffs

The field of mechanically interlocked molecules that employ a handcuff component are reviewed. The variety of rotaxane and catenane structures that use the handcuff motif to interlock different components are discussed and a new nomenclature, distilling diverse terminologies to a single approach, is proposed. By unifying the interpretation of this class of molecules we identify new opportunities for employing this structural unit for new architectures.

Mechanically interlocked molecules that employ a handcuff component provide a pathway to highly unusual structures, a new nomenclature is proposed which helps to identify opportunities for employing this structural unit for new architectures.

Formation of alkyne-bridged ferrocenophanes using ring-closing alkyne metathesis on 1,1'-diacetylenic ferrocenes

Novel alkyne-bridged ferrocenophanes [fc{CO2(CH2) n C≡}2] (2a: n = 2; 2b: n = 3) were synthesized from the corresponding terminal diacetylenic ferrocenes [fc{CO2(CH2) n C≡CH}2] (1a: n = 2; 1b: n = 3) through ring-closing alkyne metathesis (RCAM) utilizing the highly effective molybdenum catalyst [MesC≡Mo{OC(CF3)2CH3}3] (MoF6; Mes = 2,4,6-trimethylphenyl). The metathesis reaction occurs in short time with high yields whilst giving full conversion of the terminal alkynes. Furthermore, the solvent-dependant reactivity of 2a towards Ag(SbF6) is investigated, leading to oxidation and formation of the ferrocenium hexafluoroantimonate 4 in dichloromethane, whereas the silver(I) coordination polymer 5 was isolated from THF solution.

Multicavity macrocyclic hosts

Multicavity macrocyclic hosts are host molecules comprising more than one macrocyclic guest binding components connected through multipoint linkages.

Synthesis of linear [5]catenanes via olefin metathesis dimerization of pseudorotaxanes composed of a [2]catenane and a secondary ammonium salt

[5]Catenanes were synthesized by olefin metathesis dimerization.

A molecular pulley based on a triply interlocked [2]rotaxane

A novel triply interlocked [2]rotaxane was designed and synthesized, which showed pulley-like shuttling motion controlled by acid and base.

Iptycene-derived crown ether hosts for molecular recognition and self-assembly

CONSPECTUS: Synthetic macrocyclic hosts have played key roles in the development of host-guest chemistry. Crown ethers are a class of macrocyclic molecules with unique flexible structures. They have served as the first generation of synthetic hosts, and researchers have extensively studied them in molecular recognition. However, the flexible structures of simple crown ethers and their relatively limited modes of complexation with guests have limited the further applications of these molecules. In recent years, researchers have moved toward fabricating interlocking molecules, supramolecular polymers, and other assemblies with specific structures and properties. Therefore, researchers have developed more complex crown ether-based macrocyclic hosts with multicavity structures and multicomplexation modes that provide more diverse and sophisticated host-guest systems. In this Account, we summarize our research on the synthesis and characterization of iptycene-derived crown ether hosts, their use as host molecules, and their applications in self-assembled complexes. Iptycenes including triptycenes and pentiptycenes are a class of aromatic compounds with unique rigid three-dimensional structures. As a result, they are promising building blocks for the synthesis of novel macrocyclic hosts and the construction of novel self-assembled complexes with specific structures and properties. During the last several years, we have designed and synthesized a new class of iptycene-derived crown ether hosts including macrotricyclic polyethers, molecular tweezer-like hosts, and tritopic tris(crown ether) hosts, which are all composed of rigid iptycene building blocks linked by flexible crown ether chains. We have examined the complexation behavior of these hosts with different types of organic guest molecules. Unlike with conventional crown ethers, the combination of iptycene moieties and crown ether chains provides the iptycene-derived crown ether hosts with complexation properties that differ based on the structure of the guests. The rigid iptycene moieties within these synthetic host molecules both maintain their inherent three-dimensional cavities and generate multicavity structures. The flexible crown ether chains allow the iptycene-derived hosts to adjust their conformations as they encapsulate guest molecules. Moreover, the expanded complexation properties also allow the host-guest systems based on the iptycene-derived crown ethers to respond to multiple external stimuli, resulting in a variety of supramolecular assemblies. Finally, we also describe the construction of mechanically interlocked self-assemblies, molecular switches/molecular machines, and supramolecular polymers using these new host molecules. We expect that the unique structural features and diverse complexation properties of these iptycene-derived crown ether hosts will lead to increasing interest in this field and in supramolecular chemistry overall.

An acid/base switchable and reversibly cross-linkable polyrotaxane

A main chain-type polyrotaxane was fabricated based on the DP24C8/dialkylammonium recognition motif, in which the host could be controllably shuttled on the axle of the polyrotaxane upon acid–base stimuli and reversibly cross-linked via Pd coordination and decoordination.