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1. Synthesis of linear [7]- and [8]catenanes

   https://doi.org/10.1016/j.xcrp.2023.101767  

   Harlan, Gray H; Tran, Sheila L; Colley, Nathan D; Nosiglia, Mark A; Zhang, Yipei; Barnes, Jonathan C (January 2024, Cell Reports Physical Science)

   Catenanes are a family of mechanically interlocked molecules that consist of molecular rings that can be interlocked to give linear, radial, or cyclic structures. Although chemists have pursued extended linear poly[n]catenane architectures for many decades, there still exists a fundamental gap between the synthesis of well-defined, linear oligomers and that of disperse polymers that are often produced as a mixture of architectures. Here, we report two convergent one-pot syntheses that “zip-tie” together two pre-made [3]catenanes by first using orthogonal metal templation with phenanthroline (Cu(I)) and terpyridine (Fe(II)) ligands. These pre-catenate complexes were subjected to a ring-closing metathesis step to afford discrete, linear [7]- and [8]catenanes. The successful synthesis and isolation of the discrete [7]- and [8]catenanes were confirmed using multiple methods of characterization. Because these record-setting linear [n]catenanes possess open phenanthroline metal-binding sites at each end, further expansion to all-interlocked linear poly[n]catenanes is a realistic proposition. 

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2. A High‐Yielding Active Template Click Reaction (AT−CuAAC) for the Synthesis of Mechanically Interlocked Nanohoops

   https://doi.org/10.1002/anie.202401823  

   May, James H.; Fehr, Julia M.; Lorenz, Jacob C.; Zakharov, Lev N.; Jasti, Ramesh (April 2024, Angewandte Chemie International Edition)

   Abstract Mechanically interlocked molecules (MIMs) represent an exciting yet underexplored area of research in the context of carbon nanoscience. Recently, work from our group and others has shown that small carbon nanotube fragments—[n]cycloparaphenylenes ([n]CPPs) and related nanohoop macrocycles—may be integrated into mechanically interlocked architectures by leveraging supramolecular interactions, covalent tethers, or metal‐ion templates. Still, available synthetic methods are typically difficult and low yielding, and general methods that allow for the creation of a wide variety of these structures are limited. Here we report an efficient route to interlocked nanohoop structures via the active template Cu‐catalyzed azide‐alkyne cycloaddition (AT−CuAAC) reaction. With the appropriate choice of substituents, a macrocyclic precursor to 2,2′‐bipyridyl embedded [9]CPP (bipy[9]CPP) participates in the AT−CuAAC reaction to provide [2]rotaxanes in near‐quantitative yield, which can then be converted into the fully π‐conjugated catenane structures. Through this approach, two nanohoop[2]catenanes are synthesized which consist of a bipy[9]CPP catenated with either Tz[10]CPP or Tz[12]CPP (whereTzdenotes a 1,2,3‐triazole moiety replacing one phenylene ring in the [n]CPP backbone). 

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3. Template‐Directed Synthesis and Isolation of Unimolecular Oligo[ n ]catenanes Using a One‐Pot CuAAC “Click” Reaction Approach

   https://doi.org/10.1002/chem.202501344  

   Tran, Sheila_L; Harlan, Gray_H; Puckowitz, David_E; Wohlstadter, Nathan_E; Zhang, Yipei; Colley, Nathan_D; Barnes, Jonathan_C (May 2025, Chemistry – A European Journal)

   Abstract Within the field of mechanically interlocked molecules, catenanes have garnered much interest in the past few decades due to their chain‐like architecture of interlocked molecular rings. This interest stems from their unique properties and degrees of freedom that are distinct in comparison to traditional molecular architectures, a fact that makes catenanes potentially attractive building blocks in the construction of next‐generation polymeric materials. Most approaches to make unimolecular [n]catenanes are either low yielding or are laborious, often relying on multistep pathways for preparation and purification. Therefore, developing efficient syntheses for [n]catenanes remains an important challenge for chemists. Here, we describe a template‐directed one‐pot approach that overcomes the limitations of multistep syntheses by using simple, symmetrical phenanthroline‐based building blocks and CuAAC “click” chemistry to yield a series of unimolecular [n]catenanes. This methodology relies on simultaneous copper(I)‐based templation and click chemistry, ultimately resulting in a one‐pot synthetic strategy to make either a [2]catenane in high yield (82%) or a batch of well‐defined linear [2]–[5]catenanes (and trace amounts of a [6]catenane) in an 18% overall yield, depending on the rate of addition of the alkyne‐ and azide‐functionalized precursors (i.e., slowly or all at once). Such kinetic control represents a potential pathway toward the preparation of higher‐order [n]catenanes capable of further chain extension using very simple precursors. 

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4. Effect of metallosupramolecular polymer concentration on the synthesis of poly[ n ]catenanes

   https://doi.org/10.1039/D1SC02450G  

   Tranquilli, Marissa M.; Wu, Qiong; Rowan, Stuart J. (January 2021, Chemical Science)

   null (Ed.)

   Poly[ n ]catenanes are a class of polymers that are composed entirely of interlocked rings. One synthetic route to these polymers involves the formation of a metallosupramolecular polymer (MSP) that consists of alternating units of macrocyclic and linear thread components. Ring closure of the thread components has been shown to yield a mixture of cyclic, linear, and branched poly[ n ]catenanes. Reported herein are investigations into this synthetic methodology, with a focus on a more detailed understanding of the crude product distribution and how the concentration of the MSP during the ring closing reaction impacts the resulting poly[ n ]catenanes. In addition to a better understanding of the molecular products obtained in these reactions, the results show that the concentration of the reaction can be used to tune the size and type of poly[ n ]catenanes accessed. At low concentrations the interlocked product distribution is limited to primarily oligomeric and small cyclic catenanes . However, the same reaction at increased concentration can yield branched poly[ n ]catenanes with an ca. 21 kg mol −1 , with evidence of structures containing as many as 640 interlocked rings (1000 kg mol −1 ). 

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5. Kinetically Controlled Synthesis of Rotaxane Geometric Isomers

   https://doi.org/10.1039/D3SC04412B  

   McCarthy, Dillon R.; Xu, Ke; Schenkelberg, Mica; Balegamire, Nils A.; Liang, Huiming; Bellino, Shea; Li, Jianing; Schneebeli, Severin Thomas (January 2024, Chemical Science)

   Geometric isomerism in mechanically interlocked systems — which arises when the axle of a mechanically interlocked molecule is oriented, and the macrocyclic component is facially dissymmetric — can provide enhanced functionality for directional transport and polymerization catalysis. We now introduce a kinetically controlled strategy to control geometric isomerism in [2]rotaxanes. Our synthesis provides the major geometric isomer with high selectivity, broadening synthetic access to such interlocked structures. Starting from a readily accessible [2]rotaxane with a symmetrical axle, one of the two stoppers is activated selectively for stopper exchange by the substituents on the ring component. High selectivities are achieved in these reactions, based on coupling the selective formation reactions leading to the major products with inversely selective depletion reactions for the minor products. Specifically, in our reaction system, the desired (major) product forms faster in the first step, while the undesired (minor) product subsequently reacts away faster in the second step. Quantitative 1H NMR data, fit to a detailed kinetic model, demonstrates that this effect (which is conceptually closely related to minor enantiomer recycling and related processes) can significantly improve the intrinsic selectivity of the reactions. Our results serve as proof of principle for how multiple selective reaction steps can work together to enhance the stereoselectivity of synthetic processes forming complex mechanically interlocked molecules. 

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