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'Impossible' rotaxanes, which are constituted by interlocked components without obvious binding motifs, have attracted the interest of the mechanically interlocked molecules (MIMs) community. Within the synthetic efforts reported in the last decades towards the preparation of MIMs, some innovative protocols for accessing 'impossible' rotaxanes have been developed. This short review highlights different selected synthetic examples of 'impossible' rotaxanes, as well as suggests some future directions of this research area. [ABSTRACT FROM AUTHOR]

The interactions between ether naphthotube and a series of dication guests in organic solution were investigated. It was found that ether naphthotube formed stable host‐guest complexes selectively with these guests in a 1 : 1 stoichiometric ratio with association constants ranging from 102 to 106 M−1, which were confirmed by 1H‐NMR spectra and ITC experiments. The host‐guest interactions are driven by enthalpy change as the entropic factors are unfavorable. Positive correlations between ΔH and ΔS have been observed in the host‐guest complexes. Furthermore, the para‐substitution of the guests can significantly affect the binding affinities through a combination of field/inductive and resonance effects by following a linear free energy relationship. Based on the host‐guest complexes composed of ether naphthotube and organic cations, two interlocked [2]rotaxanes were prepared by cationization reaction and Huisgen cycloaddition between the cations and the stopper components. The ether naphthotube‐based host‐guest complexes are useful for creating sophisticated interlocked molecules. [ABSTRACT FROM AUTHOR]

Rotaxanes are interlocked molecules that consist of a macrocycle encircling a stoppered thread. The ability to control relative component positions makes rotaxanes ideal building blocks for constructing functional and responsive molecular machines. Despite the potential of rotaxanes, their challenging synthesis limits their application. One approach to construct rotaxanes is to use an active template synthesis, where a reaction that forms the thread is accelerated in the cavity of a macrocycle. An emerging method of active template synthesis that exploits the ability of crown ether macrocycles to accelerate simple organic reactions is discussed herein. Crown ether active template synthesis (CEATS) permits the rapid and simple synthesis of rotaxanes containing a wide range of functionality. Integrating rotaxane formation with chemical reaction networks has permitted the construction of molecular machines. The simplification of rotaxane synthesis will facilitate their widespread study and application. [ABSTRACT FROM AUTHOR]

We have developed a new approach for the synthesis of "improbable" rotaxanes by using malonate‐centered rotaxanes as interlocked surrogate precursors. Here, the desired dumbbell‐shaped structure can be assembled from two different, completely separate, portions, with the only residual structure introduced from the malonate surrogate being a methylene group. We have synthesized improbable [2]‐ and [3]rotaxanes with all‐hydrocarbon dumbbell‐shaped components to demonstrate the potential structural flexibility and scope of the guest species that can be interlocked when using this approach. [ABSTRACT FROM AUTHOR]

The development of efficient methods for the synthesis of mechanically interlocked compounds is currently considered a major challenge in supramolecular chemistry. Twofold vinylogous fumaramides, a class of conjugated bis(enaminones), successfully achieve the assembly of hydrogen-bonded amide-based rotaxanes, with a templating ability comparable to that of their parent fumaramide-based systems, showcasing full conversions and impressive yields up to 92%. Computational calculations offer a compelling explanation for the remarkable efficiency of these bis(enaminones) in driving the synthesis of unprecedented rotaxanes. The reactivity of these interlocked species was thoroughly investigated, revealing that a one-step double stopper-exchange process can be successfully performed while preserving the mechanical bond. This approach facilitates the formation of controllable rotaxanes, including a three-station molecular shuttle, whose assembly via a clipping methodology is highly unselective. The internal translational motion of this latter species has been successfully controlled in a reversible way by means of a cycloaddition/retrocycloaddition sequence. Many templates for accessing hydrogen-bonded amide-based rotaxanes have resulted in modest yields, but a novel templating method has shown significant promise. Conjugated bis(enaminones) serve as an effective template for the formation of rotaxanes, and a post-synthetic double stopper-exchange method further enables the preparation of versatile and complex rotaxane structures. [ABSTRACT FROM AUTHOR]

Rotaxanes are a type of mechanically interlocked molecules (MIMs), constituted by at least a thread surrounded by a wheel, which are widely employed in the research field of artificial molecular machines. Although applications retaining the integrity of the mechanical bond are usually reported, the dethreading of the components can be crucial to develop some advanced applications. Thus, different dethreading strategies have been reported, and advanced applications which require such a process have turned out to be suitable approaches towards machine‐like operation. This review article covers recent examples of applications of pseudorotaxanes and rotaxanes in which dethreading processes have a key role to accomplish the desired function. [ABSTRACT FROM AUTHOR]

Weakly coordinating anions (WCAs) have attracted much attention in recent years due to their ability to stabilise highly reactive cations. It may well be argued, however, that a profound understanding of what truly defines a WCA is still lacking, and systematic studies to unravel counterion effects are scarce. In this work, we investigate a supramolecular pseudorotaxane formation reaction, subject to a selection of anions, ranging from strongly to weakly coordinating, which not only aids in fostering our knowledge about anion coordination properties, but also provides valuable theoretical insight into the nature of the mechanical bond. We employ state-of-the-art DFT-based methods and tools, combined with isothermal calorimetry and 1 H NMR experiments, to compute anion-dependent Gibbs free association energies Δ G a , as well as to evaluate intermolecular interactions. We find correlations between Δ G a and the anions' solvation energies, which are exploited to calculate physico-chemical reaction parameters in the context of coordinating anions. Furthermore, we show that the binding situation within the (pseudo)rotaxanes can be mostly understood by straight-forward electrostatic considerations. However, quantum-chemical effects such as dispersion and charge-transfer interactions become more and more relevant when WCAs are employed. [ABSTRACT FROM AUTHOR]

Here is reported the synthesis and study of dibenzo‐24‐crown‐8 (DB24C8)‐based [2]‐ and [3]rotaxanes that contain an ammonium as the best molecular station and carbamate moieties as secondary molecular stations. The common post‐interlocking synthesis relies on the aminolysis of the N‐succinimidyl carbonate extremity of an activated though insulated pseudorotaxane. The N‐succinimidyl carbonate‐based thread's extremity proved to be small enough to allow the slow slippage of the DB24C8 around the thread and large enough to allow insulation of the kinetically stable pseudorotaxane. Due to its sensitivity towards amine compounds, the activated carbonate end of the encircled thread allowed post‐interlocking aminolysis‐based conversion into mechanically interlocked rotaxanes by providing the same way the carbamate secondary station for the DB24C8 in the thread backbone. Translation of the DB24C8 along the threaded axle between the two molecular stations was investigated. [ABSTRACT FROM AUTHOR]

Crown ethers are common building blocks in supramolecular chemistry and are frequently applied as cation sensors or as subunits in synthetic molecular machines. Developing switchable and specifically designed crown ethers enables the implementation of function into molecular assemblies. Seven tailor-made redox-active crown ethers incorporating tetrathiafulvalene (TTF) or naphthalene diimide (NDI) as redox-switchable building blocks are described with regard to their potential to form redox-switchable rotaxanes. A combination of isothermal titration calorimetry and voltammetric techniques reveals correlations between the binding energies and redox-switching properties of the corresponding pseudorotaxanes with secondary ammonium ions. For two different weakly coordinating anions, a surprising relation between the enthalpic and entropic binding contributions of the pseudorotaxanes was discovered. These findings were applied to the synthesis of an NDI-[2]rotaxane, which retains similar spectroelectrochemical properties compared to the corresponding free macrocycle. The detailed understanding of the thermodynamic and electrochemical properties of the tailor-made crown ethers lays the foundation for the construction of new types of molecular redox switches with emergent properties.

Abstract Rotaxane building blocks bearing 3,5‐bis(trifluoromethyl) benzenesulfonate (BTBS) stoppers have been efficiently prepared from a pillar[5]arene derivative, 3,5‐bis(trifluoromethyl) benzenesulfonyl chloride (BTBSCl) and different diols, namely 1,10‐decanediol and 1,12‐dodecanediol. The BTBS moieties of these compounds are good leaving groups and stopper exchange reactions could be achieved by treatment with different nucleophiles thus affording rotaxanes with ester, thioether or ether stoppers.

Abstract We present the concept of electrostatic field-driven supramolecular translation within electrically connected plasmonic nano-antennas. The antenna serves as an anchoring point for the mechanically interlocked molecules, as an electrode for the electrostatic field, and as an amplifier of the antenna-enhanced fluorescence. The synthesis of a push–pull donor–π–acceptor chromophore with optical properties aligned to the antenna resonance is described and its immobilization on the surface is demonstrated. Photoluminescence experiments of the chromophore on a gold nano-antenna are shown, highlighting the molecule–antenna coupling and resulting emission intensity increase. The successful synthesis of an electrostatic field-sensitive [2]rotaxane in water is described and the tightrope walk between functionality and water solubility is illustrated by unsuccessful designs. In solution, an enhanced fluorescence quantum yield is observed for the chromophore comprising the mechanically interlocked [2]rotaxane in water and DMSO compared to the reference rod, ideal for future experiments in plasmonic nano-antennas.

The syntheses of two novel mechanically chiral rotaxanes containing urea and squaramide motifs (in yields of 33 % and 22 %, respectively) are presented. 1H NMR spectroscopic titrations reveal shuttling of the macrocycle – detectable by modulation of the expression of mechanical chirality in the NMR spectrum – is possible through the addition of achiral chloride anions, a process which is reversed by the addition of sodium cations. [ABSTRACT FROM AUTHOR]

Stable pillar[5]arene‐containing [2]rotaxane building blocks with pentafluorophenyl ester stoppers have been efficiently prepared on a multi‐gram scale. Reaction of these building blocks with various nucleophiles gave access to a wide range of [2]rotaxanes with amide, ester or thioester stoppers in good to excellent yields. The rotaxane structure is fully preserved during these chemical transformations. Actually, the addition‐elimination mechanism at work during these transformations totally prevents the unthreading of the axle moiety of the mechanically interlocked system. The stopper exchange reactions were optimized both in solution and under mechanochemical solvent‐free conditions. While amide formation is more efficient in solution, the solvent‐free conditions are more powerful for the transesterification reactions. Starting from a fullerene‐functionalized pillar[5]arene derivative, this new strategy gave easy access to a photoactive [2]rotaxane incorporating a C60 moiety and two Bodipy stoppers. Despite the absence of covalent connectivity between the Bodipy and the fullerene moieties in this photoactive molecular device, efficient through‐space excited state interactions have been evidenced in this rotaxane. [ABSTRACT FROM AUTHOR]

Mechanically interlocked molecules (MIMs) have gained attention in the field of catalysis due to their unique molecular properties. Central to MIMs, rotaxanes are highly promising and attractive supramolecular catalysts due to their unique three‐dimensional structures and the flexibility of their subcomponents. This Minireview discusses the use of rotaxanes in organocatalysis and transition‐metal catalysis. [ABSTRACT FROM AUTHOR]

Weakly coordinating anions (WCAs) have attracted much attention in recent years due to their ability to stabilise highly reactive cations. It may well be argued, however, that a profound understanding of what truly defines a WCA is still lacking, and systematic studies to unravel counterion effects are scarce. In this work, we investigate a supramolecular pseudorotaxane formation reaction, subject to a selection of anions, ranging from strongly to weakly coordinating, which not only aids in fostering our knowledge about anion coordination properties, but also provides valuable theoretical insight into the nature of the mechanical bond. We employ state-of-the-art DFT-based methods and tools, combined with isothermal calorimetry and 1H NMR experiments, to compute anion-dependent Gibbs free association energies ΔGa, as well as to evaluate intermolecular interactions. We find correlations between ΔGa and the anions’ solvation energies, which are exploited to calculate physico-chemical reaction parameters in the context of coordinating anions. Furthermore, we show that the binding situation within the (pseudo)rotaxanes can be mostly understood by straight-forward electrostatic considerations. However, quantum-chemical effects such as dispersion and charge-transfer interactions become more and more relevant when WCAs are employed.

Three new hydroxyl-functionalized secondary benzyl ammonium salts were synthesized and complexed with dibenzo-24-crown-8. Three [2]semirotaxanes and then their two [2]rotaxanes each with two different stoppers were prepared successfully by reactions of the hydroxyl groups with bulky reagents. X-ray analysis of a single crystal of a [2]semirotaxane confirmed its structure. The formation of the [2]semirotaxanes can be reversibly controlled by adding KPF6 and 18-crown-6 sequentially. These new unsymmetrical [2]rotaxanes afford a way to prepare planar chiral rotaxanes and related supramolecular systems. [ABSTRACT FROM AUTHOR]

Selective monofunctionalization of substrates with distant, yet equally reactive functional groups is difficult to achieve, as it requires the second functional group to selectively modulate its reactivity once the first functional group has reacted. We now show that mechanically interlocked catalytic rings can effectively regulate the reactivity of stoppering groups in rotaxanes over a distance of about 2 nm. Our mechanism of communication is enabled by a unique interlocked design, which effectively removes the catalytic rings from the substrates by fast dethreading as soon as the first reaction has taken place. Our method not only led to a rare example of selective monofunctionalization, but also to a "molecular if function". Overall, the study presents a way to get distant functional groups to communicate with each other in a reaction‐history‐dependent manner by creating linkers that can ultimately perform logical operations at the molecular level. [ABSTRACT FROM AUTHOR]

Rotaxane building blocks bearing 3,5‐bis(trifluoromethyl) benzenesulfonate (BTBS) stoppers have been efficiently prepared from a pillar[5]arene derivative, 3,5‐bis(trifluoromethyl) benzenesulfonyl chloride (BTBSCl) and different diols, namely 1,10‐decanediol and 1,12‐dodecanediol. The BTBS moieties of these compounds are good leaving groups and stopper exchange reactions could be achieved by treatment with different nucleophiles thus affording rotaxanes with ester, thioether or ether stoppers. [ABSTRACT FROM AUTHOR]

Heterobifunctional rotaxanes serve as efficient catalysts for the addition of malonates to Michael acceptors. We report a series of four different heterobifunctional rotaxanes, featuring an amine‐based thread and a chiral 1,1′‐binaphthyl‐phosphoric‐acid‐based macrocycle. High‐level DFT calculations provided mechanistic insights and enabled rational catalyst improvements, leading to interlocked catalysts that surpass their non‐interlocked counterparts in terms of reaction rates and stereoselectivities. [ABSTRACT FROM AUTHOR]

The preparation of chiral mechanically interlocked molecules has experienced a great development in the last decade, showing a wide range of applications, including catalysis and molecular machinery. New types of chirality have emerged as a consequence of the mechanical bond, such as mechanically planar chirality, which can exist even when both components are achiral. The mechanically planar chirality in such interlocked structures is usually created during the assembly of the rotaxane architecture. Recently, Tian, Zhu and coworkers decoupled the creation of mechanically planar chirality and assembly of the mechanical bond by using a desymmetrizing Suzuki‐Miyaura reaction of a series of mechanically prochiral rotaxanes. This strategy afforded the target chiral interlocked products showing up to 96.5 : 3.5 enantiomeric ratio. [ABSTRACT FROM AUTHOR]

This minireview overviews rotaxanes and pseudorotaxanes containing cyclodextrins (CDs) as the rotor component. Since CDs interact with molecules, e.g., hydrophobic compounds of the size and shape matching their cavity, to form inclusion complexes in aqueous media, CDs are an important class of macrocyclic compounds as rotor components of rotaxanes and pseudorotaxanes. Research on CD‐based rotaxanes has begun with the synthesis of rotaxanes from low molecular weight axis molecules and then developed into the construction of molecular machines and polyrotaxanes. Recently, the research has further developed into macroscopic functional materials, e.g., slide‐ring gels, macromolecular assemblies, self‐healing materials, and soft actuators. In the present article, typical examples of CD‐based rotaxanes and pseudorotaxanes are described; synthesis of rotaxane and construction of molecular machine are described in Section 2, synthesis of polyrotaxanes is dealt with in Section 3, and development of macroscopic functional materials based on rotaxane structure is discussed in Section 4. [ABSTRACT FROM AUTHOR]

The present study discusses the crystalline packing formation of several [2]rotaxanes with Leigh‐type tetralactam macrocycle bearing different threads. The presence of solvent molecules in some structures are also addressed to shed some light on this matter. Additionally, the degree of similarity between supramolecular structures of rotaxanes was discussed using similarity indices. For this, new descriptors and crystallization mechanisms, which were proposed in terms of contact area and stabilization energy, were carried out to evaluate the rotaxane molecules. It was possible to observe similar general stages of crystallization dominated by the formation of 1D‐blocks and, in fewer cases, by dimers in the first stage of nucleation. The preference for the formation of 1D nuclei resides in the large contact area and complementarity involved in the large set of interactions between the rotaxanes at the earliest stages of crystallization. In this context, it was possible to propose when solvent molecules are trapped between the rotaxanes during crystal formation. Therefore, a unique example of a rotaxane whose topology favored the entrapment of water molecules between rotaxanes during the first stage of the crystallization process is presented. Crystallization mechanisms showed to be a valuable asset in the supramolecular investigation of rotaxanes in the crystalline state. [ABSTRACT FROM AUTHOR]

Pillar[5]arene‐containing [2]rotaxanes have been efficiently prepared under solvent‐free conditions. Specifically, solid‐to‐solid ball‐milling of primary or secondary amine reagents with the inclusion complex resulting from the association of dodecanedioyl dichloride and a pillar[5]arene derivative provided the corresponding diamide [2]rotaxanes in good to excellent yields. Importantly, [2]rotaxanes difficult or even impossible to prepare under classical reaction conditions in solution, are now easily obtained. [ABSTRACT FROM AUTHOR]

The thermally and photochemically induced dethreading of a series of pseudo[2]rotaxanes bearing tetraalkyl‐substituted fumaramide axles and polyamide macrocycles is reported herein. The length of the alkyl chains at the ends of the thread, the void size, and flexibility of the macrocycle and the intercomponent interactions are critical for a satisfactory dethreading process. 1H NMR kinetic experiments were carried out in order to calculate the rate constants of the thermal dethreading processes and stabilities of the rotaxanes, by comparing with the similar data for the deslipping of the succinamide surrogates. The deslipping reaction occurs faster with the fumaramide systems than succinamide ones. The incorporation of adamantane moieties into the polyamide macrocycle drastically slowed down the disconnecting process. Furthermore, interlocked systems with dipropylamino groups as stoppers experienced a rapid dethreading when irradiated under UV‐light, a process triggered by the fumaramide–maleamide isomerization. In this case, the n‐propyl groups are not bulky enough to keep together both components as the number of hydrogen bonds between thread and macrocycle is halved in the maleamide systems. [ABSTRACT FROM AUTHOR]

The activation energies of the shuttling of [2]rotaxanes with various N‐arylpyrrole moieties were determined by variable temperature (VT) 1H NMR experiments. The value provided a new quantitative scale for the estimation of the steric bulk of the substituents. The rigidity and the electronic effect of the substituents, which could inadequately influence the estimation of the steric bulk, were minimized in the method we presented. [ABSTRACT FROM AUTHOR]

Summary of main observation and conclusion: Rotaxane is a kind of classic supramolecule, which is usually constructed from a number of macrocycles and one axis molecule. Herein, we have expanded the supramolecular structure of [n]rotaxane to offer a precise definition of (pseudo)[n,m]rotaxane for accurately describing the two kinds of (pseudo)rotaxanes structures, which are self‐assembled from cucurbit[7/8]uril (CB[7/8]) and viologen‐naphthalene derivative, respectively. Furthermore, these CB‐based pseudorotaxanes exhibit varied photophysical properties, stimuli‐responsive behavior triggered by competitive guest, and self‐sorting behavior. A precise definition of (pseudo)[n,m]rotaxane is proposed for accurately describing the two kinds of (pseudo)rotaxanes structures, which are self‐assembled from cucurbit[7/8]uril (CB[7/8]) and viologen‐naphthalene derivative, respectively. [ABSTRACT FROM AUTHOR]

Chiral interlocked molecules in which the mechanical bond provides the sole stereogenic unit are typically produced with no control over the mechanical stereochemistry. Here we report a stereoselective approach to mechanically planar chiral rotaxanes in up to 98:2 d.r. using a readily available α‐amino acid‐derived azide. Symmetrization of the covalent stereocenter yields a rotaxane in which the mechanical bond provides the only stereogenic element. Taking (stereo)control of the mechanical bond: A stereoselective approach to mechanically planar chiral rotaxanes in up to 98:2 d.r. using a readily available α‐amino acid‐derived azide is reported. Symmetrization of the covalent stereocenter yields a rotaxane in which the mechanical bond provides the only stereogenic element in excellent enantiopurity. [ABSTRACT FROM AUTHOR]

Abstract: This work reports on the use of molecular translocators to capture a dibenzo‐24‐crown‐8 (DB24C8) and then release it onto targeted molecular axles to afford, after removal of the translocator, [2]rotaxanes that do not hold any template site. Various translocators were studied and successfully aided the synthesis, with more or less efficacy, of [2]rotaxanes of different lengths. During the releasing step, the DB24C8 macrocycle shuttles along the thread, and the localization of the macrocycle might be driven by steric repulsion on the translocator part and/or electronic attraction of the targeted part of the axle to be encircled, which depends on both the nature of the translocator and the targeted thread to be encircled. [ABSTRACT FROM AUTHOR]

A mechanical bond serves as a distinctive approach for harnessing the most beneficial features of both covalent and supramolecular chemistries, offering stability and structural adaptability owing to its unique dynamic nature. Molecules formed by mechanical bonding, known as mechanically interlocked molecules (MIMs) including catenanes, rotaxanes, and knots have opened new possibilities. Notably, the introduction of mechanically interlocked structures into polymers has led to the emergence of novel polymeric materials referred to as mechanically interlocked polymers (MIPs), such as polyrotaxanes and polycatenanes. The interlocked nature of these architectures can lead to particular conformational freedom and high mobility of their components, resulting in exceptional properties, such as ultra-stretchability, toughness, and immediate recoverability. These properties have found potential applications in diverse fields, including the development of tough hydrogels, scratch-resistant coatings, smart actuators, and batteries. Recent years have witnessed a surge in the synthesis and investigation of a diverse array of rotaxane-based MIPs, an essential class that has enabled researchers to begin grasping the impact of incorporating mechanical bonds within polymer structures, and of their mobility, on material properties. In this review, an overview of the dynamics of ring-containing polymers is presented. The review encompasses macromolecular rotaxanes, polyrotaxanes, and slide-ring networks, including the role of ring mobility in shaping the dynamics and properties of rotaxane polymers. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Operating molecular machines are based on switchable systems whose components can be set in motion in a controllable fashion. The presence of nonsymmetrical elements is a mandatory requirement to obtain and demonstrate the unidirectionality of motion. Calixarene‐based macrocycles have proved to be very efficient hosts in the design of oriented rotaxanes and of pseudorotaxanes with strict control over the direction of complexation. A series of two‐station rotaxanes based on bipyridinium–ammonium axles was synthesized and characterized. A recently reported supramolecularly assisted strategy for the synthesis of different orientational isomers was exploited, and the ammonium unit was identified as a proper secondary station for the calixarene. Displacement of the macrocycle was triggered by electrochemical reduction of the bipyridinium primary station, and it was shown that the shuttling is influenced both by the length of the chain of the axle component and by the position of the secondary station with respect to the calixarene rims. [ABSTRACT FROM AUTHOR]

A pillar[5]arene-containing rotaxane building block bearing exchangeable stoppers has been prepared in multigram scale quantities with high yields from the reaction of 2,4-dinitrophenol (DNP) with the inclusion complex resulting from the association of dodecanedioyl chloride with 1,4-diethoxypillar[5]arene. Stopper exchange reactions have been achieved by treatment of the resulting DNP diester with various amines through an addition-elimination mechanism preventing the unthreading of the axle component during the reaction and thus preserving the [2]rotaxane structures. The resulting diamide [2]rotaxane derivatives have thus been obtained in good to excellent yields. Importantly, [2]rotaxanes difficult or impossible to prepare by direct introduction of the two stoppers in a single synthetic step are now easily available. [ABSTRACT FROM AUTHOR]

New results are presented on the multicomponent supramolecular synthesis of pseudo[1]rotaxanes, achieved by designing pairs of structurally matching N‐monoalkyl‐4,4'‐bipyridinium/2,7‐diazapyrenium‐based ligands having complementary π‐donor/acceptor features, and intended to self‐assemble into the targeted supramolecules by following integrative self‐sorting processes. In all the studied cases, it was found that the envisioned species, characterized by NMR spectroscopy and MS spectrometry, arise as the main products of the self‐assembly in aqueous media by using palladium(II)/platinum(II) metal centers as the guiding force. Crucially, we have also found that by improving the π‐donor/acceptor properties of the matching pairs of ligands (L4 and L5), the integrative self‐sorting processes prevail even in the absence of metallic ions to afford the heterodimeric species with an association constant being 756±43 M−1. [ABSTRACT FROM AUTHOR]

Abstract: [2] and [3] hybrid rotaxanes are reported based on {Ti7M} rings (M is a trivalent metal such as FeIII or GaIII). NMR studies show that [2]rotaxanes can act as molecular shuttles, while EPR studies of [3]rotaxanes show weak interactions between the paramagnetic components of the supramolecular assemblies. [ABSTRACT FROM AUTHOR]

We present here the design and synthesis of a series of multicomponent supramolecular architectures, structures formed by the PdII/PtII-directed integrative social self-sorting in aqueous media of pairs of complementary N-monoalkyl-4,4′-bipyridinium/2,7-diazapyrenium-based ligands. Out of the different potential outcomes of the processes, we have found out how the designed systems selectively enhance the production of pseudo[ 1]rotaxanes, hermaphroditic host-guest aggregates that maximize the strength of the occurring π- π, C−H⋅⋅⋅ π, and hydrophobic interactions, as well as the number of those interactions per receptor. It is also demonstrated how both integrative social and narcissistic PdII-directed self-sorting can occur orthogonally and concomitantly for this type of ditopic ligands. [ABSTRACT FROM AUTHOR]

Macromolecular [2]rotaxanes comprising a polymer axle and crown ether wheel were synthesized to evaluate the effect of component mobility on the properties of the axle polymer, especially its crystallinity. Living ring-opening polymerization of δ -valerolactone with a pseudorotaxane initiator with a hydroxy group at the axle terminus was followed by end-capping with a bulky isocyanate. This yielded macromolecular [2]rotaxanes (M2Rs) possessing polyester axles of varying molecular weights. The crystallinity of the axle polymers of two series of M2Rs, with either fixed and movable components, was evaluated by differential scanning calorimetry. The results revealed that the effect of component mobility was significant in the fixed and movable M2Rs with a certain axle length, thus suggesting that the properties of the axle polymer depend on the mobility of the polyrotaxane components. [ABSTRACT FROM AUTHOR]

We report the stepwise assembly of supramolecular daisy chain rotaxanes (DCR) made of double-stranded DNA: Small dsDNA macrocycles bearing an axle assemble into a pseudo-DCR precursor that was connected to rigid DNA stoppers to form DCR with the macrocycles hybridized to the axles. In presence of release oligodeoxynucleotides (rODNs), the macrocycles are released from their respective hybridization sites on the axles, leading to stable mechanically interlocked DCRs. Besides the expected threaded DCRs, certain amounts of externally hybridized structures were observed, which dissociate into dumbbell structures in presence of rODNs. We show that the genuine DCRs have significantly higher degrees of freedom in their movement along the thread axle than the hybridized DCR precursors. Interlocking of DNA in DCRs might serve as a versatile principle for constructing functional DNA nanostructures where the movement of the subunits is restricted within precisely confined tolerance ranges. [ABSTRACT FROM AUTHOR]

The development of efficient and selective organic synthetic approaches for complex molecules has garnered significant attention due to the need for precise control over molecular structures and functions. Rotaxanes, a type of mechanically interlocked molecules (MIMs), have shown promising applications in various fields including sensing, catalysis, and material science. However, the highly selective synthesis of oligo[n]rotaxanes (mostly n≥3) through controlling host‐guest complexation and supramolecular threading assembly process still remains an ongoing challenge. In particular, the utilization of two‐dimensional (2D) macrocycles with structural shape‐persistency for the synthesis of oligo[n]rotaxanes is rare. In this concept, research on cooperatively threaded host‐guest complexation with hydrogen‐bonded (H‐bonded) aramide macrocycles and selective synthetic protocols of oligo[n]rotaxanes has been summarized. The high efficiency and selectivity in synthesis are ascribed to the synergistic interplay of multiple non‐covalent bonding interactions such as hydrogen bonding and intermolecular π–π stacking of macrocycles within the unique supramolecular structure of threaded host‐guest complexes. This review focuses on the latest progress in the concepts, synthesis, and properties of H‐bonded aramide macrocycle‐based oligorotaxanes, and presents an in‐depth outlook on challenges in this emerging field. [ABSTRACT FROM AUTHOR]

Oriented rotaxanes composed of tris( N-phenylureido)calix[6]arene wheel 1 and N, N′-dialkyl viologen-based axles were synthesized in which the span between the diphenylacetyl stoppers at the wheel upper and lower rim and the bis-pyridinium cation portion of the axial component is different in length. A sequential synthetic pathway was followed to achieve the selective formation of orientational isomers, wherein the short (or long) chain of the axle is positioned either on the upper or lower rim of the wheel. The synthetic strategy adopted involves the upper rim threading of axles 2a- c to yield oriented pseudorotaxanes, which were then stoppered in situ. The structure of the oriented rotaxanes was unravelled by detailed NMR experiments, and their spectroscopic, electrochemical and dynamic properties were investigated by UV/Vis, cyclic voltammetry, and EPR measurements. The results were compared with those of their symmetric counterparts. [ABSTRACT FROM AUTHOR]