Synthesis Of Rotaxanes Research Articles

ChemInform Abstract: The Application of CuAAC “Click” Chemistry to Catenane and Rotaxane Synthesis

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ChemInform Abstract: High Yielding and Practical Synthesis of Rotaxanes by Acylative End-Capping Catalyzed by Tributylphosphine.

A pseudorotaxane was prepared from dibenzo-24-crown-8 and a dibenzylammonium salt possessing dimethylphenyl and hydroxy groups at the both termini. Acylation of the pseudorotaxane by 3,5-dimethylbenzoic anhydride in the presence of tributylphosphine afforded corresponding rotaxane in 90% yield. Various rotaxanes were readily synthesized in excellent yields by this method.

Recent advances in the synthesis of ammonium-based rotaxanes.

The number of synthetic methods enabling the preparation of ammonium-based rotaxanes has increased very rapidly in the past ten years. The challenge in the synthesis of rotaxanes results from the rather weak interactions between the ammonium-containing rod and the crown ether macrocycle in the pseudorotaxane structure that rely mostly on O·H hydrogen bonds. Indeed, no strong base or polar solvent that could break up H-bonding can be used during the formation of rotaxanes because the two components will separate as two distinct entities. Moreover, most of the reactions have to be performed at room temperature to favor the formation of pseudorotaxane in solution. These non-trivial prerequisites have been taken into account to develop efficient reaction conditions for the preparation of rotaxanes and those are described in detail along this review.

Synthesis of a molecular trefoil knot by folding and closing on an octahedral coordination template

The advent of template-directed synthesis has provided access to a range of new interlocked molecular architectures. Although many syntheses of molecular catenanes and rotaxanes have been reported, molecular knots are a class of molecules with topologically non-planar graphs that are rather rare. Here we report a synthetic strategy for the preparation of a molecular trefoil knot from a flexible bipyridine oligomer and a zinc(II) octahedral coordination template. The oligomer folds into a stable open-knot conformation in the presence of the template, and trapping of this arrangement through esterification or ring-closing metathesis produces the closed-knot complex. Subsequent removal of the template from the metathesis product results in a molecular trefoil knot.

The application of CuAAC ‘click’ chemistry to catenane and rotaxane synthesis

The copper(I)-catalysed azide-alkyne cycloaddition (the CuAAC 'click' reaction) is proving to be a powerful new tool for the construction of mechanically interlocked molecular-level architectures. The reaction is highly selective for the functional groups involved (terminal alkynes and azides) and the experimental conditions are mild and compatible with the weak and reversible intermolecular interactions generally used to template the assembly of interlocked structures. Since the CuAAC reaction was introduced as a means of making rotaxanes by an 'active template' mechanism in 2006, it has proven effective for the synthesis of numerous different types of rotaxanes, catenanes and molecular shuttles by passive as well as active template strategies. Mechanistic insights into the CuAAC reaction itself have been provided by unexpected results encountered during the preparation of rotaxanes. In this tutorial review we highlight the rapidly increasing utility and future potential of the CuAAC reaction in mechanically interlocked molecule synthesis.

共有結合を経由するロタキサンの合成とその機能

Crownophanes which were used as rotor molecules in this review were prepared via tandem Claisen rearrangement (TCR). Primary amines having a bulky end group were also prepared to use as a part of axle molecules. Using crownophanes, a new method to prepare rotaxane systems has been developed. That is, we call it “a method via covalent bond formation”. This method contains two processes, esterification and aminolysis. The first step is the reaction of hydroxy group of macrocyclic compounds (crownophanes) with acid chloride, and the second step is the reaction of the ester produced with amine having a bulky end group. This method successfully gave [1]-, [2]-, and [3]rotaxanes in moderate yields. In the fluorescence spectrum, the efficient energy transfer from rotor molecules to end anthryl group of axle molecules was observed in the [n]rotaxanes. In the presence of lithium ion, the energy transfer occurred very efficiently, but not in the presence of other ions. Chiral recognition for phenylalaninol was also observed using achiral rotaxane having asymmetrical rotor and axle. We also reported that our rotaxanes could attach on the gold surface. We successfully observed the single rotaxanes by atomic force microscope. Thus, we report here that the rotaxane synthesis via covalent bond formation is successfully performed to give many kinds of rotaxanes starting from crownophanes which were prepared via TCR.

Ligand-assisted nickel-catalysed sp3–sp3 homocoupling of unactivated alkyl bromides and its application to the active template synthesis of rotaxanes

An efficient, mild and operationally simple Ni-catalysed sp3-carbon-to-sp3-carbon homocoupling of unactivated alkyl bromides has been developed and utilised in the active metal template synthesis of an alkyl chain axle [2]rotaxane. The key to the transformation is the use of tridentate nitrogen-donor-atom (terpy or pybox derived) ligands which inhibit competing β-hydride elimination of alkyl-Ni intermediates.

Giving a Use to Triazoles

Huisgen 1,3-dipolar cycloadditions of azides and primary alkynes are broadly used because of their high yield, functional group compatibility, and mild conditions. However, the resulting triazole rings (like the one in molecule 1) are rarely included in the resulting molecules with a purpose other than being a covalent linker. The authors take advantage of the known interaction between halides and alkylated triazoles (Y. J. Li et al. Chem. Commun. 2007, 2692; triazoliums, like 2) to template the synthesis of rotaxanes (3).

Molecular Recognition between the Constituents of a Pseudorotaxane Studied by Scanning Tunneling Microscopy

The formation of intermolecular complexes of two large molecules—a macrocycle and a semiaxle, which have been used in templated syntheses of amide rotaxanes—was studied by scanning tunneling microscopy (STM) and density functional theory (DFT). These experiments mimic the so-called “threading process”, which is based on intermolecular recognition and which is essential for the rotaxane synthesis in solution. First, ordered monolayers of a tetralactam macrocycle (TLM), i.e. the rotaxane wheel, are prepared on a Au(111) surface. Then, semiaxles (SA) are deposited on top of these ordered TLM layers at ca. 140 K. In solution, the SA molecule threads into the TLM cavity by formation of three hydrogen bonds between the amide groups of both molecules. On the Au(111) surface, the scenario is similar, although different in detail due to geometric restrictions given by the underlying Au(111) surface and conformational energy barriers due to the confinement of the TLM geometry in the ordered monolayer structure. Thr...

Getting Harder: Cobalt(III)-Template Synthesis of Catenanes and Rotaxanes

The synthesis of catenanes and rotaxanes using the hard trivalent transition metal ion cobalt(III) as a template is reported. Tridentate dianionic pyridine-2,6-dicarboxamido ligands, each with two terminal alkene groups, coordinate Co(III) in a mutually orthogonal arrangement such that entwined or interlocked molecular architectures are produced by ring-closing olefin metathesis. Double macrocyclization of two such ligands bound to Co(III) afford a non-interlocked "figure-of-eight" complex in 42% yield, the structure determined by X-ray crystallography. Preforming one macrocycle and carrying out a single macrocyclization of the second bis-olefin with both ligands attached to the Co(III) template led to the isomeric [2]catenate in 69% yield. The mechanically interlocked structure was confirmed by X-ray crystallography of both the Co(III) catenate and the metal-free catenand. A Co(III)-template [2]rotaxane was assembled in 61% yield by macrocyclization of the bis-olefin ligand about an appropriate dianionic thread. For both catenanes and rotaxanes, removal of the metal ion via reduction under acidic conditions to the more labile Co(II) gave neutral interlocked molecules with well-defined co-conformations stabilized by intercomponent hydrogen bonding.

An Approach to Thermodynamically Controlled Supramolecular Assembly Possessing an Integral Locking Mechanism

A general approach for thermodynamically controlled molecular assembly employing carbonyl addition chemistry is exemplified with a prototypical rotaxane synthesis. Recognition-driven assembly of the rotaxane proceeds under conditions of mild base catalysis, while subsequent treatment with catalytic acid triggers a dehydrative locking mechanism and fixes the evolved molecular architecture in place.

Synthesizing interlocked molecules dynamically

As the complexity of mechanically interlocked molecular architectures increases, it is important to understand the underlying principles, such as molecular recognition and self-assembly processes, that govern the practice of template-directed synthesis necessary to create these particular compounds. In this review, we explain the importance of dynamic processes in the synthesis of mechanically interlocked compounds. We show how many different dynamic covalent bonds have been used in the synthesis of rotaxanes, catenanes, and other higher-order mechanically interlocked compounds, with the goal of revealing the state of the art in dynamic covalent chemistry.

Active metal template synthesis of rotaxanes, catenanes and molecular shuttles

Active metal template synthesis is a powerful new strategy for the construction of rotaxanes, catenanes and other mechanically interlocked molecular structures. The key feature is that the metal plays a dual role during the assembly of the interlocked architecture, acting as both a template for entwining or threading the components and as a catalyst for capturing the interlocked final product by covalent bond formation. Unlike traditional "passive" metal template methods to rotaxanes and catenanes, permanent recognition motifs are not required on each of the components to be interlocked (i.e., the assembly can be traceless) and the template can often be used in sub-stoichiometric quantities. Since its inception in 2006, a rapidly growing number of different metal-catalysed reactions have proven suitable for the active metal template synthesis of both rotaxanes and catenanes, including the copper(i)-catalysed terminal alkyne-azide cycloaddition (the CuAAC "click" reaction), palladium- and copper-catalysed alkyne homocouplings and heterocouplings, and palladium-catalysed oxidative Heck couplings and Michael additions. In addition to simple rotaxanes and catenanes, the synthetic strategy has been used to construct switchable molecular shuttles with weak intercomponent interactions (a requirement for fast shuttling) and to provide insight into the mechanisms of transition metal-catalysed reactions. In this tutorial review we highlight the utility and potential of the early examples of the active metal template strategy in mechanically interlocked molecule synthesis.

Design and synthesis of porphyrin-containing catenanes and rotaxanes

Catenanes and rotaxanes containing porphyrin subunits have become popular synthetic targets because of the large variety of available synthetic strategies including the coordination chemistry of metallated porphyrins, coupled with the many attractive physical properties of porphyrins. This tutorial review outlines various synthetic approaches and templating strategies that have been used to prepare a range of mechanically interlocked architectures that incorporate porphyrins as fundamental subunits either grafted onto macrocycles or as stoppers. These species are of interest in relation to recreating natural processes such as the photosynthetic apparatus or enzyme binding sites.

Discovery and early development of squaraine rotaxanes.

The chemical and photophysical properties of a fluorescent squaraine dye are greatly enhanced when it is mechanically encapsulated inside a tetralactam macrocycle. This feature article describes the synthesis, structure, and photophysical performance of first-generation squaraine rotaxanes, and shows how they can be used as fluorescent imaging probes and chemosensors.

リング・ストッパー成分結合型プレロタキサンのアミノリシスによる新規ロタキサン合成法-プレロタキサンの置換基と反応溶媒による生成物選択的反応加速効果-

リング・ストッパー成分結合型プレロタキサンのアミノリシスによる新規ロタキサン合成法-プレロタキサンの置換基と反応溶媒による生成物選択的反応加速効果-

Solvent‐Free Synthesis of the Smallest Rotaxane Prepared to Date

Solvent‐Free Synthesis of the Smallest Rotaxane Prepared to Date

Active Template Synthesis of Rotaxanes and Molecular Shuttles with Switchable Dynamics by Four‐Component PdII‐Promoted Michael Additions

Mach's mit Michael: Wiederholte Palladium(II)-vermittelte konjugierte 1,4-Additionen verknüpfen vier Komponenten in einem Eintopfverfahren in 99 % Ausbeute zu Rotaxanen (siehe Struktur) und molekularen Shuttles. Bei diesem Prozess handelt es sich um die erste Reaktion mit einem aktiven Templat, bei der das Templatmotiv im verzahnten Produkt erhalten bleibt.

Active Template Synthesis of Rotaxanes and Molecular Shuttles with Switchable Dynamics by Four‐Component PdII‐Promoted Michael Additions

Taking the Michael: Rotaxanes (see structure) and molecular shuttles are prepared in up to 99 % yield by successive PdII-promoted 1,4-conjugate additions in a one-pot four-component assembly process. This process represents the first active template reaction in which the template motif is retained in the interlocked product.

Toward Multistation Rotaxanes Using Metalloporphyrin Coordination Templating

This paper describes some approaches toward the templated synthesis of rotaxanes incorporating strapped metalloporphyrin moieties as the shuttle unit, with the thread component containing both a neutral diimide "station" and a functionalized pyridine moiety, the latter acting not only as a template but also as a second binding motif. In the first instance, the use of appropriately 3,5-difunctionalized pyridine esters and naphthoquinol-strapped rhodium(III) chloride porphyrins in a stoppering approach to rotaxanes produced only unlinked components: the flexibility of the strap allowed sufficient room for the potential thread unit to bind on the same face of the porphyrin as the strap, while not being interlocked through it. An alternative strategy involving a 1,3-dipolar cycloaddition reaction (a "click" reaction) between azides and alkynes, producing triazole linkers in the thread component of rotaxanes, was more successful. Both porphyrinic (zinc, free base, and rhodium(III) derivatives) and crown ether rotaxanes were successfully produced, with multifunctional (triazole and naphthodiimide) thread units. The potential for molecular motion through the use of stimuli such as acid, solvent, and competing ligands was investigated, with limited success. The same cycloaddition methodology was extended to pyridine-templated analogues of the thread components in the Rh(III)-strapped porphyrins, but again, only unlinked thread and porphyrin shuttle units were produced.