Molecular Borromean Rings

Chichak, Kelly S.; Cantrill, Stuart; Pease, Anthony R.; Chiu, Sheng‐Hsien; Cave, Gareth W. V.; Atwood, Jerry L.; Stoddart, J. Fraser

doi:10.1126/science.1096914

Cited by 788 publications

(410 citation statements)

References 29 publications

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“…A series of such dumbbell-shaped molecules (9a-9fÁnPF 6 ), containing n (n = 2, 3, 4, 6, 10, 14, respectively) dialkylammonium centres, were synthesised firstly by reductive amination with derivatives of benzylamine and benzaldehydes, then by protonation of the secondary amines followed by counterion exchange. The clipping reaction of 2,6-dipyridinedicarboxaldehyde and tetraethyleneglycol bis(2-aminophenyl)ether, templated by 9a-9dÁ nPF 6 , gave the thermodynamically stable [3]-, [4]-, [5]-, and [7]rotaxanes (10a-10dÁnPF 6 ) in nearly quantitative yields in MeNO 2 . When n = 10, 4-octyloxypyridinedicarboxaldehyde was used, in a 21-component self-assembly reaction in order to improve the solubility of the product 10eÁnPF 6 .…”

Section: Oligomeric and Polymeric Main-chain [N]rotaxanesmentioning

confidence: 99%

Mechanically bonded macromolecules

et al. 2010

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Mechanically bonded macromolecules constitute a class of challenging synthetic targets in polymer science. The controllable intramolecular motions of mechanical bonds, in combination with the processability and useful physical and mechanical properties of macromolecules, ultimately ensure their potential for applications in materials science, nanotechnology and medicine. This tutorial review describes the syntheses and properties of a library of diverse mechanically bonded macromolecules, which covers (i) main-chain, side-chain, bridged, and pendant oligo/polycatenanes, (ii) main-chain oligo/polyrotaxanes, (iii) poly[c2]daisy chains, and finally (iv) mechanically interlocked dendrimers. A variety of highly efficient synthetic protocols-including template-directed assembly, step-growth polymerisation, quantitative conjugation, etc.-were employed in the construction of these mechanically interlocked architectures. Some of these structures, i.e., side-chain polycatenanes and poly[c2]daisy chains, undergo controllable molecular switching in a manner similar to their small molecular counterparts. The challenges posed by the syntheses of polycatenanes and polyrotaxanes with high molecular weights are contemplated.

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Section: Oligomeric and Polymeric Main-chain [N]rotaxanesmentioning

confidence: 99%

Mechanically bonded macromolecules

et al. 2010

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“…Three distinct reversible processes were used in parallel to enable the creation of metal–organic tetrahedral polycatenanes, namely imine bond formation,2a, 3 metal–ligand coordination,4 and donor–acceptor interactions 5. A tetrahedral cage M 4 L 6 (A; Scheme 1)6 was prepared through the reaction of a suspension (owing to poor solubility) of NDI diamine (6 equiv) with 2‐formylpyridine (12 equiv) and iron(II) bis(trifluoromethane)sulfonimide (4 equiv) in acetonitrile 7…”

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Generation of a Dynamic System of Three‐Dimensional Tetrahedral Polycatenanes

et al. 2013

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Seven of the best: A dynamic combinatorial library of polycatenated tetrahedra was prepared by complexation between a dynamic Fe4L6 tetrahedral cage, constructed from ligands containing an electron‐deficient naphthalenediimide core, and an electron‐rich aromatic crown ether, 1,5‐dinaphtho[38]crown‐10. The highest order species in the library is the tetrahedral [7]catenane.Permissions: WILEY-VCH

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“…A decade ago we introduced reversible metal-imine bond coordination as an effective means of assembling mechanically interlocked molecules under thermodynamic control 34,35 . This provides a mechanism for correcting 'mistakes' in connectivity that occur during the covalent-capture step of mechanical bond formation and has been widely adopted for this purpose ever since 10,29,36,37 .The reaction conditions (ethylene glycol, 170 8C) 31-33 used to form cyclic helicates with tris(bipyridine) ligands are not compatible with imine bond formation. Because the product distribution between cyclic double helicate, linear triple helicate and polymer is a delicate thermodynamic balance that could change significantly depending on the structure of the building blocks, reaction conditions, solvent and the nature and stoichiometry of the metal and anions, we first investigated whether it was possible to translate the self-assembly chemistry of the tris(bipyridine) ligands to an imine system.…”

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A synthetic molecular pentafoil knot

Ayme

Beves

Leigh³

et al. 2011

Nature Chem

394

243

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Knots are being discovered with increasing frequency in both biological and synthetic macromolecules and have been fundamental topological targets for chemical synthesis for the past two decades. Here, we report on the synthesis of the most complex non-DNA molecular knot prepared to date: the self-assembly of five bis-aldehyde and five bis-amine building blocks about five metal cations and one chloride anion to form a 160-atom-loop molecular pentafoil knot (five crossing points). The structure and topology of the knot is established by NMR spectroscopy, mass spectrometry and X-ray crystallography, revealing a symmetrical closed-loop double helicate with the chloride anion held at the centre of the pentafoil knot by ten CH ... Cl -hydrogen bonds. The one-pot self-assembly reaction features an exceptional number of different design elements-some well precedented and others less well known within the context of directing the formation of (supra)molecular species. We anticipate that the strategies and tactics used here can be applied to the rational synthesis of other higher-order interlocked molecular architectures.K nots are important structural features in DNA 1 , are found in some proteins [2][3][4][5] and are thought to play a significant role in the physical properties of both natural and synthetic polymers 6,7 . Although billions of prime knots are known to mathematics 8 , to date the only ones to have succumbed to chemical synthesis using building blocks other than DNA are the topologically trivial unknot (that is, a simple closed loop without any crossing points) and the next simplest knot (featuring three crossing points), the trefoil knot 9,10 . A pentafoil knot-also known as a cinquefoil knot or Solomon's seal knot (the 5 1 knot in Alexander-Briggs notation 11 )-is a torus knot 12 with five crossing points, is inherently chiral, and is the fourth prime knot (following the unknot, trefoil knot and figure-of-eight knot) in terms of number of crossing points and complexity 8,11,12 .Sauvage reported the first molecular knot synthesis 13 , using a linear metal helicate 14 to generate the three crossing points required for a trefoil knot. Although other syntheses of trefoil knots have been reported [15][16][17][18][19][20][21][22] (as have composites of trefoil knots 23 and other molecular topologies such as catenanes [24][25][26][27][28] and Borromean links 29 ), higher-order molecular knots remain elusive. Here, we report on the synthesis of a molecular pentafoil knot that combines the use of metal helicates to create crossover points 30 , anion template assembly to form a cyclic array of the correct size [31][32][33] , and the joining of the metal complexes by reversible imine bond formation 34-37 aided by the gauche effect 38 to make the continuous 160-atom-long covalent backbone of the most complex non-DNA molecular knot prepared to date.So far, attempts to make molecular knots with more than three crossing points by extending the linear helicate strategy of Sauvage to ligands with more coordination sites...

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Molecular Borromean Rings

Cited by 788 publications

References 29 publications

Mechanically bonded macromolecules

Mechanically bonded macromolecules

Generation of a Dynamic System of Three‐Dimensional Tetrahedral Polycatenanes

A synthetic molecular pentafoil knot

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