A Simple General Ligand System for Assembling Octahedral Metal–Rotaxane Complexes

Hogg, Louise; Leigh, David A.; Lusby, Paul J.; Morelli, Alessandra; Parsons, Simon; Wong, Jenny K. Y.

doi:10.1002/anie.200353186

Cited by 122 publications

(49 citation statements)

References 45 publications

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“…To have the potential to covalently connect the organic ligands to form a knot, we envisioned replacing two of the three bipyridine groups in Lehn's original building blocks with formylpyridine groups, then use their reversible reaction with amines to form imines and generate tris(bidentate) ligand strands. 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 .…”

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“…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][35][36][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.…”

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A synthetic molecular pentafoil knot

Ayme

Beves

Leigh³

et al. 2011

Nature Chem

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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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A synthetic molecular pentafoil knot

Ayme

Beves

Leigh³

et al. 2011

Nature Chem

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394

243

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“…First, dialdehyde A is well suited to generate multinuclear Cu I helical structures such as 1 and 2, and poorly suited to generate mononuclear complexes, despite the entropic driving force favoring complexes of lower nuclearity. A diimine formed by A may readily occupy three coplanar meridional coordination sites in an octahedral complex (36), but its geometry is ill-suited to tridentate chelation within the pseudotetrahedral coordination environment favored by copper(I). Multinuclear helical complexes, in contrast, are well adapted to the preferred geometry of this metal ion (37).…”

Section: Resultsmentioning

confidence: 99%

Synthetic selectivity through avoidance of valence frustration

Hutin

Bérnardinelli

Nitschke

2006

Proc. Natl. Acad. Sci. U.S.A.

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A series of di-copper(I) complexes has been prepared via the reaction of copper(I) tetrafluoroborate, 2,6-diformylpyridine, 8-aminoquinoline, and a series of aliphatic diamines and 4-substituted anilines. To avoid a ''valence-frustrated'' state, involving a mismatch between the number of ligand donor atoms and the number of metal acceptor sites, the product structures formed selectively: One of the formyl groups of the diformylpyridine reacted specifically with the aminoquinoline, whereas the other formyl group reacted with the diamine or aniline. The observed selectivity was demonstrated to be thermodynamic in nature: When two dicopper complexes that were stable yet ''valencefrustrated'' were mixed, an imine metathesis reaction was observed to occur spontaneously to generate a ''valence-satisfied'' structure. In addition to control over the constitution of the ligands, we were able to exercise control over their relative orientations within the complex. Diamines exclusively gave structures in which the ligand exhibited a head-to-head orientation along the copper-copper axis to avoid stretching. Anilines gave predominantly head-to-tail structures, with the proportion of head-to-head isomer decreasing in complexes that incorporate more electron-deficient anilines and disappearing in less polar solvents. We also demonstrated the removal of the metals and the hydrogenation of the imine bonds to generate a molecule containing nonexchanging secondary amines, suggesting potential uses of this technique in the domain of organic synthesis.coordination chemistry ͉ dynamic combinatorial chemistry ͉ synthesis ͉ self-assembly A challenging problem in chemical synthesis is the direction of two different reagents to react at two equivalent sites upon a single substrate molecule. When such a reaction is carried out under thermodynamic control (1), one may expect to generate mixtures of hetero-and homo-coupled products. This problem is compounded when one of the two reagents also possesses two reactive groups. Mixtures of oligomeric products are expected to form, as the difunctional starting materials combine to form polymeric chains and rings of different sizes (Eq. 1).Various templating (2-9) and self-recognition (10-15) phenomena have been used to shape the thermodynamics of different self-assembly processes, to select a desired product or products from a dynamic library (16-19) of structures. Here we show how this goal may be accomplished through the action of a pair of metal template ions (20), which cooperatively direct each of the two equivalent aldehyde groups of a dialdehyde molecule to react with a different amine, forming two different imine (CAN) bonds selectively. The self-assembly of this system was directed by means of the number of acceptor sites present on the Cu I template ions and the number of donor sites present on the self-assembled imine ligands. When the number of donor sites cannot readily equal the number of acceptor sites, a ''valence-frustrated'' or ''incommensurate'' (21) state results, providing a ...

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“…In 1998, the Sanders group [149] explored the use of dynamic covalent bond formation for synthesizing neutral p-associated [2]catenanes by ring-closing metathesis (RCM) [150][151][152][153][154][155][156][157][158][159][160]. The mechanically interlocked structure was achieved using the electronic complementarity of p-electron-deficient aromatic diimides substituted with olefin terminated alkyl chains and the p-electron-rich dinaphtho [38]crown-10 (DN38C10) in the presence of the catalyst 4.…”

Section: Ring-closing Metathesis Mediated Synthesesmentioning

confidence: 99%