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Rotaxane


Developments in our Rotaxane Research

Threading Synthesis. Extensive NMR titrations revealed that the macrocyclic isophthalamides that we use in our rotaxane and catenane syntheses are selective for secondary amides.[1] This is also mirrored in the synthetic yields as shown in Scheme 1.

 Rotaxan Scheme 1

Scheme 1. Rotaxane synthesis by capping of semirotaxane complexes with a
stopper acid chloride.


A X-ray crystal structure analysis of a [2]rotaxane revealed the following hydrogen bonding pattern: A hydrogen bond on one side of the wheel cavity between a carbonyl oxygen pointing inward and the axle-NH is formed in addition to a bifurcated H-bond between the axle carbonyl-O and the NH protons of the isophthalamide group of the wheel on the other side.[2]
 

Rotaxan Fig 1

Figure 1. Detail of the crystal structure of a [2]rotaxane that shows the hydrogen bonding pattern between axle (green) and wheel (cyan). H-bonded NHs in magenta.


These results strongly hint at the formation of a reactive semirotaxane complex through threading of the wheel onto an amide semiaxle as the crucial intermediate in the rotaxane synthesis. Higher Rotaxanes. By making use of the amide affinity of macrocyclic lactams higher rotaxanes with up to 5 wheels threaded onto one axle have been obtained. This is based on the ability of oligoamide semiaxles to bind more than just one wheel at a time (Scheme 2).[3]

 Rotaxan Scheme 2

Scheme 2. Iterative synthesis of [n]rotaxanes.


Trapping Synthesis. Macrocyclic isophtalamides like the ones used in the threading synthesis portraid above bind inorganic and organic anions (e.g. Cl—, Br—, acetate) strongly in nonpolar media such as dichloromethane with association constants in the order of about 105 M-1. [4]
This observation led to the conception of a modified threading route towards rotaxanes, where the key feature is the binding of a voluminous phenolate by a tetralactam wheel through hydrogen bonding.[4] In the resulting complex the stopper unit sits on top of the wheel, blocking one face of it
(Scheme 3, left). This complex then functions as a "wheeled" supramolecular nucleophile while the semiaxle is a "mere" reaction partner that gets trapped inside the wheel. In other words, the threading of the string coincides with the bond formation and does not happen in an earlier step through an assembling process as in the "conventional" threading methods.
 

 Rotaxan Scheme 3

Scheme 3. The trapping procedure: High-yield rotaxane synthesis by reaction of an anionic stopper-wheel complex with an electrophilic semiaxle.


To distinguish it, we call this new synthetic strategy trapping.[5] The differences between threading and trapping are depicted in Figure 2. Yields up to 95% have been obtained in the synthesis of rotaxanes with phenyl ether axles.[4] Similarly, other nucleophilic substitution reactions and Michael
additions that lead to ester, thioester, phosphate, acetal, sulfide, or sulfonamide axles have been succesfully applied for rotaxane synthesis.[6]

 

Rotaxan Fig 2

Figure 2. The difference between threading and trapping. In the former the threading of the wheel onto the semiaxle happens prior to the reaction with the stopper. In the latter the threading coincides with the final bond formation, the semiaxle is thus trapped by the stopper-wheel complex.


The First Cyclodiastereomeric [3]Rotaxane – Chirality through the Mechanical Assembly of Achiral Molecules! A combination of the new trapping synthesis and the "conventional" threading opened the way to a [3]rotaxane with an unprecedented peculiarity: It is chiral even though non of its molecular entities are. The key to this is the sequential information (order of amide and sulfonamide groups) in the two wheels (Scheme 4). The enantiomers and the meso form were separated by chiral HPLC. The CD spectra are shown in Figure 3.[7]

 

Rotaxan Scheme 4

Scheme 4. Synthesis of the cyclodiastereomeric [3]rotaxane as the pair of enantiomers and the meso form.


Figure 3. CD spectra of the enantiomers of the [3]rotaxane (molecular CD vs. wavelength [nm]).
Mechanically chiral [1]Rotaxanes. A whole family of cycloenantiomeric [1]rotaxanes was obtained by covalently inserting diverse bridges between the wheel and the axle.[2, 8] These [1]rotaxanes exhibit pronounced circulardichroism. For those with aromatic chromophores in the bridges it
ranges in cases in the order of magnitude typically observed for helicenes. For three of these molecules X-ray crystal structures were obtained (Figure 4).[2]Scheme 4. Synthesis of the cyclodiastereomeric [3]rotaxane as the pair of enantiomers and the meso form.


Figure 3. CD spectra of the enantiomers of the [3]rotaxane (molecular CD vs. wavelength [nm]).
Mechanically chiral [1]Rotaxanes. A whole family of cycloenantiomeric [1]rotaxanes was obtained by covalently inserting diverse bridges between the wheel and the axle.[2, 8] These [1]rotaxanes exhibit pronounced circulardichroism. For those with aromatic chromophores in the bridges it
ranges in cases in the order of magnitude typically observed for helicenes. For three of these molecules X-ray crystal structures were obtained (Figure 4).[2]

 Rotaxan Scheme 5

Scheme 5. Schematic synthesis of [1]rotaxanes.

 Rotaxan Fig 4

Figure 4. View from above on the Crystal Structure of the (R)-Enantiomers a [1]Rotaxane with m-xylylene bridge. The trityl stoppers are not shown. C-atoms of the wheel colored in cyan, C-atoms of the axle in green, C-atoms of the m-xylylene bridge in violet, O-atoms in red, N-atoms in blue, S- atoms in yellow, H-atoms involved in H-bonds in grey, H-bonds represented as
dark grey cylinders.

 

 

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[2] C. Reuter, C. Seel, M. Nieger, F. Vögtle, Helv. Chim. Acta 2000, 83, 630-640
[3] A. H. Parham, R. Schmieder, F. Vögtle, Synlett 1999, 1887—1890.
[4] G. M. Hübner, J. Gläser, C. Seel, F. Vögtle, Angew. Chem. 1999, 111, 395—398; Angew.
Chem. Int. Ed. 1999, 38, 383—386.
[5] C. Seel, F. Vögtle, Chem. Eur. J. 2000, 6, 21—24.
[6] C. Reuter, W. Wienand, G. M. Hübner, C. Seel, F. Vögtle, Chem. Eur. J. 1999, 5, 2692—
2697; G. M. Hübner, C. Reuter, C. Seel, F. Vögtle, Synthesis, 2000, 5, 103—108; C. Reuter, F.
Vögtle, Org. Letters 2000, in press.
[7] R. Schmieder, G. M. Hübner, C. Seel, F. Vögtle, Angew. Chem. 1999, 111, 3741—3743;
Angew. Chem. Int. Ed. 1999, 38, 3528—3530.
[8] C. Reuter, A. Mohry, A. Sobanski, F. Vögtle, Chem. Eur. J. 2000, 6

A. Archut, W.M. Müller, S. Baumann, M. Habel, F. Vögtle, Liebigs Ann./Recueil 1997, 495-499,
Rotaxanes with Chiral Stoppers and Complexation of Cations by Podand Axles with Sugar Terminal Groups

R. Jäger, F. Vögtle, Angew. Chem. 1997, 109/9, 966-980, Eine neue Synthesestragegie für Moleküle mit mechanischen Bindungen. Nicht-ionische Templatsynthese amidverknüpfter Catenane und Rotaxane
Angew. Chem. Int. Ed. Engl. 1997, 36/9, 930-944, A New Synthetic Strategy towards Molecules with Mechanical Bonds: Non-ionic Template Synthesis of Amide-Linked Catenanes and Rotaxanes

F. Vögtle, T. Dünnwald, T. Schmidt, Acc. Chem. Res. 1996, 29, 451-460, Catenanes and Rotaxanes of the Amide Type

F. Vögtle, T. Dünnwald, M. Händel, R. Jäger, S. Meier, G. Harder, Chem. Eur. J. 1996, 640-643
A [3]Rotaxane of the Amide Type

F. Vögtle, S. Meier, Nordrhein-Westfälische Akademie der Wissenschaften, Vorträge N 419, 7.12.1994, Westdeutscher Verlag 1996, Neue Catenane und Rotaxane in der Supramolekularen Chemie

R. Jäger, M. Händel, J. Harren, K. Rissanen, F. Vögtle, Liebigs Ann. 1996, 1201-1207, Chemistry with Rotaxanes: Intra- and Intermolecularly Covalenty Linked Rotaxanes

F. Vögtle, S. Ibach, M. Nieger, C. Chartroux, T. Krüger, H. Stephan, K. Gloe, Chem. Commun., 1997, 1809-1810, A cage ligand with three convergent pyridine donors

R. Jäger, S. Baumann, M. Fischer, O. Safarowsky, M. Nieger, F. Vögtle, Liebigs Ann./Recueil 1997, 2269-2273, Non-Ionic Template Synthesis of Amide-Linked Rotaxanes: Olefinic and Aliphatic Axle Building Blocks

T. Dünnwald, R. Jäger, F. Vögtle, Chem. Eur. J. 1997,3, 12, 2043-2051, Synthesis of Rotaxane Assemblies

C. Yamamoto, Y. Okamoto, T. Schmidt. R. Jäger, F. Vögtle, J.Am.Chem.Soc. 1997, 119, 43, 10547-10548
Enantiomeric Resolution of Cycloenantiomeric Rotaxane, Topologically Chiral Catenane, and Pretzel-Shaped Molecules: Observation of Pronounced Circular Dichroism

O. Braun, F. Vögtle, Synlett 1997, 10, 1184-1186, A Threading Method Yielding Non-Polymeric Rotaxanes Containing Urea and Carbamate Units

M. Händel, M. Plevoets, S. Gestermann, F. Vögtle, Angew. Chem. 1997, 109/11, 1248-1250 , Rotaxansynthese durch kurzes Zusammenschmelzen von Rad und Achse, Angew. Chem. Int. Ed. Engl. 1997, 36/11, 1199-2101
Synthesis of Rotaxanes by Brief Melting of Wheel and Axle Components

T. Schmidt, R. Schmieder, W.M. Müller, B. Kiupel, F. Vögtle, Eur.J.Org.Chem. 1998, 2003-2007, Chiral Amide Rotaxanes with Glucose Stoppers - Synthesis, Chiroptical Properties and Wheel-Axle Interactions

T. Dünnwald, A. H. Parham, F. Vögtle, Synthesis 1998, 3, 339-348, Non-ionic Template Synthesis of Amide-linked Rotaxanes: Axles with Benzophenone and Cinnamic Acid Units

C. Kauffmann, W.M. Müller, F. Vögtle, S. Weinman, S. Abramson, B. Fuchs, Synthesis 1999, 5, 849-853
Rotaxanes with Chiral Stoppers and Photoresponsive Central Unit

A.H. Parham, B. Windisch, F. Vögtle, Eur. J. Org. Chem. 1999, 1233-1238, Chemical Reactions in the Axle of Rotaxanes - Steric Hindrance by the Wheel

C. Heim, A. Affeld, M. Nieger, F. Vögtle, Helv. Chim. Acta 82, 1999, 746-759, Size Complementarity of Macrocyclic Cavities and Stoppers in Amide-Rotaxanes

C. Heim, D. Udelhofen, F. Vögtle, Amide-Based Catenanes, Rotaxanes and Pretzelanes, in: J.-P. Sauvage, C. Dietrich-Buchecker (eds.), Molecular Catenanes, Rotaxanes and Knots. A Journey Through the World of Molecular Topology, Wiley-VCH 1999, 177-222

F. Vögtle, O. Safarowsky, C. Heim, A. Affeld, O. Braun, A. Mohry, Pure & Appl. Chem. 1999, 71, 2, 247-251
Catenanes, rotaxanes and pretzelanes - template synthesis and chirality

O. Braun, A. Hünten, F. Vögtle, J. Prakt. Chem. 1999, 341, No. 6, 542-547, Template Synthesis of Rotaxanes with Carbamate-Linked Axles

A. Mohry, H. Schwierz, F. Vögtle, Synthesis 1999, 10, 1753-1758, Supramolecular Assemblies: A Bis(pretzelane) and a Tetrakis(rotaxane)

C. Reuter, F. Vögtle, Org. Lett. 2000, 2, 5, 593-595, Rotaxanes via Michael Addition

O. Safarowsky, B. Windisch, A. Mohry, F. Vögtle, J. Prakt. Chem. 2000, 342, 437-444, Nomenclature for Catenanes, Rotaxanes, Molecular Knots, and Assemblies Derived from These Structural Elements

C. Yamamoto, Y. Okamoto, T. Schmidt, R. Jäger, F. Vögtle, J. Am. Chem. Soc. 1997, 119, 10547-10546
Enantiomeric Resolution of Cycloenantiomeric Rotaxane, Topologically Chiral Catenane, and Pretzel-Shaped Molecules: Observation of Pronounced Circular Dichroism

G.M. Hübner, G. Nachtsheim, Q.Y. Li, C. Seel, F. Vögtle, Angew. Chem. 2000, 112, 7, 1315-1318
Zum Raumbedarf von Dendrimeren: das Abfädeln von Rotaxanen; Angew. Chem. Int. Ed. 2000, 39, 7, 1269-1272, The Spacial Demand of Dendrimers: Deslipping of Rotaxanes

A. Sobanski, R. Schmieder, F. Vögtle, Chemie in unserer Zeit 2000, 3, 160-169, Topologische Stereochemie und Chiralität

C. Reuter, A. Mohry, A. Sobanski, F. Vögtle, Chem. Eur. J. 2000, 6, 9, 1674-1682, [1]Rotaxanes and Pretzelanes: Synthesis, Chirality, and Absolute Configuration

C. Reuter, G. Pawlitzki, U. Wörsdörfer, M. Plevoets, A. Mohry, T. Kubota, Y. Okamoto, F. Vögtle,
Eur. J. Org. Chem. 2000, 3059-3067, Chiral Dendrophanes, Dendro[2]rotaxanes, and Dendro[2]catenanes: Synthesis and Chiroptical Phenomena

F. Osswald, E. Vogel, O. Safarowsky, F. Schwanke, F. Vögtle, Adv. Synth. Catal. 2001, 343, 303-309,
Rotaxane Assemblies with Dendritic Architecture

C. Reuter, R. Schmieder, F. Vögtle, Pure Appl. Chem. 2000, 72, 2233-2241, From rotaxanes to knots. Templating, hydrogen bond patterns, and cyclochirality

C. Schalley, K. Beizai, F. Vögtle, Acc. Chem. Res. 2001, 34, 465-476, On the Way to Rotaxane-Based Molecular Motors: Studies in Molecular Mobility and Topological Chirality

O. Lukin, T. Kubota, Y. Okamoto, F. Schelhase, A. Yoneva, W. M. Müller, U. Müller, F. Vögtle, Angew. Chem . 2003, 115, 4681-4684, Angew. Chem. Int. Ed. 2003, 42, No. 37, 4542-4545, Knotaxane – Rotaxane mit Knoten als Stopper ( Knotaxanes – Rotaxanes with Knots as Stopper )

 

 

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