Solution and Solvent‐Free Stopper Exchange Reactions for the Preparation of Pillar[5]arene‐containing [2] and [3]Rotaxanes

Diamine reagents have been used to functionalize a [2]rotaxane building block bearing an activated pentafluorophenyl ester stopper. Upon a first acylation, an intermediate host‐guest complex with a terminal amine function is obtained. Dissociation of the intermediate occurs in solution and acylation...

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Bibliographic Details
Published in:Chemistry : a European journal 2024-02, Vol.30 (12), p.e202304131-n/a
Main Authors: Becharguia, Nihed, Nierengarten, Iwona, Strub, Jean‐Marc, Cianférani, Sarah, Rémy, Marine, Wasielewski, Emeric, Abidi, Rym, Nierengarten, Jean‐François
Format: Article
Language:English
Subjects:
Chemical Sciences
distortion energy
molecular shuttles
pillararene
rotaxane
stopper exchange
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Summary:Diamine reagents have been used to functionalize a [2]rotaxane building block bearing an activated pentafluorophenyl ester stopper. Upon a first acylation, an intermediate host‐guest complex with a terminal amine function is obtained. Dissociation of the intermediate occurs in solution and acylation of the released axle generates a [2]rotaxane with an elongated axle subunit. In contrast, the corresponding [3]rotaxane can be obtained if the reaction conditions are appropriate to stabilize the inclusion complex of the mono‐amine intermediate and the pillar[5]arene. This is the case when the stopper exchange is performed under mechanochemical solvent‐free conditions. Alternatively, if the newly introduced terminal amide group is large enough to prevent the dissociation, the second acylation provides exclusively a [3]rotaxane. On the other hand, detailed conformational analysis has been also carried out by variable temperature NMR investigations. A complete understanding of the shuttling motions of the pillar[5]arene subunit along the axles of the rotaxanes reported therein has been achieved with the help of density functional theory calculations. Stopper exchange reactions between a rotaxane building block and diamine reagents gave dramatically different outcome in solution and in solvent‐free conditions. Upon a first acylation, an intermediate host‐guest complex with a terminal amine function is obtained. Dissociation of the intermediate occurs in solution but the inclusion complex is preserved under mechanochemical solvent‐free conditions.
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.202304131