Rotational isomerism of the amide units in rotaxanes based on a cyclic tetraamide and secondary ammonium ions

In this study, we synthesized the macrocyclic tetraamide 1, possessing four tertiary amide units, as a host for mono- and bis-ammonium ions, forming corresponding [2]pseudorotaxanes stabilized through hydrogen bonding between the components. [2]Rotaxanes comprising 1 as the macrocycle and mono- and...

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Published in:Organic chemistry frontiers an international journal of organic chemistry 2019-04, Vol.6 (7), p.1002-1009
Main Authors: Okuma, Yukari, Tsukamoto, Toshihiro, Inagaki, Takayuki, Miyagawa, Shinobu, Kimura, Masaki, Naito, Masaya, Takaya, Hikaru, Kawasaki, Tsuneomi, Tokunaga, Yuji
Format: Article
Language:English
Subjects:
Ammonium
Chemical bonds
Chemical synthesis
Conformation
Hydrogen
Hydrogen bonding
Hydrogen bonds
Ions
Organic chemistry
Rotaxanes
Shafts (machine elements)
Solvents
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Summary:In this study, we synthesized the macrocyclic tetraamide 1, possessing four tertiary amide units, as a host for mono- and bis-ammonium ions, forming corresponding [2]pseudorotaxanes stabilized through hydrogen bonding between the components. [2]Rotaxanes comprising 1 as the macrocycle and mono- and bis-ammonium ions as the axle components were synthesized through imine bond formation. The tetraamide 1 exists as a mixture of rotamers in solution; in the [2]rotaxanes, however, the conformation of this component was controlled through intramolecular hydrogen bonding between the axle and macrocyclic components. In a nonpolar solvent (CDCl3), only one conformational isomer existed for each [2]rotaxane. On the other hand, in a polar solvent (DMSO-d6), the [2]rotaxane possessing a mono-ammonium ion in the axle was partially isomerized; only a single rotational isomer existed for the [2]rotaxane featuring a bis-ammonium ion in the axle, because of a complete set of hydrogen bonds, in this polar solvent.
ISSN:2052-4110
2052-4110
DOI:10.1039/c9qo00096h