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Spacer Length‐Independent Shuttling of the Pillar[5]arene Ring in Neutral [2]Rotaxanes
Author(s) -
Ogoshi Tomoki,
Kotera Daisuke,
Nishida Shungo,
Kakuta Takahiro,
Yamagishi Tadaaki,
Brouwer Albert M.
Publication year - 2018
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201800104
Subject(s) - pillar , axle , ring (chemistry) , chemistry , rotaxane , crystallography , ring size , stereochemistry , physics , supramolecular chemistry , crystal structure , engineering , organic chemistry , structural engineering , thermodynamics
For a series of neutral [2]rotaxanes consisting of a pillar[5]arene ring and axles possessing two stations separated by flexible spacers of different lengths, the free energies of activation for the ring shuttling between the stations were found to be independent of the spacer length. The constitution of the spacer affects the activation energies: replacement of CH 2 groups by repulsive oxygen atoms in the axle increases the barrier. The explanation for the observed length‐independence lies in the presence of a barrier for re‐forming the stable co‐conformation, which makes the ring travel back and forth along the thread in an intermediate state.