Issue 7, 2019

Guest-mediated chirality transfer in the host–guest complexes of an atropisomeric perylene bisimide cyclophane host

Abstract

The dynamic equilibrium of stereoisomers of a cyclophane, which is comprised of two atropisomeric perylene bisimide (PBI) subunits, and its host–guest binding with an achiral and a series of chiral guests have been studied. Temperature-dependent 1H NMR spectroscopic studies have shown that at higher temperature all three stereoisomers ((M,M) and (P,P) enantiomers and (M,P)/(P,M) mesomers) of the cyclophane are in a dynamic equilibrium as only one set of proton signals was observed. However, at a lower temperature (260 K) two sets of signals in a ratio of 2 : 1, instead of the theoretically expected 1 : 1 ratio, were observed for the diastereomers (M,M)/(P,P) and (M,P)/(P,M) of the cyclophane presumably due to the chiral recognition of the enantiomeric (M,M)/(P,P) conformers. The 1H NMR studies further revealed that the achiral guest perylene mostly selects the (M,M)/(P,P) enantiomeric pair of the host for encapsulation. The induction of chirality in the host–guest complexes of the cyclophane with chiral guests has been investigated by circular dichroism (CD) spectroscopy. A distinct CD effect was observed upon addition of chiral guests to the solution of a racemic cyclophane host, indicating a pronounced preference of the chiral guests for one of the two homochiral stereoisomers, (M,M) and (P,P), for encapsulation. Kinetic studies by time-dependent NMR spectroscopy did not lead to conclusive results to assign the recognition process of chiral guests to either the induced fit or the conformational selection model.

Graphical abstract: Guest-mediated chirality transfer in the host–guest complexes of an atropisomeric perylene bisimide cyclophane host

Supplementary files

Article information

Article type
Research Article
Submitted
30 ⵉⵏⵏ 2019
Accepted
22 ⴱⵕⴰ 2019
First published
05 ⵎⴰⵕ 2019

Org. Chem. Front., 2019,6, 892-899

Guest-mediated chirality transfer in the host–guest complexes of an atropisomeric perylene bisimide cyclophane host

M. Sapotta, P. Spenst, C. R. Saha-Möller and F. Würthner, Org. Chem. Front., 2019, 6, 892 DOI: 10.1039/C9QO00172G

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