Premium
Stereochemistry of Molecular Figures‐of‐Eight
Author(s) -
Boyle Megan M.,
Gassensmith Jeremiah J.,
Whalley Adam C.,
Forgan Ross S.,
Smaldone Ronald A.,
Hartlieb Karel J.,
Blackburn Anthea K.,
Sauvage JeanPierre,
Stoddart J. Fraser
Publication year - 2012
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.201202070
Subject(s) - chemistry , azide , cyclophane , crystallography , nuclear magnetic resonance spectroscopy , cis–trans isomerism , stereochemistry , ab initio , alkyne , stacking , aryl , crystal structure , catalysis , organic chemistry , alkyl
A trans isomer of a figure‐of‐eight (Fo8) compound was prepared from an electron‐withdrawing cyclobis(paraquat‐ p ‐phenylene) derivative carrying trans ‐disposed azide functions between its two phenylene rings. Copper(I)‐catalyzed azide–alkyne cycloadditions with a bispropargyl derivative of a polyether chain, interrupted in its midriff by an electron‐donating 1,5‐dioxynaphthalene unit acting as the template to organize the reactants prior to the onset of two click reactions, afforded the Fo8 compound with C i symmetry. Exactly the same chemistry is performed on the cis ‐bisazide of the tetracationic cyclophane to give a Fo8 compound with C 2 symmetry. Both of these Fo8 compounds exist as major and very minor conformational isomers in solution. The major conformation in the trans series, which has been characterized by X‐ray crystallography, adopts a geometry which maximizes its CH⋅⋅⋅O interactions, while maintaining its π⋅⋅⋅π stacking and CH⋅⋅⋅π interactions. Ab initio calculations at the M06L level support the conformational assignments to the major and minor isomers in the trans series. Dynamic 1 H NMR spectroscopy, supported by 2D 1 H NMR experiments, indicates that the major and minor isomers in both the cis and trans series equilibrate in solution on the 1 H NMR timescale rapidly above and slowly below room temperature.