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Evaluation of Weak Interactions in [2]Pseudorotaxanes
Author(s) -
Nikitin Kirill,
MüllerBunz Helge,
Muldoon Jimmy
Publication year - 2014
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201300871
Subject(s) - chemistry , steric effects , density functional theory , phenylene , computational chemistry , crystallography , molecule , binding energy , nuclear overhauser effect , stereochemistry , nuclear magnetic resonance spectroscopy , organic chemistry , physics , nuclear physics , polymer
Abstract Viologens readily thread bis‐ p ‐phenylene crown ethers to form [2]pseudorotaxanes. However, the binding of sterically hindered 3,3′‐dimethylviologens is very weak. Density functional theory (DFT) calculations indicated that the additional energy cost of “flattening” is substantial, 55 kJ mol −1 , and prevents the formation of a stable host–guest complex. The structures of [2]pseudorotaxanes determined by X‐ray crystallography are in good agreement with the NMR characterisation and DFT results. Their association constants and thermodynamic parameters in solution were measured by using a dilution method and, for the first time, by host–guest nuclear Overhauser effect (NOE) correlations. The NOE approach was subsequently applied to study the sterically hindered analogues and it was shown that the binding in 3,3′‐dimethyl‐ N , N ‐dibenzyl [2]pseudorotaxane is by 8.5 kJ mol −1 weaker than in its regular analogue. The proposed technique helps to quantify weak interactions in [2]pseudorotaxanes and can be applied to other host‐guest complexes.