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The Influence of Macrocyclic Polyether Constitution upon Ammonium Ion/Crown Ether Recognition Processes
Author(s) -
Cantrill Stuart J.,
Fulton David A.,
Heiss Aaron M.,
Pease Anthony R.,
Stoddart J. Fraser,
White Andrew J. P.,
Williams David J.
Publication year - 2000
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 - 10.1002/1521-3765(20000616)6:12<2274::aid-chem2274>3.0.co;2-2
Subject(s) - crown ether , constitution , ammonium , crown (dentistry) , chemistry , ether , ion , polymer chemistry , organic chemistry , materials science , law , political science , composite material
Secondary dialkylammonium (R 2 NH 2 + ) ions are bound readily by dibenzo[24]crown‐8 (DB24C8) to form threaded complexes, namely [2]pseudorotaxanes. The effect of replacing one or both of the catechol rings in DB24C8 with resorcinol rings upon the crown ether's ability to bind R 2 NH 2 + ions has now been investigated. When only one aromatic ring is changed from catechol to resorcinol, a crown ether with a [25]crown‐8 constitution is created‐namely benzometaphenylene[25]crown‐8 (BMP25C8). A [2]pseudorotaxane is formed in the solid state when BMP25C8 is co‐crystallized with dibenzylammonium hexafluorophosphate, as evidenced by its X‐ray crystal structure. Furthermore, this crown ether has been shown to bind R 2 NH 2 + ions in solution, an observation which has been exploited in the synthesis of the first BMP25C8‐containing [2]rotaxane. The methodology employed to generate this [2]rotaxane‐the reaction of an amine with an isocyanate to form a urea‐was tested initially on a system incorporating DB24C8 and was shown to work efficiently. Both [2]rotaxanes have been fully characterized by 1 H and 13 C NMR spectroscopies, FAB mass spectrometry and X‐ray crystallography. Interestingly, the unsymmetrical nature of the dumbbell‐shaped component in each of the two [2]rotaxanes renders each face of the encircling macrocyclic polyether diastereotopic, a feature that is apparent upon inspection of their 1 H NMR spectra. The resonances associated with the diastereotopic protons on each face of the macrorings are well enough resolved to enable the faces of the crown ethers to be readily identified with respect to their protons by 1 H NMR spectroscopy. Unambiguous assignments can be made as a result of the fact that the protons on each face of the macrocyclic polyether experience a unique set of through‐space interactions, as evidenced by T‐ROESY experiments. Additionally, the two‐dimensional NMR analyses are in agreement with the X‐ray crystallographic studies performed on these [2]rotaxanes, indicating that the crown ethers are located intimately around the NH 2 + centers as expected. Replacement of both catechol rings in the DB24C8 constitution with resorcinol rings results in a crown ether with a [26]crown‐8 constitution‐namely bismetaphenylene[26]crown‐8 (BMP26C8). All the evidence to date points to the fact that this further change in constitution results in a crown ether that does not bind R 2 NH 2 + ions in either the solution or solid states.