Substituent effects in the binding of bis(4-fluorobenzyl)ammonium ions by dianilino[24]crown-8
摘要:
A series of para-substituted dianilino[24]crown-8 (DA24C8) macrocycles were synthesized and their ability to form host-guest complexes with bis(4-fluorobenzyl)ammonium ions (DFA(+)) were investigated. Although these crown ethers contain weakly hydrogen bonding aniline motifs, they do bind DFA(+) in CDCl3/CD3NO2 solution, presumably in a pseudo rotaxane-like manner. A plot of the values of the relative binding strengths (log[K-a(R)/K-a(H)]) versus the Hammett substituent constants sigma(+) of the groups at the para-position of the aniline units suggests that a linear free energy correlation exists for this self-assembly process. The strength of the binding between the crown ether and the thread-like ion can be fine-tuned over a narrow range by judicious choice of the substituting groups. (C) 2003 Elsevier Ltd. All rights reserved.
The mild and efficient reaction between triethyl phosphite and benzylic azides allows us not only to construct rotaxanes in high yield from dibenzo[24]crown-8 (DB24C8) and dibenzylammonium (DBA(+))-derived threads but also to incorporate di(p-toluidine)[24]crown-8, which binds DBA(+) ions much more weakly than does DB24C8, into a corresponding [2]rotaxane.