Substituent effects on ion complexation of para‐tert‐butylcalix[4]arene esters

Abstract

arene esters were synthesized in order to evaluate the role of electronic parameters on the complexation of alkaline metal cations. Extraction constants of metal picrates to organic phase were determined. Plots of log (K R /K H ) against Hammett s and s þ p gave good linear correlations. The best correlations with s were obtained for K þ and Rb þ , while the best correlations with s þ p were obtained for Li þ and Na þ . All Hammett plots gave a straight descending line, which is consistent with a dependence of the electronic density on the C --O. Treatment of data using the Yukawa-Tsuno equation revealed a variation in the contribution of resonance in the complexation of alkaline metal ions, which is maximum for Na þ and minimum for Rb þ . Electronic parameters were calculated for a related acyclic model structure and only the HOMO energy showed a good correlation with log (K R /K H ).

Experimental Binding Energies in Supramolecular Complexes

“…Consequently, the stability of, e.g., metal ion complexes can for suitable aromatic host compounds be correlated and predicted with Hammett-substituent constants (Figure ). Similarly, the affinity between p -substituted aniline crown ethers and bis­(4-fluorobenzyl)­ammonium ions exhibits linear correlations with Hammett σ values …”

“…Complex of p- tert -butylcalix­[4]­arene-esters with potassium picrate and Hammett-correlation with extraction constants (as lg K ) from H 2 O to CH 2 Cl 2 . Reprinted with permission from ref . Copyright 2006 Wiley VCH.…”

Binding Mechanisms in Supramolecular Complexes

“…Such host-guest associations are often referred to as donor-acceptor complexes, although electrons are never, and charges only rarely, transferred. [227] As noted in Section 3.2, the donating effect of heteroatoms in ionophores can also be quantified by using polarity Scheme 6. The complexation of alkali-metal and alkaline-earth cations by crown ethers and related compounds is based on an attraction between the ion and the free electron pairs on a heteroatom in the ligand.…”

“…[226] Complexes of p-tert-butylcalix[4]arene esters with alkalimetal ions show linear Hammett correlations with substituents , which alter the electron density at the C=O group. [227] As noted in Section 3.2, the donating effect of heteroatoms in ionophores can also be quantified by using polarity Scheme 6. Binding contributions in complexes with guanidiniocarbonylpyrrole receptors; the numbers 0-2, 4, 2, and 10 designate, for the individual interactions (stacking, hydrogen bonds, and ion pairs), the asociated DG values (in kJ mol À1 ) of the complex with Ac-Ala-O À .…”

Bindungsmechanismen in supramolekularen Komplexen

“…[226] Komplexe von p-tert-Butylcalix[4]arenestern mit Alkalimetallionen zeigen lineare Hammett-Korrelationen mit Substituenten R, die die Elektronendichte an der C = O-Gruppe steuern. [227] Wie im Abschnitt 3.2 erwähnt, kann das Donorvermögen von Heteroatomen in Ionophoren auch durch Polaritätsparameter wie a oder b quantifiziert werden; [122] diese können die Stabilitäten von Kronenether-und Kryptand-Komplexen gut beschreiben (Abbildung S5). [158] Die Ausrichtung des Elektronenpaars am N-Atom zum Kation hin ist z.…”