Fine Tuning of the Cavity Size in Calixarene-Like Cyclophanes: A Complete Series of Homooxacalix[4]arene Ligands for Quaternary Ammonium Ions

Inclusion of Organic Cations by Calix[4]arenes Bearing Cyclohepta-2,4,6-trienyl Substituents

“…The existence of the cone conformation in solution is indicated by (i) the remarkable difference between the chemical shifts of the equatorial and axial methylene protons (see Table 1) and (ii) the methylene carbon resonance at δ ϭ 32 in the 13 C NMR spectrum. [20] The cycloheptatrienyl substituents have no appreciable effect on the barrier to inversion.…”

“…[8] It has also been shown that the encapsulation of ammonium ions is strongly improved by interconnecting two calix [4]arenes at the upper rims with two spacers, but that larger iminium ions such as 34 (see Scheme 3) were not bound. [11] Calixarenes with a wider cavity, such as calix [5]arenes [12] and homooxacalix [4]arenes, [13] are fairly efficient receptors for ammonium and iminium salts.…”

Alkylammonium Guest Induced‐Fit Recognition by a Flexible Dihomo­oxacalix[4]arene Derivative

“…Previous variable temperature 1 H NMR spectroscopic10c and X‐ray crystallographic studies10e showed that 1c mainly exists in the 1,4‐alternate conformation (Figure 2) both in solution and in the solid state. DFT13 calculations performed in the present work, at the MPW1PW914/6‐31G(d) level of theory, are in full agreement with these results.…”

“…By application of Gutsche's and de Mendoza's rules,15 these data were only compatible with a n BuNH 3 + ⊂ 1c complex in which tetramethoxy‐dihomooxacalix[4]arene ( 1c ) was in a cone conformation ( n BuNH 3 + ⊂ 1c cone ). Thus, although free 1c adopts a 1,4‐alternate conformation in solution,10c,10d in the presence of a n BuNH 3 + guest it preferentially converts to a cone conformation through an adaptive structural change.…”

Organic Cations in Constrained Systems

“…4) The mobility of the cyclophanes is considerably increased. 32 Two effects may result -the higher mobility expends energy and the binding energy is diminished or the higher mobility enables the cyclophane to form the most suitable geometry of the host in the complex. The whole set of compounds methylated at the narrower rim III -1 -III -7 (Scheme 12.14 ) has been synthesized and the binding of picrates of organic cations B -2 , B -10 B -11and C -3 (Scheme 12.6 , Scheme 12.14 ) was studied.…”