The Pinched Cone Conformation of Calix[4]arenes:  Noncovalent Rigidification of the Calix[4]arene Skeleton

Abstract

Calix[4]arenes at the upper rim substituted with two (thio)urea moieties, 2a-c and 4, or substituted with two acetamido groups, 5, adopt a pinched cone conformation in CDCl 3 solution. The pinched cone conformation is the result of diametrical, intramolecular hydrogen bonds and was studied by 1 H NMR dilution and variable-temperature experiments, NOESY spectroscopy, and FTIR experiments. The pinched cone conformation in these novel calix[4]arenes is stable in C 2 D 2 Cl 4 up to at least 120°C. The bis(ureido)calix[4]arenes 2b,c give a hydrogen-bonded dimer in the pinched cone conformation.

Versatile Inclusion Behaviour of a Dinitrocalix[4]arene Having Two Ester Pendants – Preparation and X-ray Crystal Structures of Complexes

“…The calix [4]arene ring adopts similar pinched cone conformations [15] in its present complexes (Table II), which are stabilized by two intramolecular hydrogen bonds between the phenolic hydrogens and the adjacent ether oxygens (Table III). The Figures 1(a)-(c) and 5, Table II].…”

“…In general, crystals exhibiting frameworks differing by one or two non-crystallographic virtual rotation(s) of the common motifs, or the whole pattern, may be denoted as 'morphotropic'. According to the literature [21], closely related ... [17] ... [27] ... [11] ... [28] ... [15] ... [16] ... [13] ... [24] ... [12] ... [25] ... [33] ... [18] ... [34] ... [19] ... [36] ... [32] ... [37] ... [14] ... [21] ... [35] ... [22] ... [39] ... [23] . (Table IV), suggests that it may be valid also in the present case.…”

Calix[4]arenes bearing α‐amino‐ or α‐hydroxyphosphonic acid fragments at the upper rim

“…This conformation can be considered as a transition structure in a fast interconversion flattened cone-flattened cone, characteristic of tetraalkoxycalix [4]arenes [21].…”

Crystal structure of 25,26,27,28-tetrabenzyloxy-5,11,17,23-tert-butylcalix- [4]arene, C72H80O4

“…Inthe title compound, the calixarene framework adopts apinchedcone conformation [2], which is anu sualb ehavior of disubstituted calix [4]arenes [3] rather thanatetrasubstituted calix[4]arene such ashere. Moreover, the interplanarangles,formed by the opposite phenyl rings, i.e.…”