Substituent control of potassium and rubidium uptake by asymmetric calix[4]-thiacalix[4]tubes

Abstract

Herein we report on the synthesis and ionophore properties of the first asymmetric p-tert-butylcalix[4]-p-R-thiacalix[4]tubes 7a-c (R = t-Bu, H, 1-adamantyl). The target compounds were obtained by the condensation of tosyloxyethoxy-p-tert-butylcalix[4]arene with the corresponding p-R-thiacalix[4]arenes in the presence of K2CO3 in acetonitrile. The complexation with sodium, potassium and rubidium iodides was studied in CDCl3-CD3OD (4:1) medium by means of 1H NMR measurements. It was found that the ionophore properties of calixtubes 7a-c are controlled by the character of the substituents at the upper rim of the thiacalix[4]arene fragment and it was shown that only the molecular tube 7c with an adamantane-containing thiacalixarene unit is capable of quantitatively binding potassium (swiftly) and rubidium (slowly) cations.

Tuning conformations of calix[4]tubes by weak intramolecular interactions

“…exchange rate constants in CDCl 3 are 0.9 s À1 (328 K), 6b 9.3 s À1 (273 K), 7 and 2.5 s À1 (328 K), 8 respectively. Removal or replacement of tert-butyl groups with different alkyl residues or halogens may alter the rate constants but keep them measurable by NMR at ambient or even elevated temperatures.…”

Recent developments of thiacalixarene based molecular motifs

“…The complexation of heterocalix [4]tube 144 was controlled by the upper rim substitution of the thiacalixarene fragment. 133 Molecular tube 144 (Fig. 34) with an adamantine-containing thiacalixarene unit quantitatively binds to potassium and rubidium cations.…”

Emerging host–guest chemistry of synthetic nanotubes

“…These studies, initiated in the early 1990s, also triggered quite intense research on calixarene based tubular structures for metal ion tunneling and transport. [14][15][16] For example, Kim, Vicens, and co-workers reported similar multiply-connected 1,3-alternate calix [4]arene tubes 15 (Fig. 8).…”