Issue 17, 2007

Reasons for the exclusive formation of heterodimeric capsules between tetra-tolyl and tetra-tosylurea calix[4]arenes

Abstract

The selective heterodimerization of tetra-tolyl (1a) and tetra-tosylurea (1b) calixarenes, serendipitously found by Rebek et al. (R. K. Castellano, B. H. Kim and J. Rebek, Jr., J. Am. Chem. Soc., 1997, 119, 12671–12672), has been used for the construction of highly sophisticated macrocycles and well-defined supramolecular assemblies. Regrettably, hitherto, neither the exact structure of these heterodimers nor the reason for their exclusive formation is known. We present molecular dynamics simulations using the AMBER force field in explicit chloroform solvent for the two homodimers, the heterodimer and the two uncomplexed tetra-urea calixarenes. The rigid rotation about the C–S–N–C bond of the tosylurea group has been calculated for a model compound (N-mesylformamide) at the RHF/6-31G* level of theory. The calculations suggest that the heterodimer 1a·1b is energetically favored over the homodimers by a sterically relaxed conformation of the tosylurea hemisphere in 1a·1b, by a moderate degree of reorganization of the hemispheres from the uncomplexed to the complexed state and by favorable interactions between the hemispheres. The tosylurea S[double bond, length as m-dash]O groups are involved in the hydrogen bonding system which results in different sizes of the three capsules in increasing order 1a·1a < 1a·1b < 1b·1b. To prove the computational predictions, 1H NMR experiments have been carried out with solvents/guests differing in shape and size. The largest capsule 1b·1b prefers the larger guests toluene and p-xylene while the latter is not encapsulated in the smallest capsule 1a·1a.

Graphical abstract: Reasons for the exclusive formation of heterodimeric capsules between tetra-tolyl and tetra-tosylurea calix[4]arenes

Supplementary files

Article information

Article type
Paper
Submitted
07 Jun 2007
Accepted
11 Jul 2007
First published
31 Jul 2007

Org. Biomol. Chem., 2007,5, 2775-2782

Reasons for the exclusive formation of heterodimeric capsules between tetra-tolyl and tetra-tosylurea calix[4]arenes

I. Thondorf, Y. Rudzevich, V. Rudzevich and V. Böhmer, Org. Biomol. Chem., 2007, 5, 2775 DOI: 10.1039/B708679B

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