Synthesis and Self-Assembly of Pseudo-Spherical Homo- and Heterodimeric Capsules

摘要

Experimental details are given for the synthesis and characterization of several new molecules capable of self-assembly. The new molecules feature glycoluril subunits held apart by various rigid spacers, ethylene (2), naphthalene (3), and ethenoanthracene (4), and assemble through hydrogen bonds into pseudo-spherical dimeric capsules. The nature of their assembly is demonstrated by the X-ray crystal structure of capsules 1·1. The capsules are shown to enclose smaller guest molecules in a reversible manner. Direct evidence of the guest molecules inside the capsules from NMR is presented. In addition to self-assembling dimerically, these new molecules are shown to disproportionate into hybrid species or heterodimers. The resulting new capsules feature internal cavities of varying sizes and shapes. Formation of hybrid dimers 1·2, 1·4, and 3·4 is observed in solutions containing mixtures of two homodimers. The disproportionation equilibria could be manipulated by the addition of appropriately sized solvents as guests. Even the energetically unlikely hybrids 1·4 and 3·4 are found to be the dominant species when suitable guests such as CDBr_3 are present. Evidence of the existence of the heterodimers is presented from NOE measurements. Factors controlling the heterodimerization are discussed.