Self-Assembly of Tris(2-ureidobenzyl)amines: A New Type of Capped, Capsule-Like Dimeric Aggregates Derived from a Highly Flexible Skeleton

A set of tris(2‐ureidobenzyl)amines 3 was prepared and their dimerization processes thoroughly investigated. In spite of their inherent flexibility, tris(ureas) 3 form dimeric aggregates both in the solid state and in solution. Evidence for the existence of these dimeric species was provided by a combination of techniques (X‐ray analysis, NMR and IR spectroscopy, and ESI‐MS). The association constants and thermodynamic parameters for the dimerization processes of selected tris(ureas) were determined and show that they are enthalpically driven. Heterodimerization experiments in solution reveal a high degree of self‐recognition or narcissistic self‐sorting. On the other hand, desymmetrized tris(ureas) derived from 3 self‐assemble with modest regioselectivities depending on the terminal substituent of every urea functionality. Strong narcissistic self‐sorting behavior and self‐association in the solid state and solution are exhibited by tris(2‐ureidobenzyl)amines. These avid self‐assemblers, which are derived from the highly flexible tribenzylamine skeleton, dimerize to give capped capsule‐like supermolecules encircled by a belt of 12 hydrogen bonds (see scheme).