Molecular Clips Form Isostructural Dimeric Aggregates from Benzene to Water

We report the synthesis and characterization of eight C-shaped methylene-bridged glycoluril
dimers (1−8) bearing hydrogen-bonding amide groups on their aromatic rings. Compounds 1−6 undergo
tight dimerization in CDCl3 solution (Ks > 9 × 105 M-1); binary mixtures of 1−7 form mixtures of homodimers
and heterodimers in moderately selective dimerization processes (0.23 ≤ Keq ≤ 768; 0.253 ≤ χAB < 0.933).
The high affinity formation of 1·1−6·6 is due to the commensurate nature of the geometrical constraints
imposed by the π−π interactions and only two hydrogen bonds. The differential response of the strengths
of the π−π interactions and H-bonds of 2·2 to changes in solvent polarityfrom C6D6 to D2Oresults in
the formation of a solvent-independent isostructural aggregate that exhibits high affinity dimerization across
the full range of solvents.