Anion-Based Self-assembly of Resorcin[4]arenes and Pyrogallol[4]arenes

Spatial sequestration
of molecules is a prerequisite for the complexity
of biological systems, enabling the occurrence of numerous, often
non-compatible chemical reactions and processes in one cell at the
same time. Inspired by this compartmentalization concept, chemists
design and synthesize artificial nanocontainers (capsules and cages)
and use them to mimic the biological complexity and for new applications
in recognition, separation, and catalysis. Here, we report the formation
of large closed-shell species by interactions of well-known polyphenolic
macrocycles with anions. It has been known since many years that C-alkyl
resorcin[4]­arenes (R4C) and C-alkyl pyrogallol[4]­arenes
(P4C) narcissistically self-assemble in nonpolar solvents
to form hydrogen-bonded capsules. Here, we show a new interaction
model that additionally involves anions as interacting partners and
leads to even larger capsular species. Diffusion-ordered spectroscopy
and titration experiments indicate that the anion-sealed species have
a diameter of >26 Å and suggest stoichiometry (M)6(X–)24 and tight ion pairing
with cations. This self-assembly is effective in a nonpolar environment
(THF and benzene but not in chloroform), however, requires initiation
by mechanochemistry (dry milling) in the case of non-compatible solubility.
Notably, it is common among various polyphenolic macrocycles (M) having diverse geometries and various conformational lability.