Proton-Induced Assembly–Disassembly Modulation of Spiroborate Twin-Bowl Polymers Bearing Pyridyl Groups

Twin-bowl-shaped
tris-(spiroborate) cyclophanes bearing pyridyl groups have been prepared
for the construction of proton-responsive supramolecular polymers.
Preparation of the pyridyl twin bowls was carried out by the reaction
of 6,6′-(3-pyridyl)-2,2′,3,3′-tetrahydroxy-1,1′-binaphthyls
and an equimolar amount of boric acid in N,N-dimethyl­formamide in self-organization manner, as
previously reported. The reversible acid/base response of the pyridyl
twin bowls was evaluated by the addition of hydrochloric acid and
aqueous sodium hydroxide. The assembly disassembly modulation of the
supramolecular polymers composed of pyridyl twin bowls and the tricationic
iridium-(III) complex was also examined. Dissociation of the supramolecular
polymers occurred by the addition of hydrochloric acid, and its reconstruction
was realized by the addition of aqueous sodium hydroxide. The opposite
behavior was observed when the dianionic palladium-(II) complex was
employed as a guest. The addition of acid led to the formation of
the aggregate that was dissociated by the addition of base.