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.