Fast Guest Exchange of a 1:1 Zinc Porphyrin–Amine Host–Guest Complex via a Six-Coordinated Zinc Porphyrin

Abstract

A novel zinc porphyrin receptor has been synthesized that has two identical binding pockets surrounded by six phenyl rings on both sides of the porphyrin plane. The binding of amine guests to the zinc porphyrin receptor was studied by UV–vis titration experiments. Among the amine guests, 1,4-diazabicyclo[2.2.2]octane (DABCO) showed the highest binding affinity (ΔG = −36.6 kJ mol−1 at 298 K in toluene) thanks to close contacts of DABCO with the aromatic walls of the binding pocket. The binding of DABCO was further investigated by dynamic NMR experiments. DABCO was tightly bound in one binding pocket when less than 1 equivalent of DABCO was added, but it started a rapid exchange between the two binding pockets when exceeding 1 equivalent.