Kinetically-Locked Metallomacrocycle for Host-Guest Chemistry with Bulky Anions

As a robust and large molecular receptor, a kinetically-locked trinuclear Co(III) macrocycle was synthesized with bis(beta-diketone) ligands having large pi-panels of 9,10-diphenylanthracene moieties via a combination of Co(II)-assisted self-assembly and subsequent oxidation of the metal centers. The X-ray structure revealed that the macrocycle had a discrete nanocavity of more than 300 angstrom(3), which was surrounded by three anthracenyl panels in the middle. As the macrocycle has three cationic centres on each metal ion and a large cavity, it acts as a guest receptor for sodium tetraphenylborate. The binding constant was estimated to be 4.0x10(-2) M-1 from H-1 NMR titration experiments, whereas no interaction was observed between the macrocycle and potassium 1-adamantanecarboxylate.