Selective π‑Metalation of Nut[6]Arene With Large and Chiral Cavity for Recognition Toward Bulky Anions in Water

Selective π-metalation of macrocyclic arenes (MAs) featuring large and stable chiral cavities remains a considerable challenge. Consequently, the recognition of the π-metalated MAs toward bulky anions, especially organic and chiral anions, is attractive but remains unexplored. In this work, a new macrocyclic arene named nut[6]arene (NA) was reported, which showed a rigid hexagonal structure and stable chiral cavity. Starting from NA, a series of π-metalated MAs were selectively synthesized. In particular, exo-tri-metalated NA (NA-3Ru-I) with a C₃ symmetrical structure was selectively obtained in high yields by the modulation of ligand sterics, molar ratio, and reaction temperature, which showed a large and electron-deficient cavity. Consequently, water-soluble NA-3Ru-II could effectively bind large inorganic anions, including ReO₄ ^- and PF₆ ^- to form 1:1 stable host-guest complexes. Especially, NA-3Ru-II showed strong binding abilities toward various organic sulfonate anions and carboxylate anions. Moreover, a pair of enantiomeric NA-3Ru-II was also obtained, and they exhibited enantioselective recognitions for chiral anionic guests in aqueous solution, providing a new chiral platform for anion recognition.