π‑Metalated [15]Paracyclophanes: Synthesis and Binding to Oxo-Anions via Anion−π Interactions

The host–guest properties of [15]­paracyclophane ([15]­PCPs) are engendered by π-metalation, which exhibits fantastic regioselectivity toward a macrocyclic molecule. The synthesis and characterization of mono-, di-, and trimetalated [15]­PCPs are discussed in this article, and the anion binding behavior of 3Ru-[15]­PCP-II6+, one of the trimetalated [15]­PCPs, driven by anion−π interactions, is comprehensively demonstrated in both solution and the solid state. The anion binding properties of 3Ru-[15]­PCP-II6+ in solution are investigated by 1H NMR titrations, showing selectivity toward ReO4– in both organic and aqueous solutions. The binding mode is unexpected; the anionic guest stacks over the host rather than threads it. This selectivity for ReO4– is also supported by water–nitromethane extraction experiments, which demonstrate that its partition from water into the organic phase by 3Ru-[15]­PCP-II·6OTf is maintained to some extent in the presence of excess Cl–, SO42–, H2PO4–, NO3–, and ClO4–.