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

The host–guest properties of [1 5 ]paracyclophane ([1 5 ]PCPs) are engendered by π-metalation, which exhibits fantastic regioselectivity toward a macrocyclic molecule. The synthesis and characterization of mono-, di-, and trimetalated [1 5 ]PCPs are discussed in this article, and the anion binding behavior of 3Ru-[1 5 ]PCP-II 6+, one of the trimetalated [1 5 ]PCPs, driven by anion−π interactions, is comprehensively demonstrated in both solution and the solid state. The anion binding properties of 3Ru-[1 5 ]PCP-II 6+ in solution are investigated by 1 H NMR titrations, showing selectivity toward ReO 4 – 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 ReO 4 – is also supported by water–nitromethane extraction experiments, which demonstrate that its partition from water into the organic phase by 3Ru-[1 5 ]PCP-II ·6OTf is maintained to some extent in the presence of excess Cl –, SO 4 2–, H 2 PO 4 –, NO 3 –, and ClO 4 – .