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

Abstract

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 <b>3Ru-[1</b>_<b>5</b><b>]PCP-II</b>⁶⁺, 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 <b>3Ru-[1</b>_<b>5</b><b>]PCP-II</b>⁶⁺ 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 <b>3Ru-[1</b>_<b>5</b><b>]PCP-II</b>·6OTf is maintained to some extent in the presence of excess Cl^-, SO₄^2-, H₂PO₄^-, NO₃^-, and ClO₄^-.