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 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-.