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-[1 5 ]­PCP-II 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 3Ru-[1 5 ]­PCP-II 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 3Ru-[1 5 ]­PCP-II·6OTf is maintained to some extent in the presence of excess Cl–, SO4 2–, H2PO4 –, NO3 –, and ClO4 –.

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