Structures and solution dynamics of pseudorotaxanes mediated by alkali-metal cations

Abstract

Kinetic stability studies of a series of pseudorotaxanes formed from electron-rich crown ethers (hosts 1 and 2) and naphthalene diimide (guest A) in the presence of alkali salt templates MX (where M⁺ = Li⁺ and Na⁺, and X⁻ = Cl⁻, Br⁻, I⁻, NO₃⁻ and CF₃SO₃⁻) were performed by ¹H NMR. The switching between the (bound) host 1 and its linkage isomer host 2 (free) was monitored in solution in the presence and absence of alkali salts, to establish the relative thermodynamic stabilities in the series. We also report here six new crystal structures, for pseudorotaxanes of type: [1·A], [M₂·1·A]²⁺ and [M₂·2·A]²⁺. Their solution-phase structures are in good agreement with the solid-state structures determined by X-ray crystallography.