Degenerate Molecular Shuttles with Flexible and Rigid Spacers

摘要

The preparation and dynamic behavior of degenerate rotaxane molecular shuttles are described in which a benzylic amide macrocycle moves back and forth between two naphthalimide-glycine units along a diphenylethyne spacer or an aliphatic spacer consisting of a C9, C12, or C26 alkyl chain. Subtle differences in the 1H NMR spectra of the rotaxanes can be related to the presence of conformers in which the macrocycle interacts simultaneously with both glycines, especially in the case of the C9 spacer. The kinetic data of the shuttling behavior in the C26 rotaxane were obtained from dynamic NMR spectroscopy. The Eyring activation parameters were found to be ΔH‡ = 10 ± 1 kcal mol–1, ΔS‡ = −6.5 ± 2.0 cal mol–1 K–1, ΔG‡298 = 11.9 ± 0.2 kcal mol–1. For the systems with the shorter spacers, the shuttling rates were higher. Also in the diphenylethyne, rotaxane shuttling is rapid on the NMR time scale, indicating that the rigid unit does not impose a large barrier to the translocation of the macrocycle.