A new slippage synthesis

At elevated temperatures, the crown ether dibenzo[30]crown-10 (DB30C10) slips over the (relatively) bulky 3,5-(t-Bu)(2)C6H3CH2 termini of a bisammonium dication-bearing two secondary ammonium centers separated through a p-xylylene spacer-to form primarily a three-component rotaxane-like entity-stabilized by, inter alia, [N+-H ... O] and [C-H ... O] hydrogen bonds-that has been characterized by liquid secondary ion (LSI) mass spectrometry (in the "gas phase"), H-1 NMR spectroscopy (in solution) and X-ray crystallography (in the solid state). However, this species equilibrates, in solution, with the free DB30C10 macrocycle and its two-component rotaxane-like congener, a result that demonstrates that the products obtained from the slippage synthesis are pseudorotaxanes. (C) 1998 Elsevier Science Ltd. All rights reserved.