Investigating the synthesis and structure of [2]pseudorotaxanes assembled by crown ether as wheel component and dual-cation axle with phosphonium and ammonium cations

Abstract

Pseudorotaxanes have attracted attention as intriguing building blocks for the construction of stimuli-responsive supramolecular materials. One of the primary goals of our laboratory is the development of synthetic supramolecular compounds containing phosphorous atoms. Herein, we report the design and synthesis of simple [2]pseudorotaxanes containing phosphonium salts. Dual-cation axle molecules were synthesized from a dialkylammonium cation, as a recognition site for 24-crown-8 (24C8) or dibenzo-24-crown-8 (DB24C8), and an alkyltriphenylphosphonium cation; these were used to obtain [2]pseudorotaxanes in a 1:1 ratio with 24C8 and DB24C8. The formation of [2]pseudorotaxanes with crown ethers positioned at ammonium cations on the axle compounds was confirmed by nuclear magnetic resonance (NMR) and X-ray crystallography, revealing that the CH/π interaction between phenyl group of alkyltriphenylphosphonium and that of DB24C8 increases the stability of a [2]pseudorotaxane.