Rotaxane Formation\nfrom Borate Ion-Containing Crown\nEther and Ammonium Ion: Enhancement of Their Association through Ion-Pairing

We synthesized [2]rotaxanes featuring a catechol borate\nion-containing\ncrown ether and secondary ammonium ions. These rotaxane components\nshow both ion–ion interactions and hydrogen bonds. X-ray crystallography\nand NMR spectroscopy allowed elucidation of the rotaxane structure.\nMoreover, <sup>1</sup>H NMR spectroscopy revealed the rotaxane synthesis\ncan be thermodynamically controlled. The binding affinity between\nthe borate-containing crown ether and ammonium ions is enhanced by\nion-pairing.