Anion‐Assisted Complexation of Paraquat by Cryptands Based on Bis( m ‐phenylene)‐[32]crown‐10

The complexation of tightly ion‐paired divalent salts such as paraquat dichloride by cryptands based on crown ethers can be improved by the introduction of ion‐pair recognition as a means of also binding the counteranions. A series of diamide‐based cryptands derived from bis( m ‐phenylene)‐[32]crown‐10 and designed to complex the bipyridinium dication with anion assistance was synthesized. The ion‐pair recognition process was fully characterized by 1 H NMR spectroscopy, UV/Vis spectroscopy, electrospray ionization mass spectrometry and single crystal X‐ray analysis. 1 H NMR spectroscopy demonstrated that these new heteroditopic cryptand hosts can complex both the positive and negative components of the paraquat dichloride salt. UV/Vis spectroscopy showed that the addition of chloride anion into equimolar solutions of cryptands 3 c or 3 g with paraquat bis(hexafluorophosphate) salt ( 2 a ) improves the binding of the cryptands to the paraquat guest. Electrospray ionization mass spectrometry and single‐crystal X‐ray analysis confirmed the 1:1 stoichiometries and ion‐pair recognition of these cryptand/paraquat complexes. It was found that the cryptand 3 g , with 13 atoms and an isophthalamide moiety in the third chain, exhibited the best binding affinity for tightly ion‐paired paraquat dichloride ( 2 b ), due to the combination of its spatial compatibility and additional anion‐binding site.