Improved complexation of paraquats with crown ether‐based pyridyl cryptands.

Abstract: The commonly used paraquat guest <italic>N</italic>,<italic>N</italic>′‐dimethyl‐4,4′‐bipyridinium bis(hexafluorophosphate) (<bold>7</bold>) was targeted for structural alterations to improve the binding constants with crown ethers and cryptands. The association constant was improved by one order of magnitude (to <italic>K</italic>a = 1.00 × 106 mol L−1) with the dibenzo‐30‐crown‐10 pyridyl cryptand host <bold>5</bold> by changing the N‐methyl groups to benzyl and the counterions from PF6 to TFSI, that is, <bold>11</bold>. Moreover, through addition of a <italic>p</italic>‐bromobenzyloxy moiety on the 4‐position of the pyridyl ring of cryptand <bold>18</bold>, an association constant of <italic>K</italic>a = 5.35 × 106 mol L−1 was achieved with paraquat <bold>11</bold>. [ABSTRACT FROM AUTHOR]