Isomeric 2,6-Pyridino-Cryptands Based on Dibenzo-24-crown-8

摘要

Cryptands 4 and 5 were synthesized from cis- and trans-bis(hydroxymethylbenzo)-24-crown-8 by reaction with pyridine-2,6-dicarboxylic acid chloride in 42 and 48% yields, respectively. The new cryptands form pseudorotaxanes with the paraquat derivative N,N′-bis(β-hydroxyethyl)-4,4′-bipyridinium bis(hexafluo-rophosphate) ("paraquat diol", 6): K_a = 1.0 x 10~4 and 1.4 x 10~4 M~(-1), respectively. The cryptands also form complexes with ammonium hexafluorophosphate. Formation of the paraquat/cryptand-based pseudorotaxanes can be switched off and on in a controllable manner on the basis of the cryptands' abilities to complex KPF_6 strongly, providing a new mechanism for control of molecular shuttles. K~+ displaces paraquat diol from the cryptands, converting yellow-orange solutions to colorless; however, addition of 18-crown-6 binds the KPF_6 and allows the colored cryptand-paraquat complex to reform. Crystal structures are reported for both cryptands, both paraquat diol-based pseudorotaxanes, both NH_4-PF_6 complexes, and both KPF_6 complexes.