Crown Ether Appended Cyclam Receptors for Cationic Guests

A series of crown ether appended macrocyclic amines has been prepared comprising benzo-12-crown-4, benzo-15-crown-5, or benzo-18-crown-6 attached to a diamino-substituted cyclam. The CoIII complexes of these three receptors have been prepared and characterized spectroscopically and structurally. Crystal structures of each receptor in complex with an alkali metal ion and structures of the benzo-12-crown-4 and benzo-15-crown-5-receptors without guest ions are reported. 2D NMR and molecular mechanics modeling have been used to examine conformational variations upon guest ion complexation. Addition of cations to these receptors results in an appreciable anodic shift in the CoIII/II redox potential, even in aqueous solution, but little cation selectivity is observed. Evidence for complex formation has been corroborated by 23Na and 7Li NMR spectroscopy and electrospray mass spectrometry.