Orientational Isomers of Cyclodextrin Semirotaxanes and Rotaxanes With Organic and Transition Metal Complex Stoppers

Abstract

The novel asymmetric dicationic ligands [Quin(CH2)10tbp]2+, [Quin(CH2)10bpy]2+, and [Lut(CH2)10bpy]2+ (Quin+ = quinuclidinium, Lut = 3,5-lutidinium, tbp+ = 4-tert-butylpyridinium, and bpy+ = 4,4′-bipyidinium) form [2]semirotaxanes with α- and β-cyclodextrins in aqueous solution, with the cyclodextrin passage possible only over the 4-tert-pyridinium or bipyridinium end groups to yield two orientational isomers. The kinetics of the formation and dissociation of the kinetically and thermodynamically preferred orientational isomers of the [Quin(CH2)10tbp]2+[2]semirotaxane with α-CD have been investigated by 1H NMR spectroscopy. Complexation of the free nitrogen on the 4,4′-bipyridinium end groups of the [R(CH2)10bpy]2+ ligands by the aquapentacyanoferrate(II) ion results in the formation of the corresponding [2]rotaxanes.