Orientational isomers of cyclodextrin semirotaxanes and rotaxanes with organic and transition metal complex stoppers

The novel asymmetric dicationic ligands [Quin(CH2)(10)tbp](2+), [Quin(CH2)(10)bpy](2+), and [Lut(CH2)(10)bpy](2+) (Quin(+) = quinuclidinium, Lut = 3,5-lutidinium, tbp(+) = 4-tert-butylpyridinium, and bpy(+) = 4,4'-bipyidinium) form [2]semirotaxanes with alpha- and beta-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)(10)tbp](2+)[2]semirotaxane with alpha-CD have been investigated by H-1 NMR spectroscopy. Complexation of the free nitrogen on the 4,4'-bipyridinium end groups of the [R(CH2)(10)bpy](2+) ligands by the aquapentacyanoferrate(II) ion results in the formation of the corresponding [2]rotaxanes.