Stereoselective Formation of Rotaxanes Composed of Polymethylene-bridged Dinuclear Cobalt(III) Complexes and α-Cyclodextrin. II

Abstract
[2]-[[(en)2Co{XCH2S(CH2)nSCH2Y}Co(en)2]Clm]-[α-CDX]-rotaxanes (n=8, 10, and 12 for X=Y=CO2− (m=4); n=10 for X=CO2− and Y=CH2NH2(m=5); α-CDX=α-cyclodextrin) were prepared with partial stereoselectivity and characterized from their visible-UV absorption, circular dichroism(CD), and 13C NMR spectra, and elemental analysis. The rotaxane formation could be identified by the down field shift of the chemical shift due to α-CDX in the 13C NMR spectra and the increase of the CD intensity in the ligand-to-metal charge transfer band region in the CD spectra. The rotaxanes always showed apparently ΔΔ-rich CD spectra, the highest selectivity(10% ΔΔ-rich) being found in the case of n=10.