Stereoselective Formation of Rotaxanes Composed of Polymethylenebridged Dinuclear Cobalt(III) Complexes and α- or β-Cyclodextrin

Abstract

Abstract [2]-[[(en)2Co{NH2(CH2)2S(CH2)nS(CH2)2NH2}Co(en)2]Cl6]-[α- or β-CDX]-rotaxanes were prepared with partial stereoselectivity and characterized from their absorption and 13C NMR spectra, molar conductance, and elemental analysis (CDX=cyclodextrin; n=8, 10, and 12). The rotaxanes always showed apparently ΔΔ-rich. CD spectra, the highest selectivity (16% ΔΔ-rich) being found in the case of n=10 and α-CDX. The results are related to the direct preparation of [2]-[ΔΔ-[(en)2Co{NH2(CH2)2S(CH2)nS(CH2)2NH2}Co(en)2]Cl6]-[α-CDX]-rotaxanes (n=8, 10, and 12) in relatively higher yields than the corresponding ΛΛ rotaxanes: 3.5% for n=8, 21% for n=10, and 28% for n=12. Inclusion complexes of a new type [Co(en)2{NH2(CH2)2S(CH2)nBr}]Cl3·2(α-CDX) were also isolated (n=10 and 12).