Tris-ACE-(6,6′-bipyridyl)-α-cyclodextrin: synthesis and chirality of the tripodal metal complexes

A heterotritopic α-cyclodextrin tripod has been synthesized by the Staudinger-Aza-Wittig (SAW) reaction. Complexation properties and conformational events upon coordination with ‘hard’ to ‘borderline’ transition metals have been analyzed. Spontaneous formation of selective Λ-helicity has been observed via the coordination with CuII and NiII cations. This Letter describes the synthesis of a C3-symmetrical tris-ACE-(6,6′-bipyridyl)-α-CyD via ‘one-pot’ Staudinger-Aza-Wittig reaction (SAW). Metal complexation behavior was investigated by UV–vis and Circular Dichroism. Coordination of 6,6′-bipyridyl units with CuII and NiII cations, spontaneously generates a strong exciton coupling-type positive Cotton effect proving the formation of a Λ-helix with a left-handed screw propeller (M).