Altieri, A. ; Aucagne, V. ; Carrillo, R. ; Clarkson, GJ ; D’Souza, DM ; Dunnett, JA ; Leigh, DA and Mullen, KM
Chemical Science (2011) 2 (10) 1922-1928 - doi : 10.1039/C1SC00335F
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We report on the synthesis, structure and properties of rotaxanes prepared by the assembly of benzylic amide macrocycles around a series of amide and sulfide-/sulfoxide-/sulfone-containing threads. The efficacy of rotaxane formation is related to the hydrogen bond accepting properties of the various sulfur-containing functional groups in the thread, with the highest yields (up to 63% with a rigid vinyl spacer in the template site) obtained for sulfoxide rotaxanes. X-Ray crystallography of a sulfoxide rotaxane, 5, shows that the macrocycle adopts a highly symmetrical chair-like conformation in the solid state, with short hydrogen bonds between the macrocycle isophthalamide NH-protons and the amide carbonyl and sulfoxide S–O of the thread. In contrast, in the X-ray crystal structures of the analogous sulfide (4) and sulfone (6) rotaxanes, the macrocycle adopts boat-like conformations with long intercomponent NHO[double bond, length as m-dash]SO and NHS hydrogen bonds (in addition to several intercomponent amide–amide hydrogen bonds). Taking advantage of the different hydrogen bonding modes of the sulfur-based functional groups, a switchable molecular shuttle was prepared in which the oxidation level of sulfur determines the position of the macrocycle on the thread.