Template-Free Synthesis of a Phenanthroline-Containing [2]Rotaxane: A Reversible pH-Controllable Molecular Switch

Abstract

The synthesis of symmetric and asymmetric rotaxanes consisting of neutral axle and ring components without ionic templates is necessary for applications in molecular sensors and molecular switches. A phenanthroline-containing symmetric [2]rotaxane was newly synthesized by inducing hydrogen bonding and π-interaction using a template-free threading-followed-by-stoppering method. The obtained rotaxane serves as a reversible pH-controllable molecular switch.

Controlling the Molecular Shuttling of pH‐Responsive [2]Rotaxanes with Two Different Stations

“…The successful synthesis of [2]rotaxane 1 was achieved via the introduction of bulky stoppers using a reductive amination reaction. [42,43] We also proved that the macrocycle of [2]rotaxane 1 reversibly switches between two stations, i. e., a phenanthroline moiety and a protonated aniline moiety, upon changing the pH value (Scheme 1). However, in these preliminary experiments, [43] detailed molecular dynamic NMR spectroscopic studies, for the purpose of determining the free energy of activation (ΔG � ), were not conducted.…”

“…Novel [2]rotaxane 2 was obtained from the reaction of the wheel component, isophthalamide‐containing macrocycle 7 with a larger half dibenzo‐crown ether as a wheel in order to compare the effects of ring size on the activation barrier of ring shuttling, with the axle component, phenanthroline bis‐aldehyde 8 , in CH 2 Cl 2 , followed by treatment with aniline derivative 9 (the stopper; large enough to prevent dethreading the wheel component), MgSO 4 (dehydrating agent), and NaBH(OAc) 3 (reducing agent) (Scheme 2). Pure 2 and its corresponding free dumbbell ( 5 ) (Figure S8) were isolated in 29 % and 8 % yield, respectively, using preparative gel‐permeation chromatography (GPC) [43] …”

“…Previously, we have reported the synthesis of [2]rotaxane 1 and found that upon the addition of acid and base, the wheel component of 1 reversibly switches between a phenanthroline moiety and a protonated aniline moiety. [43] This paper reports the synthesis of new derivatives of [2]rotaxanes 2-4 and their detailed molecular dynamic NMR spectroscopic analysis. Novel [2]rotaxane 2 was obtained from the reaction of the wheel component, isophthalamide-containing macrocycle 7 with a larger half dibenzo-crown ether as a wheel in order to compare the effects of ring size on the activation barrier of ring shuttling, with the axle component, phenanthroline bisaldehyde 8, in CH 2 Cl 2 , followed by treatment with aniline derivative 9 (the stopper; large enough to prevent dethreading the wheel component), MgSO 4 (dehydrating agent), and NaBH(OAc) 3 (reducing agent) (Scheme 2).…”

Phenanthroline based rotaxanes: recent developments in syntheses and applications

“…Synthesis of Scheme 38 Synthesis of [2]rotaxane involving p-p stacking and hydrogen bond. 33 this rotaxane is straightforward and involves the treatment of the phenanthroline derivative with benzaldehyde moieties, 107 with the macrocyclic component 108 in CDCl 3. This resulted in a pseudorotaxane intermediate which upon introduction of the stopper, tritylaniline 109 furnished the nal [2] rotaxane 110 in 60% yield.…”

“…Muraoka and co-workers reported an efficient synthesis of a phenanthroline based [2]rotaxane by simultaneous induction of hydrogen bonding and π-interaction between the components ( Scheme 38 ). 33 This rotaxane, which incorporates the phenanthroline moiety in its axle component and an isophthalamide derived non-ionic macrocycle, was found to act as a reversible pH-controllable molecular switch. Synthesis of this rotaxane is straightforward and involves the treatment of the phenanthroline derivative with benzaldehyde moieties, 107 with the macrocyclic component 108 in CDCl 3.…”