Chemical On/Off Switching of Mechanically Planar Chirality and Chiral Anion Recognition in a [2]Rotaxane Molecular Shuttle

Abstract

We exploit a reversible acid–base triggered molecular shuttling process to switch an appropriately designed rotaxane between prochiral and mechanically planar chiral forms. The mechanically planar enantiomers and their interconversion, arising from ring shuttling, have been characterized by NMR spectroscopy. We also show that the supramolecular interaction of the positively charged rotaxane with optically active anions causes an imbalance in the population of the two enantiomeric coconformations. This result represents an unprecedented example of chiral molecular recognition and can disclose innovative approaches to enantioselective sensing and catalysis.

Photoinduced Electron Transfer Involving a Naphthalimide Chromophore in Switchable and Flexible [2]Rotaxanes

“…Rotaxanes based on a DB24C8 macrocycle surrounding an axle composed of a dialkyl‐ammonium (amH + ) and a triazolium (tria + ) station have recently been proposed as acid‐base switchable molecular devices . These rotaxanes can be readily synthesized and easily functionalized either at the ring or at the axle.…”

“…Rotaxanes based on aD B24C8 macrocycle surrounding an axle composed of ad ialkyl-ammonium (amH + )a nd at riazolium (tria + )s tation have recently been proposed as acid-base switchable molecular devices. [19][20][21][22][23][24][25][26][27][28][29][30] These rotaxanes can be readily synthesized and easily functionalized either at the ring or at the axle. Hence,w ed esigned a [ 2]rotaxane bearing a phenothiazine (PTZ) donor unit linked to the crown ether ring and ap hotoactivable naphthalimide( NI)a cceptor unit as a stopper( Scheme 1).…”

Chiroptical inversion of a planar chiral redox-switchable rotaxane

“…However, switchable planar chiral rotaxanes remain rare. So far, the modulation of chirality relies on heat, 21 the choice of solvent, anion exchange, 35 or pH. 36 Recently, we described redox-switchable rotaxanes, in which the wheels are decorated with tetrathiafulvalenes (TTF).…”

Mechanical Chirality of Rotaxanes: Synthesis and Function

“…In rubber-glove-like chirality, there is no potential bias to determine the wheel's shuttling direction on the axle in general. Credi and Baroncini et al achieved a one-directional selective shuttling by utilizing a diastereomeric salt system (Scheme 8) [27].…”

“…In rubber-glove-like chirality, there is no potential bias to determine the wheel's shuttling direction on the axle in general. Credi and Baroncini et al achieved a one-directional selective shuttling by utilizing a diastereomeric salt system (Scheme 8) [27]. [2]Rotaxane 20, derived from prochiral [2]rotaxane 19, potentially has mechanical chirality, but these are dynamic racemic mixtures because the wheel component can move freely on the axle, having a symmetrical structure.…”