Self-Assembly of Novel [3]- and [2]Rotaxanes with Two Different Ring Components:  Donor−Acceptor and Hydrogen Bonding Interactions and Molecular-Shuttling Behavior

Abstract

Three of the first kind of hetero[3]rotaxanes, which comprise one linear component and one neutral and one tetracationic ring component, have been assembled by using the intermolecular hydrogen bonding and donor-acceptor interactions. Three neutral [2]rotaxanes and three tetracationic [2]rotaxanes have also been synthesized as intermediate products or for the sake of property comparison. The linear molecules are incorporated with two glycine subunits, for templating the formation of the neutral tetraamide cyclophane, and one or two hydroquinone subunits, for inducing the formation of the tetracationic cyclophane. Variable-temperature (1)H NMR investigation reveals that the shuttling behavior of the tetracationic ring component along the linear component is substantially influenced by the existence of the neutral ring component. The spatial repelling interaction of the neutral ring on the electron-deficient tetracationic ring simultaneously weakens the latter's "positioning" tendency at both electron-rich hydroquinone sites of the linear component. As a result, the activation energy associated with the shuttling process of the tetracationic ring between the two hydroquinone sites is remarkably reduced in comparison to that of the shuttling process of the corresponding neutral ring-free [2]rotaxanes. For the first time, the rotation of the dipyridinium subunit around the axis formed by the two methylene groups connecting them within the tetracationic cyclophane has been investigated by variable-temperature (1)H NMR spectroscopy and the associated kinetic data have also been successfully obtained. Furthermore, the UV-vis and fluorescent properties of the new [2]- and [3]rotaxanes have been studied. The results demonstrate that [3]rotaxanes with different ring components possess unique kinetic features that are not available in [3]rotaxanes with identical ring components.

[2]Pseudorotaxanes Based on Naphtho‐21‐crown‐7 and Secondary Dialkylammonium Salts: Remarkably Improved Association Constants Among Four Threaded Structures

“…The organic solution was concentrated. The crude product thus obtained was subjected to column chromatography over silica gel column and elution done with mobile phase of dichloromethane/acetonitrile (10∶1, V∶V), the desired fraction thus eluted was evaporated under vacuum to afford a white solid (2.3 g, 33%) 1 …”

“…It was collected by suction filtration and recrystallized from deionized water three times to afford G2 (3.31 g, 23.3%) as a white solid. 1 …”

“…Pseudorotaxanes as synthetic templates were widely used to construct rotaxanes, [1][2][3][4][5][6][7][8][9][10][11] catenanes [12][13][14][15][16][17] and supramolecular polymers, [18][19][20][21][22][23][24][25][26][27][28][29][30] which have potential application in intelligent material such as molecular device, [31] artificial molecular machine, [32] molecular electronic device [33] and new functional materials, [34][35][36][37] etc. Pseudorataxanes as threaded structures attracted much interest from supramolecuar scientist because of their topological importance but also due to their many potential applications.…”

Hydrogen-Bond-Mediated Template Synthesis of Rotaxanes, Catenanes, and Knotanes

“…Also, pseudorotaxanes with photoswitchable threading/dethreading behavior [197] and molecular shuttles based on peptide [2]rotaxanes [198][199][200] and [3]rotaxanes [201,202] have been developed. The ring rotation around the rotaxane axle can be induced by an external alternating electric field [203] or by electrochemical means [204].…”

Self‐Assembly of a Supramolecular, Three‐Dimensional, Spoked, Bicycle‐like Wheel

“…[10] In this three-component ensemble, two different terpyridine ligands and one type of metal were self-assembled. The benzyl group in 3 was removed with ammonium formate in the presence of a Pd/C catalyst to afford 4, which underwent alkylation with N-(6-bromohexyl)phthalimide [14] to give the imide 5. Notably, very few supramolecular spokedwheel systems have been reported, [10,11] since the self-assembly of multiple components can be a synthetic challenge that requires more precise control over the geometry and connectivity.…”