From rotaxanes to knots. Templating, hydrogen bond patterns, and cyclochirality

Abstract

Rotaxanes of the amide type have been accessible in preparative yields by a variety of reactions. Beneath SN2- and SN2t-mechanisms we developed a synthesis of [2]rotaxanes that comes off a Michael addition. The motif of the attractive interactions between an axle-shaped and a macrocyclic wheel part to form rotaxanes consists of multiple hydrogen bonds in the nonionic strategy (threading), as well as in a new high yield anionic template synthesis (trapping). We introduce new synthetic routes for the preparation of [n]rotaxanes using nonionic as well as anionic templates. Furthermore, we report on the latest results of the statistical synthesis (slipping) by melting together axle and wheel to form rotaxanes. The chiroptical properties of a homologous series of cycloenantiomeric [1]rotaxanes as well as a cyclodiastereomeric [3]rotaxane have been described. The differences in the Cotton effects obtained show that small structural changes have an impact on the chiroptical properties of rotaxanes. The first X-ray structures obtained of cycloenantiomerically chiral amide-based [2]- and [1]rotaxanes as well as of the first topologically chiral amide-based knot compound were solved which show networks of H-bonds between the entities of the rotaxanes and the segments of the knot-shaped molecule. Our investigations in template effects based on hydrogen bonding for the synthesis of supramolecular structures open up a variety of strategies for the preparation of catenanes, rotaxanes andrecentlyeven molecular knots.

Anion Recognition and Templation in Coordination Chemistry

“…[23,24] It is often employed in synthetic chemistry and materials science, and Nature employs it to form complex supramolecular assemblies inside the living cell. [26][27][28][29][30][31] A template can be considered as an entity that contains the required information to help organise a collection of building blocks in a specific manner. [25] In the context of synthetic organic and inorganic chemistry, this strategy not only enables the synthesis of molecules in a more efficient manner, but also aids in the preparation of assemblies that have unusual topologies, such as rotaxanes, helicates and catenanes.…”

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

“…This short introduction into topology may serve to help understand the phenomenon of topological chirality [177][178][179]. Without any stereogenic center involved, catenanes and rotaxanes can be made chiral [180,181]. Just imagine that directionality is introduced in each of the subunits of the catenane and rotaxane in Fig.…”

Lithium‐Templated Synthesis of a Donor–Acceptor Pseudorotaxane and Catenane

“…Rotaxanes and catenanes have for some time been the subject of intense study [1][2][3][4][5][6][7] both because of their fascinating architectures, [8][9][10][11][12][13][14][15][16][17][18] and because they may have useful properties as molecular-level switches and sensors. [5,[19][20][21][22][23][24][25] Our approach has been to bring together neutral electron-rich components such as crown ether 1 (the "donor") and electron-poor components such as pyromellitic diimide 2 (the "acceptor") to create highly colored donor-acceptor systems that are neutral, chemically robust, and capable of postsynthetic modification.…”