A [2]Catenane and a [2]Rotaxane as Prototypes of Topological and Euclidean Molecular “Rubber Gloves”

Abstract

A [2]catenane and a [2]rotaxane have been prepared from a C2-symmetric, 2,9-diphenyl-1,10-phenanthroline-based (dpp-based) macrocycle incorporating a 1,5-dioxynaphthalene subunit by means of the transition metal templated technique. In the case of the catenane, this macrocycle is interlocked with a dpp-based macrocycle that is oriented through the location of a p-tolyl substituent in the 4-position of the phenanthroline subunit. In the case of the rotaxane, the C2-symmetric macrocycle is threaded onto an oriented, dumbbell-shaped molecule, based on the same 4-p-tolyl-1,10-phenanthroline subunit, which bears tetraarylmethane stoppers. Both species are chemically achiral molecules, yet they are composed entirely of asymmetric, mirror-image conformations. Conformational enantiomerization processes therefore take place exclusively by chiral pathways, conferring on these molecules the "rubber glove" property. However, while the molecular graph (constitutional formula) of the [2]rotaxane can be deformed into a planar and, hence, rigidly achiral representation, a feature shared by a few other compounds in the literature that have been characterized as "Euclidean rubber gloves", the molecular graph of the [2]catenane cannot be deformed in this way. It therefore has the unique property of being a chemically achiral "topological rubber glove".

A Chiral Macrocyclic Oligothiophene with Broken Conjugation – Rapid Racemization through Internal Rotation

“…Interesting is the enantiomerization of 1, which due to its 3D PC building block follows Mislow's 'Euclidean rubber glove' mechanism. [42] [43] In other words, the molecule becomes its mirror image by rotations around single bonds without ever adapting a flat achiral conformation. The enantiomerization mechanism thus resembles the inversion of the chirality of a rubber glove, which is achieved by the complex movement of turning the glove inside out.…”

Mechanical Chirality of Rotaxanes: Synthesis and Function

“…In fact, the authors achieved the separation of enantiomerically pure [2]rotaxanes, which displayed a mirror image CD spectra. The relationship between these enantiomers involves a chiral inversion like "turning over the rubber gloves" [25,26]. A catenane with similar chirality was also reported by Sauvage et al [25].…”

Chirality in rotaxanes and catenanes

“…77c ). 159 , 160 Neither of the rings in catenane 152 are themselves chiral, but one contains a dialkoxynaphthalene unit that can function as a conformational planar stereogenic element and the other is oriented with C 1h symmetry. When they are interlocked in catenane 152 , the resulting ensemble is chiral but the enantiomers can be exchanged by rotation of the naphthalene unit between the two enantiomeric conformations.…”