Structure and Properties of Modular Components for Applications in Topological Supramolecular Chemistry

Abstract

As a practical application of the structure of products derived from simple reactions of modular components, the background to a system for topological supramolecular assembly is introduced. Familiar base-catalyzed carbonyl condensation chemistry, acting on combinations of cyclic 1,3-diketones and aromatic aldehydes, provides thermodynamically controlled access to molecular entities of appropriate bulk to act as stoppers in rotaxane structures. Under acid-catalyzed reaction conditions, an additional, irreversible, dehydration step is introduced, thereby providing a putative mechanism for locking in place a specified topology. These ideas are illustrated with the preparation and X-ray structures of model systems derived from 5,5-dimethylcyclohexane-1,3-dione and two model aromatic dialdehydes, representing the results of the application of both reversible and irreversible reaction conditions. Additional model compounds are employed to demonstrate reaction reversibility in the former case.

An Approach to Thermodynamically Controlled Supramolecular Assembly Possessing an Integral Locking Mechanism

“…Unsurprisingly, rotaxane 7 is spectroscopically similar to the parent 6 (Figure e). The sole notable change is the diagnostic shift of the stopper methine proton (from 5.46 to 4.75 ppm) . As observed for its thermodynamically assembled precursor, rotaxane 7 is quite stable with respect to dissociation into its component parts.…”

“…For example, imine exchange may be terminated via CN reduction while processes involving olefin, disulfide, and hydrazide linkages are shut down by catalyst removal . We describe here the application to a supramolecular assembly process of a reversible carbonyl chemistry-based reaction that additionally provides the facility, via a subsequent irreversible dehydration, to permanently fix an evolved molecular structure . This approach, by nature of its derivation from familiar reactions and the application of simple base or acid catalysis, has potentially broad general utility.…”

“…From a supramolecular perspective this process offers a ready means of converting a small molecular entity (an aldehyde) into one of considerably greater bulk, an attractive overall conversion with regard to, for example, rotaxane synthesis. While the first addition of 1,3-diketone A is irreversible, forming, after dehydration, Michael adduct B , the second addition has been shown to be reversible under conditions of base catalysis. , Treatment of the resulting adducts C with catalytic acid triggers a locking mechanism whereby a dehydrative cyclization affords adduct D . The overall sequence of events is thus ideally suited to reversible supramolecular assembly processes: noncovalent interactions may be harnessed under conditions of base catalysis to direct formation of an energy minimized structure, with subsequent treatment with acid locking the assembled structure in place.…”

“…Alternatively, one could imagine employing this addition chemistry as a macrocyclization reaction, or as a means to establish libraries of adducts from a pool of aldehydes and diketones . Finally, the dehydrative locking chemistry may be conducted in the presence of amines to form, in high yield, fluorescent acridone diones. , The inclusion of linear diamines here would thus open a route to polymeric systems, including polyrotaxanes. These and other avenues are under investigation.…”

Quantitative analysis of intermolecular interactions in 2,2’-((4-bromophenyl)methylene)bis(3-hydroxy-5,5-dimethylcyclohex-2-en-1-one): insights from crystal structure, PIXEL, Hirshfeld surfaces and QTAIM analysis

“…It is of interest to note that several arylmethylene bis(3-hydroxy-5,5-dimethylcyclohex-2en-1-one) derivatives have been crystallographically analyzed. [13][14][15][16][17][18][19][20] It is known that the crystal packing is predominantly controlled by strong intermolecular hydrogen bonds such as O/N−H • • • O/N due to the presence of strong donor and acceptor atoms. 21,22 Moreover, the weak intermolecular interactions such as C−H • • • O/N, 23,24 C−H • • • halogens, 25,26 C−H • • • π 27 and π • • • π 28 interactions can also interplay a crucial role in controlling the crystal packing in the absence of strong donors and acceptors.…”