Dimeric and trimeric catenation of giant chiral [8 + 12] imine cubes driven by weak supramolecular interactions

Abstract

Mechanically interlocked structures, such as catenanes and rotaxanes, are fascinating synthetic targets and some are used for molecular switches and machines. Today, the vast majority of catenated structures are built upon macrocycles and only a very few examples of three-dimensional shape-persistent organic cages forming such structures have been reported. However, the catenation in all these cases was based on a thermodynamically favoured π–π-stacking under certain reaction conditions. Here, we show that catenane formation can be induced by adding methoxy or thiomethyl groups to one of the precursors during the synthesis of chiral [8 + 12] imine cubes, giving dimeric and trimeric catenated organic cages. To elucidate the underlying driving forces, we reacted 11 differently 1,4-disubstituted terephthaldehydes with a chiral triamino tribenzotriquinacene under various conditions to study whether monomeric cages or catenated cage dimers are the preferred products. We find that catenation is mainly directed by weak interactions derived from the substituents rather than by π-stacking.

Solvent‐Controlled Quadruple Catenation of Giant Chiral [8+12] Salicylimine Cubes Driven by Weak Hydrogen Bonding

“…After screening more solvents for the reaction of enantiopure TBTQ (+)‐( M )‐ 1 and diamine 2 , we discovered, that in chlorobenzene the product gives a complex 1 H NMR spectrum with many peaks in the aromatic region (Figure 1c) and the corresponding MALDI‐TOF mass spectrum showed not only the [8+12] cage ( M )‐ 3 ( m / z 5309.34, Na + ‐adduct) but also a [16+24] cage ( M )‐ 4 ( m / z 10595.37, Na + ‐adduct) (Figure 1d). Based on our previous experience with the NMR spectra of dimeric and trimeric catenanes of chiral [8+12] imine cubes we assumed that the new species is a dimeric catenane and not a larger single cage with another geometry than a cube [18d] …”

“…This is the number of signals expected for a chiral quadruply interlocked dimeric catenane with D 4 ‐symmetry. A singly interlocked catenane (2×12 signals), or a triply interlocked catenane (2×8 signals) can definitely be excluded [18d] …”

Porous Organic Cages

“…This observation suggests that POCs could be candidates for housing artificial molecular machines with flexible extended limbs and mechanical stability under harsh conditions. The second one is the formation of dimeric and trimeric catenated cage cubes based on the weak interactions of the substituents (methoxy or thiomethyl groups) of the constituent 1,4-disubstituted terephthaldehydes in combination with solvophobic effects. These interlocked cage structures are very promising for future molecular switches or machines.…”

[4 + 4]-Imine Cage Compounds with Nitrogen-Rich Cavities and Tetrahedral Geometry

“…9,26 Most cage compounds are synthesized by dynamic covalent chemistry (DCC). 27 Among DCC reactions, the reactions forming boronic acid esters or imines are the most common ones and for the latter a huge variety of geometries such as (truncated) 28,29 tetrahedra, [30][31][32][33] trigonal prisms, [34][35][36] cubes, 16,37,38 rhombicuboctahedra, [39][40][41] adamantoids, 35,42,43 tetrapods, 44 cucurbitimines 45 or more complex structures such as catenanes 46,47 have been realized and some of these structures have even been post-stabilized to enhance their chemical robustness. 6,[48][49][50] Cages with nitrogen-containing pyridine 9,51 or pyrrol-units 52 showed superior behavior in, e.g., ion recognition and could act as ligands for several transition metal ions as shown for numerous metal-organic cage compounds or complexes.…”