The Effect of Alcohol Structures on the Interaction Mode with the Hexameric Capsule of Resorcin[4]arene

Abstract

After more than a century of research on resorcin[4]arenes (1) it is clear that such systems form spontaneously [1(6)(H(2)O)(8)]-type hexameric capsules in wet, non-polar, organic solvents. However, the interactions of these hexameric capsules with alcohols are far from being solved. Here we provide the results of an extensive study on the interaction of different alcohols with the hexameric capsules of resorcin[4]arene 1a by focusing on the exchange of magnetization manifested in diffusion NMR measurements of such capsular systems. We found that some alcohols such as 2-octyl-1-dodecanol and 1-octadecanol do not interact with the hexamers of 1a, whereas other alcohols such as 3-ethyl-3-pentanol, 2-ethyl-1-butanol and more act as simple guests and are simply encapsulated in the hexamers. Others alcohols such as 3-pentanol, 2-methyl-1-butanol and others, are part of the hexameric structure where they can exchange magnetization with alcohols in the bulk. The bulkier alcohols, due to an increase of the chain length or in branching, have a higher tendency to be encapsulated rather than being part of the hexameric capsule superstructure. This study demonstrate the unique information that diffusion NMR spectroscopy can provide on supramolecular systems in solution and on the precaution that should be exercised when analyzing diffusion NMR data of such dynamic supramolecular capsules.

Optimized iminium-catalysed 1,4-reductions inside the resorcinarene capsule: achieving >90% ee with proline as catalyst

“…Of particular interest were alcohol additives, as their interactions with the resorcinarene capsule are well documented. 15,[35][36][37] The Cohen group investigated the incorporation of different alcohols into the resorcinarene capsule in solution and demonstrated that they can replace water molecules of the hydrogen bond network. 15,36 Additionally, in the solid state it was reported that the incorporation of nPrOH into the hydrogen network of the resorcinarene hexamer results in 25% larger assemblies.…”

“…15,[35][36][37] The Cohen group investigated the incorporation of different alcohols into the resorcinarene capsule in solution and demonstrated that they can replace water molecules of the hydrogen bond network. 15,36 Additionally, in the solid state it was reported that the incorporation of nPrOH into the hydrogen network of the resorcinarene hexamer results in 25% larger assemblies. 38 These reports prompted us to investigate the inuence of different alcohol additives on the iminium catalysis inside I.…”

“…This is in line with observations in solution from the Cohen group, who reported the replacement of water molecules in the hydrogen bond network by iPrOH without a signicant change in the assembly size. 36 Another hypothesis centered on the idea that the alcohol additive might inuence proline-proline interactions in the capsule.…”

Self-Assembled Supramolecular Structures as Catalysts for Reactions Involving Cationic Transition States

“…1c,15c,18 Furthermore, it was shown that suitable alcohol molecules can be integrated into the hexameric structure by replacing some of the water molecules. 19 The guest exchange is overall facile and is believed to occur through a pentameric intermediate via dissociation of one resorcin [4]arene subunit. 20 Like in similar systems, the guest encapsulation can be analyzed via 1 H NMR spectroscopy, taking advantage of the aromatic anisotropy of the cavity walls, and via NOESY and DOSY ex- Intrigued by the good encapsulation of tertiary amines, the Tiefenbacher group recently discovered the Brønsted acidic character of the resorcin [4]arene hexamer.…”

“…Encapsulation was evidenced by 1 H, DOSY and NOESY NMR. 19 F NMR indicated that the triflate anion was not encapsulated. The cationic catalyst is likely coordinated by water.…”