Cucurbit[n]urils (CB[n]), a family of pumpkin-shaped molecular containers, are best known for their ability to form highly stable host-guest complexes in aqueous medium. With a hydrophobic cavity and two hydrophilic carbonyl portals, CB[n]s can encapsulate a wide range of organic guests, including neutral hydrocarbons. In this study, two different families of probes (Ruthenium complexes 1 and Pyridinium salt 2) were prepared. Relative binding affinities of several hydrocarbons were measured towards the cavity formed by CB[8] and a tolyl unit linked to an auxiliary guest. Binding events were monitored by 19F NMR spectroscopy, as both probes bear a trifluoromethyl group. The CB[8]/probes pair are selective for cyclic hydrocarbons, while benzene shows weaker binding affinities (166 and 100 times weaker than cyclohexane towards the CB[8]/probe 1a and CB[8]/probe 2 systems, respectively). CH-π interactions were found to significantly contribute to the recognition event, much more so than dispersive “π-π” stacking interactions.

Probing interactions between hydrocarbons and four auxiliary guests inside cucurbit[8]uril

ACS Fall 2021

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