Aggregation Mode, Host‐Guest Chemistry in Water, and Extraction Capability of an Uncharged, Water‐Soluble, Liquid Pillar[5]arene Derivative

An uncharged, water‐soluble per‐ethylene‐glycol pillar[5]arene derivative (1) was synthesized and its aggregation mode, host‐guest chemistry in water and extraction ability was explored. Compound 1 is a liquid at room temperature; in water, limited self‐aggregation occurred at high concentrations as deduced from diffusion NMR and dynamic light scattering. Compound 1 forms pseudo‐rotaxane‐like 1 : 1 host‐guest complexes with 1,ω‐di‐substituted alkanes with association constants on the order of 103–104 m−1. Interestingly, NMR experiments showed that the guest location relative to the host ring system differs among the different complexes. In proof‐of‐concept experiments, compound 1 was shown to extract structurally related organic compounds from benzene into water with significant selectivity. Compound 1, which is a liquid at room temperature and has only limited interactions with its side arms, can, in principle, be regarded as a complement to or as a kind of type I porous liquid. A liquid host based on a per‐ethylene‐glycol pillar[5]arene derivative (1) was prepared and its self‐aggregation, host‐guest chemistry in water and extraction capabilities were studied and evaluated. 1 forms pseudo‐rotaxane‐like complexes with 1,ω‐di‐substituted alkanes, showing Ka values in the range of 103–104 M−1. Host 1 can extract such alkanes with 6–7 fold selectivity and since the interaction with its rim side‐chains is weak, 1 can be regarded as a complement to or as a sort of type 1 porous liquid.