An Investigation into Interactions between 1-Butyl-3-methyl-imidazolium Tetrafluoroborate Guest and Pillar[5]arene Hosts: An Experimental and Molecular Dynamics Approach

Various synthesized Pillar[5]arene macrocycles were allowed to form complexes with the ionic liquid; 1-Butyl-3-methyl-imidazolium tetrafluoroborate (IL). The pillar[5]arenes used in the study were synthesized by the established pioneering method of Ogoshi that involves treatment of 1,4-disubstituted benzenes with paraformaldehyde in the presence of BF₃.OEt₂. Selected synthesized pillar[5]arenes; DMpillar[5]arene (4a), DPpillar[5]arene (4b), DPGpillar[5]arene (4c) were allowed to form complexes with the ionic liquid, and complexations were confirmed by MALDI-TOF, ESI-MS, ¹H NMR, and DOSY spectroscopy. ESI-MS reveals highly intense ion peaks that correspond to [pillar[5]arene+IL]⁺ for the complexes of the three pillar[5]arenes with the ionic liquid. Changes in characteristic peaks in hosts and guests, as a result of complexation, were studied by ¹H NMR. Results obtained suggest a formation of 1 : 1 complexes between the pillar[5]arene host and the IL guest. Host-guest interactions in such complexes have also been studied using ¹H-¹H 2D ROESY NMR spectroscopy. Obtained through-space correlations revealed interactions between certain parts of the pillar[5]arene hosts and the ionic liquid. The complexation between the three pillar[5]arenes and the IL was studied by molecular dynamics (MD) simulations. The obtained results suggest the insertion of the IL inside the nanocavities of the hosts.