Neutral isocyanide-templated assembly of pillar[5]arene [2] and [3]pseudorotaxanes

Abstract

Unprecedented pillar[5]arene–isocyanide pseudorotaxane complexes are reported. Extensive ¹H-NMR experiments reveal remarkably strong binding affinities of alkyl diisocyanide guests (K_a > 10⁵ M⁻¹ in CDCl₃) by pillar[5]arenes. Characterised by multinuclear ¹H and ¹³C-NMR spectroscopy and single-crystal X-ray diffraction, it is demonstrated that pillar[5]arenes are capable of encapsulating a series of alkyl diisocyanides wherein either [2]- or [3]pseudorotaxanes can be formed by varying the alkyl chain length. Moreover, electron-deficient aryl isocyanides, are demonstrated to form inclusion complexes within the cavities of pillar[5]arenes stabilised by multiple C–H⋯π interactions.