Supramolecular protection of isocyanates from water by encapsulation within hydrophobic crystalline pillar[n]arene macrocycles

Abstract

Abstract The high reactivity of isocyanate groups not only makes them excellent precursors for polyurethanes and polyureas, but it also leads to their degradation through reactions with atmospheric moisture. Conventionally, blocking reagents containing alcohol or amine groups have been used to protect isocyanate groups. However, such covalent protection approaches often require harsh deprotection conditions. Herein, we report a non-covalent supramolecular strategy that provides both high protection efficiency and facile deprotection of isocyanate compounds. In this approach, the isocyanate groups are encapsulated within crystalline pillar[ n ]arene macrocycles. Owing to the highly hydrophobic nature of the pillar[ n ]arene crystals, the isocyanate guests are effectively protected from water in the crystalline state: the isocyanate groups are active even after the crystalline complexes are exposed to water vapour or directly immersed in water. Furthermore, although the host–guest complex is stabilized in the crystalline state, simple dissolution in an appropriate reaction solvent simultaneously triggers deprotection, enabling subsequent polyurethane synthesis.