Metal Ion-Mediated Supramolecular Nanotube Catalyst for Enantioselective Reactions

Rational control over the morphologies of supramolecular assemblies for asymmetric catalysis with enhanced enantioselectivity represents a pivotal challenge in the realm of synthetic chemistry and material technology. Herein, Cu(II) ion-mediated supramolecular nanostructures assembled from chiral amino acid-based amphiphiles (l/d-AlaC₁₆) are fabricated as chiral catalysts for Diels-Alder cycloaddition between aza-chalcone and cyclopentadiene. In particular, compared with the supramolecular nanosheet formed by l/d-AlaC₁₆ without Cu(II) ions, we found that the l/d-alanine chiral amphiphile can form supramolecular nanotubes with a multilayer structure and with the thickness of the tubular wall about 15 nm through the transition from a nanoribbon to tubular structure in the presence of Cu(II) ions. Consequently, the catalytic enantioselectivity of Diels-Alder was improved from 6% (nanosheet) to 49% (nanotube), attributed to the curved surface of the nanotube structure, which provides a preferential chiral environment and high density of the catalytic center to favor the chirality transfer. Our study presented in this work offers valuable insights for designing chiral supramolecular catalysts with a higher enantioselectivity driven by a metal ions-mediated nanostructure.