A Robust Double-walled Knotted Cage Revealed Guest Binding through Adaptive Portal Expansion

Mechanically interlocked host frameworks are expected to show dynamic guest inclusion/release without disruption of their inherent structures. Here, we synthesized a double-walled knotted cage from a kinetically inert Pt(II) block, which has a robust but semiflexible backbone to give an expansible cavity with expansible portals. The Pt cage showed great kinetic stability toward base, acid, and nucleophiles. Comparisons of the kinetics with a Pd(II) analog strongly supported the portal expansion mechanism for the guest inclusion in the double-walled cages. Mechanically interlocked host frameworks are expected to show dynamic guest inclusion/release without disruption of their inherent structures. Here, we synthesized a double-walled knotted cage from a kinetically inert Pt(II) block, which has a robust but semiflexible backbone to give an expansible cavity with expansible portals. The Pt cage showed great kinetic stability toward base, acid, and nucleophiles. Comparisons of the kinetics with a Pd(II) analog strongly supported the portal expansion mechanism for the guest inclusion in the double-walled cages.