Stereochemical Control of Redox Co/Co-Cages with Switchable Cotton Effects Based on Labile-Static States.

The structural dynamics of artificial assemblies, in aspects such as molecular recognition and structural transformation, provide us with a blueprint to achieve bioinspired applications. Here, we describe the assembly of redox-switchable chiral metal-organic cages Λ/Δ-[Pd(CoL)] and Λ/Δ-[Pd(CoL)]. These isomeric cages demonstrate an on-off chirality logic gate controlled by their chemical and stereostructural dynamics tunable through redox transitions between the labile Co-state and static Co-state with a distinct Cotton effect. The transition between different states is enabled by a reversible redox process and chiral recognition originating in the tris-chelate Co-centers. All cages in two states are thoroughly characterized by NMR, ESI-MS, CV, CD, and X-ray crystallographic analysis, which clarify their redox-switching behaviors upon chemical reduction/oxidation. The stereochemical lability of the Co-center endows the Λ/Δ-Co-cages with efficient chiral-induction by enantiomeric guests, leading to enantiomeric isomerization to switch between Λ/Δ-Co-cages, which can be stabilized by oxidation to their chemically inert forms of Λ/Δ-Co-cages. Kinetic studies reveal that the isomerization rate of the Δ-Co-cage is at least an order of magnitude slower than that of the Δ-Co-cage even at an elevated temperature, while its activation energy is 16 kcal mol higher than that of the Co-cage.