Stereochemical Control of Redox Co II /Co III -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 8 /Δ 8 -[Pd 6 (Co II L 3 ) 8 ] 28+ and Λ 8 /Δ 8 -[Pd 6 (Co III L 3 ) 8 ] 36+ . 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 II -state and static Co III -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 II -center endows the Λ 8 /Δ 8 -Co II -cages with efficient chiral-induction by enantiomeric guests, leading to enantiomeric isomerization to switch between Λ 8 /Δ 8 -Co II -cages, which can be stabilized by oxidation to their chemically inert forms of Λ 8 /Δ 8 -Co III -cages. Kinetic studies reveal that the isomerization rate of the Δ 8 -Co III -cage is at least an order of magnitude slower than that of the Δ 8 -Co II -cage even at an elevated temperature, while its activation energy is 16 kcal mol -1 higher than that of the Co II -cage.