Stereochemical Control of Redox Co<sup>II</sup>/Co<sup>III</sup>-Cages with Switchable Cotton Effects Based on Labile-Static States
Yu‐Lin Lu, Kai Wu, Yin‐Hui Huang, Weichun Li, Zhong‐Min Cao, Xiang-Han Yan, Xiaodong Zhang, Chenhui Liu, Jia Ruan, Hai‐Sen Xu, Mei Pan, Cheng‐Yong Su
Abstract
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.