Design and Enantioresolution of Homochiral Fe(Ⅱ)-Pd(Ⅱ) Coordination Cages from Stereolabile Metalloligands: Stereochemical Stability and Enantioselective Separation

摘要

The stereochemistry of chiral-at-metal complexes is much more abundant, albeit complicated, than chiral-at-carbon compounds, but how to make use of stereolabile metal-centers remains a formidable challenge due to the highly versatile coordination geometry of metal ions and racemization/epimerization problem. We demonstrate herein a stepwise assembly of configurationally stable [Pd-6(FeL3)(8)](28+) (Delta/Lambda-MOCs-42) homochiral octahedral cages from unstable D-3-symmetry trischelate-Fe type metalloligands via strong face-directed stereochemical coupling and facile chiral-induced resolution processes based on stereo-differentiating host-guest dynamics. Kinetic studies reveal that the dissociation rate of MOC-42 cages is 100-fold slower than that of Fe-metalloligands and the racemization is effectively inhibited, making the cages retain their chirality over extended periods of time (>5 months) at room temperature. Recyclable enantioseparation of atropisomeric compounds has been successfully achieved, giving up to 88% ee.