Spontaneous resolution of an electron-deficient tetrahedral Fe4L4 cage

Article abstract of DOI:10.1002/anie.201507295

A highly electron-deficient C₃-symmetric tris(bipyridyl) ligand was prepared in four steps and used for the coordination of Fe(OTf)₂, thereby resulting in the homochiral assembly of a new family of robust tetrahedral M₄L₄ cages. This homochiral T-symmetric cage containing a relatively large cavity of 330 ?³ is capable of encapsulating an anionic guest, as was determined by mass spectrometry, ¹⁹F NMR spectroscopy, and finally shown from its crystal structure. Moreover, crystallization of the cage from CH₃CN led to crystals containing both (ΔΔΔΔ and ΛΛΛΛ) enantiomers, while crystallization from CH₃OH resulted in crystals containing only the right-handed (ΔΔΔΔ) cage. The difference in the crystal packing of the two crystal structures is discussed and a feasible explanation for the unique phenomenon among supramolecular cages - spontaneous resolution - is given. Supramolecular chiral resolution: A highly electron-deficient tetrahedral cage was formed from a stable tris(bipyridyl) ligand and a Fe^II salt. Crystallization of the racemic CH₃OH solution leads to spontaneous resolution of the cages, whereas crystallization from CH₃CN does not. The encapsulation of an anionic guest was observed in CH₃CN.