Synthesis and Characterization of Self‐Assembled Chiral Fe^II₂L₃ Cages

We present here the synthesis of chiral BINOL‐derived (BINOL=1,1′‐bi‐2‐naphthol) bisamine and bispyridine‐aldehyde building blocks that can be used for the self‐assembly of novel chiral Fe^II₂L₃ cages when mixed with an iron(II) precursor. The properties of a series of chiral cages were studied by NMR and circular dichroism (CD) spectroscopy, cold‐spray ionization MS, and molecular modeling. Upon formation of the M₂L₃ cages, the iron corners can adopt various isomeric forms: mer, fac‐Δ, or fac‐Λ. We found that the coordination geometry around the metal centers in R‐Cages 1 and 2 were influenced by the chiral BINOL backbone only to a limited extent, as a mixture of cages was formed with fac and mer configurations at the iron corners. However, single cage species (fac‐RR‐Cage and fac‐RS‐Cage) that are enantiopure and highly symmetric were obtained by generating these chiral M₂L₃ cages by using the bispyridine‐aldehyde building blocks in combination with chiral amine moieties to form pyridylimine ligands for coordination to iron. Next to consistent NMR spectra, the CD spectra confirm the configurations fac‐(Λ,Λ) and fac‐(Δ,Δ) corresponding to RR‐ and RS‐Cage, respectively.