Using imine chemistry for post-synthetical covalent chiralization of MOF surfaces

Homochiral metal-organic frameworks (MOFs) are exceptional media for heterogenous enantiodifferentation processes. Their rational design, however, is challenging. An available solution for this is moving from constitutive, structure-bearing, homochiral ligands to separating chiral selector and structural roles. This introduces combinatorial modulability, which is the independent change of parts. Such modulability circumvents limitations of designability. Further considerations narrow emphasis to covalent post-synthetic methods. Covalent post-synthetic methods to introduce chirality are reported broadly, yet the diversity of pertaining linkage chemistry is modest. The present work explored the adaptation of imine chemistry for post-synthetic chiralization. A chiral aldehyde and a chiral ketone have been probed, with respective achiral controls, on two accessible amine-functionalized MOF substrates. Modifying UiO-66 NH2 with the natural product derived (R)-2,2-dimethyl-1,3-dioxolane-4-carboxaldehyde ((R)-1 aldehyde) was found to be the best-performing combination. The modification was shown to be covalent, chiral, and characteristically proceeding through imine formation. A molecular-level inquiry has furthermore revealed that the modification consists of oligomer-rich structures on the surface. In silico modeling was shown to predict the localization of the modification correctly. Recent advances in the characterization of MOF color were used to track the imine formation. A strategic approach has yielded a new synthetically facile MOF chiralization method. The modification was shown to result in a surface barrier formation. Thereby, restricted diffusion lengths in the solid phase infer good retention of resolving power in ascending van Deemter régimes in chromatography. This makes the yielding material a promising stationary phase candidate for performant chromatographic enantioseparations.