Size‐Dependent Enantioselective Adsorption of Racemic Molecules through Homochiral Metal–Organic Frameworks Embedding Helicity

Abstract

Homochiral metal-organic frameworks (HMOFs) are efficient materials for enantioselective adsorption. However, the combination of size selectivity and enantioselectivity is still a major challenge in the field of HMOFs. Herein, two enantiomorphic HMOFs built from predesigned proline-derived ligands are presented. Both of them show multiple homochiral features: they contain four different helical chains and three types of helical channels. Due to the size effect of the helical channels, each HMOF can enantioselectively adsorb methyl lactate with high ee. The results reveal a new approach toward size-dependent enantioselective separation of racemic compounds by using HMOFs built from inexpensive proline derivatives.

Missing Linker Defects in a Homochiral Metal–Organic Framework: Tuning the Chiral Separation Capacity

“…Host–guest interactions between the framework and guest molecules can vary dramatically with the changing size of guest molecules, having profound implications on the observed enantiomeric excesses (ee, %). This was demonstrated with the separation of racemic methyl and ethyl lactate, where the extra carbon caused the enantiomeric excess to drop from 65.8% to 14.9% . Similarly a homochiral hydrogen bonded framework showed dramatic decreases in enantiomeric excess from 2-butanol (77% ee) to 2-heptanol (<4% ee) …”

“…This was demonstrated with the separation of racemic methyl and ethyl lactate, where the extra carbon caused the enantiomeric excess to drop from 65.8% to 14.9%. 6 Similarly a homochiral hydrogen bonded framework showed dramatic decreases in enantiomeric excess from 2-butanol (77%ee) to 2-heptanol (<4%ee). 7 A promising homochiral MOF, ZnBLD [Zn2(bdc)(Llac)(dmf)] .…”

Metal‐Organic Frameworks as a New Platform for Enantioselective Separations

“…The size of the helical channels was appropriate for selectively adsorbing methyl lactate with high ee of 65.8 % for (S)-isomer and 68.3 % for (R)-isomer whereas, the ee values for (R) and (S) isomers of ethyl lactate and 1-phenylethanol were 12.1 %, 14.9 % and 5.3 % and 5.6 % respectively. [50] Enantiopure (1S)-1-(5-tetrazolyl)-ethylamine (5-eatz) was used to construct homochiral porous MOF [[Cu 1 2 u 11 (5eatz…”

The synthesis and applications of chiral pyrrolidine functionalized metal–organic frameworks and covalent-organic frameworks

“…The obtained MOF shows size-dependent enantioselective adsorption behavior as it can adsorb methyl lactate with higher enantioselectivity than ethyl lactate (68.3% vs. 14.9% ee value), although only a slight difference exists between the two substances. 74 Furthermore, they adopted a Scheme 1 The structure of proline and the derived ligands. mixed-ligand strategy from semi-rigid L2 and rigid 1,3,5-tri (1H-imidazol-1-yl)benzene (TIB) to react with Cd(II) for more porous MOFs.…”