Synthesis of Chiral MOF‐74 Frameworks by Post‐Synthetic Modification by Using an Amino Acid

Abstract

The synthesis of chiral metal-organic frameworks (MOFs)i sh ighly relevant for asymmetric heterogenous catalysis, yet very challenging. Chiral MOFsw ith MOF-74 topology were synthesised by using post-synthetic modification with proline. Vibrational circular dichroism studies demonstrate that prolinei st he source of chirality.T he solvents used in the synthesis play ak ey role in tuning the loading of proline and its interaction with the MOF-74 framework. In N,N'-dimethylformamide, proline coordinates monodentate to the Zn 2 + ions withint he MOF-74 framework, whereasi ti s only weakly bound to the frameworkw hen using methanol as solvent. Introducing chirality within the MOF-74f ramework also leads to the formation of defects, with both the organic linkera nd metal ions missing from the framework. The formationo fd efects combined with the coordination of DMF and prolinew ithin the framework leads to ap ore blockinge ffect. This is confirmed by adsorption studies and testingo ft he chiral MOFs in the asymmetric aldol reaction betweenacetone and para-nitrobenzaldehyde.

Role of additives and solvents in the synthesis of chiral isoreticular MOF-74 topologies

“…Previous results show a binding of l -Pro through the carboxylate group to Zn 2+ ions of Zn-MOF-74. 18 In this case, we expected that the coordination of 4-hydroxyproline to the Zn 2+ ions of Zn-IRMOF-74 via the deprotonated hydroxyl group at a high pH to be the most favourable interaction because it is less sterically hindered as compared to the carboxyl group.…”

MOF-enabled confinement and related effects for chemical catalyst presentation and utilization

“…A simpler strategy, dating back at least to work by Kim et al in 2009, 348 is to decorate MOF pores postsynthetically with chiral functionalities, such as L-proline, oligopeptides, L-tartaric acid, etc. [349][350][351][352] While the following example is not appreciably catalytic, Fig. 70 illustrates the idea, in idealized form, for MOF-74-Zn and proline.…”

Using Postsynthetic X-Type Ligand Exchange to Enhance CO2 Adsorption in Metal–Organic Frameworks with Kuratowski-Type Building Units

“…One of the earliest examples of this approach involved the substitution of axial aqua ligands with pyridine at the dicopper paddlewheel nodes of HKUST-1 . L-type ligand exchange or “dative PSM” at metal nodes has subsequently been employed to immobilize species that modify the guest adsorption properties, , introduce chirality, , or serve as catalytically active sites. , Recently, diamine-grafted MOFs have received considerable attention as adsorbents for selective CO 2 capture. − Most notably, Long and co-workers have shown that amine-grafted variants of Mg 2 (dobpdc) [dobpdc 4– = 4,4′-dihydroxy-(1,1′-biphenyl)-3,3′-dicarboxylate] exhibit steplike CO 2 adsorption, resulting from a cooperative chemisorption mechanism . Carbamate formation via CO 2 insertion into an Mg–N bond is accompanied by proton transfer to a neighboring diamine ligand, and this process propagates to form one-dimensional ammonium carbamate chains.…”