A New Set of Isoreticular, Homochiral Metal–Organic Frameworks with ucp Topology

Abstract

A new isoreticular series of metal–organic frameworks, called UHM-25 (UHM: University of Hamburg Materials), based on the copper paddle wheel motif and a novel set of homochiral linkers has been synthesized. Starting from amino acids available from the chiral pool a synthesis procedure was established that allows a straightforward, multigram scale synthesis of homochiral linkers in 4–5 steps. These linkers carry substituents that have been proven useful in stereoselective organic chemistry, such as the Evans auxiliary or chiral amino alcohols. The resulting MOFs only differ in the chiral moiety provided by the amino acid starting material. The structure of UHM-25 is composed of cuboctahedral cages of Cu2 paddle wheel motifs connected by the isophthalate moieties of the linker. These cages are linked via the bent backbone of the linker resulting in a primitive cubic arrangement, giving rise to the rare underlying (3,4)-c binodal net ucp. MOFs of the UHM-25 series show surface areas up to S BET = 1900 m2/g. Postsynthetic modification reactions with excellent conversion rates confirmed the accessibility to the chiral groups. Furthermore, UHM-25-Pro bearing a prolinol functionality was used in a self-directed, enantioselective aldol addition of acetaldehyde, demonstrating the potential of the UHM-25 series with regard to heterogeneous, stereoselective catalysis.

Recent Progress in Asymmetric Catalysis and Chromatographic Separation by Chiral Metal–Organic Frameworks

“…In 2000, Kim and co-workers reported the synthesis of chiral MOFs from the enantiopure tartaric-acid-derived bridging ligands, [Zn 3 [44]. Subsequently, the method has been developed, and many research papers have been reported that use naturally occurring enantiopure amino acids and their derivatives [45][46][47][48], tartaric acid derivatives [49,50], and modified 1,1 -binaphthalene-2,2 -diol (BINOL) derivatives [51][52][53] for designing chiral MOFs. Recently, the approach of synthesis has been extended widely with some alteration, which will be described in the review.…”

“…In 2016, Fröba and associates [47] reported the PSM of the oxazolidinone moieties connected to the MOF UHM-25-Val-Evans (12). The acylation of the MOF (12) was attained by reacting it with propionic anhydride in the presence of a nucleophilic catalyst 4-(dimethylamino)pyridine (DMAP) as shown in Figure 6.…”

“…Fröba and associates [47] synthesized a series of UHM-25 MOFs by introducing chiral amino acid substituents in diisophthalate linkers. Out of these synthesized chiral MOFs, the asymmetric catalytic activity of UHM-25-Pro (34) on aldol condensation was examined, over which the self-directed aldol condensation of acetaldehyde and the subsequent conversion of 3-hydroxybutanal to 1,1-Dimethoxy-3-hydroxybutane was scrutinized (Scheme 6).…”

“…An MOF containing chiral dihydroxyl auxiliaries was employed as a chiral stationary phase of HPLC for the enantioseparation of racemic amines. Parallel to these works, numerous other chiral MOFs, such as [47] with permission from the American Chemical Society.…”

“…Post-synthetic acylation of UHM-25-Val-Evans(12). Reproduced from[47] with permission from the American Chemical Society. r.t.: room temperature.…”