Chiral Metal‐Organic Frameworks and Their Application in Asymmetric Catalysis and Stereoselective Separation

Abstract

The targeted synthesis of a desired stereomer plays a key role in life sciences, especially in the production of drugs. Up to date, this area is dominated by homogeneous chiral catalysts. Metal-Organic Frameworks (MOFs), a new class of porous materials, consisting of metal-oxo-clusters and multifunctional ligands could offer a platform for chiral heterogeneous catalysts combining the efficiency and in particular selectivity observed for homogeneous asymmetric catalysts with the advantages of heterogeneous catalysis. This review summarizes strategies to obtain chiral Metal-Organic Frameworks and gives an overview about reactions that have been successfully conducted using chiral MOFs as asymmetric catalysts. In addition, some examples highlighting the stereoselective adsorption properties of chiral Metal-Organic Frameworks are given.

Actuation of Asymmetric Cyclopropanation Catalysts: Reversible Single‐Crystal to Single‐Crystal Reduction of Metal–Organic Frameworks

“…Interestingly, a similar cyclopropanation reaction with 1 R as the catalyst gave the desired products in less than 1 % yield and with modest ee values (Table 1, entry 4). The framework interpenetration in 1 R significantly reduced the open channel sizes, thus preventing the diffusion of the reagents into the Ru II /salen active sites in the interior of 1 R. The beneficial effect of a reducing agent for the cyclopropanation reaction was also observed for the homogeneous control reaction with the [Ru(L-Me 2 )(py) 2 ] catalyst: The cyclopropane products were obtained in a yield of 28 % and 53 % in the absence or presence, respectively, of NaBH(OMe) 3 (Table 1, entries 5 and 6). Finally, we have shown that 2 R is also an active catalyst for the cyclopropanation of both 1,3-pentadiene and ethyl vinyl ether, albeit in lower yields and with lower d.r.…”

“…[3,7] Motivated by excellent asymmetric catalytic activities exhibited by many homogeneous metal/salen complexes [where an archetypical chiral salen ligand is (R,R)-1,2-cyclohexanediamino-N,N'-bis(3-tert-butyl-salicylidene)], [8] MOFs containing metal/salen building blocks have attracted a great deal of recent interest.…”

“…Consistent with this hypothesis, the control reaction with 2 as the catalyst did not produce any cyclopropane product (Table 1, entry 3). To prevent the 2 R catalyst from oxidizing and deactivating, we carried out the cyclopropanation reaction in the presence of NaBH(OMe) 3 . A much improved yield (54 %) of cyclopropane products was obtained under these reaction conditions, with a d.r.…”

“…Numerous MOFs have been synthesized, and some of them have been explored for potential applications such as gas storage, [1] chemical sensing, [2] catalysis, [3] biomedical imaging, [4] and drug delivery. [5] Catalytic MOFs having imbedded, well-defined active sites are of particular interest owing to their utility as recyclable and reusable catalysts.…”

Biologically derived metal organic frameworks

“…Chiral ligands can be used for the generation of homochiral porous MOFs, or chirality can be induced from the arrangement of achiral ligands within the structure. [54][55][56][57] Among the chiral ligands available, [58][59][60][61][62][63][64] bio-ligands, such as natural occurring peptides, are structurally rich and versatile with numerous metal binding sites. However, robust and highly porous MOFs based on these ligands are scarce in the literature.…”