A New Set of Isoreticular,\nHomochiral Metal–Organic\nFrameworks with ucp Topology

Abstract

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