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

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 SBET = 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.