Chiral Functionalization of a Zirconium Metal-Organic Framework (DUT-67) as a Heterogeneous Catalyst in Asymmetric Michael Addition Reaction.

DUT-67, an 8-connected zirconium and 2,5-thiophenedicarboxylate-based metal-organic framework (MOF), was postsynthetically functionalized by l-proline via solvent-assisted linker incorporation to obtain a chiral base catalyst. The parent monocarboxylate could be almost completely exchanged by l-proline after 5 days of treatment. The resulting chiral DUT-67 was demonstrated to be a promising heterogeneous catalyst for the asymmetric Michael addition of cyclohexanone to trans-ß-nitrostyrene with excellent yield (up to 96%) and enantioselectivity comparable to that of l-proline in homogeneous reaction (ee of approximately 38%). The Zr-MOF could be reused at least five times without substantial degradation in the crystallinity or catalytic activity. No leaching of catalytically active species into the liquid phase was detected over five cycles.

Proline functionalization of the mesoporous metal-organic framework DUT-32.

The linker functionalization strategy was applied to incorporate proline moieties into a metal-organic framework (MOF). When 4,4'-biphenyldicarboxylic acid was replaced with a Boc-protected proline-functionalized linker (H(2)L) in the synthesis of DUT-32 (DUT = Dresden University of Technology), a highly porous enantiomerically pure MOF (DUT-32-NHProBoc) was obtained, as could be confirmed by enantioselective high-performance liquid chromatography (HPLC) measurements and solid-state NMR experiments. Isotope labeling of the chiral side group proline enabled highly sensitive one- and two-dimensional solid-state (13)C NMR experiments. For samples loaded with (S)-1-phenyl-2,2,2-trifluoroethanol [(S)-TFPE], the proline groups are shown to exhibit a lower mobility than that for (R)-TFPE-loaded samples. This indicates a preferred interaction of the shift agent (S)-TFPE with the chiral moieties. The high porosity of the compound is reflected by an exceptionally high ethyl cinnamate adsorption capacity. However, postsynthetic thermal deprotection of Boc-proline in the MOF leads to racemization of the chiral center, which was verified by stereoselective HPLC experiments and asymmetric catalysis of aldol addition.

Towards highly active and stable nickel-based metal-organic frameworks as ethylene oligomerization catalysts.

Catalytic ethylene oligomerization proceeds under mild conditions with high activity using porous or non-porous nickel-based coordination polymers/metal-organic frameworks (MOFs) as catalysts. The role of MOFs as catalyst precursors and the crucial impact of metal coordination on the catalyst activity and leaching are elucidated by comparing MOFs constructed from different clusters and linkers. The stronger the coordination bond of organic linkers to the Ni center, the lower the catalytic activity of the MOF, as shown for CPO-27(Ni). The highest activity and stability were obtained with the [Ni3(ndc)3(DMF)2((CH3)2NH)2]n catalyst.

Amine assisted top-down delamination of the two-dimensional metal-organic framework Cu2(bdc)2.

A chemically assisted top-down method for the synthesis of MOF-nanoplates was developed applying amine based delamination agents. Applied on a well described model structure, the layered MOF Cu2(bdc)2(DMF)2 (bdc - 1,4-benzenedicarboxylate), two different strategies of amine assisted delamination turned out to be successful to obtain nanoplates. Particles with thicknesses of around 70 nm were obtained by direct delamination of crystals using octylamine. The surfactant (polyvinylpyrrolidone) assisted synthesis combined with a post-synthetic amine delamination step enabled a further reduction of the thickness of the MOF nanoplates down to 4-14 nm.

Metal-Organic Frameworks for Thin-Layer Chromatographic Applications.

Preparation of thin-layer chromatographic (TLC) plates based on metal-organic frameworks (MOFs) as porous stationary phases is described. DUT-67 (DUT = Dresden University of Technology), a zirconium based MOF, was used in combination with a fluorescent indicator as stationary phase for analyzing a small selection of a wide spectrum of relevant analytes. The successful separation of benzaldehyde from trans-cinnamaldehyde and 4-aminophenol from 2-aminotoluene is reported as a model system using optimized eluent mixtures containing acetic acid.