Suchergebnisse

Zr-containing MOF-808 is a very promising heterogeneous catalyst for the selective reduction of ketosteroids to the corresponding hydroxysteroids through a Meerwein-Ponndorf-Verley (MPV) reaction. Interestingly, the process leads to the diastereoselective synthesis of elusive 17α-hydroxy derivatives in one step, whereas most chemical and biological transformations produce the 17β-OH compounds, or they require several additional steps to convert 17β-OH into 17α-OH by inverting the configuration of the 17 center. Moreover, MOF-808 is found to be stable and reusable; it is also chemoselective (only keto groups are reduced, even in the presence of other reducible groups such as C=C bonds) and regioselective (in 3,17-diketosteroids only the keto group in position 17 is reduced, while the 3-keto group remains almost intact). The kinetic rate constant and thermodynamic parameters of estrone reduction to estradiol have been obtained by a detailed temperature-dependent kinetic analysis. The results evidence a major contribution of the entropic term, thus suggesting that the diastereoselectivity of the process is controlled by the confinement of the reaction inside the MOF cavities, where the Zr active sites are located. ; Financial support by the Spanish Government is acknowledged through projects MAT2017-82288-C2-1-P and the Severo Ochoa program (SEV-2016-0683). The Microscopy Service of the Universitat Politècnica de València is gratefully acknowledged for the electron microscopy images.

Ruthenium MOF [Ru3(BTC)2Yy] ·Gg (BTC=benzene-1,3,5-tricarboxylate; Y=counter ions=Cl¿¿ , OH¿¿ , OAc¿¿ ; G=guest molecules= HOAc, H2O) is modified via a mixed-linker approach, using mixtures of BTC and pyridine-3,5-dicarboxylate (PYDC) linkers, triggering structural defects at the distinct Ru2 paddlewheel (PW) nodes. This defect-engineering leads to enhanced catalytic properties due to the formation of partially reduced Ru2-nodes. Application of a hydrogen pre-treatment protocol to the Ru¿¿ MOFs, leads to a further boost in catalytic activity. We study the benefits of (1) defect engineering and (2) hydrogen pre-treatment on the catalytic activity of Ru¿¿ MOFs in the Meerwein-Ponndorf-Verley reaction and the isomerization of allylic alcohols to saturated ketones. Simple solvent washing could not avoid catalyst deactivation during recycling for the latter reaction, while hydrogen treatment prior to each catalytic run proved to facilitate materials recyclability with constant activity over five runs. ; Funding by the Spanish Government is acknowledged through projects MAT2017‐82288‐C2‐1‐P and Severo Ochoa (SEV‐2016‐0683). This project is further funded by the Deutsche Forschungsgemeinschaft grant no. FI‐502/32‐1 ("DEMOFs"). KE and WRH would like to thank TUM Graduate School and the Gesellschaft Deutscher Chemiker (GDCh) for financial support. KE gratefully acknowledges support from the colleagues Olesia Halbherr (neé Kozachuk) and Wenhua Zhang.

Heterogeneous single-site catalysts consist of isolated, well-defined, active sites that are spatially separated in a given solid and, ideally, structurally identical. In this review, the potential of metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) as platforms for the development of heterogeneous single-site catalysts is reviewed thoroughly. In the first part of this article, synthetic strategies and progress in the implementation of such sites in these two classes of materials are discussed. Because these solids are excellent playgrounds to allow a better understanding of catalytic functions, we highlight the most important recent advances in the modelling and spectroscopic characterization of single-site catalysts based on these materials. Finally, we discuss the potential of MOFs as materials in which several single-site catalytic functions can be combined within one framework along with their potential as powerful enzyme-mimicking materials. The review is wrapped up with our personal vision on future research directions. ; S. M. J. Rogge, J. Hajek, and V. Van Speybroeck acknowledge the Fund for Scientific Research – Flanders (FWO), the Research Board of Ghent University (BOF) and BELSPO in the frame of IAP/7/05 for financial support. V. Van Speybroeck acknowledges funding from the European Union's Horizon 2020 research and innovation programme (consolidator ERC grant agreement no. 647755 – DYNPOR (2015–2020)). This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 641887 (project acronym: DEFNET). W. Dewitte and C. Caratelli are acknowledged for technical support with the figures. J. Gascon acknowledges funding from the European Union's 2020 research and innovation programme (ERC grant agreement no. 335746 – CrystEng-MOF-MMM) and from the Dutch Organization for Scientific Research (NWO, VIDI grant agreement 723.012.107 – MetMOFCat).