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Pyrazolate‐Based Cobalt(II)‐Containing Metal–Organic Frameworks in Heterogeneous Catalytic Oxidation Reactions: Elucidating the Role of Entatic States for Biomimetic Oxidation Processes

  • Crystal structures of two metal–organic frameworks (MFU‐1 and MFU‐2) are presented, both of which contain redox‐active CoII centres coordinated by linear 1,4‐bis[(3,5‐dimethyl)pyrazol‐4‐yl] ligands. In contrast to many MOFs reported previously, these compounds show excellent stability against hydrolytic decomposition. Catalytic turnover is achieved in oxidation reactions by employing tert‐butylCrystal structures of two metal–organic frameworks (MFU‐1 and MFU‐2) are presented, both of which contain redox‐active CoII centres coordinated by linear 1,4‐bis[(3,5‐dimethyl)pyrazol‐4‐yl] ligands. In contrast to many MOFs reported previously, these compounds show excellent stability against hydrolytic decomposition. Catalytic turnover is achieved in oxidation reactions by employing tert‐butyl hydroperoxide and the solid catalysts are easily recovered from the reaction mixture. Whereas heterogeneous catalysis is unambiguously demonstrated for MFU‐1, MFU‐2 shows catalytic activity due to slow metal leaching, emphasising the need for a deeper understanding of structure–reactivity relationships in the future design of redox‐active metal–organic frameworks. Mechanistic details for oxidation reactions employing tert‐butyl hydroperoxide are studied by UV/Vis and IR spectroscopy and XRPD measurements. The catalytic process accompanying changes of redox states and structural changes were investigated by means of cobalt K‐edge X‐ray absorption spectroscopy. To probe the putative binding modes of molecular oxygen, the isosteric heats of adsorption of O2 were determined and compared with models from DFT calculations. The stabilities of the frameworks in an oxygen atmosphere as a reactive gas were examined by temperature‐programmed oxidation (TPO). Solution impregnation of MFU‐1 with a co‐catalyst (N‐hydroxyphthalimide) led to NHPI@MFU‐1, which oxidised a range of organic substrates under ambient conditions by employing molecular oxygen from air. The catalytic reaction involved a biomimetic reaction cascade based on free radicals. The concept of an entatic state of the cobalt centres is proposed and its relevance for sustained catalytic activity is briefly discussed.show moreshow less

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Metadaten
Author:Markus Tonigold, Ying Lu, Andreas Mavrandonakis, Angela Puls, Reiner StaudtGND, Jens MöllmerGND, Joachim Sauer, Dirk Volkmer
Publisher:WILEY‐VCH Verlag
Date of Publication (online):2011/06/07
Language:English
GND Keyword:Cobalt; Metallorganisches Netzwerk; Oxidation
Parent Title (English):Chemistry - a European Journal
Volume:17
Issue:31
ISSN:0947-6539
First Page:8671
Last Page:8695
Document Type:Article (reviewed)
Institutes:Hochschule Offenburg / Bibliografie
Acces Right:Frei zugänglich
Release Date:2019/10/24
Licence (German):License LogoEs gilt das UrhG
DOI:https://doi.org/10.1002/chem.201003173
Pubmed Id:http://www.ncbi.nlm.nih.gov/pubmed?term=21688331