Mixed-metal MIL-100(Sc,M) (M=Al, Cr, Fe) for Lewis acid catalysis and tandem C -C bond formation and alcohol oxidation
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The trivalent metal cations Al3+, Cr3+, and Fe3+ were each introduced, together with Sc3+, into MIL-100(Sc,M) solid solutions (M=Al, Cr, Fe) by direct synthesis. The substitution has been confirmed by powder X-ray diffraction (PXRD) and solid-state NMR, UV/Vis, and X-ray absorption (XAS) spectroscopy. Mixed Sc/Fe MIL-100 samples were prepared in which part of the Fe is present as α-Fe2O3 nanoparticles within the mesoporous cages of the MOF, as shown by XAS, TGA, and PXRD. The catalytic activity of the mixed-metal catalysts in Lewis acid catalysed Friedel–Crafts additions increases with the amount of Sc present, with the attenuating effect of the second metal decreasing in the order Al>Fe>Cr. Mixed-metal Sc,Fe materials give acceptable activity: 40 % Fe incorporation only results in a 20 % decrease in activity over the same reaction time and pure product can still be obtained and filtered off after extended reaction times. Supported α-Fe2O3 nanoparticles were also active Lewis acid species, although less active than Sc3+ in trimer sites. The incorporation of Fe3+ into MIL-100(Sc) imparts activity for oxidation catalysis and tandem catalytic processes (Lewis acid+oxidation) that make use of both catalytically active framework Sc3+ and Fe3+. A procedure for using these mixed-metal heterogeneous catalysts has been developed for making ketones from (hetero)aromatics and a hemiacetal.
Wright , P A , Mitchell , L , Clarke , M , Seymour , V R , Ashbrook , S E M , Williamson , P , Ehrlichova , B , Anderson , A E , Acerbi , N , Daniels , L & Walton , R 2014 , ' Mixed-metal MIL-100(Sc,M) (M=Al, Cr, Fe) for Lewis acid catalysis and tandem C -C bond formation and alcohol oxidation ' Chemistry - A European Journal , vol 20 , no. 51 , pp. 17185-17197 . DOI: 10.1002/chem.201404377
Chemistry - A European Journal
© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. This work is made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at http://dx.doi.org/10.1002/chem.201404377
The authors thank Johnson Matthey and the EPSRC for an Industrial CASE award to L.M. We gratefully acknowledge the IAESTE UK for a scholarship to B.E. They also thank the Leverhulme Trust (F/00 268/BJ), EPSRC (EP/J501542/1), and the EaStCHEM Research Computing Facility.
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