Towards practical earth abundant reduction catalysis : design of improved catalysts for manganese catalysed hydrogenation
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Manganese catalysts derived from tridentate P,N,N ligands can be activated easily using weak bases for both ketone and ester hydrogenations. Kinetic studies indicate the ketone hydrogenations are 0th order in acetophenone, positive order in hydrogen and 1st order in catalyst. This implies that the rate determining step of the reaction was the activation of hydrogen. New ligand systems with varying donor strength were studied and it was possible to make the hydrogen activation significantly more efficient; a catalyst displaying around a 3-fold increase in initial Turn-Over Frequencies for the hydrogenation of acetophenone relative to the parent system was discovered as a result of these kinetic investigations. Ester hydrogenations and ketone transfer hydrogenation (isopropanol as reductant) are first order for both the substrate and catalysts. Kinetic studies also gained insight into catalyst stability and identified a working range in which the catalysts is stable throughout the catalytic reaction (and a larger working range where high yields can still be achieved). The new more active catalyst, combining an electron-rich phosphine with an electron-rich pyridine is capable of hydrogenating acetophenone using as little as 0.01 mol% catalyst at 65 oC. In all, protocols for reduction of 21 ketones and 15 esters are described.
Widegren , M B & Clarke , M L 2019 , ' Towards practical earth abundant reduction catalysis : design of improved catalysts for manganese catalysed hydrogenation ' , Catalysis Science & Technology , vol. 9 , no. 21 , pp. 6047-6058 . https://doi.org/10.1039/C9CY01601E
Catalysis Science & Technology
Copyright © 2019 The Author(s). This work has been made available online in accordance with publisher policies or with permission. Permission for further reuse of this content should be sought from the publisher or the rights holder. This is the author created accepted manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1039/C9CY01601E
DescriptionThe authors thank EPSRC (grant code: 1654521) for DTG funding for MBW.
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