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Open AccessArticle

Synthesis and Catalytic Application of Knölker-Type Iron Complexes with a Novel Asymmetric Cyclopentadienone Ligand Design

1
Faculty of Science and Engineering, Maastricht University, 6167 RD Geleen, The Netherlands
2
Maastricht MultiModal Molecular Imaging Institute (M4I), Maastricht University, 6229 ER Maastricht, The Netherlands
*
Author to whom correspondence should be addressed.
Catalysts 2019, 9(10), 790; https://doi.org/10.3390/catal9100790
Received: 31 August 2019 / Revised: 16 September 2019 / Accepted: 17 September 2019 / Published: 22 September 2019
(This article belongs to the Special Issue Iron and Cobalt Catalysts)
Asymmetric catalysis is an essential tool in modern chemistry, but increasing environmental concerns demand the development of new catalysts based on cheap, abundant, and less toxic iron. As a result, Knölker-type catalysts have emerged as a promising class of iron catalysts for various chemical transformations, notably the hydrogenation of carbonyls and imines, while asymmetric versions are still under exploration to achieve optimal enantio-selectivities. In this work, we report a novel asymmetric design of a Knölker-type catalyst, in which the C2-rotational symmetric cyclopentadienone ligand possesses chiral substituents on the 2- and 5-positions near the active site. Four examples of the highly modular catalyst design were synthesized via standard organic procedures, and their structures were confirmed with NMR, IR, MS, and polarimetry analysis. Density functional theory (DFT) calculations were conducted to elucidate the spatial conformation of the catalysts, and therewith to rationalize the influence of structural alterations. Transfer- and H2-mediated hydrogenations were successfully established, leading to appreciable enantiomeric excesses (ee) values up to 70%. Amongst all reported Knölker-type catalysts, our catalyst design achieves one of the highest ee values for hydrogenation of acetophenone and related compounds. View Full-Text
Keywords: asymmetric hydrogenation; homogeneous catalysis; iron; structural design; conformational analysis; NMR spectroscopy; DFT asymmetric hydrogenation; homogeneous catalysis; iron; structural design; conformational analysis; NMR spectroscopy; DFT
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MDPI and ACS Style

van Slagmaat, C.A.M.R.; Chou, K.C.; Morick, L.; Hadavi, D.; Blom, B.; De Wildeman, S.M.A. Synthesis and Catalytic Application of Knölker-Type Iron Complexes with a Novel Asymmetric Cyclopentadienone Ligand Design. Catalysts 2019, 9, 790.

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