Sustainable Redoxreactions

Dr. Kathrin Junge

The topic „Sustainable Redoxreactions“ is divided into two main areas, on the one hand enantio- and chemoselective reductions and on the other hand oxidation reactions. Combining these two parts offers the chance for an extensive study of hydrogenation and oxidation properties for new developed catalysts.

In the field of reduction, preferentially various hydrogenation reactions with molecular hydrogen are studied using autoclaves, next to transfer hydrogenation or hydrosilylation. Due to economic constrains and ecological considerations the exchange of the classical catalyst metals rhodium, ruthenium, iridium, and palladium by cheaper, less toxic, and better available non-noble metals is one of the hot topics in catalysis.[1]

Thus, many homogeneous catalysts based on manganese, iron, cobalt, or molybdenum have been developed and investigated in catalytic reductions such as semihydrogenation of alkynes [2] or hydrogenation of various carboxylic acid derivatives[3] and heterocycles[4]. In cooperation with the group “Catalysis for Energy” the first iron catalysed homogeneous hydrogenation of nitriles to amines has been developed.[5] This was the beginning of a fruitful scientific collaboration leading to numerous non-noble metal catalysts which display excellent results for hydrogenation as well as for dehydrogenation.[6] Currently, also oxidation catalysts are studied in cooperation with the Chinese company Synfuels.[7]

 

[1] W. Liu, W. Li, K. Junge, M. Beller, Nature Catal. 2019, 2, 523-528, Iron-Catalyzed Regioselective Hydrogenation of Terminal Epoxides to Alcohols under Mild Conditions.

[2] N. F. Both, A. Spannenberg, K. Junge, M. Beller, Organometallics 2022, doi.org/10.1021/acs.organomet.1c00709, Low-valent Molybdenum PNP Pincer Complexes as Catalysts for the Semihydrogenation of Alkynes (Special issue).

[3] P. Ryabchuk, K. Stier, K. Junge, M. P. Chechinski, M. Beller, J. Am. Chem. Soc. 2019, 141, 16923−16929, A Molecular-defined Manganese Catalyst for Low Temperature Hydrogenation of Carbon Monoxide to Methanol.

[4] V. Papa, Y. Cao, A. Spannenberg, K. Junge, M. Beller, Nat. Catal. 2020, 3, 135–142; Development of a Practical Non-Noble Metal Catalyst for Hydrogenation of N-Heteroarenes.

[5] C. Bornschein, S. Werkmeister, B. Wendt, H. Jiao, E. Alberico, W. Baumann, H. Junge, K. Junge, M. Beller, Nature Commun. 2014, 5, 4111, Mild and selective Hydrogenation of aromatic and aliphatic (di)nitriles with a novel well-defined Iron Pincer complex.

[6] E. Alberico, T. Leischner, H. Junge, A. Kammer, R. Sang, J. Seifert, W. Baumann, A. Spannenberg, K. Junge, M. Beller, Chemical Science 2021, 12, 13101–13119, HCOOH Dispoportionation to MeOH promoted by Molybdenum PNP Complexes.

[7] S. Mao, S. Budweg, A. Spannenberg, X. Wen, Y. Yang, Y.-W. Li, K. Junge, M. Beller, ChemCatChem 2022; 14, e202101668, Iron catalysed epoxidation of linear olefins.

 

 

The development of efficient catalytic redoxreactions is one of the major challenges in present chemical research. Here, well-established, classic organometallic catalysts are applied for catalytic reactions which are relevant for agrochemical industry or pharmacy. In cooperation with industrial partners, we work on applied catalysis in the field of hydrogenation and oxidation. Thus, a practical catalyst for the C-C double bond hydrogenation, an important step in the synthesis of an active compound, has been developed in cooperation with the process development of the Division Crop Science at Bayer AG.[8]

The design of catalyst systems involves synthesis of new ligand classes. In this respect, especially the synthesis of pincer type complexes is a very efficient concept due to the direct tuning of catalyst properties.[9]

 

[8] J. Schneekönig, W. Liu, T. Leischner, K. Junge, C. Schotes, C. Beier, M. Beller, Org. Process Res. Dev. 2020, 24, 443-447, Application of Crabtree/Pfaltz-type iridium complexes for the catalyzed asymmetric hydrogenation of an agrochemical building block.

[9] T. Leischner, A. Spannenberg, K. Junge, M. Beller, ChemCatChem 2020, 12, 4543-4549, Synthesis of Molybdenum Pincer Complexes and Their Application in the Catalytic Hydrogenation of Nitriles (Cover).

 

While the main expertise of the research group originally comes from homogeneous catalysis, heterogeneous systems have also been studied for more than 10 years.[10] The N-doped nanoparticles are generated by pyrolysis of metal complexes previously fixed on supports. These heterogeneous materials show remarkable selectivities and large substrate scope for catalytic hydrogenation[11] as well as in C-C bond cleavage[12]. The aspect of sustainability plays an important role, which is reflected in the choice of readily available and inexpensive catalyst metals, but also in the establishment of novel catalyst support from industrial waste (e.g. chitosan, chitin).

Heterogeneous non-noble metal catalysts for deuteration reactions are being explored as part of the EU FLIX project (www.flix-h2020.eu), in which research institutions and companies from Germany, France, Denmark, the Netherlands, and Hungary are collaborating.[13,14] These catalytic materials enable the selective incorporation of deuterium into biologically active substances by means of hydrogen isotope exchange (HIE), which allows, for example, better monitoring of their metabolism (Synthesis Workshop: Deuterium + Tritium Labeling with Sara Kopf and Florian Bourriquen (Episode 94) - YouTube).

[10] F. A. Westerhaus, R. V. Jagadeesh, G. Wienhöfer, M.-M. Pohl, J. Radnik, A.-E. Surkus, J. Rabeah, K. Junge, H. Junge, M. Nielsen, A. Brückner, M. Beller, Nature Chemistry 2013, 5, 537-543, Heterogenized Cobalt Oxide Catalysts for Nitroarene Reduction by Pyrolysis of Molecularly Defined Complexes.

[11] P. Ryabchuk, M.-M. Pohl, A. Agapova, H. Junge, K. Junge, M. Beller, Science Advances 2018, 4:eaat0761; Intermetallic Nickel Silicide Nanocatalyst - a Non-noble Metal Based General Hydrogenation Catalyst.

[12] W. Li, W. Liu, J. Rabeah, D. K. Leonard, K. Junge, A. Brückner, M. Beller, Angew. Chem. 2019, 131, 10803–10807; Angew. Chem. Int. Ed. 2019, 58, 10693 –10697, Practical Catalytic Cleavage of C(sp³)–C(sp³) Bonds in Amines (hot paper).

[13] W. Li, J. Rabeah, F. Bourriquen D. Yang, C. Kreyenschulte, N. Rockstroh, S. Bartling, A.-E. Surkus, K. Junge, A. Brückner, A. Lei, M. Beller, Nature Chemistry 2022, 14, 334–341, Towards a Practical Deuteration Methodology.

[14] F. Bourriquen, N. Rockstroh, S. Bartling, K. Junge, M. Beller, Angew. Chem. 2022, DOI: 10.1002/anie.202202423, Manganese catalysed deuterium labelling of anilines and electron-rich (hetero)arenes.