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 various substrates are investigated in the hydrogenation using molecular hydrogen, transfer hydrogenation and hydrosilylation. Due to economic constrains and ecological considerations the exchange of the classical catalyst metals rhodium, ruthenium und iridium by cobalt, iron or zinc is one of the hot topics in catalysis. The catalytic potential of these non-precious metals catalysts is investigated for the reduction of unsaturated compounds such as imines [1] or carboxylic acid derivatives.[2] In cooperation with the group “Catalysis for Energy” the first iron catalysed homogeneous hydrogenation of nitriles to amines has been developed.[3]

Reduction of carboxylic acid derivatives using a Fe-pincer-catalyst

[1] S. Zhou, S. Fleischer, K. Junge, M. Beller, Angew. Chem. Int. Ed. 2011, 50, 5120-5124; Cooperative Transition Metal and Chiral Brønsted Acid Catalysis: Enantioselective Hydrogenation of Imines to form Amines. (VIP-paper, cover picture)

[2] S. Werkmeister, K. Junge, B. Wendt, H. Jiao, W. Baumann, E. Alberico, H. Junge, F. Gallou, M. Beller, Angew. Chem. Int. Ed. 2014, 53, 8722-8726, Hydrogenation of Esters to Alcohols with a well-defined iron complex.

[3] 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.

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 fine chemistry or pharmacy. The design of catalyst systems involves synthesis of new ligand classes, which are tested for transformation of carboxylic acid derivatives such as esters, amides, nitriles. Furthermore, new catalytic approaches involving of CO2 [4] or carboxylic acids [5] as methylation reagent for amines are developed. In cooperation with industrial partners we work on applied catalysis in the field of hydrogenation and oxidation. Here, based on our experiences an selective reduction method for amide groups an important pharmacological active compound Cyclosporin A has been developed together with Novartis.[6]

[4] Y. Li, X. Fang, K. Junge, M. Beller, Angew. Chem. 2013, 125, 9747 –9750; Angew. Chem. Int. Ed. 2013, 52, 9568 –9571, A General Catalytic Methylation of Amines Using Carbon Dioxide. (Hot paper)

[5] I. Sorribes, K. Junge, M. Beller, J. Am. Chem. Soc. 2014, 136, 14314–14319, Direct Catalytic N-Alkylation of Amines with Carboxylic Acids.

[6] S. Das, Y. Li, C. Bornschein, S. Pisiewicz, K. Kiersch, D. Michalik, F. Gallou, K. Junge, M. Beller, Angew. Chem. Int. Ed. 2015, 54, 12389–12393; Selective Rhodium-Catalyzed Reduction of Tertiary Amide in Amino Acid Esters andl Peptides.

Next to homogeneous catalysts more and more heterogeneous systems are successfully applied in a number of organic reactions as recently reported for the reduction of nitroarenes [7] or for the reductive amination.[8] The N-doped nanoparticles are formed by pyrolysis of organometallic complexes, which are fixed on a support. These heterogeneous materials show remarkable selectivities and large substrate scopes, while they will be commercialized in cooperation with Evonik.

Composition of a heterogeneous core shell Co-nanoparticle

[7] 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.

[8] T. Stemmler, A. E. Surkus, M. M. Pohl, K. Junge, M. Beller, ChemSusChem 2014, 7, 3012-3016, Iron-catalyzed Synthesis of Secondary Amines: On the Way to Green Reductive Amination.