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Research in the group
Our research program is directed towards the development of new, atom-economic catalytic transformations. We are interested in the replacement of stoichiometric reagents (and the resulting waste products) with more environmentally friendly catalytic methods. The main focus of the current research projects lies on the development of catalysts based on first row transition metals to activate dihydrogen (H2). The metal complexes are subsequently used for catalytic hydrogenation and reductive coupling reactions. The approach is twofold: On the one hand, we strive to discover new reactivity and efficient transformations to generate useful synthetic building blocks. On the other hand, we study the reaction mechanisms to develop more efficient catalysts.
I Alkyne semihydrogenation with copper catalysts
We have identified copper(I)/NHC complexes (NHC = N-heterocyclic carbene) bearing a copper-oxygen bond that are able to activate H2 and catalyze hydrogenation reactions. The copper catalysts can be used for highly Z-stereoselective alkyne semihydrogenation reactions. Hallmarks of these processes are absence of undesired E/Z-isomerization processes and/or overreduction to the corresponding alkanes, which are commonly found with other catalysts for alkyne semihydrogenations. Two types of catalysts have been developed so far (see Chem. Eur. J. 2015, 21, 15934  and Org. Biomol. Chem. 2016, 14, 10660).
II Transfer hydrogenations with ammonia borane
We have recently discovered that ammonia borane (H3NBH3) can be employed as an easy-to-handle H2 equivalent for transfer hydrogenations catalyzed by a copper complex. Conjugate transfer hydrogenations of enones and alkyne transfer semihydrogenations can be effected in a practical manner without the need for high pressure equipment. (see Chem Commun. 2017, 53, 732-735)
III Copper-catalyzed allylic reductions
Our group has developed a highly regioselective hydride transfer from silanes to allylic bromides catalyzed by a simple copper(I)/NHC complex (NHC = N-heterocyclic carbene). The resulting products, branched alpha olefins, are versatile building blocks for synthesis. This process circumvents the need for allylic substitutions using stoichiometric amounts of metal reagents (such as organomagnesium compounds) and therefore offers a waste-reduced alternative. (See Org. Lett. 2016, 18, 2455 .)