Catalytic hydrogenation of functional groups and unsaturated carbon-carbon bonds is a fundamental transformation in organic synthesis. Due to the necessity of a high energy input in hydrogen generation and unresolved challenges in hydrogen storage, it is beneficial to directly transfer the hydrogen from hydrogen containing molecules like alcohols or formic acid to the respective educts. The most widely used catalysts in TH are ruthenium complexes bearing amine-ligands, which play an active role in the catalytic cycle (bifunctional catalysis). Our most recent results show that Ru-catalysts with more than one functionalized abnormal NHC (aNHC) ligand reach comparable activities without any amine additives. In addition to the positive impact on the catalysts performance, imidazolyl based aNHCs which are forced into this exceptional coordination mode by steric hindrance of a wingtip substituent have a potential free coordination site at the C2 position of the heterocycle. It was recently shown by our group that this provides the opportunity to synthesize heterobimetallic species by simple reaction with silver(I) oxide and subsequent transmetallation (Figure 1). The application of metals with different chemical properties provides complexes which for example can be used as tandem catalysts in TH/Suzuki-Miyaura-Coupling reaction. Furthermore, we focus on the synthesis of exceptionally active catalysts for TH reactions due to synergistic interactions between the metal atoms with similar catalytic behavior.

Abnormal <i>N</i>-heterocyclic carbenes as ligands in catalytic transfer hydrogenation and as central modules in heterobimetallic complexes

256th National Meeting (2018)

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Abnormal N-heterocyclic carbenes as ligands in catalytic transfer hydrogenation and as central modules in heterobimetallic complexes