Bond activation reactions by means of metal ligand cooperation in carbene complexes

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The activation of element element and element hydrogen bonds is a fundamental process in many transition metal catalyzed transformations. Typically, these processes directly occur at the metal center via an oxidative addition step. In the last years however, mechanisms involving both the metal as well as the ligand as active sites in the bond breaking and making steps have become an alternative tool in bond activation chemistry. The development of novel ligand systems has led to the incorporation of this metal ligand cooperativity into stoichiometric as well as catalytic transformations, thus opening new possibilities for future processes in homogenous catalysis. Well-established examples for such cooperating ligands are imido, amido or carbonyl-functionalized ligands. In contrast, carbene ligands are by far less explored in this chemistry and their application limited to only few examples. Goal of the present research proposal is to overcome this lack in carbene chemistry and to establish carbene complexes in cooperative bond activation reactions and catalysis. To this end, the systematic design of complexes with cooperating carbene ligands, their application in bond activation reactions as well as an understanding of the electronic demands on the M=C interaction will be addressed. Thereby two different types of carbene systems will be targeted: i) methandiide-derived carbene complexes as well as ii) complexes based on PCD pincer ligands. Variation of the substituents in the ligands will influence the electronics of the metal carbon interaction and thus allow for controlled E–E- and E–H bond activation reactions via addition across the M=C bond. Systematic experimental as well as computational studies will provide a profound understanding of the relations between the molecular and electronic structures of the designed systems and their applicability as cooperating ligands. Thus, reversible activation processes of different E–E- und E–H bonds as well as their transfer to organic substrates will be realized. This will be basis for the final development of catalytic transformations. Here, we will also focus on acceptor-less dehydrogenation reactions for the production and storage of dihydrogen.