Transition-Metal-Catalyzed Synthesis of Fine Chemicals

Dr. Helfried Neumann

Research activities:

“Hydrogen-borrowing“ Concept

Alcohols, epoxides and diols can be dehydrogenated by various catalysts. The resulting aldehydes or ketones can cyclize or react with numerous chemicals to generate interesting structural motifs and molecules. The term “Hydrogen-borrowing” refers to the dehydrogenation of the substrate, the hydrogen coordination to the metal center and the ensuing hydrogenation of the in situ formed double bond. These sequences represent key steps in the catalytic cycle. Beside from the well-known Ruthenium-MACHO catalyst, we are investigating iron, manganese and rhenium based catalysts as more environmentally benign alternatives.

Perfluoralkylation of Arene Compounds

The synthesis of aromatic compounds containing fluorine is a special challenge when a hydrogen atom is supposed to be substituted by a perfluoroalkyl group. We developed a heterogeneous catalyst which is capable of performing these reactions in the presence of base and perfluoroalkyl iodides or bromides. Since the CF3-group is an important structural motif, we developed a homogeneous palladium catalyzed synthesis utilizing gaseous trifluoromethyl bromide as an inexpensive CF3 source. The non-corrosive gas has some advantages compared to other CF3 reagents. Currently, we are carrying out NMR-studies to achieve a better understanding of the exact reaction mechanism.

Ligand- and Complex Syntheses

Phosphin ligands still play an outstanding role in homogeneous catalysis. In cooperation with EVONIK, we are investigating syntheses for highly efficient chelating ligands which are applied in the alkoxycarbonylation of olefins. Additionally, we synthesize the relevant palladium complexes and investigate the elementary reaction steps by NMR spectroscopy in order to achieve a better understanding of the reaction mechanism.

Carbonylation Reactions

The palladium-catalyzed carbonylation of (activated) ArX compounds represents a long standing area of research in our group. It is still fascinating how multi faced this chemistry can be. The famous CO-insertion in a Pd-Ar bond illustrates only one step in a cascade of many sequential steps which finally yield in the formation of highly substituted (hetero-)arenes. Even complicated multi-functional (hetero-)arenes can be synthesized in a very efficient manner.