Organometallic Chemistry and Homogeneous Catalyses
The goal of our research in the area of organometallic chemistry and homogeneous catalysis is to develop efficient methods to synthesize oligomers, macromolecules, and supramolecular aggregates from monomers of petrochemical and renewable feedstocks. In particular, polymeric materials with potential application as new materials are important targets. In order to avoid the use of expensive and toxicologically harmful platinum metals, we focus on the early transition and the rare earth metals. The coordination and organometallic chemistry of these metals is being actively explored, since its knowledge is a prerequisite for the development of efficient catalysts.
Synthesized from simple unsaturated molecules such as ethylene, propylene, and styrene from petroleum, polyolefins are by far the most important, inexpensive and recyclable polymeric material in industry. The synthesis currently involves organometallic catalysts and initiators which have their origin in the epoch making discoveries by Karl Ziegler and Giulio Natta in the 1950s. With the advent of single-site catalysts, new homogeneous polymerization catalysts have been introduced which have the great advantage of being molecular systems. Catalyst design therefore implies ligand construction, metal complex synthesis, and characterization as well as mechanistic studies of activation, propagation, and termination processes. We develop a series of easily modifiable catalyst precursors which have in common as design elements polydentate donor systems (chelate ligands), labile reaction site, and flexible, easily modifiable coordination sphere.
For the polymerization of heterocyclic monomers such as L-lactide, electrophilic Lewis acids are required to initiate the ring-opening process. In the context of developing new biocompatible and bioresorbable polymers for potentially biomedical applications, we have focused on the use of aluminum and rare earth metal inititators within a structurally well-defined ligand spheres. The rational harnessing of highly Lewis acidic metal centers requires a thorough understanding of the catalystsâ structure and dynamics.
New Homogeneous Catalysts
Chemical industry still uses a considerable number of processes which are not optimal technologies when environmental impact and resource efficiency are considered. The generation of wastes such as seemingly harmless salts becomes imcreasingly problematic, when sustainable development is required. Atom efficient chemical reactions such as hydrogenation and hydrometalation require transition metal catalysts which are often related to polymerization catalysts, since commonly C-H and C-C bond forming and splitting reactions play a major role. We are systematically developing new catalyst precursors for activation of dihydrogen, boranes, and silanes with the aim of obtaining practically important olefin transformations. C-H bond activation of saturated hydrocarbons still remains a challenge, but will allow the utilization of new feedstocks based on natural gas (methane). New ways to activate such extremely inert molecules by new organometallic catalysts are being sought. Stereoselective variants of each processes are considered at an early stage in order to allow the synthesis of chiral molecules as useful intermediates for organic and macromolecular synthesis.