Research Projects

Organocuprates(I) are highly valuable reagents for the formation of carbon-carbon bonds. Although less popular, organoargentates(I) can mediate C−C coupling reactions as well. By means of mass-spectrometric experiments and theoretical calculations, I investigate several aspects of organometallic copper and silver ate complexes at the molecular level, e.g., what are the gas-phase structures of different aggregation/association states of phenylcuprates(I) and -argentates(I), and what is the origin of the contrasting unimolecular reactivity of heteroleptic organocuprate(III) and -argentate(III) complexes? These studies not only aim at a better understanding of the chemistry of synthetically useful organometallic coinage-metal ate complexes, but also provide experimental data, which is used for benchmarking state-of-the-art computational chemistry methods.

Carbanions, either bound to a metal or in their unattached form, are essential for many reaction mechanisms. While there are studies regarding their gas-phase properties, these ions are usually generated by deprotonation or fragmentation while already in the gas phase. My work regards the direct measurement of carbanions from solution using ESI-MS. My current project is the applicability of this method for the investigation of reaction kinetics of e.g. Michael additions.

The investigation of mechanisms is crucial for the understanding of chemical reactions. While in Solution, the reagents often form multiple species with varying reactivity, which cannot be clearly assigned. Using an ESI source of a mass spectrometer, these species can be transferred into the gas phase, where they are isolated in a 3D quadrupol ion trap. A home-built apparatus is used to introduce a defined concentration of a neutral gas into the ion trap using its helium inlet, which enables ion-molecule-reactions without equilibrium or solvent effects. By varying the trapping duration of the ions, I can measure pseudo-first order kinetics of the reaction. My current project concerns model reactions for the oxidative addition during cross-coupling reactions.

Transmetalation is a key step in transition metal catalysis. The detailed knowledge of the potential energy surface of transmetalation reactions is a prerequisite to develop improved or novel catalytic systems on a rational basis. In a mechanistic study, I use a combination of ESI mass spectrometry, NMR spectroscopy and quantum chemical calculations to characterize the thermochemistry and reaction barriers of the transmetalation of aryl groups from boron to copper.

In order to compare results of computational chemistry to those from experiments, I determine the energy barriers of the protonation of organometallic species in the gas phase. For that sake, gaseous metal-containing anions are stored in a three-dimensional quadrupole ion trap (QIT) and then protonated by organic substrates, which were introduced into the QIT by a home-built inlet system. By varying the reaction time, kinetic measurements are performed providing information about the reaction rate coefficients. The experimental rate coefficients can be compared to theoretical ones, which were determined from computed potential energy surfaces applying statistical rate theory approaches.

Reductive elimination is one of the most important elementary steps in numerous reactions catalyzed by transition metals. ESI mass spectrometry and gas-phase fragmentation experiments can be used to compare activation energies of competing unimolecular reactions in model complexes. As model systems I investigate trifluoromethyl metal complexes and their cross-coupling reactions as well as the influence of the properties of the cross-coupling partner on the reaction.

The goal of this project is to elucidate the relative trends among selected transition metals of group 8 and higher towards reductive elimination and competing reactions with an emphasis towards probing a multitude of accessible oxidation states of these metals. Electrospray ionization mass spectrometry (ESI-MS) and collision induced dissociation (CID) experiments are the chosen tools for probing complexes innate reactivity in the gas phase. These methods will be accompanied with selected condensed phase models to gauge the transfer of the gained insights to applied synthetic systems.

Hydrogenations and dehydrogenations are among the most important transition-metal catalyzed reactions. In the past decades, efficient and robust platinum metal-based catalysts have been established for a wide variety of hydrogenation and dehydrogenation reactions. As the use of platinum metals bears problems, such as limited availability or their toxicity, I am trying to broaden the view of 3d metals with my research. In order to optimize known reactions and develop new ones by rational design, the reaction mechanism at hand must be understood as best as possible. To this end, I use mass-spectrometric experiments and DFT calculations to investigate the intermediates and elementary steps of such reactions.