Models for metal-catalyzed reactions in organic synthesis

In addition to the fundamental studies in the topic of metal catalysis, the team also investigates catalytic reactions successfully used in applied synthesis. As an example, it is referred to the Fe^III-catalyzed Michael addition of β-keto esters to α,β-unsaturated carbonyl compounds in which our gas-phase experiments could account for the experimentally observed and at the first sight quite puzzling effects of the counterions (Chemistry - A European Journal, 2005). It turned out that a crucial aspect in this context is associated with the solvation of metal ions in solution, which also makes the key difference between gas-phase experiments and applied catalysis.

Accordingly, the solvation of metal ions forms a separate subtopic examined in this project. In this respect, electrospray ionization (ESI) is a unique tool for the detailed investigation of solvation phenomena which allows a stepwise transition from solvated ions in solutions to bare, unsolvated species in the gas phase and moreover to investigate the role of solvation on the chemical reactivity of the so-formed ions. As an example, the following Figure shows the ESI mass spectra of FeCl₃ dissolved in methanol. With increasingly harsher conditions of ionization (as expressed by the cone voltage), the multiply solvated species such as [FeCl₂(CH₃OH)₅]⁺ undergo degradation step by step, first losing methanol ligands and then also redox reactions to afford atomic Fe⁺ as the terminal fragment (Chemistry - A European Journal, 2006).