Examples of Current Research
1.) Coordination Chemistry of Aminotroponiminates
Aminotroponiminates: Alkali Metal Compounds Reveal Unprecedented Coordination Modes
Organometallics 2016, 35, 894-902.
It is well known that aminotroponiminates (ATIs) can coordinate to a metal center using their two nitrogen atoms. In this contribution, it is demonstrated that ATIs can also effectively interact with a metal center via the delocalized π-electron system in their cyclic C7-backbone. This should contribute to the understanding of stoichiometric and catalytic transformations of ATI complexes.
2.) Redox Chemistry of Aminotroponiminates
Aminotroponiminates as tunable, redox-active ligands: reversible single electron transfer and reductive dimerization
C. Lichtenberg*, I. Krummenacher
Chem. Commun. 2016, 52, 10044-10047.
In this contribution, we show that aminotroponiminates (ATIs) can act as redox-active ligands. Under strongly reducing conditions, ATI complexes undergo either reversible electron transfer or electron transfer followed by rapid radical dimerization, depending on the metal center. The reductive dimerization is chemo-, regio-, and diastereoselective as well as chemically reversible. Results from preliminary catalytic investigations suggest that ATI complexes can act as electron transfer catalysts in the coupling of aryl Grignard reagents with aryl bromides.
3.) Cationic Bismuth Amides
Cationic Bismuth Amides: Accessibility, Structure, and Reactivity
H. Dengel, C. Lichtenberg*
Chem. Eur. J. 2016, 22, 18465-18475.
This contribution deals with cationic bismuth amides. It is focused on simple, monodentate amido ligands, which are promising for group transfer reactions and catalytic applications. We show that cationic bismuth complexes based on such simple, synthetically relevant amido ligands are indeed isolable. The characteristics of these species in solution and in the solid state were investigated in detail. The choice of the counter anion is crucial for the stability of these compounds. The cationic bismuth amides show an increased reactivity compared to their neutral parent compounds; this is exemplified in reactions with carbodiimides, which give direct access to cationic bismuth guanidinates.
4.) Bismuth-Mediated Double CH-Activation
Double CH Activation of a Masked Cationic Bismuth Amide
B. Ritschel, J. Poater, H. Dengel, M. Bickelhaupt,* C. Lichtenberg*
Angew. Chem. Int. Ed. 2018, 57, 3825-3829.
In this contribution, we show that the transformation of a neutral bismuth amide into a cationic species results in a dramatic change in reactivity: the cationic bismuth amide undergoes a stepwise double CH-activation of the (NPh2)- ligand. The product of the first and the second CH activation was isolated and fully characterized. The mechanism of the CH activations was investigated by DFT calculations (backed up by experimental observations). Thus, the second step of the reaction proceeds via an electrophilic aromatic substitution, which is unprecedented in this context. The CH-activated positions can be functionalized selectively in simple one-pot-protocols, generating new routes to mono- and di-substituted aryl amines.