Small Molecule Activation

Dr. Christian Hering-Junghans

Catalysis is a powerful tool to achieve the goals accompanied with “greener“ environmentally benign processes, as it is the science of accelerating chemical reactions. One of the principles of “Green Chemistry” is the use of renewable raw materials or feedstock instead of depleting ones whenever technically and economically practicable. Consequently the focus of our research is on the design of new and efficient methods to form C-N bonds directly from atmospheric nitrogen. These bonds are ubiquitous in nature and in combination with abundant, non-organic carbon sources such as CO2 or CO, C-N bond forming reactions offer fascinating opportunities to make fine and commodity chemicals in a more sustainable way. In this context we are concerned with the design of state-of-the-art ligand systems for efficient stabilization of low-valent early transition metals. Here the focus will be on the effective steric shielding of the metal center and on the other on the investigation of the electronic nature of the ligand. It is envisaged to use the ligand as an electron reservoir. We seek employ modern element-organic methods in combination with classic coordination chemistry techniques. The fundamental properties of our systems will be uncovered using comprehensive characterization methods. The overall basis for our approach in ligand design will be the structure of the FeMo-cofactor in the enzyme nitrogenase in order to realize biomimetic reactivity. 

Scheme 1. General research concept of our group: Combination of element organic transformations for the synthesis of new ligand systems and their application in coordinations chemistry while focussing on the activation of molecular nitrogen.

In a next step the prepared ligands will be coordinated to an early transition metal and the reduction chemistry of these complexes in the presence of nitrogen will be studied. In here the steric as well as the electronic properties of the ligand play a vital role and in combination with theoretical methods these will be investigated in more detail. In the beginning the focus will be on the metals present in the FeMo-cofactor such as vanadium, molybdenum and iron. The ultimate goal of these studies is the synthesis of terminal nitrides, which can then be treated with carbon nucleo- and electrophiles. In a last step we seek to uncover efficient methodologies for the cleavage of the M-N linkage in order to release the C-N coupled product, while regenerating the catalytically active species.

Moreover, we will study the telomerisation of 1,3-dienes in the presence of nucleophiles, as it combines readily available, yet inexpensive, starting materials to obtain more complex functionalized 2,7-dienes in an atom-efficient manner. In this context we seek to study the influence of the influence of the ligand coordinated to palladium with the focus being on N-heterocyclic olefins (NHOs). These zwitterionic ligands show donor properties comparable with classical phosphines and the emerging carbenes and hence represent an important ligand class.

Scheme 2. Palladium catalyzed telomerisation of 1,3-dienes in the presence of nucleophiles (X-). The focus of these studies will be on the influence of NHO-ligands towards the activity of the catalyst.

Students with special interest in synthetic inorganic chemistry, ligand design and the application of metal complexes for the activation of small molecules are welcome to discuss opportunities to pursue laboratory practica, bachelor or master thesis, PhD studies or Postdoctural work and are encouraged to contact Christian.Hering-Junghans{at}catalysis.de.