Catalysis of phosphorus materials
Dr. habil. Christian Hering-Junghans
Catalysis is an important means of achieving environmentally friendly ("green") processes, as it deals with the acceleration of reactions. In contrast to the reduction of natural resources, the use of renewable materials is a highly attractive goal in this context. Therefore, the long-term focus of our research lies in the design of new, efficient methods to build carbon-nitrogen bonds starting from atmospheric nitrogen. These bonds are widespread in nature and in combination with inorganic carbon sources such as CO2 and CO, the C-N bond formation offers fascinating possibilities to produce chemical raw materials and fine chemicals in a more sustainable way.
In this context, we are working on the design of novel ligand systems for the efficient stabilization of low-valent early transition metals. The focus is on an effective steric shielding of the metal center on the one hand and on the electronic properties of the ligand on the other hand, so that it can also be used as an electron reservoir. We aim to combine novel element-organic reaction techniques with classical coordination chemistry and the fundamental properties of our systems are elucidated using state-of-the-art analytical methods. The focus is on the incorporation of low-valent phosphorus centers into the ligands, in particular by the incorporation of phosphaalkenes (Figure 2). Phosphaalkenes can be regarded as modifiable variants of the CO molecule.
Another field of research is the investigation of the chemistry of so-called phosphanylidene phosphoranes and their heavy homologs. These systems can be regarded as phosphane-stabilized phosphinides and new ways of phosphinide transfer are being investigated. On the one hand, the activation of strong chemical bonds (e.g. C-H, N-H etc.) at a main group element center will be investigated in order to obtain new phosphorus-containing materials or to establish reversible processes, which in turn can be used in new organo-catalytic transformations. Furthermore, it is possible to exchange the phosphane in a substitution reaction, making a variety of novel compounds easily accessible (Figure 3).
We were able to show that phosphanylidene phosphoranes with small groups on the phosphorus cannot be synthesized; instead, cyclotriphosphanes are obtained selectively. We also use these as a source of phosphinides, investigate the reactivity towards early transition metals and in cyclization reactions in order to obtain new P-containing materials (e.g. phosphorus-rich dyes) and ligands.
Another project deals with the synthesis of Group 13-15 multiple bond systems and their reactivity towards small molecules. The focus here is on the synthesis of so-called phospha- and arsaalums, which are heavy homologs of alkynes. In this project, both cyclotriphosphanes and phosphanylidene phosphoranes are used to realize an effective phosphinide transfer to aluminum compounds in the +1 oxidation state.
Students with special interest in inorganic synthetic chemistry, ligand design and the application of metal complexes in small molecule activation are welcome to join the group in the framework of internships, bachelor and master theses. In addition, suitable candidates are encouraged to contact Dr. Christian Hering-Junghans regarding PostDoc fellowships.
Please send an email to Christian.Hering-Junghans{at}catalysis.de.
