Catalysis of Early Transition Metals

Dr. habil. Torsten Beweries

The group investigates fundamental aspects of early transition metal catalysed processes on the basis of synthetic organometallic chemistry and coordination chemistry. We focus on coordination and activation of small unsaturated molecules (e.g. olefins, alkynes, isocyanides, nitriles, and CO2) at group 4 metal complexes that allow for the stoichiometric and catalytic generation and stabilisation of partly unusual organometallic and organic structures.1

We are investigating the chemistry of unusual group 4 metallacycles in order to explore the scope of coordination chemistry of this class of compounds. In general, incorporation of unsaturated units into cyclic structures increases ring strain, which typically decreases the stability and the accessibility of such compounds. However, formal substitution of e.g. methylene units for suitable metal fragments allows for the synthesis of a series of exotic complexes. After evaluating different approaches and optimization of the synthesis of a suitable organolithium synthon, we have succeeded in the isolation of a titanacyclobuta-2,3-diene, which formally represents an organometallic analogue of cyclobuta-1,2-diene.2 Variation of the metallocene precursor and use of Cp2ZrCl2 results in the formation of an unusual eight-membered metallacycle. Structural and electronic properties of these and related complexes are investigated using a combined experimental and theoretical approach based on up-to-date analytical and computational tools.

Scheme 1. Synthesis of dizirconacyclooctatetraene and titanacyclobuta-2,3-diene.

In light of the question of environmentally friendly hydrogen production, activation and splitting of water using homogeneous and heterogeneous photocatalysts is a broadly investigated approach. In our group we have developed molecular titanocene system that allow for the study of elementary steps of water splitting.3 We found that the nature of the cyclopentadienyl ligand plays a decisive role for the performance of these systems as only complexes with bridged ligands possess a sufficient photochemical stability to react in a defined way for all steps of the water splitting cycle.

Schema 2. A model cycle of water activation at titanocene complexes.

Apart from this all groups within the research department jointly investigate different systems for amine borane dehydrocoupling. We have shown that dinuclear zirconocene complexes are promising catalysts for the selective dehydropolymerisation of methylamine borane to poly(N-methylaminoborane). Based on our extensive knowledge of the chemistry of group 4 metallocene complexes we develop and evaluate new catalyst structures for these reactions.

The group is equipped for working under inert conditions (high vacuum Schlenk lines and two MBraun Labmaster gloveboxes) and holds electrochemical tools (Metrohm), three fully automatic gas buret systems (Messen Nord), that can operate under photochemical conditions, as well as permanent gas GC.

Students with special interest in synthetic organometallic chemistry, ligand design and homogeneous catalysis are welcome to discuss opportunities to pursue lab practical training, bachelor or master thesis or PhD studies and are encouraged to contact torsten.beweries{at}catalysis.de.

 

 

[1] a) F. Reiß, K. Altenburger, D. Hollmann, A. Spannenberg, H. Jiao, P. Arndt, U. Rosenthal, T. Beweries, Chem. Eur. J. 2017, 23, 7891; b) M. Reiß, F. Reiß, A. Spannenberg, P. Arndt, T. Beweries, Organometallics 2018, 37, 4415.

[2] a) F. Reiß, M. Reiß, A. Spannenberg, H. Jiao, D. Hollmann, P. Arndt, U. Rosenthal, T. Beweries, Chem. Eur. J. 2017, 23, 14158; b) F. Reiß, M. Reiß, A. Spannenberg, H. Jiao, W. Baumann, P. Arndt, U. Rosenthal, T. Beweries, Chem. Eur. J. 2018, 24, 5667; c) F. Reiß, M. Reiß, J. Bresien, A. Spannenberg, H. Jiao, W. Baumann, P. Arndt, T. Beweries, Chem. Sci. 2019, 10, 5319.

[3] a) M. Kessler, S. Schüler, D. Hollmann, M. Klahn, T. Beweries, A. Spannenberg, A. Brückner, U. Rosenthal, Angew. Chem. Int. Ed. 2012, 51, 6272; b) C. Godemann, L. Dura, D. Hollmann, K. Grabow, U. Bentrup, H. Jiao, A. Schulz, A. Brückner, T. Beweries, Chem. Commun. 2015, 51, 3065; c) C. Godemann, D. Hollmann, M. Kessler, H. Jiao, A. Spannenberg, A. Brückner, T. Beweries, J. Am. Chem. Soc. 2016, 137, 16187.

 [4] a) D. Han, F. Anke, M. Trose, T. Beweries, Coord. Chem. Rev. 2019, 380, 260-286; b) M. Trose, M. Reiß, F. Reiß, F. Anke, A. Spannenberg, S. Boye, A. Lederer, P. Arndt, T. Beweries, Dalton Trans. 2018, 47, 12858.