10/28/19 - 4:00 PM to 5:00 PM
Special Seminar: Professor Christian Limberg
Understanding of functional entities in solid catalysts and enzymes with the aid of molecular mimics - mini-zeolites and COx conversion
To gain insights into the properties of certain functions and units of extended oxides/hydroxides on the molecular level suitable molecular model compounds are needed. We have accessed models of aluminosilicates by trapping of intermediates occurring during the hydrolysis of suitable aluminium precursor compounds with the aid of stabilizing tripodal trisilanols ligands. In contrast to most other known aggregates of that type they can be readily prepared at reasonable scales and dissolve in common solvents. This paves the way for reactivity studies in solution addressing the individual functions. The –Al–O(H)–Al– units proved far more acidic than should be assumed intuitively and catalytically competent in olefin isomerisations and alcohol dehydrations, which sheds some light on the properties of such entities as part of amorphous alumina/silica materials or extraframework aluminium species in the pores of zeolites.
Moreover, access to novel polynuclear iron(II) siloxide complexes is presented, featuring rare high-spin, square planar FeO4 structural motifs, that recently have been shown to be responsible for the catalytic activity of iron-modified zeolites. Corresponding chromium(II) complexes in contact with dioxygen form isolable Lewis-acid stabilized O2 adducts, with properties that strongly depend on the Lewis acid, solvent and siloxide residues.
In the final part of the lecture a Ni–CO22- complex is discussed that is unique in many ways. While its structural and electronic features help understanding the CO2 bound state in Ni,Fe carbon monoxide dehydrogenases, its reactivity sheds light on how CO2 can be converted into CO/CO32- by nickel complexes. In addition, the complex has been generated via a rare example of formate β-deprotonation, a mechanistical step relevant to nickel catalysed conversion of HxCOyz- at electrodes and formate oxidation in formate dehydrogenases.
Professor Limberg studied chemistry at the University of Bochum, Germany, where he received his doctorate in 1992. He also has a doctorate from the University of Oxford, UK, which he completed in 1995. Since 2003, he has served as professor at Humboldt University. He has been recognized numerous times for his comprehensive work on oxygen complexes and oxidation reactions in in the field inorganic chemistry. The Limberg group uses both the active sites of enzymes and solid materials as objects of investigation to deal within its major research areas with metal-oxygen systems, such as modeling of reactive metalloxo-surface-species and biomimetic O2-activation and oxidation.