Enzyme-mimicking and artificial catalysts for selective oxygenations with dioxygen and hydrogen peroxide
In biological systems, the ubiquitous cytochrome P-450 enzymes combine the activation of dioxygen by a reactive iron porphyrin center with molecular recognition. These enzymes are monooxygenases for numerous selective oxidations. Biomimetics considering the assistance of the protein environment will be investigated.
Research goals
Tuneable systems where a proton-donor-acceptor functionality (HB) is appended to a reactive iron porphyrin core will be investigated, to steer the reactivity and selectivity of substrate transformations. “Pacman architectures” will be investigated to place a second metal centre in close proximity to the metal centre inside the macrocycle for the bimetallic activation of O2.
Polymeric graphitic carbon nitride (g-C3N4) will act as functional models for the active site of cytochromes P-450, following the finding that g-C3N4 can serve as a metal-free heterogeneous photocatalyst for selective aerobic oxidation of alcohols and oxidative coupling of amines. Chemical modifications of g-C3N4 will be carried out and these materials used for stereo- and regioselective oxygenations.
The catalytic cycles of the cytochromes P-450 and those of many other oxygenating heme and non-heme iron enzymes contain high-valent Fe=O species. Besides, high-valent iron species, terminal metal oxo motifs of transition metals like cobalt, nickel and copper are particularly attractive synthetic targets, as they are potential candidates for attacking the C-H bonds of methane.
Bioinspired non-heme iron complexes as well as heterometallic (e.g., Fe-O-Mo) compounds will be used for the development of new catalysts for direct oxygenation. Particularly promising candidates will be immobilised to allow a more efficient regeneration of the catalyst.
Bioinspired dinuclear Mo-based compounds with Mo in different oxidation states (+3 -> +5) have found to be excellent homogeneous pre-catalysts for oxygenation of olefins with hydroperoxides. Mo-based precatalysts will be designed for direct oxygenation with O2 by utilising non-innocent ligands around the Mo center. Likewise, Fe- and Mn-based monooxygenation catalysts will be developed.
Extensive studies including gas-phase investigations under mass spectrometric conditions will be carried out to understand the oxidation behaviour of such systems. Furthermore, time-resolved spectroscopic methods will be developed and applied to elucidate the catalytic mechanisms.