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.
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.