Organometallic Fe complexes with exceptionally high activities in homogeneous epoxidation catalysis are reported. The compounds display FeII and FeIII oxidation states and bear a tetracarbene ligand. The more active catalyst exhibits activities up to 183 000 turnovers per hour at room temperature and turnover numbers of up to 4300 at -30°C. For the FeIII complex, a decreased Fenton-type reactivity is observed compared with FeII catalysts reported previously as indicated by a substantially lower H2O2 decomposition and higher (initial) turnover frequencies. The dependence of the catalyst performance on the catalyst loading, substrate, water addition, and the oxidant is investigated. Under all applied conditions, the advantageous nature of the use of the FeIII complex is evident.
- carbene ligands
- homogeneous catalysis