Impact of Ligand Design on an Iron NHC Epoxidation Catalyst.

An open-chain iron pyridine-NHC framework is expanded utilizing a benzimidazole moiety to deepen the understanding of the impact of electronic variations on iron NHC epoxidation catalysts, especially regarding the stability. The thereby newly obtained iron(II) NHC complex is characterized and employed in olefin epoxidation. It is remarkably temperature tolerant and achieves a TOF of ca. 10 000†h(-1) and TON of ca. 700 at 60 °C in the presence of the Lewis acid Sc(OTf)(3), displaying equal stability, but lower activity than the unmodified iron pyridine-NHC (pre-)catalyst. In addition, a synthetic approach towards another ligand containing 2-imidazoline units is described but formylation as well as hydrolysis hamper its successful synthesis.