Pushing the limits of activity and stability: the effects of Lewis acids on non-heme iron–NHC epoxidation catalysts

The catalytic performance of tetradentate iron-NHC complexes in the epoxidation of cis-cyclooctene is considerably improved by addition of strong Lewis acids. Unprecedented TOFs of up to 410 000 h 1 are obtained by applying Sc(OTf)3, Ce(OTf)4 or the significantly cheaper Fe(ClO4)3∙H2O as supporting additives. Due to reactivation of an oxo-bridged FeIII-O-FeIII deactivation species TONs of up to 1 200 at 20°C are achieved.