Unraveling the potential of backbone modifications in iron(II) NHC complexes for olefin aziridination and imination

Abstract

A model catalysis reaction for a C2 + N1 type aziridination and imination of p-tolyl azide with cis-cyclooctene in toluene is reported. Applying 10 equivalents related to the azide, cis-cyclooctene is consumed within 24 h. A reaction temperature of 90 °C is chosen for solubility and activity reasons. A variety of Fe(II) N-heterocyclic carbene (NHC) complexes (1–5) are tested as additives. All show promising formation of aziridine and its imine isomer in the benchmark reaction. However, similar activities are also achieved by a metal-free control reaction together with a similar product distribution of A (aziridine), B (imine) and C (aziridine). The metal compounds cannot be considered as catalysts, but they do indeed influence the isomeric distribution of the reaction. To contextualize the conceivable product isomers, density functional theory calculations were performed (B3LYP/6–31G(d,p)) to determine the minimum ground state energies. As expected, these are nearly identical. However, the backbone modification of the open-chain NHC ligated iron(II) complex (5) allows switching of the predominant reaction, favoring imine (B) as main product.