Catalytic heterogeneous aziridination of styrene using CuHY catalyst: an assessment of catalyst stability

Abstract

The stability of the heterogeneous CuHY catalyst for the aziridination of styrene using nitrene donors, with and without the presence of chiral bis(oxazoline) modifiers, is described in detail. Cu²⁺ is found to leach from the CuHY and the rate of Cu-leaching is dependent on the reaction time, the nature of the nitrene donor, the structure of the bis(oxazoline), the presence of solvent and the breakdown products of the nitrene donor. It is found that between 0.08–6.8% by weight of the Cu present in CuHY can be leached during standard reaction conditions. However, using short reaction times it is shown that the amount of Cu removed can be limited readily to the lower value. Detailed studies show that for this reaction system the leached Cu²⁺ plays no significant role in the formation of the aziridine, and that the high enantioselectivities observed with CuHY are due to Cu²⁺ which is electrostatically bound within the pores of the zeolite and modified by a chiral bis(oxazoline) ligand.