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

The stability of the heterogeneous CuHY catalyst for the aziridination of s tyrene using nitrene donors, with and without the presence of chiral bis(ox azoline) 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 na ture of the nitrene donor, the structure of the bis(oxazoline), the presenc e of solvent and the breakdown products of the nitrene donor. It is found t hat between 0.08-6.8% by weight of the Cu present in CuHY can be leached du ring standard reaction conditions. However, using short reaction times it i s shown that the amount of Cu removed can be limited readily to the lower v alue. Detailed studies show that for this reaction system the leached Cu2plays no significant role in the formation of the aziridine, and that the h igh enantioselectivities observed with CuHY are due to Cu2+ which is electr ostatically bound within the pores of the zeolite and modified by a chiral bis(oxazoline) ligand.