Bis(oxazoline)-copper complexes, immobilized by electrostatic interactions, as catalysts for enantioselective aziridination

Abstract

Immobilization of chiral bis(oxazoline)-copper complexes by electrostatic interactions with anionic supports leads to recyclable catalysts for aziridination between styrene and (ptoluensulfonylimino)phenyliodinane as a nitrene precursor. Although the yields are good in all the cases, enantioselectivity depends on the nature of the chiral ligand. With a bis(oxazoline) bearing phenyl substituents, the enantioselectivity is always around 25% ee, as in solution. When the chiral ligand has tert-butyl groups, enantioselectivity is noticeably lower than that observed in homogeneous phase as a consequence of the presence of free copper on the solid.

Noncovalent Immobilization of Enantioselective Catalysts

“…The use of clay-supported Box−copper catalysts in the closely related aziridination reaction of styrene with TosNIPh (Scheme ) has also been investigated. PhBox− and t BuBox−Cu(II) complexes immobilized onto laponite were also tested in the aziridination reaction.…”

“…42 Other reactions have also been tested with these kinds of supports. In the case of aziridination reaction (Scheme 7), 49 using Nafion-silica nanocomposites as the anionic supports led to results not as good as those described using CuHY exchanged zeolites (see section 2.3).…”