Asymmetric Catalysis of Hetero-Ene Reactions with Tridentate Schiff Base Chromium(III) Complexes

Tridentate Schiff base chromium(III) complex 1 catalyzes the asymmetric hetero-ene reaction between aryl aldehydes and either 2-methoxypropene or 2-trimethylsilyloxypropene to provide a series of β-hydroxyenol ether products in high yields and enantioselectivities. X-ray crystallographic analysis of a closely related chromium complex reveals a bridged, dimeric structure bearing aquo-bound six-coordinate CrIII centers. A mechanism is proposed wherein water dissociation is effected by means of a chemical desiccant (BaO or silyl enol ether), thereby revealing the site for aldehyde complexation.