On the activity of chiral chromium salen complexes covalently bound to solid silicates for the enantioselective epoxide ring opening

Two series of solid catalysts in which a chiral chromium salen complex has been anchored on aminopropyl-functionalized SiO2, ITQ-2 or MCM-41 have been prepared. In those catalysts in which anchoring of the complex was accomplished through coordination with the metal high enantiomeric excesses were obtained (up to 70% enantiomeric excess (e.e.)), but the complex leaches to the solution on a large extent. In contrast, for those other solids in which the complex is attached to the surface by covalent linkage to the ligand no leaching was observed, but the e.e. were modest (below 20%) compared to those obtained in homogeneous catalysis under comparable conditions (above 50%).