Chiral manganese(III) salen catalysts immobilized on MCM-41 and delaminated zeolites ITQ-2 and ITQ-6 through new axial coordinating linkers

We report that the catalytic behavior and enantioselectivity of three different chiral Mn(III) salen complexes anchored to traditional supports such as MCM-41 (38-Angstrom pore diameter) and delaminated zeolitic materials ITQ-2 and ITQ-6 strongly depend on whether the complexes are attached to the surfaces through the chiral equatorial tetradentate salen ligand or via the apical ligand. As for the case of unsupported complexes, this experimental observation has been accounted for strong variations in the conformational preference of the catalyst intermediate toward the approaching olefin, as well as to unfavorable structural changes in the complex. In addition, control of the hydrophobicity of the surface allows for optimization of selectivity in obtaining chiral epoxides. (C) 2004 Elsevier Inc. All rights reserved.