Highly enantioselective olefin epoxidation controlled by helical confined environments

• Helical mesostructured materials prepared by an entropy-driven procedure.
• Helical materials show excellent performance in asymmetric olefin epoxidation.
• Helical materials outperform their homogeneous counterparts.
• The ee’s reach 100% for R-(+)-limonene and trans-hex-2-en-1-ol epoxidation.
• Stereoselectivity arises from chiral backbone imposing confinement constraints.

Helical mesoporous materials of the MCM-41 type are important materials that can be prepared by onepot synthesis procedures with a co-surfactant. A control of the characteristics at a local level is of the most important in the view of the applications of such materials. However, there are not many studies relating such features with synthetic approaches. In this work, we prepared both helical and regular channel materials from Si-based MCM-41 type. Afterward, a bpy derivative was used as ligand to coordinate MoII/VI. The complexes and the new materials were tested as the catalytic precursors in the epoxidation of cis-cyclooctene, styrene, 1-octene, R-(+)-limonene and trans-hex-2-en-1-ol, using tert-butylhydroperoxide (TBHP) as oxidant. Although almost all the catalysts were 100% selective toward the epoxide, the conversions were in general good. The major achievement of these catalysts is an outstanding stereocontrol of the reaction products. In addition, these catalysts were found to be very effective under several circumstances. This is certainly an important contribution for such concept and may render such materials further applications where chiral recognition is important.

Enhanced stereoselectivity: Mesoporous materials with helical channels show enhanced stereoselectivity in asymmetric olefin epoxidation reactions. The materials with Mo active sites have superior performance compared to homogeneous counterparts. The ee’s were found to range between 32% (styrene) and 100% (R-(+)-limonene and trans-hex-2-en-1-ol). This reveals an important matrix-assisted effect arising from the rigid confined environment provided by the chiral host materials.Figure optionsDownload high-quality image (260 K)Download as PowerPoint slide