Molybdenum(II) catalyst precursors in olefin oxidation reactions

• Complexes [Mo(η3-C3H5)(CO)2X(L2)] and [Mo(CO)3X2(L2)] are active and selective catalyst precursor for alkene epoxidation.
• Immobilization in MCM-41 improves the catalytic activity for some nitrogen bidentate ligands.
• The Mo(II) catalyst precursors display only slightly lower conversions in the 2nd run.

The application of Mo(II) complexes [Mo(η3-C3H5)(CO)2X(L2)] and [Mo(CO)3X2 (L2)] to the oxidation of alkenes is described. We have synthesized, characterized and studied the catalytic activity of a series of complexes with nitrogen bidentate ligands (also a few monodentate and a few with N, O donors). They were modified with –Si(OR)3 groups to immobilize in silicon based materials, MCM-41 and silica, using several procedures. Others were deprotonated to intercalate in clays. Many complexes catalyzed selectivity of cis-cyclooctene to its epoxide with high conversions, but oxidation of styrene led to more benzaldehyde than epoxide. Other substrates could be oxidized to several products with variable success. The materials containing immobilized complexes showed in some cases better conversions, in others worse, and others similar, for all substrates tested. Recycling experiments showed that the catalysts lose only a small amount of their activity in the second and third runs, while the selectivity (when determined) was kept. We discuss the mechanisms of the catalytic epoxidation of alkenes based on DFT studies.

The complexes [Mo(η3-C3H5)(CO)2X(L2)] and [Mo(CO)3X2(L2)] are active catalyst precursors for alkene epoxidation, and the activity is enhanced when they are immobilized in MCM-41, for several L2 ligands.Figure optionsDownload as PowerPoint slide