A simple entry to (η5-C5R5)chlorodioxomolybdenum(VI) complexes (R = H, CH3, CH2Ph) and their use as olefin epoxidation catalysts

The complexes (eta(5)-C5R5)MoO2Cl (R = H, CH3 (Me), CH2Ph (Bz)) are readily prepared from the parent carbonyls (eta(5)-C5R5)Mo(CO)(3)Cl upon reaction with t-BuOOH (TBHP) in n-decane. The compounds are characterized by vibrational spectroscopy, H-1, C-13, and Mo-95 NMR spectroscopy, and elementary analysis and are compared to their (eta(5)-C5R5)ReO3 homologues. The Mo-C5R5 force constants have been determined. (eta(5)-C(5)Bz(5))MoO2Cl can be stored and handled at room temperature without decomposition, in contrast to the more temperature sensitive Cp (R = H) and Cp* (R = Me) analogues. The (eta(5)-C5R5)MoO2Cl complexes catalyze the epoxidation of cyclooctene, styrene, and I-octene with TBHP as oxidizing agent. The highest activity is found for (eta(5)-C(5)Bz(5))MoO2Cl: TOF 21000 mol/(mol x h) for cyclooctene in CH2Cl2 at 55 degreesC with a ratio catalyst:substrate:TBHP = 0.0001:1:2.5. This activity even surpasses that of the well-known MeReO3/H2O2 system. The stable parent carbonyls (eta(5)- C5R5)Mo(CO)(3)Cl can be used as catalyst precursors since they are transformed into (eta(5)-C5R5)MoO2Cl under the operating catalytic conditions.