A Simple Entry to (η⁵-C₅R₅)chlorodioxomolybdenum(VI) Complexes (R = H, CH₃, CH₂Ph) and Their Use as Olefin Epoxidation Catalysts

Abstract

The complexes (η5-C5R5)MoO2Cl (R = H, CH3 (Me), CH2Ph (Bz)) are readily prepared from the parent carbonyls (η5-C5R5)Mo(CO)3Cl upon reaction with t-BuOOH (TBHP) in n-decane. The compounds are characterized by vibrational spectroscopy, 1H, 13C, and 95Mo NMR spectroscopy, and elementary analysis and are compared to their (η5-C5R5)ReO3 homologues. The Mo−C5R5 force constants have been determined. (η5-C5Bz5)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 (η5-C5R5)MoO2Cl complexes catalyze the epoxidation of cyclooctene, styrene, and 1-octene with TBHP as oxidizing agent. The highest activity is found for (η5-C5Bz5)MoO2Cl: TOF 21000 mol/(mol × h) for cyclooctene in CH2Cl2 at 55 °C 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 (η5-C5R5)Mo(CO)3Cl can be used as catalyst precursors since they are transformed into (η5-C5R5)MoO2Cl under the operating catalytic conditions.