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

The complexes (η 5 -C 5 R 5 )MoO 2 Cl (R = H, CH 3 (Me), CH 2 Ph (Bz)) are readily prepared from the parent carbonyls (η 5 -C 5 R 5 )Mo(CO) 3 Cl upon reaction with t -BuOOH (TBHP) in n -decane. The compounds are characterized by vibrational spectroscopy, 1 H, 13 C, and 95 Mo NMR spectroscopy, and elementary analysis and are compared to their (η 5 -C 5 R 5 )ReO 3 homologues. The Mo−C 5 R 5 force constants have been determined. (η 5 -C 5 Bz 5 )MoO 2 Cl 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 (η 5 -C 5 R 5 )MoO 2 Cl complexes catalyze the epoxidation of cyclooctene, styrene, and 1-octene with TBHP as oxidizing agent. The highest activity is found for (η 5 -C 5 Bz 5 )MoO 2 Cl: TOF 21000 mol/(mol × h) for cyclooctene in CH 2 Cl 2 at 55 °C with a ratio catalyst:substrate:TBHP = 0.0001:1:2.5. This activity even surpasses that of the well-known MeReO 3 /H 2 O 2 system. The stable parent carbonyls (η 5 -C 5 R 5 )Mo(CO) 3 Cl can be used as catalyst precursors since they are transformed into (η 5 -C 5 R 5 )MoO 2 Cl under the operating catalytic conditions.