Ansa-bridged η5-cyclopentadienyl molybdenum and tungsten complexes:: synthesis, structure and application in olefin epoxidation

Ansa-bridged eta(5)-cyclopentadienyl molybdenum and tungsten tricarbonyl complexes of formula [M(eta(5)-C5H4(CH2)(3)-eta(1)-CH2)(CO)(3)] (M= Mo or W) were synthesized and the X-ray crystal structure of the tungsten complex is reported. In the epoxidation of cyclooctene the molybdenum compound shows a high catalytic activity, approaching the observed activities for the most reactive unbridged complexes of composition CpMo(CO)(3)X (X=Cl, CH3). The activity of the tungsten complex is also amongst the highest catalytic activities for the olefinic epoxidation of complexes with the composition CpW(CO)(3)X and WO2X2L2, reported so far. The low ring strain of the ansa-bridged system improves the stability of the complexes under oxidative conditions considerably in comparison to derivatives with a shorter bridge and therefore paves the way to introduction of chirality in these systems.