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

Ansa-bridged η⁵-cyclopentadienyl molybdenum and tungsten tricarbonyl complexes of formula [M(η⁵-C₅H ₄(CH₂)₃-η¹-CH ₂)(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)₃X (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)₃X 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.