Stable and catalytically highly active ansa compounds with cycloalkyl moieties as bridging units

The complexes Mo{η⁵-C₅H₄[CH(CH ₂)₃]-η¹-CH}(CO)₃ (2a) and W{η⁵-C₅H₄[CH(CH₂) ₃]-η¹-CH}CO)₃ (2b) were synthesized by reacting spiro-[4.2]bicyclo[4.1]deca-6,8-diene (1) with the tri(acetonitrile) tri(carbonyl)metal complexes M(CO)₃(CH₃CN)₃ (M=Mo, W). Thermogravimetric (TGA) measurements confirm that the complexes are stable up to 140°C in air in the solid state. The complexes 2a and 2b are very active catalysts at room temperature for the epoxidation of cyclooctene with tert-butyl hydroperoxide (TBHP) as oxidant, reaching TOFs of up to 3650 h^-1. Complex 2a achieves a quantitative product yield without formation of any by-products within 1.5 h, outperforming previously published ansa compounds and performing on par with the cyclopentadienyltri-(carbonyl) (halo)- or (alkyl)molybdenum compelxes CpMo(CO)₃R (R=Hal, Me, Et).