Catalytic Properties of the Dioxomolybdenum Siloxide MoO₂(OSiPh₃)₂ and its 2,2'-Bipyridine Adduct MoO₂(OSiPh₃)₂(bpy)

Abstract: The tetrahedral triphenylsiloxy complex MoO₂(OSiPh₃)₂ (1) and its Lewis baseadduct with 2,2'-bipyridine, MoO₂(OSiPh₃)₂(bpy) (2), were prepared and characterised byIR/Raman spectroscopy, and thermogravimetric analysis. Both compounds catalyse theepoxidation of cis-cyclooctene at 55 ^oC using tert-butylhydroperoxide (t-BuOOH) isdecane as the oxidant, giving 1,2-epoxycyclooctane as the only product. The best resultswere obtained in the absence of a co-solvent (other than the decane) or in the presence of1,2-dichloroethane, while much lower activities were obtained when hexane oracetonitrile were added. With no co-solvent, catalyst 1 (initial activity 272 mol·molMo^-1·h^-1for a catalyst:substrate: oxidant molar ratio of 1:100:150) is much more active than 2(initial activity 12 mol·molMo^–1·h^–1). The initial reaction rates showed first orderdependence with respect to the initial concentration of olefin. With respect to the initialamount of oxidant, the rate order dependence for 1 (1.9) was higher than that for 2 (1.6).The dependence of the initial reaction rate on reaction temperature and initial amount ofcatalyst was also studied for both catalysts. The lower apparent activation energy of 1 (11kcal·mol^–1) as compared with 2 (20 kcal·mol^–1) is in accordance with the higher activity ofthe former.