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.

Keywords

• Dioxomolybdenum(VI) complexes
• siloxide ligands
• Lewis base adducts
• 2
• 2'-bipyridine
• olefin epoxidation.