Catalytic properties of the dioxomolybdenum siloxide MoO2(OSiPh3)2 and its 2,2'-bipyridine adduct MoO2(OSiPh3)2(bpy).
The tetrahedral triphenylsiloxy complex MoO(2)(OSiPh(3))(2) (1) and its Lewis base adduct with 2,2'-bipyridine, MoO(2)(OSiPh(3))(2)(bpy) (2), were prepared and characterised by IR/Raman spectroscopy, and thermogravimetric analysis. Both compounds catalyse the epoxidation of cis-cyclooctene at 55 degrees C using tert-butylhydroperoxide (t-BuOOH) is decane as the oxidant, giving 1,2-epoxycyclooctane as the only product. The best results were obtained in the absence of a co-solvent (other than the decane) or in the presence of 1,2-dichloroethane, while much lower activities were obtained when hexane or acetonitrile were added. With no co-solvent, catalyst 1 (initial activity 272 mol x molMo(-1) x h(-1)for a catalyst:substrate: oxidant molar ratio of 1:100:150) is much more active than 2(initial activity 12 mol x molMo(-1) x h(-1)). The initial reaction rates showed first order dependence with respect to the initial concentration of olefin. With respect to the initial amount 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 of catalyst was also studied for both catalysts. The lower apparent activation energy of 1 (11 kcal x mol(-1)) as compared with 2 (20 kcal x mol(-1)) is in accordance with the higher activity of the former.
Bruno
Sofia M
SM
Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal.
Monteiro
Bernardo
B
Balula
Maria Salete
MS
Lourenço
Catarina
C
Valente
Anabela A
AA
Pillinger
Martyn
M
Ribeiro-Claro
Paulo
P
Gonçalves
Isabel S
IS
D015082:2,2'-Dipyridyl / Q000737:chemistry*; D002384:Catalysis; D009682:Magnetic Resonance Spectroscopy; D008982:Molybdenum / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013059:Spectrum Analysis, Raman
D015082:2,2'-Dipyridyl; D008982:Molybdenum