The catalytic activity of [Cp*2M2O5] (M = Mo, W) for the homogeneous epoxidation of cyclooctene in a MeCN/toluene solvent mixture follows the order Mo >> W when using TBHP/decane as oxidant, in contrast to the inverse order (W >> Mo) when using aqueous H2O2 as oxidant. The catalytic activity for the Mo system strongly depends on the solvent used to deliver the oxidant (TBHP/decane >> TBHP/H2O). The low activity of the W system is also decreased when using TBHP/water in place of TBHP/decane. For both metals, H2O2/H2O is a better oxidant than TBHP/H2O. However, while the Mo-based catalyst is much more active for the TBHP/decane epoxidation in spite of the lower TBHP oxidizing power (TBHP/decane > H2O2/H2O > TBHP/H2O), the W-based system is much more active for the H2O2/H2O epoxidation in spite of the negative effect of water (H2O2/H2O > TBHP/decane > TBHP/H2O). The kinetic profile of the TBHP/decane epoxidation process is affected by product inhibition. Initial rate measurements show that the rate law is first order in substrate and has saturation behaviour in oxidant.
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