## 2 Results and Discussion
### Mo-Catalyzed Epoxidation with TBHP  
Most substrates were quantitatively converted by the Mo-catalysts. However, the higher temperatures resulted in partial water elimination of product B to a new unsaturated structure as seen for product C in Scheme 2. This side product was identified and quantified using GC-MS and NMR but was not further isolated and characterized as only small amounts were formed (\(\leq\)7%). Additionally, some unidentified oligomeric side products were observed. The oligomers were likely formed through intermolecular reactions of the epoxide intermediates, as the double bond seemed to be reacting to products containing alcohol and ether functions. Analyses using high pressure size exclusion chromatography (HPSEC) revealed that the oligomers consisted mostly of di- and trimers. At 80 \({}^{\circ}\)C, traces of benzaldehydes were also formed through oxidative cleavage of double bond. Due to these various side reactions, the yield of products A and B were moderate, although the conversions to epoxides were quantitative (Table 1). For the Mo-catalyzed reactions, no or very slow reactions were observed with less than 5 equivalents of TBHP or with reaction temperatures lower than 80 \({}^{\circ}\)C, which restricted the optimization of this reaction by lowering the reaction temperature. As a consequence, lower yields of the final products were obtained using MoO\({}_{2}\)L complexes performed at 80 \({}^{\circ}\)C (20%-40% formation of products **A** and **B** according to NMR of the reaction mixtures) compared to reactions with _m_CPBA operated at room temperature (>90% formation of products **A** and **B**). The resulting reaction mixtures for each substrate were similar in the processes using both catalysts [MoO\({}_{2}\)(SAP)]\({}_{2}\) and [MoO\({}_{2}\)(SATP)]\({}_{2}\). However, the reaction rates were higher with [MoO\({}_{2}\)(SATP)]\({}_{2}\). This observation was in agreement with previous kinetic studies with both catalysts for epoxidation of cyclootene, under solvent-free conditions with TBHP at 80 \({}^{\circ}\)C [20]. Substrate 1 reacted to identical reaction mixtures with both Mo-catalysts (Entries 1 and 2). As a side note, analyses of these reactions were done at one and three hours, and quantitative conversion for the [MoO\({}_{2}\)(SATP)]\({}_{2}\)-catalyzed reaction (Entry 3) was reached in a shorter time compared to the [MoO\({}_{2}\)(SAP)]\({}_{2}\)-catalyzed reaction (Entry 2). In the absence of Mo-catalyst, even a large excess (10 equivalents) of TBHP did not react with substrate **1**, exhibiting the role of the MoO\({}_{2}\)L complexes as catalyst. To further investigate this, reaction kinetic studies were performed with substrate **2** (14.5 mM) in toluene, using 0.5 mol% dimeric Mo(VI)-precatalyst (i.e. 1% mol Mo) and 5 equivalents of TBHP (70 wt% in water) at 80 \({}^{\circ}\)C. The reaction was followed by GC-MS using dimethyl-dihydro imperanene as internal standard (Figure 4). Samples were taken at specific time intervals and dried in a vacuum. Derivatization of the samples was done using tetramethyldisilazane and chlorotrimethylsilane in pyridine prior to GC-MS analysis [27]. The results showed that the reaction catalyzed by [MoO\({}_{2}\)(SATP)]\({}_{2}\) was faster (as mentioned previously), with a quantitative conversion reached after 3 h 40 min (Figure 5). For comparison, at 3 h 40 min, the [MoO\({}_{2}\)(SAP)]\({}_{2}\)-catalyzed reaction showed a conversion of less than 50% and, calculated from the trend of the reaction rate, a quantitative conversion was reached after approximately 9 h 30 min. The rate was 2.6 times slower than the [MoO\({}_{2}\)(SATP)]\({}_{2}\)-catalyzed reaction. For both catalysts, the final reaction mixture gave products **2A**, **2B** and **2C** in roughly 3:5:1 ratio. Quantification using GC analyses showed a total conversion to products **2A**, **2B** and **2C** at around 95%, for both reactions.