Rhenium complexes, olefin epoxidation

Re-peroxo complexes, e. g., in olefin epoxidation. Nevertheless, 2 reacts stoichio-metrically with cyclobutanone in the absence of H2O2. This reversed behavior may be due to substrate binding to rhenium. The unsymmetrical geometry of compound 2a, displaying a polarity within the peroxo ligands, may also be responsible for the observed behavior. 

The two seminal contributions of Mimoun and Sharpless laboratories led to a controversy on the reaction mechanism that was lasting longer than for two decades [82] and expanded to the olefin epoxidation with other metal peroxo complexes, in particular those of rhenium. Kinetic studies of Al-Ajlouni and Espenson [83,84] on the MTO-catalyzed olefin epoxidation with H2O2 revealed the importance of both mono- and diperoxo species in the catalytic process as well as substituent effects on reaction rates, but the molecular mechanism remained uncertain. 

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