Kinetic Studies on Olefin Epoxidation by Peroxo Molybdenum Complex (MoO(O2)2HMPT)

Oxidation of olefin by peroxo molybdenum complex selectively yields epoxide at room temperature. The nature of the interaction of olefin with molybdenum and that of the peroxo molybdenum complex has been investigated in terms of coordination constant K of olefin and rate constant k2 of decomposition of the peroxo molybdenum-olefin complex, attention being paid to the substituent effect of olefin. The coordination constant increases with the extent of alkyl substitution on double bonded carbon, a tendency opposite to that on Pd(II), or Rh(I). The coordination state of olefin on molybdenum seems to differ from that on Pd(II) or Rh(I), for which π-back donation of metal d-electron is accepted to play an important role. The coordination complex on molybdenum is accordingly assigned to a π-complex with some electron donated to molybdenum. A remarkable steric effect of alkyl substituent is observed, disclosing a difference from the oxidation of uncoordinated olefin. Since k2 increases with K, revealing a similar substituent effect of olefin, the peroxo oxygen seems to be electrophilic, and the peroxo oxygen-molybdenum bond seems to be rather covalent than ionic, thus giving rise to epoxidation.