A Computational Study of the MoO2(acac)2 Catalyzed Epoxidation of Ethylene with Hydrogen Peroxide and t‐Butyl Hydroperoxide

Abstract

AbstractThe cis‐MoO2(acac)2 catalyzed epoxidation of ethylene by H2O2 or tert‐butyl hydroperoxide (TBHP) was studied by density functional theory at ωB97x–D using the 6‐31G(d,p) and 6‐311G(2d,p) basis sets and the PCM model to include the effect of acetonitril solvation. Three initial MoO2(acac)2⋅H2O2 adducts were identified. An associative pathway with a barrier of 26.7 kcal/mol is favored for H2O2 which inserts first into an acac ligand coordination site of the catalyst. TBHP favors instead a step‐wise mechanism in which a catalyst's Mo=O bond inserts into the oxidant upon which ethylene gets epoxidized by the hepta‐coordinate MoO(OH)(acac)2 (TBHP‐κ2O,O’) intermediate with an activation energy of 33.8 kcal/mol. The reaction barriers for H2O2 and TBHP are both within the typical temperature range (70 °C) used for Mo catalyzed epoxidations. The results indicate that the mechanism depends largely on the nature of the oxidant and the dioxo molybdenum catalysts used.