A Computational Study of the MoO2(acac)2 Catalyzed Epoxidation of Ethylene with Hydrogen Peroxide and t‐Butyl Hydroperoxide. Issue 1 (5th December 2022)

• Record Type: Journal Article
• Authors: Dhimba, George; Muller, Alfred; Lammertsma, Koop
• Is Part Of: ChemCatChem. Volume 15:Issue 1(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-12-05
• Subjects: epoxidation mechanism -- density functional theory -- MoO2(acac)2 -- catalysis -- molybdenum; Catalysis -- Periodicals; 541.39505
• DOI: 10.1002/cctc.202201031
• Languages: English
• ISSNs: 1867-3880

Abstract

Abstract: The cis ‐MoO2 (acac)2 catalyzed epoxidation of ethylene by H2 O2 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 ⋅H2 O2 adducts were identified. An associative pathway with a barrier of 26.7 kcal/mol is favored for H2 O2 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‐κ 2 O, O') intermediate with an activation energy of 33.8 kcal/mol. The reaction barriers for H2 O2 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. Abstract : Epoxidation of ethylene with the cis ‐MoO2 (acac)2 catalyst and the H2 O2 and tert ‐butyl hydroperoxide oxidants to ethylene oxide reveals different mechanisms based on density functional theory calculations. H2 O2 favors an associative pathway slightly over others while a step‐wise mechanism is preferred for tert ‐butyl hydroperoxide.