Protonation of Propene on Silica-Grafted Hydroxylated Molybdenum and Tungsten Oxide Metathesis Catalysts: A DFT Study

Theoretical assessment of the protonation reaction in the activation of propene on hydroxylated Mo(VI) and W(VI) metathesis catalysts is presented in this paper using the density functional theory calculations and five support clusters varying from simple SiO4H3 clusters to a large Si4O13H9 cluster. The bond distances and thermochemical data were similar for most of the clusters. The formation of isopropoxide was more favorable than a propoxide counterpart bonded via the primary carbon atom, with the Gibbs free energies of –3.73 and –7.78 kcal/mol, respectively, for the W catalyst. Overall, the 1T cluster models with optimized H atoms or an all-relaxed alternative would be considered appropriate replacements for a larger 4T cluster model saturated with OH groups and optimized terminal hydrogen atoms. The largest deviations in the energetic data were observed between the protonated structures formed on the two larger clusters saturated with either OH or H groups.