Permanganyl chloride-mediated oxidation of tetramethylethylene: A density functional theory study

The mechanisms of the oxidation of tetramethylethylene (TME) by permanganyl chloride (MnO₃Cl) have been explored on the singlet and triplet potential energy surfaces at the B3LYP LANL2DZ/6-31G (d) level of theory. The results show that the pathway leading to the formation of the five-membered dioxylate through concerted [3 + 2] addition is favored kinetically and thermodynamically over the three other possible pathways, namely the [2 + 2] addition via the transient metallaoxetane intermediate, epoxidation, and hydrogen transfer pathways. The epoxide precursor that on hydrolysis would yield the epoxide product will most likely arise from a stepwise path through the intermediacy of an organometallic intermediate. This pathway affords the product that is more stable (thermodynamically favorable). However, kinetically, both the stepwise and the concerted [2 + 1] addition pathways leading to the epoxide precursors are very competitive (activation barrier difference of <0.7 kcal/mol).