A density functional theory study of the mechanisms of oxidation of ethylene by rhenium oxide complexes†
The oxo complexes of group VII B are of great interest for their potential toward epoxidation and dihy-droxylation. In this work, the mechanisms of oxidation of ethylene by rhenium-oxo complexes of thetype LReO3(L = O−, Cl, CH3, OCH3, Cp, NPH3) have been explored at the B3LYP/LACVP* level of theory.The activation barriers and reaction energies for the stepwise and concerted addition pathways involvingmultiple spin states have been computed. In the reaction of LReO3(L = O−, Cl, CH3, OCH3, Cp, NPH3) withethylene, it was found that the concerted [3 + 2] addition pathway on the singlet potential energy sur-faces leading to the formation of a dioxylate intermediate is favored over the [2 + 2] addition pathwayleading to the formation of a metallaoxetane intermediate and its re-arrangement to form the dioxylate.The activation barrier for the formation of the dioxylate on the singlet PES for the ligands studied isfound to follow the order O−>CH3> NPH3>CH3O−>Cl−> Cp and the reaction energies follow theorder CH3>O−> NPH3>CH3O−>Cl−> Cp. On the doublet PES, the [2 + 2] addition leading to the for-mation the metallaoxetane intermediate is favored over dioxylate formation for the ligands L = CH3,CH3O−,Cl−. The activation barriers for the formation of the metallaoxetane intermediate are found toincrease for the ligands in the order CH3<Cl−<CH3O−while the reaction energies follow the order Cl−<CH3O−<CH3. The subsequent re-arrangement of the metallaoxetane intermediate to the dioxylate isonly feasible in the case of ReO3(OCH3). Of all the complexes studied, the best dioxylating catalyst isReO3Cp (singlet surface); the best epoxidation catalyst is ReO3Cl (singlet surface); and the best metalla-oxetane formation catalyst is ReO3(NPH3) (triplet surface).
An article published by Elsevier and also available at DOI: 10.1039/c3dt50539a
DaltonTrans., 2013,42, 10885