A density functional theory study of the mechanisms of oxidation of ethyleneby technetium oxo complexes

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Elsevier B.V
The mechanisms of oxidation of ethylene by transition metal-oxo complexes of the type LTcO3(L = O , Cl,CH3, OCH3, Cp, NPH3) have been explored by computing the activation barriers and reaction energies forthe concerted and stepwise addition pathways at the density functional theory B3LYP/LACVP level oftheory. The results indicate that in the reaction of LTcO3(L = O , Cl, CH3, OCH3, Cp, NPH3) with ethylene,the formation of the dioxylate intermediate through the concerted [3 + 2] addition pathway on the singletpotential energy surface is favored kinetically and thermodynamically over its formation through thetwo-step process via the metallaoxetane intermediate. The activation barrier for the formation of thedioxylate on the singlet PES for the ligands studied is found to follow the order: O >CH3> NPH3>CH3O >Cl > Cp while the reaction energies follow the order: Cl >O >CH3> NPH3>CH3O > Cp. Onthe doublet PES, the [2 + 2] addition leading to the formation of the four-membered metallacycle inter-mediate is favored kinetically and thermodynamically for the ligands when L = NPH3. The direct [2 + 1]addition of ethylene across the oxo- ligand of doublet TcO3(CH3) to form the epoxide precursor is favoredwhen L = CH3. The activation barriers for the formation of the dioxylate intermediate are found to followthe order: Cl <CH3O <CH3whiles the reaction energies follow the order Cl <CH3O <CH3. The re-arrangement of the metallaoxetane intermediate to the dioxylate is not a feasible pathway for the forma-tion of the dioxylate. The formation of the epoxide precursor will not result from the reaction of LTcO3(L = O , Cp) with ethylene on all the surfaces explored. There does not appear to be a spin-crossover inany of the pathways studied.
An article published by Elsevier B.V. and also available at http://dx.doi.org/10.1016/j.comptc.2013.01.006
Density functional theory, Organometallic reaction mechanisms, Oxidation of alkenes, Technetium oxide complexes, Metallaoxetane, Dioxylate
A. Aniagyei et al./Computational and Theoretical Chemistry 1009 (2013) 70–80. http://dx.doi.org/10.1016/j.comptc.2013.01.006