A computational study of the addition of ReO(3)L (L = Cl(−), CH(3), OCH(3) and Cp) to ethenone

The periselectivity and chemoselectivity of the addition of transition metal oxides of the type ReO(3)L (L = Cl, CH(3), OCH(3) and Cp) to ethenone have been explored at the MO6 and B3LYP/LACVP* levels of theory. The activation barriers and reaction energies for the stepwise and concerted addition pathways involving multiple spin states have been computed. In the reaction of ReO(3)L (L = Cl(−), OCH(3), CH(3) and Cp) with ethenone, the concerted [2 + 2] addition of the metal oxide across the C=C and C=O double bond to form either metalla-2-oxetane-3-one or metalla-2,4-dioxolane is the most kinetically favored over the formation of metalla-2,5-dioxolane-3-one from the direct [3 + 2] addition pathway. The trends in activation and reaction energies for the formation of metalla-2-oxetane-3-one and metalla-2,4-dioxolane are Cp < Cl(−) < OCH(3) < CH(3) and Cp < OCH(3) < CH(3) < Cl(−) and for the reaction energies are Cp < OCH(3) < Cl(−) < CH(3) and Cp < CH(3) < OCH(3) < Cl CH(3). The concerted [3 + 2] addition of the metal oxide across the C=C double of the ethenone to form species metalla-2,5-dioxolane-3-one is thermodynamically the most favored for the ligand L = Cp. The direct [2 + 2] addition pathways leading to the formations of metalla-2-oxetane-3-one and metalla-2,4-dioxolane is thermodynamically the most favored for the ligands L = OCH(3) and Cl(−). The difference between the calculated [2 + 2] activation barriers for the addition of the metal oxide LReO(3) across the C=C and C=O functionalities of ethenone are small except for the case of L = Cl(−) and OCH(3). The rearrangement of the metalla-2-oxetane-3-one–metalla-2,5-dioxolane-3-one even though feasible, are unfavorable due to high activation energies of their rate-determining steps. For the rearrangement of the metalla-2-oxetane-3-one to metalla-2,5-dioxolane-3-one, the trends in activation barriers is found to follow the order OCH(3) < Cl(−) < CH(3) < Cp. The trends in the activation energies for the most favorable [2 + 2] addition pathways for the LReO(3)–ethenone system is CH(3) > CH(3)O(−) > Cl(−) > Cp. For the analogous ethylene–LReO(3) system, the trends in activation and reaction energies for the most favorable [3 + 2] addition pathway is CH(3) > CH(3)O(−) > Cl(−) > Cp [10]. Even though the most favored pathway in the ethylene-LReO(3) system is the [3 + 2] addition pathway and that on the LReO(3)–ethenone is the [2 + 2] addition pathway, the trends in the activation energies for both pathways are the same, i.e. CH(3) > CH(3)O(−) > Cl(−) > Cp. However, the trends in reaction energies are quite different due to different product stabilities. The formation of the acetic acid precursor through the direct addition pathways was unsuccessful for all the ligands studied. The formation of the acetic acid precursor through the cyclization of the metalla-2-oxetane-3-one is only possible for the ligands L = Cl(−), CH(3) whiles for the cyclization of metalla-2-oxetane-4-one to the acetic acid precursor is only possible for the ligand L = CH(3). Although there are spin-crossover reaction observed for the ligands L = Cl(−), CH(3) and CH(3)O(−), the reactions occurring on the single surfaces have been found to occur with lower energies than their spin-crossover counterparts.