Aluminum derivative peroxides in the (t-BuO)3Al–2t-BuOOH catalytic system as a source of electron-excited dioxygen: a quantum chemical study on a model

Abstract

The quantum chemical study of the MeOOH/(MeO)₃Al model system has been carried out in order to predict the mechanism of the catalytic decomposition of t-BuOOH under mild conditions for the t-BuOOH/(t-BuO)₃Al system being a powerful synthetic tool for selective oxidation. To elucidate the chemical excitation of O₂ eliminated in the catalytic reaction and to predict the electronic state of O₂, the topology of the potential energy surface (PES), the structures of intermediates and transition states, the activation and reaction energies were obtained at the B3LYP/cc-pVTZ theory level. It was shown that the peroxide, (MeO)₂AlOOMe, corresponding to the experimentally obtained (t-BuO)₂AlOOBu-t, is formed in the first step of the reaction. After that, in the main pathway, the aluminum-containing peroxide reacts with the second MeOOH molecule through the nucleophilic substitution of the second methoxy group forming the MeOAl(OOMe)₂ diperoxide. The diperoxide rearranges to aluminum-containing ozonide MeOAlOOOMe. The ozonide isomerizes in the mononuclear-metal dioxygen intermediate (MeO)₃Al·O₂. The latter decomposes through the adiabatic ((MeO)₃Al + O₂(b¹Σ⁺_g)) and non-adiabatic ((MeO)₃Al + O₂(X³Σ⁻_g)) pathways, which corresponds to experimental data about the incomplete conversion of O₂ to O₂(b¹Σ⁺_g). The generation of O₂(b¹Σ⁺_g) was revealed by the analysis of the energy diagram calculated with the CCSD(T), CCSDT(Q), and CASSCF methods. It was suggested that the η¹-(MeO)₃Al·O₂ and, thus, (t-BuO)₃Al·O₂ complexes are new sources of O₂(b¹Σ⁺_g).