Theoretical Investigation of the Reaction of Mn⁺ with Ethylene Oxide

The potential energy surfaces of Mn⁺ reaction with ethylene oxide in both the septet and quintet states are investigated at the B3LYP/DZVP level of theory. The reaction paths leading to the products of MnO⁺, MnO, MnCH₂⁺, MnCH₃, and MnH⁺ are described in detail. Two types of encounter complexes of Mn⁺ with ethylene oxide are formed because of attachments of the metal at different sites of ethylene oxide, i.e., the O atom and the CC bond. Mn⁺ would insert into a C–O bond or the C–C bond of ethylene oxide to form two different intermediates prior to forming various products. MnO⁺/MnO and MnH⁺ are formed in the C–O activation mechanism, while both C–O and C–C activations account for the MnCH₂⁺/MnCH₃ formation. Products MnO⁺, MnCH₂⁺, and MnH⁺ could be formed adiabatically on the quintet surface, while formation of MnO and MnCH₃ is endothermic on the PESs with both spins. In agreement with the experimental observations, the excited state a⁵D is calculated to be more reactive than the ground state a⁷S. This theoretical work sheds new light on the experimental observations and provides fundamental understanding of the reaction mechanism of ethylene oxide with transition metal cations