Theoretical Investigation Of Reaction Mechanisms Of Feo~+/CoO~+ With Propane

Density functional theory (DFT) has been employed to survey the gas-phase reactions of FeO⁺/CoO⁺ with propane. For the reaction of FeO⁺ with propane,the geometries and energies of all the stationary points involved are located. Four types of stable (i.e.,α,β,γ-,2α,3β³ and 2α,2γ-η⁴) complexes could be formed between FeO⁺ and propane. Various mechanisms leading to the loss of CH3, H2O, C3H7OH (H₂O+C₃H₆), and C₃H₆ are analyzed in term of the topology of PES. The reaction of FeO⁺ with propane involves initial C-H activation, while initial C-C activation is unlikely to be important. The loss of CH₃ takes place adiabatically on the sextet PES via the simple C^a-to-O H shift fromη⁴-OF^e+(C₃H₈) followed by CH3 shift. The C3H7OH elimination proceeds via direct C?-to-O hydrogen shift followed by C-O coupling, while the loss of H₂O, C₃H₆, and (H₂O+C₃H₆) proceeds via theα,β-H andα,β-H abstraction mechanisms from all theη³ complexes. Theα,β-H abstraction mechanism for water loss is the most favorable because it is not only energetically and dynamically favorable but also has a high crossing probability between the sextet and quartet PESs. In the reaction of CoO+ with propane, geometries and energies for all the stationary points involved are investigated at the B3LYP/DZVP(d)(opt+3f)+6-311++G(2df,2pd) level. Coordinations of the metal center of CoO⁺ toα,β,γ-,^- and 2α,β,-H atoms could account for three types of complexes, i.e., twoη³- and oneη⁴-OFe+-C₃H₈ complexes. The reaction of CoO⁺ with propane involves initial C-H activation and C-C activation in propane. All the two reaction mechanisms are both important if the spin inversion is considered; If the spin inversion is not considered, theα,β-H abstraction channel is the most favorable because it is not only simple (direct C?-to-O H shift) but also energetically and dynamically favorable. The C₃H₇OH elimination occurs through the direct C-to-O hydrogen shift from 2α,β,γ- andα,β,γ-η³-OCo+(C3H8) followed by a C-O coupling on both the quintet and triplet PESs, while the loss of H2O and C₃H₆ could take place via both the quintet and triplet pathways ofα,β-,α,β- andβ,2α-H abstraction mechanisms in which spin-orbit coupling plays an important role. The theoretical work sheds new light on the title reactions and can be considered as a new approach to the reaction mechanisms of transition metal oxide ions with propane.