title: Mechanism insights of ethane C-H bond activations by bare [Fe(III)═O]+: explicit electronic structure analysis.
abstract: Alkane C-H bond activation by various catalysts and enzymes has attracted considerable attention recently, but many issues are still unanswered. The conversion of ethane to ethanol and ethene by bare [Fe(III)═O](+) has been explored using density functional theory and coupled-cluster method comprehensively. Two possible reaction mechanisms are available for the entire reaction, the direct H-abstraction mechanism and the concerted mechanism. First, in the direct H-abstraction mechanism, a direct H-abstraction is encountered in the initial step, going through a collinear transition state C···H···O-Fe and then leading to the generation of an intermediate Fe-OH bound to the alkyl radical weakly. The final product of the direct H-abstraction mechanism is ethanol, which is produced by the hydroxyl group back transfer to the carbon radical. Second, in the concerted reaction mechanism, the H-abstraction process is characterized via overcoming four/five-centered transition states (6/4)TSH_c5 or (4)TSH_c4. The second step of the concerted mechanism can lead to either product ethanol or ethene. Moreover, the major product ethene can be obtained through two different pathways, the one-step pathway and the stepwise pathway. It is the first report that the former pathway starting from (6/4)IM_c to the product can be better described as a proton-coupled electron transfer (PCET). It plays an important role in the product ethene generation according to the CCSD(T) results. The spin-orbital coupling (SOC) calculations demonstrate that the title reaction should proceed via a two-state reactivity (TSR) pattern and that the spin-forbidden transition could slightly lower the rate-determining energy barrier height. This thorough theoretical study, especially the explicit electronic structure analysis, may provide important clues for understanding and studying the C-H bond activation promoted by iron-based artificial catalysts.
authors.affiliation: State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry, Jilin University, Changchun 130023, People's Republic of China.
authors.forename: Xiao-Li
authors.initials: XL
authors.lastname: Sun
authors.forename: Xu-Ri
authors.initials: XR
authors.lastname: Huang
authors.forename: Ji-Lai
authors.initials: JL
authors.lastname: Li
authors.forename: Rui-Ping
authors.initials: RP
authors.lastname: Huo
authors.forename: Chia-Chung
authors.initials: CC
authors.lastname: Sun