A Theoretical Study on Methane C-H Bond Activation by Bare [FeO]+/0/.

The first C-H bond activation of methane by bare diatomic FeO in different charge states (cationic + , neutral 0, and anionic - ) has been studied by means of density functional theory (DFT) and CCSD(T) methods. The structures were optimized by using 10 popular different density functionals (DFs) with different Hartree-Fock exchange fractions, as well as the CCSD method and then were subjected to single point energy calculations at both the DFT level and the CCSD(T) level. The performance of these methods on the energies and structures in different charged states of the systems was discussed. The results show that the cationic system has lower barrier than the neutral and anionic systems. In most cases, the impact of density functionals is larger than that of structures on energies. Among the three charged states, the anionic system is the least sensitive to the density functionals. The electronic structure analysis demonstrates that the cationic and neutral systems proceed by either hydrogen-atom transfer (HAT) or proton-coupled electron transfer (PCET), while the anionic system only employs the proton transfer (PT) mechanism. Knowledge from this study is of value for further studies on methane activation.