Methane C−H Bond Activation by Neutral Lanthanide and Thorium Atoms in the Gas Phase: A Theoretical Prediction

Density functional theory (DFT) and Hartree−Fock effective core potential calculations have been performed to investigate the reactivity of neutral f-block atoms toward methane C−H bond activation. The first step of the methane dehydrogenation process, which corresponds to an oxidative insertion, was studied for all lanthanide and actinide thorium atoms. The DFT/B3LYP-correlated results indicate more favorable kinetic and thermochemical conditions for the insertion of the lanthanides with a three non-f valence electron 2D([fn]s2d1) as compared to a two non-f1S([fn+1]s2d0) electronic configuration. Among all the lanthanides, only 2D([fn]s2d1)La, Ce, Gd, and Lu may react exergonically with methane; the lowest activation barrier is calculated for La and Ce atoms (ΔG⧧ = 25 kcal·mol-1). A semiquantitative analysis from a simple two-state model shows that an indirect participation of the 4f-orbitals is expected to modify the [4fn+1]s2d0 reactivity of the Pr, Nb, and Tb−Tm lanthanides as a configuration mixing w...