An inductively coupled plasma tandem mass spectrometry investigation of the activation of methane by lanthanide cations

The activation of C-H and C-C bonds by atomic metal cations remains a profitable area of research to utilize environmentally abundant methane and produce useful hydrocarbon fuel. Although methane activation by transition metal cations has been the focus of catalysis research for decades, less is known about the catalytic capabilities of lanthanide cations. Here we employ inductively coupled plasma tandem mass spectrometry to examine the kinetic energy dependences of the reactions of lanthanide cations Ce⁺, Pr⁺, Nd⁺, Sm⁺, and Eu⁺ with methane. The resulting energy-dependent reaction cross sections enable a measurement of the reaction thermochemistry and provide fundamental insight into the physical characteristics that enable Ln⁺ reactivity. We report values for the Ln⁺-D bond dissociation energies, <i>D</i>₀(Ln⁺-D), and the first experimentally obtained values for <i>D</i>₀(Ln⁺-CD₃) and <i>D</i>₀(Ln⁺-CD). We find that the observed reaction efficiencies correlate to the promotion energies (<i>E</i>_p) from the Ln⁺ ground state electronic configurations to the 5d² or 5d6s electronic configuration. This indicates that the Ln⁺ requires an electron configuration with two unpaired valence electrons in non-f orbitals to effectively insert into C-H bonds.