Methane activation by closed-shell tantalum sulfide anions TaS3−

Methane is a vital feedstock while the intrinsic inertness of CH4 molecule hinders the conversion of methane under mild conditions. Investigating and understanding the mechanism of methane activation is of great importance in chemistry. In this study, tantalum sulfide anions TaS3− were generated by laser ablation method and mass-selected by a quadrupole mass filter to react with methane, ethane, and propane in an ion funnel trap reactor under thermal collision conditions. The reactant and product ions were detected by a time-of-flight mass spectrometer. Experimental results demonstrate that TaS3− is able to adsorb all of the alkane molecules and break the robust C-H bonds. Further density functional theory calculations reveal that TaS3− is a closed-shell species and effectively activates methane via the Ta/δ+–Sδ− Lewis acid-base pair (LABP, CH4+Taδ+−Sδ− → CH3-Ta-S-H). With a comparative study with NbS3− that contains the Nbδ+–Sδ− LABP, the higher reactivity of TaS3− than that of NbS3− can be attributed to the more acidity of Taδ+ than that of Nbδ+. To the best of our knowledge, this study reports the first example of gas phase species TaS3− to activate methane through the metal-sulfur LABP under thermal collision conditions.