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 \rmTaS_3^- 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 \rmTaS_3^- is able to adsorb all of the alkane molecules and break the robust C–H bonds. Further density functional theory calculations reveal that \rmTaS_3^- is a closed-shell species and effectively activates methane via the Ta^δ+–S^δ− Lewis acid-base pair (LABP, CH₄+Ta^δ+–S^δ−→CH₃-Ta-S-H). With a comparative study with \rmNbS_3^- that contains the Nb^δ+–S^δ− LABP, the higher reactivity of \rmTaS_3^- than that of \rmNbS_3^- can be attributed to the more acidity of Ta^δ+ than that of Nb^δ+. To the best of our knowledge, this study reports the first example of gas phase species \rmTaS_3^- to activate methane through the metal-sulfur LABP under thermal collision conditions.