Reactivity of Nb3N3–xOx+ (x = 0–3) toward Methane: Ligand-Controlled Modulation of Nb–Nb σ Bonds

Mild activation of methane remains a fundamental challenge due to its chemical inertness. While metal–metal σ-bond-mediated pathways have recently emerged as an effective strategy, how mixed ligands regulate reactivity of dual-metal centers remains poorly understood. Herein, we investigate the reactivity of Nb₃N_3–xO_x⁺ (x = 0–3) clusters toward CH₄ using time-of-flight mass spectrometry combined with theoretical calculations. A clear evolution of reactivity is observed upon stepwise substitution of N with O, with reaction channels shifting from exclusive adsorption (Nb₃N₃⁺) to concurrent adsorption and dehydrogenation (Nb₃N₂O⁺, Nb₃NO₂⁺), and ultimately to efficient dehydrogenation (Nb₃O₃⁺). Mechanistic analysis reveals that methane activation occurs at Nb–Nb dual-metal centers, whose reactivity is governed by ligand-controlled number and distribution of Nb–Nb σ bonds. Nitrogen ligands disrupt σ bonding and reduce active sites, whereas oxygen ligands preserve intact dinuclear motifs and promote synergistic C–H activation. These findings clarify how ligand coordination controls metal–metal bonding and governs dual-metal site reactivity, providing molecular-level insights into methane activation.