C-N Coupling in N₂ Fixation by the Ditantalum Carbide Cluster Anions Ta₂C₄

The construction of C-N bonds by the direct incorporation of dinitrogen (N₂) instead of ammonia (NH₃) into active species is particularly desirable but has been rarely reported. Herein, a ditantalum carbide cluster anion (Ta₂C₄^-) capable of cleaving the N≡N bond and constructing a C-N bond under mild conditions has been identified using mass spectrometry, photoelectron imaging spectroscopy, and quantum-chemical calculations. The photoelectron spectrum of Ta₂C₄N₂^- is remarkably different from that of Ta₂C₄^- and matches the simulated spectrum of the Ta₂C₄N₂^- species with an end-on-bonded CN unit. The formation of the C-N bond has also been supported by the CN^- fragment observed in the collision-induced dissociation of Ta₂C₄N₂^-. The exceptional reactivity of Ta₂C₄^- is ascribed to the low-valent metal center serving as an electron reservoir. This study provides a non-NH₃ route to construct C-N bonds by incorporating N₂ into carbide compounds to produce nitrogenous species.