C-N Coupling in N 2 Fixation by the Ditantalum Carbide Cluster Anions Ta 2 C 4 .

The construction of C-N bonds by the direct incorporation of dinitrogen (N ₂ ) instead of ammonia (NH ₃ ) into active species is particularly desirable but has been rarely reported. Herein, a ditantalum carbide cluster anion (Ta ₂ C ₄ ^- ) 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 Ta ₂ C ₄ N ₂ ^- is remarkably different from that of Ta ₂ C ₄ ^- and matches the simulated spectrum of the Ta ₂ C ₄ N ₂ ^- 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 Ta ₂ C ₄ N ₂ ^- . The exceptional reactivity of Ta ₂ C ₄ ^- is ascribed to the low-valent metal center serving as an electron reservoir. This study provides a non-NH ₃ route to construct C-N bonds by incorporating N ₂ into carbide compounds to produce nitrogenous species.