In light of the current energy requirements, the conversion of CO2 and N2 into useful C–N bond-containing products under mild conditions has become an area of intense research. However, the inert nature of N2 and CO2 renders their coupling extremely challenging. Herein, nitrogen and carbon atoms originating from N2 and CO2, respectively, are fixed sequentially by NbH2 – anions in the gas phase at room temperature. Isocyanate and NbO2CN– anions were formed under thermal collision conditions, thus achieving the formation of new C–N bonds directly from simple N2 and CO2. The anion structures and reaction details were studied by mass spectrometry, photoelectron spectroscopy, and quantum chemical calculations. A novel N2 activation mode (metal–ligand activation, MLA) and a related mechanism for constructing C–N bonds mediated by a single non-noble metal atom are proposed. In this MLA mode, the C atom originating from CO2 serves as an electron reservoir to accept and donate electrons.