With the two components of H 2 splitting and N 2 reduction to a (N 2 ) 2-in hand, we focused on their synergy in relation to N 2 hydrogenation, relevant to the Haber-Bosch process. We were interested in the reactivity of 5 towards H 2 as Ln III dinitrogen complexes, which feature formally oxidized metal centers, have been shown to act as "masked" low-valent synthons. In these examples, twoelectron reduction processes occurred upon addition of reducible substrates (CO, CO 2 , aromatic Nheterocycles), with the systematic release of the N 2 ligand. Similar reductive reactivity has also been recently reported in the case of N 2 complexes of U IV , Mg II and Ca II , where the coordinated and reduced (N 2 ) 2-moiety acted as a redox-active ligand, able to reversibly store two electrons. Initial reactivity attempts in NMR tubes showed that heating a purple suspension of 5 in C 6 D 6 under H 2 atmosphere at 80 °C led to the full consumption of 5 over several hours, as evidenced by the formation of a clear colorless solution. H NMR analysis revealed the formation of 3-H as a major product (ca. 90%) along with a minor species (ca. 10%) assigned to [Lu(Cp ttt ) 2 NH 2 ] (6) (Figure ). The identity of 6 was testified by N labelling experiments as well as independent in situ synthesis of 6 upon exposure of 2 with NH 3 gas (Figures ). In the 1 H NMR spectrum, the singlet at  3.07 ppm for the NH 2 protons in 6 was replaced by a doublet ( 1 J HN = 62.8 Hz) when performing the experiment with the isotopically labelled 5-15 N. Accordingly, the As decoordination of the N 2 ligand in 5 is favored with temperature, we hypothesized that the formation of 3-H might arise from the reaction of in situ liberated 2 with H 2 . We reasoned that lower temperatures should be beneficial for higher conversions into 6 vs. 3-H. Although the reaction appeared kinetically blocked below 0 °C, full conversion was observed upon stirring a toluene or pentane suspension of 5 under H 2 atmosphere over 1-5 days at 0 °C or room temperature. Under these conditions, 6 was consistently formed in 20-32% NMR yields (Figures S19-20).