We report the first discrete molecular Cr-based catalysts for the reduction of N-2. This study is focused on the reactivity of the Cr-N-2 complex, trans-[Cr(N-2)(2)((P4N4Bn)-N-Ph)] (P4Cr(N-2)(2)), bearing a 16-membered tetraphosphine macrocycle. The architecture of the [16]-(P4N4Bn)-N-Ph ligand is critical to preserve the structural integrity of the catalyst. P4Cr(N-2)(2) was found to mediate the reduction of N-2 at room temperature and 1 atm pressure by three complementary reaction pathways: (1) Cr-catalyzed reduction of N-2 to N(SiMe3)(3) by Na and Me3SiCl, affording up to 34 equiv N(SiMe3)(3); (2) stoichiometric reduction of N-2 by protons and electrons (for example, the reaction of cobaltocene and collidinium triflate at room temperature afforded 1.9 equiv of NH3, or at -78 degrees C afforded a mixture of NH3 and N2H4); and (3) the first example of NH3 formation from the reaction of a terminally bound N-2 ligand with a traditional H atom source, TEMPOH (2,2,6,6-tetramethylpiperidine-1-ol). We found that trans-[Cr(N-15(2))(2)((P4N4Bn)-N-Ph)] reacts with excess TEMPOH to afford 1.4 equiv of (NH3)-N-15. Isotopic labeling studies using TEMPOD afforded ND3 as the product of N2 reduction, confirming that the H atoms are provided by TEMPOH.