Isolation of Dysprosium and Yttrium Complexes of a Three-Electron Reduction Product in the Activation of Dinitrogen, the (N₂)³⁻ Radical

DyI2 reacts with 2 equiv of KOAr (OAr = OC6H3(CMe3)2-2,6) under nitrogen to form not only the (N2)2− complex, [(ArO)2(THF)2Dy]2(μ-η2:η2-N2), 1, but also complexes of similar formula with an added potassium ion, [(ArO)2(THF)Dy]2(μ-η2:η2-N2)[K(THF)6], 2, and [(ArO)2(THF)Dy]2(μ3-η2:η2:η2-N2)K(THF), 3. The 1.396(7) and 1.402(7) Å N−N bond distances in 2 and 3, respectively, are consistent with an (N2)3− ligand, but the high magnetic moment of 4f9 Dy3+ precluded definitive identification. The Y[N(SiMe3)2]3/K reduction system was used to synthesize yttrium analogues of 2 and 3, {[(Me3Si)2N]2(THF)Y}2(μ-η2:η2-N2)[K(THF)6] and {[(Me3Si)2N]2(THF)Y}2(μ3-η2:η2:η2-N2)K, that had similar N−N distances and allowed full characterization. EPR, Raman, and DFT studies are all consistent with the presence of (N2)3− in these complexes. 15N analogues were also prepared to confirm the spectroscopic assignments. The DFT studies suggest that the unpaired electron is localized primarily in a dinitrogen π orbital isolated spatially, energetically, and by symmetry from the metal orbitals.