Counterion Dependence of Dinitrogen Activation and Functionalization by a Diniobium Hydride Anion

We report the synthesis of anionic diniobium hydride complexes with a series of alkali metal cations (Li⁺ , Na⁺ , and K⁺ ) and the counterion dependence of their reactivity with N₂ . Exposure of these complexes to N₂ initially produces the corresponding side-on end-on N₂ complexes, the fate of which depends on the nature of countercations. The lithium derivative undergoes stepwise migratory insertion of the hydride ligands onto the aryloxide units, yielding the end-on bridging N₂ complex. For the potassium derivative, the N-N bond cleavage takes place along with H₂ elimination to form the nitride complex. Treatment of the side-on end-on N₂ complex with Me₃ SiCl results in silylation of the terminal N atom and subsequent N-N bond cleavage along with H₂ elimination, giving the nitride-imide-bridged diniobium complex.