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 Me3SiCl 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. Identity dictates destiny: N2 activation has been investigated with anionic diniobium hydride complexes containing a series of alkali cations (Li+, Na+, and K+). In all cases, the μ‐η1:η2 N2 complexes are formed as an initial product upon exposure to N2. While the conversion of the N2 binding mode from μ‐η1:η2 to μ‐η1,η1 is observed with the Li+ countercation, N−N bond cleavage takes place for K+. The Na+ derivative reacts with Me3SiCl to give a nitride‐imide complex.