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 N-2. Exposure of these complexes to N-2 initially produces the corresponding side-on end-on N-2 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 N-2 complex. For the potassium derivative, the N-N bond cleavage takes place along with H-2 elimination to form the nitride complex. Treatment of the side-on end-on N-2 complex with Me3SiCl results in silylation of the terminal N atom and subsequent N-N bond cleavage along with H-2 elimination, giving the nitride-imide-bridged diniobium complex.