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.