The reductive coupling of dinitrogen

The coupling of two or more molecules of dinitrogen (N₂) occurs naturally under the radiative conditions present in the ionosphere and may be achieved synthetically under ultrahigh pressure or plasma conditions. However, the comparatively low N–N single-bond enthalpy generally renders the catenation of the strongly triple-bonded N₂ diatomic unfavorable and the decomposition of nitrogen chains a common reaction motif. Here, we report the surprising organoboron-mediated catenation of two N₂ molecules under near-ambient conditions to form a complex in which a [N₄]2− chain bridges two boron centers. The reaction entails reductive coupling of two hypovalent-boron-bound N₂ units in a single step. Both this complex and a derivative protonated at both ends of the chain were characterized crystallographically.