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.