Nitrogen fixation and reduction at boron

Currently, the only compounds known to support fixation and functionalization of dinitrogen (N-2) under nonmatrix conditions are based on metals. Here we present the observation of N-2 binding and reduction by a nonmetal, specifically a dicoordinate borylene. Depending on the reaction conditions under which potassium graphite is introduced as a reductant, N-2 binding to two borylene units results in either neutral (B2N2) or dianionic ([B2N2](2-)) products that can be interconverted by respective exposure to further reductant or to air. The N-15 isotopologues of the neutral and dianionic molecules were prepared with N-15-labeled dinitrogen, allowing observation of the nitrogen nuclei by N-15 nuclear magnetic resonance spectroscopy. Protonation of the dianionic compound with distilled water furnishes a diradical product with a central hydrazido B2N2H2 unit. All three products were characterized spectroscopically and crystallographically.