Nitrogen fixation and reduction at boron

Abstract

Currently, the only compounds known to support fixation and functionalization of dinitrogen (N₂) under nonmatrix conditions are based on metals. Here we present the observation of N₂ binding and reduction by a nonmetal, specifically a dicoordinate borylene. Depending on the reaction conditions under which potassium graphite is introduced as a reductant, N₂ 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 ¹⁵N isotopologues of the neutral and dianionic molecules were prepared with ¹⁵N-labeled dinitrogen, allowing observation of the nitrogen nuclei by ¹⁵N 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.