Nitrogen Oxyanion Reductive Borylation at Low-Coordinate Iron: A Struggle between Two Oxophiles

With the advent of the Haber-Bosch process over a century ago, the world's population experienced tremendous growth due to the million tons of fixed nitrogen used in fertilizer each year. However, the majority of the fixed nitrogen is metabolized to various nitrogen oxyanions by soil organisms that are lost to waterways, leading to eutrophication and hypoxia. Therefore, there is a need to convert the anthropogenic nitrogen content to more useful forms. In this work, the synthesis and characterization of iron nitrate (PhB(ⁱPr₂Im)₃FeNO₃) complex (2) is reported. Subsequent stepwise deoxygenation via a bis(boryl) reduced N-heterocycle (BPin₂pz) to its downstream counterparts is thermodynamically favorable by DFT. Reaction of iron nitrate with (BPin₂)pz led to the formation of iron (pinacolato)boralanolate complex (3) and a proposed diiron dinitrosyl complex having bridged hydroxide ligands ([PhB(ⁱPr₂Im)₃Fe(NO)(OH)]₂) (4). The formation of these complexes demonstrates the oxophilicity of both iron and boron.