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.