Characterization of a Proposed Terminal Iron(III) Nitride Intermediate of Nitrogen Fixation Stabilized by a Trisphosphine‐Borane Ligand. (20th September 2022) - Schild, Dirk J.
Abstract: Terminal iron nitrides (Fe≡N) have been proposed as intermediates of Fe‐mediated nitrogen fixation, and well‐defined synthetic iron nitrides have been characterized in high oxidation states, including Fe IV, Fe V, and Fe VI . This study reports the generation and low temperature characterization of a terminally bound iron(III) nitride, P3 B Fe(N) (P3 B =tris(o‐diisopropylphosphinophenyl)borane), which is a proposed intermediate of iron‐mediated nitrogen fixation by the P3 B Fe‐catalyst system. CW‐ and pulse EPR spectroscopy (HYSCORE and ENDOR), supported by DFT calculations, help to define a 2 A ground state electronic structure of this C3 ‐symmetric nitride species, placing the unpaired spin in a sigma orbital along the B−Fe−N vector; this electronic structure is distinct for an iron nitride. The unusual d 5 ‐configuration is stabilized by significant delocalization (≈50 %) of the unpaired electron onto the axial boron and nitrogen ligands, with a majority of the spin residing on boron. Abstract : The generation and low‐temperature characterization of a terminally bound iron(III) nitride, P3 BFe(N) (P3 B=tris(o‐diisopropylphosphinophenyl) borane), a plausible intermediate of iron‐mediated nitrogen fixation, is reported. EPR spectroscopy supported by DFT calculations define a 2 A ground state electronic structure for this C 3 ‐symmetric nitride, placing an unpaired spin in a sigma orbital along the B−Fe−N vector.