Crystals of an Iron Nitride

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Science  14 Mar 2008:
Vol. 319, Issue 5869, pp. 1461
DOI: 10.1126/science.319.5869.1461b

Both industrial and enzymatic nitrogen reduction catalysts rely on iron centers. However, high valent molecular iron nitride complexes (FeN) have stubbornly eluded crystallographic characterization, in contrast to analogous terminal oxo structures (Fe=O). Vogel et al. now find that a tridentate ligand comprising three coordinating N-heterocyclic carbene moieties offers the solution. Reaction of the ligand (bearing either xylyl or mesityl groups for steric protection) with ferrous chloride followed by reduction with sodium amalgam and treatment with trimethylsilylazide yields a cationic Fe-N3 complex that loses dinitrogen under xenon lamp photolysis to afford the terminal iron nitride. Air-stable purple crystals of the compound were characterized by x-ray diffraction, revealing a short FeN bond length of 1.53 . Mssbauer spectroscopy further suggested an iron center more electron-rich than a previously prepared phosphorus-coordinated iron nitride characterized in solution; the authors attribute the difference to -donation from the carbene ligands. JSY

Angew. Chem. Int. Ed. 47, 10.1002/anie.200800600 (2008).

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