XAS Characterization of a Nitridoiron(IV) Complex with a Very Short Fe−N Bond

X-ray absorption spectroscopy has been used to characterize the novel nitridoiron(IV) units in two [PhBPR3]Fe(N) complexes (R = iPr and CyCH2) and obtain direct spectroscopic evidence for a very short Fe−N distance. The distance of 1.51−1.55 Å reflects the presence of an Fe⋮N triple bond in accord with the observed Fe⋮N vibration observed for one of these species (νFeN = 1034 cm-1). This highly covalent bonding interaction results in the appearance of an unusually intense pre-edge peak, whose estimated area of 100(20) units is much larger than those of the related tetrahedral complexes with FeI−N2−FeI, FeII−NPh2, and FeIII⋮NAd motifs, and those of recently described six-coordinate FeV⋮N and FeVI⋮N complexes. The observation that the FeIV−N distances of two [PhBPR3]Fe(N) complexes are shorter than the FeIV−O bond lengths of oxoiron(IV) complexes may be rationalized on the basis of the greater π basicity of the nitrido ligand than the oxo ligand and a lower metal coordination number for the Fe(N) complex.