XAS characterization of a Nitridoiron(IV) complex with a very short fe-n bond

Abstract

X-ray absorption spectroscopy has been used to characterize the novel nitridoiron(IV) units in two [PhBP3R]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 A reflects the presence of an FeN triple bond in accord with the observed FeN vibration observed for one of these species (nu(FeN) = 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 Fe-I-N-2-Fe-I, Fe-II-NPh2, and Fe(III)NAd motifs, and those of recently described six-coordinate (FeN)-N-V and (FeN)-N-VI complexes. The observation that the Fe-IV-N distances of two [PhBP3R]Fe(N) complexes are shorter than the Fe-IV-O bond lengths of oxoiron(IV) complexes may be rationalized on the basis of the greater pi basicity of the nitrido ligand than the oxo ligand and a lower metal coordination number for the Fe(N) complex