Low-Coordinate Iron(II) Amido Complexes of β-Diketiminates: Synthesis, Structure, and Reactivity

The synthesis, structure, and reactivity of a series of low-coordinate Fe(II) diketiminate amido complexes are presented.
Complexes LRFeNHAr (R = methyl, tert-butyl; Ar = para-tolyl, 2,6-xylyl, and 2,6-diisopropylphenyl) bind Lewis
bases to give trigonal pyramidal and trigonal bipyramidal adducts. In the adducts, crystallographic and 1H NMR
evidence supports the existence of agostic interactions in solid and solution states. Complexes LRFeNHAr may be
oxidized using AgOTf, and the products LRFe(NHAr)(OTf) are characterized with 19F NMR spectroscopy, UV/vis
spectrophotometry, solution magnetic measurements, elemental analysis, and, in one case, X-ray crystallography.
In the structures of the iron(III) complexes LRFe(NHAr)(OTf) and LRFe(OtBu)(OTf), the angles at nitrogen and
oxygen result from steric effects and not π-bonding. The reactions of the amido group of LRFeNHAr with weak
acids (HCCPh and HOtBu) are consistent with a basic nitrogen atom, because the amido group is protonated by
terminal alkynes and alcohols to give free H2NAr and three-coordinate acetylide and alkoxide complexes. The
trends in complex stability give insight into the relative strength of bonds from three-coordinate iron to anionic C-,
N-, and O-donor ligands.