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

Abstract

The synthesis, structure, and reactivity of a series of low-coordinate Fe(II) diketiminate amido complexes are presented. Complexes L^RFeNHAr (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 L^RFeNHAr may be oxidized using AgOTf, and the products L^RFe(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 L^RFe(NHAr)(OTf) and L^RFe(OtBu)(OTf), the angles at nitrogen and oxygen result from steric effects and not π-bonding. The reactions of the amido group of L^RFeNHAr 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.