Chelating or Bridging? Halide-Controlled Binding Mode of Diamido Donor Ligands in Iron(III) Complexes

In a series of iron(III) halide complexes of the form {FeX[MesN(SiMe2)]2O}2 (Mes = mesityl; X = Cl, Br, I), the ancillary
diamidosilylether ligand can either chelate to one metal or instead
bridge two metal centers, as a function of the halide coligand.
The complexes are prepared from diamidosilyletheriron(II) precursors, which are oxidized with iodine, benzyl bromide, or PhICl2 to
yield the appropriate iron(III) halide. The bromide analogue can
also be synthesized by reacting the iron(II) precursor with a
bromonium transfer agent (stabilized by adamantylideneadamantane). The latter reaction may proceed via an iron(IV) intermediate,
which can oxidize the normally noncoordinating, inert [B(ArF)4]-
counteranion [ArF = 3,5-(CF3)2Ph].