Chelating or bridging? Halide-controlled binding mode of diamido donor ligands in iron(III) complexes.

In a series of iron(lll) halide complexes of the form {FeX[MesN-(SiMe 2 )] 2 O} 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(ll) precursors, which are oxidized with iodine, benzyl bromide, or PhlCl 2 to yield the appropriate iron(lll) halide. The bromide analogue can also be synthesized by reacting the iron(ll) precursor with a bromonium transfer agent (stabilized by adamantylideneadaman-tane). The latter reaction may proceed via an iron(IV) intermediate, which can oxidize the normally noncoordinating, inert [B(Ar F ) 4 ] - counteranion [Ar F = 3,5-(CF 3 ) 2 Ph].