Synthesis and characterization of a series of halide-bridged, multinuclear iron(ii) and cobalt(ii) diamido complexes and a dinuclear, high-spin cobalt(ii) alkyl derivative

Abstract

The synthesis and structural characterization of four multinuclear, halide-bridged iron(II) and cobalt(II) diamidosilylether complexes of the form{Fe₂Br₂[^tBuNON]}₂ (1), {Co₂Br₂[^tBuNON]}₂ (2), {Fe₂Cl₂[^tBuNON]}_n (3) and {Co₂Cl₂[^tBuNON](LiCl)·2THF}₂ (4) ([^tBuNON]²⁻ = [Me₃CN(SiMe₂)]₂O²⁻) are reported. Thus, reaction of one equivalent of Li₂[^tBuNON] with two equivalents of MX₂ (X = Cl or Br; M = Co or Fe) form 1–4, which structurally contain one diamido ligand bridging two metal centres. Each amido group interacts with both metal centres to yield binuclear M₂X₂[^tBuNON] units which dimerize via bromide bridges to form tetranuclear {Fe₂Br₂[^tBuNON]}₂ (1) and {Co₂Br₂[^tBuNON]}₂ (2) or form an infinite 1D chain of chloride-bridged dinuclear clusters {Fe₂Cl₂[^tBuNON]}_n (3). Replacing bromide for chloride in 2 results in a tetranuclear “ate” complex {Co₂Cl₂[^tBuNON](LiCl)·2THF}₂ (4) in which the tetranuclear core is capped with one LiCl and two THF molecules on each side. The reaction of four equivalents of LiCH₂SiMe₃ with 4 generated the high-spin cobalt(II) alkyl complex {Co₂(CH₂SiMe₃)₂[^tBuNON]} (5), in which each amide in [^tBuNON]²⁻ bridges two Co(II) centres, but the silylether donor only binds to one metal; each Co(II) centre has a terminal –CH₂SiMe₃ unit bonded as well. Variable temperature (1.8–300 K) magnetic susceptibility data for 1–5 showed significant antiferromagnetic coupling between metal centres.