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

The synthesis and structural characterization of four multinuclear, halide-bridged iron(II) and cobalt(II) diamidosilylether complexes of the form {Fe2Br2[(NON)-N-tBu]}(2) (1), {Co2Br2[(NON)-N-tBu]}(2) (2), {Fe2Cl2[(NON)-N-tBu]}(n) (3) and {Co2Cl2[(NON)-N-tBu](LiCl)center dot 2THF}(2) (4) ([(NON)-N-tBu](2-) = [Me3CN(SiMe2)](2)O2-) are reported. Thus, reaction of one equivalent of Li-2[(NON)-N-tBu] 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[(NON)-N-tBu] units which dimerize via bromide bridges to form tetranuclear {Fe2Br2[(NON)-N-tBu]}(2) (1) and {Co2Br2[(NON)-N-tBu]}(2) (2) or form an infinite 1D chain of chloride-bridged dinuclear clusters {Fe2Cl2[(NON)-N-tBu]}(n) (3). Replacing bromide for chloride in 2 results in a tetranuclear ate complex {Co2Cl2[(NON)-N-tBu](LiCl)center dot 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 {Co-2(CH2SiMe3)(2)[(NON)-N-tBu]} (5), in which each amide in [(NON)-N-tBu](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.