Iron(II) Complexes of a Hemilabile SNS Amido Ligand: Synthesis, Characterization, and Reactivity

We report an easily prepared bis(thioether) amine ligand, SMeNHSMe, along with the synthesis, characterization, and reactivity of the paramagnetic iron(II) bis(amido) complex, [Fe(κ3-SMeNSMe)2] (1). Binding of the two different thioethers to Fe generates both five- and six-membered rings with Fe–S bonds in the five-membered rings (av 2.54 Å) being significantly shorter than those in the six-membered rings (av 2.71 Å), suggesting hemilability of the latter thioethers. Consistent with this hypothesis, magnetic circular dichroism (MCD) and computational (TD-DFT) studies indicate that 1in solution contains a five-coordinate component [Fe(κ3-SMeNSMe)(κ2-SMeNSMe)] (2). This ligand hemilability was demonstrated further by reactivity studies of 1with 2,2′-bipyridine, 1,2-bis(dimethylphosphino)ethane, and 2,6-dimethylphenyl isonitrile to afford iron(II) complexes [L2Fe(κ2-SMeNSMe)2] (3–5). Addition of a Brønsted acid, HNTf2, to 1produces the paramagnetic, iron(II) amine–amido cation, [Fe(κ3-SMeNSMe)(κ3-SMeNHSMe)](NTf2) (6; Tf = SO2CF3). Cation 6readily undergoes amine ligand substitution by triphos, affording the 16e–complex [Fe(κ2-SMeNSMe)(κ3-triphos)](NTf2) (7; triphos = bis(2-diphenylphosphinoethyl)phenylphosphine). These complexes are characterized by elemental analysis; 1H NMR, Mössbauer, IR, and UV–vis spectroscopy; and single-crystal X-ray diffraction. Preliminary results of amine–borane dehydrogenation catalysis show complex 7to be a selective and particularly robust precatalyst.