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

We report an easily prepared bis­(thioether) amine ligand, S^MeN^HS^Me, along with the synthesis, characterization, and reactivity of the paramagnetic iron­(II) bis­(amido) complex, [Fe­(κ³-S^MeNS^Me)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 1 in solution contains a five-coordinate component [Fe­(κ³-S^MeNS^Me)­(κ²-S^MeNS^Me)] (2). This ligand hemilability was demonstrated further by reactivity studies of 1 with 2,2′-bipyridine, 1,2-bis­(dimethylphosphino)­ethane, and 2,6-dimethylphenyl isonitrile to afford iron­(II) complexes [L₂Fe­(κ²-S^MeNS^Me)₂] (3–5). Addition of a Brønsted acid, HNTf₂, to 1 produces the paramagnetic, iron­(II) amine–amido cation, [Fe­(κ³-S^MeNS^Me)­(κ³-S^MeN^HS^Me)]­(NTf₂) (6; Tf = SO₂CF₃). Cation 6 readily undergoes amine ligand substitution by triphos, affording the 16e^– complex [Fe­(κ²-S^MeNS^Me)­(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 7 to be a selective and particularly robust precatalyst.