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

We report an easily prepared bis(thioether) amine ligand, (SNHSme)-N-me, along with the synthesis, characterization, and reactivity of the paramagnetic iron(II) bis(amido) complex, [Fe(K-3-(SNSme)-N-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 angstrom) being significantly shorter than those in the six membered rings (av 2.71 angstrom()), 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(K-3-(SNSme)-N-me)(K-2-(SNSme)-N-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(k(2)-(SNSme)-N-me)(2)] (3-5). Addition of a Bronsted acid, HNTf2, to 1 produces the paramagnetic, iron(II) amine amido cation, [Fe(K-2-3-S-(NSme)-N-me)(k(3)-(SNHSme)-N-me)](NTf2) (6; Tf = SO2CF3). Cation 6 readily undergoes amine ligand substitution by triphos, affording the 16e(-) complex [Fe(k(2)-(SNSme)-N-me)(K-3-triphos)](NTf2) (7; triphos = bis(2-diphenylphosphinoethyl)phenylphosphine). These complexes are characterized by elemental analysis; H-1 NMR, Mossbauer, 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 robustprecatalyst.