Synthesis, Structure, and Reactivity Study of Iron(II) Complexes with Bulky Bis(anilido)thioether Ligation

Temperature-Dependent Reactivity of a Non-heme FeIII(OH)(SR) Complex: Relevance to Isopenicillin N Synthase

Non-heme iron complexes with cis-Fe^III(OH)(SAr/OAr) coordination were isolated and examined for their reactivity with a tertiary carbon radical. The sulfur-ligated complex shows a temperature dependence on ^•OH versus ArS^• transfer, whereas the oxygen-ligated complex does not. These results provide the first working model for C-S bond formation in isopenicillin N synthase and indicate that kinetic control may be a key factor in the selectivity of non-heme iron "rebound" processes.

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.

Mononuclear, Dinuclear, and Trinuclear Iron Complexes Featuring a New Monoanionic SNS Thiolate Ligand

The new tridentate ligand, S(Me)N(H)S = 2-(2-methylthiophenyl)benzothiazolidine, prepared in a single step from commercial precursors in excellent yield, undergoes ring-opening on treatment with Fe(OTf)2 in the presence of base affording a trinuclear iron complex, [Fe3(μ2-S(Me)NS(-))4](OTf)2 (1) which is fully characterized by structural and spectroscopic methods. X-ray structural data reveal that 1 contains four S(Me)NS(-) ligands meridionally bound to two pseudooctahedral iron centers each bridged by two thiolates to a distorted tetrahedral central iron. The combined spectroscopic (UV-vis, Mössbauer, NMR), magnetic (solution and solid state), and computational (DFT) studies indicate that 1 includes a central, high-spin Fe(II) (S = 2) with two low-spin (S = 0) peripheral Fe(II) centers. Complex 1 reacts with excess PMePh2, CNxylyl (2,6-dimethylphenyl isocyanide), and P(OMe)3 in CH3CN to form diamagnetic, thiolate-bridged, dinuclear Fe(II) complexes {[Fe(μ-S(Me)NS(-))L2]2}(OTf)2 (2-4). These complexes are characterized by elemental analysis; (1)H NMR, IR, UV-vis, and Mössbauer spectroscopy; and single crystal X-ray diffraction. Interestingly, addition of excess P(OMe)3 to complex 1 in CH2Cl2 produces primarily the diamagnetic, mononuclear Fe(II) complex, {Fe(S(Me)NS(-))[P(OMe)3]3}(OTf) (5).

Sulfuration of the C(sp2)–H bond of enaminones: a protocol for the synthesis of thioether using elemental sulfur as a sulfurating reagent

Sulfuration reaction of the C(sp²)–H bond of enaminones with elemental sulfur in the presence of CuBr/K₃PO₄ was carried out. It provided an efficient method for the synthesis of thioethers and selenides in moderate to good yields.

Deprotonation/protonation-driven change of the σ-donor ability of a sulfur atom in iron(II) complexes with a thioamide SNS pincer type ligand

A new iron complex with a thioamide SNS pincer type ligand, [FeBr2(κ(3)-H2L(DPM))] (κ(3)-H2L(DPM) = 2,6-bis(N-2,6-bis(diphenylmethyl)-4-isopropylphenylthioamide)pyridine), was synthesized. This complex reacts with NaH in THF to yield a unique Fe(ii) complex with two THF molecules, [Fe(THF)2(κ(3)-L(DPM))] (κ(3)-L(DPM) = 2,6-bis(N-2,6-bis(diphenylmethyl)-4-isopropylphenyliminothiolate)pyridine). The THF molecules of [Fe(THF)2(κ(3)-L(DPM))] can be substituted with CO and CN-xylyl to give [Fe(CO)3(κ(3)-L(DPM))] and [Fe(CN-xylyl)3(κ(3)-L(DPM))], respectively. The complex [Fe(CN-xylyl)3(κ(3)-L(DPM))] reacts with HBF4 to produce [Fe(CN-xylyl)3(κ(3)-H2L(DPM))](2+) with protonated thioamide units. The differences of the IR spectra before and after protonation indicate that the major binding mode of CN-xylyl to iron(ii) changes from π-back donation from metal to isocyanide to σ-donation from isocyanide to iron(ii). This indicates that the σ-donor ability of the thioamide sulfur atom is tuned by deprotonation/protonation of thioamide.

Iron-mediated C-H bond amination by organic azides on a tripodal bis(anilido)iminophosphorane platform

The bis(anilido)iminophosphorane complex, abbreviated as [((Mes)N2N(Ad))Fe(THF)], can react with alkyl azides to yield ligand-based C-H bond amination products suggesting the high reactivity of iron(IV)-imido species supported by the tripodal bis(anilido)iminophosphorane ligand platform [(Mes)N2N(Ad)](2-).