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Unexpected Assembly of a Novel Triply Bridged Diiron(II) Core by a Bidentate Schiff Base Ligand.

ABSTRACT: The unusual dinucleating properties of a simple bidentate Schiff base (LH, 1) in the presence of weakly coordinating methanol solvent lead to the self-assembly of [Fe(II) (2)(L(b))(2)(L(t))(2)(?-MeOH)] (2) (b and t refer to bridging and terminally bound ligands, respectively). Complex 2 is the first diiron(II) species in which the two metal centers are triply bridged by single atoms in an asymmetric fashion, involving both ?-O(Ph) and ?-OH(Me) bridges. This binding mode produces an Fe···Fe distance of 3.139(1) Å. Dinucleation appears to be driven by a combination of ligand deficiency and solvent-mediated chemistry reminiscent of host-guest interactions. The presence of a ?-MeOH ligand is unprecedented in iron chemistry. Parallel-mode EPR spectra of complex 2 recorded at 4 K show an intense negative signal at g(||) ? 16, suggesting the dimeric form exists in solution.

SUBMITTER: Smith AL

PROVIDER: S-EPMC2713441 | biostudies-literature | 2007 May

REPOSITORIES: biostudies-literature

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Unexpected Assembly of a Novel Triply Bridged Diiron(II) Core by a Bidentate Schiff Base Ligand.

Smith Aubrey L AL Day Cynthia S CS Que Lawrence L Zhou Yuming Y Bierbach Ulrich U

Inorganica chimica acta 20070501 8

The unusual dinucleating properties of a simple bidentate Schiff base (LH, 1) in the presence of weakly coordinating methanol solvent lead to the self-assembly of [Fe(II) (2)(L(b))(2)(L(t))(2)(μ-MeOH)] (2) (b and t refer to bridging and terminally bound ligands, respectively). Complex 2 is the first diiron(II) species in which the two metal centers are triply bridged by single atoms in an asymmetric fashion, involving both μ-O(Ph) and μ-OH(Me) bridges. This binding mode produces an Fe···Fe dista ...[more]

PMID: 19626127

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Project description:A dinucleating macrocycle, H(2)PIM, containing phenoxylimine metal-binding units has been prepared. Reaction of H(2)PIM with [Fe(2)(Mes)(4)] (Mes = 2,4,6-trimethylphenyl) and sterically hindered carboxylic acids, Ph(3)CCO(2)H or Ar(Tol)CO(2)H (2,6-bis(p-tolyl)benzoic acid), afforded complexes [Fe(2)(PIM)(Ph(3)CCO(2))(2)] (1) and [Fe(2)(PIM)(Ar(Tol)CO(2))(2)] (2), respectively. X-ray diffraction studies revealed that these diiron(II) complexes closely mimic the active site structures of the hydroxylase components of bacterial multicomponent monooxygenases (BMMs), particularly the syn disposition of the nitrogen donor atoms and the bridging ?-?(1)?(2) and ?-?(1)?(1) modes of the carboxylate ligands at the diiron(II) centers. Cyclic voltammograms of 1 and 2 displayed quasi-reversible redox couples at +16 and +108 mV vs ferrocene/ferrocenium, respectively. Treatment of 2 with silver perchlorate afforded a silver(I)/iron(III) heterodimetallic complex, [Fe(2)(?-OH)(2)(ClO(4))(2)(PIM)(Ar(Tol)CO(2))Ag] (3), which was structurally and spectroscopically characterized. Complexes 1 and 2 both react rapidly with dioxygen. Oxygenation of 1 afforded a (?-hydroxo)diiron(III) complex [Fe(2)(?-OH)(PIM)(Ph(3)CCO(2))(3)] (4), a hexa(?-hydroxo)tetrairon(III) complex [Fe(4)(?-OH)(6)(PIM)(2)(Ph(3)CCO(2))(2)] (5), and an unidentified iron(III) species. Oxygenation of 2 exclusively formed di(carboxylato)diiron(III) compounds, a testimony to the role of the macrocylic ligand in preserving the dinuclear iron center under oxidizing conditions. X-ray crystallographic and (57)Fe Mössbauer spectroscopic investigations indicated that 2 reacts with dioxygen to give a mixture of (?-oxo)diiron(III) [Fe(2)(?-O)(PIM)(Ar(Tol)CO(2))(2)] (6) and di(?-hydroxo)diiron(III) [Fe(2)(?-OH)(2)(PIM)(Ar(Tol)CO(2))(2)] (7) units in the same crystal lattice. Compounds 6 and 7 spontaneously convert to a tetrairon(III) complex, [Fe(4)(?-OH)(6)(PIM)(2)(Ar(Tol)CO(2))(2)] (8), when treated with excess H(2)O.

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Unexpected Assembly of a Novel Triply Bridged Diiron(II) Core by a Bidentate Schiff Base Ligand.

Publications

Unexpected Assembly of a Novel Triply Bridged Diiron(II) Core by a Bidentate Schiff Base Ligand.

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