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Evaluating the identity and diiron core transformations of a (?-oxo)diiron(III) complex supported by electron-rich tris(pyridyl-2-methyl)amine ligands.

ABSTRACT: The composition of a (?-oxo)diiron(III) complex coordinated by tris[(3,5-dimethyl-4-methoxy)pyridyl-2-methyl]amine (R(3)TPA) ligands was investigated. Characterization using a variety of spectroscopic methods and X-ray crystallography indicated that the reaction of iron(III) perchlorate, sodium hydroxide, and R(3)TPA affords [Fe(2)(?-O)(?-OH)(R(3)TPA)(2)](ClO(4))(3) (2) rather than the previously reported species [Fe(2)(?-O)(OH)(H(2)O)(R(3)TPA)(2)](ClO(4))(3) (1). Facile conversion of the (?-oxo)(?-hydroxo)diiron(III) core of 2 to the (?-oxo)(hydroxo)(aqua)diiron(III) core of 1 occurs in the presence of water and at low temperature. When 2 is exposed to wet acetonitrile at room temperature, the CH(3)CN adduct is hydrolyzed to CH(3)COO(-), which forms the compound [Fe(2)(?-O)(?-CH(3)COO)(R(3)TPA)(2)](ClO(4))(3) (10). The identity of 10 was confirmed by comparison of its spectroscopic properties with those of an independently prepared sample. To evaluate whether or not 1 and 2 are capable of generating the diiron(IV) species [Fe(2)(?-O)(OH)(O)(R(3)TPA)(2)](3+) (4), which has previously been generated as a synthetic model for high-valent diiron protein oxygenated intermediates, studies were performed to investigate their reactivity with hydrogen peroxide. Because 2 reacts rapidly with hydrogen peroxide in CH(3)CN but not in CH(3)CN/H(2)O, conditions that favor conversion to 1, complex 1 is not a likely precursor to 4. Compound 4 also forms in the reaction of 2 with H(2)O(2) in solvents lacking a nitrile, suggesting that hydrolysis of CH(3)CN is not involved in the H(2)O(2) activation reaction. These findings shed light on the formation of several diiron complexes of electron-rich R(3)TPA ligands and elaborate on conditions required to generate synthetic models of diiron(IV) protein intermediates with this ligand framework.

SUBMITTER: Do LH

PROVIDER: S-EPMC3288163 | biostudies-literature | 2012 Feb

REPOSITORIES: biostudies-literature

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Evaluating the identity and diiron core transformations of a (μ-oxo)diiron(III) complex supported by electron-rich tris(pyridyl-2-methyl)amine ligands.

Do Loi H LH Xue Genqiang G Que Lawrence L Lippard Stephen J SJ

Inorganic chemistry 20120120 4

The composition of a (μ-oxo)diiron(III) complex coordinated by tris[(3,5-dimethyl-4-methoxy)pyridyl-2-methyl]amine (R(3)TPA) ligands was investigated. Characterization using a variety of spectroscopic methods and X-ray crystallography indicated that the reaction of iron(III) perchlorate, sodium hydroxide, and R(3)TPA affords [Fe(2)(μ-O)(μ-OH)(R(3)TPA)(2)](ClO(4))(3) (2) rather than the previously reported species [Fe(2)(μ-O)(OH)(H(2)O)(R(3)TPA)(2)](ClO(4))(3) (1). Facile conversion of the (μ-oxo ...[more]

PMID: 22264120

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Project description:Progress toward the development of functional models of the carboxylate-bridged diiron active site in soluble methane monooxygenase is described in which potential substrates are introduced as substituents on bound pyridine ligands. Pyridine ligands incorporating a thiol, sulfide, sulfoxide, or phosphine moiety were allowed to react with the preassembled diiron(II) complex [Fe(2)(mu-O(2)CAr(R))(2)(O(2)CAr(R))(2)(THF)(2)], where (-)O(2)CAr(R) is a sterically hindered 2,6-di(p-tolyl)- or 2,6-di(p-fluorophenyl)benzoate (R = Tol or 4-FPh). The resulting diiron(II) complexes were characterized crystallographically. Triply and doubly bridged compounds [Fe(2)(mu-O(2)CAr(Tol))(3)(O(2)CAr(Tol))(2-MeSpy)] (4) and [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(2-MeS(O)py)(2)] (5) resulted when 2-methylthiopyridine (2-MeSpy) and 2-pyridylmethylsulfoxide (2-MeS(O)py), respectively, were employed. Another triply bridged diiron(II) complex, [Fe(2)(mu-O(2)CAr(4)(-)(FPh))(3)-(O(2)CAr(4)(-)(FPh))(2-Ph(2)Ppy)] (3), was obtained containing 2-diphenylphosphinopyridine (2-Ph(2)Ppy). The use of 2-mercaptopyridine (2-HSpy) produced the mononuclear complex [Fe(O(2)CAr(Tol))(2)(2-HSpy)(2)] (6a). Together with that of previously reported [Fe(2)(mu-O(2)CAr(Tol))(3)(O(2)CAr(Tol))(2-PhSpy)] (2) and [Fe(2)(mu-O(2)CAr(Tol))(3)(O(2)CAr(Tol))(2-Ph(2)Ppy)] (1), the dioxygen reactivity of these iron(II) complexes was investigated. A dioxygen-dependent intermediate (6b) formed upon exposure of 6a to O(2), the electronic structure of which was probed by various spectroscopic methods. Exposure of 4 and 5 to dioxygen revealed both sulfide and sulfoxide oxidation. Oxidation of 3 in CH(2)Cl(2) yields [Fe(2)(mu-OH)(2)(mu-O(2)CAr(4)(-)(FPh))(O(2)CAr(4)(-FPh))(3)(OH(2))(2-Ph(2)P(O)py)] (8), which contains the biologically relevant {Fe(2)(mu-OH)(2)(mu-O(2)CR)}(3+) core. This reaction is sensitive to the choice of carboxylate ligands, however, since the p-tolyl analogue 1 yielded a hexanuclear species, 7, upon oxidation.

Dataset Information

Evaluating the identity and diiron core transformations of a (?-oxo)diiron(III) complex supported by electron-rich tris(pyridyl-2-methyl)amine ligands.

Publications

Evaluating the identity and diiron core transformations of a (μ-oxo)diiron(III) complex supported by electron-rich tris(pyridyl-2-methyl)amine ligands.

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