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Tetranuclear iron(III) complexes of an octadentate pyridine-carboxylate ligand and their catalytic activity in alkane oxidation by hydrogen peroxide

Gutkina, EA ; Trukhan, VM ; Pierpont, CG ; Mkoyan, S ; Strelets, VV ; Nordlander, Ebbe LU and Shteinman, AA (2006) In Dalton Transactions p.492-501
Abstract
Reaction of the octadentate ligand 2,6-bis{3-[N,N-di(2-pyridylmethyl)amino]propoxy}benzoic acid (LH) with Fe(ClO4)(3) leads to the formation of the tetranuclear complexes [Fe-4(mu-O)(2)(LH)(2)(ClCH2 CO2)(4)](ClO4)(4) (1), [{Fe-2(mu-O)L(R-CO2)}(2)](ClO4)(4) (2 R = C6H5-, 3 R = CH3-, 4, R = ClCH2-). The crystal structures of complexes 1 and 2 reveal that they consist of two Fe-2(III)(mu-O)(mu-RCO2)(2) cores that are linked via the two LH/L ligands to give a "dimer of dimers" structure. Complex I assumes a helical shape, with protonated carboxylic acid moieties of the two ligands forming a hydrogen-bonded pair at the center of the cation. In complexes 2, 3 and 4, central carboxylates of the two ligands bridge the iron ions in each of the two... (More)
Reaction of the octadentate ligand 2,6-bis{3-[N,N-di(2-pyridylmethyl)amino]propoxy}benzoic acid (LH) with Fe(ClO4)(3) leads to the formation of the tetranuclear complexes [Fe-4(mu-O)(2)(LH)(2)(ClCH2 CO2)(4)](ClO4)(4) (1), [{Fe-2(mu-O)L(R-CO2)}(2)](ClO4)(4) (2 R = C6H5-, 3 R = CH3-, 4, R = ClCH2-). The crystal structures of complexes 1 and 2 reveal that they consist of two Fe-2(III)(mu-O)(mu-RCO2)(2) cores that are linked via the two LH/L ligands to give a "dimer of dimers" structure. Complex I assumes a helical shape, with protonated carboxylic acid moieties of the two ligands forming a hydrogen-bonded pair at the center of the cation. In complexes 2, 3 and 4, central carboxylates of the two ligands bridge the iron ions in each of the two Fe, O units, with an interdimer iron-iron separation of approximately 10 angstrom and an intradimer separation of approximately 3.1 angstrom. The second carboxylate bridge within the Fe2O units is defined by exogenous benzoate (2), acetate (3) or chloroacetate (4) ligands. The aqua complex [{Fe-2(mu-O)L(H2O)(2)}(2)](ClO4)(6) (5) is proposed to have a similar structure, but with the exogenous bridging carboxylates replaced by two terminal water ligands. These complexes exhibit electronic and Mossbauer spectral features that are similar to those of (mu-oxo)diiron(iii) proteins as well as other related (mu-oxo)bis(mu-carboxylato)diiron(III) complexes. This similarity shows that these properties are not significantly affected by the nature of the bridging exogenous carboxylate, and that the octadentate framework ligand is essential in stabilizing the "dimer of dimers" structure. This structural feature remains in highly diluted solution (10(-5) M) as evidenced by electrospray ionization mass-spectroscopy (ES MS). Cyclic voltammetric studies of complexes 2 and 5 showed two irreversible two-electron reductions, indicating that the two Fe2O units of the tetranuclear complexes behave as distinct redox entities. Complexes 2, 3 and, especially, the aqua complex 5 are active alkane oxidation catalysts. Catalytic reactions carried out with alkane substrate molecules and hydrogen peroxide predominantly gave alcohols. High stereospecificity in the oxidation of cis- 1,2-dimethylcyclohexane supports the metal-based molecular mechanism of O-insertion into C-H bonds postulated for non-heme iron enzymes such as methane monooxygenase. (Less)
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organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Dalton Transactions
issue
3
pages
492 - 501
publisher
Royal Society of Chemistry
external identifiers
  • wos:000234920200020
  • scopus:33645539097
  • pmid:16395449
ISSN
1477-9234
DOI
10.1039/b512069a
language
English
LU publication?
yes
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The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Chemical Physics (S) (011001060)
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8728776c-fc8a-4e91-a227-35a22e1e7bca (old id 419501)
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2016-04-01 12:38:46
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2020-01-12 10:12:42
@article{8728776c-fc8a-4e91-a227-35a22e1e7bca,
  abstract     = {Reaction of the octadentate ligand 2,6-bis{3-[N,N-di(2-pyridylmethyl)amino]propoxy}benzoic acid (LH) with Fe(ClO4)(3) leads to the formation of the tetranuclear complexes [Fe-4(mu-O)(2)(LH)(2)(ClCH2 CO2)(4)](ClO4)(4) (1), [{Fe-2(mu-O)L(R-CO2)}(2)](ClO4)(4) (2 R = C6H5-, 3 R = CH3-, 4, R = ClCH2-). The crystal structures of complexes 1 and 2 reveal that they consist of two Fe-2(III)(mu-O)(mu-RCO2)(2) cores that are linked via the two LH/L ligands to give a "dimer of dimers" structure. Complex I assumes a helical shape, with protonated carboxylic acid moieties of the two ligands forming a hydrogen-bonded pair at the center of the cation. In complexes 2, 3 and 4, central carboxylates of the two ligands bridge the iron ions in each of the two Fe, O units, with an interdimer iron-iron separation of approximately 10 angstrom and an intradimer separation of approximately 3.1 angstrom. The second carboxylate bridge within the Fe2O units is defined by exogenous benzoate (2), acetate (3) or chloroacetate (4) ligands. The aqua complex [{Fe-2(mu-O)L(H2O)(2)}(2)](ClO4)(6) (5) is proposed to have a similar structure, but with the exogenous bridging carboxylates replaced by two terminal water ligands. These complexes exhibit electronic and Mossbauer spectral features that are similar to those of (mu-oxo)diiron(iii) proteins as well as other related (mu-oxo)bis(mu-carboxylato)diiron(III) complexes. This similarity shows that these properties are not significantly affected by the nature of the bridging exogenous carboxylate, and that the octadentate framework ligand is essential in stabilizing the "dimer of dimers" structure. This structural feature remains in highly diluted solution (10(-5) M) as evidenced by electrospray ionization mass-spectroscopy (ES MS). Cyclic voltammetric studies of complexes 2 and 5 showed two irreversible two-electron reductions, indicating that the two Fe2O units of the tetranuclear complexes behave as distinct redox entities. Complexes 2, 3 and, especially, the aqua complex 5 are active alkane oxidation catalysts. Catalytic reactions carried out with alkane substrate molecules and hydrogen peroxide predominantly gave alcohols. High stereospecificity in the oxidation of cis- 1,2-dimethylcyclohexane supports the metal-based molecular mechanism of O-insertion into C-H bonds postulated for non-heme iron enzymes such as methane monooxygenase.},
  author       = {Gutkina, EA and Trukhan, VM and Pierpont, CG and Mkoyan, S and Strelets, VV and Nordlander, Ebbe and Shteinman, AA},
  issn         = {1477-9234},
  language     = {eng},
  number       = {3},
  pages        = {492--501},
  publisher    = {Royal Society of Chemistry},
  series       = {Dalton Transactions},
  title        = {Tetranuclear iron(III) complexes of an octadentate pyridine-carboxylate ligand and their catalytic activity in alkane oxidation by hydrogen peroxide},
  url          = {http://dx.doi.org/10.1039/b512069a},
  doi          = {10.1039/b512069a},
  year         = {2006},
}