Iron(III) complexes with meridional ligands as functional models of intradiol-cleaving catechol dioxygenases

Tünde Váradi, J. Pap, Michel Giorgi, L. Párkányí, Tamás Csay, G. Speier, J. Kaizer

Research output: Contribution to journalArticle

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Abstract

Six dichloroiron(III) complexes of 1,3-bis(2′-arylimino)isoindoline (BAIH) with various N-donor aryl groups have been characterized by spectroscopy (infrared, UV-vis), electrochemistry (cyclic voltammetry), microanalysis, and in two cases X-ray crystallography. The structurally characterized Fe IIICl2(Ln) complexes (n = 3, L3 = 1,3-bis(2′-thiazolylimino)isoindoline and n = 5, L5 = 1,3-bis(4-methyl-2′-piridylimino)isoindoline) are five-coordinate, trigonal bipyramidal with the isoindoline ligands occupying the two axial and one equatorial positions meridionally. These compounds served as precursors for catechol dioxygenase models that were formed in solution upon addition of 3,5-di-tert-butylcatechol (H2DBC) and excess triethylamine. These adducts react with dioxygen in N,N-dimethylformamide, and the analysis of the products by chromatography and mass spectrometry showed high intradiol over extradiol selectivity (the intradiol/extradiol product ratios varied between 46.5 and 6.5). Kinetic measurements were performed by following the change in the intensity of the catecholate to iron ligand-to-metal charge transfer (LMCT) band, the energy of which is influenced by the isoindolinate-ligand (827-960 nm). In combination with electrochemical investigations the kinetic studies revealed an inverse trend between reaction rates and oxidation potentials associated with the coordinated DBC2-. On the basis of these results, a substrate activation mechanism is suggested for this system in which the geometry of the peroxide-bridged intermediate may be of key importance in regioselectivity.

Original languageEnglish
Pages (from-to)1559-1569
Number of pages11
JournalInorganic Chemistry
Volume52
Issue number3
DOIs
Publication statusPublished - Feb 4 2013

Fingerprint

Dioxygenases
Iron
Ligands
iron
ligands
Regioselectivity
Dimethylformamide
Kinetics
X ray crystallography
Peroxides
kinetics
peroxides
Electrochemistry
chromatography
electrochemistry
products
Chromatography
microanalysis
adducts
Cyclic voltammetry

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Physical and Theoretical Chemistry

Cite this

Iron(III) complexes with meridional ligands as functional models of intradiol-cleaving catechol dioxygenases. / Váradi, Tünde; Pap, J.; Giorgi, Michel; Párkányí, L.; Csay, Tamás; Speier, G.; Kaizer, J.

In: Inorganic Chemistry, Vol. 52, No. 3, 04.02.2013, p. 1559-1569.

Research output: Contribution to journalArticle

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abstract = "Six dichloroiron(III) complexes of 1,3-bis(2′-arylimino)isoindoline (BAIH) with various N-donor aryl groups have been characterized by spectroscopy (infrared, UV-vis), electrochemistry (cyclic voltammetry), microanalysis, and in two cases X-ray crystallography. The structurally characterized Fe IIICl2(Ln) complexes (n = 3, L3 = 1,3-bis(2′-thiazolylimino)isoindoline and n = 5, L5 = 1,3-bis(4-methyl-2′-piridylimino)isoindoline) are five-coordinate, trigonal bipyramidal with the isoindoline ligands occupying the two axial and one equatorial positions meridionally. These compounds served as precursors for catechol dioxygenase models that were formed in solution upon addition of 3,5-di-tert-butylcatechol (H2DBC) and excess triethylamine. These adducts react with dioxygen in N,N-dimethylformamide, and the analysis of the products by chromatography and mass spectrometry showed high intradiol over extradiol selectivity (the intradiol/extradiol product ratios varied between 46.5 and 6.5). Kinetic measurements were performed by following the change in the intensity of the catecholate to iron ligand-to-metal charge transfer (LMCT) band, the energy of which is influenced by the isoindolinate-ligand (827-960 nm). In combination with electrochemical investigations the kinetic studies revealed an inverse trend between reaction rates and oxidation potentials associated with the coordinated DBC2-. On the basis of these results, a substrate activation mechanism is suggested for this system in which the geometry of the peroxide-bridged intermediate may be of key importance in regioselectivity.",
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AU - Csay, Tamás

AU - Speier, G.

AU - Kaizer, J.

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N2 - Six dichloroiron(III) complexes of 1,3-bis(2′-arylimino)isoindoline (BAIH) with various N-donor aryl groups have been characterized by spectroscopy (infrared, UV-vis), electrochemistry (cyclic voltammetry), microanalysis, and in two cases X-ray crystallography. The structurally characterized Fe IIICl2(Ln) complexes (n = 3, L3 = 1,3-bis(2′-thiazolylimino)isoindoline and n = 5, L5 = 1,3-bis(4-methyl-2′-piridylimino)isoindoline) are five-coordinate, trigonal bipyramidal with the isoindoline ligands occupying the two axial and one equatorial positions meridionally. These compounds served as precursors for catechol dioxygenase models that were formed in solution upon addition of 3,5-di-tert-butylcatechol (H2DBC) and excess triethylamine. These adducts react with dioxygen in N,N-dimethylformamide, and the analysis of the products by chromatography and mass spectrometry showed high intradiol over extradiol selectivity (the intradiol/extradiol product ratios varied between 46.5 and 6.5). Kinetic measurements were performed by following the change in the intensity of the catecholate to iron ligand-to-metal charge transfer (LMCT) band, the energy of which is influenced by the isoindolinate-ligand (827-960 nm). In combination with electrochemical investigations the kinetic studies revealed an inverse trend between reaction rates and oxidation potentials associated with the coordinated DBC2-. On the basis of these results, a substrate activation mechanism is suggested for this system in which the geometry of the peroxide-bridged intermediate may be of key importance in regioselectivity.

AB - Six dichloroiron(III) complexes of 1,3-bis(2′-arylimino)isoindoline (BAIH) with various N-donor aryl groups have been characterized by spectroscopy (infrared, UV-vis), electrochemistry (cyclic voltammetry), microanalysis, and in two cases X-ray crystallography. The structurally characterized Fe IIICl2(Ln) complexes (n = 3, L3 = 1,3-bis(2′-thiazolylimino)isoindoline and n = 5, L5 = 1,3-bis(4-methyl-2′-piridylimino)isoindoline) are five-coordinate, trigonal bipyramidal with the isoindoline ligands occupying the two axial and one equatorial positions meridionally. These compounds served as precursors for catechol dioxygenase models that were formed in solution upon addition of 3,5-di-tert-butylcatechol (H2DBC) and excess triethylamine. These adducts react with dioxygen in N,N-dimethylformamide, and the analysis of the products by chromatography and mass spectrometry showed high intradiol over extradiol selectivity (the intradiol/extradiol product ratios varied between 46.5 and 6.5). Kinetic measurements were performed by following the change in the intensity of the catecholate to iron ligand-to-metal charge transfer (LMCT) band, the energy of which is influenced by the isoindolinate-ligand (827-960 nm). In combination with electrochemical investigations the kinetic studies revealed an inverse trend between reaction rates and oxidation potentials associated with the coordinated DBC2-. On the basis of these results, a substrate activation mechanism is suggested for this system in which the geometry of the peroxide-bridged intermediate may be of key importance in regioselectivity.

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