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Redox processes in the iron(III)/9,10-phenanthraquinone system.

Petr Milko1, Jana Roithová

  • 1Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Praha, Czech Republic.

Inorganic Chemistry
|November 26, 2009
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Summary

Iron(III) complexes with 9,10-phenanthraquinone (PQ) facilitate methanolate oxidation to formaldehyde. This involves redox processes with PQ, potentially generating toxic radicals linked to PQ

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Area of Science:

  • Inorganic Chemistry
  • Organometallic Chemistry
  • Biochemistry

Background:

  • 9,10-phenanthraquinone (PQ) and 1,10-phenanthroline (phen) are ligands studied in iron complexes.
  • Iron complexes play crucial roles in various chemical and biological processes.
  • Understanding ligand reactivity in metal complexes is key to controlling chemical transformations.

Purpose of the Study:

  • To investigate the reactivity of phenanthraquinone (PQ) within iron(III) complexes.
  • To elucidate the role of PQ and 1,10-phenanthroline (phen) in redox processes involving iron.
  • To explore the mechanism of methanolate oxidation catalyzed by these iron complexes.

Main Methods:

  • Synthesis and characterization of model iron complexes: [(PQ)FeCl(CH3O)]+, [(phen)FeCl(CH3O)]+, and [(PQ)(phen)FeCl(CH3O)]+.
  • Investigation of complex reactivity using mass spectrometry and infrared multiphoton dissociation (IRMPD) spectroscopy.
  • Computational analysis employing density functional theory (DFT) calculations.

Main Results:

  • PQ participates in redox reactions, enabling the oxidation of methanolate to formaldehyde.
  • The oxidation is coupled with the reduction of iron(III) to iron(II) and PQ to its radical form.
  • 1,10-Phenanthroline acts as an innocent ligand, while hexacoordination in [(PQ)(phen)FeCl(CH3O)]+ facilitates methanolate oxidation.
  • PQ-iron complexes can generate toxic semihydroquinone radicals under reducing conditions.
  • Strong phen-iron binding confirmed, supporting its use as an iron chelator.

Conclusions:

  • PQ's involvement in redox cycling within iron complexes drives methanolate oxidation.
  • Hexacoordination of iron in PQ-phen complexes enhances catalytic activity.
  • The study provides insights into the mechanism of PQ toxicity and the utility of phen as an iron chelator.