title: Spectroscopic investigation and direct comparison of the reactivities of iron pyridyl oxidation catalysts.
abstract: The growing interest in green chemistry has fueled attention to the development and characterization of effective iron complex oxidation catalysts. A number of iron complexes are known to catalyze the oxidation of organic substrates utilizing peroxides as the oxidant. Their development is complicated by a lack of direct comparison of the reactivities of the iron complexes. To begin to correlate reactivity with structural elements, we compare the reactivities of a series of iron pyridyl complexes toward a single dye substrate, malachite green (MG), for which colorless oxidation products are established. Complexes with tetradentate, nitrogen-based ligands with cis open coordination sites were found to be the most reactive. While some complexes reflect sensitivity to different peroxides, others are similarly reactive with either H2O2or tBuOOH, which suggests some mechanistic distinctions. [Fe(S,S-PDP)(CH3CN)2](SbF6)2and [Fe(OTf)2(tpa)] transition under the oxidative reaction conditions to a single intermediate at a rate that exceeds dye degradation (PDP=bis(pyridin-2-ylmethyl) bipyrrolidine; tpa=tris(2-pyridylmethyl)amine). For the less reactive [Fe(OTf)2(dpa)] (dpa=dipicolylamine), this reaction occurs on a timescale similar to that of MG oxidation. Thus, the spectroscopic method presented herein provides information about the efficiency and mechanism of iron catalyzed oxidation reactions as well as about potential oxidative catalyst decomposition and chemical changes of the catalyst before or during the oxidation reaction.
authors.affiliation: Department of Chemistry & Biochemistry, University of Missouri St. Louis, St. Louis, MO 63121, United States; Center for Nanoscience, University of Missouri St. Louis, St. Louis, MO 63121, United States.
authors.forename: Yang
authors.initials: Y
authors.lastname: Song
authors.affiliation: Department of Chemistry & Biochemistry, University of Missouri St. Louis, St. Louis, MO 63121, United States; Center for Nanoscience, University of Missouri St. Louis, St. Louis, MO 63121, United States.
authors.forename: Howard G
authors.initials: HG
authors.lastname: Mayes
authors.affiliation: Department of Chemistry & Biochemistry, University of Missouri St. Louis, St. Louis, MO 63121, United States.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Queensen
authors.affiliation: Department of Chemistry & Biochemistry, University of Missouri St. Louis, St. Louis, MO 63121, United States. Electronic address: bauere@umsl.edu.
authors.forename: Eike B
authors.initials: EB
authors.lastname: Bauer
authors.affiliation: Department of Chemistry & Biochemistry, University of Missouri St. Louis, St. Louis, MO 63121, United States; Center for Nanoscience, University of Missouri St. Louis, St. Louis, MO 63121, United States. Electronic address: cdup@umsl.edu.
authors.forename: Cynthia M
authors.initials: CM
authors.lastname: Dupureur
keywords: Iron catalysis; Malachite green; Oxidation; Peroxide