title: Rate-determining water-assisted O-O bond cleavage of an Fe(III)-OOH intermediate in a bio-inspired nonheme iron-catalyzed oxidation.
abstract: Hydrocarbon oxidations by bio-inspired nonheme iron catalysts and H2O2 have been proposed to involve an Fe(III)-OOH intermediate that decays via a water-assisted mechanism to form an Fe(V)(O)(OH) oxidant. Herein we report kinetic evidence for this pathway in the oxidation of 1-octene catalyzed by [Fe(II)(TPA)(NCCH3)](2+) (1, TPA = tris(2-pyridylmethyl)amine). The (TPA)Fe(III)(OOH) intermediate 2 can be observed at -40 °C and is found to undergo first-order decay, which is accelerated by water. Interestingly, the decay rate of 2 is comparable to that of product formation, indicating that the decay of 2 results in olefin oxidation. Furthermore, the Eyring activation parameters for the decay of 2 and product formation are identical, and both processes are associated with an H2O/D2O KIE of 2.5. Taken together with previous (18)O-labeling data, these results point to a water-assisted heterolytic O-O bond cleavage of 2 as the rate-limiting step in olefin oxidation.
authors.affiliation: Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: Williamson N
authors.initials: WN
authors.lastname: Oloo
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Fielding
authors.forename: Lawrence
authors.initials: L
authors.lastname: Que
mesh_terms: D000475:Alkenes / Q000737:chemistry; D005290:Ferric Compounds / Q000737:chemistry*; D006860:Hydrogen Bonding; D007202:Indicators and Reagents; D007700:Kinetics; D008744:Methylamines; D019159:Nonheme Iron Proteins / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D010103:Oxygen Isotopes / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D014867:Water / Q000737:chemistry*
chemical_list: D000475:Alkenes; D005290:Ferric Compounds; D007202:Indicators and Reagents; D008744:Methylamines; D019159:Nonheme Iron Proteins; D010103:Oxygen Isotopes; D014867:Water; C045319:4-pyridylmethylamine; C037690:1-octene; D010100:Oxygen