Rate-determining water-assisted O-O bond cleavage of an Fe III-OOH intermediate in a bio-inspired nonheme iron-catalyzed oxidation

Williamson N. Oloo; Andrew J. Fielding; Lawrence Que

doi:10.1021/ja402759c

Rate-determining water-assisted O-O bond cleavage of an Fe ^III-OOH intermediate in a bio-inspired nonheme iron-catalyzed oxidation

Williamson N. Oloo, Andrew J. Fielding, Lawrence Que

Chemistry (Twin Cities)

Research output: Contribution to journal › Article › peer-review

105 Scopus citations

Abstract

Hydrocarbon oxidations by bio-inspired nonheme iron catalysts and H ₂O₂ 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)(NCCH ₃)]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 ¹⁸O-labeling data, these results point to a water-assisted heterolytic O-O bond cleavage of 2 as the rate-limiting step in olefin oxidation.

Original language	English (US)
Pages (from-to)	6438-6441
Number of pages	4
Journal	Journal of the American Chemical Society
Volume	135
Issue number	17
DOIs	https://doi.org/10.1021/ja402759c
State	Published - May 1 2013

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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 H 2O2 have been proposed to involve an FeIII-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 [FeII(TPA)(NCCH 3)]2+ (1, TPA = tris(2-pyridylmethyl)amine). The (TPA)FeIII(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 18O-labeling data, these results point to a water-assisted heterolytic O-O bond cleavage of 2 as the rate-limiting step in olefin oxidation.",

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T1 - Rate-determining water-assisted O-O bond cleavage of an Fe III-OOH intermediate in a bio-inspired nonheme iron-catalyzed oxidation

AU - Oloo, Williamson N.

AU - Fielding, Andrew J.

AU - Que, Lawrence

PY - 2013/5/1

Y1 - 2013/5/1

N2 - Hydrocarbon oxidations by bio-inspired nonheme iron catalysts and H 2O2 have been proposed to involve an FeIII-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 [FeII(TPA)(NCCH 3)]2+ (1, TPA = tris(2-pyridylmethyl)amine). The (TPA)FeIII(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 18O-labeling data, these results point to a water-assisted heterolytic O-O bond cleavage of 2 as the rate-limiting step in olefin oxidation.

AB - Hydrocarbon oxidations by bio-inspired nonheme iron catalysts and H 2O2 have been proposed to involve an FeIII-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 [FeII(TPA)(NCCH 3)]2+ (1, TPA = tris(2-pyridylmethyl)amine). The (TPA)FeIII(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 18O-labeling data, these results point to a water-assisted heterolytic O-O bond cleavage of 2 as the rate-limiting step in olefin oxidation.

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Rate-determining water-assisted O-O bond cleavage of an Fe ^III-OOH intermediate in a bio-inspired nonheme iron-catalyzed oxidation

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