ortho-Hydroxylation of benzoic acids with hydrogen peroxide at a non-heme iron center

Taktak, Sonia; Flook, Margaret M.; Foxman, Bruce M.; Que, Lawrence; Rybak‐Akimova, Elena V.

doi:10.1039/b508004e

Cited by 92 publications

(63 citation statements)

References 33 publications

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“…Competition experiments also showed no preference of 1 in reacting with either protio or deuterio isotopomers, so C À H bond breaking on the phenyl ring cannot be a rate limiting step in this transformation. [36] Similarly small H/D KIE values ( 1) were also reported for other aromatic oxidations promoted by biological and synthetic iron centers, [8,27,29,[61][62][63][64] and interpreted in terms of either a rate-limiting formation of an iron-oxo intermediate [29] or a rate-limiting electrophilic attack of the aromatic ring by a metal-based oxidant (a process that is typically characterized by only a small but inverse isotope effect). [27,61,62,65,66] 18 O-labeling experiments with H 2 18 O 2 unambiguously showed the incorporation of one oxygen atom into the phenolate or salicylate product derived from the oxidations of benzoic acids, underscoring the fact that hydrogen peroxide is the sole source of the oxygen atom incorporated into the products.…”

Section: Mechanistic Insightsmentioning

confidence: 82%

“…[36,55] The reaction was accompanied by the appearance of a deep blue color (l max = 590 nm). The final UV/Vis spectrum was identical to that of the independently prepared salicylate complex [Fe…”

Section: Resultsmentioning

confidence: 99%

“…In one example of this strategy, phenols pre-bound to the iron center were hydroxylated selectively into the corresponding catecholato complexes. [35] We and others recently communicated additional examples of selective inner-sphere aromatic hydroxylation at non-heme iron centers: ortho-hydroxylation of benzoic acid with hydrogen peroxide promoted by [36] and self-hydroxylation of perbenzoic acids promoted by [Fe [37] (see Scheme 1 for ligand structures). Both complexes have aminopyridine ligands and are known to catalyze a number of oxidation reactions by activating H 2 O 2 , [38][39][40][41] including olefin epoxidation or cis-dihydroxylation [42][43][44] and alkane hydroxylation.…”

Section: A C H T U N G T R E N N U N G (Bpmen)-a C H T U N G T R E N mentioning

confidence: 99%

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Iron‐Promoted ortho‐ and/or ipso‐Hydroxylation of Benzoic Acids with H₂O₂

Makhlynets

Das

Taktak

et al. 2009

Chemistry A European J

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Regioselective hydroxylation of aromatic acids with hydrogen peroxide proceeds readily in the presence of iron(II) complexes with tetradentate aminopyridine ligands [Fe(II)(BPMEN)(CH(3)CN)(2)](ClO(4))(2) (1) and [Fe(II)(TPA)(CH(3)CN)(2)](OTf)(2) (2), where BPMEN=N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)-1,2-ethylenediamine, TPA=tris-(2-pyridylmethyl)amine. Two cis-sites, which are occupied by labile acetonitrile molecules in 1 and 2, are available for coordination of H(2)O(2) and substituted benzoic acids. The hydroxylation of the aromatic ring occurs exclusively in the vicinity of the anchoring carboxylate functional group: ortho-hydroxylation affords salicylates, whereas ipso-hydroxylation with concomitant decarboxylation yields phenolates. The outcome of the substituent-directed hydroxylation depends on the electronic properties and the position of substituents in the molecules of substrates: 3-substituted benzoic acids are preferentially ortho-hydroxylated, whereas 2- and, to a lesser extent, 4-substituted substrates tend to undergo ipso-hydroxylation/decarboxylation. These two pathways are not mutually exclusive and likely proceed via a common intermediate. Electron-withdrawing substituents on the aromatic ring of the carboxylic acids disfavor hydroxylation, indicating an electrophilic nature for the active oxidant. Complexes 1 and 2 exhibit similar reactivity patterns, but 1 generates a more powerful oxidant than 2. Spectroscopic and labeling studies exclude acylperoxoiron(III) and Fe(IV)=O species as potential reaction intermediates, but strongly indicate the involvement of an Fe(III)--OOH intermediate that undergoes intramolecular acid-promoted heterolytic O-O bond cleavage, producing a transient iron(V) oxidant.

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Section: Mechanistic Insightsmentioning

confidence: 82%

Section: Resultsmentioning

confidence: 99%

Section: A C H T U N G T R E N N U N G (Bpmen)-a C H T U N G T R E N mentioning

confidence: 99%

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Iron‐Promoted ortho‐ and/or ipso‐Hydroxylation of Benzoic Acids with H₂O₂

Makhlynets

Das

Taktak

et al. 2009

Chemistry A European J

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“…No diol is observed. The nature of oxidizing species formed under these conditions is not established and has been the subject of some discussion [26,27]. Ryu et al investigated the use of the 5-Mesubstituted analogue of TPA (12) under similar conditions [15].…”

Section: Olefin Epoxidation and Cis-dihydroxylation With High Substramentioning

confidence: 99%

Bio-inspired nonheme iron catalysts for olefin oxidation

Oldenburg¹,

Que²

2006

Catalysis Today

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“…Hydrogen peroxide is capable of oxidizing iron(II) into iron(III) in its complexes with bpmen, especially in the presence of additional carboxylate ligands [20]. The initially formed mononuclear iron(III) complex may undergo further reactions with various components of epoxidizing solutions, producing an active oxidant [21,22].…”

Section: Introductionmentioning

confidence: 99%