How axial ligands control the reactivity of high-valent iron(IV)–oxo porphyrin π-cation radicals in alkane hydroxylation: A computational study

Kamachi, Takashi; Kouno, Tomohisa; Nam, Wonwoo; Yoshizawa, Kazunari

doi:10.1016/j.jinorgbio.2006.01.007

Cited by 40 publications

(31 citation statements)

References 25 publications

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“…Similar conclusions were drawn from studies of nonheme oxoiron catalysts of which the catalysis appears strongly affected by the nature of the axial ligand trans to the oxo group [21]. Yoshizawa and co-workers [22] and Choe and Nagase [23] did a systematic theoretical study into the alkane hydroxylation by heme models with different axial ligands. Thus, a series of anionic ligands (OH À , acetate, Cl À and CF 3 SO À 3 ) revealed that the electron donating ability of the ligand influences the activation energy of cyclohexane hydroxylation.…”

Section: Introductionmentioning

confidence: 53%

How does the push/pull effect of the axial ligand influence the catalytic properties of Compound I of catalase and cytochrome P450?

Wang

Visser

2007

Journal of Inorganic Biochemistry

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Section: Introductionmentioning

confidence: 53%

How does the push/pull effect of the axial ligand influence the catalytic properties of Compound I of catalase and cytochrome P450?

Wang

Visser

2007

Journal of Inorganic Biochemistry

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“…Calculations on ferryl porphyrins have indicated that the activation barrier for H-atom abstraction is inversely correlated to the Fe-O bond length in the transition state, which itself is related to the Fe-OH bond length in compound II. 12 Systems with the most donating ligands were predicted to have the longest Fe-OH bonds and be the most reactive with respect to C-H bond activation. 12 …”

Section: Discussionmentioning

confidence: 99%

“… 12 Systems with the most donating ligands were predicted to have the longest Fe-OH bonds and be the most reactive with respect to C-H bond activation. 12 …”

Section: Discussionmentioning

confidence: 99%

Significantly shorter Fe–S bond in cytochrome P450-I is consistent with greater reactivity relative to chloroperoxidase

et al. 2015

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Cytochrome P450 (P450) and chloroperoxidase (CPO) are thiolate ligated heme proteins that catalyze the activation of carbon hydrogen bonds. The principal intermediate in these reactions is a ferryl radical species called compound I. P450 compound I (P450-I) is significantly more reactive than CPO-I, which only cleaves activated C-H bonds. To provide insight into the differing reactivities of these intermediates, we examined CPO-I and P450-I with variable temperature Mössbauer and X-ray absorption spectroscopies. These measurements indicate that the Fe-S bond is significantly shorter in P450-I than in CPO-I. This difference in Fe-S bond lengths can be understood in terms of variations in hydrogen bonding patterns within the “cys-pocket” (a portion of the proximal helix that encircles the thiolate ligand). Weaker hydrogen bonding in P450-I results in a shorter Fe-S bond, which enables greater electron donation from the axial-thiolate ligand. This observation may in part explain P450's greater propensity for C-H bond activation.

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“…[12] Further studies on the axial ligand effect showed it to correlate with substrate oxygenation barriers through the electron affinity of the oxidant. [13] Interestingly, the axial ligand even has an effect on the regioselectivity of product distributions. Thus, Groves et al have shown that [Fe IV =OA C H T U N G T R E N N U N G (TMP + C)Cl] gives both cyclohexene oxide and cyclohexen-3-ol, in a 14:1 ratio, in a reaction with cyclohexene.…”

Section: Introductionmentioning

confidence: 99%

“…The axial ligand effect was characterised and assigned to two contributing factors, namely an electric field effect due to the charge of the system and a quantum mechanical effect from orbital mixing 12. Further studies on the axial ligand effect showed it to correlate with substrate oxygenation barriers through the electron affinity of the oxidant 13…”

Section: Introductionmentioning

confidence: 99%

How Does the Axial Ligand of Cytochrome P450 Biomimetics Influence the Regioselectivity of Aliphatic versus Aromatic Hydroxylation?

Visser

Tahsini

Nam

2009

Chemistry A European J

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The catalytic activity of high-valent iron-oxo active species of heme enzymes is known to be dependent on the nature of the axial ligand trans to the iron-oxo group. In a similar fashion, experimental studies on iron-oxo porphyrin biomimetic systems have shown a significant axial ligand effect on ethylbenzene hydroxylation, with an axial acetonitrile ligand leading to phenyl hydroxylation products and an axial chloride anion giving predominantly benzyl hydroxylation products. To elucidate the fundamental factors that distinguish this regioselectivity reversal in iron-oxo porphyrin catalysis, we have performed a series of density functional theory calculations on the hydroxylation of ethylbenzene by [Fe(IV)=O(Por(+.))L] (Por = porphyrin; L = NCCH(3) or Cl(-)), which affords 1-phenylethanol and p-ethylphenol products. The calculations confirm the experimentally determined product distributions. Furthermore, a detailed analysis of the electronic differences between the two oxidants shows that their reversed regioselectivity is a result of differences in orbital interactions between the axial ligand and iron-oxo porphyrin system. In particular, three high-lying orbitals (pi*(xz), pi*(yz) and a(2u)), which are singly occupied in the reactant complex, are stabilised with an anionic ligand such as Cl(-), which leads to enhanced HOMO-LUMO energy gaps. As a consequence, reactions leading to cationic intermediates through the two-electron reduction of the metal centre are disfavoured. The aliphatic hydroxylation mechanism, in contrast, is a radical process in which only one electron is transferred in the rate-determining transition state, which means that the effect of the axial ligand on this mechanism is much smaller.

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How axial ligands control the reactivity of high-valent iron(IV)–oxo porphyrin π-cation radicals in alkane hydroxylation: A computational study

Cited by 40 publications

References 25 publications

How does the push/pull effect of the axial ligand influence the catalytic properties of Compound I of catalase and cytochrome P450?

How does the push/pull effect of the axial ligand influence the catalytic properties of Compound I of catalase and cytochrome P450?

Significantly shorter Fe–S bond in cytochrome P450-I is consistent with greater reactivity relative to chloroperoxidase

How Does the Axial Ligand of Cytochrome P450 Biomimetics Influence the Regioselectivity of Aliphatic versus Aromatic Hydroxylation?

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