A Density Functional Study on a Biomimetic Non‐Heme Iron Catalyst: Insights into Alkane Hydroxylation by a Formally HOFe<sup>V</sup>O Oxidant

Bassan, Arianna; Blomberg, Margareta R. A.; Siegbahn, Per E. M.; Que, Lawrence

doi:10.1002/chem.200400383

Cited by 81 publications

(86 citation statements)

References 52 publications

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“…[7,8] The corresponding sextet and doublet states of HOÀFe V =O lie more than 10 kcal mol À1 higher in energy than the quartet ground state. [9] Further DFT calculations presented herein provide new insight into how this unique oxidant can carry out both olefin epoxidation and cis-dihydroxylation. Hence, the present study focuses on the subsequent reaction of 2 with olefins (see the Supporting Information) to reveal that olefin epoxidation and cis-dihydroxylation in fact represent different faces of the same oxidant.…”

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confidence: 97%

Two Faces of a Biomimetic Non‐Heme HOFe^VO Oxidant: Olefin Epoxidation versus cis‐Dihydroxylation

et al. 2005

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The family of non-heme iron complexes-exemplified by [Fe II (tpa)(CH 3 CN) 2 ] 2+ , where tpa is the tetradentate tripodal tris(2-pyridylmethyl)amine ligand-efficiently utilizes H 2 O 2 to carry out stereospecific olefin epoxidation and cis-dihydroxylation. [1][2][3][4] The latter reaction was not previously known to be catalyzed by a synthetic iron complex and is precedented only in the chemistry of Rieske dioxygenases, [5] non-heme iron enzymes responsible for cis-dihydroxylation in the biodegradation of arenes by soil bacteria. Isotope-labeling experiments on the biomimetic reaction show the involvement of a highly selective metal-based oxidant capable of introducing water into the product. [1,2] This oxidant is proposed to result from the low-spin complex [Fe III (tpa)(H 2 *)(OOH)] 2+ (1) and be a formally H*ÀFe V =O species (2; * indicates an oxygen atom with isotope labeling), both shown in Figure 1.Previous DFT calculations have demonstrated the feasibility of an OÀO bond heterolysis mechanism that leads to an S = 3/2 cis-HOÀFe V =O species with a short FeÀO bond (1.66 ) and a longer FeÀOH bond (1.77 ).[6] The three unpaired electrons are mainly distributed on the iron atom (1.58), the oxo oxygen atom (1.0), and the hydroxo oxygen atom (0.44): a spin distribution not unlike that found for compounds I of heme peroxidases and cytochrome P450 and related model complexes. [7,8] The corresponding sextet and doublet states of HOÀFe V =O lie more than 10 kcal mol À1 higher in energy than the quartet ground state.[9]Further DFT calculations presented herein provide new insight into how this unique oxidant can carry out both olefin epoxidation and cis-dihydroxylation. Hence, the present study focuses on the subsequent reaction of 2 with olefins (see the Supporting Information) to reveal that olefin epoxidation and cis-dihydroxylation in fact represent different faces of the same oxidant.The key results of our DFT study are illustrated by the energy profiles in Figure 2, showing that 2 can react with olefins (namely, 2-butene) through two different channels. As shown on the left, the oxo group attacks the olefin to form the C1ÀO1 bond and intermediate A-Fe IV (path A). On the right, the hydroxo ligand attacks the olefin to form the C2ÀO2 bond and intermediate B-Fe IV (path B). Both intermediates have an iron(iv) center and a radical on the partially oxidized substrate.Intermediate A-Fe IV is an iron(iv) complex with a hydroxide (r Fe-O2 = 1.79 ) and the partially oxidized olefin as ligands. The formation of the new C1ÀO1 bond is exergonic by 2.5 kcal mol À1 and involves an activation energy of 7.8 kcal mol À1 ; solvent effects (+ 3.1 kcal mol À1 ), entropy effects (+ 0.6 kcal mol À1 ), and big-basis effects (+ 2.1 kcal mol À1 ) contribute to increase the barrier by 5.6 kcal mol À1 . Unpaired spin density can be found on the metal center (1.53), the partially oxidized olefin (0.97), and the remaining ligands (0.50). Antiferromagnetic coupling of the unpaired electron on the partially oxidized olefin with those ...

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Two Faces of a Biomimetic Non‐Heme HOFe^VO Oxidant: Olefin Epoxidation versus cis‐Dihydroxylation

et al. 2005

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“…This may explain the diversity of alkane hydroxylation reaction mechanisms found in the literature. 23,25,29,30 For this reason, we studied the gas-phase hydroxylation mechanisms of methane and cyclohexane and we compared them with those obtained in solution.…”

Section: Comparison Between Gas-phase and Solvent-phase Mechanismsmentioning

confidence: 99%

Computational Insight into the Mechanism of Alkane Hydroxylation by Non-heme Fe(PyTACN) Iron Complexes. Effects of the Substrate and Solvent

et al. 2015

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The reaction mechanisms for alkane oxidation processes catalyzed by non heme Fe V O complexes presented in literature vary from rebound stepwise to concerted highly asynchronous processes. The origin of these important differences is still not completely understood. Herein, in order to clarify this apparent inconsistency, the stereospecific hydroxylation of a series of alkanes (methane and substrates bearing primary, secondary, and tertiary C-H bonds) through a Fe V O species, iii) The HAT is the rate determining step for all analyzed cases; and iv)The barrier for the HAT decreases along methane  primary  secondary  tertiary carbon. The second part of the reaction mechanism corresponds to the rebound process. Therefore, the stereospecific hydroxylation of alkane C-H bonds by nonheme Fe V (O) species occurs through a rebound stepwise mechanism that resembles that taking place at heme analogues. Finally, our study also shows that to properly describe alkane hydroxylation processes mediated by Fe V O species, it is essential to consider the solvent effects during geometry optimizations. The use of gas-phase 3 geometries explains the variety of mechanisms for the hydroxylation of alkanes reported in the literature.

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“…[139,140] Eisen wird entweder mit dem tripodalen vierzähnigen N 4 -Liganden Tris(2-pyridylmethyl)amin (TPA) [134] oder durch das lineare N,N'-Bis(2-pyridylmethyl)-N,N'-dimethyl-1,2-diaminoethan [141] [140,[142][143][144] Für diese Katalysatoren gibt es fast keine Daten zur Oxidation anderer Substrate als Cyclohexan und Adamantan. Da die C-H-Bindungsdissoziationsenergie von Cyclohexan mit 99 kcal mol À1 [145] vergleichbar ist mit der von sekundären C-H-Bindungen in linearen Alkanen, [146] macht eine Extrapolation der katalytischen Aktivität dieser Substrate trotzdem Sinn.…”

Section: Biomimetische Einkernige Nicht-häm-eisenkomplexeunclassified

“…[146] Bei der Modellierung der Reaktivität der hochwertigen Eisen-Oxo-Spezies [HO-(TPA)Fe V = O] mit Propan und Methan nach dem Häm-Mechanismus [147] ist die berechnete Aktivierungsenergie für die Wasserstoffabspaltung von der primären C-H-Bindung in Methan zu hoch für diesen Katalysator. Dagegen wäre die homolytische Spaltung von sekundären C-H-Bindungen in Propan durch die reaktive Spezies, die zu 2-Propanol führen würde, experimentell machbar.…”

Section: Biomimetische Einkernige Nicht-häm-eisenkomplexeunclassified

Katalytische, milde und selektive Oxyfunktionalisierung von linearen Alkanen: aktuelle Herausforderungen

2012

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Es besteht eine große Nachfrage nach selektiven Katalysatoren für die nachhaltige Oxidation von Alkanen, denn die in der Umwelt sehr häufig vorkommenden Alkane kçnnen dadurch in hçherwertige Verbindungen, z.B. Chemikalien oder synthetische Brennstoffe, umgewandelt werden. Für diese – kinetisch gesehen – schwierige Reaktion wurde in den letzten Jahrzehnten eine Vielzahl von chemischen und biologischen Katalysatoren entwickelt, was einen Uberblick über das Gebiet erschwert. Dieser Kurzaufsatz gibt zunächst eine Definitiondes idealen Katalysators für die Alkan-Oxyfunktionalisierung und behandelt dann die heute verfügbaren Katalysatoren, die einem solchen idealen Katalysator am nächsten kommen

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A Density Functional Study on a Biomimetic Non‐Heme Iron Catalyst: Insights into Alkane Hydroxylation by a Formally HOFe^VO Oxidant

Cited by 81 publications

References 52 publications

Two Faces of a Biomimetic Non‐Heme HOFe^VO Oxidant: Olefin Epoxidation versus cis‐Dihydroxylation

Two Faces of a Biomimetic Non‐Heme HOFe^VO Oxidant: Olefin Epoxidation versus cis‐Dihydroxylation

Computational Insight into the Mechanism of Alkane Hydroxylation by Non-heme Fe(PyTACN) Iron Complexes. Effects of the Substrate and Solvent

Katalytische, milde und selektive Oxyfunktionalisierung von linearen Alkanen: aktuelle Herausforderungen

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A Density Functional Study on a Biomimetic Non‐Heme Iron Catalyst: Insights into Alkane Hydroxylation by a Formally HOFeVO Oxidant

Cited by 81 publications

References 52 publications

Two Faces of a Biomimetic Non‐Heme HOFeVO Oxidant: Olefin Epoxidation versus cis‐Dihydroxylation

Two Faces of a Biomimetic Non‐Heme HOFeVO Oxidant: Olefin Epoxidation versus cis‐Dihydroxylation

Computational Insight into the Mechanism of Alkane Hydroxylation by Non-heme Fe(PyTACN) Iron Complexes. Effects of the Substrate and Solvent

Katalytische, milde und selektive Oxyfunktionalisierung von linearen Alkanen: aktuelle Herausforderungen

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A Density Functional Study on a Biomimetic Non‐Heme Iron Catalyst: Insights into Alkane Hydroxylation by a Formally HOFe^VO Oxidant

Two Faces of a Biomimetic Non‐Heme HOFe^VO Oxidant: Olefin Epoxidation versus cis‐Dihydroxylation

Two Faces of a Biomimetic Non‐Heme HOFe^VO Oxidant: Olefin Epoxidation versus cis‐Dihydroxylation