Catalytic H2O2 activation by a diiron complex for methanol oxidation

Thomas Philipp Zimmermann, Nicole Orth, Sebastian Finke, Thomas Limpke, Anja Stammler,

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Catalytic H O Activation by a Diiron Complex for Methanol

Oxidation

†

Hartmut Bogge, Stephan Walleck, Ivana Ivanovic-Burmazovic,* and Thorsten Glaser*

Cite This: https://dx.doi.org/10.1021/acs.inorgchem.0c02698

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sı Supporting Information

ABSTRACT: In nature, C−H bond oxidation of CH involves a

peroxo intermediate that decays to the high-valent active species of

either a “closed” {Fe (μ-O) Fe } core or an “open” {Fe (O)(μ-

O)Fe (O)} core. To mimic and to obtain more mechanistic

insight in this reaction mode, we have investigated the reactivity of

the bioinspired diiron complex [(susan){Fe(OH)(μ-O)Fe-

(

OH)}] [susan = 4,7-dimethyl-1,1,10,10-tetrakis(2-pyridylmeth-

yl)-1,4,7,10-tetraazadecane], which catalyzes CH OH oxidation

with H O to HCHO and HCO H. The kinetics is faster in the

presence of a proton. O-labeling experiments show that the active

species, generated by a decay of the initially formed peroxo

intermediate [(susan){Fe (μ-O)(μ-O )Fe }] , contains one

III

III 2+

IV IV

reactive oxygen atom from the μ-oxo and another from the μ-peroxo bridge of its peroxo precursor. Considering an Fe Fe

active species, a “closed” {Fe (μ-O) Fe } core explains the observed labeling results, while a scrambling of the terminal and

bridging oxo ligands is required to account for an “open” {Fe (O)(μ-O)Fe (O)} core.

INTRODUCTION

complexes induced by slight variations of the tpa-based ligand

■

III

substituents. In some instances, a transient {Fe (μ-O)(μ-

Nonheme diiron enzymes activate dioxygen (O ) in biological

III

O )Fe } intermediate could be observed by its characteristic

systems to catalyze various oxidation and/or oxygenation

−

−3

absorption features around 15500 and 20000 cm assigned to

μ-peroxo → Fe and μ-oxo → Fe ligand-to-meatl charge

transfers, respectively.

reactions.

Examples are soluble methane monooxygenase

sMMO), which selectively catalyzes the two-electron

III

(

19−22

III

−6

Also, a {Fe (μ-OH)(μ-O )Fe }

oxidation of methane (CH ) to methanol (CH OH),

arylamine N-oxygenase (CmlI), which catalyzes the six-

transient intermediate with a broad maximum of around 14300

−

cm was postulated. However, the peroxo intermediates

were not observable in the majority of cases even at low

electron oxidation of aminoarenes to nitroarenes in three

two-electron steps. The generalized catalytic cycle employs a

^dⁱ^f^e^r^r^o^u^s^f^o^r^m^t^h^a^t^r^e^a^c^t^s^wⁱ^t^h^O2 to a peroxo diferric

temperatures because of their high reactivity. Instead, their

IV III23−25

decay with the formation of high-valent Fe Fe

intermediate. The active species is proposed to be either this

IV IV26−31

Fe Fe

species could be established.

peroxo intermediate or a high-valent species resulting from its

conversion. In sMMO, the active species is thought to be a

To mimic the reactivity of oxygenating enzymes and to

develop bioinspired homogeneous catalysts, we synthesized a

dinucleating ligand system consisting of two ethylene-bridged

IV IV

1,4−6

high-valent Fe Fe intermediate termed Q,

with a

9,10

“

closed” {Fe (μ-O) Fe } core or, more recently proposed,

11,12

tripodal ligand compartments with varying terminal do-

an “open” {Fe (O)(μ-O)Fe (O)} core

structure. After

32−34

nors,

e.g., the ligand 4,7-dimethyl-1,1,10,10-tetrakis(2-

substrate oxidation, the active site is in a diferric form, which

must be reduced by two electrons to retrieve the starting

diferrous form. However, the diferric form can also react with

hydrogen peroxide (H O ) to form the peroxo intermediate

pyridylmethyl)-1,4,7,10-tetraazadecane (susan; Figure 1a).

Here, we present a detailed study on the reactivity of diferric

complexes of susan toward H O in CH OH. We observed a

13,14

(

peroxide shunt).

Besides the structural characterization of diiron model

Received: September 9, 2020

5−18

complexes with a μ-1,2-peroxo bridge,

important

mechanistic insights were obtained by studying the reactions

of diferric complexes of tris(2-pyridylmethyl)amine (tpa)-

based ligands with H O . These studies have provided strong

diﬀerences in the stabilities and reactivities of the peroxo

XXXX American Chemical Society

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

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performed the reaction with more concentrated solutions and

obtained reproducible yields of 71%, which would require 9.8

mM concentrations of formate. Gas chromatography−mass

spectrometry (GC−MS) analysis ruled out contaminations in

this order of magnitude [see the Supporting Information (SI)

for details]. Moreover, without the addition of H O , there is

no indication for the formation of 1 , and in the absence of

the iron species, no signiﬁcant formate concentrations could be

detected by the reaction of CH OH and H O , under

analogous conditions even after 3 days. Thus, a dinuclear

susan complex is required to activate an excess of H O toward

the in situ four-electron oxidation of CH OH to formate in

two two-electron steps, as demonstrated by various labeling

experiments utilizing H₂O and H O (vide infra).

To investigate this reactivity in more detail, we employed

[

(susan){Fe(OH)(μ-O)Fe(OH)}](ClO ) [3(ClO ) ] with

4 2 4 2

−

terminal OH ligands as a well-deﬁned precursor. In a CH OH

solution, 3(ClO₄)₂undergoes solvolysis to [(susan){Fe-

(

OMe)(μ-O)Fe(OMe)}] (4 ) even at −80 °C (see the SI

for details). We reacted 4 in CH OH with 1360 equiv of

H O at room temperature and quenched the reaction after 30

min by the addition of aqueous hydrochloric acid. Through

extraction with trichloromethane (CHCl ; or CDCl ), we

identiﬁed two reaction products in the organic phase by

independent GC−MS and NMR analysis: the methyl ester of

formic acid (HCO CH ; a four-electron oxidation product)

Figure 1. Structural presentations of the ligand and complex: (a) the

and the dimethyl acetal of formaldehyde [H C(OCH ) ; a

2 3 2

ligand susan; (b) molecular structure of 1 in single crystals of

two-electron oxidation product]. Quantitative analysis (see the

SI for details) provided turnover numbers of 74(5) and 62(5)

for HCO CH and H C(OCH ) , respectively. It should be

[

(susan){Fe(μ-O)(μ-O CH)Fe}](ClO ) · / MTBE. Hydrogen

2 4 3 2

atoms have been omitted for clarity. Selected bond lengths: Fe1−

O3 1.785(6), Fe1−O51 2.075(8), Fe1−N1 2.199(9), Fe1−N2

3 2

noted that these numbers constitute only lower limits as

2.225(10), Fe1−N3 2.133(9), Fe1−N4 2.131(8), Fe2−O3

1.800(6), Fe2−O52 1.990(10), Fe2−N41 2.266(11), Fe2−N42

2.176(10), Fe2−N43 2.140(10), Fe2−N44 2.200(10), Fe1···Fe2

3.288(2).

gaseous products were detected: on the one hand, O , which is

38,39

indicative of catalase activity,

^aⁿ^d^,^oⁿ^t^h^e^o^t^h^e^r^h^aⁿ^d^,^C^O2^,

which is indicative of six-electron oxidation of CH OH. These

gaseous products could facilitate the loss of other volatile

oxidation products into the gaseous phase.

To obtain more insight into the second two-electron

catalytic oxidation of CH OH to formaldehyde (HCHO) and

formic acid (HCO H). A peroxo intermediate was formed,

oxidation from HCHO to HCO H, we performed the same

which then converted to an even more reactive high-valent

species. The role of protonation of the coordinated peroxide

was investigated, and isotope-labeling studies provided

important mechanistic insight.

reaction but preadded 74 equiv of HCHO, yielding 127(15)

and 78(11) equiv of H C(OCH ) and HCO CH ,

respectively. It should be considered that under these

conditions also the oxidation of CH OH contributes to these

yields (vide supra). A comparison of the observed yields

indicates that 3²⁺does not signiﬁcantly utilize free HCHO as a

RESULTS AND DISCUSSION

■

Reactivity and Catalytic Studies. The reaction of susan

with 2 equiv of Fe(ClO ) ·6H O and an excess of H O in

substrate for the oxidation by H

These experiments indicate that (i) H

susan diiron species, which is (ii) capable of oxidizing CH

to HCO

is activated by a

CH OH resulted in a bubble release and a temperature

increase. Diﬀusion of methyl tert-butyl ether (MTBE) yielded

single crystals of the formato-bridged complex [(susan){Fe(μ-

O)(μ-O CH)Fe}](ClO ) ·0.5MTBE [1(ClO ) ·0.5MTBE;

by two electrons to a HCHO derivative but (iii) not active

toward the oxidation of free HCHO; thus, (iv) the second two-

electron oxidation most likely occurs, while HCHO is still

coordinated.

4 3

Figure 1b]. The closely related acetato-bridged complex

(susan){Fe(μ-O)(μ-OAc)Fe}](ClO ) [2(ClO ) ] was syn-

Mechanistic Studies. The reaction of 4²⁺in CH

OH with

H O was followed by UV−vis−near-IR (NIR) spectroscopy

[

4 3

thesized in a straightforward reaction of susan with 2 equiv of

Fe(ClO ) ·6H O and 1 equiv of (Bu N)OAc under basic

(Figure 2). The addition of 100 equiv of H O at room

2 2

conditions in an ethanol/acetone mixture, i.e., without the

temperature generated a new species (∼20 s, red in Figure 2a)

−1

addition of H O .

with increased intensity around 17000 cm . The diﬀerence

The unexpected presence of formate in 1 , without

providing its source, raises a question of its origin. Que and

co-workers obtained a μ-oxo-μ-formato-bridged diferric

spectrum after and before H O addition (magenta in Figure

−

2a) reveals two absorption maxima at 16000 and 19300 cm ,

which match the two characteristic absorption bands of μ-1,2-

peroxo-μ-oxo-bridged diferric complexes of Que et al. and

III

complex in the reaction of tpa with Fe (ClO ) ·10H O and

19,22

triethylamine in CH OH. They assigned the origin of the

Kodera et al. with related ligand environments (vide infra),

formato bridge to the oxidation of coordinated CH OH by O .

In order to exclude impurities as a formate source, we

indicating formation of the peroxo-bridged complex [(susan)-

III

III 2+

{Fe (μ-O)(μ-O )Fe }] (5 ; Figure 3, top pathway).

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

bands and the band around 27000 cm⁻(inset in Figure 2 a).

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The resulting species (blue in Figure 2a) comprises the same

spectral features as 4 , indicating again a μ-oxo-bridged

III

[

(susan){Fe X(μ-O)Fe X}] entity. The addition of 1 equiv

of HClO results in new absorptions at 14000, 20180, and

−

0800 cm (cyan in Figure 2a) that are the signature of

III

doubly bridged complexes [(susan){Fe (μ-O)(μ-O CR)-

III 3+ 40

Fe }] . A comparison with 1 (green in Figure 2b)

strongly argues for formation of the μ-formato species 1³

upon the addition of HClO . This reactivity initiated by acid

addition can be assigned to the protonation and dissociation of

−

a terminal anionic donor X (here X = MeO or HCO ),

followed by a carboxylate shift from the terminal to bridging

coordination mode (Figure 3, top pathway). In the case of

acetato complexes, we have shown that this carboxylate shift

III

from [(susan){Fe (OAc)(μ-O)Fe (OAc)}] to [(susan)-

{

III

III 3+

Fe (μ-O)(μ-OAc)Fe }] is reversible upon consecutive

additions of acid and base. From these data, it can be

concluded that either the peroxo intermediate 5 or a

converted high-valent species Y initiates the oxidation of

CH OH with the formation of a μ-oxo-bridged complex

possessing a terminal formato ligand that undergoes a

carboxylate shift upon the addition of H⁺(Figure 3, top

pathway). Note that this reactivity is not observed upon the

addition of H only.

The addition of 100 equiv of H O at lower temperatures

(

−40 °C) caused only minor spectral changes over an hour.

This is in line with the observed kinetic inertness of 3 toward

ligand exchange, where water exchange on the hydroxido 3²

complex and its monoprotonated (μ-O H )-bridge form was

too slow to be measured. In contrast, double protonation led

to the formation of two terminal aqua ligands, which shows

increased kinetic lability with a water exchange rate of k

3.9 ± 0.2) × 10 s .

−1

(

A further inﬂuence of protonation on the oxidation reactivity

is shown by its dependence on the sequence of addition of

H O and HClO (the data at −50 °C are shown as an

Figure 2. Spectroscopic observation of the reactions with H O : (a)

example in Figure 4). Monoprotonation resulted in a small

shift on a second time scale of the shoulder around 17700

UV−vis−NIR spectra and time traces at selected wavenumbers for

the reaction of 3(ClO ) (0.28 mM) in CH OH with 100 equiv of

−1

cm (Figure 4a) analogous to monoprotonation of 3 in

H O , followed by the addition of 1 equiv of HClO at room

H O. Accordingly, this shift is assigned to protonation of a

temperature. The sequence of the addition is indicated in the time

terminal methoxido ligand (Figure 3, bottom pathway). The

subsequent addition of 2 equiv of H O initiated intensity

traces inset. (b) Comparison of the ﬁnal spectrum after the addition

of HClO to the spectrum of [(susan){Fe(μ-O)(μ-O CH)Fe}] (for

−

a better comparison, the absorption is corrected to a concentration of

.28 mM).

increases in the spectrum of around 14000 and 20000 cm

(blue in Figure 4a). The diﬀerence spectrum, 60 min after and

before the addition of H O , indicates the formation of

5²⁺

decays exponentially on a slower time scale (∼1000 s)

formato-bridged 1 , eﬀected by the addition of H O (green

2 2

than its formation, as is evident by the decrease of the peroxo

in Figure 4a) to the monoprotonated form of 4²(Figure 3,

bottom pathway).

Figure 3. Proton dependence of the reactivity: Diﬀerent reaction pathways depending on the sequence of addition of oxidant and protons.

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

no reactivity (black and cyan in Figure 4 b), in line with the

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signiﬁcantly slower exchange of coordinated OCH ⁻versus

CH OH at −50 °C. The subsequent addition of one proton

equivalent resulted in changes indicative for two reactions

(

Figure 4b, right). A fast reaction, completed in seconds,

consistent with monoprotonation of 4 (red in Figure 4b) and

a slower reaction associated with an intensity increase of

−

around 14000 at 20000 cm . The diﬀerence spectrum, 47 min

and 19 s after HClO addition (green in Figure 4b), indicates

that the slow reaction is again correlated with the formation of

μ-formato-bridged 1 .

These diﬀerences demonstrate that protonation of 4²⁺

accelerates the reaction with H O to a transient peroxo

species. Neither the transient peroxo species nor the converted

species can be detected under these conditions but only the

ﬁnal product 1 . This implies the formation of an intermediate

more reactive than 5²⁺in₆_,₂t₈h_,₄e₁presence of a proton, presumably

a hydroperoxo species.

To obtain more information, we investigated this reaction by

ultrahigh-resolution cold-spray-ionization mass spectrometry

(

CSI-MS) in CH OH at −80 °C. 3 (ClO ) dissolved in

4 2

CH OH provides solvolyzed 4 (Figure S2). Upon the

addition of 100 equiv of H O , besides 4 at m/z 364.1276 as

the major peak (Figure S14 ), a new signal at m/z 349.1047 for

the peroxo complex 5²⁺was detected. A signal at m/z 371.1166

corresponding to [(susan){Fe(O CH)(μ-O)Fe(OMe)}] in-

dicates that some oxidation of CH OH to formate occurs

Figure 4. (a) UV−vis−NIR spectra of a 0.73 mM solution of

already at −80 °C. The addition of 1 equiv of HClO

(ClO ) in CH OH at −50 °C and after the consecutive addition of

equiv of HClO and 2 equiv of H O . (b) UV−vis−NIR spectra of a

signiﬁcantly changed the MS spectrum (Figure S15). The

ﬁnal product 1³⁺(m/z 237.0724) and {1(ClO )} (m/z

.65 mM solution of 3(ClO ) in CH OH at −50 °C and after the

consecutive addition of 2 equiv of H O and 1 equiv of HClO . Right:

405.0822) appeared as the main peaks. Furthermore, a species

^tⁱ^m^e^t^r^a^c^e^s^a^t^s^e^l^e^c^t^e^d^w^a^v^eⁿ^u^m^b^e^r^sⁱⁿ^dⁱ^c^a^tⁱⁿ^g^t^h^e^tⁱ^m^e^s^o^f^H^C^l^O4

at m/z 378.1067 corresponding to ([(susan){Fe(O CH)(μ-

and H O additions.

O)Fe(O CH)}] was observed. The signal at m/z 349.1034

for the peroxo complex 5 was of decreased intensity.

Warming the reaction to −10 °C slightly changed the ratios

of the signals. The peroxo species 5²⁺was still detected. This

In contrast, the addition of 2 equiv of H O initially caused

Figure 5. Diﬀerent reaction pathways in the ¹⁸O-labeling experiments, with H₂¹⁸O (left) and H₂¹⁸O (right) considering “open” and “closed” core

oxidants.

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

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temperature stability of 5²⁺suggests that it is not the oxidizing

species itself but rather a precursor to a transient high-valent

species Y, which is too reactive to be detected even at −80 °C.

On the other hand, protonation of 4²strongly accelerates the

ligand exchange with H O , presumable forming a hydro-

unequivocally demonstrate that the formate in 1³⁺originates

from the oxidation of CH OH initiated by formation of the

peroxo complex 5 . Moreover, O incorporation in formate

from the μ- O-bridged 5 cannot be explained by this peroxo

or corresponding hydroperoxo species as the active species.

6,28,41

peroxo species,

active oxidant Y and the formato-bridged 1 .

which on a fast time scale generates the

Thus, 5 must rearrange into the active oxidant Y, which has

two oxygen atoms that can be transferred onto the substrate:

one originating from H O and one from the oxo bridge. The

Isotope-Labeling Studies. To further substantiate the

proposed reaction scheme, we performed isotopic labeling

latter suggests that the active oxidant Y is a high-valent species

IV IV

experiments. Performing the reaction in CH OH shifted the

favoring the formation of a transient Fe Fe intermediate.

11,12

main signal in CSI-MS for 4 from m/z 364.1275 to 365.1311,

In analogy to MMO,

the peroxo complex 5 can

proving the incorporation of two ¹³CH O ligands from the

−

convert to either a “closed” core intermediate, [(susan)-

IV 4+

solvent (Figure S16 ). The addition of 100 equiv of H O

{Fe (μ-O) Fe }] (6 ), or an “open” core intermediate,

resulted in the formato species [(susan){Fe(O CH )(μ-

[(susan){Fe (O)(μ-O)Fe (O)}] (7b ; Figure 5). Consid-

O)Fe(O ₂ CH)}] at m/z 372.1212 as the main species

ering the “closed” core structure, the use of H O results via

peroxo species 5a²⁺to the oxidant 6 with one μ- O

(

{

Figure S17 ), and the addition of HClO provided

1(ClO )} as the main species but shifted due to

incorporated. The same species results by the use of H O via

peroxo species 5b²⁺after O− O splitting. Both oxo bridges

incorporation (m/z 405.5843 in Figure S18). The only

unshifted signal is m/z 349.1038, proving its assignment to

the peroxo complex 5 , which contains no solvent-based

ligand.

can be incorporated in formate, consistent with the observation

16 18

of both μ- O CH and μ- O OCH. In the H O -labeling

experiment, the ratio of H O/H₂O is 616:1, with 1 equiv of

Using the commercially available 2% H₂¹⁸O₂solutions

H₂O resulting from splitting of the O− O bond. The

increased the H O content signiﬁcantly, so that CSI-MS

excess of H O exchanges μ- O in 1a , resulting in 1d . In

measurements were not possible because of plugging of the

spray needle by strong ice formation. Therefore, we performed

experiments using 1(ClO ) obtained from bulk synthesis with

the H₂O-labeling experiment, there is still enough H O

present in solution, so that also some unlabeled 1d can be

detected.

Considering an “open core” 7 , the reaction with H₂¹⁸O₂

labeled H₂O and H₂O (see the SI for details). CSI-MS

experiments in CH CN at −40 °C on unlabeled samples

would generate 7b , whereas the reaction with H O would

showed peaks for 1³at m /z 237.0711 and for {1(ClO )} at

IV 16

result in [(susan){Fe ( O)(μ- O)Fe ( O)}] (7a ).

Under the highly probable assumption that only the terminal

oxo ligands can be incorporated into the formato bridge, one

would expect the formation of only μ-HC O O (1b ) from

the reaction with H and μ-HC O

reaction with H O. The formation of other observed

m/z 405.0814 (Figure S19). Samples prepared with H₂¹⁸O₂

2% in H₂O) showed additional peaks at m/z 237.7384 and

06.0827 corresponding to the incorporation of one

(

18 16

Figure S20a −c). MS/MS experiments demonstrated that this

(1a ) from the

O was incorporated only in formate because, after formate

isotopically labeled products through the “open core” pathway

would require a scrambling between terminal and bridging oxo

ligands.

release, only a μ- O species was present, whereas after release

of the oxo bridge, both μ- O OCH and μ- O CH were

detected (Figure S20d,e ). Note that the ligand susan is

monodeprotonated upon the release of formate and doubly

deprotonated upon release of the oxo dianion. Thus, it can be

concluded that stable dinuclear species exist with the highest

SUMMARY AND CONCLUSIONS

We have carefully studied the catalytic oxidation of CH OH

■

overall charge of 3+. In summary, the reaction with H O in

with H O to HCHO, HCO H, and CO by a dinuclear iron

the presence of excess H O results in the formation of

Fe(μ- O)(μ- O OCH)Fe} (1b ) and {Fe(μ- O)-

complex. The electrocatalytic oxidation of CH OH to CO is

18 16

42,43

{

the basis for the direct CH OH fuel cell.

The

(μ- O CH)Fe} (1d ; Figure 5, left).

homogeneous catalytic oxidation of CH OH to HCHO has

Samples prepared with H O in H₂¹⁶O dissolved in H₂¹⁸O

ﬁnal H₂O:H O = 26:1) provided in the addition to peaks

with only O at m/z 237.0720 and with the incorporation of

one O at m/z 237.7392 (Figure S21a ) and also 1 with two

O incorporated at m/z 238.4073 (Figure S21b; analogous

results for {1(ClO )} in Figure S21c ), which accounts for the

been established for copper(II) phenoxyl radical models of the

44−47

(

enzyme galactose oxidase.

The application of homoge-

neous Fe catalysts for the oxidation of CH OH has rarely been

reported. Lecomte and Bolm reported the combination of

[Fe(acac) ] with H O to oxidize CH OH to HCHO that is

used in situ for an Aldol coupling.

fact that oxygen from water was incorporated as an oxo atom

in the high-valent oxidant Y. In the CSI-MS/MS experiments

To the best of our knowledge, we have in detail investigated

for the ﬁrst time the homogeneous catalytic oxidation of

Figure S21d ), we detected the formato-bridged μ- O OCH

CH OH by a high-valent diiron complex and obtained

and μ- O CH species (resulting from removal of an oxo

bridge; Figure S21e ), as well as the oxo-bridged μ- O and

μ - O species (resulting from removal of a formate bridge;

Figure S21f ). Thus, the four diﬀerently labeled species 1d ,

mechanistic insight into the nature of the active oxidant and

the inﬂuence of the protonation state. The complex 4 reacts

with H O to the peroxo complex 5 . Without protonation,

−

exchange of the CH O ligands is slow, while its protonation

1 6

3 +

1 8

{

(

Fe(μ- O)(μ- O CH)Fe} (1a ), {Fe(μ- O)-

accelerates exchange even at −80 °C. Furthermore, the

protonation state aﬀects the half-life of the peroxo

intermediate: without protonation, the μ-peroxo intermediate

converts slower to the active oxidant Y than in the protonated,

16 18

μ- O OCH)} (1c ), and {Fe(μ- O)(μ- O OCH)Fe}

(

1b ) were formed as the parent species.

These experiments clearly show that the μ-oxo atom, as well

6,28,41

as one oxygen from peroxide (obtained after O−O bond

presumably a μ-hydroperoxo, form.

The highly reactive

splitting), is able to be transferred to CH OH and

oxidant Y initiates the oxidation of CH OH. O-labeling

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

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experiments demonstrate that Y contains two distinguishable

reactive oxygen atoms from its peroxo precursor: one from the

μ-oxo bridge and one from the μ-peroxo bridge. This is in

contrast to sMMO, where both oxygen atoms of the μ-peroxo

Notes

The authors declare no competing ﬁnancial interest.

ACKNOWLEDGMENTS

■

bridge in P are reactive in Q. The observed isotopic labeling

T.G. acknowledges the DFG and Bielefeld University of

ﬁnancial support. I.I.-B. thanks the DFG for support through

Project IV 80/13-1.

can be explained with a “closed” {Fe (μ-O) Fe } core active

species 6 , while its formulation as an “open” {Fe (O)(μ-

O)Fe (O)} core 7 requires a scrambling between terminal

and bridging oxo ligands, which was formulated in a related

REFERENCES

■

system by Kodera et al. In order to better distinguish

between the “closed” or “open” core nature of oxidant Y,

further studies are needed. We will vary the substitution

pattern of the ligand susan, in analogy to the work with tpa-

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ASSOCIATED CONTENT

sı Supporting Information

The Supporting Information is available free of charge at

https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c02698.

■

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CCDC 1986459 contains the supplementary crystallographic

data for this paper. These data can be obtained free of charge

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AUTHOR INFORMATION

Corresponding Authors

■

(9) Shu, L.; Nesheim, J. C.; Kauffmann, K.; Munck, E.; Lipscomb, J.

Ivana Ivanovic-

Pharmazie, Friedrich-Alexander-Universitat

Erlangen, Germany; Department Chemie, Ludwigs-

Maximilians-Universitat, 81377 Munchen, Germany ;

Email: Ivana.Ivanovic-Burmazovic@cup.uni-muenchen.de

Thorsten Glaser − Fakultat fur Chemie, Universitat Bielefeld,

D-33615 Bielefeld, Germany; orcid.org/0000-0003-2056-

701; Email: thorsten.glaser@uni-bielefeld.de

Burmazovic

− Department Chemie und

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Erlangen-Nurnberg,

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Soluble Methane Monooxygenase. J. Am. Chem. Soc. 2017, 139,

Authors

Thomas Philipp Zimmermann − Fakultat

Universitat Bielefeld, D-33615 Bielefeld, Germany

Nicole Orth − Department Chemie und Pharmazie, Friedrich-

Alexander-Universitat Erlangen-Nurnberg, Erlangen, Germany

Sebastian Finke − Fakultat fur Chemie, Universitat Bielefeld, D-

3615 Bielefeld, Germany

Thomas Limpke − Fakultat

D-33615 Bielefeld, Germany

Anja Stammler − Fakultat fu

3615 Bielefeld, Germany

Hartmut Bogge − Fakultat

3615 Bielefeld, Germany

Stephan Walleck − Fakultat

D-33615 Bielefeld, Germany

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