Site-selective formation of an iron(iv)-oxo species at the more electron-rich iron atom of heteroleptic μ-nitrido diiron phthalocyanines

Article abstract of DOI:10.1039/c5sc01811k

Iron(iv)-oxo species have been identified as the active intermediates in key enzymatic processes, and their catalytic properties are strongly affected by the equatorial and axial ligands bound to the metal, but details of these effects are still unresolved. In our aim to create better and more efficient oxidants of H-atom abstraction reactions, we have investigated a unique heteroleptic diiron phthalocyanine complex. We propose a novel intramolecular approach to determine the structural features that govern the catalytic activity of iron(iv)-oxo sites. Heteroleptic μ-nitrido diiron phthalocyanine complexes having an unsubstituted phthalocyanine (Pc1) and a phthalocyanine ligand substituted with electron-withdrawing alkylsulfonyl groups (PcSO₂R) were prepared and characterized. A reaction with terminal oxidants gives two isomeric iron(iv)-oxo and iron(iii)-hydroperoxo species with abundances dependent on the equatorial ligand. Cryospray ionization mass spectrometry (CSI-MS) characterized both hydroperoxo and diiron oxo species in the presence of H₂O₂. When m-CPBA was used as the oxidant, the formation of diiron oxo species (PcSO₂R)FeNFe(Pc1)=O was also evidenced. Sufficient amounts of these transient species were trapped in the quadrupole region of the mass-spectrometer and underwent a CID-MS/MS fragmentation. Analyses of fragmentation patterns indicated a preferential formation of hydroperoxo and oxo moieties at more electron-rich iron sites of both heteroleptic μ-nitrido complexes. DFT calculations show that both isomers are close in energy. However, the analysis of the iron(iii)-hydroperoxo bond strength reveals major differences for the (Pc1)FeN(PcSO₂R)Fe^IIIOOH system as compared to (PcSO₂R)FeN(Pc1)Fe^IIIOOH system, and, hence binding of a terminal oxidant will be preferentially on more electron-rich sides. Subsequent kinetics studies showed that these oxidants are able to even oxidize methane to formic acid efficiently.

Full text of DOI:10.1039/c5sc01811k

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Site-selective formation of an iron(IV)-oxo species at the more
electron-rich iron atom of heteroleptic -nitrido diiron
phthalocyanines
Received 00th January 20xx,
Accepted 00th January 20xx
Ümit İşci,a Abayomi S. Faponle,b Pavel Afanasiev,c Florian Albrieux,d Valérie Briois,e Vefa Ahsen,a
DOI: 10.1039/x0xx00000x
Fabienne Dumoulin,*a Alexander B. Sorokin,*c and Sam P. de Visser*b
www.rsc.org/
Iron(IV)-oxo species have been identified as the active intermediates in key enzymatic processes, and their catalytic
properties are strongly affected by the equatorial and axial ligands bound to the metal, but details of these effects are still
unresolved. In our aim to create better and more efficient oxidants of H-atom abstraction reactions, we have investigated
a unique heteroleptic diiron phthalocyanine complex. We propose a novel intramolecular approach to determine the
structural features that govern the catalytic activity of iron(IV)-oxo sites. Heteroleptic -nitrido diiron phthalocyanine
complexes having an unsubstituted phthalocyanine (Pc1) and a phthalocyanine ligand substituted with electron-
withdrawing alkylsulfonyl groups (PcSO2R) were prepared and characterized. A reaction with terminal oxidants gives two
isomeric iron(IV)-oxo and iron(III)-hydroperoxo species with abundances dependent on the equatorial ligand. Cryospray
ionization mass spectrometry (CSI-MS) characterized both hydroperoxo and oxo diiron species in the presence of H2O2.
When m-CPBA was used as the oxidant, the formation of diiron oxo species (PcSO2R)FeNFe(Pc1)=O was also evidenced.
Sufficient amounts of these transient species were trapped in the quadrupole region of the mass-spectrometer and
underwent a CID-MS/MS fragmentation. Analyses of fragmentation patterns indicated a preferential formation of
hydroperoxo and oxo moieties at more electron-rich iron sites of both heteroleptic -nitrido complexes. DFT calculations
show that both isomers are close in energy. However, the analysis of the iron(III)-hydroperoxo bond strength reveals
major differences for the (Pc1)FeN(PcSO2R)FeIIIOOH system as compared to (PcSO2R)FeN(Pc1)FeIIIOOH system, and, hence
binding of terminal oxidant will be preferentially on more electron-rich sides. Subsequent kinetics studies showed that
these oxidants are able to even oxidize methane to formic acid efficiently.
heme monoxygenases, like the cytochromes P450, whereas in
the structurally analogous peroxidases the detoxification of
hydrogen peroxide to water is catalyzed.2 By contrast, non-
Introduction
High-valent iron(IV)-oxo species are key intermediates in
biology and involved in essential oxidation processes in
Nature.1 Metalloenzymes often include an iron(IV)-oxo active
species in their catalytic cycle, however, large variations in
chemical reactivity and biochemical properties are observed
due to the iron coordination environment. For instance,
iron(IV)-oxo intermediates contribute as the active oxidant in
heme iron dioxygenases utilize an iron(IV)-oxo active species in
their catalytic cycle to transfer an oxygen atom to substrates
with functions ranging from DNA base repair and the
biosynthesis of antibiotics.3 Why nature has this large variety
of metalloenzymes that are structurally and functionally
diverse is an important question that remains the key focus of
extensive research. The differences in chemical reactivity
between heme and non-heme iron(IV)-oxo species have been
identified as originating from the metal-substrate orbital-
interactions and the electron-transfer pathways during the
chemical reaction.4 In order to understand the sophisticated
chemistry of iron(IV)-oxo intermediates in chemistry and
biology, many studies have been devoted to the preparation
and spectroscopic characterization of these short-lived species
using enzymes5 as well as model complexes.6–9 A great variety
of mononuclear high-valent iron(IV)-oxo species on the
porphyrin,6 corrole,7 phthalocyanine,8 and non-heme ligand9
platforms have been prepared at low temperatures and
characterized. These studies have given detailed insight into
the mechanisms of oxygen atom transfer under difficult
a.Gebze Technical University, Department of Chemistry, P.O. Box 141, Gebze, 41400
Kocaeli, Turkey.
b.Manchester Institute of Biotechnology and School of Chemical Engineering and
Analytical Science, The University of Manchester, 131 Princess Street, Manchester
M1 7DN, United Kingdom.
c. Institut de Recherches sur la Catalyse et l’Environnement de Lyon (IRCELYON),
UMR 5256, CNRS-Université Lyon 1, 2, av. A. Einstein, 69626 Villeurbanne Cedex,
France.
d.Centre Commun de Spectrométrie de Masse UMR 5246, CNRS-Université Claude
Bernard Lyon 1, Université de Lyon, Bâtiment Curien, 43, bd du 11 Novembre,
69622 Villeurbanne Cedex, France.
e. Synchrotron Soleil, L’orme des merisiers, St-Aubin, 91192 Gif-sur-Yvette, France.
Electronic Supplementary Information (ESI) available: Experimental and
computational details, Cartesian coordinates, characterization data, and ESI-MS
spectra. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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catalytic conditions, which in Nature happens under mild [(Pc)FeIVNFeIV(Pc+•)=O]. The addition of H2O2 to
Journal Name
-VnieitwriAdrtoicledOiinrloinne

tBu
conditions. The studies have led to the development of series tetra-t-butylphthalocyanine
8
, [(PctBu)FeNDFeO(IP: 1c0.10)3]9(/SCc5hSeCm01e8111)K,
of bio-inspired chemical systems for selective oxidations, resulted in the formation of the hydroperoxo complex,
mostly based on mononuclear iron complexes.10
[(PctBu)FeIVNFeIII(PctBu)-OOH], followed by the generation of the
Until recently, the research involving binuclear complexes was diiron-oxo species, [(PctBu)FeIVNFeIV(PctBu+•)=O], as identified by
mainly focused on non-heme diiron, due to its relationship to electrospray ionization-mass spectrometry (ESI-MS) using
the enzyme soluble methane monooxygenase,11 although labelled H218O2.14a With the tetraphenylporphyrin (TPP)
some studies have been reported on oxo and hydroxo bridged platform, we were also able to prepare the corresponding oxo
diiron porphyrin complexes.12 One particular ligand system for complex [(TPP)FeIVNFeIV(TPP+•)=O] with m-CPBA oxidant at –
iron that has gained increasing attention in recent years are 90C, and characterize it by ESI-MS, low-temperature UV-vis,
those based on phthalocyanine ligands, which specifically electron paramagnetic resonance (EPR) and Mössbauer
showed high reactivity in oxidation reactions under mild spectroscopic techniques.21 It should be noted that high-valent
conditions.13
diiron oxo species on the phthalocyanine and porphyrin
platforms show superior oxidizing properties compared with
mononuclear counterparts, but the origin of these reactivity
differences is still poorly understood.
The macrocyclic
-nitrido diiron phthalocyanine provides a
unique possibility to probe the differences in chemical
properties of the two iron centers within the same molecule.
The question, therefore, is: How do the functional properties
of the iron(IV)-nitrido group affect the catalytic functions of
the iron(IV)-oxo moiety and how can these be modified? In
order to answer these questions, we decided to synthesize
localized structures with non-equivalent iron sites, where each
of the iron atoms is placed into macrocyclic ligands with very
different electronic properties. Our approach opens interesting
possibilities but also leads to deeper insight into the formation
of the active species responsible for the catalysis. In particular,
since such complexes with localized structure have two
possible sites where an iron(IV)-oxo species can be formed.
Therefore, we designed unique chemical complexes that are
based on the same phthalocyanine ligand structure, but
exhibiting different electronic properties due to different
substitution patterns. In particular, we created structures with
one macrocyclic ligand with an electron-poor phthalocyanine
group with four or eight alkylsulfonyl substituents, whereas
the other macrocyclic ligand contained a more electron-rich
unsubstituted phthalocyanine macrocycle. We report here the
first synthesis and characterization of this series of unique
Scheme 1. Iron(IV)-oxo species of
(top) and structures of the complexes used in this work (bottom).
-nitrido diiron phthalocyanine complexes
Thus,
-nitrido diiron phthalocyanines ([(Pc)FeNFe(Pc)],
Scheme 1), show surprising catalytic properties, and were
found to be able to hydroxylate methane and benzene at near-
ambient conditions,14 but also defluorinate perfluorinated
compounds under oxidative conditions.14d None of these
reactions are native to the cytochrome P450 enzymes.
heteroleptic structures (3 and 7, Scheme 1), with alkylsulfonyl
electron-withdrawing at the periphery of the Pc moiety. In
addition, computational modelling was performed on the
abbreviated system 9 with either oxo (9=O) or hydroperoxo (9-
OOH) bound. The studies show that the electron-withdrawing
character of the equatorial ligand, i.e. the phthalocyanine
moiety, affects the strength of the iron(III)-hydroperoxo bond,
and, thereby determines the site where the oxo group will
bind. The work reveals the subtleties of ligand binding on the
chemical and ultimately catalytic properties of metal-oxo
complexes. The ESI-MS and DFT results suggest the higher
catalytic activity for more electron-rich iron sites. This
prediction was confirmed in the catalytic heterogeneous
-Nitrido diiron phthalocyanines belong to the class of stable
binuclear single atom bridged complexes that are known to
bind metal ions in high oxidation states,15 although the nature
of the reactivity patterns was determined on whether
electron-withdrawing or electron-donating substituents on the
periphery of the phthalocyanine moieties were added.16,17
These complexes were shown to give a large versatility of
chemical and catalytic properties and can adopt FeIIIFeIV and
FeIVFeIV oxidation states.18–20 The
-nitrido diiron macrocyclic
complexes were found to be able to activate oxygen-atom
oxidation of methane with H2O2 using three -nitrido diiron
phthalocyanine complexes with different substitution
patterns.
donors, such as H2O2 and m-chloroperbenzoic acid (m-CPBA),
to
form
a
high-valent
diiron-oxo
species,
i.e.
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DOI: 10.1039/C5SC01811K
Scheme 2. Preparation of heteroleptic -nitrido alkylsulfonyl phthalocyaninato iron(II) 3 and 7.
making monomeric iron(III) complexes, which are then mixed
in a solution with sodium azide and -chloronaphthalene to
form the -nitrido diiron complexes.
Results and Discussion


Synthesis and characterization of diiron complexes
The synthesis of alkylsulfonyl substituted phthalonitriles
(Scheme 2) is achieved through the oxidation of the
corresponding alkylthio substituted derivatives: 1,2-dicyano-
Tetrapyrrolic ligands, such as porphyrin and phthalocyanine,
can be used to form dimeric complexes.18 Heteroleptic
complexes of
-nitrido tetrapyrroles can be formed of two
4,5-bis (hexylsulfonyl) benzene
procedure23 from
with H2O2 in acetic acid at 79% yield.
Iron(II) octahexylsulfonyl phthalocyanine is obtained by
heating in an o-dichlorobenzene: dimethylformamide (3:1)
mixture commonly used for alkylsulfonyl phthalonitriles24 in
the presence of FeCl2 (Scheme 2). The preparation of -nitrido
diiron phthalocyanines is achieved by refluxing iron(II)
phthalocyanine in -chloronaphthalene in the presence of
NaN3.25 Such a reaction applied to an equimolar mixture of
two differently substituted phthalocyanines results in
5 is prepared by a modified
chemically different ligands. It should be emphasized that the
the iron sites of the Fe(III)Fe(IV) unit are not necessarily
inequivalent in terms of the oxidation state,18,22 because the
influence of the different ligand field strength of the two
macrocycles on iron ions is overcome by the mediated action
of the nitrogen bridging atom.22b Alternatively, heteroleptic
complexes based on the same tetrapyrrolic ligand type but
with different substitution patterns, i.e. with different
electronic properties,18 can provide access to localized
structure with two different iron sites. Heteroleptic structures
with different ligand features can be prepared by initially
4
6
5


a
mixture of the two corresponding homoleptic complexes as
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Journal Name
well as the targeted heteroleptic derivative. To restrict the low-spin complex with equivalent iron centersVaiesw AcrtoicnlecOenrlnines
amount and yield of possible by-products, the heteroleptic
both geometry and electronic orbital manifold.15
DOI: 10.1039/C5SCE0X18A1F1KS
nitrido dimers and were prepared by using a 10-fold excess spectra (Fig 1) of and demonstrate striking similarity of iron
of unsubstituted iron phthalocyanine relative to the coordination in the two complexes, which is characteristic of a
monomeric alkylsulfonyl phthalocyaninatoiron(II)
-
3
7
3
8
1
2
or
6
,
linear Fe–N–Fe unit with Fe–N distances of 1.65 Å.
respectively. These conditions allow the formation of the
desired heteroleptic complexes (Scheme 2) together with the
homoleptic unsubstituted derivative, which are separated by a
procedure that starts with the evaporation of the
-
chloronaphthalene, addition of dichloromethane, followed by
filtration. Silica gel column chromatography afforded the
desired heteroleptic complexes
52% based on and , respectively). The lower yield of
respect to is attributed to a steric hindrance of the
octasubstituted ligand
The successful preparation of and 7 was confirmed by FT-IR,
3
and
7
in high yields (64 and
2
6
7
with
3
6
.
3
UV-Vis and EPR spectroscopy and ESI-MS studies. The ESI-MS
spectra of these mixed ligand complexes exhibit prominent
molecular peaks corresponding to the expected values of the
molecular ion: m/z = 1943.4 [M]+ for
3
and m/z = 2335.6 [M]+
Fig 1. EXAFS spectra of the solid samples of heteroleptic complex
homoleptic complex 8.
3 and
for
isotopic patterns fit the theoretical simulations perfectly and
confirm the proposed structures. The IR spectra of and
7 (Figs S1 and S5, Electronic Supporting Information). Their
3
7
No significant differences in the interatomic distances of the
heteroleptic complex with respect to the homoleptic
complex can be inferred from the analysis of the EXAFS
spectra (Fig 1) in either k- or R-space. The only detectable
difference between and is the somewhat larger intensity of
the Fourier transfer (FT) module peaks of for the first
show characteristic anti-symmetric Fe-N–Fe stretch vibrations
at 930 and 929 cm–1, respectively (Figs S2 and S6, Electronic
Supporting Information), which are close to those observed for
the heteroleptic complex [(TPP)Fe+3.5NFe+3.5(Pc)] at 930 cm–1
and for homoleptic complex [(Pc)FeNFe(Pc)] at 915 cm–1.14–18
3
8
3
8
3
coordination shell. This is most likely due to differences in their
Debye-Waller factors, as a result of more position isomers for
X-ray absorption and emission spectroscopies
Over the past few years, synchrotron radiation core hole
spectroscopy has shown great utility to address problems
related to the oxidation state of iron in iron-containing
enzymes and biomimetic iron structures.26 In previous work,
we have successfully used X-ray absorption (XAS) and X-ray
emission (XES) methods to gain insight into oxidation and spin
8
as compared to
3. The effective disorder is therefore higher
in
8
, and manifests itself in the EXAFS spectra with increased
Debye-Waller parameters. Note that asymmetrization of the
Fe–N–Fe fragment would lead to the decrease of Fe–N–Fe
related features, as a result of weakening of the multiple
scattering effects,28 whereas the opposite is observed here.
states of
-nitrido diiron phthalocyanines and compared
Consequently, the EXAFS comparison of
symmetric Fe–N–Fe fragment in both complexes despite
differences in the ligand properties in
3 and 8 reveals a
electronic and structural properties of -carbido, -oxo and -
nitrido diiron complexes.27 To probe a non-equivalence of iron
sites in this work we performed detailed XES and XAS studies
3
.
on heteroleptic complex
3
and homoleptic complex
8 as
reference. Interestingly, the XES spectra of
3
and are virtually
8
identical in the solid phase (Fig S9, Electronic Supporting
Information), which implies that the two structures have the
same metal coordination and oxidation state. Changes to the
ligand system, therefore, appear to have had little effect on
the electronic ground state of these diiron phthalocyanine
systems.
Extended X-ray absorption fine structure (EXAFS)
In order to find out whether the different phthalocyanine rings
lead to changes in the oxidation states of the iron atoms and
the metal ligand distances, and in particular the bonds
associated with the Fe–N–Fe moiety, we compared the Fe K-
core hole spectra of complex
of the symmetric structure
3
with the corresponding spectra
. The latter compound was
Fig 2. Experimental XANES spectra of heteroleptic complex
complex . Inset – superposition of their pre-edge regions.
3 and homoleptic
8
8
extensively studied in our previous studies and proved to be a
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X-ray absorption near edge structure (XANES) studies
gas. The collision induced dissociation of the parent ion leads
to its fragmentation patterns into primary monomer units,
View Article Online
DOI: 10.1039/C5SC01811K
To gain further insight into the molecular and electronic
which provides information on their composition, and enables
structural characterization, and, in particular, will establish the
iron site of the heteroleptic diiron complex that bears the oxo
ligand. The optimal energy of the collision gas (N2) was
determined to be ~60 eV for the fragmentation of the diiron
species into monomeric units without consecutive dissociation
patterns. Fragmentation patterns of the heteroleptic
compounds (Scheme 3) should give different products,
depending on the nature of the phthalocyanine site
coordinating the iron(IV)-oxo species, whether it is electron-
rich or electron-deficient. Indeed, the analysis of the initial
fragmentation pattern provides a composition of two different
phthalocyanine species with or without oxo and/or nitrogen
ligands, which enables us to conclude whether the oxo species
is attached to the electron-deficient Fe(PcSO2R) ligand or to
the more electron-rich Fe(Pc) fragment (Scheme 3).
properties of
3 and 8, we performed a series of XANES
experiments. In contrast to the XAS, XES and EXAFS studies
reported above, the XANES studies reveal a difference
between the two structures (Fig 2). The energy values of the
pre-edge peak in the XANES spectra of
7114.7 eV, respectively. Most probably a 0.3 eV shift to higher
energy for arises due to the electron-withdrawing
substituents on the phthalocyanine scaffold. The main jump
for both compounds has a maximum derivative near 7126.1
eV. Due to complex structure of the main jump, the energies
cannot be directly compared with the same precision as pre-
edges.
3 and 8 are 7115.0 and
3
ESI-MS analysis of high-valent diiron oxo complexes
Despite the initial high oxidation state of iron, the
-nitrido
diiron phthalocyanine complexes form the high-valent iron(IV)-
oxo species readily in a reaction with active oxygen atom
donors. The formation of the iron(IV)-oxo species, therefore,
comprises of two fundamental steps: (i) coordination of the
oxygen donor to the iron and (ii) heterolytic cleavage of the O–
O bond of the peroxide unit. In the homoleptic complex both
iron sites are identical and, as such, only one isomeric iron(IV)-
oxo species can be formed. In the heteroleptic complex, by
contrast, there are, in principle, two isomeric iron(IV)-oxo
products possible (Scheme 3). The question arises then: can
non-equivalence of the iron sites in terms of their electronic
properties induce a discrimination in the formation of the
iron(IV)-oxo complex? In order to find out whether a site-
specific iron(IV)-oxo complex will be formed and what the
properties of the ligands are that determine these issues, we
performed a detailed combined ESI-MS and DFT study.
Highly sensitive mass spectrometry methods are particularly
suitable for detection and characterization of elusive short
lived active species.9e,29 In addition, advanced MS techniques
allow one to obtain valuable mechanistic information on
reaction mechanisms.30 In particular, tandem MS-MS method
can be used to analyze a composition of diiron oxo complexes.
To this aim, the molecular ion of the high-valent diiron-oxo
species is mass selected and bombarded with neutral nitrogen
Reaction of [(Pc1)FeNFe(Pc2)] (3) with oxidants
H2O2. To a ~10–6 M solution of
3 in CH3CN, 1000 equiv. of H2O2
was added at room temperature and the resulting solution
was continuously introduced into the mass spectrometer.
Along with a strong molecular peak of the initial complex
with m/z 1943.46, two signals centered at m/z 1977.46 and
1959.46 were observed that are assigned to [
+HOOH]+ and
+O]+, respectively. The mass-selected peroxo and oxo
3
3
[
3
species were further characterized by collision induced
dissociation (CID MS/MS) and the results are schematically
depicted in Figs 3 and 4.
The principal ions formed upon fragmentation of [3
+HOOH]+
(Fig 3) are ions with mass representing [M–H2O]+ at m/z
+
1959.4, [M–H2O2]+ at m/z 1943.4 and [M–SO2Ad
]
at m/z
1744.4. In addition, fragments are observed containing
monomeric phthalocyanine moieties. The abundance of
fragments with the Fe(Pc
containing N, OH and H2O2 ligands are much larger than those
with Fe(Pc ) fragments that are found in the m/z range of
1376 – 1379 and 1397. The intensity of naked [Fe(Pc
)]+ ion at
m/z 568 obtained after loss of oxygen ligands is also much
higher than that of protonated [Fe(Pc
)+H]+ ion at m/z 1362.
1) core at m/z 582 – 585 and 603
2
1
2
Scheme 3. Formation of isomeric iron(IV)-oxo complexes with heteroleptic ligands and schematic representation of its fragmentation patterns. Blue ligand:
substituted with SO2R groups. Red ligand: unsubstituted phthalocyanine.
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The exact molecular mass and isotopic distribution pattern of
+O]+ are identical to those theoretically predicted for the
[
3
diiron-oxo complex (3=O), which confirms its formation. Upon
CID MS/MS conditions, the 3=O ion behaves very similarly to
[3
+HOOH]+ (Compare Figs 3 and 4). Again, dominant peaks in
the m/z range of 568 - 600 are observed, which suggest site-
selective oxygen binding to unsubstituted phthalocyanine unit.
Fig 3. CID MS/MS spectrum of the hydroperoxo complex obtained from
3 and
H2O2. Inset: comparison of experimental (top) and simulated (bottom) isotopic
distribution of molecular peak.
Fig. 5. CID MS/MS spectrum of the oxo complex obtained from [(Pc2)FeNFe(Pc1)]
and m-CPBA. An enlarged region of the spectrum with assignment of fragments
is shown in the inset.
The molecular peak for [
ligand to give [(Pc )FeNFe(Pc
Importantly, the fragmentation of [
exclusively [Fe(Pc
)]+ ions at m/z 568, 585, 600, whereas only
minor amounts of [Fe(Pc
)]+ ions are detected at m/z 1362.
3
+O]+ at m/z 1959.46 loses the oxygen
)]+
at m/z 1943.46.
+O]+ produces almost
1
2
(3)
3
1
2
It should be noted here that fragments containing oxo ligands
were only detected at the unsubstituted, i.e. more electron-
rich, Fe(Pc
attributed to [(Pc
1
) platform. Signals centered at m/z 585 and 600 are
1
)Fe=O + H]+ and [(Pc )(N)Fe=O + 2H]+ ions
1
on the basis of exact molecular mass and isotopic distribution
of the cluster. A large signal at m/z 585 is attributed to either
[(Pc1 1
)(N)Fe=O + H+]+ or [(Pc )(N)Fe-OH]+ ion formed by
hydrogen atom abstraction from organic solvent by the oxo
species with strong oxidizing properties. As expected, all these
Fe(Pc
ligands to form naked [Fe(Pc
conditions. The analysis of the fragmentation of [
+O]+ ions suggests that high valent diiron species containing
oxo ligands preferentially bind at more electron-rich iron sites
such as Fe(Pc ).
1
) oxygen containing species lose oxygen and nitrogen
)]+ ions under CID-MS/MS
+H2O2]+ and
1
3
[
3
1
Fig 4. CID MS/MS spectrum of the oxo complex (3=O) obtained from
3 and H2O2.
Inset: comparison of experimental (top) and simulated (bottom) isotopic
distribution of molecular peak. An enlarged region of spectrum with assignment
of fragments is shown below.
M
-CPBA. The diiron oxo complex 3=O was also obtained using
m-chloroperbenzoic acid as the oxygen donor. Importantly, the
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CID-MS2 spectrum of 3=Om-CPBA shows only fragments derived
ARTICLE
View Article Online
DOI: 10.1039/C5SC01811K
Fe1 = 0.32
from the Fe(Pc ) core (Fig 5). The signals of Fe(Pc ) fragments
1
1
bearing an oxo-ligand at m/z 585 and 600 are much stronger
(Fig 5) compared to those obtained from 3=OH2O2 species (Fig
4). This suggests that the oxo species most likely can be
stabilized by acid via its coordination on the opposite iron
site.21 We have also obtained hydroperoxo- and oxo diiron
1.662 (1.653)
1.689 (1.668)
N = 0.39
species of
only Fe(Pc
7
1
using H2O2 and m-CPBA oxygen donors. Again,
Fe2 = 0.29
)
fragments with oxo-ligands are observed
(Electronic Supporting Information, Figs S10 and S11). Thus, all
CID-MS/MS results obtained with two heteroleptic complexes
29
3
and 7 and with two oxidants H2O2 and m-CPBA indicate that
Fig. 6. DFT optimized geometries of 2
9
at the B3LYP (BP86) level of theory. Bond
lengths are in angstroms and spin densities () in atomic units.
the oxo complex is preferentially formed at the more electron-
rich iron site of unsubstituted phthalocyanine ligand.
1.521
1.849
Computational studies of 9, [9=O] and [9-OOH]–


OOH = –0.16
Fe1 = –0.80
N = 1.56
To support the experimental results and gain insight into the
relative stability of
-nitrido diiron phthalocyanines with
1.887
1.758

different substitution patterns of the distal ligand, we
performed a detailed density functional theory (DFT) study on

Fe2 = 0.36
structure
adamantylsulfonyl groups are replaced by methylsulfonyl:
[(Pc )FeNFe(PcSO2Me)]. In addition, we calculated the
iron(IV)-oxo form of , i.e. [9=O], and finally the iron(III)-
9, which is an analogue of 3 whereby the
1
DE+ZPE = 0.0 kcal mol–1
9
–
2[9-OOH]A
hydroperoxo complex [9-OOH]–. Although we calculated all
structures in the lowest lying doublet, quartet and sextet spin
states, actually in all cases the doublet spin state is the ground
state and well separated from the other spin states. We,
therefore, will focus in the main text on the doublet spin state
only; all other results can be found in the Electronic Supporting
Information document.
1.520
1.852


OOH = –0.19
Fe1 = –0.75
N = 1.47
Fe2 = 0.40
1.880
1.747


We initially optimized the geometry of doublet spin
9 with
UB3LYP and UBP86 methods and the structures (Fig 6) show
only small deviations from a symmetric Fe–N–Fe core with Fe–
N distances of 1.689 (1.668) and 1.662 (1.653) Å at the B3LYP
(BP86) levels of theory. These optimized geometries agree
with the spectroscopic (EXAFS, XANES) results described above
as well as with homoleptic structures calculated previously of
1.65 Å.27b,31 Although the optimized geometry implicates a
structure that is close to symmetric, actually the minor
differences between the two Fe–N bond lengths have a
significant effect on the radical character of the two iron
DE+ZPE = +1.8 kcal mol–1
–
2[9-OOH]B
2
Fig. 7. DFT optimized geometries of
[
9-OOH] at the B3LYP level of theory. Bond
) in atomic units.
lengths are in angstroms and spin densities (

Subsequently, we added a hydroperoxo group to form [9-
OOH]– and reoptimized all geometries in the gas phase, see Fig
7.
[HOO(Pc
[(Pc
We
1
calculated
two
isomers,
namely
atoms. Thus, the iron of the Fe(Pc1) group has a spin of 0.32,
–
)FeIIINFeIV(PcSO2Me)]–, designated [9-OOH]A , and
whereas the other iron atom has a spin of only 0.29. This small
change in radical character between the two iron atoms, due
to the electron-withdrawing/donating groups attached to the
phthalocyanine ligands may be responsible for the preferred
site of hydrogen peroxide binding. In particular, the larger
–
1
)FeIVNFeIII(PcSO2Me)OOH]– or
[
9-OOH]B . Similarly to
previous studies on iron(III)-hydroperoxo porphyrin complexes
of mononuclear iron systems, the doublet spin state is the
ground state in all cases.32 This doublet spin state is formed
from the antiferromagnetic coupling of a triplet spin iron(IV)-
nitrido group with an unpaired electron on the iron(III)-
hydroperoxo group. Although the energy gap between the two
structures is small, the most stable isomer is structure [9-
radical character of the Fe(Pc1) group will favour the binding
of an active oxidant over the Fe(PcSO2Me) group.
–
A
–
OOH
]
by 1.8 kcal mol–1 over [9-OOH]B . Therefore, the
iron(III)-hydroperoxo is preferentially bound to the site with
electron-donating substituents attached to the phthalocyanine
manifold. This is a surprising result as previous computational
and experimental studies found very little effect, for instance,
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ARTICLE
Journal Name
of meso-substitution of porphyrin rings on the electron affinity effect of desymmetrization of the diiron unit. However, the
View Article Online
of the iron(IV)-oxo group.33 Nevertheless, the stability CID-MS/MS data on [3=O] clearly indicate the preferential
DOI: 10.1039/C5SC01811K
–
–
difference of
experimental MS results described above that more i.e. unsubstituted, phthalocyanine unit (Pc
fragmentation is found from the [9-OOH same trend was observed with either heteroleptic dimer
– isomer.
and and too was found to be independent on the nature of the
[
9-OOH
]
versus
[
9-OOH
]
confirms the formation of an iron(IV)-oxo species at the more electron-rich,
). Noteworthy, the
or 7
A
B
1
]
3
A
–
The group spin densities reported in Fig 7 for [9-OOH
]
A
–
[
9-OOH
]
show some critical differences between the two oxygen donor, i.e. H2O2 or m-CPBA.
B
structures. Thus, the iron(III)-hydroperoxo group has larger To find out, whether there are stability differences for
radical character on the metal when it has a ligand with nitrido diiron-oxo complexes with heteroleptic ligand systems
electron-donating substituents (Pc ) than one with electron- as well, we decided to do an additional DFT study into the two
withdrawing substituents (PcSO2Me): Fe1 = –0.80 for [9-
9=O] isomers, namely [O=FeIV(Pc )NFeIV(PcSO2Me)] or [9=O
Fe1 = –0.75 for [9-OOH]B . The same is true for the and [FeIV(Pc )NFeIV(PcSO2Me)=O] or [9=O]B. The structures of
iron(IV)-nitrido group that sees the spin density polarize more 9=O]A and [9=O]B were calculated with B3LYP and BP86. The
towards the iron with the Pc ligand rather than the PcSO2Me B3LYP and BP86 optimized structures show dramatic
-
1
[
1
]
A
–
OOH
]
– and

1
A
[
1
ligand. Therefore, electron-withdrawing substituents on the differences in chemical structure but follow the same trends
phthalocyanine scaffold create metal centers with lesser upon adding substituents to one of the phthalocyanine
radical character and as such should be less reactive.
In summary, the computational results implicate preferential for structure [9=O
scaffolds. Firstly, the iron-oxo bond is short with B3LYP (1.647Å
and 1.652Å for structure [9=O]B), which
]
A
binding on the iron center with electron-donating substituents implicates an iron(IV)-oxo double bond. These values match
by a few kcal mol–1, however, it is not ruled out that a mixture computational and experimental measurements of
of isomers will be formed in the process dependent on mononuclear iron(IV)-oxo complexes of porphyrin systems
temperature, pressure, solvent environment etc. Indeed, the excellently.5–9,36 Furthermore, the iron(IV)-oxo bond length
mass spectra show the presence of both type
complexes as major and minor species, respectively.
A
and type
B
drops by 0.005 / 0.004Å at B3LYP / BP86 level of theory when
electron-withdrawing substituents are added at a distance of
High-valent iron complexes bearing iron-oxygen5–9 or iron- more than 8Å from the iron center in the equatorial plane.
nitrogen34 multiple bonds have been well-documented in the Consequently, a significant difference in iron-oxo bond length
literature as active species involved in a variety of oxidative is obtained between structures [9=O]A and [9=O]B, which leads
transformations. In contrast, high-valent iron complexes to stability differences and may be the primary reason for the
containing both oxo and nitrido/imido ligands are rare entities. difference in stability between doublet [9=O
] and [9=O]
A B

-Nitrido diiron macrocyclic complexes are particularly structures. A change of this magnitude was not observed
interesting since they combine this rare structural feature, previously in meso-substituted iron porphyrins.33 Therefore,
which results in remarkable catalytic properties.13,14,21 These
phthalocyanines are more sensitive to substitution patterns on
-
nitrido diiron macrocyclic complexes generally contain the periphery of the ligand system and this has a direct effect
equivalent iron sites despite the fact that both metals formally on a generated iron(IV)-oxo species.
have a different oxidation state, i.e. FeIIIFeIV.18 On the other To establish the origin of the hydroperoxo binding to
hand, studies on related
-oxo/-hydroxo diiron porphyrin [(Pc1)FeNFe(PcSO2Me)], we decided to calculate the bond
–
complexes show that they often have non-equivalent iron dissociation energy (BDE) of the hydroperoxo unit in [9-OOH
]
A
–
sites, whereby their oxidation states are very sensitive to and [9-OOH
]
based on Eq 1. The calculated values for both
B
structural and environmental perturbations.12,35 This complexes are given in Fig 8, where we bisected the BDEFeOOH
delocalized structure retains even in heteroleptic porphyrin- into different contributions as explained below. Of course, the
phthalocyanine dimers.22b To probe the non-equivalence of BDEFeOOH difference between [9-OOH
]
and [9-OOH
]
is the
B
–
A
–
iron sites in the heteroleptic
complexes we applied XAS and XES techniques. The XES
spectra of the heteroleptic and reference homoleptic

-nitrido diiron phthalocyanine same as the stability difference reported in Fig 7.
3
8
[
9-OOH
]
–  + OOH– + BDEFeOOH
9
(1)
complexes are practically the same, which indicates little or no
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Chemical Science
View Article Online
DOI: 10.1039/C5SC01811K
Chemical Science
ARTICLE
Fig. 8. Effect of the axial ligand and second phthalocyanine group on the binding strength of the hydroperoxo moiety. All values are in kcal mol–1
.
Subsequently, we removed the phthalocyanine group of the To check the conclusions of ESI-MS and computational studies
–
N=FeIV(Pc) moiety and replaced it by (NH3)2(NH2 )2 with these on the influence of the structure of
-nitrido diiron species on
nitrogen atoms in the same position as the nitrogen atoms of the catalytic properties, we have tested homoleptic complexes
t
the phthalocyanine group. A single point calculation for these [FePc(SO2 Bu)4]2N, (FePc)2N and [FePc(tBu)4]2N (
8
) in the
–
–
modified structures for
effect of the second Pc unit on the BDE values for Eq 1, EPc, silica (loading = 20
namely through stacking interactions. As can be seen, the the heterogeneous oxidation of methane was performed in
9
, [9-OOH
]
and [9-OOH]
A B
gives the oxidation of methane. The complexes were supported onto

mol g–1, specific surface = 200 m2 g–1) and
-
size and shape of the second Pc group has a major impact on water containing 75 mM H2SO4 at 60°C (Table 1).
the BDEFeOOH value, even though this bond is at a distance of With all the catalysts, methane was efficiently oxidized to
well over 4Å. Thus, the BDEFeOOH is strongly increased for the formic acid with 88 – 97% selectivity. Methanol was detected
(PcSO2Me)FeOOH system as compared to the (Pc
H
)FeOOH by GC-MS in trace amounts and formaldehyde is readily
oxidized under the reaction conditions. Interestingly, with
system by more than 20 kcal mol–1.
In a final set of calculations, we removed the N=FeIV(Pc) unit growth of the electron-donating properties of phthalocyanine
t
altogether and replaced it by a point charge. Again a single ligand along the series [FePc(SO2 Bu)4]2N
<
(FePc)2N
<
point calculation was performed to determine the relative [FePc(tBu)4]2N the values of total turnover numbers (
BDEFeOOH values using Eq 1. These values establish the products/ mol of catalyst) strongly increase: 32.1
quantum mechanical effect (EQM) of the axial ligand upon the 223.4. These turnover numbers reflect the difference in O–H
Fe–OOH binding energy. Thus, the axial N=FeIV(PcSO2Me
bond strength of iron(III)-hydroxo complexes with different

mol of

 102.9 
)
group gives a quantum mechanical effect that is dominated by phthalocyanine groups. Thus, previously we showed that the
the presence of the PcSO2Me interaction with the rest of the rate constant of hydrogen atom abstraction reactions
system and has little contribution from the FeIV=N moiety. By correlates linearly with the O–H bond dissociation energy of
contrast, the removal of the N=FeIV(Pc ) group has a major the corresponding iron(III)-hydroxo complex formed.37 In
H
effect on the BDEFeOOH value and the system is considerably agreement with the ESI-MS and DFT results, the
-nitrido
stabilized. Clearly, the equatorial ligands have a major dimer on the unsubstituted phthalocyanine platform was 3
contribution towards the binding of hydroperoxo groups to an times more active than the complex with alkylsulfonyl
iron scaffold and strengthen its bonding. This further shows substituents. Moreover, further increase of the electron
that electron-withdrawing and electron-donating substituents density at Fe sites led to significant gain in the catalytic
can be used to manipulate the binding site of (hydro)peroxo activity. The [FePc(tBu)4]2N complex bearing donating alkyl
moieties, and affect their stability and ultimately their catalytic substituents showed an excellent performance in the mild
properties.
methane oxidation providing a very high turnover number of
223.
Comparison of µ-nitrido diiron complexes in the oxidation of
methane by H2O2
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spectrometer, equipped with a cold spray ionization source
with a spray voltage of 5 kV. The temperature of the spray gas
Table 1. Heterogeneous oxidation of methane by H2O2 catalyzed by -nitrido diiron
View Article Online
DOI: 10.1039/C5SC01811K
phthalocyanine complexes.a
was –30°C and that of the dry gas was –5°C. The solutions of
Entry
Catalyst
TONb HCOOH, mol
CH2O, mol
7.4
the complexes (10–6 M) in acetonitrile in the presence of 1000
1
2
3
[FePc(tBu)4]2N-SiO2
(FePc)2N-SiO2
223.4
102.9
32.1
216.0
90.0
28.6
equiv. of oxidant were introduced into the gas flow at 180 L
12.9
3.5
h–1. In experiment with H2O2 oxidant, the reaction mixtures
were prepared and incubated for 5 min at room temperature.
The m-CPBA oxidant was added to the frozen complex solution
in acetonitrile and the sample was introduced immediately
after melting. All mass spectra were recorded in the positive
ion mode.
t
[FePc(SO2 Bu)4]2N-SiO2
a Reaction conditions: 2 mL of 75 mM H2SO4, 50 mg of catalyst containing 1 mol
of the complex, 32 bar methane, 685 mol H2O2, 60°C, 20 h. b TON - turnover
number, mol of products/ mol of catalyst.
Conclusion
The molecular ions (M+) of the oxo and peroxo diiron
phthalocyanine species observed in the regular MS experiment
cannot be trapped in the quadrupole region due to the
In addition to remarkable catalytic properties exemplified by
mild oxidation of methane and unprecedented activation of
the aromatic C–F bonds under oxidative conditions,14 diiron
macrocyclic platforms provides novel, previously unexplored
possibilities to examine fine mechanistic details. In this work,
two diiron phthalocyanine complexes with electronically
different iron sites have been synthesized and used for the
preparation of high-valent diiron oxo active species possessing
powerful oxidizing ability. Such a construction provides direct
intra-molecular approach to assess the reactivity of iron sites
in binuclear complexes. Combined EXAFS, XANES, ESI-MS and
DFT studies show that the hydroperoxo oxidant will
preferentially bind on the more electron-rich iron site, which
will then also be the place where the oxo species is formed.
The results of this study are instructive for the development of
formation of multimers by
-stacking interactions. To
overcome this problem, a low activation of ions during
transmission through the ion funnels was applied by In Source
Collision Induced Dissociation (ISCID) at 20 eV, which enabled
us to do MS/MS measurements. This activation allowed us to
mass select the oxo and peroxo diiron phthalocyanine species
in the quadrupole part of the mass spectrometer. The collision
energy applied in the collision cell was about 60 eV and the
collision gas was nitrogen.
Materials
Solvents were dried and distilled according to published
procedures.38 Hydrogen peroxide (35%) was obtained from
Sigma-Aldrich. m-Chloroperbenzoic acid (m-CPBA) purchased
from Sigma-Aldrich with 85% peroxide content was
-nitrido diiron catalysts. Since the formation of diiron oxo
species occurs at the electron-rich site of the dimer, complexes
bearing electron-donating groups might provide better
catalytic properties. This prediction was confirmed in the
catalytic oxidation of methane by H2O2 in aqueous solution
recrystallized
from
pentane
),39
),40 1,2-dicyano-4,5-bis (hexylthio)
prior
to
use.
Phthalocyaninatoiron(II)
phthalocyaninatoiron(II) (
(1
tetra-(adamantylsulfonyl)
2
benzene (4 ,
),41 homoleptic complex 8 14a (FePc)2N,25 and
using
-nitrido diiron complexes supported by different
t
[FePc(SO2 Bu)4]2N,16 were prepared according to literature
phthalocyanine ligands. Indeed, the catalyst with electron-
donating alkyl substituents provided a remarkably high TON of
223 compared with TON of 32 obtained using the counterpart
with electron-withdrawing properties. Based on the results of
this study, the further development of the bio-inspired
catalysts with improved catalytic properties for challenging
reactions can be envisaged.
protocols.
1,2-DICYANO-4,5-BIS(N-HEXYLSULFONYL)BENZENE (5). 1,2-
Dicyano-4,5-bis(hexylthio)benzene (
4) (1.5 g, 4.16 mmol) was
stirred in acetic acid (50 mL) at 90 C, and subsequently a 33%

solution of hydrogen peroxide (23 mL) was added in 1 mL
portions over 4 h. The resulting mixture was allowed to cool to
room temperature and stirred overnight. The resulting white
precipitate was collected by filtration, washed with water and
Experimental
crystallized from ethanol (30 mL) to give
5
as a white powder.
Anal. calcd. for
General methods
Yield 79% (1.4 g). Mp 113–114 C.

C20H28N2O4S2: C, 66.62; H, 7.83; N, 7.77; S, 17.79. Found: C,
Infrared spectra (IR) were recorded on a Bio-Rad FTS 175C FTIR
spectrophotometer. UV-visible absorption spectra were
obtained using a Shimadzu 2001 UV spectrophotometer. High
resolution mass spectra were measured on a Bruker microTOF
spectrometer equipped with electronspray ionization (ESI)
source. 1H spectra were recorded in deuterated chloroform
(CDCl3) on a Varian 500 MHz spectrometer. X-band (9.5 GHz)
EPR spectra were recorded at 77 K on a Bruker ESP 300E
spectrometer using a standard rectangular (TE102) EPR cavity
(Bruker ER4102ST) with a microwave power of 1.6 mW and
modulation amplitude of 1 G.
1
67.20; H, 7.70; N, 7.93; S, 17,57. H NMR (500 MHz CDCl3):
0.8 (t, 3 H, CH3), 1.3 – 1.7 (m, 8 H, CH2), 3.7 (t, 2 H, CH2), 8.6 (s,
1 H, ArH) ppm. ESI-MS: m/z: 447.23 [M+Na]+; IR (KBr) (cm–1):
 =

3097, 2959, 2928, 2861, 2244, 1545, 1464, 1336, 1314, 1149,
1125, 919, 795, 728, 648, 570, 525, 512, 474.
O
CTA-(N-HEXYLSULFONYL)PHTHALOCYANINATO IRON(II) (6).
A mixture of 1,2-dicyano-4,5-bis(n-hexylsulfonyl)benzene (
5)
(250 mg, 0.6 mmol) was heated at 130 C in a mixture of o-

dichlorobenzene-DMF (3:1) under argon for 8 h in the
presence of iron(II) chloride (0.15 mmol). The solvent was then
concentrated under reduced pressure and the resulting green
The mass spectra were recorded on a MicroTOF Q II (Bruker
Daltonics, Bremen), a quadrupole time of flight (Q-TOF) mass
10 | J. Name., 2012, 00, 1-3
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Page 11 of 14
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ARTICLE
solid was recovered with dichloromethane and washed with quartet, and sextet spin states, but the doubletVsiepwinArtisctleaOtenlinise
DOI: 10.1039/C5SC01811K
water. Phthalocyanine
6 was purified by chromatography on the ground state in all cases.
silica gel using a mixture of di-chloromethane:ethanol (100:1) To test the effect of the basis set on the spin state ordering
as the eluent. Yield: 23% (61 mg). ESI-MS: m/z calc. for and relative energies, we calculated single points with a triple-
C80H112FeN8O16S8, 1172.5; found 1753.3 [M+H]+. UV-Vis
 type basis set on iron (LACV3P+) and 6-311+G* on the rest of
(CHCl3):

max (log
) = 670 (5.2), 354 (5.0) nm; IR (KBr)

(cm–1): the atoms: basis set BS2. Finally, solvent corrections were
obtained from single point calculations in Jaguar using the
1310, 1100, 1070, 808, 740.
polarized continuum model with
ETEROLEPTIC mimicking dichlorobenzene. However, none of these
FePc1 (1 calculations changed the spin state ordering or site preference,
mmol), sodium azide (1.5 g) and alkylsulfonyl phthalocy- see Supporting Information for details.
aninato-iron(II) (0.1 mmol) were suspended in These DFT methods have been extensively used in calculations
chloronaphthalene (20 mL) under argon. The mixture was of iron-porphyrin complexes and were shown to reproduce
a dielectric constant
G
ENERAL
P
ROCEDURE FOR
PREPARATION OF
H
N-BRIDGED
D
IIRON HTHALOCYANINE
P
D
IMERS.
-
heated for 24h at 190C under intensive stirring. The solvent experimental rate constants and spin state orderings in good
was removed under reduced pressure. The remaining blue agreement with experiment.47 Each chemical structure was
solid was diluted in CH2Cl2 (100 mL), filtrated and concentrated characterized as a local minimum via a harmonic frequency
to be loaded on a silica gel column first eluted with CH2Cl2 to calculation, which gave real vibrational frequencies only.
remove impurities. Then, the desired heteroleptic dimer was
collected using CH2Cl2:EtOH (10:1) as the eluent. Evaporation
Acknowledgements
of solvent afforded the pure heteroleptic dimer (
below) as a dark blue powder.
3 or 7, see
The Scientific and Technological Research Council of Turkey
(project 112M370) is gratefully acknowledged. We
acknowledge the Soleil (Gif-sur-Yvette, France) and the ESRF
(Grenoble, France) for provision of time on the SAMBA and
ID26 beamlines, respectively. ASF thanks the Tertiary Research
Fund for a studentship and SdV acknowledges cpu-time
support from the National Service of Computational Chemistry
Software (NSCCS).
[(PC1)FENFE(PC2)] (3). Yield: 64% (124 mg). ESI-HRMS: m/z
calc. for C104H88Fe2N17O16S8, 1943.8; found, [M]+, dicharged
species calc. for 971.2287; found 971.2332. UV-Vis (CHCl3):
max (log
(Fe=N-Fe).
[(P 1)F NF
calc. for C112H128Fe2N17O16S8, 2334.6186; found, 2334.6091
[M]+. UV-Vis (CHCl3): max (log
) = 645 (4.3), 338 (4.1) nm. IR
(KBr)
(cm–1): 935 (Fe=N-Fe).
) = 635 (4.5), 338 (4.3) nm. IR (KBr) 
(cm–1): 929
C
E
E(PC6)] (7). Yield: 52% (120 mg). ESI-HRMS: m/z


Notes and references
Catalytic oxidation of methane
1
a) J. M. Bollinger Jr and C. Krebs, J. Inorg. Biochem., 2006,
100, 586; b) W. Nam, Acc. Chem. Res., 2007, 40, 522.
t
The [FePc(SO2 Bu)4]2N, (FePc)2N and [FePc(tBu)4]2N complexes
were supported onto silica (Degussa aerogel, 200 m2 g–1) with
2
a) M. Sono, M. P. Roach, E. D. Coulter and J. H. Dawson,
Chem. Rev., 1996, 96, 2841; b) J. T. Groves, Proc. Natl. Acad.
Sci. USA, 2003, 100, 3569; c) B. Meunier, S. P. de Visser and
S. Shaik, Chem. Rev., 2004, 104, 3947; d) P. R. Ortiz de
Montellano (Ed) Cytochrome P450: Structure, Mechanism
and Biochemistry. 3rd ed, Kluwer Academic/Plenum
Publishers, New York, 2004; e) I. G. Denisov, T. M. Makris, S.
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loading of 20 µmol g–1 according to
a
published
procedure.14a,14b The heterogeneous oxidation of methane was
performed as previously described.14a,14b
Computational methods
Density functional theory (DFT) procedures were employed
using previously calibrated and benchmarked methods42 as
implemented in the Gaussian-09 and Jaguar software
packages.43 Initially, structures were constructed ab initio and
optimized using the unrestricted BP86 and B3LYP density
functional methods44,45 and basis set BS1,46 which consists of
LANL2DZ on Fe and 6-31G on the other atoms. We set up an
3
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abbreviated model of structure
3, namely structure 9
[(Pc
H
)FeIIINFeIII(PcSO2Me)], whereby the t-adamantyl-sulfonyl
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addition, structures were calculated with one iron(IV)-oxo
group, namely [(Pc
[O=(Pc
)FeIVNFeIII(PcSO2Me)] (9=OB). Furthermore, structures
were generates with an iron(III)-hydroperoxo group, i.e.
[(Pc 9-OOHA and
)FeIIINFeIII(PcSO2Me)OOH]
[HOO(Pc 9-OOHB). All individual
)FeIIINFeIII(PcSO2Me)]
H (9=OA) and
)FeIIINFeIV(PcSO2Me)=O]
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H
(
)
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a) S. P. de Visser, Angew. Chem. Int. Ed., 2006, 45, 1790; b) S.
Ye and F. Neese, Proc. Natl. Acad. Sci. USA, 2011, 108, 1228;
c) P. C. Andrikopoulos, C. Michel, S. Chouzier and P. Sautet,
H
(
structures were calculated in the lowest energy doublet,
ACS Catal., 2015, 5, 2490.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 11
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DOI: 10.1039/C5SC01811K
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ARTICLE
Table of Contents Figure:
Active species formation on electron-rich site
OR
electron-rich
O
O
+3.5
Fe
FeIII
FeIV
.
N
N
N
R
R
R
R
R
R
+3.5
Fe
FeIV
FeIV
R
R
R
R
R
R
electron-poor
ESI-MS, DFT, Reactivity in methane oxidation
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