Catalytic oxidation of dibenzothiophene and thioanisole by a diiron(III) complex and hydrogen peroxide

Article abstract of DOI:10.1016/j.molcata.2014.09.030

One diiron(III) complex of the dinucleating ligand HPTP (N,N,N', N'-tetrakis(2-pyridylmethyl)-2-hydroxy-1,3-diaminopropane) and one mononuclear iron(III) complex of the BPMEN ligand(N, N'-dimethyl-N, N'-bis-2-pyridinylmethyl)-1,2-ethanediamine) have been synthesized and charac-terized by X-ray diffraction analysis, high resolution mass spectrometry, and electronic absorptionspectroscopy. The diiron(III) complex reacts with hydrogen peroxide to generate a short lived blue inter-mediate comparable to the previously described μ-peroxo-diiron(III) intermediate, obtained from theinteraction of the corresponding HPTP diiron(II) complex with dioxygen. Both mononuclear and dinucleariron complexes were tested for the catalytic oxidation of sulphides with H₂O₂, and the diiron complexshowed good activity for the oxidation of dibenzothiophene (DBT), a fuel contaminant naturally presentin crude oil. It catalyzed the total conversion of DBT into the corresponding sulfone via the formation ofthe sulfoxide, in acetonitrile at room temperature.

Full text of DOI:10.1016/j.molcata.2014.09.030

Journal of Molecular Catalysis A: Chemical 396 (2015) 40–46
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Catalytic oxidation of dibenzothiophene and thioanisole by a
diiron(III) complex and hydrogen peroxide
∗
Alexandre Trehoux, Yoann Roux, Régis Guillot, Jean-Pierre Mahy , Frédéric Avenier
Laboratoire de Chimie Bioorganiqe et Bioinorganique, Institut de Chimie Moléculaire et des Matériaux d’Orsay (UMR CNRS 8182), Université Paris Sud,
Orsay 91405 Cedex, France
a r t i c l e i n f o
a b s t r a c t
ꢀ
ꢀ
Article history:
Received 7 June 2014
Received in revised form
One diiron(III) complex of the dinucleating ligand HPTP (N,N,N ,N -tetrakis(2-pyridylmethyl)-2-
hydroxy-1,3-diaminopropane) and one mononuclear iron(III) complex of the BPMEN ligand
ꢀ ꢀ
N,N -dimethyl-N,N -bis-2-pyridinylmethyl)-1,2-ethanediamine) have been synthesized and charac-
(
1
9 September 2014
terized by X-ray diffraction analysis, high resolution mass spectrometry, and electronic absorption
spectroscopy. The diiron(III) complex reacts with hydrogen peroxide to generate a short lived blue inter-
mediate comparable to the previously described ␮-peroxo-diiron(III) intermediate, obtained from the
interaction of the corresponding HPTP diiron(II) complex with dioxygen. Both mononuclear and dinuclear
iron complexes were tested for the catalytic oxidation of sulphides with H2O2, and the diiron complex
showed good activity for the oxidation of dibenzothiophene (DBT), a fuel contaminant naturally present
in crude oil. It catalyzed the total conversion of DBT into the corresponding sulfone via the formation of
the sulfoxide, in acetonitrile at room temperature.
Accepted 20 September 2014
Available online 30 September 2014
Keywords:
Diiron complex
Catalytic oxidation
Bio-inspired catalysis
©
2014 Elsevier B.V. All rights reserved.
1
. Introduction
and H O /porphyrins [9,10] have demonstrated a good catalytic
2 2
activity for this reaction. However, the development of new envi-
ronmentally friendly and cheap processes is still needed, and
bio-inspired iron complexes of readily accessible ligands combined
to H O , are good candidates for ODS since iron presents low tox-
Sulfur compounds are fuel contaminants naturally present in
crude oil. They cause several disagreements during the process
of oil refinement, such as corrosion of surfaces and poisoning of
the catalysts. Upon combustion, they also generate sulfur oxi-
dation compounds responsible for the generation of acid rain.
Those major industrial and environmental issues have prompted
the oil industry to develop efficient desulfurization processes [1]
in order to meet new legislation standards about production of
ultra-low-sulfur diesels (ULSD). Hydrodesulfurization (HDS) is the
conventional process for the removal of sulfur compounds in fuels,
but this process requires hydrogen under high pressure and high
temperature conditions, which are energy demanding and expen-
sive. Although HDS is efficient for the transformation of thiols,
sulfides and disulfides, some sulfur containing compounds such as
dibenzothiophene (DBT) and its derivatives are refractory to this
process [2,3]. The alternative to HDS is the oxidative desulfurization
2
2
icity and since hydrogen peroxide is a benign oxidant. Bio-inspired
concepts have indeed already been successful in many areas of
science such as the development of artificial hydrogenases for he
production of hydrogen [11] or the creation of nanodevices via
the incorporation of enzymes in materials for various applications
[12]. For instance, mononuclear iron(IV)-oxo complexes, obtained
from the reaction of the corresponding iron(II) complexes and
iodosylbenzene [13], have been demonstrated to oxidize DBT in
stoichiometric amounts.[14] This shed light on the potential of non-
heme iron catalysts inspired from iron mono-oxygenases for DBT
oxidation. Amongst the members of the large family of iron mono-
oxygenases, one of the most powerful catalyst described so far is
the dinuclear iron enzyme, methane mono-oxygenase (MMO) [15].
Although this enzyme exhibits impressive catalytic activity, dinu-
clear iron complexes inspired from this system [16] have always
been described as sluggish oxidants compared to heme catalysts
and even to mononuclear non-heme iron complexes [17]. Only
recently, highly active diiron complexes have been reported for
hydrogen abstraction and oxygen atom transfer [18,19]. Interest-
ingly, a ␮-oxo dinuclear iron complex has been demonstrated to
be a better catalyst for sulfide oxidation than the corresponding
(
ODS) which works in two steps: (1) oxidation of sulfur into sulf-
oxide and sulfone, and (2) extraction of the oxidized compounds
by polar solvents. Some catalytic systems such as H O /organic
2
2
acids [4], H O /polyoxometalates [5,6], H O /ionic liquids [7,8]
2
2
2
2
∗ Corresponding author. Tel.: +33 1 69 15 74 21; fax: +33 1 69 15 72 81.
E-mail address: jean-pierre.mahy@u-psud.fr (J.-P. Mahy).
http://dx.doi.org/10.1016/j.molcata.2014.09.030
1
381-1169/© 2014 Elsevier B.V. All rights reserved.

A. Trehoux et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 40–46
41
[
21], and the corresponding diiron(III) complex was obtained by
the addition of 2 equiv. of iron(III) perchlorate hexahydrate in
methanol. Slow evaporation of this solution yielded crystals of suf-
ficient quality for X-ray diffraction analysis and an ORTEP plot of
compound [1] is shown in Fig. 1 (top). In this rather symmetrical
structure, both iron have similar octahedral coordination geome-
tries with exactly the same average distances of 2.053 A˚ with the
various ligands, and a Fe–Fe distance of 3.734 A˚ . The diiron(III) cen-
tre is bridged by the alkoxo group of the ligand and both Fe(1) and
Fe(2) coordinate two pyridyl moities in a trans geometry. The coor-
dination sphere is completed by two methanol molecules for Fe(1),
and one methanolate and one methanol for Fe(2). It is worth noting
that one methanol ligand of Fe(1) forms an hydrogen bond with the
methanolate ligand of Fe(2).
Synthesis of the BPMEN mononucleating ligand was realized
according to Ref. [29], and the corresponding mononuclear iron
complex was obtained by adding one equivalent of iron chlo-
ride, followed by precipitation with sodium hexafluorophosphate.
Crystallization of this compound upon ether diffusion into an ace-
tonitrile solution yielded crystals of sufficient quality for X-ray
diffraction analysis. The ORTEP representation of this compound [2]
is shown in Fig. 1 (bottom). This structure is comparable to struc-
tures previously described for other BPMEN mononuclear iron(III)
complexes but bears different exogeneous ligands or different
counter ions [30,31]. Two pyridyl moieties coordinate to the iron in
a trans geometry, while two amine groups and two chloride ligands
Scheme 1. Dinucleating ligand (HPTP) and monucleating ligand (BPMEN) used in
this study.
mononuclear iron complex [20], suggesting a better intrinsic
capability of dinuclear centres for sulfide oxidation compared to
mononuclear complexes. Dinuclear systems synthesized from the
ꢀ
ꢀ
dinucleating ligand HPTP (N,N,N ,N -tetrakis(2-pyridylmethyl)-2-
hydroxy-1,3-diamino-propane) [21] (Scheme 1) have been widely
used to study dioxygen activation at diiron(II) centres [22–25].
However, very little is known about the catalytic properties of its
readily available diiron(III) counterparts with hydrogen peroxide
[
26,27].
Here, we report the synthesis and characterization a new HPTP
diiron(III) complex bearing four coordination positions occupied
by exchangeable solvent molecules, in order to allow simulta-
neous interaction of hydrogen peroxide and substrate at the iron
centres. The activity of this simple diiron(III) complex was then
tested for the catalytic oxidation of sulfides and a good activity for
DBT oxidation was observed. For comparison with a mononuclear
iron(III) complex, we have also tested the catalytic activity of
coordinate in a cis geometry with an average coodination distance
of 2.220 A˚ for the six ligands. A similar BPMEN iron(III) complex
was also synthesized by the addition of 1 equiv. of iron perchlo-
rate hexahydrate. Unfortunately no crystal of the corresponding
complex could be obtained.
[
BPMENFe(III)]Cl2 and [BPMENFe(III)](ClO4)2 complexes and both
showed very poor activity for DBT oxidation. This is in sharp con-
trast with the activity of the [BPMENFe(II)](CH CN)2 counterpart
3
which is known to be very active in catalytic oxidations, but for
which the synthesis is much more restricting and time consuming,
since it has to be prepared under inert atmosphere with multiple
purification steps [28].
2
.2. Reactivity with hydrogen peroxide
In terms of reactivity, when the orange acetonitrile solution of
[
1] is submitted to the addition of hydrogen peroxide (10 equiv.), it
2
. Results and discussion
instantly turns into a deep blue stable solution for about one minute
at room temperature, with a maximum absorbance at 610 nm
2.1. X-ray diffraction analysis
−1 −1
(ε = 1660 M cm ) (Fig. 2). This is similar to what was described
The one step synthesis of the HPTP dinucleating ligand was
adapted from the original synthesis developed by Suzuki et al.
previously for the interaction of the corresponding diiron(II) com-
plex with dioxygen, and for which the blue intermediate was
Fig. 1. ORTEP drawing (50% probability level) of [FeIII2(HPNP)(CH3OH)3(CH3O)](ClO4)4 [1] (left), and [FeIII(BPMEN)(Cl)2](PF6) [2] (right). Uncoordinated anions and solvent
molecules are excluded for clarity.

4
2
A. Trehoux et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 40–46
O
S
O
O
S
S
[
1]
+
2 2
H O
DBT
DBTO
DBTO
2
Scheme 2. Oxidation of dibenzothiophene (DBT) into the corresponding sulfoxide
DBTO) and sulfone (DBTO2).
(
2.3. Catalysis experiments
The catalytic activity of complex [1] was then studied for the
oxidation of DBT in acetonitrile under aerobic conditions. When
H O was added to a solution of [1] in the presence of DBT, the blue
2
2
intermediate disappeared immediately after its formation at room
temperature, suggesting that DBT reacted either directly with the
peroxo intermediate, or with a product of its degradation such as
an iron(IV)-oxo species previously observed for mononuclear com-
plexes [14]. The reaction was then followed by HPLC, looking at the
degradation of DBT and the formation of the corresponding sulfox-
Fig. 2. UV–vis absorption spectra of complex [1] (dashed black line) and of the blue
intermediate obtained 5 s after mixing compound [1] with 50 equiv. of H2O2 (solid
red line). Conditions: 0.5 mM in MeCN at 20 C. (For interpretation of the references
◦
to color in this figure legend, the reader is referred to the web version of the article.)
ide and sulfone upon sequential additions of H O2 (Scheme 2).
2
The results are summarized in Fig. 4, and one can observe that
DBT is rapidly consumed to form exclusively the corresponding
sulfoxide (DBTO) in the early stage of the reaction. The sulfone
assigned to a ␮-peroxo-diiron(III) species by vibrational Raman
spectroscopy experiments [24]. Unfortunately, the high fluores-
cence of our complex did not allow the characterization of the
intermediate, neither by conventional vibrational Raman spec-
troscopy, nor by using a system equipped with a rotating cell.
In order to compare the catalytic capabilities of diiron(III) com-
plexes with mononuclear iron(III) complexes, we have also tested
the reactivity of the mononuclear complex [2] under the same
conditions, and no UV–vis spectroscopic modifications could be
observed in the first 5 s of reaction. Taking in consideration that
chloride ions strongly coordinate to iron(III), and that this may
affect the accessibility to the iron centre, we have also tested
(
DBTO ) only appears after the addition of eight equivalents of
2
H O , suggesting that its formation arises only from the oxidation
2
2
of DBTO and not directly from the oxidation of DBT. This step-
wise oxidation of DBT into DBTO and DBTO2 was confirmed by
ESI-MS analysis, showing the formation of both DBTO and DBTO2
for 20 equiv. of H O2 and exclusively DBTO2 above the addition of
2
4
4 equiv. of H O with respect to the catalyst. The complete conver-
2 2
sion of DBT (10 equiv./catalyst) was reached for 36 equiv. of H O ,
2
2
and the complete oxidation into DBTO2 was reached after addition
of 44 equiv. of oxidant.
The interesting catalytic activity of complex [1] raised the ques-
tion of which active species was involved in the mechanism. The
observation of a blue intermediate, upon addition of hydrogen
peroxide to the complex strongly suggests the formation a ␮-
peroxo-diiron(III) as previously described for the reaction of similar
diiron(II) complex with dioxygen. The rapid consumption of this
intermediate in the presence of DBT suggests either its direct impli-
cation as an active species, or the formation of an active Fe(IV)-oxo
species resulting from its homolytic cleavage. In order to clarify this
mechanism, catalysis was carried out in the presence 1000 equiv.
of H218O. In that case, ESI-MS analysis shows 38% incorporation
its reactivity for higher H O2 concentration and for longer reac-
2
tion time (Fig. 3). In this case, only changes are observed in the
region between 300 nm and 400 nm, where amine- and pyridine-
to iron(III) charge transfers are expected, suggesting that chloride
ions are actually exchanged in solution. However, no absorption
band in the UV–vis region, that may be associated to the forma-
tion of an iron(III)-hydroperoxo species, as previously described
for similar mononuclear iron(II) complexes [32], could be observed.
This is in line with the huge instability of such a species with the
tetradentate BPMEN ligand, for which only traces could be detected
◦
at temperatures below −60 C [33].
3,5
3,0
2,5
2,0
1,5
1,0
0,5
0,0
300
400
500
600
700
800
Wavelength (nm)
Fig. 4. Catalytic degradation of DBT (ꢀ), and formation of DBTO (
) and DBTO2
Fig. 3. UV–vis absorption spectra of complex [2] after addition of 100 equiv. of H2O2
(
) in MeCN at 20 ◦C followed by HPLC. Conditions: [1]/H O /DBT (1/x/10) with
2
2
◦
(
from 0 to 60 min). Conditions: 0.5 mM in MeCN at 20 C.
x = 0–60.

A. Trehoux et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 40–46
43
Fig. 5. ESI-MS spectra of DBTO (m/z 223) and DBTO2 (m/z 239) after catalytic oxidation of DBT with complex [1] and H2O2 in the absence (A and B) and in the presence of
18
H2 O (C and D).
of labelled oxygen for DBTO (Fig. 5C) and about 31% incorpora-
tion for the first oxygen of DBTO2 (Fig. 5D). As one would expect,
the labelling of the second oxygen is less important, but can still
be observed on the spectrum. This implies that both sulfoxide and
sulfone products are formed via a similar metal centred iron-oxo
intermediate capable of oxo/hydroxo tautomerism as previously
described for porphyrin [34], mononuclear [35] and dinuclear iron
complexes [36] (Scheme 3). These isotope labelling experiments
also exclude the direct implication of a peroxo intermediate as the
active species.
When catalysis is performed with the mononuclear complex
[
2], DBT is not consumed upon the sequential addition H O2 and
2
no traces of oxidized products, neither DBTO nor DBTO , can be
2
detected (Fig. 6). Control experiment, using solely H O , shows
2
2
no DBT conversion at all (Fig. 6), while control experiments with
H O and Fe(ClO4)3 salts only show very little conversion into
2
2
DBTO (Fig. S1, supporting information). Recent reports have shown
that Fe(III)OOH intermediates supported by tetradentate ligands,
formed upon addition of hydrogen peroxide to iron(II) complexes,
can generate Fe(V)O species provided there is a labile ligand in
cis with respect to the hydroperoxo ligand. These Fe(O) species,
formed upon reaction of iron(II) complexes with H O are active
Fig. 6. Catalytic degradation of DBT using complex [1] (ꢀ), complex [2] ( ) and
◦
[
BPMENFe(III)](ClO4)3 prepared in situ (
) in MeCN at 20 C followed by HPLC.
Conditions: [1] or [2]/H2O2/DBT (1/x/10) with x = 0 to 60.
2
2
complex directly in solution by mixing the ligand with iron(III) per-
chlorate, and tested its activity under the same conditions. In this
case, one can observe a small improvement in the catalytic activ-
ity, but nothing significantly better than the control realized with
Fe(ClO4)3 in solution (Fig. 6). The inertness of complex [2] and of
its iron(III) perchlorate analogue could also be explained by the
formation of oxo-bridged diiron(III) complexes which are known
for aromatic hydroxylation [37] or epoxidation reactions [38,39].
In the case of complex [2], it is likely that both chloro ligands
could not be substituted at the same time, preventing the evolution
III
+
of the putative [(BPMEN)Fe Cl(OOH)] into a high valent Fe(V)O. In
order to avoid the coordination of chloride ions to the iron centre,
we also prepared the corresponding BPMEN mononuclear iron(III)
Scheme 3. Mechanism proposed for the catalytic oxidation of DBT by complex [1] and H2O2.

4
4
A. Trehoux et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 40–46
Fig. 8. Turn over numbers observed for the conversion of thioanisole with complex
[
1] and H2O2. Conditions: [1]/H2O2/thioanisole (1/x/100) with x = 0–160 equiv., in
Fig. 7. Turn over numbers observed for the conversion of DBT with complex [1] and
H2O2. Conditions: [1]/H2O2/DBT (1/x/100) with x = 0–300 equiv., in MeCN at 20 C.
MeCN at 20 ◦C.
◦
difficult oxidation of DBT. Control experiment with iron(III) per-
chlorate hydrate showed no significant conversion compared to
the blank reaction using H2O2 only (see Fig. S3, supporting infor-
mation). The oxidation of thioanisole using dioxygen with a similar
diiron(II) HPTP complex bearing a carboxylate bridge, was pre-
viously described by Costas et al. [23] In this case, the authors
describe the formation of a blue peroxo intermediate which cat-
alyzes the sub-stoichiometric sulfoxidation of thioanisole with a
59% yield (no over oxidation into the corresponding sulfone was
observed). Interestingly, the same diiron(II) complex, bearing two
carboxylate bridges, generates a similar and even more stable per-
oxo intermediate which is completely inactive for sulfide oxidation.
This confirms the importance of the four exchangeable coordina-
tion sites present on our diiron(III) complexes, in order to perform
efficient catalytic oxidation of sulfides.
to be poorly active in substrate oxidation with hydrogen peroxide.
The inertness of these mononuclear iron(III) complexes towards
hydrogen peroxide stands out from the good catalytic activity of
the corresponding iron(II) systems which are highly performing in
oxidation catalysis (see Fig. S2, supporting information) but rather
difficult to obtain in terms of conditions of preparation (inert atmo-
sphere) and in terms of purification.
Complex [1] was then tested when increasing the proportions
of substrate up to 100 equiv. in order to evaluate its long-term
stability. Fig. 7 shows that for the first 20 equiv. of oxidant, DBT
conversion is quantitative (20 turnovers observed), and above this
value the activity slows down to reach a maximum of 85 turnovers.
To the best of our knowledge, this is the first example of effi-
cient catalytic oxidation of DBT by a dinuclear iron complex with
hydrogen peroxide. It is also another example showing a better
activity of dinuclear iron complexes for sulfide oxidation compared
to mononuclear iron(III) complexes which can easily be prepared
from stable iron(III) salts without any further precautions. Iron(II)
complexes are better candidates for catalytic oxidations, but their
preparation requires specific conditions and multiple purifications
steps which are not convenient for the development of useful cata-
lysts potentially used for fuel desulfurization. Conversely, complex
3. Conclusions
Through this work, we have synthesized and characterized a
new HPTP diiron(III) complex bearing four coordination positions
occupied by exchangeable solvent molecules. Its capacity to oxidize
sulfides was then tested with hydrogen peroxide, and this com-
plex appeared to be a very good catalyst for thioanisole oxidation
but also for the difficult oxidation of dibenzothiophene, a natu-
ral contaminant of crude oil. HPLC and ESI-MS analysis revealed
the formation of the sulfoxide product in the early stage of the
reaction and total conversion into the corresponding sulfone after
addition of about 3.5 equiv. of oxidant with respect to the substrate.
Experiments in the presence of H218O coupled to ESI-MS analy-
sis also demonstrate the involvement of a metal centred iron-oxo
[1] can easily be synthetized on the bench by mixing the dinuclea-
ting ligand with two equivalents of stable iron(III) salts. The overall
activity of complex [1] is comparable to other catalytic systems
recently described and working under mild conditions [5,6,40–42],
with a total conversion of DBT for about three equivalents of hydro-
gen peroxide, and a maximum of 85 turnovers. It is worth noting
that this capability of dinuclear iron complexes for the oxidation of
thiophene derivatives into the corresponding sulfone could also be
of high interest for the oxidation of thiophene-based oligomers,
which are important active components for potential electronic
applications [43].
IV
species, most probably a short lived Fe (O) species formed upon
the homolytic cleavage of the ␮-peroxo-diiron(III) intermediate.
Interestingly, catalysis performed with the BPMEN mononuclear
iron(III) complex as catalyst shows very poor activity for this reac-
tion. This points out the intrinsic capabilities of readily available
dinuclear iron(III) complexes for the difficult desulfurization of
dibenzothiophene and opens new routes for the facile oxidation of
refractory thiophene-based oligomers, which are interesting com-
ponent for potential electronic applications.
Complex [1] was also tested for catalytic oxidation of thioanisole
with hydrogen peroxide under the same conditions as DBT, and
Fig. 8 shows that complex [1] easily achieves the complete conver-
sion of 100 equiv. of thioanisole into the corresponding sulfoxide
and sulfone with a slight excess of H O . The linear conversion up
2
2
to 70 equiv. of H O with respect to the catalyst also demonstrates
2
2
the good robustness of the catalyst for this reaction.
Complete conversion of thioanisole is reached for 1.3 equiv.
4. Experimental
of H O2 with respect to the substrate. ESI-MS analysis show the
2
formation of both sulfoxide and sulfone compounds during the
reaction, as we have previously observed for the much more
Synthesis: The mononucleating ligand BPMEN was synthe-
sized according to Ref. [29] and the dinucleating ligand HPTP was

A. Trehoux et al. / Journal of Molecular Catalysis A: Chemical 396 (2015) 40–46
45
synthesized via the following method, adapted from the original
http://www.ccdc.cam.ac.uk/Community/Requestastructure. In the
case of compound [1] crystals were very small and diffraction inten-
sity was extremely low. In these conditions, it was not possible to
get a model with an R factor less than 10.06%.
synthesis developed by Suzuki et al. [21].
ꢀ
ꢀ
N,N,N ,N -tetrakis(2-pyridylmethyl)-1,3-diaminopropan-
-ol (HPTP): (2-Chloromethyl)pyridine hydrochloride was
2
dehydrochlorinated by dissolution in an aqueous solution
saturated with sodium carbonate and then extracted with
dichloromethane. To a 7 mL solution of 1,3-diamino-2-propanol
Electronic absorption spectroscopy: UV–vis experiments were
all carried out in a Varian carry300Bio spectrophotometer.
Catalytic oxidation of DBT: A 5 mL acetonitrile solution of
[FeIII (TPDP)(CH O)(CH OH) ](ClO ) (0.5 mM) and dibenzothio-
(
(
144 mg) in acetonitrile was added dropwise a 5 mL solution of
2-chloromethyl)pyridine (815 mg) in acetonitrile. Then, triethyl-
2
3
3
3
4 4
phene (5 mM) was subjected to 25 successive injections of 10 ␮L
of a 0.5 M hydrogen peroxide solution in acetonitrile every two
minutes (60 equiv. with respect to the catalyst). For HPLC measure-
ments, 10 ␮L of the reaction mixture and 50 ␮L of a 10 mM solution
of anisole were filtered off on silica (1 cm in Pasteur pipette) and
eluted with 1.5 mL of acetonitrile. Finally, 12.5 ␮L of this filtered
solution were injected in a C18 grafted silica column (Agilent
eclipse plus C18, 3.5 ␮m, 4.6 × 10 mm) and eluted with a mixture
amine (1.75 mL) was added dropwise to the reaction mixture that
was then allowed to stir at room temperature for 5 days. After
removing the solvent under vacuum, the mixture was dissolved in
dichloromethane and washed three times with water. Purification
by silica gel column chromatography (CHCl /CH OH) yielded
3
3
1
3
51 mg (48%) of the expected product as a pale yellow oil. H NMR
analysis (CDCl , 360 MHz): ı (ppm): 8.529 (4H, d, JHH = 4.7 Hz),
3
−
1
7
7
2
4
.616 (4H, td, JHH = 7.7 Hz, JHH = 1.8 Hz), 7.402 (4H, d, JHH = 7.9 Hz),
.152 (4H, td, JHH = 4.7 Hz, JHH = 1.4 Hz), 3.935–4.101 (9H, m),
.72 (4H, m). HR ESI-MS analysis: m/z 455.2551, calculated m/z
of MeCN/H O (70/30) at a rate of 1 mL min . Elution times (min.):
2
DBTO (1.24); DBTO2 (1.50); anisole (1.80); DBT (4.54). All catalytic
experiments were carried out under aerobic conditions.
55.2554.
Catalytic oxidation of thioanisole:
A
5 mL acetonitrile
III
III
[
Fe (HPTP)(CH O)(CH OH) ](ClO )
[1], was prepared
solution of [Fe (TPDP)(CH O)(CH OH) ](ClO ) (0.05 mM) and
2
3
3
3
4
4
2
3
3
3
4 4
by adding dropwise a 5 mL solution of iron(III) perchlorate
hexahydrate (Fe(ClO ) , 6H O) (527 mg) to a 20 mL solution
thioanisole (5 mM) was subjected to 20 successive injections of
10 ␮L of a 0.25 M hydrogen peroxide solution every two minutes
(200 equiv. with respect to the catalyst). For HPLC measurements, a
10 ␮L sample of the reaction mixture, to which were added 50 ␮L of
anisole as internal standard (10 mM), was filtered off on silica (1 cm
in Pasteur pipette) and eluted with 1.5 mL of acetonitrile. Finally,
12.5 ␮L of this filtered solution were injected on a C18 grafted sil-
ica column (Agilent eclipse plus C18, 3.5 ␮m, 4.6 mm × 10 mm) and
4
3
2
ꢀ ꢀ
N,N,N N -tetrakis(2-pyridylmethyl)-1,3-diaminopropan-2-ol
of
HPTP) (259 mg) in methanol under stirring at room tem-
(
perature. Slow evaporation of the orange solution yielded
orange crystals of the desired complex. HR ESI-MS analysis
III
+
[
8
Fe (HPTP)(CH O) (ClO ) ] : m/z 825.0426; Calculated: m/z
2 3 2 4 2
III
+
25.0500 and [Fe (HPTP)(CH O) (ClO )] : m/z 757.1119;
2 3 3 4
−
1
Calculated: m/z 757.1200. Elemental Analysis: calculated for
eluted with a mixture of MeCN/H O (70/30) at a rate of 1 mL min
.
2
C31H44Cl Fe N O21, C 34.15%, H 4.07%, N 7.71%, Fe 10.24%. Found,
C 34.09%, H 4.28%, N 7.62%, Fe 9.84%
Elution times (min): methyl phenyl sulfoxide (1.03); methyl phenyl
sulfone (1.03); anisole (1.80); thioanisole (2.25). All catalytic exper-
iments were carried out under aerobic conditions.
4
2
6
Warning: Perchlorate salts are explosive compounds when led
to dryness and have to be handled carefully and in small quantities.
III
[
Fe (BPMEN)(Cl) ](PF ) [2], was prepared by adding drop-
2
6
Acknowledgements
wise a 10 mL solution of iron(III) chloride (FeCl ) (288 mg) to a
0 mL solution of N,N -dimethyl-N,N -bis-2-pyridinylmethyl)-1,2-
3
ꢀ
ꢀ
1
We thank Prof. F. Banse for fruitful discussions about reactiv-
ity of mononuclear iron complexes and the “Agence Nationale
de la Recherche” (ANR BIOXICAT), the “Région Ile de France”
ethanediamine (BPMEN) (480 mg) in methanol under stirring at
room temperature. The complex precipitated as a yellow solid upon
addition of a 5 mL solution of potassium hexafluorophosphate (1 g)
in methanol. Recrystallization by ether diffusion in acetonitrile
yielded yellow crystals of the desired complex. HR ESI-MS analysis
(“DIM développement soutenable”) and the Labex CHARMMMAT
for financial support.
III
+
for [Fe (BPMEN)(Cl) ] : m/z 396.0579; calculated: m/z 396.0566.
2
Appendix A. Supplementary data
Elemental analysis: calculated for C16H24Cl2F12FeN P , C 27,89%, H
4
2
3
.51%, N 8.13%. Found, C 27.83%, H 3.25%, N 8.25%.
X-ray crystallography procedures: X-ray diffraction data were
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.molcata.
collected by using a Kappa X8 APPEX II Bruker diffractometer with
graphite-monochromated MoK␣ radiation (ꢀ = 0.71073 A˚ ). Crystals
2
014.09.030.
were mounted on a CryoLoop (Hampton Research) with Paratone-
N (Hampton Research) as cryoprotectant and then flashfrozen
in a nitrogen-gas stream at 100 K. The temperature of the crys-
tal was maintained at the selected value (100 K) by means of
a 700 series Cryostream cooling device to within an accuracy
of ± 1 K. The data were corrected for Lorentz polarization, and
absorption effects. The structures were solved by direct meth-
ods using SHELXS-97 [44] and refined against F2 by full-matrix
least-squares techniques using SHELXL-97 [45] with anisotropic
displacement parameters for all non-hydrogen atoms. Hydrogen
atoms were located on a difference Fourier map and introduced
into the calculations as a riding model with isotropic thermal
parameters. All calculations were performed using the Crystal
Structure crystallographic software package WINGX [46]. The crys-
tal data collection and refinement parameters are given in Table
S1. CCDC 964616-964617 contains the supplementary crystal-
lographic data for this paper. These data can be obtained free
of charge from the Cambridge Crystallographic Data Centre via
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