Sulfonamide-substituted iron phthalocyanine: Design, solubility range, stability and oxidation of olefins

Article abstract of DOI:10.1039/c4dt02412e

4-tert-Butylbenzenesulfonamide was used as a substituent of tetra peripherally substituted Fe(ii) phthalocyanine, taking into account several parameters crucial for the design of potential oxidation catalysts such as solubility and stability. The resulting phthalocyanine exhibits a remarkable stability under oxidative conditions. The main product of the oxidation of cyclohexene using H₂O₂ as the oxidant is the allylic ketone, 2-cyclohexen-1-one. Styrene oxidation led mainly to the formation of benzaldehyde.

Full text of DOI:10.1039/c4dt02412e

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Sulfonamide-substituted iron phthalocyanine:
design, solubility range, stability and oxidation
of olefins†
Cite this: DOI: 10.1039/c4dt02412e
Received 8th August 2014,
Accepted 17th October 2014
DOI: 10.1039/c4dt02412e
Ümit İşci,* Celal Caner, Yunus Zorlu, Ayşe Gül Gürek, Fabienne Dumoulin and
Vefa Ahsen*
www.rsc.org/dalton
4-tert-Butylbenzenesulfonamide was used as a substituent of tetra listed above, especially regarding the choice of the substitu-
peripherally substituted Fe(II) phthalocyanine, taking into account ents, which must be chemically resistant to the oxidation con-
several parameters crucial for the design of potential oxidation ditions. This is why tert-butyl substituted phthalocyanines,
catalysts such as solubility and stability. The resulting phthalo- which are easily prepared from a commercially available
cyanine exhibits a remarkable stability under oxidative conditions. phthalonitrile, are widely used, either for Fe(II) phthalo-
1
1,12
The main product of the oxidation of cyclohexene using H
2
O
2
cyanines or for their dimeric N-bridged derivatives.
Since
as the oxidant is the allylic ketone, 2-cyclohexen-1-one. Styrene then, such dimeric iron phthalocyanines bearing electron-
oxidation led mainly to the formation of benzaldehyde.
withdrawing sulfonyl substituents have been identified as
particularly interesting, thanks to the stability conferred by
this type of substituents already oxidized.
Aiming at enlarging the scope of possible catalysts, we were
interested in sulfonamide-substituted iron phthalocyanines
and designed the targeted phthalocyanine 1 represented in
Fig. 1.
The oxidation of cycloalkenes is of considerable interest in
industrial organic synthesis, because derivatives containing an
oxygen substituent in the ring are crucial intermediates in the
synthesis of fine chemicals. Many reports have been published
concerning the oxidation of cyclohexene using different
13,14
1
–6
oxidants in various solvents. Allylic oxidations of olefins are
in general focusing on the use of transition metal salt-based
Substitution patterns including or based on sulfonamide
function are scarcely used for phthalocyanines: tetra-
7
,8
catalysts.
15
sulfophthalocyanines were amidified by octylamine, and tetra-
Environmental preoccupations of our modern world,
together with economic factors are the key considerations to
be taken into account when designing potential catalysts: their
synthesis must be cheap, short and high yielding. Besides,
their catalytic efficiency must be elevated, which implies the
best possible stability to maximize the turnover. To be versa-
tile, their solubility must cover a wide range of solvents.
sulfonamide Co(II) phthalocyanine was used for the catalytic
When appropriately metallated, phthalocyanines have cata-
9
,10
lytic properties, in most of the cases for oxidation reactions.
So far, iron phthalocyanines have proven to be particularly
relevant, due to the availability of the metal as opposed to pre-
cious transition metals (ruthenium, rhodium, platinum, etc.),
and their heme-like biomimetic action mechanism. The
design of phthalocyanines for catalytic applications must be
carefully achieved, taking into account the considerations
Department of Chemistry, Gebze Institute of Technology, PO Box 141, Gebze,
4
1400 Kocaeli, Turkey. E-mail: u.isci@gyte.edu.tr, ahsen@gyte.edu.tr;
Fax: +90 262 605 3005; Tel: +90 262 605 3092
Electronic supplementary information (ESI) available: Experimental part: syn-
thesis, characterization, oxidation procedure and crystallographic data. CCDC
25679. For ESI and crystallographic data in CIF or other electronic format see
†
9
DOI: 10.1039/c4dt02412e
Fig. 1 Structure of targeted phthalocyanine 1.
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Fig. 2 ORTEP molecular structure of 4. Displacement ellipsoids are
drawn at the 50% probability level. H-atoms are shown as small spheres
of arbitrary radii.
Scheme 1 Preparation of phthalonitrile 4 and of targeted phthalo-
cyanine 1.
1
6
oxidative sweetening of LPG. Amidified tetrasulfo phthalo-
cyanines proved to be as well good NO sensors, thanks to the
possible intermolecular interactions with nitrogen dioxide.
Cavaleiro et al. introduced sulfonamide functions on aromatic
x
1
7
1
8
substituents of the phthalocyanine ring, and evidenced
the high non-linear transmission properties of these
1
9
derivatives.
As far as we could find out, no substituent linked to the
phthalocyanine ring via the nitrogen atom of the sulfonamide
function exists, when the interests are obvious: the simple
synthesis of the corresponding phthalonitrile from the
commercially available 4-aminophthalonitrile 2 (as well easily
accessible on a large scale by the quantitative reduction of
Fig. 3 UV-vis spectra of 1 in acetone (blue), tetrahydrofuran (red),
dimethylsulfoxide (black), chloroform (pink), dimethylformamide (green)
and acetonitrile (yellow).
2
1
4
-nitrophthalonitrile) and from a substituted chlorosulfonyl Fe(II) phthalocyanines, and are allowed to obtain 1 in a 32%
2
1
benzene (Scheme 1), here 4-tert-butylbenzene-1-sulfonyl yield particularly good for Fe(II) phthalocyanines.
chloride 3. Phthalonitrile 4 was indeed readily obtained, and
Phthalocyanine 1 exhibits a wide range of solubility, as
suitable crystals of 4 were grown by recrystallization from evidenced by the UV-vis spectra recorded in different solvents
ethanol at room temperature by slow evaporation. Its structure of various polarities, namely acetone, tetrahydrofuran,
and geometries were established by single-crystal X-ray struc- dimethylsulfoxide, chloroform, dimethylformamide and aceto-
ture analysis.
nitrile (Fig. 3).
The ORTEP molecular structure with atomic numbering
The split in the UV-Vis spectra near 640 nm comes from the
scheme is represented in Fig. 2. The compound crystallizes in aggregation species, as reported on related derivatives.
22
the orthorhombic space group Pca2
that the C1uN1 and C2uN2 bond lengths are 1.141(3) Å and hydrogen peroxide was used to evaluate the stability of 1 in
.143(3) Å, respectively, and are similar to values reported acetonitrile. With a 1000-fold excess of the oxidant (Fig. 4),
1
. The structure shows
The stability of a potential oxidation catalyst is crucial and
1
2
0
in the literature. The C9–C14 ring is nearly orthogonal to UV-vis spectra was recorded at regular intervals over 2 hours,
the phthalonitrile aromatic ring (C3–C8) with an angle and then overnight. Phthalocyanine 1 proved to be as stable as
of 86.98(9)°. The NH group forms a linear intermolecular the N-bridged dimeric derivatives, which are the most stable
N–H⋯N hydrogen bonding interaction with a N⋯N distance reported iron phthalocyanines, and the most powerful oxi-
2
3
of 3.062(3) Å.
Phthalonitrile 4 was converted into the corresponding tar- with H
geted phthalocyanine 1 in the presence of FeCl
in refluxing inution of the Q band intensity would reveal a degradation
ethylene glycol, which are the routine conditions for preparing of the phthalocyanine, the increased absorbance between
dation catalysts. During the titration of phthalocyanine 1
O
2 2
, some spectral changes were observed. When a dim-
2
2
4
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Scheme 3 Oxidation of styrene by 1.
were clearly identified using GC-MS, in respective yields
of 40, 8 and 6%. The excellent predominance of allylic oxi-
dation (88.9% of all the oxidation products) must be
noted to acknowledge the potential of this new catalyst,
the largely predominant allylic oxidation product being
the enone (cyclohex-2-en-1-one, 74.1% of all the oxidation
products).
To enlarge the scope of the study, the oxidation of cyclohex-
ene by 1 was tested in different solvent systems (Table 1). DMF
appeared to have a limiting effect on the cyclohexene conver-
sion. Compared to acetonitrile, conversion in acetone and
dichloromethane is slower, but the oxidation products are
formed in similar proportions.
Fig. 4 UV-vis spectra of 1 in acetonitrile in the presence of a 1000-fold
excess of H O , recorded over two hours and overnight. Inset: plot of
2 2
the Q band max vs. time.
In dichloromethane (entry 3), the yield of cyclohexene-
1-ol increased, while the lowest yield in cyclohexene oxide
is observed. While the yield of cyclohexene oxide increased
in acetone (entry 2) and acetonitrile (entry 1), the
cyclohexene oxide yield decreased in the other solvents
(
entries 3 and 4).
Styrene was also studied as another oxidation substrate
Scheme 3) in acetonitrile, with 60% conversion after 3 h.
(
Styrene was converted into benzaldehyde (38%), the main oxi-
dation product, and styrene oxide (22%).
To conclude, this work, based on the rational design of a
phthalocyanine to be a potential new oxidation catalyst,
demonstrated the relevance of sulfonamide substitution
pattern, as it provides a wide range of solubilities, and exhibits
excellent stability under oxidative conditions. Catalytic oxi-
Scheme 2 Cyclohexene oxidation products.
4
00 and 600 nm over 24 h can be interpreted as the result of dation experiments of olefins were conducted using the
the metal-oxidation by H O into its iron-oxo form, without environmentally friendly oxidant H O . The main oxidation
2
2
2 2
2
5
significant transformation of the phthalocyanine macrocycle,
products of cyclohexene are allylic oxidation products under
the apparition of the shoulder after 24 h suggesting the for- different conditions. Benzaldehyde was the main product of
2
3
mation of the μ-oxo dimeric species.
Iron phthalocyanine complex 1 was tested in the catalysis
styrene oxidation.
These results prompted us to carry out more oxidation
of cyclohexene oxidation. The reactions were performed investigations and the activity of phthalocyanine 1 in the
at 25 °C in acetonitrile. The oxidation of cyclohexene oxidation of several pollutants is currently being investigated.
afforded full conversion after 2 h, and three products (cyclo- Furthermore, other sulfonamide substituents are also being
hexene-one, cyclohexene-ol, cyclohexene oxide, Scheme 2) tested.
2 2
Table 1 Solvent effect in the allylic oxidation of cyclohexene with H O catalysed by 1
a
a
a
b
Entry
Solvent
Time (h)
Conversion (%)
ON (%)
OL (%)
E (%)
TON
1
2
3
4
CH
CH
CH
3
3
2
CN
COCH
2
100
95
80
40
43
41
13
8
8
10
2
6
5
1
2
108
112
104
34
3
3.5
3.5
3
Cl
2
DMF
45
a
b
ON: 2-cyclohexen-1-one, OL: 2-cyclohexen-1-ol, E: cyclohexene oxide. TON: mmol product/mmol catalyst.
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1
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Acknowledgements
The Scientific and Technological Research Council of Turkey
(TUBITAK) is gratefully acknowledged for its funding through 15 M. Sanchez, E. Fache, D. Bonnet and B. Meunier,
the project 112M370 coupled to the COST Action CM1205
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