4,5-, 3,6-, and 3,4,5,6-tert-butylsulfanylphthalonitriles: synthesis and comparative structural and...
TRANSCRIPT
ORIGINAL RESEARCH
4,5-, 3,6-, and 3,4,5,6-tert-Butylsulfanylphthalonitriles: synthesisand comparative structural and spectroscopic analyses
Ufuk Kumru • Fabienne Dumoulin •
Erwann Jeanneau • Fatma Yuksel •
Yari Cabezas • Yunus Zorlu • Vefa Ahsen
Received: 22 June 2011 / Accepted: 21 July 2011 / Published online: 17 August 2011
� Springer Science+Business Media, LLC 2011
Abstract Three tert-butylsulfanylphthalonitriles have
been prepared with optimized synthetic procedures. Their
comparative structural analyses have been completed, with
a focus on IR and NMR spectroscopy and refined X-ray
structural data. Miscellaneous parameters such as UV
absorption, melting points, and related polarity of the
compounds are summarized.
Keywords Phthalonitrile � tert-Butanethiol �tert-Butylsulfanylphthalonitrile � Single-crystal �IR � NMR � Structural analysis
Introduction
Phthalonitriles are among the most widely used precursors
for phthalocyanine synthesis [1]. Despite their use as high-
tech materials in the recent decades [2, 3], phthalocyanine
derivatives still suffer from aggregation which prevent
wider general uses. Such aggregation properties, due to the
large aromatic core including eight nitrogen atoms, are a
limitation for their use in several applications as it affects
their desired properties and in particular UV–vis spectra.
Aggregation could be suppressed to some extend by several
structural factors. The nature of the metal (possibly axially
substituted) is one of them [4]. Another important and
widely used possibility is to tune the nature, number, and
position of the substituents, an easily properties-modulat-
ing parameter: the nature, number, and position of sub-
stituents can strongly influence the aggregation and
modulate a phthalocyanine’s optical, photophysical, and
photochemical properties [4–13]. Substitution by bulky
substituents is indeed a general strategy to limit one of the
main phthalocyanines’ problems. In the particular case of
N-bridged phthalocyanines, it proved to affect the central
iron atoms electronic state [14]. The presence of tert-butyl
substituents on phthalocyanines is therefore common, and
tert-butylphthalonitrile is even commercially available.
Nevertheless it has the disadvantage to lead to mixtures of
positional isomers of phthalocyanines, complicating their
characterization and preventing deep structure-related
activities effects studies. This drawback is prevented by
using isomerically pure octasubstituted (peripherally or
nonperipherally) or persubstituted phthalocyanines bearing
bulky substituents. The synthetic accessibility of the pre-
cursors is then essential.
Alkylthiosubstitution, on a synthetic point of view, offers
the advantage of an easy synthesis of the precursors: the
condensation of alkylthiols to dichlorophthalonitrile is a
very well-known method [15, 16], when the more recently
described condensation performed on 3,6-bis(40-methyl-
phenylsulfonyloxy)phthalonitrile proved to be effective
with several alkanethiols [17]. Alkylthiosubstitution offers
in addition the advantage to shift the electronic absorption
properties towards the near-infrared region of the spectrum
[18], a strongly desired effect for several applications
[19–21]. This effect is reinforced by non-peripheral
U. Kumru � F. Dumoulin � F. Yuksel � Y. Cabezas � Y. Zorlu �V. Ahsen (&)
Department of Chemistry, Gebze Institute of Technology,
P. O. Box 141, 41400 Gebze, Kocaeli, Turkey
e-mail: [email protected]
E. Jeanneau
CNRS UMR 5615, Laboratoire des Multimateriaux et Interfaces,
Universite Lyon1, 69622 Villeurbanne, France
Y. Cabezas
Ecole Nationale Superieure de Chimie de Clermont-Ferrand,
Clermont Universite, BP 10448, 63000 Clermont-Ferrand,
France
123
Struct Chem (2012) 23:175–183
DOI 10.1007/s11224-011-9850-8
substitution, which is known as well to limit aggregation
compared to analogous peripheral substitution [4, 7]. This
effect was highlighted by concomitantly published first
reports by Cook’s [22] and Nyokong [23] of octa
non-peripherally alkylsulfanyl substituted phthalocyanines,
followed by more derivatives [24]. Isomerically pure
phthalocyanines substituted by tert-butylsulfanyl moieties
have been reported in the recent years by Zimcik [25–27]
prepared from 4,5-disubstituted phthalonitrile 1 (Fig. 1). To
enlarge the scope of possible precursors, we prepared the
whole set of tert-butylsulfanylsubstituted phthalonitriles
(1, 2, and 3) represented in Fig. 1. The synthesis of phthalo-
nitriles 1 [25, 26] and 3 [28] has been previously reported.
We optimized the synthesis and present in this paper the
comparative analytical data of the three phthalonitriles.
Experimental
Materials and methods
tert-Butanethiol 4 and tetrafluorophthalonitrile (7) were
purchased from Aldrich and used as received. 4,5-Dichlor-
ophthalonitrile (5) [15] and 3,6-bis(40-methylphenylsulfo-
nyloxy) phthalonitrile (6) [17] were prepared following
described procedures.
Synthesis of 4,5-bis(tert-butylsulfanyl)phthalonitrile (1)
tert-Butanethiol (13.3 g, 147 mmol), 4,5-dichlorophthalo-
nitrile (3) (9.7 g, 49 mmol), and anhydrous potassium
carbonate (80 g, 590 mmol) were stirred in N,N0-dimeth-
ylformamide (DMF) (100 mL) under a nitrogen atmo-
sphere overnight at room temperature. Water was then
added to the reaction mixture and the stirring continued 2 h
more. The resulting precipitate was then filtered, thor-
oughly washed with water, and crystallized from ethanol.
Yield: 12.8 g (86%). C16H20N2S2, MW 304.47. White
powder, mp: 163–165 �C. 1H NMR (CDCl3): d, ppm 7.86
(2H, s, Ar–CH), 1.46 (18H, s, CH3). 13C NMR (CDCl3): d,
ppm 146.96 (Ar–CH), 136.99 (Ar–C-S), 115.19 (Ar–C–
CN), 112.56 (CN), 49.46 (C–S), 31.04 (CH3). ATR-IR:
mmax, cm-1 3068, 2978, 2964, 2939, 2899, 2867, 2228
(CN), 1505, 1451, 1396, 1366, 1283, 1221, 1158 (Ar–S–C),
1105, 931, 873 (C–H). LC–MS (ESI) m/z: calcd for
C16H20N2NaS2: 327.099; found 327.107.
Synthesis of 3,6-bis(tert-butylsulfanyl)phthalonitrile (2)
tert-Butanethiol (5.7 g, 64 mmol) was dissolved in DMF
(50 mL) under a nitrogen atmosphere and 2,3-dicyano-
1,4-phenylene bis(4-methylbenzenesulfonate) (6) (10 g,
21 mmol) and anhydrous potassium carbonate (14.6 g,
106 mmol) were added. The mixture was stirred under a
nitrogen atmosphere during 3 days at room temperature.
Water was added and the resulting precipitate was filtered
then dissolved in dichloromethane. The aqueous filtrate
was extracted by dichloromethane (3 9 50 mL). The
organic extracts were further treated with 5% sodium car-
bonate solution (2 9 250 mL). The organic phase was
dried on sodium sulfate, filtered, and evaporated. The
product was crystallized from ethanol. Yield: 2.2 g (34%).
C16H20N2S2, MW 304.47. Pale yellow powder, mp:
177–178 �C. 1H NMR (CDCl3): d, ppm 7.84 (2H, s,
Ar–CH), 1.41 (18H, s, CH3). 13C NMR (CDCl3): d, ppm
140.86 (Ar–CH), 139.75 (Ar–C–S), 124.94 (Ar–C–CN),
114.82 (CN), 50.55 (C–S), 31.07 (–CH3). ATR-IR: mmax,
cm-1 3071, 3054, 2979, 2962, 2941, 2923, 2897, 2868,
2228 (CN), 1553, 1534, 1456, 1441, 1387, 1365, 1171,
1158 (Ar–S–C), 865 (C–H). LC–MS (ESI) m/z: calcd for
C16H20N2NaS2: 327.099; found 327.090.
Synthesis of 3,4,5,6-tetra(tert-
butylsulfanyl)phthalonitrile (3)
tert-Butanethiol (4.7 g, 40 mmol) and 3,4,5,6-tetra-
fluorophthalonitrile (7) (1 g, 5 mmol) were dissolved in
DMF (80 mL) under a nitrogen atmosphere, then anhy-
drous potassium carbonate (27 g, 25 mmol) was added.
The mixture was stirred under a nitrogen atmosphere at
room temperature for 5 days and then stirred at 80 �C 5 h
further. Water was added and the resulting precipitate was
filtered then dissolved in dichloromethane. The aqueous
filtrate was extracted by dichloromethane (3 9 50 mL).
The organic extracts were further treated with 5% sodium
carbonate solution (2 9 250 mL), then water. The organic
phase was dried on sodium sulfate, filtered, and evaporated.
The product was crystallized from ethanol. Yield: 1.4 g
(60%). C24H36N2S4, MW 480.82, mp: 216–218 �C. 1H
NMR (CDCl3): d, ppm 1.25, 1.39 (s, CH3). 13C NMR
(CDCl3): d, ppm 148.01, 159.50 (Ar–CH), 126.42 (Ar–C–
CN), 115.72 (CN), 53.72, 54.01 (C–S), 31.56, 31.72 (CH3).
ATR-IR: mmax, cm-1 2959, 2921, 2899, 2862, 2230 (CN),
1487, 1470, 1455, 1363, 1305, 1218, 1147 (Ar–S–C), 1023,
928, 804 (C–H).
Fig. 1 Structure of phthalonitriles 1, 2, and 3
176 Struct Chem (2012) 23:175–183
123
X-ray data collection and structure refinement
For each compound, a suitable crystal was selected and
mounted on a Bruker AXS SMART-APEXII CCD dif-
fractometer using Mo radiation (k = 0.71073 A).
Indexing was performed using APEX2 [29] (Difference
Vectors method). Data integration and reduction were
carried out with SaintPlus 6.01. [30]. Absorption correction
was performed by multi-scan method implemented in
SADABS [31]. Space groups were determined using
XPREP implemented in APEX2 [29]. The structures of
compound 1 and 3 were solved by direct methods with
SIR97 [32] while the structure of compound 2 was solved
with the charge-flipping algorithm implemented in
SUPERFLIP [33]. The least-square refinement on F2 was
achieved with the CRYSTALS software [34].
All non-hydrogen atoms were refined anisotropically.
The hydrogen atoms were all located in a difference map,
but those attached to carbon atoms were repositioned
geometrically. The H atoms were initially refined with soft
restraints on the bond lengths and angles to regularize their
geometry (C–H in the range 0.93–0.98 A) and Uiso(H) (in
the range 1.2–1.5 times Ueq of the parent atom), after which
the positions were refined with riding constraints.
Further details may be found in Table 1.
Results and discussion
Synthesis
1 was prepared as described in literature for other thiols
[15, 16], by reacting tert-butanethiol (2-methylpropane-2-
thiol) (4) with 4,5-dichlorophthalonitrile (5) in the presence
of potassium carbonate in DMF at room temperature
overnight (Scheme 1). 1 was obtained in 86% yield,
Table 1 Crystal data and structure refinement for 1, 2, and 3
Crystal parameters 1 2 3
Empirical formula C16H20N2S2 C16H20N2S2 C24H36N2S4
Formula weight (g mol-1) 304.48 304.48 480.83
Temperature (K) 293(2) 293(2) 293(2)
Wavelength (A) 0.71073 0.71073 0.71073
Crystal system Triclinic Orthorhombic Monoclinic
Space group P - 1 Cmca P21/n
Unit-cell dimensions
a (A) 9.395(4) 7.931(1) 17.850(3)
b (A) 9.577(4) 8.782(1) 9.554(2)
c (A) 11.080(5) 24.080(2) 18.087(3)
a (�) 80.79(1) 90 90
b (�) 75.76(1) 90 117.939(5)
c (�) 63.31(1) 90 90
Crystal size (mm) 0.32 9 0.31 9 0.31 0.43 9 0.12 9 0.10 0.40 9 0.32 9 0.21
V (A3) 861.9(6) 1677.2(3) 2725.0(9)
Z 2 4 4
qcalcd (mg m-3) 1.173 1.206 1.172
l (mm-1) 0.30 0.31 0.36
F(000) 324 648 1032
h range for data collection (�) 2.8–30.4 1.7–27.6 1.3–25.0
h/k/l -10,12/-11,12/-14,14 -10,10/-11,11/-31,28 -21,21/-11,11/-21,21
Reflections collected 11393 13327 30558
Independent reflections 3906 1046 4812
Tmax and Tmin 0.91 and 0.91 0.964 and 0.970 0.89 and 0.93
Data/restraints/parameters 3905/181/0 1046/62/2 4812/271/0
Goodness-of-fit on F2 0.96 0.97 1.04
Final R indices [I [ 2r(I)] R1 = 0.047, wR2 = 0.128 R1 = 0.040, wR2 = 0.101 R1 = 0.042, wR2 = 0.113
Largest diff. peak and hole (e A-3) -0.27 and 0.41 -0.42 and 0.36 -0.34 and 0.81
Struct Chem (2012) 23:175–183 177
123
superior than the reported conditions using sodium hydride
in DMF in the presence of copper oxide, even after opti-
mization [16, 25, 26].
For the preparation of 3,6-dialkylsulfanylphthalonitriles,
two activated precursors are known to undergo nucleo-
philic substitution by thiolates: 1,2-dicyano-3,6-bis(tolu-
enesulfonyl)benzene (6) and the more active analogous
1,2-dicyano-3,6-bis(trifluorosulfonyl)benzene. In our case,
satisfying yields were obtained by stirring 4 and 6 in the
presence of potassium carbonate in DMF at room tem-
perature during 3 days (Schemes 2, 3).
The reaction of tetrachlorophthalonitrile with thiols has
been described in detail, with the successive substitution of
the chloride atoms by different thiols and phenols, includ-
ing 4 [35, 36]. The analogous 3,4,5,6-tetra(octylsulfanyl)-
phthalonitrile was prepared using ionic liquids as the solvent
in quite good yields [37]. In our case, the substitution was
performed on the tetrafluorophthalonitrile 7, known to react
with nucleophiles [38]. The reaction was completed in DMF
using potassium carbonate as the base.
We manage to improve the yields of compounds com-
pared to their previously described synthesis (Table 2).
Nevertheless it is still desirable to increase it, especially in
the case of 2. Its reproducible yield, lower compared to the
tetrasubstituted derivative 3, is probably due to a lower
reactivity of the corresponding tosylated precursor 6
compared to the fluorinated derivative 7. It will be useful in
the future to use a more active 3,6-disubstituted phthalo-
nitrile, such as for example the corresponding trifluoro-
sulfinate previously used for similar reactions.
To easily check and compare the melting point and
polarity (quantified here by the Rf in a same eluent) of each
phthalonitriles, these data are summarized in Table 3.
Single-crystal structural analysis
The structures and geometries of compounds 1, 2, and 3 in
the solid state were established by single-crystal X-ray
structural analysis. ORTEP representation of these three
structures is shown in Figs. 2, 3, and 4, respectively. The
inter-molecular interactions for the three compounds are
gathered in Table 4.
In compound 1, one of the butylsulfanyl groups is nearly
situated in the same plane as the phenyl ring with an angle
of 16.62(7)� between the mean plane of the phenyl ring and
the plane that goes through atoms C5, S1, and C9. On the
other hand, the second butylsulfanyl group is nearly
Scheme 1 Preparation of the 4,5-bis-tert-butylsulfanylphthalonitrile 1
Scheme 2 Preparation of the 3,6-bis-tert-butylsulfanylphthalonitrile 2
Scheme 3 Preparation of the 3,4,5,6-tetra-tert-butylsulfanylphthalo-
nitrile 3
Table 2 Optimized synthetic conditions and yields for 1, 2, and 3
Compound Previous works Our results
Yield (%) Conditions base/solvent equiv.
phthalonitrile/4/base
Ref. Yield (%) Conditions base/solvent, equiv.
phthalonitrile/4/base
1 65 NaH/Cu2O/DMF 1/2/2.5 [26] 86 K2CO3/DMF, 1/3/12
2 Not reported 34 K2CO3/DMF, 1/3/5
3 55 1/8 [28] 60 K2CO3/DMF, 1/8/40
Table 3 Melting point and polarity of the three phthalonitriles
Phthalonitrile 1 2 3
mp (�C) 163–165 177–178 216–218
Rf (hexane/ethyl acetate 4:1) 0.73 0.53 0.80
178 Struct Chem (2012) 23:175–183
123
perpendicular to the phenyl ring with an angle of 80.90(7)�between the plane formed by C6, S2, and C13 and the
plane of the phenyl ring.
The molecules form dimeric units through a double
C–H���N interaction. These interactions are completed by
p���p intermolecular contacts which lead to the formation
of chains running along the a axis of the unit-cell. Finally
those chains interact through C–N���p contacts to form
layers perpendicular to the c axis of the unit-cell (Fig. 5).
In compound 2, both butylsulfanyl groups are perpen-
dicular to the phenyl ring with an angle of 90.00(4)�between the plane formed by C2, S1, and C6 and the plane
of the phenyl ring.
The molecules form infinite chains along the a axis of
the unit-cell through two C–H���N interactions, as shown in
Fig. 6. These interactions are completed by double C–N���pand p���p intermolecular contacts which lead to the for-
mation of two-dimensional sheets in the (ab) plane of the
unit-cell.
The butylsulfanyl groups in compound 3 are nearly
perpendicular to the phenyl ring with angles ranging from
79.58(8)� to 86.6(1)� and the groups are disposed alterna-
tively over and under the phenyl ring. The steric hindrance
of the four butylsulfanyl groups leads to puckering of the
phenyl ring with the following Cremer and Pople param-
eters [39]: Q = 0.104(2) A, h = 69(1)� and u = 291(1)�.
Two molecules form a dimer through a double C–N���pinteraction and a dipole–dipole interaction between anti-
parallel cyano groups. The observed C–H���N and C–H���Cinteractions lead to a two-dimensional framework (Fig. 7).
ATR-IR
The ATR-IR spectrum of 1, 2, and 3 are presented in
Fig. 8. They are quite similar, only the relative vibration
peak of the C–H bonds in the fingerprint area, much more
intense for 3 than for 1 and 2 can be noticed, in accordance
with the molecular structure. The CN peaks are sharp and
centered at 2230 cm-1.
UV absorption
Each phthalonitriles has a maximum absorption at 275 nm,
with similar extinction coefficients (log e at 5.4).
1H and 13C NMR
The symmetric structures of the phthalonitriles lead to
simple NMR spectra (Figs. 9, 10).
A strong effect of the tetrasubstitution compared to the
disubstitution pattern is observed for the protons and car-
bons of the tert-butyl groups.
Fig. 2 Molecular structure of 1 (ORTEP, 30% probability ellipsoids)
Fig. 3 Molecular structure of 2 (ORTEP, 30% probability ellipsoids).
Symmetry codes: (i) 2 - x, y, z; (ii) x, 1 - y, 1 – z; (iii) 2 - x, 1 - y,
1 - z
Fig. 4 Molecular structure of 3 (ORTEP, 30% probability ellipsoids)
Struct Chem (2012) 23:175–183 179
123
Methyl protons of the disubstituted phthalonitriles 1 and
2 resonate nearly at the same frequency, when those of the
tetrasubstituted phthalonitrile 3 resonate separately into
two singlets separated by 0.15 ppm (Fig. 9). Similarly,
when the methyl carbons of the disubstituted phthalonitr-
iles 1 and 2 have very close chemical shifts, the tetrasub-
stitution pattern induces a differentiation of 0.15 ppm. The
frequencies of the quaternary carbons are shifted to lower
fields by nearly 4 ppm compared to the disubstituted
derivatives (Fig. 10). The resonance of the nitrile carbon is
less affected by the substitution pattern.
Table 4 Intermolecular interactions of the three phthalonitriles
Compound p���p interactions between phenyl rings
Cg Alpha (�) Beta (�) Cg–Cg (A)
1 C3–C4–C5–C6–C7–C8 0 19.18 3.898(2)
2 C2–C3–C3ii–C2ii–C3iii–C3i 0 54.25 5.917(1)
C–N���p interactions
Y–X���Cg N���Cg (A) C–N���Cg (�) C���Cg (A)
1 C1–N1���(C3–C4–C5–C6–C7–C8) 3.656(4) 110.5(2) 4.194(3)
2 C4–N5���(C2–C3–C3ii–C2ii–C3iii–C3i) 3.492(4) 103.6(3) 3.922(4)
3 C4–N5���(C2–C3–C6–C7–C13–C14) 3.569(2) 121.7(2) 4.282(3)
C–H���X interactions
C–H���X H���N (A) C–H���N (�) C���N (A)
1 C7–H2���N2i 2.741(2) 164.4(1) 3.658(3)
2 C3–H31���N5ii 2.449(3) 169.5(2) 3.363(4)
3 C29–H291���N26iii 2.715(2) 154.1(2) 3.603(3)
C28–H283���N26iii 2.698(2) 152.5(2) 3.596(3)
C17–H173���C25iv 2.779(2) 166.3(2) 3.728(4)
Alpha: dihedral angle between the planes; Beta: angle between the planes; Cg–Cg: distance between ring centroids
Symmetry codes: (i) 1 - x, -y, 2 – z; (ii) 1 - x, y, z; (iii) � ? x, 1/2 - y, 1/2 ? z; (iv) x, 1 ? y, z
Fig. 5 View of one of the sheet of compound 1 showing the inter-
molecular interactions as dotted lines (blue: C–N���p, green: p���p,
red: C–H���N) (Color figure online)
Fig. 6 View of one of the sheet of compound 2 showing the inter-
molecular interactions as dotted lines (blue: C–N���p, green: p���p,
red: C–H���N) (Color figure online)
180 Struct Chem (2012) 23:175–183
123
Conclusion
We reported here the optimized syntheses of three pht-
halonitriles likely to play an increased role in the chemistry
of phthalocyanine as they bear bulky substituents, able to
lower the aggregation of the corresponding phthalocya-
nines without leading to isomeric mixtures. Their complete
analysis gathered key parameters that have been compared
and interpreted relatively to the structural variations. The
synthesis of the corresponding phthalocyanines is in
progress.
Supplementary materials
CCDC-798223, 829161, and 829162 contain the supple-
mentary crystallographic data for this paper. These data
can be obtained free of charge at www.ccdc.cam.ac.uk/
conts/retrieving.html [or from the Cambridge Crystallo-
graphic Data Centre (CCDC), 12 Union Road, Cambridge
Fig. 7 View of one of the sheet of compound 3 showing the inter-
molecular interactions as dotted lines (blue: C–N���p, light blue:
cyano–cyano interactions, red: C–H���N, black: C–H���C) (Color
figure online)
Fig. 8 ATR-IR spectrum
of 1, 2, and 3
Struct Chem (2012) 23:175–183 181
123
CB2 1EZ, UK; fax: ?44(0)1223-336033; email: deposit@
ccdc.cam.ac.uk].
Acknowledgments The Scientific and Technological Research
Council of Turkey TUBITAK (PIA Turkey-France bilateral project
Bosphorus 109M356) is gratefully acknowledged. YC thanks the
long-life learning Erasmus funding.
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