Studies of the complexes of the 4-cyanophenyl[bis(ethylsulfonyl)]methane and 4-cyanophenyl[bis(benzylsulfonyl)]methane C-acids and TBD and MTBD N-bases

Article abstract of DOI:10.1016/j.molstruc.2008.05.021

The 1:1 complexes of 4-cyanophenyl[bis(ethylsulfonyl)]methane (CHA) and 4-cyanophenyl[bis(benzylsulfonyl)]methane (CHB) with 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) have been examined by ESI MS,

Full text of DOI:10.1016/j.molstruc.2008.05.021

Journal of Molecular Structure 892 (2008) 188–194
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Studies of the complexes of the 4-cyanophenyl[bis(ethylsulfonyl)]methane
and 4-cyanophenyl[bis(benzylsulfonyl)]methane C-acids and TBD
and MTBD N-bases
*
Iwona Binkowska , Adam Huczy n´ ski, Bogumił Brzezinski, Arnold Jarczewski
Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Pozna n´ , Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 April 2008
Received in revised form 22 April 2008
Accepted 6 May 2008
Available online 20 May 2008
The 1:1 complexes of 4-cyanophenyl[bis(ethylsulfonyl)]methane (CHA) and 4-cyanophenyl[bis(benzyl-
sulfonyl)]methane (CHB) with 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and 7-methyl-1,5,7-triazabicy-
clo[4.4.0]dec-5-ene (MTBD) have been examined by ESI MS, H NMR and FT-IR spectroscopy. In all
complexes, the proton transfer from the CAH acid to the N-base was observed with the formation of
the ionic pairs. The presence of carbanions within the complexes was directly detected in the negative
ion mode ESI MS spectra. The fragmentation pathways of the carbanions of CHA and CHB are proposed.
Ó 2008 Elsevier B.V. All rights reserved.
1
Keywords:
Carbon acids
TBD
MTBD
Negative ESI-MS
FT-IR
1
. Introduction
Also the interaction of the TBD base with the oxygen atoms of
the p-NO
2
group of 4-nitrophenyl[bis(ethylsulfonyl)]methane
The carbon acids derivatives of methane activated by 4-X-
phenyl (where X = H, Cl, NO , CN) and two sulfonyl groups
2
was unexpectedly observed in acetonitrile solvent to make the
complex which was indicated by FT-IR spectrum [3,10,13]. How-
ever, this last complex was unexpected, so the ab initio compu-
tations of this structure and the energetics at the MP2/cc-pVDZ
level were completed [14]. This ion-pair complex was predicted
to be the least favorable in the solid state because of its high rel-
ative energy (ꢀ25.4 kcal mol ). However, the solvation of the
complex by acetonitrile solvent shifts its relative energy value
closer to that, estimated for complex in which the hydrogen
bonding between sulfonyl oxygens and NH groups of TBD base
takes place [14], thus making it possible in the solution.
substituted by ethyl or benzyl groups have much different prop-
erties in comparison with 1-nitro-1-(4-nitrophenyl)alkanes [1–8].
The nitroalkanes react with strong organic bases giving anions,
which are mostly dissociated into free anions in polar acetoni-
trile solvent, whereas in the less polar THF there were the ion
pairs as indicated by a blue shift in the UV–VIS spectra suggest-
ing an interaction with the countercation [5,9]. However, the C-
acids activated by cyano electron withdrawing group substituted
ꢁ1
on an
case, the negative charge is mostly localized on an
atom, but not diffused on the other electron withdrawing sub-
stituents [2]. The sulfonyl groups on an -carbon atom of the
a
-carbon atom have much different characteristics. In this
a-carbon
It is obvious that the strong organic bases such as TBD and
MTBD are the interesting compounds for kinetic and spectro-
scopic studies due to their similar pK values [15] but different
a
a
carbon acid, modifies the polarity of the molecule in such a
way that the negative charge of the anion formed after the pro-
ton abstraction can be delocalized to the oxygen atoms of these
groups. The negative charge can be shifted, in some extent to the
steric hindrance caused by the frontal methyl group in the vicin-
ity of the reaction center of the latter [1,3,16–21]. Recently, we
discussed the spectroscopic and crystallographic data of the 4-
nitrophenyl[bis(ethylsulfonyl)]methane and phenyl[bis(ethyl-
sulfonyl)]methane complexes with TBD and MTBD in solid as
well as in chloroform and acetonitrile solutions [10,13]. In these
complexes, the protons have been transferred from carbon acid
to TBD or MTBD molecules yielding ion-pairs. On the basis of
p-substituted electron withdrawing group such as: Cl, F, CN, NO
via the phenyl ring depending on their withdrawal force [1–12].
2
1
the FT-IR and H NMR studies it was demonstrated that the
MTBD complexes in acetonitrile have been fully dissociated. In
the case of the phenyl[bis(ethylsulfonyl)]methane–TBD complex
*
Corresponding author. Tel.: +48 61 8291479; fax: +48 61 829 1505.
E-mail addresses: iwonakal@amu.edu.pl (I. Binkowska), arnold@amu.edu.pl (A.
Jarczewski).
0
022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2008.05.021

I. Binkowska et al. / Journal of Molecular Structure 892 (2008) 188–194
189
the formation of the cyclic hydrogen-bonded structure has been
found. In the solution this complex is however partially dissoci-
ated. The calculated structure of the phenyl[bis(ethylsulfo-
nyl)]methane–TBD complex by PM5 semiempirical method has
shown very high similarity to the structure in the solid state
[10,13]. Hence, the study of the structures of the complexes be-
tween 4-cyanophenyl[bis(ethylsulfonyl)]methane and 4-cyano-
phenyl[bis(benzylsulfonyl)]methane and TBD and MTBD bases
seems to be promising in the aspect of characterization of the
delocalization and distribution of the negative charge in the
hydrogen-bonded complex formed.
N
C
N
C
3
2
3
2
3
2
3
2
1
O S
SO 2
2
1
6
6
O S
SO 2
2
4
4
5
5
7
8
7
8
4
4
6
6
2. Experimental
5
5
CHA
7
CHB
7
4
-Cyanophenyl[bis(ethylsulfonyl)]methane (CHA) was origi-
nally synthesized according to the method described earlier by
Cronyn [22]. Synthesis of the carbon acid involved oxidation
of thioacetal of p-nitrobenzaldehyde obtained in reaction be-
tween ethanethiol and 4-nitrobenzaldehyde in the presence of
p-toluenesulfonic acid as catalyst. The synthesis of 4-cyano-
phenyl[bis(benzylsulfonyl)]methane (CHB) was performed by a
method proposed by Westlake and Dougherty [23] and devel-
oped by Ang and Lee [24]. The EI MS spectrometry (AMD
CH 3
H
N
N
5'
N
7'
N
5'
7
'
N
N
1
'
1
'
TBD
MTBD
6
04/402) and melting points controlled the purity of the
Scheme 1. The formula of the substances studied together with the atom
numbering.
compounds.
100
3374
3238
2
758
5
0
3318
0
4
000
3500
3000
2500
2000
1500
1000
500
-
1
Wavenumber [cm ]
100
5
0
1
095
1330
1290
1
135
0
1
800
1700
1600
1500
1400
1300
1200
1100
1000
-
1
Wavenumber [cm ]
CN of: (ꢂꢂꢂ), CHA; (—), 1:1 mixture of CHA with TBD; and (---), 1:1 mixture of CHA with MTBD in the range of (a) 4000–400 cmꢁ and (b) 1800–
1
Fig. 1. FT-IR spectra in CH
3
ꢁ
1
1
000 cm .

1
90
I. Binkowska et al. / Journal of Molecular Structure 892 (2008) 188–194
1
00
3374
5
0
3336
0
4000
3500
3000
2500
2000
1500
1000
500
-
1
Wavenumber [cm ]
100
50
1
126
1336
1296
1
095
0
1
800
1700
1600
1500
1400
1300
1200
1100
1000
-
1
Wavenumber [cm ]
Fig. 2. FT-IR spectra in CH
3
CN of: (ꢂꢂꢂ), CHB; (—), 1:1 mixture of CHB with TBD; and (---), 1:1 mixture of CHB with MTBD in the range of (a) 4000–400 cmꢁ1 and (b) 1800–
ꢁ
1
1
000 cm .
Table 1
The FT-IR spectra of CHA, CHB and their 1:1 complexes
0.1 mol dm ) with TBD and MTBD were recorded in the mid
1
H NMR chemical shifts (ppm) of CHA and its 1:1 complex with TBD and MTBD and of
CHB and its 1:1 complexes with TBD and MTBD in CD
ꢁ3
(
3
CN
infrared region in acetonitrile solutions using an IFS 113v spec-
trometer (Bruker, Karlsruhe) equipped with a DTGS detector; reso-
Compound
H-1
H-2
H-3
H-4
H-5
H-6
H-7
H-8
NH
ꢁ
1
CHA
CHB
CHA–TBD
CHA–MTBD
CHB–TBD
CHB–MTBD
5.91
5.76
7.85
7.74
7.33
7.34
6.29
6.09
7.85
7.84
7.45
7.46
6.98
6.84
3.30
4.58
3.18
3.18
4.50
4.49
1.30
lution 2 cm , NSS = 64.
7.32
7.41
7.41
The Happ-Genzel apodization function was used. A cell with Si
windows and wedge-shaped layers was used to avoid interferences
1.23
1.23
7.15
7.50
5.00
6.35
(
mean layer thickness 170
l
m). All manipulations with the com-
-free glove box.
The H NMR measurements of CHA and CHB and their 1:1 com-
7.33
7.32
7.43
7.46
7.43
7.46
pounds were performed in a carefully dried and CO
2
1
ꢁ3
plexes with organic bases: TBD and MTBD (0.1 mol dm ) in
CD CN were carried out at the operating frequency sfrq =
00.075 MHz; pw = 45°; sw = 4500 Hz; t = 2.0 s, T = 293 K and
3
a
b
3
SO CH Ph
SO Et
2
2
TMS as an internal standard.
2
N
C
N
C
The ESI (Electrospray Ionization) mass spectra were recorded on
a Waters/Micromass (Manchester, UK) ZQ mass spectrometer
equipped with a Harvard Apparatus syringe pump. All sample solu-
tions were prepared in acetonitrile. The measurements were per-
formed for the solutions of (1:1) complexes of CHA and CHB with
TBD. The samples were infused into the ESI source using a Harvard
SO CH Ph
SO Et
2
2
2
Scheme 2. The proposed structure of: (a) CHA anion and (b) CHB anion.
ꢁ1
The N-bases: 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and 7-
methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) were commer-
cial products of Fluka and were used without any purification.
pump at a flow-rate of 20 ll min . The ESI source potentials were:
capillary 3 kV, lens 0.5 V, extractor 4 V. ESI mass spectra were re-
corded at the cone voltages: 30, 50, 70 and 90 V. The source tem-

I. Binkowska et al. / Journal of Molecular Structure 892 (2008) 188–194
191
perature was 120 °C and the dessolvation temperature was 300 °C.
ton relatively strong acidic. 4-cyanophenyl[bis(ethylsulfonyl)]-
methane is carbon acid with pK value found by Sorensen et al.
in water 10.06 [25], by Jarczewski et al. in acetonitrile
pK = 22.34 [26]. The pK value for 4-cyanophenyl[bis(benzylsulfo-
nyl)]methane in 80% w/w DMSO/H O is 8.55 [24]. The FT-IR spec-
tra of the 1:1 complexes of C-acids CHA and CHB with both TBD
and MTBD N-bases in acetonitrile are given in Figs. 1 and 2, respec-
tively. For comparison the respective spectra of C-acids are also
shown.
Nitrogen was used as the nebulizing and dessolvation gas at flow-
a
ꢁ1
rates of 100 and 300 1 h , respectively. Mass spectra were
acquired in the negative ion detection mode with unit mass reso-
lution at a step of 1 m/z unit. The mass range for ESI experiments
was from m/z = 100 to 600.
a
a
2
3
. Results and discussion
The formula of studied compounds together with the atom
numbering is presented in Scheme 1.
The C-acids: 4-cyanophenyl[bis(ethylsulfonyl)]methane and 4-
cyanophenyl[bis(benzylsulfonyl)]methane belong to the family of
specific group of carbon acids. The presence of two sulfonyl elec-
tron withdrawing groups within the structure makes the CAH pro-
In the spectrum of the CHA–TBD (Fig. 1, solid line) complex, a
ꢁ1
broad band in the region of 3500–2000 cm with maximum at
ꢁ1
ca. 2758 cm
indicates the formation of the hydrogen-bonded
complex between the protonated TBD molecule and the deproto-
nated CHA. The formation of this complex is however not complete
ꢁ1
because the presence of the band at 3318 cm , characteristic for
Fig. 3. The negative ion mode ESI mass spectra of 1:1 mixture of CHA with TBD at various cone voltages (cv).

1
92
I. Binkowska et al. / Journal of Molecular Structure 892 (2008) 188–194
+
+
v(NH ) vibrations of protonated and non-hydrogen-bonded TBD
molecules, indicates its partial dissociation The structure of the
complex is probably cyclic as it was earlier observed in the solid
and in the solution for other derivatives of the C-acids including
sulfonyl groups [10,13].
above. In both spectra only the bands of the v(NH ) vibrations of
ꢁ1
protonated and non-hydrogen-bonded TBD (3336 cm
) and
ꢁ1
MTBD (3374 cm ) molecules without any bands of hydrogen-
bonded species are observed. Thus, in the acetonitrile both com-
plexes are fully dissociated. The intensities of theses band also
confirm such statement.
In the FT-IR spectrum of CHA-MTBD (Fig. 1, dashed line) the
band of v(NH ) vibrations of protonated and non-hydrogen-
+
1
The H NMR data summarized in Table 1 confirms the
ꢁ1
bonded MTBD molecules is observed at 3374 cm . The intensity
of this band, especially in comparison with the corresponding
spectrum of the CHB–MTBD complex shown in Fig. 2, demon-
strates that a partially hydrogen-bonded complex in the solution
also occurs. The formation of such complex is indicated in the spec-
trum by the structured band in the region 3500–3000 cm . The
position of this band indicates that these hydrogen bonds are rela-
tively weak.
above interpretation of the FT-IR spectra of the respective
complexes. The signals of the acidic CAH protons in the spec-
tra of C-acids are observed at 5.91 and 5.76 ppm for CHA and
CHB, respectively. In the spectra of 1:1 complexes these CAH
+
signals disappear and the new signals assigned to the N H pro-
ꢁ1
tons of protonated TBD and MTBD molecules are found at 7.15
and 7.50 ppm, respectively, indicating the complete proton
transfer from the respective C-acids to N-bases. The compari-
son of these chemical shifts with those observed in the spectra
of the respective CHB complexes at 5.00 and 6.35 ppm indi-
The FT-IR spectra of the CHB–TBD (Fig. 2, solid line) and CHB–
MTBD (Fig. 2., dashed line) complexes are different that discussed
Fig. 4. The negative ion mode ESI mass spectra of 1:1 mixture of CHB with TBD at various cone voltages (cv).

I. Binkowska et al. / Journal of Molecular Structure 892 (2008) 188–194
193
charge distribution. The proposed charge distributions within
the structure of the CHA and CHB carbanions are shown in
Scheme 2.
N
C
N
C
N
C
rH
The formation of the carbanions within the complexes of
CHA and CHB with TBD and MTBD is demonstrated by the neg-
ative ion mode ESI MS spectra of these species. The negative
ion mode ESI MS spectra of CHA and CHB with TBD base per-
formed at various cone voltages are shown in Figs. 3 and 4,
respectively. In the spectrum of the 1:1 mixture of CHA with
TBD at cv = 30 V only one signal at m/z = 300 is observed indi-
cating that after proton abstraction the carbanion of CHA is
formed (structure A in Scheme 3). At cv = 50 V the signal at
m/z = 300 is still dominant and some new signals of lower
intensity at m/z = 208, 178 and 130 appeared, showing a frag-
mentation of the carbanion A. The new m/z signals can be as-
signed to the anions: B–D, respectively (Fig. 3). With further
increasing of the cv values the m/z = 300 signal of the carbanion
A is no more observed and the dominant becomes signal of the
anion E at m/z = 102.
O
S
O
O
O
O
O
S
O
HC
C
CH
S
S
S
O
O
O
C
B
m/z = 130
A
m/z = 208
m/z= 300
CH =CH
CH
3
CH
3
2
2
O
S
O
N
C
N
C
The ESI spectra of the 1:1 complex of CHB with TBD at various
cv values (Fig. 4) are comparable with the discussed above. In the
spectrum at cv = 30 only the signal of molecular anion at m/z = 424
is observed (Scheme 4, A ). With increasing cone voltages the
intensity of this signal decreases and new signals at m/z = 268,
O
C
S
O
E
0
D
m/z= 102
m/z = 178
2
04 and 178 indicating the fragmentation of the molecular anion
Scheme 3. The proposed fragmentation pathways of CHA anion.
appears. These new signals demonstrate that the fragmentation
pathway of carbanion A’ (Scheme 4) is different than that of the
CHA–TBD complex although the fragmentation final products are
the same.
cates that the protonated N-bases are partially hydrogen-
bonded with the deprotonated CHA molecules.
In conclusion, the obtained results gives the important
knowledge about delocalization and distribution of the negative
charge in the complexes formed between studied carbon acids
and N-bases in acetonitrile solution. We can say that 4-cyano-
phenyl-[bis(benzylsulfonyl)]methane is able to form 1:1 com-
plex with TBD and MTBD bases and they are fully dissociated
in acetonitrile solution. In the case of 4-cyanophenyl[bis(ethyl-
sulfonyl)]methane-TBD, the hydrogen-bonded complex has been
found, partially dissociated in acetonitrile and the odds are in
favor of cyclic as previously observed in solid and in solution
for other disulfonyl carbon acids. The 4-cyanophenyl[bis(ethyl-
sulfonyl)]methane-MTBD complex is partially hydrogen-bonded
in solution and these bonds are relatively weak. The distribu-
tion of the negative charge in the studied complexes occurs
in the cyanophenyl ring direction and sulfonyl groups directly
The comparison of the FT-IR spectrum of the carbon acids
CHA or CHB with the spectra of their complexes with TBD
and MTBD provides informations about the negative charge
delocalization within the complexes. There are two groups,
which are very sensitive for the charge delocalization, and they
are visible in the FT-IR spectra. The first group is the cyano
group. In the spectra of acetonitrile solution of CHA and CHB
ꢁ
1
the band of the v(C„N) vibrations arises at 2234 cm
and
ꢁ1
shifts after deprotonation towards 2215 cm , indicating the
distribution of the negative charge in the cyanophenyl ring
direction. It is interesting to note that the similar shifts of the
v(C„N) vibration were previously observed in the spectra of
the complexes of 4-cyanophenol with TBD and MTBD [27,28].
The second charge sensitive group is the sulfonyl one, which
is directly bonded with the CAH carbon atom. The bands of
bonded to
a-carbon atom.
the asymmetrical stretching vibrations [vas(SO
2
)] in the spectra
Acknowledgments
ꢁ1
of CHA and CHB shifts from about 1330 cm
towards
290 cm and the two bands of symmetrical stretching vibra-
ꢁ
1
1
We gratefully acknowledge the financial support from MNiSW
Grant No. N204 087 32/2496. Adam Huczy n´ ski wishes to thank
the Foundation for Polish Science for fellowship.
ꢁ1
ꢁ1
tions [v
s
(SO
2
)] from about 1140 cm
towards 1095 cm
indi-
cating that also these groups are engaged in the negative
N
C
N
C
N
C
N
C
N
C
C6H5
C CH
O
S
O
C H
O
SO2
6
5
O
O
C
O
O
C H
6
5
S
C
C
6 5
C H
C
S
O
C H
H
O
6
5
S
S
O
O
S
C6H5
O
C6H5
C6H5
D'
E'
C'
B'
m/z = 178
m/z = 204
m/z = 102
A'
m/z= 268
m/z = 424
Scheme 4. The proposed fragmentation pathways of CHB anion.

1
94
I. Binkowska et al. / Journal of Molecular Structure 892 (2008) 188–194
[
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