The computational study of the complex between 4-nitrophenyl[bis(methylsulfonyl)]methane and TBD base in acetonitrile and tetrahydrofuran solution

Article abstract of DOI:10.1016/j.molstruc.2009.04.006

The electronic spectra of the complex between 4-nitrophenyl[bis(methylsulfonyl)]methane and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) in acetonitrile and tetrahydrofuran solvent are predicted at the CIS(D)/cc-pVDZ and PBE0/cc-pVDZ levels of theory taking

Full text of DOI:10.1016/j.molstruc.2009.04.006

Journal of Molecular Structure 929 (2009) 125–127
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Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
The computational study of the complex between
4-nitrophenyl[bis(methylsulfonyl)]methane and TBD base in acetonitrile
and tetrahydrofuran solution
*
Iwona Binkowska , Jacek Koput, Arnold Jarczewski
´
Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
The electronic spectra of the complex between 4-nitrophenyl[bis(methylsulfonyl)]methane and 1,5,7-
triazabicyclo[4.4.0]dec-5-ene (TBD) in acetonitrile and tetrahydrofuran solvent are predicted at the
CIS(D)/cc-pVDZ and PBE0/cc-pVDZ levels of theory taking into account the macroscopic solvent effect.
The obtained results for 4-nitrophenyl[bis(methylsulfonyl)]methane/TBD system are discussed taking
into consideration the experimental data for 4-nitrophenyl[bis(ethylsulfonyl)]methane/TBD system.
Ó 2009 Elsevier B.V. All rights reserved.
Received 27 February 2009
Received in revised form 3 April 2009
Accepted 6 April 2009
Available online 17 April 2009
Keywords:
4-Nitrophenyl[bis(methylsulfonyl)]methane
4-Nitrophenyl[bis(ethylsulfonyl)]methane
TBD
Carbon acid
Acetonitrile
Tetrahydrofuran
1. Introduction
However, in the previous experimental paper dealing with the for-
mation of carbanions of C-acids activated by ethylsulfonyl or benzyl-
The proton abstraction reaction from carbon acids induced by
strong organic bases in solution has attracted our attention for
many years involving the nature of the products, stabilization of
the transition state and mechanism of these reactions. The electron
withdrawing groups such as: cyano, nitro or sulfonyl change the
properties of the molecule of methane derivative in such a way
that its proton donor properties are changed in a wide range mak-
ing carbon acid (C-acid) [1–10]. The family of disulfonyl carbon
acids, have a strong acidic character [5,11] due the presence of
sulfonyl groups in the presence of different organic bases, we found
that the electronic spectra taken in acetonitrile solvent for 4-nitro-
phenyl[bis(ethylsulfonyl)]methane/TBD system has the intense
absorption maxima around kmax ꢁ 444 nm. The spectra for this com-
plex in tetrahydrofuran solvent has intense absorption band with
kmax ꢁ 440 nm. However, the change of the solvent from acetonitrile
to less polar tetrahydrofuran causes quite unexpectedly the bato-
chromic, instead hipsochromic, shift for4-nitrophenyl[bis(benzylsul-
fonyl)]methane/TBD 1:1 complex, amounting to
The reverse tendency was visible, however smaller, D
8 nm, for other complexes formed between 4-nitrophenyl[bis(ben-
zylsulfonyl)]methane and MTBD, DBU, and TMG bases in acetonitrile
solvent. The unusual trend suggest that the complexes formed retain
more ionic character in the lower polarity solvent.
D
kmax = ꢁ16 nm.
two sulfonyl groups attached to the central
a-carbon atom. In
kmax = ꢁ6–
our previous paper [12], four feasible conformations in the ground
electronic state were discussed and energetics of the ion-pair
hydrogen bonded complexes of 4-nitrophenyl[bis(methylsulfo-
nyl)]methane with 1,5,7-triazabicyclo[4.4.0]dec-5-ene in vacuum
and acetonitrile solvent are predicted at the MP2/cc-pVDZ level
of theory. In the gas phase, the energies of four possible ion-pair
complexes are calculated to be ꢀ92.0, ꢀ100.4, ꢀ100.7 and
ꢀ75.3 kcal molꢀ1, relative to the energy of the separated ions. In
acetonitrile solvent, the corresponding relative energies are pre-
dicted to be ꢀ109.6, ꢀ116.0, ꢀ114.8 and ꢀ105.7 kcal molꢀ1 [12].
To shed some light on this problem, we performed the compu-
tational study, in the hope that the calculated electronic transition
energies for the 4-nitrophenyl[bis(methylsulfonyl)]methane/TBD
complex in acetonitrile and tetrahydrofuran solvent will confirm
the previous, unexpected experimental data for 4-nitrophenyl
[bis(ethylsulfonyl)]methane/TBD complex [10]. Because of the large
size of the complexes in question, 4-nitrophenyl[bis(methylsulfonyl)]
methane was considered instead of 4-nitrophenyl[bis(ethylsulfo-
nyl)]methane used in the spectrophotometric measurements [10].
* Corresponding author. Tel.: +48 61 829 1479/80; fax: +48 61 829 1505.
E-mail address: iwonakal@amu.edu.pl (I. Binkowska).
0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.04.006

126
I. Binkowska et al. / Journal of Molecular Structure 929 (2009) 125–127
Recently, we discussed the crystallographic, NMR and FT-IR
2. Experimental
2.1. Synthesis
results for the complexes of 4-nitrophenyl[bis(ethylsulfo-
nyl)]methane and TBD and MTBD bases in solution and in the solid
state [20,21]. In the crystal form of the 1:1 complex, the N–H
protons of the protonated molecule of TBD are hydrogen bonded
with two sulfonyl groups of carbon acid by two weak hydrogen
bonds. A similar structure of the complex was proposed in chloro-
form solution whereas in acetonitrile it changed and the complex
with two intermolecular hydrogen bonds of protonated TBD with
the oxygen atoms of the nitro group of carbon acid appeared.
The FT-IR results demonstrate that the negative charge after depro-
tonation of 4-nitrophenyl[bis(ethylsulfonyl)]methane C-acid is
delocalized in such a way that the nitro groups are strongly
engaged in this conjugation process. Furthermore, the strong shift
4-nitrophenyl[bis(ethylsulfonyl)]methane was originally syn-
thesized according to the method described by Aiken and Cronyn
[7,13]. The melting point and NMR spectroscopy confirmed the
purity of the obtained compound (mp = 202 °C). 1,5,7-triazabicy-
clo[4.4.0]dec-5-ene (TBD) from Fluka was used as a commercial
reagent.
Acetonitrile, the isocratic grade solvent from J.T. Baker, was
stored over CaH2, distilled over P4O10 and finally, fractionally dis-
tilled over CaH2. The fraction of 81.5–82 °C was collected and
stored under argon to prevent CO2 and moisture. Tetrahydrofuran
(Aldrich) was stored and next distilled from blue sodium/benzo-
phenone ketyl, under argon atmosphere. All solutions for spectro-
photometric measurements were freshly prepared before
experiments and handled with precautions to protect them from
atmospheric carbon dioxide and moisture.
of the bands of the
m(SO2) vibrations indicates that also the
sulfonyl groups are involved in the delocalization process of the
electron lone pair after the abstraction of the proton from carbon
acid takes place.
The same conclusions were drawn from the ab initio calcula-
tions for 4-nitrophenyl[bis(methylsulfonyl)]methane, where the
complexes with double hydrogen NHO bonds were found [11].
These results in the solid state indicate that the ion-pair complexes
are formed between the oxygen atoms of the sulfonyl groups and
TBD molecule. It appear, that the lowest relative energy has been
found for two structures having double hydrogen NHO bonds. First
one is formed between nitrogen atoms of TBD base and the oxygen
atom of one sulfonyl group. In the second one, two NHO bonds in-
volve the oxygen atoms of both sulfonyl groups. However, in ace-
tonitrile the probability of formation of the complex with the
hydrogen bonds between oxygen atoms of the nitro group of car-
bon atom and TBD base certainly rises, as indicated by the reduced
relative energy values.
2.2. Calculation
The electronic excited state energies and transition oscillator
strengths of the complexes were determined using the configu-
ration interaction methods, CIS and CIS(D) [14,15], both in con-
junction with the cc-pVDZ basis set [16]. In the CIS approach,
the calculations included all singly-excited configurations within
the valence active space. The CIS(D) method includes addition-
ally a second-order perturbational correction to the CIS excita-
tion energy and, therefore, it is analogous to the MP2 approach
for the ground electronic state. The solvent effects were ac-
counted for within the conductor-like polarizable continuum
model (CPCM) [17] at the CIS/cc-pVDZ level of theory. To esti-
mate the electronic transitions energies in solution, the solvent
shifts determined at the CIS level were added to the transitions
energies in vacuo determined at the CIS(D) level. Electronic tran-
sition energies of the complexes were also calculated by means
of the time-dependent density functional theory (TD-DFT) using
the PBE0 hybrid functional [18] in conjunction with the cc-pVDZ
basis set. The calculations were performed using the Gaussian 03
package [19].
However, the most astonishing fact that the absorption maxi-
mum for the ionized complex in acetonitrile (kmax ꢁ 444 nm) has
been changed, after acetonitrile was replaced with tetrahydrofu-
ran, showing the batochromic, instead hipsochromic, shift required
additional support. Therefore, the theoretical ab initio CIS(D)/cc-
pVDZ and TD-DFT PBE0/cc-pVDZ methods were used to estimate
the electronic excitation energies of the complexes and to deter-
mine the maximum absorption position kmax (the transition to
the lowest excited state S1) in solvents in question. The calculated
values of kmax for the complexes of interest are given in Table 1.
The electronic excited state S1 is predicted to have the p,
p* char-
2.3. Spectrophotometric measurements
acter. The solvent shift of the S1 S0 transition was determined
at the CIS/cc-pVDZ level to be ꢀ390 and ꢀ440 cmꢀ1 for acetonitrile
and tetrahydrofuran, respectively. At the PBE0/cc-pVDZ level, the
coresponding solvent shifts were predicted to be ꢀ680 and
The electronic spectra in acetonitrile and tetrahydrofuran were
recorded on a Hewlett Packard Diode Array Spectrophotometer
(HP 8452) fitted with thermostated cell holder to keep the temper-
ature constant within 0.1 °C.
ꢀ720 cmꢀ1
, respectively. Apparently, there is no difference
between the calculated solvent shifts and the estimated kmax val-
ues for the 4-nitrophenyl[bis(methylsulfonyl)]methane (1)/TBD
complex in acetonitrile and tetrahydrofuran solutions. For compar-
ison, the experimental kmax values for the 4-nitrophenyl[bis(ethyl-
sulfonyl)]methane (2)/TBD complex in both solvents are shown.
3. Results and discussion
The formula of studied compounds is presented in Fig. 1.
Table 1
R
The calculated and experimental values of kmax for the complexes between TBD base
and 4-nitrophenyl[bis(methylsulfonyl)]methane (1) and 4-nitrophenyl[bis(ethyl-
sulfonyl)]methane (2) carbon acids in acetonitrile and tetrahydrofuran solvent.
O
O
S
O
N
O2N
CH
Products
(1)–TBD
PBE0/cc-
pVDZ
(1)–TBD
CIS(D)/cc-
pVDZ
(2)–TBD
Spectrophotometric
method
N
H
N
S
O
kmax (nm) in
MeCN
kmax (nm) in THF
413
414
337
337
444-6
440
R
TBD
R = CH3, C2H5
Fig. 1. Formula of the carbon acids and organic base used in this work.

I. Binkowska et al. / Journal of Molecular Structure 929 (2009) 125–127
127
MeCN
- 0.863
CH3
2.102
0.459
H
- 0.428
O
- 0.271
- 0.049
- 0.218
O
- 0.976
S
O
- 1.005
- 0.693
- 0.673
N
N
0.038
-
- 0.850
0.512
N
C
N
O
- 0.417
2.099
O
H
0.458
- 0.227 - 0.218
O
- 0.969
S
- 0.991
CH3
- 0.863
THF
- 0.868
CH3
2.102
0.461
H
- 0.427
O
- 0.220 - 0.272
- 0.050
O
S
O
- 1.004
N - 0.693
- 0.970
0.038
0.510
N
C- 0.848
2.098
N
O
- 0.412
H
0.459
N
- 0.673
O
- 0.968
S
O
- 0.987
- 0.227 - 0.217
CH3
- 0.863
Fig. 2. Atomic charges (e) determined by natural-bond-orbital (NBO) population analyses of the Hartree–Fock electron density for 4-nitrophenyl[bis(methylsulfonyl)]meth-
ane (1)–TBD complex in acetonitrile (MeCN) and tetrahydrofuran (THF).
The change of the solvent from acetonitrile to tetrahydrofuran
shifts the maximum absorption position kmax by just 4–6 nm to-
ward the shorter wavelength. The kmax values for the (1)/TBD com-
plex estimated by means of the TD-DFT method PBE0/cc-pVDZ are
in a much better agreement with the experimental data for the (2)/
TBD complex than those obtained by the ab initio method CIS(D)/
cc-pVDZ.
Acknowledgements
We gratefully acknowledge the financial support from MNiSW
Grant No. N204 087 32/2496. The calculations were performed at
´
the Poznan Supercomputer Center PCSS.
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