Synthesis and spectral properties of 3,3′-bis(dipyrrolylmethene)

Article abstract of DOI:10.1134/S1070363211110223

Bis(2,4,7,8,9-pentamethyldipyrrolylmethene-3-yl)(4′-methoxyphenyl) methane dihydrobromide was synthesized and its spectral properties were studied. It was found that the basicity of the ligand 3,3′-bis-(dipyrrolylmethene) decreases upon insertion of the m

Full text of DOI:10.1134/S1070363211110223

ISSN 1070-3632, Russian Journal of General Chemistry, 2011, Vol. 81, No. 11, pp. 2352–2354. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © N.A. Dudina, M.B. Berezin, G.B. Guseva, A.S. Semeikin, 2011, published in Zhurnal Obshchei Khimii, 2011, Vol. 81, No. 11,
pp. 1901–1903.
Synthesis and Spectral Properties
of 3,3'-Bis(dipyrrolylmethene)
N. A. Dudinaa, M. B. Berezina, G. B. Gusevaa, and A. S. Semeikinb
a Institute of Solution Chemistry, Russian Academy of Sciences, ul. Akademicheskaya 1, Ivanovo, 153945 Russia
e-mail: eva@isc-ras.ru
b Ivanovo State University of Chemical Engineering, Ivanovo, Russia
Received October 14, 2010
Abstract—Bis(2,4,7,8,9-pentamethyldipyrrolylmethene-3-yl)(4'-methoxyphenyl)methane dihydrobromide was
synthesized and its spectral properties were studied. It was found that the basicity of the ligand 3,3'-bis-
(dipyrrolylmethene) decreases upon insertion of the methoxyphenyl group in the 3,3'-spacer.
DOI: 10.1134/S1070363211110223
To study the influence of the central spacer nature
on spectral properties of alkylated 3,3'-bis(dipyrrolyl-
methenes), we have synthesized bis(2,4,7,8,9-penta-
methyldipyrrolylmethene-3-yl)(4'-methoxyphenyl)-
methane dihydrobromide (H2L·2HBr) in which, as
differentiated from the ligands synthesized earlier
[1, 2], one of hydrogen atoms in the 3,3'-spacer is
replaced by a methoxyphenyl group. The compound
The synthesis of bis(2,4,7,8,9-pentamethyldipyrrolyl-
methene-3-yl)(4'-methoxyphenyl)methane dihydro-
bromide (III) was carried out according to the scheme
bellow.
The previous studies [1, 2] have shown that the
increase in the degree of alkylating pyrrole nuclei of
3,3'-bis(dipyrrolylmethene) molecules results in a
significant amplification of the basicity of nitrogen
1
was identified and characterized by the H NMR, IR,
and electron spectroscopy, and elemental analysis
methods.
–
atoms of (>N and >N–H) coordination centers and to
increase in the stability of coordination compounds
H3CO
OCH3
CH3
CO2Et
MeOH
H3C
HN
H3C
H
+
HBr
H3C
N
H
EtO2C
CO2Et
CHO
NH
CH3
H3C
I
KOH
(CH2OH)2
H3CO
CH3O
CH3
CH3
H3C
H3C
CH3
H
H3C
H3C
MeOH
HBr
H
H3C
H3C
CH
+
OHC
N
H
+
NH
Br−
HN
Br−
+NH
HN
NH
HN
CH3
H3C
CH3
H3C
2352

SYNTHESIS AND SPECTRAL PROPERTIES
2353
(b)
(a)
A
A
λ, nm
λ, nm
Fig. 1. Electronic absorption spectra of bis(2,4,7,8,9-pentamethyldipyrrolylmethene-3-yl)(4'-methoxyphenyl)methane solutions:
(a) in С6Н6 (c 7.1×10–6 M); (b) in DMF (c 1.8×10–4 M, H2L·2HBr, c 8.9×10–6 M, H2L); (1) H2L and (2) H2L·2HBr.
with d-metals. According to the published data [3], the
СН3O group in anisol exhibits positive mesomeric and
negative inductive effects. The aim of this work was to
estimate the effect of the methoxyphenyl substituent in
the central spacer on practically significant
physicochemical properties of the ligand.
dissociation of the salt in DMSO and pyridine
solutions (c < 5×10–5 M) proceeds partially. The
equilibrium between protonated and molecular forms
of the ligand is established in solutions, which is
proved by the presence of corresponding bands in the
regions of 498–504 and 455–460 nm. Comparison of
the positions of the maxima of an intensive band in the
spectra of the salt and the molecular ligand points to an
Comparison of the spectral data for dihydro-
bromides of the synthesized ligand and of bis(2,4,7,8,9-
pentamethyldipyrrolylmethene-3-yl)methane, the ligand
with a similar type of alkylation of pyrrole fragments
shows that the insertion of the methoxyphenyl group
into the 3,3'-spacer results in a low-frequency (by
26 cm–1) shift of the band of stretching vibrations of
N–H bonds in the IR spectrum, a small down field shift
increase in the auxochromic proton effect (Δλmax
=
salt
λ
– λlmigaaxnd ) up to 50 nm (see Fig. 1b) as compared
max
with bis(2,4,7,8,9-pentamethyldipyrrolylmethene-3-yl)
methane [2], for which the value Δλmax does not
exceed 40 nm.
According to the regularities [2] found earlier, the
revealed distinctions in spectral properties point to a
small decrease in the basicity of the ligand 3,3'-bis-
(dipyrrolylmethene) upon insertion of the methoxy-
phenyl group in the 3,3'-spacer, which, obviously, is
caused by a domination of the negative induction
effect of the substituent over the positive mesomeric
effect in the composition of the synthesized ligand
1
of the signals of protons of NH-groups in the H NMR
spectrum [2], and a bathochromic shift (up to 8 nm) of
the maximum of the long-wave band in the electron
absorption spectra of solutions in organic solvents.
The hydrobromide salt of bis(2,4,7,8,9-penta-
methyldipyrrolylmethene-3-yl)(4'-methoxyphenyl)-
methane is stable in inert (С6Н6) and proton-donor
(СHCl3) solvents (see Fig. 1a). Quantitative charac-
teristics of electron absorption spectra of cor-
responding solutions remain unchanged within several
months even on storage in light.
EXPERIMENTAL
Electron absorption spectra in organic solvents
were recorded in the range of 300–700 nm on an SF-
103 spectrophotometer (“Akvilon,” Russia) driven by
the Spectr 1.0 program complex. The experiments
were carried out in quartz cells with absorbing layer
thickness of 1 and 10 mm at a concentration 10–6–10–4 M
of the solutions under study. Temperature (298.15 K)
of solution in the cell was maintained by means of
Peltier cell accurate to ±0.1°С. The IR spectra of the
dihydrobromide in KBr tablets were taken on an
The salt H2L·2HBr undergoes an irreversible
solvolytic dissociation up to the free base in diluted
(c <5×10–5 M) DMF solutions.
H2L·2HBrSolv + 2ВSolv → H2LSolv + 2[В·HBr]Solv
.
Here B is an electron-donor solvent.
Unlike such ligands as alkyl-substituted 3,3'-bis-
(dipyrrolylmethenes) studied earlier [1, 2], solvolytic
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 11 2011

2354
DUDINA et al.
1
Avatar 360 FT–IR ESP device. The H NMR spectra
in deuterated chloroform were recorded on a Bruker
500 NMR spectrometer. Organic solvents (chemically-
pure grade) were additionally purified according to the
known procedures [4]. According to the results of
titration by Fisher’s method, water contents in solvents
did not exceed 0.02%.
To a solution of 1.4 g of bis(2,4-dimethylpyrrole-3-yl)-
(4'-methoxyphenyl)methane and 1.3 g of 2-formyl-
3,4,5-trimethylpyrrole in 50 ml of methanol 1.5 ml of
hydrobromic acid was added. The precipitate was
filtered off, washed out with methanol, and dried up in
air at room temperature. Yield 3.2 g (98%). Electronic
absorption spectrum, λmax, nm (log ε): 374–396 (4.00)
ctb, 465 (4.72) sh, 504 (4.97) (DMF, c ~ 1×10–4 M),
454 (4.71) (DMF, c ~ 1×10–6 M); 364 (4.03) ctb, 465
(4.82), 505 (5.20) (CHCl3); 374 (4.02) ctb, 467 (4.81),
Bis(2,4-dimethyl-5-ethoxycarbonylpyrrole-3-yl)-
(4'-methoxyphenyl)methane (I). A solution of 5.0 g
of 2,4-dimethyl-5-ethoxycarbonylpyrrole, 2 ml of
anisic aldehyde, and 4 ml of hydrobromic acid in
50 ml of methanol was boiled within 2 h. Then the
solution was cooled, the precipitate was filtered off,
washed out with methanol, and dried up in air at room
1
507 (5.17) (C6H6). IR spectrum, νNH 3454 cm–1. H
NMR spectrum, δ, ppm: 13.19 s (2H, NH), 12.98 s
(2H, NH), 7.06 s (2H, ms-H), 6.96 d (2H, H-Ph), 6.87
d (2Н, H-Ph), 5.37 s (1H, ms-H), 3.82 s (3H, OCH3),
2.68 s (6H, CH3), 2.30 s (6H, CH3), 2.26 s (6H, CH3),
2.00 s (6H, CH3), 1.98 s (6H, CH3). Found, %: C
60.92; Н 6.17; N 7.87. C36H44N4ОBr2. Calculated, %:
C 61.02; Н 6.26; N 7.91.
1
temperature. Yield 6.7 g (98.7%), mp 195–197°С. H
NMR spectrum, δ, ppm: 9.04 s (2H, NH), 7.04 d (2H,
CHAr), 6.83 d (2H, CHAr), 5.32 s (1H, ms-CH), 4.29 q
(4H, OCH2CH3), 3.81 s (3H, OCH3), 2.08 s (6H, CH3),
1.71 s (6H, CH3), 1.36 t (6H, OCH2CH3). Found, %: C
68.90; Н 7.03; N 6.02. C26H32N2O5. Calculated, %: C
69.01; Н 7.13; N 6.19.
ACKNOWLEDGMENTS
This work was supported by the program of basic
researches no. 7 of Presidium of Russian Academy of
sciences.
Bis(2,4-dimethylpyrrole-3-yl)(4'-methoxyphenyl)-
methane (II). A solution of 2.0 g of bis(2,4-dimethyl-
5-ethoxycarbonylpyrrole-3-yl)(4'-methoxyphenyl)-
methane and 2.0 g of potassium hydroxide in 60 ml of
ethylene glycol was boiled within 1 h. The mixture
was poured out in 200 ml of water, sodium acetate was
added, and the precipitate was filtered off, washed out
with water, and dried up in air at room temperature.
REFERENCES
1. Guseva, G.B., Dudina, N.A., Antina, E.V., V’yugin, A.I.,
and Semeikin, A.S., Zh. Obshch. Khim., 2008, vol. 78,
no. 6, p. 987.
1
Yield 1.3 g (99%). H NMR spectrum, δ, ppm: 7.42 s
2. Antina, E.V., Guseva, G.B., Dudina, N.A., V’yugin, A.I.,
and Semeikin, A.S., Zh. Obshch. Khim., 2009, vol. 79,
no. 11, p. 1903.
(2H, NH), 7.02 d (2H, CHAr), 6.88 d (2H, CHAr), 5.38 s
(1H, ms-H), 3.84 s (3H, OCH3), 1.78 s (6H, 4,4'-CH3),
1.70 s (6H, 2,2'-CH3). Found, %: C 77.61; Н 7.21; N
8.87. C20H24N2O. Calculated, %: C 77.89; H 7.84; N
9.08.
3. Traven’, V.F., Organicheskaya khimiya (Organic
Chemistry), Moscow: IKTs Akademkniga, 2008, p. 65.
4. Gordon, A.J. and Ford, R.A., The Chemist’s Com-
panion. A Handbook of Practical Data, Techniques and
References, New York: Wiley, 1972.
Bis(2,4,7,8,9-pentamethyldipyrrolylmethene-3-
yl)(4'-methoxyphenyl)methane dihydrobromide (III).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 11 2011