Thermal oxidative degradation of the functionally substituted 2,2′-dipyrrolylmethenes hydrobromides and difluoroborates

Article abstract of DOI:10.1134/S1070363213030237

Thermal oxidative decomposition of samples of crystalline hydrobromide and borofluoride complexes (BODIPY) of a series of 2,2′-dipyrrolylmethenes (HL) was studied by means of thermogravimetry in an atmosphere of air oxygen. An increase in the degree and symmetry of substitution, aromaticity, and the length of the substituents in 4,4′-positions of the pyrrole ligand rings increases stability of the BODIPY-dyes to oxidative degradation. A comparative analysis of the influence of structural factors on the thermolability of hydrobromdes (HL·HBr), d-metal (ML₂) and boron(III) complexes with 2,2′-dipyrrolylmethenes was carried out.

Full text of DOI:10.1134/S1070363213030237

ISSN 1070-3632, Russian Journal of General Chemistry, 2013, Vol. 83, No. 3, pp. 545–551. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © S.L. Yutanova, M.B. Berezin, A.S. Semeikin, E.V. Antina, G.B. Guseva, A.I. V’yugin, 2013, published in Zhurnal Obshchei Khimii,
2013, Vol. 83, No. 3, pp. 492–498.
Thermal Oxidative Degradation
of the Functionally Substituted 2,2'-Dipyrrolylmethenes
Hydrobromides and Difluoroborates
S. L. Yutanovaa, M. B. Berezina, A. S. Semeikinb,
E. V. Antinaa, G. B. Gusevaa, and A. I. V’yugina
a Krestov Institute of Solution Chemistry, Russian Academy of Sciences,
ul. Akademicheskaya 1, Ivanovo, 153045 Russia
b Ivanovo State University of Chemical Technology, pr. Engelsa 7, Ivanovo, 153000 Russia
e-mail: semeikin@isuct.ru
Received March 1, 2012
Abstract―Thermal oxidative decomposition of samples of crystalline hydrobromide and borofluoride
complexes (BODIPY) of a series of 2,2'-dipyrrolylmethenes (HL) was studied by means of thermogravimetry
in an atmosphere of air oxygen. An increase in the degree and symmetry of substitution, aromaticity, and the
length of the substituents in 4,4'-positions of the pyrrole ligand rings increases stability of the BODIPY-dyes to
oxidative degradation. A comparative analysis of the influence of structural factors on the thermolability of
hydrobromdes (HL·HBr), d-metal (ML2) and boron(III) complexes with 2,2'-dipyrrolylmethenes was carried out.
DOI: 10.1134/S1070363213030237
An urgent problems of modern chemistry is the
creation and improvement of fluorescent dyes suitable
for application in various fields, like medicine, biology,
biotechnology and analytical chemistry, laser and other
optical instrumentation. To date, a lot of organic dyes
have already been created and applied, including
fluorescein [1], rhodamine [2], etc., but in recent
decades a new class of fluorophores became an object
of the scientists attention, the BF2 complexes of dipyrrolyl-
methenes (BODIPY) [3, 4]. These compounds are
promising for use as fluorescent probes and labels [5],
photosensitizers [6, 7], antioxidants [8], limiters of
hard laser radiation [9, 10], active components of new
nanomaterials [11] etc. The practical application of
BODIPY can often occur at elevated temperature and
vacuum sublimation. An important indicator of the
effectiveness of using such compounds in polythermal
conditions is their thermal stability to decomposition,
including that in the presence of oxidants like
atmospheric oxygen. While quite a large database is
accumulated on the thermal stability of d-metal di-
pyrrolylmethenates and their analogs in both oxidizing
and inert (argon, nitrogen) atmosphere [12, 13], there
is no data in the literature on the thermal analysis of
the BODIPY. It is obvious that the main influence on
the BODIPY thermolability should have the variations
in the structure of the dipyrrolylmethene ligands, the
most common of which are the properties of the
substituents at the pyrrole rings and the meso-spacer
[12, 14, 15].
As the objects of investigation of the BODIPY
thermal destruction processes, we selected 2,2'-
dipyrrolylmethenes (HL) with varied degree and nature
of substitution at the pyrrole rings. For a comparative
evaluation of the effect of thermal stabilization of the
ligand in the BODIPY composition, we obtained the
data on thermal oxidative degradation of the ligands as
hydrobromide salts.
The dipyrrolylmethene hydrobromides were prepared
according to the schemes bellow.
The first procedure consist in the condensation of
the corresponding trialkylpyrrole with formylpyrrole in
methanol in the presence of HBr as a catalyst. Another
one-step method for the synthesis of symmetrical
hexaalkyldipyrrolylmethenes is the self-condensation
of 4-alkyl-3,5-dimethylpyrrolecarboxylic acids in a
mixture of formic and hydrobromic acids. In this case,
the methylene carbon source is formic acid, and the
545

546
YUTANOVA et al.
R
Me
R
Me
Me
Me
MeOH
R
R
+
+
Me
HBr
Me
CHO
N
H
N
H
NH HN
Br−
Me
Me
Me
Me
R
Me
HCOOH
HBr
R
R
+
Me
COOEt
NH HN
Br−
N
H
Me
Me
yield of hydrobromide dipyrrolylmethenes, apparently,
is determined by their solubility in the reaction
mixture.
Difluoroborate complexes Ia–Xa were prepared
from the respective ligands hydrobromides at room
temperature according to the scheme:
CH3
CH3
Et3N, BF3 OEt2
CH2Cl2
CH3
CH3
CH3
+
N
N
NH HN
Br−
B
CH3
CH3
F
F
Iа
I
H3C
CH3
H3C
Et3N, BF3
OEt2
R
R
R
R
+
CH2Cl2
N
N
NH HN
Br−
B
H3C
CH3
H3C
CH3
F
F
II−X
IIа−Xа
R = H (II, IIa), CH3 (III, IIIa), C2H5 (IV, IVa), C3H7 (V, Va), C4H9 (VI, VIa), C5H11 (VII, VIIa), C6H13 (VIII, VIIIa),
C7H15 (IX, IXa), CH2C6H5 (X, Xa).
Examples of syntheses are described in the experi-
mental section.
I–X, Fig. 1 shows a typical thermogram. Destruction
of salts I–X proceeds in two separate stages, as was
observed previously for other dipyrrolylmethene
oligopyrrole hydrobromides [14, 15]. The first stage
comprises the process of thermal dissociation of salt
through the removal of gaseous HBr from the crystal-
line sample:
The main difference in the molecular structure of
the investigated salts, hydrobromides of dipyrrolyl-
methenes (HL·HBr, compounds I–X) and BF2-
complexes (BODIPY, compounds Ia–Xa) consist in
the degree of substitution at the pyrrole rings of the
ligands: from three (compounds I, Ia) or four (II, IIa)
methyl groups to a fully substituted pyrrole rings in
compounds III–X and IIIa–Xa, length (from two to
seven carbon atoms) of alkyl substituents R (IV–IX,
IVa–IXa) and benzyl substituents (compound X and
Xa) in the 4,4'-positions of the pyrrole rings.
t
HL·HBr(solid)
HL(solid) + HBr(gas).
The process is accompanied by endoeffect on the
DTA curve; therewith the sample mass loss (from the
curve TG) at this stage is consistent with the
theoretical amount of HBr in the initial weighed
portion of the salt (Table 1). The most unstable dipyr-
rolylmethene hydrobromide is that containing the fully
Dipyrrolylmethene hydrobromides I–X. Table 1
lists the results of thermogravimetric analysis of the
samples of crystalline dipyrrolylmethene hydrobromides
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THERMAL OXIDATIVE DEGRADATION
547
Table 1. The results of thermogravimetric analysis of 2,2'-dipyrrolylmethene hydrobromides (HL·HBr) in atmospheric oxygena
Thermal dissociation of HL·HBr
Thermal oxidative degradation of HL
Compound
tonset1
Δtheor
Δexp
tonset2
tmax. exo
tend
127
200
255
210
200
194
193
192
189
226
30.3
28.8
26.2
23.9
22.2
20.6
19.2
18.0
16.9
17.5
30.8
29.0
25.7
24.0
21.6
20.5
20.0
18.5
17.0
17.8
301
299
300
318
306
300
298
295
285
346
382
370
389
422
410
408
395
395
405
391
421
425
470
496
465
457
464
460
470
455
I
II
III
IV
V
VI
VII
VIII
IX
X
a
tonset1 is the temperature of the beginning of the thermal dissociation of HL·HBr, °C; tonset2 is the temperature of the beginning of termal
oxidative degradation of HL; tmax. exo is the temperature of the maximum exo effect, °C; tend is the temperature of the end of thermal
decomposition, °C; Δtheor and Δexp are theoretical and experimental weight loss at the salt decomposition, %.
unsubstituted pyrrole rings: its temperature of the onset
of salt dissociation (tonset1) is as low as 127ºC (Table 1).
The hydrobromides with symmetric incompletely (II)
and completely (III–X) substituted two pyrrole rings
are much stabler. The maximum tonset1 value is
observed in the salt of hexamethylated ligand (III,
252ºC), the next is the salt of the ligand with the
benzyl substituent (X, 226ºC). With increasing length
of 4,4'-dialkyl substituents in the series of compounds
from III to IX, the tonset1 value decreases mono-
tonically from 255ºC to 189ºC. Thus, there is a
tendency of increased resistance to thermal decom-
position of the investigated salts HL·HBr with an
increase in total +I-effect of substituents, which is
consistent with results for the previously studied
dipyrrolylmethene hydrobromide analogs [14–16], and
it is explained by the increased binding of the HBr
proton to the pyrrole nitrogen atom.
The BF2 complexes of dipyrrolylmethenes Ia–Xa.
By the example of compounds Ia–Xa we obtained the
first data (Table 2, Fig. 2) on the stability of the
dipyrrolylmethene BF2-complex in polythermal
conditions in an oxidizing atmosphere of air oxygen.
The thermogravimetric analysis showed that the initial
stage at heating the crystalline samples of compounds
Δm, %
t, °C
After removal of gaseous HBr from the solid
sample in the temperature range 285–346ºC (Table 1)
the second stage begins: the thermal-oxidative de-
gradation of the organic ligand HL. In the thermo-
grams this process is manifested as several stages of
mass loss with expressed exothermic peaks on the
DTA curve (Fig. 1). The temperature of beginning the
thermal oxidative degradation of the ligands (tonset2
)
weakly depends on the degree of substitution and the
length of the substituents. For compounds I–IX the
tonset2 values fall within the range of 285–318ºC, and
only for the ligand X with benzyl group the tonset2
increases to 346ºC.
τ, min
Fig. 1. Derivatogram of compound X. (1) T, (2) TG, (3) DTG,
and (4) DTA.
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548
YUTANOVA et al.
Table 2. The results of thermogravimetric analysis of 2, 2'-dipyrrolylmethenes difluoroborates (BODIPY) in an environment
of atmospheric oxygena
Residual weight
Compound
tconf
tonset1
tonset3
tonset3
tend
Δtheor
Δexp
155
152
143
141
139
138
130
129
127
190
185
188
199
203
206
212
235
236
245
254
287
298
255
290
294
309
342
334
335
459
407
442
–
595
607
531
637
548
539
551
550
559
596
29.7
28.1
25.2
22.9
20.9
19.3
17.9
16.7
15.7
16.3
29.2
27.5
24.8
22.0
20.5
18.5
17.1
16.2
15.0
15.8
Iа
IIа
IIIа
IVа
Vа
476
441
442
447
473
438
–
VIа
VIIа
VIIIа
IXа
Xа
a
tconf is the maximum temperature of the conformational transition, °C; tonset1, tonset2, and tonset3 are the temperatures of onset of the first and
subsequent stages of termal oxidative degradation of BODIPY, °C; tend is the temperature of the end of thermal decomposition, °C; Δtheor.
and Δexp are theoretical (calculated on B2O3) and experimental weight of the solid residue.
Ia–Xa is associated with conformational transition,
which results in a small endo effect on the DTA curve
while the weight of the sample remains unchanged
(Fig. 2). For BODIPY Ia–IXa an increase in the
number and length of the substituents leads to a
decrease in the maximum of conformational transition
temperature (tconf) from 155 to 127ºC. The conforma-
tional rearrangements in benzyl-substituted BODIPY
Xa occur at much higher temperature (tconf = 190ºC).
Note that the conformational transitions in the range
130–190ºC with intense endo- or exo-effects are
typical also for the crystalline samples of d-metal
dipyrrolylmethenates [12].
Δm, %
t, °C
The processes of thermal oxidative degradation of
crystalline samples of compounds Ia–Xa begin in the
temperature range of 185–254ºC. Changes in TG,
DTG, and DTA curves in the thermograms of all the
samples are similar in nature. The process involves
three stages of weight loss (TG and DTG curves),
which are accompanied by low intensity extended exo-
effects on the DTA curve.
Comparison of the experimentally observed and
calculated values of the weight of a solid residue
produced at the decomposition of complexes Ia–Xa, as
well as the results of its elemental analysis suggest that
the main solid product of BODIPY decomposition is
B2O3. Then the total equation of thermal oxidative
degradation process of the dipyrrolylmethene
borofluoride complexes can be written as:
t
[BF2L](solid) + О2(gas)
B2O3(solid) + HF(gas)
+ CO2(gas) + H2O(gas) + N2(gas).
The results of thermogravimetric analysis of the
crystalline samples Ia–Xa indicate that the thermal
stability of the BODIPY with alkylated pyrrole nuclei
τ, min
Fig. 2. Derivatogram of compound Xa. (1) T, (2) TG, (3) DTG,
and (4) DTA.
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THERMAL OXIDATIVE DEGRADATION
549
significantly increases with the number and length of
the substituents in the ligand. The lowest thermal
resistance shows compound Ia with one unsubstituted
pyrrole fragment, its temperature of degradation onset
(tonset1) is 185ºC. The introduction of the fourth methyl
group into the dipyrrolylmethene ligand slightly (by
about 3ºC) increases the stability of compound IIa
compared to Ia, while the complete methylation of the
two pyrrole rings increases the tonset1 value of
compound IIIa compared with Ia by 14ºC. In the
series of compounds IIIa–IXa the length of the alkyl
substituents in the 4,4'-position varies from one to
seven carbon atoms, which causes an increase in tonset1
of compound IXa by ~46ºC as compared with Ia. An
even greater (by ~55ºC) growth of the effect of thermal
stability is observed in the compound Xa with benzyl
radicals in the 4,4'-positions.
Thermogravimetric studies were performed on a
1000D derivatograph (MOM, Hungary) in a static air
atmosphere in a non-isothermal mode in the tempera-
ture range of 15–600°C. For compounds I–X the heating
rate was 2.5 deg min–1, a sample weight ~18–25 mg;
for compounds Ia–Xa the heating rate was
1.25°C min–1, sample weight 15–20 mg.
The signals recorded by the instrument (T is tem-
perature curve, TG is the curve of sample weight
change under the influence of temperature variation in
time, DTG is differential curve of the rate of weight
change, DTA is the curve of differential thermal
analysis of the sample) were processed using the
PowerGraph software. The error in measuring
temperature did not exceed ±1°C.
Compounds I, III, and IV were synthesized,
isolated, and identified according to [16]. Other
ligands were prepared as follows.
Comparison of the data in Tables 1 and 2 shows
that for BF2-complex Ia with unsubstituted pyrrole
ring occurs maximum (by ~58ºC) increase in thermal
stability in comparison with the salt I of the same
ligand. Temperature of the decomposition onset of the
complexes IIa, IIIa, and IVa is slightly lower than for
the corresponding salts II, III, and IV. Complexes
Va–Xa with longer substituents and with benzyl
substituents in 4,4'-positions are markedly more stable
than the corresponding salt V–X. Moreover, with
increasing alkyl chain length of 4,4'-substituents in a
series of complexes Va–IXa the effect of thermal
stabilization increases from 6 to 56ºC compared with
the corresponding HL·HBr, while for Xa with the
benzyl radical it grows by ~28ºC only.
3,3',5,5'-Tetramethyl-2,2'-dipyrrolylmethene hyd-
robromide (II). To a solution of 1.2 g (12.6 mmol) of
2,4-dimethylpyrrole and 1.55 g (12.6 mmol) of 2-
formyl-3,4-dimethylpyrrole in 20 ml of methanol while
stirring at room temperature was added 2 ml of HBr
(conc.). The mixture was stirred for 2 h, the precipitate
was filtered off, washed with methanol, ether, and
dried at room temperature in air. Yield 2.4 g (67.7%).
1H NMR spectrum, δ, ppm: 13.12 br.s (2H, NH); 7.09
s (1H, meso-H); 6.19 s (2H, 4,4'-H); 2.71 s (6H , CH3);
2.37 s (6H, CH3). Found, %: C 55.25, H 6.05, N 9.89.
C13H17BrN2. Calculated, %: C 55.70, H 6.12, N 10.00.
3,3',5,5'-Tetramethyl-4,4'-dipropyl-2,2'-dipyrrolyl-
methene hydrobromide (V). A mixture of 5.0 g
(19.5 mmol) of 2-ethoxycarbonyl-4-propyl-3,5-di-
methylpyrrole, 10 ml of HBr (conc.), and 20 ml of
90% formic acid was stirred for 4 h at heating on a
boiling water bath. After cooling the mixture, the
precipitate was filtered off, washed with methanol and
ether, and dried at room temperature in air. Yield 1.3 g
It should be noted that the stability of coordination
compounds of d-metals with 2,2'-dipyrrolylmethenes,
in some cases is higher than that of the BODIPY
formed by the same ligands [12].
Thus, our results suggest that the increase in the
degree and symmetry of the substitution, in the length
of the alkyl substituents, as well as the introduction of
the benzyl substituent in the 4,4'-positions of the
pyrrole rings of the homologs of BODIPY dyes based
on 2,2'-dipyrrolylmethene markedly increases the
stability of the compounds against the oxidative degrada-
tion compared to the not fully substituted analogs.
1
(84.8%). H NMR spectrum, δ, ppm: 12.94 s (2H,
NH); 7.06 s (1H, meso-H); 2.67 s (6H, 5,5'-CH3); 2.40
t (4H, J = 7.4 Hz, 4,4'-CH2-Pr); 2.27 s (6H, 3,3'-CH3);
1.50 q (4H, J = 7.4 Hz, CH2-Pr); 0.94 t (6H, J = 7.4
Hz, CH3-Pr). Found, %: C 62.11, H 7.91, N 7.49.
C19H29BrN2. Calculated, %: C 62.61, H 8.03, N 7.69.
Other dipyrrolylmethene hydrobromides were syn-
thesized similarly.
EXPERIMENTAL
1H NMR spectra were recorded on a Bruker NMR
500 instrument (Germany), solvent deuterated
chloroform, internal reference TMS.
3,3',5,5'-Tetramethyl-4,4'-dibutyl-2,2'-dipyrrolyl-
methene hydrobromide (VI) was obtained from 2-
ethoxycarbonyl-4-butyl-3,5-dimethylpyrrole. Yield
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 83 No. 3 2013

550
YUTANOVA et al.
1
75.2%. H NMR spectrum, δ, ppm: 12.92 s (2H, NH);
7.04 s (1H, meso-H); 2.67 s (6H, 5,5'-CH3); 2.41 t (4H,
J = 7.5 Hz, 4,4'-CH2-Bu); 2.27 s (6H, J = 7.5 Hz, 3,3'-
CH3); 1.43 q (4H, J = 7.5 Hz, CH2-Bu); 1.35 q (4H,
J = 7.5 Hz, CH2-Bu); 0.94 t (6H, J = 7.5 Hz, CH3-Bu).
Found, %: C 64.55, H 8.12, N 7.01. C21H33BrN2.
Calculated, %: C 64.26, H 8.48, N 7.14.
Substituted pyrroles required for the synthesis of
dipyrrolylmethene hydrobromides were prepared
according to methods described in [17].
3,4,5-Trimethyl-2,2'-dipyrrolylmethene difluoro-
borate (Ia). To a solution of 0.25 g (0.94 mmol) of
3,4,5-trimethyl-2,2'-dipyrrolylmethene hydrobromide
in 40 ml of methylene chloride at room temperature at
stirring was added 1.32 ml (9.4 mmol) of triethylamine
then immediately was also added 1.19 ml (9.4 mmol )
of boron trifluoride etherate. The mixture was stirred
for 3 h, then washed 3 times with water, the organic
layer was separated and evaporated to dryness on a
rotary evaporator at a reduced pressure. The solid
residue was dissolved in methylene chloride and
chromatographed on silica gel. The eluate was eva-
porated, the complex was precipitated with methanol,
filtered, and dried in air at room temperature. Yield
3,3',5,5'-Tetramethyl-4,4'-dipentyl-2,2'-dipyrrol-
ylmethene hydrobromide (VII) was obtained from 2-
ethoxycarbonyl-4-pentyl-l-3,5-dimethylpyrrole. Yield
1
60.7%. H NMR spectrum, δ, ppm: 12.91 s (2H, NH);
7,04 s (1H, meso-H); 2.67 s (6H, 5,5'-CH3); 2.40 t (4H,
J = 7.5 Hz, Hz, 4,4'-CH2-pentyl); 2.27 s (6H, 3,3'-
CH3); 1.44 q (4H, J = 7.5 Hz, CH2-pentyl); 1.34 q (4H,
J = 7.5 Hz, CH2-pentyl); 1.29 m (4H, CH2-pentyl);
0.91 t (6H, J = 7.5 Hz, CH3-pentyl). Found, %: C
65.21, H 8.39, N 6.32. C23H37BrN2. Calculated, %: C
65.68, H 8.87, N 6.66.
1
0.23 g (92.9%). H NMR spectrum, δ, ppm: 7.60 s,
7.14 s, 6.87 d (3H, J = 2.4 Hz, CH-pyrole); 6.41 s (1H,
meso-H); 2.57 s, 2.19 s, 1.98s (9H, CH3). Found, %: C
61.28, H 5.45, N 11.57. C12H13BF2N2. Calculated, %:
C 61.58, H 5.60, N 11.97.
3,3',5,5'-Tetramethyl-4,4'-dihexyl-2,2'-dipyrrolyl-
methene hydrobromide (VIII) was obtained from 2-
ethoxycarbonyl-4-hexyl-3,5-dimethylpyrrole. Yield
1
79.5%. H NMR spectrum, δ, ppm: 12.92 s (2H, NH);
7.04 s (1H, meso-H); 2.67 s (6H, 5,5'-CH3); 2.40 t
(4H , J = 7.5 Hz, 4,4'-CH2-pentyl); 2.27 s (6H, 3,3'-
CH3); 1.44 q (4H, J = 7.5 Hz, CH2-pentyl); 1.34 q
(12H, J = 7.5 Hz, CH2-pentyl); 1.29 m (4H, CH2-
pentyl), 0.90 t (6H, J = 7.5 Hz, CH3-pentyl). Found, %:
C 66.11, H 8.99, N 6.03. C25H41BrN2. Calculated, %: C
66.93, H 9.22, N 6.25.
Dipyrrolylmethene difluoroborates IIa–Xa were
synthesized similarly.
3,3',5,5'-Tetramethyl-2,2'-dipyrrolylmethene di-
1
fluoroborate (IIa). Yield 65.9%. H NMR spectrum,
δ, ppm: 7.07 s (1H, meso-H); 6.07 s (2H, 4,4'-H); 2.55
s (6H, CH3); 2.27 s (6H, CH3). Found, %: C 62.83, H
6.0, N 11.18. C13H15BF2N2. Calculated, %: C 62.94, H
6.09, N 11.29.
3,3',5,5'-Tetramethyl-4,4'-diheptyl-2,2'-dipyrrolyl-
methene hydrobromide (IX) was obtained from 2-
ethoxycarbonyl-4-heptyl-3,5-dimethylpyrrole. Yield
3,3',4,4',5,5'-Hexamethyl-2,2'-dipyrrolylmethene
difluoroborate (IIIa). Yield 96%. 1H NMR spectrum,
δ, ppm: 6.96 s (1H, meso-CH); 2.49 s (6H, 5,5'-CH3);
2.16 s (6H, 3,3'-CH3); 1.94 s (6H, 4,4'-CH3). Found,
%: C 65.18, H 6.85, N 10.04. C15H19BF2N2. Cal-
culated, %: C 65.25, H 6.94, N 10.14.
1
69.1%. H NMR spectrum, δ, ppm: 12.91 s (2H, NH);
7.03 s (1H, meso-H); 2.67 s (6H, 5,5'-CH3); 2,40 t (4H,
J = 7.4 Hz, 4,4'-CH2-heptyl); 2.27 s (6H, 3,3'-CH3);
1.43 m (4H, CH2-heptyl); 1.30 m (16H, CH2-heptyl);
0.90 t (6H, J = 7.4 Hz, CH3-heptyl). Found, %: C
67.91, H 9.06, N 5.62. C27H45BrN2. Calculated, %: C
68.03, H 9.52, N 5.88.
3,3',5,5'-Tetramethyl-4,4'-diethyl-2,2'-dipyrrolyl-
methenea-2,2'-difluoroborate (IVa). Yield 91.1%. 1H
NMR spectrum, δ, ppm: 6.97 s (1H, meso-CH); 2.52 s
(6H, 5,5'-CH3); 2.40 q (4H, J = 7.6 Hz, 4,4'-CH2-Et );
2.19 s (6H, 3,3'-CH3); 1.09 t (6H, J = 7.6 Hz, CH3-Et).
Found, %: C 67.03, H 7.51, N 9.16. C17H23BF2N2.
Calculated, %: C 67.12, H 7.62, N 9.21.
3,3',5,5'-Tetramethyl-4,4'-dibenzyl-2,2'-dipyrrolyl-
methene hydrobromide (X) was obtained from 2-
ethoxycarbonyl-4-benzyl-3,5-dimethylpyrrole. Yield
1
84.8%. H NMR spectrum, δ, ppm: 12.91 s (2H, NH);
7.28 t (4H, J = 7.2 Hz, 3",5"-H-Ph); 7.22 t (2H, J =
7.2 Hz, 4"-H-Ph) ; 7.13 s (1H, meso-H); 7.09 d (4H, J =
7.2 Hz, 2",6"-H-Ph); 3.83 s (4H, CH2-Bz); 2.64 s (6H,
5,5'-CH3); 2.27 s (6H, 3,3'-CH3). Found, %: C 70.11, H
6.18, N 5.23. C27H29BrN2. Calculated, %: C 70.41, H
6.35, N 6.09.
3,3',5,5'-Tetramethyl-4,4'-dipropyl-2,2'-dipyrrolyl-
methene difluoroborate (Va). Yield 72.2%. 1H NMR
spectrum, δ, ppm: 6.97 s (1H, meso-H); 2.51 s (6H,
5,5'-CH3); 2.35 t (4H, J = 7.4 Hz, 4,4'-CH2-Pr); 2.17 s
(6H, 3,3'-CH3); 1.49 q (4H, J = 7.4 Hz, CH2-Pr); 0.95 t
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 83 No. 3 2013

THERMAL OXIDATIVE DEGRADATION
551
(6H, J = 7.4 Hz, CH3-Pr). Found, %: C 68.29, H 8.03,
N 8.13. C19H27BF2N2. Calculated, %: C 68.69, H 8.19,
N 8.43.
Sciences, 7-P “Directed synthesis of inorganic
materials with desired properties and the creation of
functional materials based on them” (2012).
3,3',5,5'-Tetramethyl-4,4'-dibutyl-2,2'-dipyrrolyl-
methene difluoroborate (VIa). Yield 56.8%. 1H
NMR spectrum, δ, ppm: 6.96 s (1H, meso-H); 2.51 s
(6H, 5,5'-CH3); 2.37 t (4H, J = 7.3 Hz, 4,4'-CH2-Bu);
2.18 s (6H, 3,3'-CH3); 1.43 q (4H, J = 7.3 Hz, CH2-
Bu); 1.37 q (4H, J = 7.3 Hz, CH2-Bu); 0.95 t (6H,
CH3-Bu). Found, %: C 69.93, H 8.56, N 7.69.
C21H31BF2N2. Calculated, %: C 70.01, H 8.67, N 7.78.
REFERENCES
1. Ueno, T., Urano, Y., Setsukinai, K., Takakusa, H.,
Kojima, H., Kikuchi, K., Ohkubo, K., Fukuzumi, S., and
Nagano, T., J. Am. Chem. Soc., 2004, vol. 126, no. 43,
p. 14079.
2. French, P.M.W. and Taylor, J.R., Opt. Commun., 1986,
vol. 58, no. 1, p. 53.
3. Haugland, R.P., Handbook of Fluorescent Probes and
Research Chemicals, 1996.
4. Burghart, A., Kim, H., Welch, M.B., Thoresen, L.H.,
Reibenspies, J., Burgess, K.J., Bergstroem, F., and
Johansson, L.B.A., J. Org. Chem., 1999, vol. 64, no. 21,
p. 7813.
3,3',5,5'-Tetramethyl-4,4'-dipentyl-2,2'-dipyrrolyl-
1
methene difluoroborate (VIIa). Yield 86.7%. H
NMR spectrum, δ, ppm: 6.96 s (1H, meso-H); 2.50 s
(6H, 5,5'-CH3); 2.36 t (4H, J = 7.3 Hz, 4,4'-CH2-
pentyl ); 2.18 s (6H, 3,3'-CH3); 1.45 q (4H, J = 7.3 Hz,
CH2-pentyl); 1.33 q (8H, J = 7.3 Hz, CH2-pentyl); 0.92
t (6H, CH3-pentyl). Found, %: C 71.01, H 8.95, N
7.14. C23H35BF2N2. Calculated, %: C 71.13, H 9.08, N
7.21.
5. Wang, W., Fan, J., Gao, X., Wang, B., Sun, S., and
Peng, X., J. Org. Chem., 2009, vol. 74, no. 20, p. 7675.
6. Loudet, A. and Burgess, K., Chem. Rev., 2007, vol. 107,
no. 11, p. 4891.
7. Wood, E. and Thompson, A., Chem. Rev., 2007, vol. 107,
3,3',5,5'-Tetramethyl-4,4'-dihexyl-2,2'-dipyrrolyl-
methene difluoroborate (VIIIa). Yield 58.5%. H
no. 5, p. 1831.
1
8. Chepelev, L.L., Beshara, C.S., MacLean, P.D., Hatfield, G.L.,
Rand, A.A., Thompson, A., Wright, J.S., and Barc-
lay, L.R.C., J. Org. Chem., 2006, vol. 71, no. 1, p. 22.
9. Garcia-Moreno, I., Costela, A., Campo, L., Sastre, R.,
Amat-Guerri, F., Liras, M., Lopez, A.F., Banuelos, P.J.,
and Lopez, A.I., J. Phys. Chem. A., 2004, vol. 108,
no. 16, p. 3315.
10. Liras, M., Prieto, J.B., Pintado-Sierra, M., Arbeloa, F.L.,
Garcia-Moreno, I., Costela, A., Infantes, L., Sastre, R.,
and Amat-Guerri, F., Org. Lett., 2007, vol. 9, no. 21,
p. 4183.
11. Chen, X., Lenhert, S., Hirtz, M., Lu, N., Fuchs, H., and
Chi, L., Acc. Chem. Res., 2007, vol. 40, no. 6, p. 393.
12. Antina, E.V., Guseva, G.B., Rumyantsev, E.V., and
Dudina, N.A., Zh. Obshch. Khim., 2009, vol. 79, no. 9,
p. 1543.
13. Gresser, R., Hoyer, A., Hummert, M., Hartmann, H.,
Leo, K., and Riede, M., Dalton Trans., 2011, vol. 40,
p. 3476.
14. Lebedeva, N.Sh., Antina, E.V., Berezin, M.B.,
Semeikin, А.S., and Bukushina, G.B., Zh. Fiz. Khim.,
2000, vol. 74, no. 7, p. 1141.
15. Chermova, О.М., Berezin, M.B., and Antina, E.V., Zh.
Fiz. Khim., 2003, vol. 77, no. 6, p. 1002.
16. Berezin, M.B., Semeikin, А.S., Antina, E.V., Pasha-
nova, N.А., Lebedeva, N.Sh., and Bukushina, G.B., Zh.
Obshch. Khim, 1999, vol. 69, no. 12, p. 2040.
NMR spectrum, δ, ppm: 6.96 s (1H, meso-H); 2.50 s
(6H, 5,5'-CH3); 2.36 t (4H, J = 7.3 Hz, 4,4'-CH2-
hexyl ); 2.17 s (6H, 3,3'-CH3); 1.44 q (4H, J = 7.3 Hz,
CH2-hexyl); 1.32 m (12H, CH2-hexyl); 0.91 t (6H,
CH3-hexyl). Found, %: C 72.01, H 9.32, N 6.59.
C25H39BF2N2. Calculated, %: C 72.11, H 9.44, N 6.73.
3,3',5,5'-Tetramethyl-4,4'-diheptyl-2,2'-dipyrrolyl-
methene difluoroborate (IXa). Yield 97.2%. 1H
NMR spectrum, δ, ppm: 6.96 s (1H, meso-H); 2.50 s
(6H, 5,5'-CH3); 2.36 t (4H, J = 7.5 Hz, 4,4'-CH2-
heptyl ); 2.17 s (6H, 3,3'-CH3); 1.44 q (4H, J = 7.5 Hz,
CH2-heptyl); 1.32 m (16H, CH2-heptyl); 0.91 t (6H,
J = 7.5 Hz, CH3-heptyl). Found, %: C 72.85, H 9.63, N
6.21. C27H43BF2N2. Calculated, %: C 72.96, H 9.75, N
6.30.
3,3',5,5'-Tetramethyl-4,4'-dibenzyl-2,2'-dipyrrolyl-
methene difluoroborate (Xa). Yield 81.2%. 1H NMR
spectrum, δ, ppm: 7.29 t (4H, J = 7.3 Hz, 3",5"-H-Ph);
7.21 t (2H, J = 7.3 Hz, 4"-H-Ph); 7.15 d (4H, J = 7.3
Hz, 2",6"-H-Ph); 7.07 s (1H, meso-H); 3.80 s (4H,
CH2-Bz); 2.47 s (6H, 5,5'-CH3); 2.18 s (6H , 3,3'-CH3).
Found, %: C 75.67, H 6.29, N 6.42. C27H27BF2N2.
Calculated, %: C 75.71, H 6.35, N 6.54.
ACKNOWLEDGMENTS
17. Berezin, M.B., Semeikin, А.S., V’yugin, А.I., and
Krestov, G.А., Izv. Ross. Akad. Nauk, Ser. Khim., 1993,
no. 3, p. 495.
This work was supported by the Basic Research
Program of the Presidium of Russian Academy of
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 83 No. 3 2013