Synthesis and coordination properties of nitro derivatives of 5,15-diphenyl-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphyrin

Article abstract of DOI:10.1134/S1070363217090444

Methods were developed for the synthesis of nitro derivatives of 5,15-diphenyl-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphyrin containing nitro groups at the meso positions of the porphyrin core and at the para positions of the phenyl substituents. Th

Full text of DOI:10.1134/S1070363217090444

ISSN 1070-3632, Russian Journal of General Chemistry, 2017, Vol. 87, No. 9, pp. 2181–2187. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © E.M. Kuvshinova, I.A. Vershinina, S.A. Syrbu, O.A. Golubchikov, 2015, published in Rossiiskii Khimicheskii Zhurnal, 2015, Vol. 59,
No. 4, pp. 51–57.
Synthesis and Coordination Properties of Nitro Derivatives of
5,15-Diphenyl-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphyrin
E. M. Kuvshinovaa*, I. A. Vershininab, S. A. Syrbua**, and O. A. Golubchikova***
a Ivanovo State University of Chemistry and Technology, Sheremetevskii pr. 7, Ivanovo, 153000 Russia
b Krestov Institute of Solution Chemistry, Russian Academy of Sciences, ul. Akademicheskaya 1, Ivanovo, 153045 Russia
e-mail: *kuvshinovae@isuct.ru; **syrbu@isuct.ru; ***golubch@isuct.ru
Received March 1, 2015
Abstract—Methods were developed for the synthesis of nitro derivatives of 5,15-diphenyl-3,7,13,17-tetra-
methyl-2,8,12,18-tetraethylporphyrin containing nitro groups at the meso positions of the porphyrin core and at
the para positions of the phenyl substituents. The formation kinetics of the zinc, copper, and cobalt complexes
of the resultant porphyrins in pyridine and in an acetic acid–benzene (7 : 3) mixed solvent was studied. It was
found that the properties of the porphyrin ligands are determined both by the electronic effect of the nitro
groups and by the effects of spatial distortion of the porphyrin core.
Keywords: synthesis, nitro derivatives, porphyrin, metal complex, kinetics
DOI: 10.1134/S1070363217090444
INTRODUCTION
from [21]; 3,7,13,17-tetramethyl-2,8,12 ,18-tetraethyl-
5,15-bis(4'-nitrophenyl)porphyrin (2), 3,7,13,17-tetra-
methyl-2,8,12,18-tetraethyl-5,15-diphenyl-10-nitro-
porphyrin (3), 3,7,13,17-tetramethyl-2,8,12,18-tetra-
ethyl-5,15-diphenyl-10,20-dinitroporphyrin (4),
3,7,13,17-tetramethyl-2,8,12,18-tetraethyl-5-phenyl-10-
(4'-nitrophenyl)-15-phenyl-10,20-dinitroporphyrin (5),
and 3,7,13,17-tetramethyl-2,8,12,18-tetraethyl-5,15-bis-
(4'-nitrophenyl)-10,20-dinitroporphyrin (6) were syn-
thesized by the techniques from [19, 21, 22] (Scheme 1).
The deformation of the aromatic tetrapyrrole
macrocycle was found earlier [1–12] to increase with
accumulation of bulky substituents at the meso and
beta positions of porphin. A kinetic study of the
coordination of such ligands with transition metal salts
showed [13–20] that their reactivity is dramatically
dependent on the degree of distortion of the planar
structure of the tetrapyrrole macrocycle.
Scheme 1.
To further elucidate how the kinetic parameters of
the complexation reactions with 3d-metal salts are
affected by the structure of the porphyrin molecules we
examined here the kinetics of the formation of zinc,
copper, and cobalt complexes with 5,15-dipheny-l
3,7,13,17-tetramethyl-2,8,12, 18-tetraethylporphyrin (1)
and its nitro derivatives (2–6) in pyridine and in an
acetic acid–benzene (7 : 3) binary solvent. Pyridine
was chosen as basic solvent, and acetic acid–benzene,
as acidic solvent. Benzene was added to acetic acid for
improving the solubility of porphyrins.
Me
Me
R
Et
R1
Et
Et
R3
Et
N
NH
N
HN
R2
1−6
Me
Me
R = R2 = Ph; R1 = R3 = H (1), R = R2 = 4-NO2Ph; R1 = R3 =
H (2), R = R2 = Ph; R3 = H; R1 = NO2 (3), R = R2 = Ph; R1 =
R3 = NO2 (4), R=Ph; R2 =4-NO2Ph; R1 =R3 =NO2 (5), R =
R2 = 4-NO2Ph. R1 = R3 = NО2 (6).
EXPERIMENTAL
3,7,13,17-Tetramethyl-2,8,12,18-tetraethyl-5,15-di-
phenylporphyrin (1) was synthesized by the technique
2181

2182
KUVSHINOVA et al.
Stereo images of 3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphyrin and its nitro derivatives.
Porphyrins 1–6 were purified by repetitive column chro-
matography on silica gel and on alumina. Their indi-
viduality was proven by thin-layer chromatography on
Silufol plates. The electronic absorption spectra of the
porphyrins were identical to those reported in [19, 21, 22].
crystals of the salt on the filter with hexane and drying
in a vacuum desiccator over potassium hydroxide.
Pyridine (pure grade) was held over potassium
hydroxide and double-distilled with a dephlegmator
[15]. Acetic acid (chemically pure grade) was de-
hydrated by fractional freezing and distilled with a
dephlegmator. Benzene (analytically pure grade) was
distilled with a dephlegmator. The water content of the
solvents, as controlled by the Fischer titration tech-
nique [23], was no higher than 0.03%.
Zinc(II) acetate (chemically pure grade), copper(II)
acetate (analytically pure grade), and cobalt(II) acetate
(chemically pure grade) were purified by recrystalliza-
tion from aqueous acetic acid. Сu(АсО)2 and Zn(АсО)2
were dehydrated by heating at 370–390 K; Co(AcO)2
was dehydrated by refluxing for 3 h with acetic
anhydride, followed by filtering off and washing the
The rate of the formation reaction of the metal
complexes of porphyrins 1–6 was examined spectro-
Table 1. Effective rate constants of the coordination of porphyrins 1–6 to zinc acetate in pyridine and in the acidic acid–
benzene mixed solvent
Pyridine
Acetic acid–benzene (7 : 3)
C[Zn(OAc)2] = 3.5×10–3
M
C[Zn(OAc)2] = 3.5×10–3
T, K keff
M
Porphyrin
λa, nm
507
T, K
Reaction does not proceed during 3 days
keff
×
103, s–1
λa, nm
574
×
103, s–1
1
2
Reaction is instantaneous upon mixing the solutions
508
318
328
338
318
328
338
318
328
338
318
328
338
318
328
338
0.0012±0.0001
0.0034±0.0002
0.0103±0.0003
0.078±0.004
0.184±0.005
0.39±0.02
626
318
328
338
318
328
338
318
328
338
318
328
338
318
328
338
0.44±0.02
0.90±0.03
1.80±0.12
3
4
5
6
564
543
587
586
543
709
713
586
0.033±0.001
0.120±0.006
0.41±0.02
0.44±0.02
0.031±0.001
0.097±0.004
0.280±0.008
0.036±0.001
0.090±0.004
0.210±0.009
0.042±0.002
0.100±0.005
0.225±0.014
0.86±0.03
1.67±0.08
0.37±0.02
0.78±0.04
1.55±0.08
0.48±0.01
0.84±0.03
1.42±0.04
a (λ) Analytical wavelength.
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SYNTHESIS AND COORDINATION PROPERTIES OF NITRO DERIVATIVES
2183
Table 2. Effective rate constants of the coordination of porphyrins 1–4, 6 to copper acetate in pyridine and in the acetic acid–
benzene mixed solvent
Pyridine
Acetic acid–benzene (7 : 3)
C[Cu(OAc)2] = 3.5×10–4
M
C[Cu(OAc)2] = 2.5×10–3
M
×
Porphyrin
1
λa, nm
T, K
318
328
338
318
328
338
298
308
З18
288
298
308
318
keff
105, s–1
λa, nm
T, K
298
308
318
298
308
З18
298
308
З18
298
308
318
keff
×
103, s–1
507
2.23±0.13
5.2±0.3
12.0±0.6
1.24±0.07
2.32±0.11
4.7±0.3
44±3
532
5.1±0.4
14±0.6
29.5±1.2
10±0.6
2
3
4
559
521
573
534
606
564
22.5±0.8
50.3±1.2
2.49±0.12
6.03±0.3
13.6±1
79±4
136±8
210±10
340±17
520±30
790±50
1.08±0.04
3.0±0.15
8.8±0.6
6
Reaction is instantaneous upon mixing the solutions
562
298
308
318
0.945±0.056
3.0±0.12
8.84±0.44
a (λ) Analytical wavelength.
photometrically on a Hitachi U-2000 instrument in
ground-glass-joint thermostatted cells over the tem-
perature range from 228 to 338 K. The temperature
fluctuations were within 0.1 K.
The structure of porphyrin 3 is much more strongly
affected by the introduction of a nitro group to the
meso positions of the macrocycle. The inclusion of the
second nitro group in the opposite meso position of
porphyrin 4 leads to a sharp distortion of the structure
of the macrocyclic core. These structural features of
the porphyrins characteristically affect their reactivity
towards metal salts in nonaqueous solutions.
The spectra of all the reaction systems exhibited
clear isobestic points. During each experiment, 15–25
measurements of the optical density of the solution at a
certain wavelength were made at fixed time intervals.
The root mean square error in determining the effective
rate constants (keff) did not exceed 5%. Tables 1–6
summarize the kinetic parameters of the formation
reactions of zinc, copper, and cobalt complexes of
porphyrins 1–6.
Complexation of porphyrins 1–6 with zinc, copper,
and cobalt acetates [M(AcO)2]:
Н2Р + М(АсО)2 → МР + 2АсОН
adheres to kinetic equation (2):
d[H2P]/dt = –k[H2P][М(AcО)2]n.
(1)
(2)
RESULTS AND DISCUSSION
Here H2P is porphyrin, MP, metalloporphyrin, and k,
rate constant of reaction (1). The formation reaction of
zinc, copper, and cobalt complexes of the porphyrins
of interest shows the first order with respect to the
ligand. This is confirmed by the linearity of the
log [C0(H2P)/C(H2P)]–t plots [C0(H2P) and C(H2P) are
Molecular mechanics (MM+ force field) calcula-
tions of the geometric structure showed that porphyrin
1 (see figure) has a planar structure of the porphyrin
macrocycle. The introduction of two nitro groups to
the para positions of the phenyl substituents caused a
saddle-shaped macrocycle distortion from planarity.
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KUVSHINOVA et al.
Table 3. Effective constants of the coordination of porphyrins 1–6 to cobalt acetate in pyridine and in the acetic acid–
benzene mixed solvent
Pyridine
Acetic acid–benzene (7 : 3)
C[Co(OAc)2] = 3.5×10–4
M
C[Co(OAc)2] = 2.5×10–3
M
×
Porphyrin
1
λa, nm
T, K
keff
103, s–1
λa, nm
T, K
318
328
338
318
328
338
318
328
338
318
328
338
318
328
338
318
keff
×
103, s–1
508
Reaction does not proceed during
3 days
622
0.46±0.02
1.4±0.7
3.84±0.15
0.74±0.04
2.08±0.08
5.2±0.3
2
3
4
5
6
508
521
703
693
618
318
328
338
318
328
338
308
318
328
308
318
328
0.023±0.001
0.076±0.003
0.24±0.01
0.211±0.019
0.50±0.02
1.10±0.05
1.60±0.07
3.56±0.14
7.07±0.03
2.15±0.11
4.14±0.18
8.4±0.4
626
670
713
709
701
0.040±0.002
0.153±0.006
0.501±0.018
0.109±0.004
0.322±0.016
0.90±0.05
0.12±0.03
0.302±0.015
0.71±0.03
0.174±0.008
Reaction is instantaneous upon
mixing the solutions
328
338
0.40±0.02
0.85±0.04
a (λ) Analytical wavelength.
the initial and the current concentrations of the por-
phyrin, respectively]. Kinetic experiments were carried
out under at least hundredfold excess of the metal
acetates over porphyrin, which allowed calculating the
effective constants (keff) of reaction (1) by Eq. (3).
[25]; the reaction order with respect to Co(AcO)2 and
Zn(AcO)2 in pyridine and in the acetic acid–benzene
(7 : 3) binary solvent was estimated at unity [18, 26].
The activation energy of the metalloporphyrin
formation reactions was calculated using the Arrhenius
equation (5).
keff = (1/t) ln [(А0 – А∞)/(А– А∞)].
(3)
k = Ае–Е/RT
The pre-exponential factor (A) was calculated by
Eq. (6)
.
(5)
Here, А0, А, А∞ are the optical densities of the solution
at the initial moment, at time t, and at the end of the
reaction, respectively.
The rate constants kn+1 were calculated by Eq. (4).
ln A= ln k1+n + Е/RT.
(6)
kn
=
keff/Cn[Ме(АсО)2],
where n is the reaction order with respect to the salt.
(4)
The kinetic data on the formation of zinc, copper,
and cobalt complexes of porphyrins 1–6 in pyridine
possessing weakly basic properties (Tables 1–6) show
that, with increasing nonplanarity of the tetrapyrrole
aromatic macrocycle, the reaction rate tends to
increase, and the activation energy and the pre-
+1
We found earlier that the reaction order with respect
to copper acetate in the acetic acid–benzene (7 : 3)
mixed solvent is 0.5 [19], and that in pyridine, 0.4
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SYNTHESIS AND COORDINATION PROPERTIES OF NITRO DERIVATIVES
2185
Table 4. Kinetic parameters of the reaction of coordination of porphyrins 1–6 to zinc acetate in the acetic acid–benzene (7 : 3)
mixed solvent and in pyridine
Acetic acid–benzene (7 : 3)
Pyridine
k1318
×
103 ,
k1318
×
103 ,
Porphyrin
Еa, kJ/mol
А, s–1
Еa, kJ/mol
А, s–1
L mol–1 s–1
L mol–1 s–1
1
2
3
4
5
6
Reaction is instantaneous upon mixing the solutions
Reaction does not proceed during 3 days
126±3
9.4±0.4
10.2 ±0.4
8.9±0.3
12.4±0.5
62±1
110±2
78±2
98±2
74±1
1.94×109
1.11×1016
6.67×1010
1.13×1014
1.74×1010
0.322 ±0.013
22.2±1.1
126±8
100±1
72±1
57±1
64±2
48±1
8.2×1012
1.5×1010
2.9×108
3.5×107
1.06×107
106±5
137±4
Table 5. Kinetic parameters of the reaction of coordination of porphyrins 1–4, 6 to copper acetate in the acetic acid–benzene
(7 : 3) mixed solvent and in pyridine
Acetic acid–benzene (7 : 3)
Pyridine
Еa, kJ/mol
74±1
Porphyrin
298
1. 5
298
k
,
L mol–1 s–1
Еa, kJ/mol
64±2
А, s–1
5.97
4.67
5.82
5.42
4.49
k
1. 5
,
L mol–1 s–1
А, s–1
1
2
3
4
6
0.360±0.014
0.63±0.04
0.245±0.014
0.132±0.009
14.9±0.9
35×107
94×104
25×104
22×103
62±2
60±3
0.157±0.011
0.068±0.003
0.190±0.008
66±1
44±1
85±1
87±5
33±2
82±1
Reaction is instantaneous upon mixing the solutions
Table 6. Kinetic parameters of the reaction of coordination of porphyrins 1–6 to cobalt acetate in the acidic acid–benzene
(7 : 3) mixed solvent and in pyridine
Acetic acid–benzene (7 : 3)
Pyridine
k2318
×
103 ,
Porphyrin
298
Еa, kJ/mol
А, s–1
k
1. 5
,
L mol–1 s–1
Еa, kJ/mol
А, s–1
L mol–1 s–1
131.4±0.6
212±4
1
2
3
4
5
6
94±1
86±2
112±1
98±2
78±2
72±2
3.7×1014
2.8×1013
2.9×1016
3.7×1014
2.3×1011
3.2×1010
Reaction does not proceed during 3 days
6.6±0.2
60±3
104±2
74±2
65±1
58±2
8.1×1014
8.7×1010
2.2×1010
4×109
11.4±0.4
28.6±1.1
34.3±1.7
49±2
457±19
1190±60
Reaction is instantaneous upon mixing the solutions
exponential factor tend to decrease. The highest
reactivity in the formation reactions of the metal
complexes was exhibited by porphyrins 4, 6 whose
aromatic macrocycles are distorted maximally due to
the presence of nitro groups at the meso positions.
Porphyrin 6 is more active in the complexation
reaction than porphyrin 5. This is apparently due to the
fact that the latter is more strongly solvated in the
initial state than in the transition state due to the
presence of an electron-withdrawing substituent (NO2)
in the para position of the phenyl core.
A different situation is observed in the reaction of
complexation of porphyrins 1–6 with zinc, copper, and
cobalt acetates in the acetic acid–benzene (7 : 3) mixed
solvent (Tables 1–6). Highly distorted porphyrins
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KUVSHINOVA et al.
exhibit extremely low reactivity in complexing. The
distortion effect leads to increased basicity of the
tertiary nitrogen atoms which form strong hydrogen
bonds with the acetic acid molecules blocking the
coordination center of the porphyrin. Slight accelera-
tion of the complexation reaction on changing from 5
to 6 is apparently due to the fact that the distortion
effect and the –I effect of the NO2 groups in the phenyl
cores have mutually opposite impacts on the rate of the
metalloporphyrin formation reaction. Due to its
negative induction effect the nitro group slightly
acidifies the NH bonds of the porphyrin, thereby
facilitating their stretching in the transition state.
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ACKNOWLEDGMENTS
This study was financially supported by the Russian
Science Foundation (agreement no. 14-23-00204)
(synthesis of porphyrins) and within the framework the
State task of the Ministry of Education and Science of
the Russian Federation, performed by the University
(kinetic studies) (no. 4.7305.2017/8.9).
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SYNTHESIS AND COORDINATION PROPERTIES OF NITRO DERIVATIVES
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