Synthesis and Dissociation Kinetics of Zinc, Copper, Cobalt, and Manganese Complexes with 2,3,7,8,12,18-Hexamethyl-5-phenyl-13,17-diethylporphin and Its Nitro-Substituted Analogs in Proton-Donor Media

Article abstract of DOI:10.1134/S1070363219040169

Nitro-substituted 2,3,7,7,8,12,18-hexamethyl-5-phenyl-13,17-diethylporphins with nitro groups in positions 10 and 20 of the porphyrin core and in the para-position of the benzene ring have been synthesized. The structure of the obtained compounds has been confirmed by H¹ NMR, UV, and IR spectroscopy as well as mass spectrometry. The kinetics of dissociation of zinc, copper, cobalt, and manganese complexes of the obtained porphyrins in proton-donor media has been studied. The stability of the porphyrin metal complexes has been related to the electronic effects of the substituents in the tetrapyrrole cycle and spatial distortion of the latter.

Full text of DOI:10.1134/S1070363219040169

ISSN 1070-3632, Russian Journal of General Chemistry, 2019, Vol. 89, No. 4, pp. 736–740. © Pleiades Publishing, Ltd., 2019.
Russian Text © The Authors(s), 2019, published in Zhurnal Obshchei Khimii, 2019, Vol. 89, No. 4, pp. 607–612.
Synthesis and Dissociation Kinetics of Zinc, Copper,
Cobalt, and Manganese Complexes
with 2,3,7,8,12,18-Hexamethyl-5-phenyl-13,17-diethylporphin
and Its Nitro-Substituted Analogs in Proton-Donor Media
E. M. Kuvshinovaa*, M. A. Bykovaa, I. A. Vershininab,
O. V. Gornukhinaa,c, and A. S. Semeikina,c
a Ivanovo State University of Chemistry and Technology, Sheremetevskii pr. 7, Ivanovo, 153000 Russia
*e-mail: kuvshinovae@isuct.ru
b G.A. Krestov Institute of Solutions Chemistry of the Russian Academy of Sciences, Ivanovo, Russia
c Research Institute of Macroheterocyclic Chemistry, Ivanovo State University of Chemistry and Technology, Ivanovo, Russia
Received November 15, 2018; revised November 15, 2018; accepted November 24, 2018
Abstract—Nitro-substituted 2,3,7,7,8,12,18-hexamethyl-5-phenyl-13,17-diethylporphins with nitro groups in
positions 10 and 20 of the porphyrin core and in the para-position of the benzene ring have been synthesized.
The structure of the obtained compounds has been confirmed by H1 NMR, UV, and IR spectroscopy as well as
mass spectrometry. The kinetics of dissociation of zinc, copper, cobalt, and manganese complexes of the
obtained porphyrins in proton-donor media has been studied. The stability of the porphyrin metal complexes
has been related to the electronic effects of the substituents in the tetrapyrrole cycle and spatial distortion of the
latter.
Keywords: porphyrins, coordination properties, dissociation kinetics, metal complexes
DOI: 10.1134/S1070363219040169
Porphyrins are known for catalyzing of a series of
chemical, electrochemical, and photochemical reac-
tions [1, 2]; therefore, the synthesis of novel por-
phyrins and the study of their physico-chemical
properties are among the topical issues in modern
science. Incorporation of nitro groups in the porphyrin
molecule is one of the approaches to its modification
leading to the distortion of the macrocycle and the
changes in its physico-chemical properties [3–5].
Extending our earlier studies on the effect of deforma-
tion of the tetrapyrrole macrocycle on its coordination
properties, we investigated the stability of zinc, copper,
cobalt, and manganese complexes with 2,3,7,8,12,18-
hexamethyl-5-phenyl-13,17-diethylporphin and its nitro-
substituted derivatives in proton-donor media (Scheme 1).
followed by cyclization of the intermediate biladiene 6
with benzaldehyde (R2 = H) or 4-nitrobenzaldehyde
(R2 = NO2) and oxidation (Scheme 2) [6, 7].
2,3,7,8,12,18-Hexamethyl-10,20-dinitro-5-phenyl-
13,17-diethylporphyn 2 was prepared via oxidative
electrophilic nitration of porphyrin 1 with sodium
Scheme 1.
R1
Me
Me
Me
Et
N
NH
N
R2
HN
Me
Et
2,3,7,8,12,18-Hexamethyl-5-phenyl-13,17-diethyl-
porphin 1 and 2,3,7,8,12,18-hexamethyl-5-(4-nitro-
phenyl)-13,17-diethylporphin 3 were prepared via acid
condensation of 3,4-dimethylpyrrole-2-carbaldehyde 4
with 3,3'-diethyl-4,4'-dimethyldipyrrolylmethane 5,
R1
1−3
R1 = R2 = H (1); R1 = NO2, R2 = H (2); R1 = H, R2 = NO2 (3).
Me
Me
736

SYNTHESIS AND DISSOCIATION KINETICS OF ZINC, COPPER, COBALT, AND MANGANESE
737
Scheme 2.
Me
Me
Me
Me
Et
Et
HN+
2Br−
Me
Me
+ 2
NH
NH
NH
NH
HBr
BuOH
CHO
HN
N
H
Me
Et
Et
Me
Me
Me
5
4
6
CHO
Me
Me
Me
Et
N
R2
NH
N
R2
[O]
HN
Me
Et
Me
Me
1−3
keff = (1/t)ln [(А0 – А∞)/(А – А∞)].
(2)
nitrite in trifluoroacetic acid [7] (Scheme 3) followed
by separation of the side product, 10,15-isomer 7, via
preparative thin-layer chromatography on Silufol in
benzene.
Here А0, А, and А∞ are absorbances of the solution at
the start of the experiment, at time t, and after the
reaction was complete, respectively.
Composition and structure of the formed com-
pounds were confirmed by means of MALDI-TOF mass
spectrometry as well as UV, Н1 NMR, and IR spectroscopy.
The activation energy (Е) was calculated using Eq. (3).
Е = 8.3Т1Т2/(Т2 – Т1)ln(k2/k1).
(3)
Kinetics of dissociation of zinc (ZnP), copper (CuP),
cobalt (CoP), and manganese [(АсО)MnP] complexes
of porphyrins 1‒3 was studied in the solutions in acetic
acid containing 1.5 wt % of a H2SO4‒CF3COOH
mixture (1 : 1). The considered metal complexes (МР)
dissociated (1) with the formation of the doubly
protonated porphyrins form (Н4Р2+). The spectra of the
reacting mixtures contained distinct isosbestic points
(see the figure).
МР + 4Н+ = М2+ + Н4Р2+.
(1)
The kinetic experiments were performed with
~100-fold excess of the H2SO4‒CF3COOH mixture
with respect to МР, which allowed calculation of the
effective rate constants (keff) using Eq. (2).
λ, nm
Evolution of electronic absorption spectra in the course of
dissociation of CoР(1) in acetic acid with 1.5 wt % of
a 1 : 1 H2SO4‒CF3COOH mixture.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 4 2019

738
KUVSHINOVA et al.
Scheme 3.
Me
O2N
Me
Me
Me
Me
Me
Et
Et
N
NH
N
NH
N
NaNO2
CF3CO2H
HN
N
HN
Me
Me
Et
Et
Me
NO2
Me
Me
Me
1
2
Me
O2N
Me
Me
Et
N
NH
+
HN
N
Me
Et
Me
Me
7
Kinetic parameters of dissociation of the ZnP, CuP,
CoP, and (АсО)MnP complexes are collected in the table.
bonds more available for the attack by the solvated
proton, which reduced the said bond strength.
Comparative analysis of the data in the table
showed that the increase in the number of the nitro
groups in the porphyrin molecule led to the decrease in
the rate constant of dissociation of the Mn3+, Co2+, and
Сu2+ complexes and the increase in the activation
energy.
The increase in the distortion of the porphyrin
molecule 3 in comparison with porphyrin 1 decelerated
the dissociation of the studied metal complexes and
increased the activation energy of the process. Likely,
that was due to the partial compensation for the
distortion of the porphyrin in the metal complexes,
making the macrocycle more planar. The steric
distortions of the planar structure of the porphyrins
gave relatively minor effect on the kinetic parameters
of the solvoprotolytic dissociation of the metal
complexes. The effect of distortion and the –I-effect of
the nitro groups affected oppositely the dissociation
rate [5]. Evidently, the major contribution to the
energy of the transition state was due to the stretching
of the M‒N bonds owing to the presence of electron-
accepting nitro groups in the meso-positions 10, 20 of
the porphyrin and the para-position of the benzene ring.
The simulation of geometry parameters of the
structures by means of the РМ3 method (force field
ММ+) showed that the aromatic tetrapyrrole core of
porphyrin 1 was planar. The introduction of nitro
groups at the meso-positions 10 and 20 led to
significant distortion of the macrocycle due to the
steric interaction of the nitro groups with neighboring
methyl substituents. The distortion of the molecule
core taking a grooved shape was typical of nonplanar
porphyrins [8–10].
Distortion of the tetrapyrrole macrocycle in the
porphyrin molecule reduced its aromaticity and
enhanced the electron density at the central nitrogen
atoms [8, 11]. Therefore, the basic properties of the
porphyrins were strengthened [12, 13]. The increase in
the degree of the planarity distortion made the М‒N
The obtained data revealed that the stability of the
metal complexes was affected by the nature of the salt
cation, being decreased in the [(АсО)MnP](1‒3) >
CoР(1‒3) > CuР(1‒3) > ZnP(1‒3) series. Expectedly,
the complexes of triply charged Mn3+ cation were the
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 4 2019

SYNTHESIS AND DISSOCIATION KINETICS OF ZINC, COPPER, COBALT, AND MANGANESE
739
Kinetic parameters of dissociation of zinc, copper, cobalt, and manganese complexes of porphyrins 1‒3 in acetic acid
containing 1.5 wt % of the H2SO4‒CF3COOH mixture (1 : 1)
keff×103, s–1
Е,
kJ/mol
Porphyrin
λ, nm
298 K
308 K
318 K
328 K
ZnP
Reaction occurred during the solutions mixing
СuР
1
2
3
56±1
58±2
65±2
564
563
650
13±0.6
3.2±17
–
27.00±1.350
6.90±0.290
0.11±0.008
55.00±2.70
14.00±0.72
0.24±0.01
–
0.54±0.000
24
СоР
1
2
3
59±1
63±2
72±2
532
553
643
2.30±0.1100
0.60±0.0300
0.03±0.0013
5.000±0.2500
1.400±0.0600
0.079±0.0039
10.5±0.5
3±0.14
–
–
–
0.187±0.009
МnP
1
2
3
78±1
82±2
600
578
568
–
–
–
0.1100±0.0050
0.0720±0.0030
0.0048±0.0001
0.3±0.012
0.2±0.01
0.700±0.030
0.520±0.025
0.103±0.006
129±2
0.023±0.0011
most stable in the proton-donor medium, due to high
strength of the Mn‒N covalent bonds. The higher
stability of the CoР(1‒3) complexes in comparison
with the CuР(1‒3) ones was due to the capacity of the
3d9 cation of Сu2+ to form the square-pyramidal
complexes with the М‒Solv bonds weakened owing to
the Jahn‒Teller effect. The zinc complexes of por-
phyrins 1‒3 dissociated immediately during the solu-
tions mixing. The acceleration of dissociation of the
zinc complexes in comparison with the cobalt ones
was also related to the structure of the complexes [14].
Electronic absorption spectra were recorded using a
SPEL SSP-715 scanning spectrometer in chloroform.
IR spectra were recorded using an Avatar 360 FT-IR
1
spectrometer in KBr pellets. Н NMR spectra were
recorded using a Bruker 500 spectrometer in deuterated
chloroform (residual solvent signals as internal reference).
Mass spectra were recorded using a Shimadzu Axima
Confidence MALDI-TOF spectrometer.
2,3,7,8,12,18-Hexamethyl-5-phenyl-13,17-diethyl-
porphin (1). IR spectrum, ν, cm–1: 2961, 2923, 2863,
1446, 1264, 1226, 1117, 1062, 1030, 951, 834, 751,
701. Electronic absorption spectrum, λmax, nm (log ε):
623 (3.51), 571 (3.83), 536 (3.86), 502 (4.15), 403
EXPERIMENTAL
1
(5.22). H NMR spectrum, δ, ppm: ‒3.18 br. s and
Acetic acid (“chemical pure” grade) was dried via
refluxing with the calculated amount of acetic
anhydride during 20 h and distillation with reflux
condenser. The content of water in the solvent
(0.02 wt %) was determined via the Fischer’s titration.
Monohydrate of Н2SO4 was prepared via saturation of
95% sulfuric acid with oleum (potentiometric
monitoring of the water content). Trifluoroacetic acid
(“pure” grade) was mixed with concentrated sulfuric
acid in the 10 : 1 ratio. The dried acid was distilled off
at atmospheric pressure with reflux condenser,
collecting the fraction with bp 72‒73°С, which was
then distilled again.
‒3.27 br. s (2H, NH), 10.19 s (2H, H10,20),
9.98 s (1H, H15), 8.07 d (2H, H2,6-Ph, J = 7.4 Hz),
7.82 t (1H, H4-Ph, J = 7.4 Hz), 7.75 t (2H, H3,5-Ph,
J = 7.4 Hz), 4.09 q (4H, CH2,13, 17-Et, J = 7.7 Hz),
3.67 s (6H, 12,18-CH3), 3.55 s (6H, 2,8-CH3),
2.47 s (6H, 3,7-CH3), 1.90 t (6H, CH3, 13,17-Et,
J = 7.7 Hz). Mass spectrum (MALDI-TOF), m/z: 526.184
[M]+. Мcalc 526.728.
2,3,7,8,12,18-Hexamethyl-10,20-dinitro-5-phenyl-
13,17-diethylporphin (2). IR spectrum, ν, cm–1: 2971,
2930, 2876, 1533, 1447, 1361, 1158, 1137, 1058, 947,
855, 798, 705, 664. Electronic absorption spectrum,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 4 2019

740
KUVSHINOVA et al.
λmax, nm (log ε): 648 (3.57), 591 (3.87), 518 (4.15),
413 (5.08). Н NMR spectrum, δ, ppm: ‒3.22 br. s
REFERENCES
1
(2H, NH), 9.86 s (1H, H15), 8.04 d (2H, H2,6-Ph,
J = 7.0 Hz), 7.85 t (2H, H4-Ph, J = 7.0 Hz), 7.80 t (4H,
H3,5-Ph, J = 7.0 Hz), 3.61 q (4H, CH2, Et, J = 7.6 Hz),
3.20 s (6H, 12,18-CH3), 3.02 s (6H, 2,8-CH3), 2.12 s
(6H, 3,7-CH3), 1.56 t (6H, CH3, Et, J = 7.6 Hz). Mass
spectrum (MALDI-TOF), m/z: 617.169 [M + H]+.
Мcalc 617.793.
1. Berezin, D.B. and Enikolopyan, N.S., Metalloporfiriny
(Metalloporphyrins), Moscow: Nauka, 1988.
2. Vashurin, A., Maizlish, V., Kuzmin, I., Petrov, O.,
Razumov, M., Pukhovskaya, S., Golubchikov, O., and
Koifman, O., J. Incl. Phenom. Mac. Chem., 2016,
vols. 1–2, p. 37. doi 10.1007/s10847-016-0674-4
3. Semeikin, A.S., Kolodina, E.A., Kuvshinova, E.M., S
yrbu, S.A., and Golubchikov, O.A., Russ. J. Gen.
Chem., 2012, vol. 82, no. 3, p. 488. doi 10.1134/
S1070363212030218
2,3,7,8,12,18-Hexamethyl-5-(4-nitrophenyl)-13,17-
diethylporphin (3). Electronic absorption spectrum,
4. Kuvshinova, E.M., Vershinina, I.A., Syrbu, S.A., and
Golubchikov, O.A., Russ. J. Gen. Chem., 2017, vol. 87,
no. 9, p. 2181. doi 10.1134/S1070363217090444
5. Kuvshinova, E.M., Vershinina, I.A., Islyaikin, М.K.,
Syrbu, S.A., and Golubchikov, O.A., Russ. J. Gen.
Chem., 2019, vol. 89, no. 3, p. 570. doi 10.1134/
S107036321903037X
6. Kolodina, E.A., Lubimova, T.V., Syrbu, S.A., and
Semeikin, A.S., Macroheterocycles, 2009, vol. 2, no. 1,
p. 33.
7. Kolodina, E.A., Syrbu, S.A., Semeikin, A.S., and
Koifman, O.I., Russ. J. Org. Chem., 2010, vol. 46, no. 1,
p. 138. doi 10.1134/S107042801001015X
λ
max, nm (log ε): 624 (3.50), 573 (3.82), 537 (3.87),
1
505 (4.15), 403 (5.18). Н NMR spectrum, δ, ppm:
‒3.25 br. s (2H, NH), 10.16 s (2H, H10,20), 9.97 s (1H,
H15), 8.56 d (2H, H2,6-Ph, J = 7.2 Hz), 8.20 s
(2H, H3,5-Ph, J = 7.2 Hz), 4.05 q (4H, CH2, Et,
J = 7.4 Hz), 3.62 s (6H, 12,18-CH3), 3.62 s (6H,
2,8-CH3), 2.38 s (6H, 3,7-CH3). Mass spectrum
(MALDI-TOF), m/z: 571,363 [M]+. Мcalc 571.725.
ZnP, CuP, CoP, and (АсО)MnP complexes were
prepared via refluxing of porphyrins 1‒3 with excess
of the corresponding metal acetate in the 1 : 1 mixture
of acetic acid and chloroform and purified twice via
8. Barkigia, K.M., Berber, M.D., Fajer, J., Medforth, C.J.,
Renner, M.W., and Smith, K.M., J. Am. Chem. Soc.,
1990, vol. 112, no. 24, p. 8851. doi 10.1021/
ja00180a029
9. Barkigia, K.M., Fajer, J., Berber, M.D., and Smith, K.M.,
Acta Crystallogr. Sect. (C), 1995, vol. 51, p. 511. doi
10.1107/S0108270194008978
10. Medforth, C.J., Hobbs, J.D., Rodriguez, M.R., Abra-
ham, R.J., Smith, K.M., and Shelnutt, J.A., Inorg.
Chem., 1995, vol. 34, no. 6, p. 1333. doi 10.1021/
ic00110a008
chromatography
of
alumina
(activity
grade
Brockman III) using chloroform as eluent. The
complexes purity was confirmed by the electronic
absorption spectra.
Kinetics of dissociation of the metal complexes in
acetic acid containing 1.5 wt % of the H2SO4‒
CF3COOH mixture (1 : 1) was studied by means of
spectrophotometry using
instrument equipped with a constant-temperature cell
(298–338 K within ±0.1 K).
a
Shimadzu UV-1800
11. Kuvshinova, E.M., Semeikin, A.S., Syrbu, S.A., and
Golubchikov, O.A., Russ. J. Phys. Chem. (A), 2010,
vol. 84, no. 9, p. 1516. doi 10.1134/S0036024410090128
12. Advanced Biologically Active Polyfunctional Com-
pounds and Composites: Health, Cultural Heritage and
Environmental Protection, Lekishvili, N., Zaikov, G.,
and Howell, B., Eds., New York: Nova Biomedical,
2010, p. 169.
13. Berezin, D.B., Ivanova, Yu.B., and Sheinin, V.B., Russ.
J. Phys. Chem. (A), 2007, vol. 81, no. 12, p. 1986. doi
10.1134/S003602440712014X
14. Berezin, D.B. and Golubchikov, O.A., Koordina-
tsionnaya khimiya sol’vatokompleksov solei pere-
khodnykh metallov (Coordination Chemistry of
Solvatocomplexes of Transition Metal Salts), Moscow:
Nauka, 1992.
FUNDING
This study was performed in the scope of
the governmental task from Ministry of Education
and Science of Russian Federation (project
no. 4.7305.2017/8.9) using the equipment of the
Center for Collective Usage of Ivanovo State
University of Chemistry and Technology and the
Upper Volga Regional Center for Physico-Chemical
Studies.
CONFLICT OF INTERESTS
No conflict of interest was declared by authors.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 89 No. 4 2019