Basic and Coordination Properties of Tetraphenylporphine Derivatives

Article abstract of DOI:10.1134/S1070363218100122

Basic and coordination properties of 5,10,15,20-tetrakis(3,5-dibromophenyl)porphine and 5,10,15,20-tetrakis(4-methoxy-3-bromophenyl)porphine in acetonitrile have been investigated by means of spectrophotometry. The optimization of the geometry parameters of polysubstituted porphyrins has been performed using quantum-chemical method (РМ3). The relationship between geometric structure of the studied porphyrins and their coordination, basic, and spectral properties is discussed.

Full text of DOI:10.1134/S1070363218100122

ISSN 1070-3632, Russian Journal of General Chemistry, 2018, Vol. 88, No. 10, pp. 2103–2107. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © Yu.B. Ivanova, A.O. Plotnikova, A.S. Semeikin, S.G. Pukhovskaya, N.Zh. Mamardashvili, 2018, published in Zhurnal Obshchei
Khimii, 2018, Vol. 88, No. 10, pp. 1659–1664.
Basic and Coordination Properties
of Tetraphenylporphine Derivatives
Yu. B. Ivanovaa*, A. O. Plotnikovab, A. S. Semeikinb,
S. G. Pukhovskayab, and N. Zh. Mamardashvilia
a Krestov Institute of Solutions Chemistry, Russian Academy of Sciences,
ul. Akademicheskaya 1, Ivanovo, 153045 Russia
*e-mail: jjiv@yandex.ru
b Ivanovo State University of Chemistry and Technology, Ivanovo, Russia
Received April 16, 2018
Abstract—Basic and coordination properties of 5,10,15,20-tetrakis(3,5-dibromophenyl)porphine and 5,10,15,20-
tetrakis(4-methoxy-3-bromophenyl)porphine in acetonitrile have been investigated by means of
spectrophotometry. The optimization of the geometry parameters of polysubstituted porphyrins has been
performed using quantum-chemical method (РМ3). The relationship between geometric structure of the studied
porphyrins and their coordination, basic, and spectral properties is discussed.
Keywords: porphyrins, basic properties, metal porphyrins, coordination properties
DOI: 10.1134/S1070363218100122
Polysubstituted porphyrins deformed due to the
presence of many side substituents containing alkyl
groups and halides in the β-positions and phenyl sub-
stituents in the meso-positions are the best investigated
derivatives of tetraphenylporphine [1–9]. Firstly, it is
related to the availability of these compounds, in
particular via improved Rothemund method which
includes condensation reactions involving β-sub-
stituted pyrroles and aldehydes containing meso-
substituents [8, 9]. However, successful resolution of
the issues arisen in the course of fundamental and
applied studies of these compounds demands optimiza-
tion of methods of preparation and modification of the
porphyrins. Thus, the investigation of the influence of
electronic and steric effects of the porphyrin
macrocycle substituents as a tool of tuning the coor-
dination, acid-basic, and spectral properties of por-
phyrins is an important and topical task for creation of
physicochemical background for the preparation of
new materials.
According to computer simulation with the optimiza-
tion of geometry parameters of polysubstituted
porphyrins using quantum-chemical method РМ3
(HyperChem, version 7.02), porphyrins 1 and 2 as well
as non-substituted tetraphenylporphyrin were planar
(Fig. 1). Incorporation of the substituents at the phenyl
rings of the macrocycle of porphyrin ligand almost did
not affect the deformation of tetrapyrrole macrocycle,
but electronic effects of substituents led to the change
in coordination and basic properties of porphyrins.
The activity of ligands in such systems is mainly
determined by the structure of the acid-base complexes
formed in the solution; their ionizing ability is affected
by the degree of proton transfer from acid molecule to
base (solvent) molecule.
Ligands 1 and 2 were studied using spectrophoto-
metry in the HClO4–CH3CN (298 K) and Zn(OAc)2–
CH3CN (288–308 K) systems. Porphyrins (H2P) in
organic solvents are amphoteric and can be protonated
or deprotonated at the transannular nitrogen atoms in
the presence of acids or bases, respectively:
Here we report the results of spectrophotometric
study of basic (interaction with HClO4) and coordina-
tion [with Zn(OAс)2] properties of 5,10,15,20-tetrakis-
(3,5-dibromophenyl)porphine 1 and 5,10,15,20-tetrakis-
(4-methoxy-3-bromophenyl)porphine 2 in acetonitrile at
298 and 288–308 K, respectively.
Kb1
(1)
H3P+
H2P + H+,
Kb2
H4P2+
H3P+ + H+,
(2)
2103

2104
IVANOVA et al.
Fig. 1. The structures of investigated porphyrins (PM3 optimization).
Ka1
Ka2
did not rule out the stepwise ionization processes but
rather indicated that the equilibrium constants of the
protonation reactions should be close [10]. The
existence of isosbestic points and the character of the
absorption evolution indicated that the ratio of the
ionized forms was not changed with the protonation of
the porphyrin molecule. Effective molar absorptivity
of the forms of the studied porphyrins involved in
equilibria (1) and (2) in the HClO4–CH3CN system
were determined using the data on absorption and total
concentration of the porphyrins (Table 1). The overall
protonation constant of processes (1) and (2) was
calculated using Eq. (5).
HP− + H+,
(3)
(4)
H2P
HP−
−
P2 + H+.
Hereafter, Н2Р, HР–, Р2–, H3P+, H4P2+ are intramole-
cular, mono- and bis- deprotonated and protonated
forms of porphyrin ligand.
In the case of porphyrin ligands 1 and 2, only
protonation processes (1) and (2) occurred. The
electron absorption spectra of the studied ligands
recorded with the increasing HClO4 concentration in
the HClO4–CH3CN system could be divided into two
sets with their own sets of isosbestic points (Fig. 2a).
The presence of two sets of isosbestic points in the
electron absorption spectra is characteristic of stepwise
protonation processes. However, the spectrophoto-
metric titration curves plotted from the experimental
data did not contain distinct steps (Fig. 2b). That fact
pKb1,2 = –log K = log Ind + pH.
(5)
Here K is the overall protonation constant for the first
and second steps and Ind is the indicator ratio [H2P]/
[H4P2+]. The pH–log с(HClO4) dependence was cal-
culated [11] using the previously obtained data on
A
(а)
(b)
A
λ, nm
log с(HClO4), mol/L
Fig. 2. The evolution of electronic spectra (a) and spectrophotometric titration curve (λ = 417 nm) (b) of 5,10,15,20-tetrakis(3,5-
dibromophenyl)porphine in the CH3CN–HСlO4 system at 298 K (cporph = 1.73×10–5 mol/L, c(HClO4) = 0–3.16×10–5 mol/L).
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BASIC AND COORDINATION PROPERTIES OF TETRAPHENYLPORPHINE DERIVATIVES
2105
Table 1. Parameters of electron absorption spectra of molecular and ionic forms of tetraphenylporphine derivatives and their
zinc complexes; values of overall protonation constant pKb1,2
λ(log ε)
Cоре
Porphyrin
λ4(log ε)
λ3(log ε)
λ2(log ε)
λ1(log ε)
pKb1,2
Н2TPP
H4TPP2+
413 (5.02)
441 (5.04)
470 (5.25)
490 (5.19)
417 (5.01)
344 sh (3.98)
419 (5.32)
418 (5.03)
452 (4.90)
424 (5.11)
512 (3.56)
–
546 (3.12)
–
589 (2.92)
661 (4.17)
738 (3.85)
741 (4.52)
588 (3.66)
596 sh (3.72)
–
646 (2.96)
19.8 [15]
(18.61) [16]
–
–
H2Br8TPP
H4Br8TPP2+
568 (3.95)
–
622 (4.10)
–
16.60 [16, 17]
17.50
–
H2(3,5-BrPh)P
H4(3,5-BrPh)P2+
Zn(3,5-BrPh)P
H2(4-MeO-3-BrPh)P
H4(4-MeO-3-BrPh)P2+
Zn(4-MeO-3-BrPh)P
513 (3.91)
442 (4.95)
550 (4.15)
515 (3.84)
–
546 (3.67)
492 sh (3.76)
597 (3.58)
552 (3.70)
–
649 (4.59)
650 (4.06)
654 sh (3.35)
651 (3.750)
–
593 (3.62)
685 (4.21)
18.09
558 (3.91)
599 (3.72)
653 sh (3.51)
spectrophotometric study of the pH function of the
glass electrode (ESL 43-07) in acetonitrile and
temperature calibration of the ESL 43-07–silver
chloride electrode system (EVL 1 M3 filled with
Et4NCl solution saturated at 293 K) using m-nitro-
aniline (pKa = 7.6) [11–13]. Those data were used for
the calculation of the protonation constants. The
uncertainty of the constants determination did not
exceed 3–5% (Table 1).
obtained parameters of the electron absorption spectra
of porphyrins 1 and 2 and their zinc complexes as well
as kinetic parameters of the reaction (6) in the
Zn(OAc)2–CH3CN system are given in Tables 1 and 2.
Analysis the porphyrins 1 and 2 protonation in the
HClO4–CH3CN system showed that incorporation of
bromine atoms and methoxy groups affected the
basicity of the molecule (despite of “phenyl buffer”
effect), reducing the respective constants for 5,10,15,20-
tetrakis(3,5-dibromophenyl)porphin and 5,10,15,20-
tetrakis(4-methoxy-3-bromophenyl)porphin by 2.3 and
1.7 orders of magnitude as compared to the un-
substituted tetraphenylporphine. Quantum-chemical
simulation [23] has shown that incorporation of meso-
phenyl groups exhibiting weak electron-withdrawing
properties provides the shift of the electron density
from the macrocycle compared to the unsubstituted
ligand, whereas phenyl substitution in porphine
decreases the effective negative charge on the meso-
atoms of carbon by ≈0.03 ē, the effective charge on the
nitrogen atoms of the reaction site remaining
practically the same. The change in the basicity of the
studied ligands compared to tetraphenylporphine
(Table 1) was probably caused by overall donor-
acceptor influence of σ-bonds of the introduced side
groups on the electron density of the transannular
nitrogen atoms of the porphyrin macrocycle.
Substitution of the side groups changed the properties
of ligand much weaker than the substitution at the
β-position of tetraphenylporphine. For comparation,
incorporation of eight bromine atoms at the β-position
The kinetics of the formation of zinc complexes
with compounds 1 and 2 in acetonitrile were ivestigated
using spectrophotometry [18, 19]. That method was
applicable because of significant difference in the
electronic spectra of porphyrins and their complexes.
The coordination of porphyrin ligand with zinc acetate
in a pure solvent can be expressed by Eq. (6) (with Н2P
porphyrin 1 or 2, Solv solvent molecule, n coordination
number of metal cation).
Н2P + [Zn(OAc)2(Solv)n–2] → ZnР + 2НOAc + (n – 2)Solv. (6)
The electron absorption spectra and rates of the
complexes formation for compounds 1 and 2 were
measured over the 288–308 K temperature range, at
least in triplicate at each temperature. The accuracy of
temperature setting was at least ±0.1 K. The measured
spectra contained distinct isosbestic points (Fig. 3).
The reaction (6) had the first order with respect to the
porphyrin, as judged from the linear dependences of
log ([H2P]/[H2P]) on time τ(с). The reaction rate order
with respect to the salt was determined from the slope
of the log keff–log [Zn(ОAc)2] dependences. The
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IVANOVA et al.
Table 2. Kinetic parameters of the formation of zinc complexes of porphyrins in the Zn(OAc)2–CH3CN system
[Zn(OAc)2]×103,
mol/L
kv298×103,
Ea,
kJ/mol
ΔS≠,
Porphyrin
H2TPP [20]
L mol–1 s–1
J mol–1 K–1
1.84
1.84
1.84
4.5
302±1
875±1
3405±2
69±1
70±2
60±3
22±2
56±1
78±2
80±1
–28± 2
–53±3
–154±9
–88±2
–11±1
–5±1
H2T(4-OH-C6H4)TPP [21]
H2T(4-NH2-C6H4)TPP [22]
H2Br8TPP [17]
H2(3,5-Br-C6H3)P
4.5
88±1
H2(4-MeO-3-Br-C6H3)P
4.5
91±1
of tetraphenylporphine has changed the π-electron
density of the macrocycle and decreased basic
properties of tetraphenylporphine by more than 3
orders of magnitude, imparting the acid properties
[Eqs. (3), (4)] in the reaction with organic bases with
the formation of mono- and bis-deprotonated forms [17].
respective kinetic data for several other substituted
tetraphenylporphines are given in Table 2 for
comparison. The data indicated that the substitution
could significantly enhance or suppress the complexing
properties of tetraphenylporphine, and the reaction can
be decelerated (~4 times in the case of compounds 1
and 2) or accelerated (~3 or 11 times in the case of
hydroxy or amino derivatives of tetraphenylporphine)
compared to the parent tetraphenylporphine. The Ea–
ΔS≠ dependence indicated the existence of kinetic
compensation effect due to the solvation in the transition
state of the МХ salt and NH-porphyrin [24]. The Ea–
ΔS≠ dependence for tetraphenylporphine derivatives
showed good correlation. This fact confirmed the
conclusion about the same mechanism of complexing
reaction of the discussed porphyrins and the more
polar transition state of the formed complex molecule
in comparison with the initial state (as indicated by
negative value of the entropy change).
The plotted dependences of true rate constants kv on
рKа1,2 of the studied porphyrins and tetraphenyl-
porphine (Tables 1 and 2) showed sufficiently strong
correlation; that fact indicated the relationship between
the changes in kinetic and basic properties of the
investigated ligands and the change in their structure.
Substitution of porphyrins 1 and 2 at phenyl rings
decreased the compound basicity and decreased the
rate of the zinc complexes formation in the Zn(OAc)2–
CH3CN system. Analysis of the data given in Table 2
showed that the formation of the zinc complex with
porphyrin 1 was faster than that of porphyrin 2, but the
difference was less than an order of magnitude. The
In summary, we showed that chemical modification
of a macrocycle could directly lead to the change in
basic and coordination properties of macroheterocyclic
ligands and thus provide the control of the reactivity of
porphyrins.
A
A
EXPERIMENTAL
Compounds 1 and 2 were synthesized as described
in [25, 26]. The ligands were purified using chromato-
graphy on Al2O3 (Brockmann III type). Dichloro-
methane was used as eluent. The compounds purity
was confirmed using TLC on Silufol plates (layer
thickness 0.5 mm) (Merck) with CH2Cl2 as eluent.
Purification and identification of the compounds were
performed as described in [27]. Bipolar aprotic solvent
(acetonitrile containing less than 0.03% of water) was
used as solvent. Initial compounds were in the
molecular form which was confirmed by the spectral
λ, nm
λ, nm
Fig. 3. The evolution of electronic spectra of 5,10,15,20-
tetrakis(3,5-dibromophenyl)porphine in the CH3CN–Zn(OAc)2
system at 298 K (cporph = 0.8×10–5 mol/L, c[Zn(OAc)2] =
4.5×10–3 mol/L).
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BASIC AND COORDINATION PROPERTIES OF TETRAPHENYLPORPHINE DERIVATIVES
2107
10.7868/S0044453717090278
data. Spectrophotometric titration with perchloric acid
solutions in acetonitrile was performed using a Cary
100 Varian spectrometer. The experiment technique,
preparative chemistry, and data processing are
described in detail in [28, 29].
12. Kolthoff, I.M., Chantooni, M.K., and Sadhana, I., Anal.
Chem., 1967, vol. 39, no. 13, p. 1627. doi 10.1021/
ac50156a039
13. Sheinin, V.B., Ivanova, Yu.B., and Berezin, B.D., Zh.
Analit. Khim., 1993, vol. 48, no. 7, p. 1205.
ACKNOWLEDGMENTS
14. Sheinin, V.B., Ivanova, Yu.B., and Berezin, B.D., Izv.
Vuzov, Ser. Khim. Khim. Tekhnol., 2000, vol. 43, no. 5,
p. 120.
This study was financially supported by the Russian
Foundation for Basic Research (project no. 18-03-
00048_a) and performed using the equipment of Upper-
Volga Regional Center for Physicochemical Studies.
15. Andrianov, V.G. and Malkova, O.V., Makrogeterotsikly,
2009, vol. 2, no. 2, p. 130.
16. Pukhovskaya, S., Ivanova, Yu., Nam, D.T., Kuzmin, I.,
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CONFLICT OF INTERESTS
No conflict of interests was declared by the authors.
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