Acid–base and coordination properties of Meso-substituted porphyrins in nonaqueous solutions

Article abstract of DOI:10.1134/S0036024417090242

Acid–base and coordination properties of alkyl and aryl meso-substituted porphyrins are studied spectrophotometrically in nonaqueous solutions. It is found that the nature of the substituent greatly affects the basicity of ligands for porphyrins characterized by a flat structure of macrocycle. The electronic effects of substituents have a much weaker influence on the kinetics of complexing. These effects could be due to the opposite orientation of some factors: an increase in the basicity and stability of the N–H bonds of porphyrin reaction centers. Dissociation constants pK_b of the cationic forms of meso-substituted derivatives of porphyrin are measured. The values of pK_b are in good agreement with classic concepts of the nature of substituents, particularly those indirectly included in the macrocycle through phenyl buffer rings.

Full text of DOI:10.1134/S0036024417090242

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2017, Vol. 91, No. 9, pp. 1692–1702. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © S.G. Pukhovskaya, Dao Tkhe Nam, Chan Ding Fien, E.N. Domanina, Yu.B. Ivanova, A.S. Semeikin, 2017, published in Zhurnal Fizicheskoi Khimii, 2017,
Vol. 91, No. 9, pp. 1508–1519.
PHYSICAL CHEMISTRY
OF SOLUTIONS
Acid–Base and Coordination Properties of Meso-Substituted
Porphyrins in Nonaqueous Solutions
a,
b
a
a
S. G. Pukhovskaya *, Dao Tkhe Nam , Chan Ding Fien , E. N. Domanina ,
b
a
Yu. B. Ivanova , and A. S. Semeikin
a
Ivanovo State University of Chemical Technology, Ivanovo, 153000 Russia
Krestov Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, 153045 Russia
e-mail: jjiv@yandex.ru
Received October 6, 2016
b
*
Abstract—Acid–base and coordination properties of alkyl and aryl meso-substituted porphyrins are studied
spectrophotometrically in nonaqueous solutions. It is found that the nature of the substituent greatly affects
the basicity of ligands for porphyrins characterized by a flat structure of macrocycle. The electronic effects of
substituents have a much weaker influence on the kinetics of complexing. These effects could be due to the
opposite orientation of some factors: an increase in the basicity and stability of the N–H bonds of porphyrin
reaction centers. Dissociation constants pK of the cationic forms of meso-substituted derivatives of porphyrin
b
are measured. The values of pK are in good agreement with classic concepts of the nature of substituents,
b
particularly those indirectly included in the macrocycle through phenyl buffer rings.
Keywords: porphyrins, acid–base properties, electronic effects of substituents, structure, kinetics, coordina-
tion properties
DOI: 10.1134/S0036024417090242
INTRODUCTION
eral orders of magnitude slower than with other
ligands). On the other hand, we can control the com-
plexing process by means of common chemical kinet-
ics (e.g., via spectrophotometry). It is important that
porphyrins are chemically stable in the basic state and
when ionized, particularly in doubly protonated and
Tetrapyrrole-containing proteins are one of the
most important and numerous types of ferment found
in nature. Even though more than 150 natural tetrapy-
rrole compounds (including porphyrins) have been
identified, there are many fundamental biochemical
processes where the mechanism of the porphyrin doubly deprotonated forms [18, 19].
cofactor effect is unclear. It is known that natural por-
It is known that proton transport is a multistage
phyrins are characterized by a complex set of substitu-
ents which greatly affect all properties of a macrohet-
erocycle [1–11].
process and can result in the formation of a range of
acid–base forms in the case of complex acids and
bases. Investigating specific features of such polycen-
tric acids and bases as porphyrins [20, 21] is thus of
special interest in developing the modern theory of
acid–base interaction. The concept of the acid–base
properties of porphyrins includes the formation of
anionic and cationic forms, followed by changes in
charge due to proton exchange in basic or acidic
media; this is one of the most important physico-
chemical properties of porphyrins [1]. Protons that
interact with porphyrin form covalent σ bonds charac-
terized by considerable degrees of ionicity with pyrro-
lenine nitrogen atoms. Compounds formed via coor-
dination between protons and ligands can essentially
It is therefore important that we study synthetic
porphyrins characterized by different substituent sys-
tems and the influence of their electronic and steric
effects as instruments for controlled changes in the
coordination, physicochemical, and acid–base prop-
erties of porphyrin molecules [12–17].
The diversity of useful properties of porphyrins and
their analogs is due to specific features of their struc-
ture. Porphyrins form stable coordination compounds
of 1 : 1 composition (one metal ion corresponds to one
ligand) with most metals (except alkali metals). It is
important that porphyrins and their metal complexes
exhibit typical electronic absorption spectra and max-
imally large molar absorption coefficients (ε) as high be classified as coordination compounds, and the pro-
as 600000 at the absorption band lying within 400– tons themselves can be defined as a coordinating par-
5
00 nm (the so-called Soret band [1]). The reactions ticles, due to similarity between the acceptor proper-
of metal–porphyrin formation are usually slow (sev- ties of protons and metals. From this point of view,
1692

ACID–BASE AND COORDINATION PROPERTIES
1693
coordination and the protonation of ligands are com- electron density from macrocycles toward meso-atoms
peting reactions.
of carbon, compared to unsubstituted porphin. Sub-
stituting phenyl fragments for electron donor alkyl
groups at the meso-positions of porphyrin macrocycles
shifts the bands in electron absorption spectra
In this work, we present the results from spectro-
photometric investigations of the basic and complex-
ing properties of meso-substituted porphyrin deriva-
tives containing substituents of different natures. The
structural formulas of these compounds are
(
EASes) slightly. tert-Butyl groups are an exception:
introducing these groups to meso-positions results in a
bathochromic shift of all of absorption bands in a
spectrum (Table 1), due to considerable out-of-plane
deformation of the macrocycles. According to the data
in [37, 38] and our calculations (Fig. 1), the greatest
deviation of atoms from the average plane of a cycle is
I R= −СН СН СН СН ,
2
2
2
3
R
R
5,10,15,20-tetra(n-butyl)porphyrin
N
N
Н (n-Bu) P
2
4
NH
HN
II R = −СН СН(СН ) ,
2 3 2
~
1 Å. The above structural changes indirectly affect
5,10,15,20-tetra(iso-butyl)porphy-
the electron structure of a macrocycle, reducing its
aromaticity and raising the electron density on the
nitrogen atoms of porphyrin coordination centers,
increasing both the basic and acidic properties of the
molecule [39, 40].
rin Н (i-Bu) P
2
4
R
R
III R= −С(СН ) 5,10,15,20-tetra
3
3,
(
tert-butyl)porphyrin Н (t-Bu) P
2 4
IV R= −С H , 5,10,15,20-tetracy-
6
11
clohexylporphyrin Н (CyHex) P
The basic properties of porphyrins I–VIII were
investigated via spectrophotometric titration. The
experiment was performed in acetonitrile (AN)–per-
chloric acid (a 0.01 mol/L solution in acetonitrile) at
2
4
V R= −С H , 5,10,15,20-tetrap-
6
5
henylporphin Н TPP
2
VI R= o-BrС H , 5,10,15,20-tetra
6
4
298 K. HClO , which is characterized by a high value
4
(
(
o-bromophenyl)porphyrin H2T
o-BrP)4P
of the dissociation constant in acetonitrile [41], exists
in a totally dissociated form under these conditions,
and protonation takes place due to solvated protons
[42].
Singly or doubly charged ions coexisting in equilib-
rium with each other and their neutral forms can be
obtained, depending on the acidity of the medium and
the type of tetrapyrrole ligand. Equilibria in the solu-
tion are described by the below equations when the
dissociation of cationic forms proceeds in an acidic
medium:
VII R = m-BrС H , 5,10,15,20-
6
4
tetra(m-bromophenyl)porphyrin
H T(m-BrP) P
2
4
VIII R = m-OНС H , 5,10,15,20-
6
4
tetra(m-hydroxyphenyl)porphyrin
H T(m-OНP) P
2
4
EXPERIMENTAL
Porphyrins were synthesized and categorized in the
2+
K
+
+
b1
H P ←⎯ ⎯ → H P + H ,
(1)
(2)
4
3
same manner as in [22–27]. The spectral data of the
obtained compounds matched the data given in litera-
ture.
+
K
+
b2
H P ←⎯ ⎯ → H P + H ,
3
2
+
2+
where Н P, Н P , and H P are the free base and sin-
2
3
4
The solvents used in this work (perchloric acid and
acetonitrile) and copper acetate of analytical grade
were purified by standard means [28–30].
gly and doubly protonated forms of porphyrins,
respectively.
No stable protonated forms of a compound were
registered upon spectrophotometric titration of aceto-
nitrile solutions of Н (t-Bu) P with perchloric acid.
Spectrophotometric titration was performed on a
Shimadzu UV1800, Hitachi U2000 spectrophotome-
ter. Experimental techniques and procedures for data
processing were described in detail in [31–33]. The
error in calculating the corresponding constants was
2
4
However, the authors of [37, 38], who used methanol
(
a more polar solvent) found that the protonation of
two opposite meso-atoms of carbon occurs alongside
±
3–5ꢀ.
the formation of cationic form. This results in the for-
The reactions of complexing between porphyrins
3
mation of porphodimethene with sp hybridized car-
and copper acetate were studied by means of spectro-
photometry in the range of 293–318 K. The change in
temperature during the experiment did not exceed
bon atoms, eliminating the deformation stresses
caused by the protonation of central nitrogen atoms
and ensuring stabilization of the dicationic form of the
obtained compound.
±
0.1 K. The experimental technique was described in
detail in [34, 35].
Spectrophotometric investigations of meso-alkyl
derivatives of porphin (compounds I, II, IV) in the
RESULTS AND DISCUSSION
AN–HClO system showed that two families of spec-
4
According to quantum-chemical calculations [36], tral curves formed within the electron spectra as the
phenyl meso-groups generally facilitate the shift of concentration of perchloric acid grew in the system. A
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 91 No. 9 2017

1694
PUKHOVSKAYA et al.
Table 1. Parameters of the absorption electronic spectra of molecular and doubly protonated forms of meso-substituted
porphyrins
Porphyrin
λ(logε) Soret
λ4(logε)
λ3(logε)
λ2(logε)
λ1(logε)
Н (n-Bu) P
409 (4.85)
413 (4.83)
415 (4.84)
410 (5.04)
414 (5.00)
418 (5.04)
446
516 (3.84)
–
550 (3.69)
–
580 (3.65)
550 (3.88)
–
597 (3.41)
587 (3.64)
–
597 (3.57)
590 (3.77)
–
656 (3.54)
634 (3.63)
627 (3.92)
655 (3.72)
637 (3.80)
630 (4.03)
692
2
4
+
2
H (n-Bu) P
3
4
+
H (n-Bu) P
–
4
4
Н (i-Bu) P
517 (4.02)
473 (3.47)
470 (3.49)
552
2
4
+
H (i-Bu) P
3
4
2
+
H (i-Bu) P
583 (3.76)
596
4
4
Н (t-Bu) P
628
2
4
Н CyHex P
416 (5.20)
418 (5.18)
426 (5.19)
413 (5.02)
413 (5.01)
441 (5.04)
409
409
429
414
447
521 (3.85)
557 sh (3.16)
549 (3.08)
512 (3.56)
442 (4.16)
–
511 (4.13)
512 (3.30)
–
558 (3.68)
599 (3.32)
596 (3.27)
546 (3.12)
512 (3.69)
–
541 (3.37)
547 (2.77)
540 (3.48)
547
603 (3.34)
–
659 (3.50)
648 (3.95)
646 (4.11)
646 (2.96)
660 (3.47)
661 (4.17)
641 (2.91)
631 (3.76)
628 (4.12)
648
2
4
+
HCyHex P
4
CyHex4P2
+
–
Н TPP
589 (2.92)
547 (3.42)
–
587 (3.59)
580 (3.94)
579 (4.03)
591
2
+
H TPP
3
2+
H TPP
4
H T(o-BrP) P
2
4
+
H T(o-BrP) P
3
4
2+
H T(o-BrP) P
4
4
H T(m-BrP) P
512
513
2
4
+
H T(m-BrP) P
547
592
609
651
663
3
4
2
+
H T(m-BrP) P
445
–
–
4
4
H T(m-OHP) P
414 (5.41)
410
450
512 (4.25)
512 (4.01)
–
546 (3.83)
546 (3.67)
–
588 (3.75)
591 (3.73)
607 (3.92)
644 (3.58)
662 (4.15)
659 (4.59)
2
4
+
H T(m-OHP) P
3
4
2+
H T(m-OHP) P
4
4
set of isosbestic points corresponds to every family of and diprotonated forms are similar to each other, and
curves, confirming that protonation is a two-step pro- the difference between their values is less than three
cess (Fig. 2). Distinguishing two families of curves of orders of magnitude. These specific features of spec-
isobestic points in the electron absorption spectra trophotometric titration were described in detail in
allowed us to determine the concentration intervals of [43]. Similar titration curves were also obtained for
the existence of the intermediate mono-protonated meso-phenyl-substituted porphyrins V–VIII. A typical
+
form Н P and its spectral characteristics. The EAS example is given in Fig. 5 for the compound H
(m-
3
2
parameters of the molecular and resulting protonated OHP)
P.
4
forms are given in Table 1.
The presence of substituents that exhibit strong
Spectrophotometric titration curves plotted on the electronic effects in a macrocycle is one factor that
basis of experimental data for compounds I and IV allows the spectrophotometric registering of monoca-
(
Figs. 2, 3) also showed that interaction with HClO is tionic forms. Generally, stepwise equilibrium of pro-
4
also a two-step process and is described by Eqs. (1) tonation is easily registered for porphyrins character-
and (2).
However, the curve of the spectrophotometric
titration of Н (i-Bu) P (Fig. 4) displayed a smooth
ized by appreciably different electron densities of
nitrogen atoms. Stronger polarization of a molecule
obviously allow us to differentiate the cationic forms of
porphyrins (which may be considered acids), as is
clearly reflected on titration curves.
2
4
monotonic character with no clear resolution of the
steps of protonation. With two families of isobestic
points present, such behavior is typical of processes of
Quantitative values of the stepwise constant of the
protonation characterized by similar values of the con- basic ionization of the investigated compounds in
stants of the formation of ionic forms. The two-step AN–HClO at 298 K were calculated according to
4
and monotonic curves of spectrophotometric titration
show that protonation is a sequential process if there
are two families of isobestic points. With compounds
Eq. (3); the corresponding values are given in Table 2.
The error in measuring the constants was ±3–5ꢀ.
(
II, V–VIII), the constants of the formation of mono-
pK = pH + log Ind ,
(3)
b
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ACID–BASE AND COORDINATION PROPERTIES
C15
1695
Å
.0
C5
1
0
.5
0
N23
N22
N24
N21
−0.5
−1.0
−1.5
C20
C10
(
5,10,15,20-tetra(tert-butyl)porphyrin H
2 4
(t-Bu) P)
Å
0.5
C10
C20
N22
N23
0
N21
N24
C5
−0.5
C15
−1.0
2 4
(5,10,15,20-tetra(iso-butyl)porphyrin H (i-Bu) P)
Å
0.5
C5
C15
N21
N22 N21
C10
N24
0
C20
−
0.5
1.0
−
(5,10,15,20-tetrabutylporphyrin H
2 4
(n-Bu) P)
Å
.5
0
N21
C5
N22
C10
N23
N24
0
C15
C20
−
0.5
1.0
−
(5,10,15,20-tetracyclohexylporphyrin H
2
CyHex P)
4
Fig. 1. Deviation of atoms from the average plane of a macrocycle, plotted through 24 carbon atoms of the porphyrin macrocycle.
Also shown is the structure of porphyrin according to data from calculations using the B3LYP/6-311G(*) approach.
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 91 No. 9 2017

1696
PUKHOVSKAYA et al.
А
(а)
А
0
.8
.6
.4
.2
0
0
0
2
450
500
550
600
650
700
λ, nm
300
400
500
600
700 λ, nm
А
(b)
0.72
0.36
10
11
12
13
14
15 рН
Fig. 2. Change in (a) the electronic absorption spectra and (b) the curve of spectrophotometric titration (λ = 627 nm) of com-
pound I in system (1): (сporph = 1.71 × 10−5 mol/L, сHClO4 = 0–3.40 × 10 mol/L), 298 K.
−5
where K is the constant of basicity for the first (K ) or density on the nitrogen atoms of reaction centers,
b
b1
second (K ) step; Ind is the indicator ratio compared to unsubstituted porphin. As a result, basic
b2
+
[
[
H P ]/[Н Р] of the first step or the indicator ratio properties of porphyrins increase in the order IV > I >
3
2
2+
+
H P ]/[Н Р ] of the second step of protonation; рН II ~ H P.
4
3
2
is the analytical value of the acidity of solution formed
Introducing steric substituents into the meso-posi-
tion of a macrocycle partially distorts the plane of an
aromatic macrocycle and probably has a lesser effect
by the titrant (0.01 mol/L solution of HClO in aceto-
4
nitrile).
The presence of alkyl substituents in meso-posi- on the state of the electron density of intracycle nitro-
tions that exhibit +I-effects increases the electron gen atoms. The results from calculating the geometri-
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ACID–BASE AND COORDINATION PROPERTIES
1697
А
(а)
А
1
1
0
0
0
0
.2
.0
.8
.6
.4
.2
2
450
500
550
600
650
700
λ, nm
0
300
400
500
600
700
λ, nm
А
(b)
1.05
0.70
0.35
0
8
10
12
14
рН
Fig. 3. Change in (a) the EAS and (b) the curve of spectrophotometric titration (λ = 629 nm) of compound II in the AN–HСlO
system: (сporph = 1.4 × 10−5 mol/L; сHClO4 = 0–3.3 × 10 mol/L), 298 K.
4
−5
cal parameters of meso-alkyl substituted porphyrins
As was noted above, phenyl substituents demon-
using the density functional theory (DFT), functional strate weak electron acceptor properties, but their
B3LYP, and basis set 6-311G(*) showed that the presence in Н ТРР molecules results in a substantial
2
Н (i-Bu) P (II) macrocycle has a more pronounced (approximately three orders of magnitude) increase in
2
4
corrugation of structure (Fig. 1); this somewhat reduces compound basicity (Table 2). The authors of [21, 44]
its basic properties relative to the less deformed analog explained the increase in the basic properties of
Н (n-Bu) P (I) and flat Н CyHex P (IV).
Н ТРР (compared to porphin) by the more pro-
2
2
4
2
4
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PUKHOVSKAYA et al.
а)
(
А
3
.0
.5
.0
.5
.0
.5
А
1
0
0
0
.2
2
2
1
1
0
.9
.6
.3
500
550
600
650
700
750
λ, nm
300
400
500
600
700 λ, nm
(b)
А
1
.2
.0
.8
.6
.4
.2
1
0
0
0
0
10
11
12
13
14
15
16
рН
Fig. 4. Change in (a) the EAS and (b) the curve of the spectrophotometric titration (λ = 646 nm) of compound III in the AN–
= 1.73 × 10−5 mol/L; сHClO4 = 0–3.32 × 10 mol/L), 298 K.
−5
HСlO system: (с
4
porph
nounced tendency of this macrocycle toward defor- tem of conjugated bonds, allowing the inductive effect
mation upon the formation of cationic forms.
of the substituents to predominate.
According to X-ray analysis and computer model-
With H T(o-BrP) P containing bromine atoms in
2
4
ing, the phenyl fragments of Н ТРР cannot fit the the ortho-positions of phenyl rings of tetraphenylpor-
2
plane of a porphyrin macrocycle. The slope angle is phin, which exhibit a (−I) induction effect and a weak
~
70°–75° [45, 46]. This restricts the probability of the (+С) conjugation effect, a weakening of the basic
transfer of electron density from a functional substitu- properties of the molecules (Table 2) is observed.
ent to the reaction centers of porphyrin along the sys- Introducing functional groups into the meta-positions
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ACID–BASE AND COORDINATION PROPERTIES
1699
А
1
1
0
.5
.0
.5
0
6
7
8
9
10
11
12
рН
A
2
0
500
600
700 λ, nm
Fig. 5. Changes in the EAS of H (m-OHP) P (с
1
= 4.66 × 10−5 mol/L) upon titration with HClO (с
= 0–5.89 ×
HClO4
2
4
porph
4
0−4 mol/L) in acetonitrile.
of the benzene fragments of (H (m-BrP) P) reduces with the results from pyridyl-substituted porphyrin
2
4
titration [47, 48].
the influence of substituent on the basic properties of
ligand. Our experimental data are in good agreement
However, introducing OH groups into the meta-
positions of the phenyl rings of tetraphenylporphyrin,
which are characterized by an (−I) induction effect
weaker than the (+C) effect, weakens the basic prop-
erties of the molecule, compared to meta-substitution
with bromine atoms in the phenyl rings of tetraphenyl-
porphyrin. It should be noted the dissociation con-
stants of the protonated forms of substituted porphy-
rins are in good agreement with the classic concepts of
the nature of substituents, even those that are intro-
duced indirectly (through a phenyl buffer) into a mac-
rocycle.
Table 2. Values of the stepwise constants of basicity for
compounds (I)–(VII) in system (1) at 298 K, compared to
unsubstituted porphin
Porphyrin
pKb1
pKb2
pKb1,2
H P [19]
6.20 ± 0.15 9.15 ± 0.15 15.35 ± 0.30
10.50 ± 0.02 13.56 ± 0.03 24.06 ± 0.50
8.82 ± 0.01 9.59 ± 0.03 18.41 ± 0.20
10.67 ± 0.02 14.16 ± 0.03 24.83 ± 0.50
8.94 ± 0.02 9.69 ± 0.03 18.61 ± 0.15
5.31 ± 0.01 8.05 ± 0.02 13.36 ± 0.50
9.33 ± 0.03 10.14 ± 0.05 19.47 ± 0.10
2
Н (n-Bu) P
2
4
Н (i-Bu) P
2
4
Н CyHex P
2
4
Н TPP
2
The coordination properties of porphyrins II–VIII
were studied via spectrophotometry, using the exam-
ple of a complexing reaction with copper acetate (4) in
a proton donor solvent (acetic acid).
H T(o-BrP) P
2
4
H T(m-BrP) P
2
4
H T(m-OНP) P 7.23 ± 0.02 9.59 ± 0.03 16.82 ± 0.50
2
4
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PUKHOVSKAYA et al.
Table 3. Kinetic parameters of the formation of copper complexes of porphyrins in acetic acid
2
98
× 103
k v2 98, L0.5 mol−0.5 s−1
≠
Porphyrin
cCuAcO2 , mol/L
Ea, kJ/mol
−ΔS , J/(mol K)
k
ef
Н СyHex P
3.62 × 10−4
9.1 ± 0.30
8.6 ± 0.30
28.5 ± 0.10
4.20 ± 0.30
34.81 ± 1.00
17 ± 1.0
0.48 ± 0.03
0.45 ± 0.03
0.67 ± 0.02
0.11 ± 0.01
0.79 ± 0.05
0.38 ± 0.02
71 ± 4
75 ± 2
81 ± 4
66 ± 1
83 ± 2
85 ± 2
24 ± 5
10 ± 5
29 ± 6
37 ± 3
4 ± 2
2
4
−4
Н (i-Bu) P
3.62 × 10
2
4
1.81 × 10−
3
Н ТPP
2
−
3
H T(o-BrP) P
1.72 × 10
1.98 × 10−
2
4
3
H T(m-BrP) P
2
4
H Т(m-OНP) P
1.98 × 10−3
25 ± 2
2
4
The formation of complexes between porphyrins porphyrin. The order of the reaction against salt (n)
and double-charged metal cations (in this case, copper was measured experimentally by taking the depen-
acetate) in nonaqueous solutions proceeds according dence of the effective constant (k ) of reaction (4) on
eff
to the equation
the salt concentration (c); for copper acetate in acetic
acid, it is 0.5 [49]. The value of k correlates with the
eff
H P +
[
Cu
(
OAc)2 (Solv)n−2
n − 2 Solv.
]
2
true rate constant (k ) according to the equation
v
(
4)
→
CuP + 2HOAc +
(
)
n
k' = k c
.
(6)
eff
v
MX2
Reaction (4) is the one of the first kinetic order against
Н P, as in the case of the porphyrins studied in [1].
The kinetic parameters of complexing reactions for
porphyrins II–VIII are given in Table 3. It should be
noted that clear isobestic points were registered in the
spectra of the reacting system for all of the studied por-
phyrins; a typical example is given in Fig. 6.
According to the mechanism behind the formation
of metaloporphyrins, introduced by Berezin [1] and
confirmed by subsequent investigations [50–54], the
main factors that affect the rate of reaction (4) are first
the realignment and partial destruction of the coordi-
2
This is confirmed by the linear dependences in coor-
0
H2P
0
dinates log(c /cH2P) – t (where cH2P and c are the
H2P
current and initial concentrations of porphyrin,
respectively, and t is time):
n
−dcH2P /dt = kcH2P
c
,
(5)
MX2
n
where k is the rate constant of the reaction, c
salt concentration, and cH2P is the concentration of nation spheres of the metal solvate complex; second,
is the
MX2
A × 10−
1
2.0
1.5
1.0
0.5
0
500
550
600
650
λ, nm
Fig. 6. Changes in EAS during the coordination reaction between porphyrin II and copper acetate in acetic acid at 298 K (с
1
=
porph
.79 × 10−5 mol/L, сCu(OAc)2 = 3.62 × 10 mol/L).
−4
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 91
No. 9
2017

ACID–BASE AND COORDINATION PROPERTIES
1701
the emergence of coordination bonds between the 10. A. Harriman and J. P. Sauvage, Chem. Soc. Rev.,
No. 25, 41 (1996).
metal cations and the tertiary nitrogen atoms of por-
phyrin; and third, the extension and polarization of 11. C. K. Mathews, in Biochemistry, Ed. by C. K. Mathews,
N–H ligand.
K. E. van Holde, and K. G. Ahern (Addison Wesley,
San Francisco, CA, 2000).
As was mentioned above, the meso-substituents in
porphyrin macrocycles greatly affect both the elec-
tronic structure and geometry of a molecule. They dis-
play certain electronic effects (±С– and ±I) and
determine the distribution of π-electron density
within a macrocycle. They also determine the degree
of solvation in the basic state, resulting in the different
protonation of N–H bonds.
1
2. Yu. B. Ivanova, N. V. Chizhova, S. G. Pukhovskaya,
and N. Zh. Mamardashvili, Russ. J. Gen. Chem. 84,
939 (2014).
1
3. Dao Nam Tkhe, Yu. B. Ivanova, S. G. Puhovskaya, and
M. M. Kruk, RSC Adv., No. 5 (2015). doi
0.1039/c5ra01323b
4. S. Pukhovskaya, Yu. Ivanova, Dao The Nam,
A. Vashurin, and O. Golubchikov, J. Porphyr. Phthalo-
cyan., No. 19, 858 (2015). doi
10.1142/S1088424615500649
5. V. Valderrey, G. Aragay, and P. Ballester, Coord.
Chem. Rev. 258–259, 137 (2014).
1
1
The basicity of the ligand is increased for the alkyl
substituents of porphyrins II–III, strengthening (in
the intermediate state) the N → M bonds and raising
the rate of metaloporphyrin formation. However, the
greater electron density on the central nitrogen atoms
intensifies the interaction with protons of reaction
center. This obviously requires additional expenditure
of the energy needed for the extension and deforma-
tion of N–H bonds. An opposite effect of substituents
is observed for meso-phenyl derivatives of porphin. As
a result, the constants of the rate of complex formation
between copper and porphyrins II–VIII differ within
one order of magnitude (Table 2) at the close energy
parameters of reaction (4), despite the substantial dif-
ferences between the basicities of porphyrins
1
1
6. P. D. Beer, D. P. Cormode, and J. J. Davis, Chem.
Commun., 414 (2004).
1
7. S. Pukhovskaya, Yu. Ivanova, Nam Dao The, et al.,
Eur. Chem. Bull. 5, 18 (2016).
1
8. Yu. B. Ivanova, N. N. Kruk, A. S. Starukhin, and
N. Zh. Mamardashvili, Ros. Khim. Zh. (Zh. Ros.
Khim. Ob-va Im. D. I. Mendeleeva) 3 (2), 47 (2009).
1
9. Yu. B. Ivanova, N. V. Chizhova, and M. M. Kruk, Russ.
J. Gen. Chem. 83, 558 (2013).
2
0. Y. I. Fialkov, The Role of the Solvent in the Technological
Process (Khimia, Leningrad, 1990), p. 238.
(
Table 3). The most pronounced differences in the
2
1. V. G. Andrianov and O. V. Malkova, Macroheterocy-
rate of formation of copper complex was registered for
cles 2, 130 (2009).
the least basic H (o-BrP) P.
2
4
2
2. D. Oulmi, P. Maillard, J.-L. Guerquin-Kern, C. Huel,
and M. Momenteau, J. Org. Chem. 60, 1554 (1995).
2
2
2
2
2
3. M. O. Senge, I. Bischoff, N. Y. Nelson, and
ACKNOWLEDGMENTS
K. M. Smith, J. Porphyr. Phthalocyan. 3, 99 (1999).
This work was supported by the Russian Foundation
for Basic Research, project no. 16-53-00100 Bel_a. Por-
phyrin was synthesized as part of a State Task from the
RF Ministry of Education and Science.
4. A. M. d’A. Rocha Gonsalves, J. M. T. B. Varejao, and
M. M. Pereira, J. Heterocycl. Chem. 28, 635 (1991).
5. M. Veyrat, R. Ramasseul, I. Turowska-Tyrk, et al.,
Inorg. Chem. 38, 1772 (1999).
6. A. D. Adler, F. R. Longo, J. D. Finarelli, et al., Org.
Chem. 32, 476 (1967).
REFERENCES
. B. D. Berezin, Coordination Compounds of Porphyrins
and Phthalocyanines (Wiley, New York 1981).
. J. W. Buchler, in Porphyrins and Metalloporphyrins, Ed.
by K. M. Smith (Elsevier, Amsterdam, 1975).
. M. O. Senge, Chem. Commun., No. 51, 17031 (2015).
doi 10.1039/c5cc06254c
. M. O. Senge, in The Porphyrin Handbook, Ed. by
K. M. Kadish, K. M. Smith, and R. Guilard (Aca-
demic, New York, 2000), Vol. 1, p. 239.
. J. A. Shelnutt, in The Porphyrin Handbook, Ed. by
K. M. Kadish, K. M. Smith, and R. Guilard (Aca-
demic, New York, 2000), Vol. 7, p. 167.
7. A. S. Semeikin, O. I. Koifman, B. D. Berezin, and
1
2
3
4
S. A. Syrbu, Chem. Heterocycl. Compd. 19, 1082
(
1983).
2
8. A. Gordon and R. Ford, The Chemist’s Companion, A
Handbook of Practical Data. Techniques and References
(
Wiley, New York, 1972).
29. A. Weissberger, E. Proskauer, J. Riddick, and E. Toops,
Organic Solvents (Interscience, New York, 1955).
3
0. Yu. V. Karyakin and I. I. Angelov, Pure Chemical
Reagents (Khimiya, Moscow, 1974) [in Russian],
p. 407.
5
3
1. Yu. B. Ivanova, V. B. Sheinin, and N. Zh. Mamardash-
vili, Russ. J. Gen. Chem. 77, 1458 (2007). doi
0.1134/S1070363207080270
6
. W. R. Scheidt, Struct. Bonding 64, 1 (1987). doi
1
1
0.1007/BFb0036789
3
2. S. G. Pukhovskaya, Yu. B. Ivanova, Dao The Nam, and
A. S. Vashurin, Russ. J. Phys. Chem. A 88, 1670 (2014).
doi 10.1134/S0036024414100288
7
. K. M. Barkigia, L. Chantranupong, K. M. Smith, and
J. Fajer, J. Am. Chem. Soc., No. 110, 7566 (1988). doi
1
0.1021/ja00230a063
3
3. Yu. B. Ivanova, Yu. I. Churakhina, and N. Zh. Mamar-
dashvili, Russ. J. Gen. Chem. 78, 673 (2008). doi
10.1134/S1070363208040269
8
9
. R. A. Huber, Eur. J. Biochem. 187, 283 (1990).
. B. Morgan, Struct. Bonding 64, 115 (1987).
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 91 No. 9 2017

1702
PUKHOVSKAYA et al.
3
4. O. A. Golubchikov, T. N. Lomova, E. M. Kuvshinova, 45. G. J. Foran, P. Turner, and T. W. Hambley, Aust.
et al., Zh. Fiz. Khim. 63, 346 (1989).
J. Chem. 49, 1273 (1996).
4
6. J. A. Shelnutt, in The Porphyrin Handbook, Ed. by
K. M. Kadish, K. M. Smith, and R. Guilard (Aca-
demic, San Diego, 2000), Vol. 7, p. 167.
3
5. N. S. Dudkina, P. A. Shatunov, E. M. Kuvshinova,
S. G. Pukhovskaya, A. S. Semeikin, and O. A. Golub-
chikov, Russ. J. Gen. Chem. 68, 1955 (1998).
4
7. Yu. B. Ivanova, A. S. Semeikin, A. V. Glazunov, and
N. Zh. Mamardashvili, Russ. J. Org. Chem. 46, 144
2010).
36. R. Slota, M. A. Broda, G. Dyrda, et al., Molecules 16,
9957 (2011). doi 10.3390/molecules16129957
(
37. T. Ema, M. O. Senge, N. Y. Nelson, et al., Angew.
4
8. Yu. B. Ivanova, A. S. Semeikin, A. V. Glazunov, and
N. Zh. Mamardashvili, Russ. J. Org. Chem. 46, 917
(2010).
Chem. 106, 1951 (1994).
38. M. O. Senge, T. Ema, and K. M. Smith, J. Chem. Soc.,
Chem. Commun., 733 (1995).
49. T. A. Ageeva, E. L. Ponomareva, O. A. Golubchikov,
and B. D. Berezin, Koord. Khim. 13, 886 (1987).
39. S. G. Pukhovskaya, L. Zh. Guseva, O. V. Malkova,
A. S. Semeikin, and O. A. Golubchikov, Russ. J. Gen. 50. O. A. Golubchikov, S. G. Pukhovskaya, and
Chem. 73, 473 (2003).
E. M. Kuvshinova, Russ. Chem. Rev. 74, 249 (2005).
5
1. E. M. Kuvshinova, S. G. Pukhovskaya, O. A. Golub-
4
0. D. B. Berezin, Yu. B. Ivanova, and V. B. Sheinin, Russ.
chikov, and B. D. Berezin, Koord. Khim. 19, 630
J. Phys. Chem. A 81, 1986 (2007).
(
1993).
41. I. M. Kolthoff, S. Bruckenstein, and M. K. Chantooni,
52. O. A. Golubchikov, A. V. Vakhonin, and S. G. Pukhovskaya,
J. Am. Chem. Soc. 83, 3927 (1961).
Koord. Khim. 19, 240 (1993).
42. I. M. Kolthoff, M. K. Chantooni, and Ir. Sadhana,
5
3. S. G. Pukhovskaya, V. A. Efimovich, A. S. Semeikin,
and O. A. Golubchikov, Russ. J. Inorg. Chem. 55, 1494
(2010).
Anal. Chem. 39, 1627 (1967).
43. I. Ya. Bernshtein, Spectrophotometrical Analysis in
Organic Chemistry (Khimiya, Leningrad, 1986), p. 202 54. S. Pukhovskaya, Yu. Ivanova, Dao The Nam,
[
in Russian].
A. Vashurin, and O. Golubchikov, J. Porphyr. Phthalo-
cyan. 19, 858 (2015). doi 10.1142/S1088424615500649
4
4. T. V. Lomova and D. B. Berezin, in The Problems of
Solution Chemistry, Ed. by A. M. Kutepov (Nauka,
Moscow, 2001), p. 326 [in Russian].
Translated by P. Vlasov
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 91
No. 9
2017