Kinetic stability of corrole complexes with manganese, copper, and zinc in environments based on acetic and sulfuric acids

Article abstract of DOI:10.1134/S0036023614120067

Complexes of some meso- and undeca-substituted corroles with manganese, copper, and zinc are synthesized. Their stability in protolytic dissociation processes studied using spectroscopy methods increases for meso-triphenylcorrole (I) complexes in the following series of metals: Zn < Mn < Cu. The stability of copper complexes in the HOAc-H₂SO₄ environment increases after electron-donor substitution of molecules in the series: Cu(ms-Ph)₃Cor (Ib) > Cu(ms-4-OCH₃Ph)₃Cor (IIb) ≈ Cu(β-Br)₈(ms-Ph)₃Cor (IVb) > Cu(ms-4-NO₂Ph)₃Cor (IIIb). Contrariwise, the dissociation rates of manganese corroles increase with increasing electron-donating properties of the substituents in the macrocycle: IVb < IIIb < Ia < IIa. Dissociation of metallocorroles is accompanied by donor-acceptor and acid-base interactions, as well as by intramolecular redox processes, to result in low selectivity of dissociation and formation of side products. The dissociation scheme of corrole complexes with mixed-valence d metals was proposed for the first time.

Full text of DOI:10.1134/S0036023614120067

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2014, Vol. 59, No. 12, pp. 1522–1529. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © D.B. Berezin, O.V. Shukhto, Vu Thi Thao, D.R. Karimov, B.D. Berezin, 2014, published in Zhurnal Neorganicheskoi Khimii, 2014, Vol. 59, No. 12,
pp. 1769–1776.
PHYSICAL CHEMISTRY
OF SOLUTIONS
Kinetic Stability of Corrole Complexes with Manganese, Copper,
and Zinc in Environments Based on Acetic and Sulfuric Acids1
†
D. B. Berezina, O. V. Shukhtoa, Vu Thi Thaoa, D. R. Karimovb, c, and B. D. Berezina, b,
a Ivanovo State University of Chemical Technology, Research Institute of Macroheterocyclic Compounds, Ivanovo, Russia
b Krestov Institute of Chemistry of Solutions, Russian Academy of Sciences, Ivanovo, Russia
c Ivanovo State Medical Academy, Federal Agency for Public Health and Welfare of the Russian Federation, Russia
eꢀmail: berezin@isuct.ru
Received March 19, 2014
Abstract—Complexes of some mesoꢀ and undecaꢀsubstituted corroles with manganese, copper, and zinc are
synthesized. Their stability in protolytic dissociation processes studied using spectroscopy methods increases
for mesoꢀtriphenylcorrole (
per complexes in the HOAc–H2SO4 environment increases after electron–donor substitution of molecules
in the series: Cu(msꢀPh)3Cor (Ib) > Cu(msꢀ4ꢀOCH3Ph)3Cor (IIb Cu( ꢀBr)8(msꢀPh)3Cor (IVb) > Cu(msꢀ4ꢀ
NO2Ph)3Cor IIIb). Contrariwise, the dissociation rates of manganese corroles increase with increasing elecꢀ
tronꢀdonating properties of the substituents in the macrocycle: IVb IIIb Ia IIa. Dissociation of metalꢀ
locorroles is accompanied by donorꢀacceptor and acid–base interactions, as well as by intramolecular redox
processes, to result in low selectivity of dissociation and formation of side products. The dissociation scheme
I) complexes in the following series of metals: Zn < Mn < Cu. The stability of copꢀ
)
≈
β
(
<
<
<
of corrole complexes with mixedꢀvalence d metals was proposed for the first time.
DOI: 10.1134/S0036023614120067
1†
Corroles (H3Cor, compounds I–IV) form a unique oxidation to isoꢀcorrole and other florineꢀlike moleꢀ
family of tetrapyrrolic macrocyclic ligands that are cules, attempts at performing dissociation of corrole
structurally similar to porphyrins (Н2Р). The contracꢀ complexes have recently been made [6]. However, neiꢀ
tion of the coordination cavity after one mesoꢀmethiꢀ ther quantitative kinetic data nor mechanisms of this
nyl bridge was removed from the Н2Р structure, elecꢀ reaction have been reported [3].
tron density redistribution in the macrocycle, and the
In order to find the general trends of disintegration
emergence of the third intracyclic NH proton makes
of MCor, a spectral kinetic study was performed into
the properties of H3Cor and Н2Р ligands significantly
the dissociation of complexes of mesoꢀphenylꢀsubstiꢀ
differ [1–3].
tuted corroles I–IV with manganese in the systems
Corroles, which are usually used as metal comꢀ
plexes (MCor, compounds Ia–IVa, Ib–IVb, Ic)
exhibit pronounced catalytic properties and show high
promise for use in energy engineering and medicine,
which places these porphyrinoids among the most
popular research objects [1, 4, 5].
based on acetic acid (HOAc) and sulfuric acid
(H2SO4) and conditions were selected for converting
copper complexes in the НОАс–H2SO4 system and
zinc complexes in the С6Н6–НОАс environment.
Dissociation of metallocorroles (1) in protonꢀ
donating environments is an important method to
evaluate the chemical stability of complexes; in some
cases, it is the only way to obtain the corresponding
metalꢀfree compounds (e.g., ligand IV) [6].
EXPERIMENTAL
Ligands I–III were synthesized using the proceꢀ
dures described earlier [7, 8].
The corrole complexes with manganese (Ia–IIIa
)
+
2+
[9], copper (Ib–IIIb) [10], and zinc (Ic) [11] were preꢀ
pared via complexation of the corresponding ligand
with a tenfold molar excess of metal acetate in the
(X–)MnCor +
→
[H CorH]2+ +
(1)
(MnX)(Solv).
5H(Solv)
4
Despite the fact that the release of unbound corrole
from its metal complex can be accompanied by ligand
N,Nꢀdimethylformamide (DMF) environment folꢀ
lowed by chloroform extraction of the product. The
reaction of copper complex formation ends while the
reagents are mixed at room temperature, whereas the
formation of MnCor requires refluxing the reaction
mixture for 15 min and the formation of ZnCorH
requires heating the mixture at 60°C for 1.5 h.
†
Deceased.
1
On the occasion of 85th anniversary of Boris Dmitrievich
Berezin (1929–2012), full member of the Russian Academy of
Natural Sciences, Professor, Honored Scientist of Russia,
awardee of the USSR State Award (1987) and the Russian Fedꢀ
eration Government Award (2004).
1522

KINETIC STABILITY OF CORROLE COMPLEXES WITH MANGANESE
1523
Y
Y
Y
X
X
X
X
X
X
X
X
X
X
X
X
N
N
N
NH
N
N
N
N
N
BH+
Y
Y
Y
Zn
M
N−
NH HN
X
X
X
X
X
X
X
X
X
X
X
X
Y
Ic, В = DMF, Py
Y
. X = Y = –H
II. X = H; Y = –OCH3
III. X = H; Y = –NO2
IV. X = Br; Y = H
Y
I–IV
I
(
: M = Mn;
)
a,b
: M = Cu
a
b
β
ꢀOctabromoꢀmesoꢀtriphenylcorrole complexes lated amount of HOAc; the HOAc–H2SO4 mixture
with copper and manganese (IVa IVb) [6, 7] were synꢀ with the known concentrations of components was
thesized by direct bromination of ꢀunsubstituted then added. The mixture was placed in the spectroꢀ
,
β
complexes Ia or Ib in a 30ꢀfold excess of bromine in photometer cell holder and the change in absorbance
chloroform (CHCl3) followed by binding the releasing at the operating wavelength λexp was measured after
HBr to pyridine. The products were purified by silica temperatureꢀcontrolled exposure. The inaccuracy of
gel column chromatography with CHCl3 used as an temperature measurement was less than 0.1°C. Reacꢀ
eluent. The yield of compounds IVa and IVb is ~ 25%; tion (1) took place when one of the reagents was in a
the yield of compounds Ia–IIIa
,
Ib–IIIb, and Ic is significant excess, which allows one to describe it with
60–80%.
the pseudoꢀfirstꢀorder kinetic equation
The structures of the resulting compounds were
verified by H NMR spectra and electronic spectrosꢀ
n
n
n
1
–dC/dτ
=
=
k
(2)
kvCMnCorCHХ
effCMnCor
copy data. Proton nuclear magnetic resonance
(1H NMR) spectra were recorded on an Avance 500
spectrometer (Bruker) with the operating frequency of
500 MHz at 303 K in CDCl3. The electronic adsorpꢀ
tion spectra (EAS) and the kinetics of reaction (1)
The order of reaction (1) with respect to metal comꢀ
plex, , was always unity, as evidenced by the strictly
linear dependences ln(C0 ) = (Fig. 1). Effective
reaction rate constants (
eff, s–1) were calculated using
n
/C
f(τ)
k
were recorded on a Shimadzu UV 1800 spectrophoꢀ Eq. (3). The energy of activation (Ea, kJ/mol) and
tometer.
Organic solvents were additionally purified accordꢀ
entropy of activation (
Δ
S#, J/(mol K)) were calculated
using Eqs. (4) and (5), respectively. The order of the
НS+olv
ing to recommendations [12]. Acetic acid (HOAc,
pure grade) was twice frozen and twice thawed, boiled
with the calculated amount of acetic anhydride, and
distilled on a fractionation column; the 117.5–
118.0°C fraction was collected. Anhydrous sulfuric
acid was prepared from a commercially available
H2SO4 sample (pure grade) and 15% oleum; the conꢀ
centration was monitored conductometrically and
reaction with respect to solvated proton was
determined graphically from log(keff) = f(H0) (Fig. 1),
where the current acidity function H0 in the НОАс–
H2SO4 system was calculated from experimental data
[13]. The kinetic parameters of reaction (1) are listed
in the table.
C0
A0 − A∞
Aτ − A∞
1
τ
1
τ
densitometrically (ρ = 1.8384).
keff
=
(3)
(4)
(5)
ln
=
ln
,
Cτ
The kinetics of dissociation reaction (1) for comꢀ
plexes Ia–IVa was recorded spectrophotometrically in
the НОАс–H2SO4 environment. Equal volumes of the
CHCl3 solution of MCor complex with the known
concentration prepared in advance were placed in test
tubes; the solvent was evaporated. The dry residue of
metal corrole was completely dissolved in the calcuꢀ
T1T2
k2
Eа
=
19.15
log
,
T2 − T1
k1
Eavg Eerr
298
Δ
S#
=
– 253.22.
19.15logk
+
298
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 59 No. 12 2014

1524
BEREZIN et al.
lnC0/C
3.0
–logkeff
5.0
1
4.5
4.0
3.5
3.0
2.5
2.0
2.5
2.0
1.5
1.0
0.5
2
298
308
318
3
4
1.5
1.7 1.9 2.1 2.3 2.5 2.7 2.9 H0
0
1000
2000
3000
τ, s
lnC0MCor
/
C
) =
f
(
τ
)
curves for the dissociation reaction of complex IIa in the НОАс–H SO system at
T
= 298 K
) 0.029 (leftꢀhand panel) and the logarithmic dependence of the effective rate
= 1.16–1.25) at 298, 308,
MCor
Fig. 1.
f
(
2
4
(
mol/L): (
1
) 0.296; (
2
) 0.148; (
3
) 0.074; (
4
CН SO
,
2
4
constant
k
of reaction (1) on the Hammett acidity function H in the HOAc–H SO system (tan
α
eff
0
2
4
and 318 K (rightꢀhand panel).
RESULTS AND DISCUSSION
(1H NMR signals at 7–8 ppm) as opposed to copꢀ
per(II) porphyrin complexes [1, 10]. The H NMR
spectra of paramagnetic MnCor belong to a broad
range of chemical shifts δ from –42 to +34 ppm.
1
Metallocorroles exist in solutions in extra coordiꢀ
nated ((L)MCor) and uncoordinated (MCor) forms.
Metals that can change their valence (e.g., mangaꢀ
nese) in these complexes typically can acquire a cerꢀ
Solvoprotolytic dissociation of metalloporphyrins
tain valence depending on the type of extra ligand (
on whether it is a charged ligand (X–) or an electronꢀ
donating molecule ( ) (6). In this case the ligand
L),
(MPs) (dissociation induced by the solvated proton
+
[16]) gives rise to a protonated ligand and a metal
НSolv
В
salt (1). It has been believed for a long time that dissoꢀ
ciation of corrole complexes (MCor) to an unbound
ligand is fundamentally infeasible [1, 6]. This opinion
was caused by the fact that the formation of corrole
monoꢀ (H4Cor+, 8) or dications (H4CorH2+, 9) caused
by the interaction of acids with some of their metal
complexes is either observed extremely rarely or is
unobserved at all, while the absorption spectra of the
products of treating MCor with an acid correspond to
H3Cor is referred to as having a nonꢀinnocence effect
[3, 14, 15], since there is an uncertainty in the metal
oxidation state in MCor as it forms ligandꢀlocalized
radical species. The H3Cor macrocycle exhibits stronꢀ
ger electronꢀdonating properties compared to porphyꢀ
rins (Н2Р), thus resulting in stabilization of metals in
high oxidation states by these ligands [1–10]. Substiꢀ
tution of the X– ligand at high concentrations of B,
e.g., DMF (6–10 mol/L), in MCor is described by
equilibrium (6) and characterized by drastic changes neither the EAS of the ligand nor any of its protonated
in the EAS [3].
species (Fig. 2).
Similar equilibrium is also observed for copper corꢀ
role complexes (7); however, since the metal does not
tend to coordinating extra ligands, it is almost indeꢀ
pendent of the solvent nature and the EAS of the two
species are virtually identical.
+
Н4Cor(+solv) ꢀ H(solv)
+ Н3Cor(solv)
.
(8)
(9)
Н4CorН2+
ꢀ H+
)
Н4Cor(solv)
.
+
+
solv
(
(solv)
(X)MnIVCor– + B
CuIIICor
(B)MnIIICor + X–.
CuIICor+.
(6)
(7)
Manganese corroles (compounds Ia–IVa) are the
rare example of MCor complexes whose electronic
absorption spectra of the dissociation products coinꢀ
cide with the EAS of the corresponding dications
(Figs. 2, 3), which indicates that reaction (1) of these
compounds is distinguished by a high degree of selecꢀ
tivity in the HOAc–H2SO4 system. The kinetic stability
of mesoꢀsubstituted manganese corroles considerably
ꢀ
ꢀ
Equilibrium (7) shifts leftward at room temperaꢀ
ture, toward the copper(III) complex with a neutral
ligand. This fact shows agreement with the literature
data reporting the absence of signals from the CuCor
radical species in the electron paramagnetic resonance
(EPR) spectra and diamagnetic properties of CuCor depends on the nature of substituents in phenyl rings
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 59 No. 12 2014

KINETIC STABILITY OF CORROLE COMPLEXES WITH MANGANESE
1525
Kinetic parameters of dissociation reactiona of manganese complexes of mesoꢀsubstituted corroles and porphyrins in the
HOAc–H2SO4 system,
C
MCor = 4
×
10–5 mol/L
mol/L
Complex
H0
T
, K
keff
×
103, c–1
Ea,
kJ/mol
ΔS, J/(mol K)
C
,
Н2SO4
(Cl)Mn(msꢀPh)4P [17]
3.00
–0.76
–1.07
–1.57
–1.74
–1.85
298
0.0005 0.0003
0.00047 0.00003
0.0031 0.0006
0.087 0.005
0.14 0.01
0.36 0.02
0.026 0.003
0.15 0.04
0.37 0.03
0.76 0.06
0.72 0.06
1.43*
80
105
100
97
100
67
2
1
4
5
7
9
–105
–22
–30 10
–3 16
11 24
–93 13
–147 69
4
2
4.00
5.00
6.61
7.13
7.85
0.19
0.46
0.89
1.31
1.70
3.00
4.00
0.03
Mn(msꢀPh)3Cor, Ia
λexp = 601 nm
–0.76
–1.07
–1.57
–1.74
–1.85
298
58 20
40
55
54
1
4
3
–193
2
–135 13
–132 10
–102 47
63 14
1.93*
Mn(msꢀ4ꢀMeOPh)3Cor,
IIa
λexp = 650 nm
–0.67
–1.10
–1.55
–1.83
298
308
318
298
308
318
298
308
318
298
308
318
298
298
308
318
298
308
318
298
308
318
298
308
318
298
308
318
298
308
318
298
308
318
0.09 0.01
0.14 0.01
0.27 0.05
0.28 0.01
0.99 0.10
1.47 0.05
0.85 0.09
1.79 0.07
3.92 0.10
1.10 0.09
2.34 0.06
6.17 0.01
15.28*
0.140 0.007
0.312 0.007
0.625 0.013
0.233 0.034
0.454 0.016
0.816 0,060
68
60
7
3
–81 24
0.07
0.15
0.29
–110
8
64 20
–158 55
–177 16
46
5
4.00
2.50
Mn(msꢀ4ꢀNO2Ph)3Cor,
IIIa
λexp = 460 nm
–3.73
–3.91
–4.15
–4.44
–3.47
–4.04
–4.46
59
49
2
1
–129
–158
4
4
2.83
3.40
3.99
2.01
3.14
4.07
75**
0.586 0.003
1.475 0,007
0.420 0.013
0.785 0.053
1.802 0.016
0.081 0.006
0.198 0.006
0.376 0.013
0.183 0.008
0.345 0.028
0.712 0.031
0.252 0.010
0.643 0.015
1.570 0.115
57
60
53
72
7
5
4
1
–126 21
Mn(
β
ꢀBr)8(msꢀPh)3Cor,
–325
4
IVa
λexp = 730 nm
–319 4
–314
5
* Obtained by extrapolation.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 59 No. 12 2014

1526
BEREZIN et al.
664
426
A
1.4
A
1.4
4
2
699
1
1.2
1.0
0.8
0.6
0.4
0.2
1.2
1.0
0.8
0.6
0.4
0.2
0
2
3
2
3
4
1
1
400
500
600
700
800
, nm
0
5
10
TFA, mol/L
15
λ
C
2+
Fig. 2. Absorption spectra of compound II: (
1
) ligand H Cor; (
2
) monocation H CorН ; (
3
) MeOꢀprotonated monocation; (
4)
3
4
2+
dication H CorН (leftꢀhand panel) and titration curves for compound
I
(
1) and II
(
2) (rightꢀhand panel) in the MeCn–TFA
4
system.
and βꢀpositions of the macrocycle; it decreases in the phenyl substituents on the stability of corrole–mangaꢀ
2
nese(III) complexes is observed for porphyrins. Thus,
ꢀmethoxy substitution in a manganese–tetrapheꢀ
series of complexes as follows ((10), table):
p
nylporphyrine (AcO)Mn(msꢀPh)4P molecule reduces
the stability of the complex almost 20ꢀfold [17].
The stability of Mn(msꢀPh)3Cor in 3 M H2SO4 is
almost 3000 times as low as that of a metalloporphyrin
having a similar structure, (Cl)MnIIITPP. Thus, while
(Cl)MnIIITPP dissociates in the НОАс–H2SO4 enviꢀ
(X)Mn(msꢀPh)4P (>8)
> Mn(βꢀBr)8(msꢀPh)3Cor (IVa, >4)
> Mn(msꢀ4ꢀNO2Ph)3Cor (IIIa, ~4)
(10)
> Mn(msꢀPh)3Cor (Ia, 1.1)
> Mn(msꢀ4ꢀOCH3Ph)3Cor (IIa, 0.1).
ronment at
(0.05–36.0)
= 3.00–7.85 mol/L with keff =
C
×
H2SO4
Thus, dissociation of Mn(msꢀ
IIIa occurs in the environment under study at a rate
of ~5
10–4 s–1 in 4 M H2SO4; dissociation of Mn(msꢀ
Ph)3Cor (Ia occurs in the presence of 1.1 M acid;
while only 0.1 M H2SO4 is needed to decompose the
most ꢀelectronꢀexcessive Mn(msꢀ MeOPh)3Cor
complex (table). Dissociation of complex IIa can
occur very slowly even in glacial HOAc. Eight
ꢀbromo substituents have a more pronounced
accepting effect on the macrocycle compared to the
4ꢀNO2Ph)3Cor
10–5 s–1 [14], Mn(msꢀPh)3Cor decomꢀ
(
)
×
poses in the range of concentrations as low as 0.19–
1.70 M H2SO4 ( eff = (2.6–72.0)
k
×
10–5 s–1) (table).
)
Protonated acetic acid H2OAc+ acts as an active
species in the HOAc–H2SO4 environment [17]; the
order of reaction (1) with respect to it at the limiting
stage is close to unity (0.97–1.25 for compounds Ia
and IIa) and 0.55–0.90 for IIIa and IVa according to
the log(keff) = f(H0) relationships (Fig. 1). Thus, one
can say that the dissociation mechanisms of the manꢀ
ganese corroles in the НОАс–Н2SO4 system are simiꢀ
π
4ꢀ
β
three nitro groups at para positions of phenyl rings
(table).
298
The comparison of the effective constants
obtained by extrapolation of the experimental values
(3)
keff
lar when
is in the range from 0.03 to 4.10 mol/L.
C
H2SO4
For complexes of variableꢀvalence metals (copper and
(table) to = 4 mol/L indicates that addition of manganese), this is a complex process that involves
C
H2SO4
both coordination and acid–base interactions as well
as redox stages [11]. Based on the bimolecular nature
of the limiting stage, we can assume that the dissociaꢀ
tion of manganese corroles starts with the rapid reversꢀ
ible stage of protonation of innerꢀcyclic tertiary nitroꢀ
gen (=N–) and simultaneous attachment of the acid
anion via the acidoprotolytic mechanism [16, 18]
π
ꢀelectronꢀdonating substituents (ꢀОСН3) at the para
position of phenyl rings of corrole molecule Ia reduces
the stability of Mn(msꢀ MeOPh)3Cor metal complex
eightfold, while the electronꢀaccepting substitution by
nitro groups in the Mn(msꢀ NO2Ph)3Cor molecule staꢀ
bilizes it by almost 4.5 times at = 4 mol/L comꢀ
ꢀ
4ꢀ
4ꢀ
C
H2SO4
pared to the unsubstituted complex. A similar effect of
involving M
←
N22 coordination bond rupture (11).
The product of this stage is spectrally observed as a
bathochromic shift of the Soret band relative to the
EAS in HOAc (Fig. 4).
2
The H SO concentration (mol/L) required to provide occurꢀ
2
4
–4 –1
rence of reaction (1) with the rate constant
k
~ 5
×
10
s
is
eff
given in parentheses.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 59 No. 12 2014

KINETIC STABILITY OF CORROLE COMPLEXES WITH MANGANESE
1527
401
A
1.8
455
657
422
A
1.2
621
1.6
1.4
1.0
0.8
0.6
0.4
0.2
0
581
1.2
1.0
0.8
0.6
0.4
681
0.2
0
350
450
550
650
750
, nm
300
400
500 600
700 λ, нм
λ
Fig. 3. Evolution of the EAS during dissociation of the Mn(msꢀ
4
ꢀ
MeOPh) Cor complex (IIa) in the НОАс–H SO system
3
2
4
(
= 0.45 mol/L, Δτ = 60 s) (leftꢀhand panel) and Zn(msꢀPh) Cor (Iс
)
in the С H ꢀHOAc environment (
C
= 2.6–
HOAc
C
Н2SO4
3
6
6
7.9 mol/L,
Т = 298 K) (rightꢀhand panel, the spectrum of the ligand in 8 M HOAc in benzene is given for comparison).
+
NH
+
22N
N
N
N
22NH
N
III
Mn
III
IV
–
+
+
HOAc
rapidly
+e , H
rapidly
H solv
Mn
Mn
23N
23NH
slowly
–
N
OAc
N
N
OAc
OAc
(11)
OAc
+
+
NH
+
NH
NH
N
HOAc
III
Mn
+ Mn(AOc) .
3
unstable
+
NH
NH
NH
NH
OAc
Equilibrium (6) in an acidic environment strongly
shifts to the left; (X)MnIVCor participates in reaction
(1). Protonation of the tertiary N atom promotes the
The H2SO4 concentration required to disintegrate
copper corrole complexes in the HOAc–H2SO4 enviꢀ
ronment (as opposed to manganese corrole comꢀ
plexes) increases as electron–donor substitution of the
occurrence of the subsequent stage of MnIV
↔
MnIII
reduction that takes place in an acidic environment
and involves the rupture of the N23–M bond (11). This
bond is the most labile one as it is formed upon the disꢀ
sociation of the most protonated N23–Н bond that is
prone to form Hꢀassociates with weak electron donors
3
macrocycle occurs:
Cu(msꢀ4ꢀNO2Ph)3Cor (IIIb, 0.3)
[3, 19, 20]. The 5Сꢀ or 10Cꢀprotonation of one of meso
ꢀ
< Cu(βꢀBr)8(msꢀPh)3Cor (IVb, 5.0)
(12)
bridges of (Х–)MCor molecules is the limiting stage in
the НОАсꢀH2SO4 environment; this stage results in
the rupture of another (N–M) covalent bond. The
resulting intermediate is unstable and easily dissociꢀ
ates in this environment giving rise to the [Н4CorH]2+
ligand (which is usually doubleꢀprotonated).
≈
Cu(msꢀ4ꢀMeOPh)3Cor (IIb, 5.0)
< Cu(msꢀPh)3Cor (Ib, 11.5).
3
(mol/L) at which the dissociation is completed is given
C
H2SO4
in parentheses.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 59 No. 12 2014

1528
BEREZIN et al.
409
A
2.0
425
A
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
414
11.3 M H2SO4
9.3 M H2SO4
H2SO4
441
1.5
1.0
0.5
0
CH3COOH
592
640
350
400
450
500
550
600
650
, nm
400
500
600
700
, nm
λ
λ
–5
–5
Fig. 4. Evolution of the EAS during formation of complex Ib in DMF at 298 K,
= 4
×
10 mol/L,
С
= 5.5 × 10 mol/L,
С
H3Cor
Cu(OAc)2
τ
= 30 s (leftꢀhand panel); the absorption spectra of compound Ib in acetic and sulfuric acids and their mixtures (rightꢀhand
panel).
In the series of analyzed complexes with copper, exposure to 2.0–8.0 M acetic acid in benzene at 298 K;
compound Ib (Cu(msꢀPh)3Cor) is distinguished by the
highest stability. After H2SO4 is added to the HOAc
solution of this complex, the Soret band in the EAS
shifts bathochromically by more than 30 nm; the specꢀ
trum in the visible range changes negligibly. The soluꢀ
bility of the complex increases abruptly when sulfuric
acid concentrations in the HOAc–H2SO4 system are
higher than 11.5 mol/L; the complex is disintegrated
the final spectrum (in 8 M HOAc) of the product corꢀ
responds to the EAS of neither H3Cor nor H4Cor+
(Fig. 3).
The spectral changes accompanying the converꢀ
sion of compound Ic consist in the reduction of the
Soret band at 401 nm in intensity and the increase in
the only band at 581 nm and its bathochromic shift to
very rapidly and a band at 592 nm appears in its EAS 621 nm. The triphenylcorrole monocation Н4Cor+
(Fig. 4). This behavior is likely to be caused by the high
degree of reversibility of dissociation for copper corꢀ
role complexes [6]. The EAS of the reaction products
weakly correlate with the spectra of protonated ligands
(Fig. 2). The rates of CuCor formation are extremely
high. Thus, the reaction is completed as soon as in 300 s
at 298 K in DMF environment even at virtually
equimolar ratio between Н3Cor and copper acetate
existing in the acidity range under analysis has bands at
422, 452, and 681 nm (Fig. 3). The EAS of the dissoꢀ
ciation products of complex Ic in H2SO4 environment is
close to that of [H4(msꢀPh)3CorH]2+ dication (449 and
600 nm, respectively); however, the intensity of the Soret
band in this case is extremely high; furthermore, the
dication cannot be formed at such a low acidity [3].
((4–5.5)
×
10–5) (Fig. 4, leftꢀhand panel). The dissoꢀ
The conversion of the zinc complex of compound
steadyꢀstate ( = 0.52); the tangent of the function
log(Ind) = (logCHOAc is close to three. Unfortunately,
I is
pK
ciation product in this case is presumably a mixture of
the dication and sideꢀproducts (isoꢀcorroles) [6].
f
)
the range of concentrations at which the conversion of
Ic takes place does not allow one to take into account
the acidity function Н0 in the C6H6–HOAc system to
determine the actual number of HOAc molecules parꢀ
ticipating in the reaction. The case of steadyꢀstate disꢀ
sociation was previously detected in the С6Н6ꢀHОАс
system for the labile zinc complex with Nꢀmethylꢀ
substituted porphyrinoid [21]; however, it decomꢀ
posed giving rise strictly to protonated forms of the
H(N–Me)TPP ligand. For the sake of comparison, the
Н2(msꢀРh)4Р zinc complex is a relatively stable comꢀ
pound in the environment under study; it slowly dissociꢀ
The position of compound IIb in series (12) is
attributed to the electronꢀaccepting properties of the
methoxy group protonated by H2SO4 molecule [3].
The equilibrium of protonation of compound II at
methoxy groups is observed in the acetonitrile
(
MeCN)–trifluoroacetic acid (TFA) system at acid
concentrations of mol/L (Fig. 2), while the dissoꢀ
≤4
ciation of complex IIb takes place at higher environꢀ
ment acidities (12).
The stability of the studied complexes of comꢀ
pound I in acidic environment decreases in the followꢀ
ing series of metals: Cu > Mn > Zn. Thus, H3(msꢀ
Ph)3Cor complex undergoes conversions even after
ates only in glacial HOAc ( 298 = 0.26
×
10–3 s–1) [16].
keff
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 59 No. 12 2014

KINETIC STABILITY OF CORROLE COMPLEXES WITH MANGANESE
1529
9. J. Shen, M. El Ojaimi, M. Chkounda, et al., Inorg.
Chem. 47, 7717 (2008).
10. I. H. Wasbotten, T. Wondimagegn, and A. Ghosh,
J. Am. Chem. Soc. 124, 8104 (2002).
11. R. Paolesse, S. Licoccia, and T. Boschi, Inorg. Chim.
In summary, metallocorroles are distinguished by
high degrees of specificity as they stabilize the unusual
metal oxidation states via the formation of ligandꢀ
localized radical species, which significantly impedes
selective dissociation of these complexes.
Acta 178 (1), 9 (1990).
12. K. Burger, Experimental Methods for Investigation of
Solvation, Ionic and Complex Formation Reactions in
Nonaqueous Solutions (Akademiai Kiado, Budapest,
1982).
ACKNOWLEDGMENT
This study was supported by the Russian Foundaꢀ
tion for Basic Research (project No. 14ꢀ23ꢀ00204).
13. S. M. Bruchenstein and I. M. Kolthoff, J. Am. Chem.
Soc. 78, 2974 (1956).
14. K. P. Butin, Yu. K. Beloglazkina, and N. V. Zhuk, Usp.
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Translated by D. Terpilovskaya
(2006).
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 59 No. 12 2014