Synthesis and spectral characteristics of (tetrabenzoporphyrinato) chloromanganese(III)

Article abstract of DOI:10.1134/S107036321002026X

A method is developed of synthesis of (tetrabenzoporphyrinato) chloromanganese(III) from tetrabenzoporphyrinatocadmium( II) (as a donor of the macrocyclic ligand) and the salts, manganese acetate MnAc2 and dichloromanganese MnCl2, in boiling dimethylformamide in the presence of atmosperic oxygen in 80% yield. It is found that under the conditions of the synthesis tetrabenzoporphyrinatomanganese(II) is formed which can be oxidized by the atmospheric oxygen to (tetrabenzoporphyrinato)chloromanganese(III). Absorption spectra in the visible and infrared regions, R _f and the data of elemental analysis characterizing the resulting compound are given.

Full text of DOI:10.1134/S107036321002026X

ISSN 1070-3632, Russian Journal of General Chemistry, 2010, Vol. 80, No. 2, pp. 351–356. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © V.B. Sheinin, N.V. Chizhov, A.O. Romanova, 2010, published in Zhurnal Obshchei Khimii, 2010, Vol. 80, No. 2, pp. 326–331.
Synthesis and Spectral Characteristics
of (Tetrabenzoporphyrinato)chloromanganese(III)
V. B. Sheinin, N. V. Chizhov, and A. O. Romanova
Institute of Solution Chemistry, Russian Academy of Sciences,
ul. Academicheskaya 1, Ivanovo, 153045 Russia
e-mail: vbs@isc-ras.ru
Received January 29, 2009
Abstract―A method is developed of synthesis of (tetrabenzoporphyrinato)chloromanganese(III) from tetra-
benzoporphyrinatocadmium(II) (as a donor of the macrocyclic ligand) and the salts, manganese acetate MnAc2
and dichloromanganese MnCl2, in boiling dimethylformamide in the presence of atmosperic oxygen in 80%
yield. It is found that under the conditions of the synthesis tetrabenzoporphyrinatomanganese(II) is formed
which can be oxidized by the atmospheric oxygen to (tetrabenzoporphyrinato)chloromanganese(III).
Absorption spectra in the visible and infrared regions, Rf and the data of elemental analysis characterizing the
resulting compound are given.
DOI: 10.1134/S107036321002026X
Metalloporphyrins play an important role in nature.
They are a part of the chloroplasts, hemoglobin,
myoglobin, cytochromes, and other life-important
supermolecules [1]. Porphyrin complexes of iron,
manganese, and cobalt created by the nature as a result
of biological evolution are characterized by low
potential E(M2+ 3+ of the cations recharge, and are
of porphin (22.35±0.02 [3]), tetrabenzoporphyrin
(18.53±0.05 [3]), porphyrazine (11.94±0.18 [4]), and
phthalocyanine (10.55 [5]) in DMSO indicates that
benzofusion has a strong effect on the compound
acidity (–3.82 pKa units), but it is three times less than
the effect of aza-substitution (–10.41 pKa units), which
determines mainly the properties of phthalocyanine.
)/(M
)
biocatalysts and highly effective carriers. Structural
modification of the porphin macrocycle allows its
adaptation to the specific reaction conditions. Bio-
mimetic approach to finding efficient catalysts for the
chemical technology led to the syntheses of metal
complexes with phthalocyanine ligands, which are
characterized by higher chemical and thermal stability
and can, in contrast to metalloporphyrins, work in
severe conditions of a process [2]. The phthalo-
cyanines and metallphthalocyanines have been
obtained in a high yield and are produced currently on
an industrial scale. The phthalocyanine can be
considered as a result of deep chemical modification of
porphin molecule (Fig. 1) by fusion of pyrrole
fragments in conjunction with the replacement of the
methine spacers by the aza-bridges. This circumstance
causes increased interest in the tetrabenzoporphyrin
(H2TBP) metal complexes, which, along with por-
phyrazine, represents a transitional structures beween
The basis of all known to-date methods of
synthesis of H2TBP and its metallocomplexes [reaction
(1)–(5) are shown in Fig. 2] lies in high temperature
cation-template cyclotetramerization (1), consisting in
assembling a complex on the metal cation from the
precursors, the donors of the methyleneisoindole frag-
ment. The most successful is the classic Linsted’s
method [6], based on the fusion of 3-carboxymethyl-
enephthalimidine with a metal acetates at 345°C in a
nitrogen atmosphere (1). This method allows the
preparation of complexes CdTBP and ZnTBP in a
yield of about 14.5%. Complexes of other metals can
be obtained by the reaction of the respective salts with
H2TBP (3) in universal solvents well dissolving
organic and inorganic compounds. In these cases, the
demetallation of CdTBP (2) or ZnTBP is preliminary
carried out in highly acidic media [7]. At the stage of
the demetallation a loss of H2TBP is about 25%, which
decreases the overall yield of the target complex. In the
previous paper [8] we showed that stable metalo-
the actual porphyrin (H2P) and phthalocyanine. The
298K
a1
estmation of the constants of acid dissociation (pK
)
351

352
SHEININ et al.
NH
N
N
HN
N
N
Tetrabenzoportphyrin
H2TBP
NH
N
N
NH
N
N
N
N
HN
HN
N
Porphin
NH
N
N
Phthalocyanine
N
N
HN
N
Porphyrazine
Fig. 1. Porphin and its derivatives.
NH N
N HN
(
3
)
%
1
0
0
%
2
7
)
2
(
O
N
X
N
N
CdAc2, N2,
345°C
N
N
N
MnX2, DMF,
158οC
N
N
M
O
[O]
M
Cd
N
N
(1) 14.5%
(5) 80%
N
OH
(4) 100%
N
N
Fig. 2. Scheme of synthesis of XMnTBP. For reactions (1), (2), (3)–(5), and (4)–(5) are indicated yields of pure products, for
reactions (3) and (4) the data of spectrophotometric evaluation.
complexes with H2TBP could be obtained in good
yield by using labile complexes CdTBP or ZnTBP as
donors of the macrocyclic ligand TBP2– (4) avoiding
the stage of demetallation (2). Along the reaction (4)
were obtained PdTBP and NiTBP in the yield about
80% per parent CdTBP. In this report, which continues
this research, are given the results of the successful
synthesis of (tetrabenzoporphyrinato)chloromanga-
nese(III) XMnTBP from CdTBP and salts MnX2 (X =
Ac– and Cl–).
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SYNTHESIS AND SPECTRAL CHARACTERISTICS
353
Fig. 3. Electron absorption spectra in dimethylformamide: (1) H2TBP, (2) CdTBP, and (3) MnTBP.
To compare the efficiency of H2TBP and CdTBP
as donors of the macrocyclic ligand TBP2– the
synthesis of XMnTBP was carried out along two
parallel schemes, (1), (2), (3), (5) and (1), (4), (5). The
process monitoring has been performed by recording
electron absorption spectra that are shown in Fig. 3. In
boiling DMF the product of reactions (3) and (4) is
MnTBP. With ninefold excess of MnAc2 the reac-
tion (3) is completed in 1 h, while the reaction with
MnCl2 (3) does not proceed. Reaction (4) proceeds
equally well with MnAc2 and MnCl2 and is completely
finished already at boiling the reaction mixture with
twofold amount of the salt. The molar ratio of CdTBP
to MnX2 is reduced from 1:10 to 1:2 because in this
interval the rate of reaction (4) does not depend on the
concentration of salt [9]. As already noted, the
manganese complexes of simple porphin derivatives
are characterized by a low E(M3+ 2+ potential of the
lead to anodic shift of the recharge potential E(M3+
2+
)/(M
)
and stabilize XMnP, while electron-acceptors lead to
the cathodic shift, and stabilize MnP [2, 10]. For this
reason, for the manganese complexes with por-
phyrazine and phthalocyanine ligands is more typical
the degree of oxidation II, while for the porphyrin
itself, III. According to the published data, the first
product of the reaction of salts MnX2 with simple
porphin derivatives is extremely unstable complex
MnP, which almost instantly is oxidized by
atmospheric oxygen to XMnP [11]. Extra coordination
with electron-deficient ligands such as pyridine
stabilizes MnP as (Py)2MnP [12]. In the short-wave
region of electron spectra of the complexes XMnP
there is a unique charge transfer band which allow
unambiguous evaluation of the degree of oxidation of
the complex cation [2]. We have used all these factors
for the identification of the products of synthesis.
)/(M
)
complex cation recharge. The magnitude of this
potential is largely determined by donor-acceptor
properties of tetrapyrrole ligands and can vary within a
wide range [2, 10]. Electron-donor substituents (ligands)
As already noted, the product of reactions (3) and
(4) in boiling dimethylformamide is MnTBP. This can
be explained by a combined effects of the reaction
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354
SHEININ et al.
Fig. 4. Electron absorption spectra in dimethylformamide: (1) MnTBP, (2) a mixture of MnTBP and XMnTBP, (3) XMnTBP from
acid solution of MnTBP, and (4) TBP2–.
medium and the electronic effect of benzofusion. Due
to residual water, the boiling dimethylformamide is
hydrolyzed [13], which results in the formation of the
reducing agents such as hydroxide [14–18] and
formate (6).
Fig. 4. In contrast to XMnP, the reduced form, MnP, is
extremely labile. In acidic media MnP is easily
demetallated with the formation of H2P [19]. For this
reason MnTBP is partially decomposed in acidified
DMF, as evidenced by the appearance of the ab-
sorption maxima of H2TBP at 412, 428, and 661 nm in
the electron absorption spectrum which belong to the
formed XMnTBP. In the short-wave region of the
electronic spectrum of XMnTBP appears a band with
the absorption maximum at 377 nm, which apparently
corresponds to the charge transfer band characteristic
of the porphyrin complexes of manganese(III) [2]. This
band remains unchanged at the action on XMnTBP of
a mild oxidant such as PbO2 [21] in tetrahydrofuran.
CH(O)N(CH3)2 + H2O → CH(O)O– → CO + OH–. (6)
In addition, the hydroxide can also appear as a
product of the reaction of the fairly basic DMF with
the residual water in the solvent.
At introducing a portion of the reaction mixture (3)
or (4) into dimethylformamide, MnTBP reacts with the
atmospheric oxygen dissolved theret (5) and is
partially oxidized to XMnTBP.
XMnTBP within a few minutes is reduced to
MnTBP at shaking of its solution in dimethyl-
formamide or dimetilsulfoxide with a pellet off alkali
in a sealed cell without access of atmospheric oxygen.
Prolonged contact with alkaline solution leads to
demetallation of MnTBP, which resulted in trans-
The natural oxidation of the cooled reaction
mixture proceeds in a few days. This time is reduced to
1 h at adding acid (in this case, HCl), which deac-
tivates the reducing agents dissolved in DMF. Changes
in the electronic spectrum of solution at the oxidation
of MnTBP to XMnTBP in acidified DMF are shown in
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SYNTHESIS AND SPECTRAL CHARACTERISTICS
355
formation of its electron spectrum into a spectrum of
free TBP2– [3] (Fig. 4). Despite the fact that MnP
complexes are extremely labile and readily undergo
metal exchange [20], the TBP2– complexes with the
sodium cations were not found in the applied
experimental conditions. The most likely cause of the
destruction of labile MnTBP is the ligand exchange
with replacement of TBP2– by hydroxide ions. The fact
that electron spectrum attributed to TBP2– does not
correspond to a form of MnTBP or to the product of
reduction of the latter, was proved by experiments on
the acid ionization of H2TBP. In addition, acidification
of the solution of TBP2– obtained from MnTBP also
leads to the formation of H2TBP (Fig. 3). At dissolving
XMnTBP in pyridine are formed consecutively two
products, with the electron spectra identical to the
spectrum of MnTBP which is characterized by
absorption bands at 437, 631, 445, and 631 nm,
respectively, that can be assigned to (Py)MnTBP and
(Py)2MnTBP. The results of the tests indicate that the
properties of MnTBP, XMnTBP, (Py)MnTBP, and
(Py)2MnTBP are close to the those of the porphyrin
analogs, but MnTBP is more resistant to oxidation by
atmospheric oxygen.
a. 0.05 g of tetrabenzoporphyrin and 0.17 g of
MnAc2 (molar ratio 1:10) were dissolved together in
150 ml of dimethylformamide, the mixture was
refluxed for 60 min, then cooled, and left at room
temperature for 7 days. Then NaCl was added and the
mixture was poured into water, the precipitate formed
was filtered off, washed with water, dried, and then
subjected to chromatography on aluminum oxide,
eluting with a mixture of pyridine–diethyl ether (1:4).
Yield 0.042 g (0.07 mmol, 72%), Rf 0.68.
b. 0.05 g of tetrabenzoporphyrinatocadmium(II)
and 0.028 g of MnAc2, or 0.02 g of MnCl2 (molar ratio
1:2) were dissolved in 80 ml of dimethylformamide
and the mixture was heated to boiling and refluxed for
30 s, then cooled, 2 ml of hydrochloric acid was added
to it and the mixture was kept at room temperature for
1 h, and then poured into water. After adding NaCl the
precipitate was filtered off, washed with water, dried,
and subjected to chromatography on aluminum oxide,
eluting with a mixture of pyridine–diethyl ether (1:4).
Yield 0.038 g (0.063 mmol, 80%), Found, %: C 72.11,
H 3.35, N 9.30. C36 H20ClMnN4. Calculated,%: C
72.19, H 3.37, N 9.35. Rf 0.68.
IR spectrum, cm–1 : 2954 s, 2923 s, 2854 m, 1626 s,
1599 s, 1462 w, 1432 w, 1362 m, 1249 w, 1157 w,
1121 m, 1099 m, 1645 m, 945 w, 873 w, 757 m, 741
m, 702 w, 501 w, 481 w, 418 w.
EXPERIMENTAL
Tetrabenzoporphyrin (H2TBP) and tetrabenzopor-
phyrinatocadmium(II) (CdTBP) are obtained by the
Linstead method [6].
Electron absorption spectra of the solution of (Cl)
MnTBP, λ, nm (log ε): 377 (4.21), 458 (4.21), 589
(3.73), 645 (4.02).
Dimethylformamide of “chemically pure” grade
was used without additional purification. MnCl2 of
chemically pure grade was calcined at 200°C for 4 h.
MnAc2 of chemically pure grade was recrystallized
from glacial acetic acid of chemically pure grade and
dried at 80°C for 1 h.
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