Reaction of metal exchange of cadmium 5,10,15,20-tetraphenylporphyrinate and its β-bromo derivative with zinc acetate in dimethylformamide

Article abstract of DOI:10.1134/S1070363213050198

Metal exchange of cadmium 5,10,15,20-tetraphenylporphyrinate (CdTPP) and cadmium 2-bromo-5,10,15,20-tetraphenylporphyrinate (CdTPPBr) with zinc acetate in dimethylformamide was spectrophotometrically examined. The kinetic parameters of the metal exchange reaction were determined. A possible stoichiometric mechanism of the reaction was suggested. The effect of the bromo substituent in β-position of the pyrrole in the cadmium tetraphenylporphyrinate on the metal exchange reaction with Zn(OAc)₂ in DMF was found.

Full text of DOI:10.1134/S1070363213050198

ISSN 1070-3632, Russian Journal of General Chemistry, 2013, Vol. 83, No. 5, pp. 989–992. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © S.V. Zvezdina, N.V. Chizhova, N.Zh. Mamardashvili, 2013, published in Zhurnal Obshchei Khimii, 2013, Vol. 83, No. 5, pp. 855–
858.
Reaction of Metal Exchange of Cadmium
5,10,15,20-Tetraphenylporphyrinate
and Its β-Bromo Derivative with Zinc Acetate
in Dimethylformamide
S. V. Zvezdina, N. V. Chizhova, and N. Zh. Mamardashvili
Krestov Institute of Solution Chemistry, Russian Academy of Sciences,
ul. Akademicheskaya 1, Ivanovo, 153040 Russia
e-mail: svvr@isc-ras.ru
Received April 26, 2012
Abstract―Metal exchange of cadmium 5,10,15,20-tetraphenylporphyrinate (CdTPP) and cadmium 2-bromo-
5,10,15,20-tetraphenylporphyrinate (CdTPPBr) with zinc acetate in dimethylformamide was spectrophoto-
metrically examined. The kinetic parameters of the metal exchange reaction were determined. A possible
stoichiometric mechanism of the reaction was suggested. The effect of the bromo substituent in β-position of
the pyrrole in the cadmium tetraphenylporphyrinate on the metal exchange reaction with Zn(OAc)2 in DMF
was found.
DOI: 10.1134/S1070363213050198
CdP + M(ОАс)2(Solv)n–2
→ Cd(ОАс)2(Solv)n–2 + MP.
Interest to the synthesis of metal porphyrins (MP) is
associated with the development of modern trends in
the chemistry of porphyrins. Metal complexes of
porphyrins are studied in chemistry of supramolecular
architecture, structures for electron transport, self-
organizing systems, biosensors, etc. One of the
important reactions, which may include the porphyrin
complexes, is the metal exchange. Metal exchange
reactions have found wide application in the synthesis
of low-accessible complexes of natural and synthetic
porphyrins. For this purpose readily available com-
plexes of porphyrins and phthalocyanines [1, 2] are
used as starting materials. Thus, the palladium com-
plex with octaphenyltetraazaporphyrin (PdOPhTAP)
was synthesized according to the simplified procedure
[2] in boiling dimethylformamide starting from
MgOPhTAP and PdCl2. Furthermore, the metal
exchange reaction in Mg-complexes of chlorophyll
derivatives may be used for the synthesis of the stable
ecofriendly dyes of chlorophyll series [3] and to create
anti-cyanide drugs [4].
(1)
Here CdP and MP are metalloporphyrins,
M(ОАс)2(Solv)n–2 is solvate complex of metal acetates.
In this work we studied the effect of monobromo-
substitution in β-position of the pyrrole of cadmium
tetraphenylporphyrinate and the nature of the metal
ions on the rate of metal exchange reaction of
cadmium 5,10,15,20-tetraphenylporphyrinate (CdTPP)
and cadmium 2-bromo-5,10,15,20-tetraphenylporphyri-
nate (CdTPPBr) with zinc acetate in dimethylform-
amide.
Ph
R
N
N
N
N
Ph
Cd
Ph
Almost all metal exchange reactions involve the
transition metal salts as various solvate complexes [5].
The equation of the metal exchange reaction can be
generally presented as follows:
Ph
CdTPP: R = H; CdTPPBr: R = Br.
989

990
log (с0СdТРP/cСdTPP
ZVEZDINA et al.
log (с0СdТРPBr/cСdTPPBr
)
)
τ, min
Fig. 2. Dependence of log ([СdТРPBr]0/[СdTPPBr]) on
time of the reaction of CdTPPBr with Zn(ОАс)2 in DMF at
[Zn(ОАс)2] = 1.5×10–3 M and Т 288 (1), 293 (2), 298 K (3).
τ, min
Fig. 1. Dependence of log ([СdТРP]0/[СdTPP]) on time of
the reaction of CdTPP with Zn(ОАс)2 in DMF at
[Zn(ОАс)2] = 1.5×10–3 M and Т 288 (1), 293 (2), 298 K (3).
–log kef2
–log kef1
–log c[Zn(ОAc)2]
–log c[Zn(ОAc)2]
Fig. 4. Dependence of log kef on log c[Zn(ОAc)2] of the
reaction of CdTPPBr with Zn(ОAc)2 in DMF at Т 288 (1),
293 (2), 298 K (3).
Fig. 3. Dependence of log kef on log c[Zn(ОAc)2] of the
reaction of CdTPP with Zn(ОAc)2 in DMF at Т 288 (1),
293 (2), 298 K (3).
–dсCdP/dτ = kv[CdP][M(ОAc)2].
(2)
The metal exchange reaction (1) corresponds to the
complex associative and dissociative type of chemical
reactions [6]. In the elementary chemical act occurs
simultaneous dissociation of one complex and forma-
tion of another. There is not only metal exchange (Cd,
and Zn), but also the ligands exchange (P2– and Solv).
By classical concepts [6], the reaction (1) belongs to
the substitution reactions, in contrast to the addition and
decomposition reactions of the chemical compounds.
Our results on the kinetics of the metal exchange
reaction of CdTPP and CdTPPBr with Zn(OAc)2 in
DMF (Fig. 5, Tables 1, 2) suggest that the reaction (1)
proceeds by an associative mechanism [4, 7, 8]. At the
first step of this process an intermediate is likely to be
rapidly formed [Eq. (3)].
CdP + [Zn(Solv)n–2(OAc)2]
[Cd–P–Zn(Solv)n–4]2+···2(OAc)– + 2Solv,
quickly
(3)
Experimental data show that the rate of the metal
exchange reaction of СdTPP and СdTPPBr with
Zn(OAc)2 in DMF is described as the first order
reaction with respect to the complex concentration as
evidenced by the linear dependence: log ([СdТРP]0/
[СdTPP]) = f(τ) and log ([CdТРPBr]/[СdTPPBr]) =
f(τ), respectively (Figs. 1, 2). The reaction order with
respect to the salt, determined as the slope of the linear
Solv = DMF.
In the second monomolecular rate-limiting step, the
intermediate decays slowly to form a more stable
complex of Zn2+ and cadmium solvate salt [Eq. (4)].
[Cd–P–Zn(Solv)n–4]2+···2(OAc)–
slowly
ZnP + [Cd(OAc)2(Solv)n–2].
(4)
dependence log kef1 = f(log [Zn(OAc)2]0) and log kef2
=
f(log [Zn(OAc)2]0) in the case of the metal exchange
between CdTPP or CdTPPBr with Zn(OAc)2 in DMF,
respectively, is 1 (Figs. 3, 4). Thus, the overall rate of
the metal exchange reaction obeys the second-order
kinetic Eq. (2).
Data from Tables 1 and 2 show that the true rate
constants (kv) of the metal exchange reactions of
CdTPP and CdTPPBr with Zn(OAc)2 in DMF do not
depend on the salt concentration. Therefore, in the
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 83 No. 5 2013

REACTION OF METAL EXCHANGE OF CADMIUM
studied concentration range of the salt the structure of
991
А
its coordination sphere does not change. This is in
good agreement with the literature data [9].
Comparing the effective rate constants of the metal
exchange of zinc acetate with CdTPP and CdTPPBr in
DMF, we observed the effect of monobromo-
substitution in β-position of the pyrrole of CdTPP. The
incorporation of one bromine atom in the resulting
macrocycle leads to a 5-fold increase in the rate of the
metal exchange. This is probably due to a weakening
of Cd–N σ-bond owing to the negative inductive effect
of the bromine atom. Analysis of the influence of the
nature of the metal cation of salt (Cu2+ and Zn2+) on
the metal exchange reaction of CdTPP and CdTPPBr
with copper acetate in DMF shows that the reaction
λ, nm
Fig. 5. Variations in electronic spectra in the course of
reaction of CdTPP with Zn(ОAc)2 in DMF at [СdТРP] =
2.5×10–5 M, [Zn(ОАс)2] = 2.5×10–3 M at initial time
(1) and after 35 min (2), T 288 K.
covalence, and the energy of Cd–N bonds is
compensated by the energy of solvation of Cd2+ cation.
These findings can be attributed to the metal exchange
reaction of Cd2+ with Zn2+. The low stability of cad-
mium porphyrinate promotes successful attack of the
complex solvates ZnX2(Solv)n–2, which unlike Cd2+
form the ionic-covalent bonds of a high covalence with
the nitrogen atoms of a coordination center of the
tetrapyrrole macrocycle. This contributes to the easy
298
298
rate (k 8.0×10–3 s–1 and k 1.4×10–2 s–1, respec-
ef
ef
tively) is comparable to the rate of the metal exchange
reaction of cadmium porphyrinates with zinc acetate in
DMF.
In [10] the dissociation of Cd(II)- and Zn(II)-
containing chlorophyll analogs were studied in detail.
The Cd–N bond is ionic with a small degree of
Table 1. Rate of the metal exchange between Cd2+ and Zn2+ in СdTPP complex in DMF (сСdTPP 2.5×10–5 M)
c[Zn(ОAc)2]×103, M
Т, K
288
293
298
288
293
298
288
293
298
kef×102, s–1
1.60±0.09
2.90±0.11
3.50±0.09
1.40±0.03
2.40±0.15
2.80±0.15
1.00±0.06
1.80±0.04
2.20±0.09
kv, l mol–1 s–1
Еа, kJ mol–1
ΔS≠, J mol–1 K–1
2.5
0.64
56±27
–117±89
1.16
1.40
2.0
1.5
0.70
49±27
55±28
–138±89
–115±94
1.20
1.40
0.67
1.20
1.47
Table 2. Rate of the metal exchange between Cd2+ and Zn2+ in СdTPPBr complex in DMF (сСdTPP 2.5×10–5 M)
c(ZnAc2)×103, M
Т, K
kef×102, s–1
kv, l mol–1 s–1
Еа, kJ mol–1
ΔS≠, J mol–1 K–1
2.5
288
293
298
0.88±0.01
1.32±0.02
1.75±0.10
3.52
5.28
7.00
49±8
–123±27
2.0
1.5
288
293
298
0.73±0.03
1.14±0.03
1.35±0.07
3.65
5.70
6.75
43±19
48±5
–143±64
–129±18
288
293
298
0.58±0.01
0.85±0.03
1.14±0.06
3.87
5.67
7.60
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 83 No. 5 2013

992
ZVEZDINA et al.
formation of an intermediate in reaction (1), if the
formation of the chemical bond M–N compensates the
energy consumption for detachment of two solvent
molecules from the complex solvate salt.
00003_a) and the Program no. 1 of the Department of
Chemistry and Materials Science of the Russian
Academy of Sciences “The theoretical and experi-
mental study of the nature of the chemical bond and
the most important mechanisms of chemical reactions
and processes.”
Thus, the metal exchange reaction of cadmium
5,10,15,20-tetraphenylporphyrinate and cadmium 2-
bromo-5,10,15,20-tetraphenylporphyrinate with zinc
acetate in dimethylformamide was spectrophoto-
metrically studied. The kinetic parameters of the metal
exchange reaction were examined. A possible stoi-
chiometric mechanism of the reaction was suggested.
The incorporation of one bromine atom into the β-
position of the pyrrole ring of the macrocycle
accelerates the metal exchange reaction with zinc
acetate in dimethylformamide about 5 times.
REFERENCES
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4. Porphyrin Handbook, Smith, K., Kadish, K., and
Guillard, R., Eds., San Diego: Wiley, 1990, vol. 3,
p. 129.
EXPERIMENTAL
Cadmium tetraphenylporphyrinate was synthesized
and purified according to the known literature
procedure [11]. Cadmium 2-bromo-5,10,15,20-tetra-
phenylporphyrinate was prepared as described in [11,
12]. The identification was carried out by electron
5. Berezin, B.D. and Golubchikov, O.A., Koordinatsion-
naya khimiya sol’vatokompleksov solei perekhodnykh
metallov (Coordination Chemistry of Transition Metal
Salts Complex Solvates), Moscow: Nauka, 1992.
1
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sovremennoi khimii (The Basic Concepts of Modern
Chemistry), Leningrad: Khimiya, 1986.
absorption spectra, H NMR, and IR spectra that are
fully consistent with those described in the literature.
Zinc acetate was recrystallized from glacial acetic acid.
DMF (Merck) was used in the experiments.
7. Berezin, M.B., and Berezin, B.D., Koord. Khim., 2010,
vol. 36, no. 12, p. 925.
Spectrophotometric study of the metal exchange
reactions was carried out on a Cary 100 Varian spec-
trophotometer. The experimental procedure and the
processing of the experimental data is described in [7].
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i ftalotsianina.(Coordination Compounds of Porphyrin
and Phthalocyanine), Moscow: Nauka, 1978.
Measurements were made at
a
wavelength
corresponding to the maximum absorption band of the
complexes formed [ZnTPP (λ 558 nm) and ZnTPPBr
(λ 562 nm)].
10. Berezin, B.D., Klopova, L.V., and Drobysheva, L.N.,
Zh. Neorg. Khim., 1971, vol. 16, no. 8, p. 2053.
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Nucl. Chem., 1970, vol. 32, p. 2443.
ACKNOWLEDGMENTS
This work was financially supported by the Russian
Foundation for Basic Research (grant no. 11-03-
12. Lembo, A., Tagliatesta, P., and Guldi, D.M., J. Phys.
Chem. (A), 2006, vol. 110, no. 40, p. 11424.
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