Metal-exchange reaction between cadmium tetraphenylporphyrinates and copper(II) in dimethylformamide

Article abstract of DOI:10.1134/S0036023613040219

The metal-exchange reaction of cadmium 5,10,15,20-tetraphenylporphyrinate (CdTPP) and cadmium 2-bromo-5,10,15,20-tetraphenylporphyrinate (CdTPPBr) with copper acetate (Cu(OAc)₂) in dimethylformamide was studied spectrophotometrically. The kinetic parameters of the metal-exchange reaction were determined. A possible stoichiometric reaction mechanism was proposed.

Full text of DOI:10.1134/S0036023613040219

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2013, Vol. 58, No. 4, pp. 486–490. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © S.V. Zvezdina, O.V. Mal’tseva, N.V. Chizhova, I.G. Scheblykin, N.Zh. Mamardashvili, 2013, published in Zhurnal Neorganicheskoi Khimii, 2013, Vol. 58,
No. 4, pp. 553–557.
PHYSICAL CHEMISTRY
OF SOLUTIONS
MetalꢀExchange Reaction between Cadmium
Tetraphenylporphyrinates and Copper(II) in Dimethylformamide
a
a
a
b
a
S. V. Zvezdina , O. V. Mal’tseva , N. V. Chizhova , I. G. Scheblykin , and N. Zh. Mamardashvili
a
Krestov Institute of Solution Chemistry, Russian Academy of Sciences, ul. Akademicheskaya 1, Ivanovo, 153045 Russia
b
Chemical Physics, University of Lund, PO Box 124, Lund 22100, Sweden
Received November 30, 2011
Abstract—The metalꢀexchange reaction of cadmium 5,10,15,20ꢀtetraphenylporphyrinate (CdTPP) and
cadmium 2ꢀbromoꢀ5,10,15,20ꢀtetraphenylporphyrinate (CdTPPBr) with copper acetate (Cu(OAc)2) in
dimethylformamide was studied spectrophotometrically. The kinetic parameters of the metalꢀexchange reacꢀ
tion were determined. A possible stoichiometric reaction mechanism was proposed.
DOI: 10.1134/S0036023613040219
Porphyrins constitute the most important class of nylporphyrinate ligand with Cu(ОАс)2 in DMF has
macrocyclic tetrapyrrols. Chemically modified porꢀ been performed.
phyrins and metalloporphyrins form stable supramoꢀ
Ph
R
lecular assemblies, which very sensitively and selecꢀ
tively respond to weak energetic actions, thus opening
wide opportunities for the creation of controlled funcꢀ
tional materials and their application in different fields
of science and engineering. Among the promising
trends of the practical application of metalloporphyꢀ
rins are photodynamic therapy of cancer diseases [1,
N
N
N
N
Ph
Cd
Ph
2
] and design of highly selective catalysts, organic
semiconductors [3–5], and coloring pigments [6].
One important reactions which porphyrin complexes
can enter is metal exchange. Metalꢀexchange reacꢀ
tions are classified with complex associative–dissociaꢀ
tive metalꢀexchange reactions between macroheteroꢀ
cycles. In the general form, a metalꢀexchange reaction
may be written as
Ph
CdTPP: R = H
CdTPPBr: R = Br
EXPERIMENTAL
Cadmium tetraphenylporphyrinate was syntheꢀ
sized and purified by a known literature method [12],
and cadmium 2ꢀbromoꢀ5,10,15,20ꢀtetraphenylporꢀ
phyrinate was synthesized as described in [12, 13].
CdP + M(OAc)2
Cd(OAc)2 solv
(
solv
)
n − 2
(1)
→
(
)
+ MP,
n − 2
where CdP and MP are metalloporphyrins and Identity of the synthesized compounds was established
1
M(ОАс) (solv)n
plexes.
are metal acetate solvatocomꢀ by electron absorption, H NMR, and IR spectra,
2
– 2
which completely corresponded to the characteristics
described in the literature. Copper acetate was recrysꢀ
tallized from glacial acetic acid. In the course of experꢀ
iment, we used DMF (Merck).
Metalꢀexchange reactions have found a wide appliꢀ
cation in metal cluster design [7], isotope exchange
[
8], and the production of metalloporphyrins, whose
direct synthesis is lowꢀefficient or hindered [9–11].
The spectrophotometric study of the metalꢀ
In continuation of our studies on the effect of the exchange reaction was performed on a Varian Cary
chemical modification of the tetrapyrrol macrocycle 100 spectrophotometer. A solution of cadmium porꢀ
on the metalꢀexchange rate in reactions with metal phyrinate (CdP) and the salt of known concentration
cations of different nature, we have studied the effect was placed into thetemperatureꢀcontrolled cell of the
of monoꢀbromosubstitution in the
β
ꢀpyrrol position of spectrophotometer. DMF, which has filled nonbondꢀ
orbits and ꢀdonor properties, was selected to
cadmium tetraphenylporphyrinate on the rate of the ing
ϕ
N
σ
metalꢀexchange reaction with Cu(ОАс)2 in dimethylꢀ be the organic solvent. In certain time intervals, the
formamide (DMF). The comparative analysis of the absorbance of a solution was measured at the waveꢀ
reaction rate constants obtained for metal exchange length corresponding to the maximum absorption
and complexation of 2ꢀbromoꢀ5,10,15,20ꢀtetrapheꢀ band of the complex to be formed ( = 543 nm for the
λ
486

METALꢀEXCHANGE REACTION
487
Table 1. Characteristics of the UVꢀVis spectra of tetraphenylporphyrin, 2ꢀbromoꢀ5,10,15,20ꢀtetraphenylporphyrin, and
their cadmium complexes in DMF
Band,
λ
max, nm (log
ε
)
I
II
III
IV
Cope
H TPP*
646 (3.68)
651 (3.76)
613 (4.19)
590 (3.73)
595 (3.75)
–
548 (3.91)
552 (3.68)
571 (4.29)
513 (4.28)
519 (4.10)
416 (5.62)
420 (5.31)
437 (5.68)
2
H TPPBr
2
CdTPP
529 (3.75)
Shoulder
CdTPPBr
627 (4.19)
–
583 (4.18)
–
441 (5.04)
*
Data from [14].
Table 2. Exchange rates of Cd2+ for Cu2+ in the CdTPP complex in DMF (cCdTPP = 2.5 10–5 mol/L)
×
3
3
–1
≠
cCu(ОAc)2
×
10 , mol/L
T
, K
keff
×
10 , s
k
, L/(mol s)
Ea, kJ/mol
Δ
S
, J/(mol K)
v
2
.5
.0
.5
283
2.5 ± 0.08
3.8 ± 0.12
5.5 ± 0.24
8.0*
1.00
1.52
2.20
3.20*
0.95
1.30
2.00
2.80*
0.93
1.40
2.00
2.87*
54 ± 2
–112 ± 8
2
88
93
2
298
2
1
283
1.9 ± 0.08
2.6 ± 0.11
4.0 ± 0.28
5.6*
51 ± 9
52 ± 2
–124 ± 30
–123 ± 8
2
88
93
2
298
283
1.4 ± 0.06
2.1 ± 0.10
3.0 ± 0.09
4.3*
2
88
93
2
298
*
Calculated value.
formation of CuTPPBr in the metalꢀexchange reacꢀ
tion and = 538 nm for CuTPP). The measurements
were performed within temperature ranges of 288–298 K
and 283–293 K for the metalꢀexchange reaction of
CdTPPBr with Cu(ОАс)2 and CdTPP with the same mined by the equation of the theory of absolute reacꢀ
T1T2
k2
k1
E = 19.1
− log
.
(4)
) was deterꢀ
λ
a
T2 −T1
≠
ΔS
The activation entropy change (
tion rates [15]
salt in DMF, respectively. In both cases, cCuCl2 = 1.5
×
–3
–3
1
0 –2.5
The current CdP concentration was calculated as
с0 )/( А0), (2)
, and are the absorbance of a solution
×
10 mol/L.
Ea
≠
298
+
ΔS = 8.314 ln k
− 253.22.
(5)
298
The electron absorption spectra (UVꢀVis) of tetꢀ
raphenylporphyrin, 2ꢀbromoꢀ5,10,15,20ꢀtetrapheꢀ
nylporphyrin, and their cadmium complexes in DMF
are given in Table 1. Experimental data are listed in
Tables 2 and 3. The evolution of EASs during the
metalꢀexchange reaction between cadmium tetrapheꢀ
nylporphyrinate and Cu(ОАс)2 in DMF is illustrated
in Fig. 1.
c
=
(А
–
А
А –
∞
τ
∞
where А0
,
А
А
τ
∞
at the initial time moment, at a time moment
τ
, and
after the reaction is completed, and с0 and are the
с
initial and current concentrations of the cadmium
complex, respectively.
The effective reaction rate constants (keff) were calꢀ
culated as
RESULTS AND DISCUSSION
–dсCdР
/dτ
=
k с
eff CdР
.
(3)
Cadmium porphyrins are dominantly ionic and
The activation energy ( а
Arrhenius equation
Е
) was calculated by the kinetically unstable porphyrin complexes [16], so the
2+
metalꢀexchange reactions with salts such as Zn ,
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 58 No. 4 2013

488
ZVEZDINA et al.
Table 3. Exchange rates of Cd2+ for Cu2+ in the CdTPPBr complex in DMF (cCdTPPBr = 2.5
×
10–5 mol/L)
3
2
–1
≠
cCu(ОAc)2
×
10 , mol/L
T
, K
keff
×
10 , s
k , L/(mol s)
v
Ea, kJ/mol
Δ
S
, J/(mol K)
2
.5
.0
.5
288
0.62 ± 0.03
0.93 ± 0.04
1.40 ± 0.05
0.52 ± 0.02
0.76 ± 0.02
1.10 ± 0.03
0.43 ± 0.01
0.63 ± 0.02
0.88 ± 0.01
2.48
3.72
5.60
2.60
3.80
5.50
2.87
4.20
5.87
58 ± 2
–94 ± 8
2
93
98
2
2
1
288
53 ± 2
51 ± 3
–112 ± 9
–122 ± 8
2
93
98
2
288
2
93
98
2
Co , Ni2+, or Cu2+ proceed with the formation of 2ꢀbromoꢀ5,10,15,20ꢀtetrapenylporphyrin complexes
2+
more stable compounds [17].
(Tables 2, 3) allows us to conclude that reaction (1)
proceeds by the associative mechanism [9, 18, 19]. It
is likely that an intermediate is quickly formed at the
first stage of this process. At the second stage controlꢀ
ling the rate of this process, the intermediate dissociꢀ
ates to form the final reaction products.
Experimental data show that the rate of the metalꢀ
exchange reaction of CdTPP and CdTPPBr with
Cu(ОАс)2 in DMF is described by firstꢀorder equation
with respect to the concentration of the complex, as
indicated
by
the
linear
dependences
0
0
log(c
cСdTPP
)
=
f
(τ)
and log(c
cСdTPPBr
)
=
Comparing the effective rate constants for the
СdТРP
СdТРPBr
f( ) (Figs. 2 and 3), respectively. The rate of the metalꢀ metalꢀexchange reaction of copper acetate with
τ
exchange reaction depends on the concentration of CdTPP and CdTPPBr in DMF, we have found that
the salt. The reaction order with respect to the salt the introduction of a bromine atom into the macrocyꢀ
determined as the slope of the linear plot logkeff1
f (logcCu(OAc)2
(for the metal exchange between
CdTPP and Cu(ОAc)2) and logkeff2
=
cle nearly twice accelerates the metalꢀexchange reacꢀ
tion. This seems to be caused by the weakening of the
)
Cd–N
the bromine atom. In the literature it has been repeatꢀ
for the metal exchange between CdTPPBr and the edly noted that metal exchange of metalloporphyꢀ
σ
bond due to the negative induction effect of
=
f (logcCu(OAc)2
)
(
same salt in DMF) is unity (Figs. 4, 5). Hence, the rin(MP) complexes with transitionalꢀmetal salts may
metalꢀexchange reaction is bimolecular and its total occur either more or less quickly in comparison with
rate obeys the secondꢀorder kinetic equation
dcCdP [CdP][M(ОAc)2].
the complexation reaction between H2P and the same
salts [9, 20–22]. However, in the overwhelming majorꢀ
ity of cases, the exchange reaction is one to three
–
/dτ
=
k
(6)
v
Our results on the kinetics of the exchange of cadꢀ orders of magnitude faster, especially for labile MPs
mium for copper in tetraphenylporphyrin and [9, 22].
log(c0CdTPP/cCdTPP
)
A
1
2
1
0
.8
3
0
0
0
.8
.6
.4
2
0
.4
1
0
5
00
550
600
650
λ
, nm
0.2
0
100 200 300 400 500 600 700
, s
τ
Fig. 1. Evolution of UVꢀVis spectra in the metalꢀexchange
Fig. 2. lo gg (c0
cСdTPP)
versus the time of the reaction
reaction between cadmium tetraphenylporphyrinate
СdТРP
–5
and Cu(OAc) in DMF at сСdТРP = 2.5
×
10 mol/L,
between cadmium tetraphenylporphyrinate and Cu(ОАс)2
2
10–3 mol/L, and
Т
= 298 K ( ) at the iniꢀ
1
in DMF at cCu(ОАс)2 = 2.0
) 288, and ( ) 293 K.
× Т of (1) 283,
10–3 mol/L and
cCu(
= 2.5
×
ОАс 2
)
tial time moment and ( ) in 20 min.
2
(
2
3
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 58 No. 4 2013

METALꢀEXCHANGE REACTION
–log
489
log(c0CdTPP/cCdTPP
)
k
eff
1
3
.0
.8
1.6
1.2
0.8
0.4
1
2
3
3
2
2
2.6
2.4
2
.2
.0
1
2
2.55 2.60 2.65 2.70 2.75 2.80 2.85
–
logcCu(OAc)2
0
50 100 150 200 250 300 350
, s
Fig. 4. logkeff1 versus logcCu(ОAc)2 in the metalꢀexchange
reaction between cadmium tetraphenylporphyrinate and
τ
Cu(ОAc)2 in DMF at
T
of (
1) 283, (
2) 288, and (3) 293 K.
Fig. 3. log(c0
cСdTPPBr
)
versus the time of the
reaction between cadmium 2ꢀbromoꢀ5,10,15,20ꢀtetꢀ
raphenylporphyrinate and Cu(ОАс)2 in DMF at cCu(ОАс)2
СdТРPBr
=
A
2
.5 of ( ) 288, ( ) 293, and ( ) 298 K.
10–3 mol/L and
×
T
1
2
3
0
.5
1
2
–
logkeff2
0.4
0.3
1
1
2.4
1
2
3
2
2
1
1
.2
.0
.8
.6
0
.2
.1
0
500
550
600
650
λ
, nm
2
.55 2.60 2.65 2.70 2.75 2.80 2.85
–
logcCu(OAc)2
Fig. 6. Evolution of UVꢀVis spectra in the
complexation reaction between 2ꢀbromoꢀ5,10,15,20ꢀtetꢀ
Fig. 5. logkeff2 versus logcCu(ОAc)2 in the metalꢀexchange
reaction between cadmium 2ꢀbromoꢀ5,10,15,20ꢀtetꢀ
raphenylporphyrinate and Cu(ОAc)2 in DMF at
raphenylporphyrine and Cu(ОAc)2 in DMF at
c
=
Н ТРPBr
2
2.5
298 K (
×
10–5 mol/L,
c
Cu ОАс = 2.5
×
10–3 mol/L, and
) in 90 min.
T =
Т
of
(
)
2
(1
) 288, ( ) 293, and ( ) 298 K.
2
3
1
) at the initial time moment and (2
In this connection, we have studied the complexꢀ 65 times slower than metal exchange with the same
ation reaction between 2ꢀbromoꢀ5,10,15,20ꢀtetrapheꢀ salt in DMF. It is probable that the state of intracyclic
nylporphyrin (Н TPРBr) and Cu(ОАс)2 in DMF. The N–H bonds in the porphyrin molecule is one of the
2
evolution of EASs during then complexation reaction factors determining the complexation reaction rate.
between Н TPРBr and Cu(ОАс)2 in DMF is illustrated The absence of the need for the disruption of N–H
2
in Fig. 6. In the general form, the equation of the comꢀ bonds in labile cadmium porphyrinate during the
plexation reaction may be written as
metalꢀexchange reaction accelerates the formation of
copper porphyrinates. This fact indicates that metal
exchange is more preferable for the synthesis of copper
complexes in preparative chemistry. The obtained
result may be used in the synthesis of mesoꢀsubstituted
porphyrin metallocomplexes (for example, palladium
and platinum porphyrinates), whose direct synthesis is
lowꢀefficient or hindered.
H P + MX
2
(
solv
)
2
n − 2
(
7)
ꢀ
(
solv
)
MP + 2HX + (n − 2 − m)solv,
m
where H2P is the porphyrin ligand, MX (solv)
n – 2
the metal salt solvate complex, solv is the solvent, and
MP is a metalloporphyrin.
We performed a comparative analysis of reaction
rate constants for metal exchange between CdTPPBr
and copper acetate (Eq. (1)) and the formation of a
is
2
ACKNOWLEDGMENTS
Н TPРBr complex with the same salt in DMF
2
This work was supported by the Russian Foundaꢀ
tion for Basic Research (project no. 11ꢀ03ꢀ00003ꢀa),
(
Eq. (7)). The complexation of Н TPРBr with copper
2
2
98
–4
acetate (
k
= 2.14 ×
10 s–1) was established to be the Department of Chemistry and Materials Sciences
eff
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 58 No. 4 2013

490
ZVEZDINA et al.
of the Russian Academy of Sciences, program no. 1
Theoretical and Experimental Investigation of the
Nature of Chemical Bonds and the Mechanisms of
Most Important Chemical Reactions and Processes,”
by the Seventh Framework Program of the European
9. P. Hambright, Porphyrin Handbook, Ed. by K. Smith,
K. Kadish, and R. Guillard (Wiley, San Diego, 1990),
Vol. 3, p. 129.
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1
0. N. V. Chizhova, O. G. Khelevina, and B. D. Berezin,
Zh. Obshch. Khim. 73, 1738 (2003).
Community for Research, Technological Developꢀ 11. N. V. Chizhova and N. Zh. Mamardashvili, Zh. Neorg.
Khim. 56, 484 (2011).
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Nucl. Chem. 32, 2443 (1970).
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for 2009–2013” (state contract no. 02.740.11.0857).
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