Coordination dimer based on zinc octaethylporphyrin and meso-pyridyl-substituted porphyrin

Article abstract of DOI:10.1134/S1070363209010228

New dimeric porphyrin was synthesized as a result of coordination interaction between 2,3,7,8,12,13,17,18-octaethylporphyrinatozinc(II) and 5-(3,5-di-tert-butylphenyl)-2,8,12,18-tetraethyl-3,7,13,17-tetramethyl-15- (pyridin-4-yl)porphyrin. The new compoun

Full text of DOI:10.1134/S1070363209010228

ISSN 1070-3632, Russian Journal of General Chemistry, 2009, Vol. 79, No. 1, pp. 138–141. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © L.Zh. Guseva, S.G. Pukhovskaya, A.S. Semeikin, O.A. Golubchikov, 2009, published in Zhurnal Obshchei Khimii, 2009, Vol. 79,
No. 1, pp. 142–145.
Coordination Dimer Based on Zinc Octaethylporphyrin
and meso-Pyridyl-Substituted Porphyrin
L. Zh. Gusevaa,b, S. G. Pukhovskayab, A. S. Semeikinb, and O. A. Golubchikovb
a Institute of Solution Chemistry, Russian Academy of Sciences, ul. Akademicheskaya 1, Ivanovo, 153045 Russia
e-mail: lgg@isc-ras.ru
b Ivanovo State University of Chemical Technology, Ivanovo, Russia
e-mail: puhovskaya@isuct.ru
Received November 29, 2007
Abstract—New dimeric porphyrin was synthesized as a result of coordination interaction between
2,3,7,8,12,13,17,18-octaethylporphyrinatozinc(II) and 5-(3,5-di-tert-butylphenyl)-2,8,12,18-tetraethyl-3,7,13,17-
tetramethyl-15-(pyridin-4-yl)porphyrin. The new compound was characterized by spectral and TLC data, and
equilibrium constant for the formation of molecular ensemble was determined.
DOI: 10.1134/S1070363209010228
In the recent years, many publications were
concerned with the design of self-organized
supramolecular systems via coordination interactions
between porphyrin metal complexes and porphyrins
containing peripheral electron-donating groups [1, 2].
The results of studies performed in some laboratories
in USA, Japan, Germany, and France showed that
porphyrins and related compounds are quite promising
for the design of supramolecular assemblies for highly
effective directional transformation of light energy and
creation of new materials for nonlinear optics, sensor
systems, and membrane technology [2–5]. The main
approach to such systems is based on studies on axial
coordination to metal porphyrin complexes. It is
known that the ability to take up extra ligands is very
inherent to porphyrin complexes with triply charged
metal cations (Al3+, Mn3+, Fe3+, Co3+, etc.) and
complexes with metals in the oxidation state 2+ which
have either considerable effective positive charge (Zn,
Mg, etc.) or unpaired electrons (Fe, Co, Re, etc.). The
charge on the metal ion and the nature of extra ligand
are crucial factors for the formation of stable axial
complexes by metal porphyrins [6].
We have synthesized dimeric porphyrin III as a
result of coordination interaction between
2,3,7,8,12,13,17,18-octaethylporphyrinatozinc(II) (I) and
5-(3,5-di-tert-butylphenyl)-2,8,12,18-tetraethyl-
3,7,13,17-tetramethyl-15-(pyridin-4-yl)porphyrin II.
Et
Et
Et
Et
Bu-t
Et
Me
Et
Me
N
N
N
HN
Zn
N
N
NH
N
N
Et
Me
Et
Me
Bu-t
Et
Et
Et
Et
I
II
Compound II was obtained following a specially
developed procedure by mixed condensation of bis(3-
ethyl-4-methyl-1H-pyrrol-2-yl)methane (VI) with
pyridine-4-carbaldehyde (IV) and 3,5-di-tert-butylbenz-
aldehyde (V) in methylene chloride in the presence of
chloroacetic acid, followed by oxidation (without
138

COORDINATION DIMER BASED ON ZINC OCTAETHYLPORPHYRIN
139
t-Bu
Bu-t
condensation without additional purification. Apart
from porphyrin II, the condensation gave symmetric
5,15-bis(3,5-di-tert-butylphenyl)-2,8,12,18-tetraethyl-
3,7,13,17-tetramethylporphyrin and 2,8,12,18-tetra-
ethyl-3,7,13,17-tetramethyl-5,15-bis(pyridin-4-yl)-
porphyrin as by-products.
Me
Me
Et
Et
Et
N
HN
N
Me
COOEt
Et
NH
NH
KOH
Et
VI
(CH2OH)2
NH
Me
Me
Et
COOEt
Me
N
Et
Et
Systematic studies on the ability of metal
porphyrins to coordinate nitrogen-containing extra
ligands showed that zinc porphyrins give rise to fairly
stable five-coordinate complexes with pyridine,
piperidine, and other nitrogen-containing bases. Such
complexes are characterized by a considerable red shift
of absorption bands in the electronic spectra (Fig. 1).
The stability constants (Ks) of extra coordination
compounds derived from zinc porphyrins with planar
macroring structure range from 4×103 to 6×103 l mol–1,
depending on the substituents [2, 7, 8]. Therefore, we
were able to detect molecular complex III by spectral
methods. Complex III is formed via donor–acceptor
interaction between octaethylporphyrin zinc complex I
and 5-(3,5-di-tert-butylphenyl)-2,8,12,18-tetraethyl-
3,7,13,17-tetramethyl-15-(pyridin-4-yl)porphyrin (II).
When solutions of porphyrins I and II with a
Et
Et
N
N
N
N
Zn
Et
Et
Et
Et
III
isolation) of the resulting porphyrinogen mixture with
p-chloranil. The porphyrin mixture was separated by
column chromatography.
CHO
CHO
+
N
t-Bu
Bu-t
IV
V
D
Me
2
Et
Et
0.4
NH
NH
(1) H+
(2) [O]
1
+
II
0.3
0.2
0.1
0
Me
VI
Initial bis(3-ethyl-4-methyl-1H-pyrrol-2-yl)-
methane (VI) was prepared from diethyl 5,5′-methyl-
enebis(4-ethyl-3-methyl-1H-pyrrole-2-carb-oxylate)
by simultaneous hydrolysis and decarboxyla-tion in
ethylene glycol. Compound VI was then used in the
500
520
540
560
λ, nm
Fig. 1. Electronic absorption spectra of 2,3,7,8,12,13,17,18-
octaethylporphyrinatozinc(II) (I) in (1) benzene and (2) in
benzene containing 0.2 mol l–1 of pyridine.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 1 2009

140
GUSEVA et al.
Electronic absorption spectra of porphyrins I–III in benzene at 298 K and their Rf values
a
Comp. no.
λmax, nm (log ε)
Rf
620 (3.74)
625 (3.61)
–
568 (3.86)
573 (3.79)
568 (4.12)
575
535 (4.04)
540 (3.96)
530 (3.93)
539
499 (4.15)
507 (4.36)
–
400 (5.25)
407 (5.39)
403 (5.19)
412
–
I
II
0.21
0.85
0.46
Zn(I)
III
506
a
Benzene–chloroform (1:1) + 2% of EtOH.
concentration of (1–2.5)×10–5 M were mixed at a ratio
of 1:2 and kept in an inert atmosphere (argon), new
bands appeared in the electronic absorption spectra. By
analytical thin-layer chromatography we succeeded in
separating the mixture into three zones, two of which
corresponded to zinc complex I and free ligand II. The
second intermediate zone was isolated and
characterized by electronic spectra (Fig. 2). The
positions of the absorption maxima and Rf values are
given in table. Addition of excess nitrogen-containing
reagent, e.g., pyridine, leads to decomposition of the
molecular assembly. The spectrum of the mixture thus
obtained is superposition of the spectra of porphyrin II
and pyridine complex of zinc porphyrin I. According
to the TLC data, the chromatogram contained no third
zone. The stability constant of coordination dimer III
(Zn-I + II ↔ III) was estimated on the basis of the
reactant concentrations used in the spectral
measurements: Ks = 9 × 106 l mol–1.
of silica gel (Merck F254, layer thickness 0.5 mm;
CHCl3–C6H6–C2H5OH) and by spectrophotometry.
The electronic absorption spectra of porphyrins I–III
are given in table.
The extra coordination process was studied at
293.15 0.1 K by spectrophotometry using a Specord
M-400 instrument (50-ml cells with a path length of
100 mm). A required volume of extra ligand solution
was added with the aid of a microsyringe to a solution
of metal porphyrin. The volume of the reaction
mixture increased during the process by no more than
1
0.05%. The H NMR spectra were recorded on a
Bruker-200 spectrometer in CDCl3; the chemical shifts
were measured relative to tetramethylsilane as internal
reference. The solvents used (benzene, chloroform,
and pyridine) were preliminarily purified according to
standard procedures [9, 10].
2,3,7,8,12,13,17,18-Octaethylporphyrin was
prepared as described in [11]. It was purified by chro-
matography on aluminum oxide of activity grades II
and III (eluent chloroform). Octaethylorphyrin zinc
complex I was synthesized by reaction of 2,3,7,8,12,-
13,17,18-octaethylporphyrin with excess zinc(II) acetate
in boiling dimethylformamide. The complex was
purified by chromatography on aluminum oxide of
activity grade III using chloroform as eluent. 1H NMR
spectrum, δ, ppm: 10.07 s (4H, meso-H), 3.98 q (16H,
CH2CH3), 1.70 t (24H, CH2CH3).
EXPERIMENTAL
The purity of the synthesized compounds was
checked by TLC on aluminum plates with a fixed layer
D
3
1
0.4
2
Bis(3-ethyl-4-methyl-1H-pyrrol-2-yl)methane
(VI). A mixture of 1 g of diethyl 5,5-methylenebis(4-
ethyl-3-methyl-1H-pyrrole-2-carboxylate), 0.1 g of hy-
drazine sulfate, 1 g of potassium hydroxide, and 30 ml
of ethylene glycol was heated to the boiling point,
maintained boiling for 1 h, poured into 200 ml of
water, and kept for 3 h at room temperature. The
precipitate was filtered off, washed with water, and
dried at room temperature. Yield 0.56 g. Compound VI
was used in further synthesis without additional
purification.
0.2
0
500
550
600
λ, nm
Fig. 2. Electronic absorption spectra in benzene of
(1) 5-(3,5-di-tert-butylphenyl)-2,8,12,18-tetraethyl-3,7,13,17-
tetramethyl-15-(pyridin-4-yl)porphyrin, (2) 2,3,7,8,12,13,17,18-
octaethylporphyrinatozinc(II) (I), and (3) coordination dimer
III.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 1 2009

COORDINATION DIMER BASED ON ZINC OCTAETHYLPORPHYRIN
141
ACKNOWLEDGMENTS
5-(3,5-Di-tert-butylphenyl)-2,8,12,18-tetraethyl-
3,7,13,17-tetramethyl-15-(pyridin-4-yl)porphyrin
(II). A solution of 0.45 g of chloroacetic acid in 20 ml
of methylene chloride was added under stirring at
room temperature in carbon dioxide atmosphere to a
solution of 0.56 g of compound VI, 0.13 g of pyridine-
4-carbaldehyde, and 0.26 g of 3,5-di-tert-butyl-
benzaldehyde in 150 ml of methylene chloride. The
mixture was stirred for 4 h with protection from direct
light, a solution of 0.9 g of p-chloranil in 20 ml of THF
was added, the mixture was stirred for 16 h at room
temperature, and the solvent was distilled off to
dryness on a rotary evaporator. The residue was treated
with a 5% solution of sodium hydroxide, and the pre-
cipitate was filtered off, washed with water, and dried
at 70°C in air. The product (a mixture of porphyrins)
was dissolved in chloroform, and the solution was
subjected to chromatography on aluminum oxide of
activity grade III using chloroform as eluent. The first
fraction contained 5,15-bis(3,5-di-tert-butylphenyl)-
2,8,12,18-tetraethyl-3,7,13,17-tetramethylporphyrin,
the second fraction contained the desired 5-(3,5-di-
tert-butylphenyl)-2,8,12,18-tetraethyl-3,7,13,17-
tetramethyl-15-(pyridin-4-yl)porphyrin, and from the
third fraction we isolated 2,8,12,18-tetraethyl-
3,7,13,17-tetramethyl-5,15-bis(pyridin-4-yl)porphyrin.
The second fraction was concentrated to a small
volume and was subjected to repeated chromatography
on aluminum oxide of activity grade III using
chloroform as eluent, the eluate was evaporated, and
the product was precipitated with methanol, filtered
off, washed with methanol, and dried at 70°C in air.
Yield 0.20 g (22%). Electronic absorption spectrum
(CHCl3), λmax, nm (logε): 625 (3.68), 573 (4.06), 540
This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 06-03-32537a).
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