A novel synthetic approach to 27-aryltetrabenzo[5,10,15]triazaporphyrins

Article abstract of DOI:10.1016/j.mencom.2011.03.011

Magnesium 27-aryltetrabenzo[5,10,15]triazaporphyrinates were obtained by heating of phthalodinitrile, arylacetonitrile and magnesium powder.

Full text of DOI:10.1016/j.mencom.2011.03.011

Mendeleev
Communications
Mendeleev Commun., 2011, 21, 92–93
A novel synthetic approach to
27-aryltetrabenzo[5,10,15]triazaporphyrins
Valery V. Kalashnikov,a Victor E. Pushkareva,b and Larisa G. Tomilova*a,b
a Institute of Physiologically Active Compounds, Russian Academy of Sciences, 142432 Chernogolovka,
Moscow Region, Russian Federation. Fax: +7 496 524 9508; e-mail: kalashn2000@mail.ru
b Department of Chemistry, M. V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation.
Fax: +7 495 939 0290; e-mail: tom@org.chem.msu.ru
DOI: 10.1016/j.mencom.2011.03.011
Magnesium 27-aryltetrabenzo[5,10,15]triazaporphyrinates were obtained by heating of phthalodinitrile, arylacetonitrile and magnesium
powder.
CN
Tetrabenzo[5,10,15]triazaporphyrins are close analogues of phthalo-
cyanines differing in the presence of a hydrocarbon bridge instead
of the nitrogen atom in the meso-position. Although they are widely
used as photoconductive materials,1 fluorescent markers in medi-
cine2,3 and gas sensors,4 the number of methods for their prepara-
tion is limited. It was recently reported5 that 1,4,8,11,15,18,22,25-
octahexyltetrabenzo[5,10,15]triazaporphyrin was isolated as a
side product in the synthesis of 1,4,8,11,15,18,22,25-octahexyl-
phthalocyanine by treatment of 3,6-dihexylphthalodinitrile with
lithium pentoxide in n-pentanol, whereas no tetrabenzo[5,10,15]-
triazaporphyrin derivatives but only substituted phthalocyanines
were formed from 4,5-disubstituted phthalodinitriles.
A synthesis of copper tetrabenzo[5,10,15]triazaporphyrin by
heating a mixture of phthalodinitrile, 3-methylenephthalimidine
and copper chloride at 250°C was first reported in 1938.6 One of
the general methods for synthesizing tetrabenzo[5,10,15]triaza-
porphyrins involves treatment of phthalodinitrile with organoman-
ganese reagents followed by refluxing in a high-boiling solvent.7,8
Studies on the synthesis of 27-phenyltetrabenzo[5,10,15]triaza-
porphyrins by reaction of 1,3-diiminoisoindoline with phenyl-
acetic acid in the presence of template agents at 280°C have
been published recently.9,10 However, these approaches are either
unpractical as they involve several stages and anhydrous con-
ditions,8 or result in hardly separable mixtures of metal com-
plexes.10
The low solubility of tetrabenzo[5,10,15]triazaporphyrin com-
plicates its isolation in individual form because chromatographic
purification cannot be used. The incorporation of a non-coplanar
substituent at a meso-position of the macrocyclic system should
increase the solubility of the target products and hence facilitate
preparation of pure individual compounds.
Here we report on novel approach to 27-aryltetrabenzo-
[5,10,15]triazaporphyrins by simple heating to 300°C of phthalo-
dinitrile accessible in industrial amounts with arylacetonitriles
possessingreactivehydrogenatomsinthepresenceofmagnesium
metal. The primary products are the corresponding magnesium
complexes 1 (Scheme 1).†
N
CN
N
Mg
240–300 °C
R
R
N
N
N
Mg
+
N
NC
N
1a–e
from 1a H2SO4
a R = H
N
b R = o-Me
c R = m-Me
d R = p-Me
NH
N
R
N
N
HN
e R = p-OMe
N
2a
Scheme 1
version of phthalodinitrile occurred in another 5 min. The yield
(11%) was 2% higher than that in the fusion method.
Owing to the high solubility of magnesium complexes of
27-aryltetrabenzo[5,10,15]triazaporphyrins in organic solvents,
the products were separated by column chromatography. The
synthesis resulted in dark-blue crystalline compounds soluble in
most of common organic solvents (benzene, chloroform, acetone,
dimethylsulfoxide) but insoluble in hexane and methanol. The elec-
tronic absorption (UV-VIS) spectra of the products are characterised
by intense bands in the long-wave region (600–675 nm, Q-bands)
and less intense bands in the short-wave region (350–450 nm,
†
Synthesis of magnesium complexes 1a–e (general procedure). A flask
equipped with a reflux condenser and an inert gas inlet and containing a
mixture of phthalodinitrile (2.0 mmol), arylacetonitrile (0.5 mmol) and
magnesium powder (0.5 mmol) was placed under argon in an oil bath
heated to 190°C. The resulting reddish-orange melt soon turned cyan and
then was heated with a gradual temperature increase from 195–200°C to
290–300°C and kept for 2 h at that temperature. The resulting dark blue crys-
talline product was dissolved with heating in THF. The solution was filtered
from the magnesium phthalocyanine admixture, then chromatographed on
a column with silica gel using THF as the eluent. The cyan-colored fraction
was chromatographed once again on silica gel (hexane–THF, 5:1). The solvent
was removed in vacuo and the dark-blue precipitate was refluxed in methanol
for 15 min. The product was filtered off and dried in vacuo at 140°C.
For 1a: yield 9%. UV-VIS [THF, lmax/nm (I/Imax)]: 397 (0.437), 443
(0.195), 594 (0.174), 618 (0.176), 648 (0.674), 670 (1.000). 1H NMR
(DMSO-d6) d: 9.53 (d, 2H, b2-HAr, J 7.5 Hz), 9.43 (m, 4H, b1-HAr),
7.94–8.29 (m, 11H, g1-HAr, g2-HAr, HPh), 7.66 (t, 2H, g3-HAr, J 7.5 Hz),
6.98 (d, 2H, b3-HAr, J 8.1 Hz). MS (MALDI-TOF), m/z: 612 [M+].
The target 27-aryltetrabenzo[5,10,15]triazaporphyrin com-
plexes 1 were also prepared by microwave irradiation of the
reactants. As we have shown previously, optimum yields of
substituted phthalocyanines are reached by applying a microwave
power of 650–700 W for 6–10 min.11 To synthesise compound
1a, a mixture of phthalodinitrile, phenylacetonitrile and magne-
sium powder was kept at 600 W for 8 min.‡ It was found that the
melt acquired a phthalocyanine colour in 2 min. Complete con-
© 2011 Mendeleev Communications. All rights reserved.
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Mendeleev Commun., 2011, 21, 92–93
Hm-Tol
β2-H
B-bands). The nature of the aryl substituent in the magnesium
β1-H
α1-H
β3-H
α3-H
complex insignificantly affects the character of the spectra and
the positions of the absorption band maxima. Figure 1 shows the
UV-VIS of complex 1a in tetrahydrofuran as an example.
The mass spectra (MALDI-TOF) of the complexes obtained
exhibit molecular ion peaks which contain signals matching the
isotopic composition of magnesium.
α2-H
2.01 3.97
4.24 6.20 2.25
2.10
7.0
7.5
8.0
8.5
1
Complexes 1 were also characterised by H and 13C NMR
spectroscopy. The signals in the spectra were assigned using two-
dimensional (2D) techniques. Figure 2 presents a 1H–1H COSY
spectrum of complex 1c having characteristic cross-peaks as an
example. A specific feature of the spectrum is that the signals
of a3-H protons are shifted upfield by 2.39 ppm with respect to
those of a1-H protons; this effect is because the former are located
in the shielding cone of the aryl substituent arranged orthogonally
to the macrocycle plane. A similar effect, albeit not so pronounced,
is also observed for the b3-HAr and b2-HAr protons, which are
shielded by 0.58 and 0.32 ppm, respectively, relative to b1-HAr.
Conversely, in the case of a2-H protons, weak deshielding of signals
by 0.09 ppm with respect to a1-H is observed, which suggests that
weakening of the magnetic effect of the meso-aryl group occurs.
The signals of carbon atoms in the 13C NMR spectrum of 1c were
assigned using 1H–13C COSY and DEPT-135 techniques, as well
as the scarce literature data.5 Note that the methine carbon atom in
1c is deshielded (d 125.88) with respect to the meso-unsubstituted
analogue,5 which displays the corresponding signal at d 104.6.
The magnesium complexes 1 can be readily demetallated to
give free 27-aryl-29H,31H-tetrabenzo[5,10,15]triazaporphyrins 2.
N
Me
N
N
N
Mg
N
N
α3-H
β3-H
9.0
9.5
N
α1-H
α2-H
β1-H
β2-H
9.5
9.0
8.5
8.0
7.5
7.0
d/ppm
Figure 2 1H–1H COSY NMR spectrum of compound 1c (aromatic region)
in DMSO-d6.
In fact, treatment of compound 1a with concentrated sulfuric
acid gave the respective ligand 2a in a quantitative yield;§ it was
characterised by MALDI-TOF mass spectrometry (see Online
Supplementary Materials, Figure 1S) and UV-VIS spectroscopy
(Figure 1). The electronic spectrum of this ligand, similarly to that
of compounds 1 with C2v symmetry, is also characterised by a
split Q-band. It is evident from Figure 1 that demetallation
increases the degree of this splitting: the Q1 component is shifted
hypsochromically by 5 nm, whereas the Q2 band shows a batho-
chromic shift of 15 nm.
1.0
0.8
2a
0.6
0.4
0.2
0.0
1a
The ligand 2 has been proved to be promising in syntheses of
sandwich rare-earth metal complexes that represent a new type
of complexes of these elements.
300
400
500
600
700
800
l/nm
Online Supplementary Materials
Supplementary data associated with this article can be found
in the online version at doi:10.1016/j.mencom.2011.03.011.
Figure 1 Electronic absorption spectra of magnesium complex 1a and the
corresponding free-base ligand 2a in THF.
For 1c: yield 10%. UV-VIS [THF, lmax/nm (I/Imax)]: 397 (0.432), 444
(0.180), 594 (0.173), 619 (0.187), 648 (0.653), 670 (1.000). 1H NMR
(DMSO-d6) d: 9.53 (d, 2H, b2-HAr, J 7.5 Hz), 9.43–9.45 (m, 4H, b1-HAr),
8.23–8.26 (m, 4H, g1-HAr), 7.93–7.99 (m, 6H, g2-HAr, Hm-Tol), 7.67 (t, 2H,
g3-HAr, J 7.5 Hz), 7.05 (d, 2H, b3-HAr, J 8.1 Hz), 2.65 (s, 3H, HMe). 13C NMR
(DMSO-d6) d: 155.32, 152.30, 151.16, 138.63 (C-5, C-7, C-12, C-14, C-19,
C-21, C-26, C-28), 141.73, 141.64 (Cm-Tol-1, Cm-Tol-3), 139.35, 139.06, 138.85,
138.22 (C-4a, C-7a, C-11a, C-14a, C-18a, C-21a, C-25a, C-28a), 132.24,
130.02, 129.10, 128.76 (Cm-Tol-2, Cm-Tol-4, Cm-Tol-5, Cm-Tol-6), 129.72, 129.42
(C-9, C-10, C-16, C-17), 127.64 (C-2, C-24), 126.92 (C-3, C-23), 125.88
(C-27), 124.30 (C-1, C-25), 122.74, 122.54, 122.45 (C-4, C-8, C-11,
C-15, C-18, C-22), 21.25 (C–Me). MS (MALDI-TOF), m/z: 626 [M+].
For characteristics of complexes 1b,d,e, see Online Supplementary
Materials.
References
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‡
A mixture of phthalodinitrile (0.77 g), phenylacetonitrile (0.18 g) and
magnesium powder (0.11 g) was irradiated at 600 W for 8 min in a
8 C. C. Leznoff and N. B. McKeown, J. Org. Chem., 1990, 55, 2186.
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2002, 38, 1251 (Russ. J. Org. Chem., 2002, 38, 1200).
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Samsung M1915NR microwave oven to afford compound 1a, yield 11%.
§
27-Phenyl-29H,31H-tetrabenzo[b,g,l,q][5,10,15]triazaporphyrin 2a.
The magnesium complex 1a (10 mg, 0.016 mmol) was dissolved in con-
centrated H2SO4 and kept for 1 min, then poured onto ice. The precipitate
was filtered off, washed consecutively with H2O to neutral pH and 80%
aqueous MeOH (3×20 ml) and finally dried in vacuo.Yield 98%. UV-VIS
[THF, lmax/nm (I/Imax)]: 380 (0.719), 590 (0.257), 617 (0.369), 643 (0.658),
685 (1.000). MS (MALDI-TOF), m/z: 589 [M+].
Received: 21st July 2010; Com. 10/3571
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