Phthalocyanines with phosphonate moiety via C-nucleophilic substitution in phthalonitriles

Article abstract of DOI:10.1142/S108842461350051X

Interaction of isomeric 4-nitro- or 3-nitrophthalonitrile with triethyl phosphonoacetate, diethyl cyanomethylphosphonate or tetraethyl methylenediphosphonate in basic conditions resulted in regioselective C-nucleophilic oxidative substitution of hydrogen ortho-located to nitro group, new phthalonitriles with diethoxyphosphorylmethyl or bis(diethoxyphosphoryl) methyl group were isolated in modest yields. In the same conditions one chlorine atom of tetrachlorophthalonitrile was regioselectively substituted with triethyl phosphonoacetate. In basic conditions, both parent phthalonitriles and corresponding zinc phthalocyanines with ortho-located nitro and diethoxyphosphoryl substituted methyl groups are involved in reversible acid-base interaction accompanied with large bathochromic shift of their long wavelength absorption maxima in visible or NIR region, correspondingly. Formation of tetraazachlorin- and tetraaza(iso)bacteriochlorin-like anions is proposed for explanation of this unprecedent bathochromic shift for phthalocyanines.

Full text of DOI:10.1142/S108842461350051X

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2013; 17: 1–9
DOI: 10.1142/S108842461350051X
Published at http://www.worldscinet.com/jpp/
Phthalocyanines with phosphonate moiety via C-nucleophilic
substitution in phthalonitriles
Vladimir Negrimovsky*a◊, Aleksey Komissarova, Alexandr Perepukhovb,
Kyrill Suponitskyc, Valery Perevalovd and Evgeny Lukyanetsa◊
a Organic Intermediates and Dyes Institute, B. Sadovaya 1/4, Moscow 123995, Russia
b Moscow Institute of Physics and Technology, Institutskii pereulok 9, Dolgoprudny 141700, Russia
c A.N. Nesmeyanov Institute of Organoelement Compounds, Vavilov str. 28, Moscow 119991, Russia
d Mendeleev University of Chemical Technology of Russia, Miusskaya sq. 9, Moscow 125047, Russia
Dedicated to Professor Özer Bekaroğlu on the occasion of his 80th birthday
Received 5 March 2013
Accepted 8 April 2013
ABSTRACT: Interaction of isomeric 4-nitro- or 3-nitrophthalonitrile with triethyl phosphonoacetate,
diethyl cyanomethylphosphonate or tetraethyl methylenediphosphonate in basic conditions resulted
in regioselective C-nucleophilic oxidative substitution of hydrogen ortho-located to nitro group, new
phthalonitriles with diethoxyphosphorylmethyl or bis(diethoxyphosphoryl)methyl group were isolated in
modest yields. In the same conditions one chlorine atom of tetrachlorophthalonitrile was regioselectively
substituted with triethyl phosphonoacetate. In basic conditions, both parent phthalonitriles and
corresponding zinc phthalocyanines with ortho-located nitro and diethoxyphosphoryl substituted
methyl groups are involved in reversible acid-base interaction accompanied with large bathochromic
shift of their long wavelength absorption maxima in visible or NIR region, correspondingly. Formation
of tetraazachlorin- and tetraaza(iso)bacteriochlorin-like anions is proposed for explanation of this
unprecedent bathochromic shift for phthalocyanines.
KEYWORDS: phthalonitriles, C-nucleophilic substitution, oxidative nucleophilic substitution,
phosphonates, zinc phthalocyanine, synthesis, electronic absorption spectra, NIR absorption.
On the other hand, the substances containing phospho-
nate groups are widely used in various fields: medicine (as
antiviral [13, 14], anti-inflammatory [15–17], anticancer
drugs [18], inhibitors of bone resorption [19–21], etc.), ion
exchange resins [22, 23], catalysts [22, 24], memory cells
[25] and so on. Therefore, the interest in phthalocyanines
INTRODUCTION
Due to a number of unique physical and chemical
properties phthalocyanines are widely used as dyes [1, 2],
catalysts [3], materials for nonlinear optics [4], gas
sensors [5], etc. Phthalocyanines are effective in light
harvesting and in molecular photovoltaics [6–9] and
stubstituted with phosphonate groups and corresponding
used as photosensitizers for photodynamic therapy of
phthalonitriles steadily grows [26–41].
cancer [10, 11]. This variety of applications needs the
In continuation of our work on synthesis and study of
availability of corresponding starting compounds for
phthalogensandphthalocyanineswithphosphonategroups
their preparation — derivatives of substituted phthalic
acids, preferably phthalonitriles [12].
[33–38], in this work we have examined the possibility of
introduction of substituents with phosphonate group(s)
in phthalonitrile molecule via aromatic nucleophilic
substitution using C-nucleophiles — compounds with a
◊SPP full member in good standing
methylene group activated by electron-withdrawing sub-
stituents including phosphonic acid derivatives.
*Correspondence to: Vladimir Negrimovsky, email: vnegri-
movsky@mail.ru, tel: +7 (495)-576-2445, fax: +7 (495)-408-7872
Copyright © 2013 World Scientific Publishing Company

2
V. NEGRIMOVSKY ET AL.
Asitwasrecentlypublished[42],anionsofb-dicarbonyl
conpounds including b-diketones and b-oxocarboxylates
react with 4-bromo-5-nitrophthalonitrile initially as
C-nucleophile with substitution of bromine atom and then
as O-nucleophile completing formation of benzofuran
skeleton.
Malonic ester anion substitutes nitro group and one
chlorine atom in 4-nitrophthalonitrile [43–45] and 4,5-
dichlorophthalonitrile[46,47],correspondingly,butaction
of dimedone on 4-nitrophthalonitrile leads to oxidative
substitution of hydrogen and further cyclization into
corresponding dibenzofuran derivative [43, 44].
In the context of this dual reactivity, it was of interest to
study the reactions of the above-mentioned nucleophiles
with various phthalonitriles.
by the full-matrix least-squares procedure against F2 in
anisotropic approximation using SHELXTL program [52].
Crystal data for complex 3aa. C16H18N3O7P, mono-
clinic,spacegroupP21/n:a =9.7501(6)Å,b = 9.3349(6)Å,
c = 20.8769(14)Å, b = 98.5110(10)°, V = 1879.2(2) Å3,
Z = 4, M = 395.30, dcalc = 1.397 g.cm-3, wR2 = 0.1597
calculated on F2hkl for 6541 independent reflections (Rint =
0.0461) with 2q < 64°, (GOF = 1.031, R = 0.0589 were
calculated on Fhkl for 4355 reflections with I > 2s(I)).
Synthesis
Triethyl 2-(4,5-dicyano-2-nitrophenyl)-2-phospho-
noacetate(3aa). Triethylphosphonoacetate(2a;1.38mL,
7 mmol) was added to the suspension of potassium
tert-butoxide (2.02g, 18mmol) in 20mL of dry THF
cooled to -20°C. Reaction mixture was stirred at
the same temperature for 15 min and solution of
4-nitrophthalonitrile (1a; 1.0 g, 5.8 mmol) in 8 mL of dry
THF was added dropwise under vigorous stirring. Then
cooling bath was removed, suspension was allowed to
warm to room temperature and stirred for additional one
hour. Resulting mixture was poured in water, acidified
to pH 5–6 and extracted with ethyl acetate. Evaporated
extracts were purified by column chromatography on
silicagelusingchloroformaseluent.Productwasobtained
as a yellowish solid (0.73g, 32.0%). mp 78–81°C.
Anal. calcd. for C16H18N3O7P: C, 48.61; H, 4.56; N,
10.63; P, 7.85%. Found C, 49.00; H, 4.65; N, 10.66; P,
8.15. IR (KBr): n, cm-1 2980 (C–H), 2260 (C≡N), 1730
(C=O), 1550 and 1350 (NO2), 1260 (P=O), 1050 (PO–C),
800 (O–P–O). 1H NMR:dH, ppm 8.89 (1H, d, JHH 0.5 Hz,
Ar), 8.44 (1H, d, JHP 2 Hz, Ar), 5.24 (1H, d, JHP 26 Hz,
CH), 4.08–4.24 (4H, m, –OCH2), 3.97–4.03 (2H, m,
–OCH2), 1.23 (6H, dt, JHH 6.5 Hz, JHP 6.5 Hz, CH3), 1.11
(3H, t, JHH 6.5 Hz, CH3). 31P NMR (DMSO; 85% H3PO4):
dP, ppm 15.40–15.60 (m). MS: m/z 396 (calcd. for [M +
H]+ 396).
Triethyl 2-(3,4-dicyano-2-nitrophenyl)-2-phospho-
noacetate (3ba). Compound 3ba was prepared using the
same procedure as for 3aa except 3-nitrophthalonitrile
(1b) was used instead of 1a. Product was obtained as
yellow-orange oil (0.57 g, 24.8%). Anal. calcd. for
C16H18N3O7P: C, 48.61; H, 4.56; N, 10.63; P, 7.85%.
Found C, 48.95; H, 4.55; N, 10.58; P, 7.80. 1H NMR: dH,
ppm 8.75 (1H, d, JHH 9 Hz, Ar), 8.42 (1H, dd, JHH 9 Hz,
JHP 2 Hz, Ar), 4.94 (1H, d, JHH 25 Hz, CH), 4.09–4.29
(4H, m, –OCH2), 3.92–4.06 (2H, m, –OCH2), 1.22–1.28
(6H, m, CH3), 1.15 (3H, t, JHH 7 Hz, CH3).
EXPERIMENTAL
Equipment and materials
Electronic absorption spectra were recorded on
spectrophotometers Cary 50 UV-vis (Varian) in quartz
cells of 1.0 cm thickness. For TLC Silufol UV-254 plates
used. Elemental analysis of C, H, N were performed on
the C,H,N,S-analyzerVario EL cube (Abacus). Elemental
analysis of Cl and P were determined using methods of
quantitative microanalysis [48]. IR-spectra were recorded
on a FMS-1201 FT spectrometer in KBr pellets.A suitable
crystal was selected and mounted on a Bruker SMART-
1
APEX II CCD diffractometer. H and 13C NMR spectra
were recorded on aVarian INOVA 500 MHz spectrometer
using DMSO-d6 as solvent and TMS as internal reference
unless otherwise stated. High-performance liquid
chromatography perfomed on Surveyor MSQ (Thermo
Fisher Scientific) device with APCI and ELSD detectors
and Phenomenex Onyx Monolythic C18 (25 × 4.6 mm)
column. 3,5-dinitrophthalonitrile was synthesized by a
known procedure [49]; 4-bromo-5-nitrophthalonitrile [50]
was a kind gift from Prof. I.G. Abramov (Yaroslavl State
Technical University, Russia); 4-bromophthalonitrile was
purchased fromABCR GmbH, Germany; all other ragents
and solvents were purchased from Sigma-Aldrich Rus.
Commercial starting reagents were at least 98% purity
and used as received. Solvents were distilled prior use.
Single crystal X-ray diffraction analysis
of compound 3aa
Single crystals of 3aa were obtained after two weeks
of slow evaporation from its hexane solution. All data
were collected at SMART APEX2 CCD difractometer
(l(Mo-Ka) = 0.71073 Å, graphite monochromator, w-
scans) at 220 K. The analysis of measured intensities
was carried out with the SAINT and SADABS programs
incorporated in the APEX2 program package [51]. The
structure was solved by the direct methods and refined
Diethyl 4,5,a-tricyano-2-nitrobenzylphosphonate
(3ab). Compound 3ab was prepared using the same
procedure as for 3aa except diethyl cyanomethyl-
phosphonate (2b) was used instead of 2a. Product was
obtained as dark red oil (0.20 g, 10.0%). Anal. calcd.
for C14H13N4O5P: C, 48.28; H, 3.74; N, 16.09; P, 8.91%.
Found C, 47.86; H, 4.34; N, 15.64; P, 8.45. 1H NMR: dH,
ppm 14.58 (1H, s, CH), 8.23 (1H, d, Ar), 8.13 (1H, d, Ar),
Copyright © 2013 World Scientific Publishing Company
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PHTHALOCYANINES WITH PHOSPHONATE MOIETY VIA C-NUCLEOPHILIC SUBSTITUTION IN PHTHALONITRILES
3
4.05–4.25 (4H, m, OCH2), 1.23–1.35 (6H, m, CH3). MS:
m/z 349 (calcd. for [M + H]+ 349).
(0.23 g, 27.0%). Anal. calcd. for C16H16Cl3N2O5P: C,
42.34; H, 3.53; N, 6.17; Cl, 23.48; P, 6.94%. Found C,
42.65; H, 3.76; N, 6.00; Cl, 22.72; P, 7.36. H NMR:
1
Tetraethyl 4,5-dicyano-2-nitrobenzylidenediphos-
phonate (3ac). To a suspension of NaH (0.24 g, 10 mmol)
in dry THF (5 mL) the solution of tetraethyl methylenedi-
phosphonate (2c; 2.00 mL, 8 mmol) in dry THF (10 mL)
was added dropwise at 0 °C. The mixture was stirred
until hydrogen bubbles disappeared and cooled to -20 °C.
Solution of 1a (1.38 g, 8 mmol) in 10 mL of dry THF
was added dropwise under vigorous stirring at the
same temperature. Then suspension was allowed to
warm to room temperature, stirred for 2 h and then for
additional 2 h at 40 °C. Resulting mixture was poured
in water, acidified to pH 5–6 and extracted with ethyl
acetate. Evaporated extracts was purified by column
chromatography on silica gel using chloroform as eluent.
Product was obtained as orange oil (1.36 g, 37.0%). Anal.
calcd. for C17H23N3O8P2: C, 44.43; H, 5.01; N, 9.15; P,
dH, ppm 4.24–4.30 (2H, m, OCH2), 4.10–4.17 (4H, m,
OCH2), 3.00 (1H, d, JHP 22 Hz, CH), 1.27–1.33 (6H, m,
CH3), 1.23–1.27 (3H, m, CH3). MS: m/z 453 (calcd. for
[M + H]+ with 35Cl3 453).
4-hydroxy-5-nitrophthalonitrile. 4-hydroxyphthalo-
nitrile was prepared using the same procedure as for 3ca
except 4-bromo-5-nitrophthalonitrile was used instead
of 1c and four drops of water was added to the mixture
additionally. Product was obtained as yellow solid after
recrystallization from mixture ethanol-water 4:1 (80 mg,
21.2%). mp 210–212 °C (182–184 °C [53]). Anal. calcd.
for C8H3N3O3: C, 50.79; H, 1.59; N, 22.22%. Found C,
51.17; H, 1.72; N, 21.90. 1H NMR: dH, ppm 8.62 (1H, s,
Ar), 7.59 (1H, s, Ar), 4.09 (1H, br, OH).
2,9(10),16(17),23(24)-tetrakis[1-diethoxyphos-
phoryl-1-(ethoxycarbonyl)methyl]-3,10(9),17(16),
24(23)-tetranitrophthalocyaninatozinc(II) (4a). Phtha-
lonitrile 3aa (0.11 g, 0.28 mmol) was mixed with zinc
acetate (15 mg, 0.08 mmol), ammonium molybdate (4 mg,
0.02 mmol) and 0.3 mL of 1,3,5-trichlorobenzene. This
mixture was heated to 140 °C for 2 h, cooled to room
temperature and volatiles were removed in vacuum.
Product was purified by column chromatography on
silica gel and obtained as green solid (0.05 g, 43.5%).
Anal. calcd. for C64H72N12O28P4Zn: C, 46.68; H, 4.38; N,
10.21; P, 7.54%. Found C, 46.90; H, 4.60; N, 10.54; P,
7.15. UV-vis (DMF): lmax, nm (log e) 343 (3.66), 627
(3.20), 699 (4.35).
2,9(10),16(17),23(24)-tetrakis[bis(diethoxyphosp-
horyl)methyl]-3,10(9),17(16),24(23)-tetranitrophth-
alocyaninatozinc(II) (4b). Complex 4b was prepared
using the same procedure as for phthalocyanine 4a
except dinitrile 3ac was used instead of 3aa. Product was
obtained as green solid (0.035 g, 26.0%). Anal. calcd. for
C68H92N12O32P8Zn: C, 42.90; H, 4.84; N, 8.83; P, 13.04%.
Found C, 43.29; H, 5.06; N, 8.62; P, 12.66. UV-vis (DMF):
1
13.50%. Found C, 45.60; H, 4.90; N, 9.55; P, 12.90. H
NMR: dH, ppm 8.91 (1H, s, Ar), 8.39 (1H, t, JHP 2 Hz,
Ar), 4.60 (1H, t, JHP 24.5 Hz, CH), 4.07–4.14 (4H, m,
OCH2), 3.95–4.02 (4H, m, OCH2), 1.22 (6H, t, JHH 7 Hz,
CH3), 1.11 (6H, t, JHP 7 Hz, CH3). 31P NMR (DMSO;
85% H3PO4): dP, ppm 14.70–15.00 (P, m). MS: m/z 460
(calcd. for [M + H]+ 460).
Synthesis of diethyl 2-(3,4-dicyano-2-nitrophenyl)-
malonate (3bd). Diethyl malonate (2d; 9.0 mL, 60 mmol)
and 1b (2.0 g, 12 mmol) were added to the suspension
of potassium carbonate (3.0 g, 22 mmol) in 30 mL of
dry DMF cooled to -15 °C. Reaction mixture was
stirred at the same temperature for 2 h and suspension
was allowed to warm to room temperature. Resulting
mixture was poured in water, acidified to pH 5–6 and
extracted with ethyl acetate. Evaporated extracts was
purified by column chromatography on silica gel using
chloroform:ethyl acetate of 4:1 as eluent. A mixture of
1b and 3bd of 17:1 was obtained as yellow solid after
recrystallization from ethanol (0.31 g). mp 140–142 °C.
Anal. calcd. for C8H3N3O2·0.06C15H13N3O6: C, 55.38; H,
1.96; N, 23.08%. Found C, 54.99; H, 1.93; N, 23.04. 1H
NMR: dH, ppm 8.67 (1H, d, Ar of 1b), 8.52 (1H, d, Ar of
1b), 8.47 (0.06H, d, Ar of 3bd), 8.14 (1H, t, Ar of 1b),
7.95 (0.06H, d, Ar of 3bd), 5.37 (0.06H, s, CH), 4.15–
4.25 (0.24H, m, OCH2), 1.20 (0.36H, t, CH3). MS: m/z
286 (calcd. for 3bd [M + H]+ –C2H5O 286). IR (KBr): υ,
cm-1 2991 and 2965 (C–H), 2240 (C≡N), 1750 and 1735
(C=O), 1564 and 1540 (NO2).
Triethyl 2-(2,3,6-trichloro-4,5-dicyanophenyl)-
2-phosphonoacetate (3ca). Solution of 2a (0.38 mL,
1.92 mmol) in DMF (3 mL) was added portionwise to the
stirred mixture of tetrachlorophthalonitrile (1c; 0.49 g,
1.88 mmol), potassium carbonate (0.55 g, 4 mmol) and
5 mL of DMF. The mixture was stirred at 40 °C for 6 h,
then poured in water, acidified to pH 5–6 and extracted
with ethyl acetate. Evaporated extracts was purified by
column chromatography on silica gel using chloroform
as eluent. Product was obtained as orange oily solid
lmax, nm (log e) 355 (4.02), 630 (3.23), 699 (4.26).
RESULTS AND DISCUSSION
As a model of initial study, we chose the reactions
of commercially available 4-nitrophthalonitrile (1a)
and triethyl phosphonoacetate (2a). Their reaction in
DMF in the presence of potassium carbonate at room
temperature under aerobic conditions resulted in complex
mixture of mostly unidentified products. After extensive
chromatography we separated starting material as well as
new compound 3aa with low yield (Scheme 1).
Structureofphosphonate3aawasestablishedasproduct
of hydrogen oxidative substitution by X-ray analysis, as
well as by other routine methods (elemental analysis,
mass-spectroscopy, IR, 1H and 31P NMR spectroscopy).
Copyright © 2013 World Scientific Publishing Company
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V. NEGRIMOVSKY ET AL.
Table 1. Optimization of reaction conditions for synthesis
of 3aa
Entry
Base/oxidanta/
solvent
Temperatureb, °C Yieldc, %
1
2
K2CO3/O2/DMF
K2CO3/O2/DMF
Et3N/O2/DMF
20
80
12
—
—
15
20
12
32
30
20
—
25
Scheme 1. Synthesis of ethyl 2-(4,5-dicyano-2-nitrophenyl)-2-
(diethoxyphosphoryl)acetate 3aa
3
20
4
KOH/O2/DMSO
t-BuOK/O2/THF
t-BuOK/O2/THF
t-BuOK/O2/THF
NaH/O2/THF
20
5
20
6
60
7
-15
-15
-15
-15
-15
8
9
t-BuOK/DDQ/THF
t-BuOK/CAN/THF
t-BuOK/—/THF
10
11
a
Notes: air dioxygen used for entry 1-8, Ar atmosphere
used for entry 11, DDQ — 2,3-dichloro-5,6-dicyano-
benzoquinone, CAN — cerium(IV) ammonium nitrate;
btemperature of 1a addition to pre-reacted mixture of
c
triethylphosphonoacetate with base given; isolated yeild
after chromatography.
Fig. 1. ORTEP view (50% probability level) of 3aa
The dinitrile 1a reacted by oxidative nucleophilic
substitution with diethyl cyanomethylphosphonate 2b
and tetraethyl methylenediphosphonate 2c as well. In
first case product 3ab was isolated as red oil in optimal
conditions with yield of only 10%. Diphosphonate 2c did
not form 3ac in the presence of t-BuOK, but with NaH as
a more strong base [59, 60] 3ac was isolated with yield
of 37% (Scheme 2).
Next we used phosphonoacetate 2a as pro-nucleophile
with other phthalonitriles containing nitro group(s) and/
or halogen atoms to study the scope and limitation of this
reaction.
Unlike phthalonitrile 1a its isomer — 3-nitrophthalo-
nitrile (1b) — was never used for C-nucleophilic
substitution. Reaction of 1b with phosphonate 2a in
our conditions affords product 3ba with 25% yield as a
result of oxidative nucleophilic substitution (Scheme 3).
Its structure was resolved by 1H NMR spectroscopy where
spin-spin coupling constant of two remaining aromatic
protons (9 Hz) indicates their ortho location. In this case
substituents in phthalonitrile could be located in positions
3 and 4 or 3 and 6. We deduced that substitution takes
place in position 4 on the basis of literature data stating
that the nucleophile enters in ortho position to nitro group
during oxidative nucleophilic substitution [57, 61].
It was interesting that only trace amount of analogous
product 3bd was formed in the reaction of phthalonitrile
1b with diethyl malonate (2d). We managed to isolate it
from the reaction as a mixture with starting material 1:17;
characterisic vibrations for both nitro and ethoxycarbonyl
groups beside cyano groups were present in IR spectrum
An asymmetric unit cell contains one molecule of 3aa
(Fig. 1). The phosphorous atom adopts usual tetrahedral
coordination. The P–O and P–C bond lengths are in the
range of normally observed distances for these bonds
[54, 55]. The conformation of 3aa can be described by
an orientation of substituents relative to P1–C7 bond:
torsion angles O2–P1–C7–C5 and O3–P1–C7–C8 are
equal to 56.84(13) and -72.74(13)°, respectively.
To improve the yield of new phosphonate containing
phthalonitrile 3aa, we have taken some effort to optimize
the reaction conditions (Table 1). Increasing the reaction
temperature to 80 °C (entry 2) or use of triethylamine
instead of potassium carbonate (entry 3) resulted only in
traces of the product. The use of potassium hydroxide as
a base in DMSO slightly increased the yield up to 15%
(entry 4). But the best combination of "base-solvent" was
t-BuOK in THF at room temperature yielding 3aa in 20%
(entry 5). The increase of the temperature decreased the
yield (entry 6). Lowering of the temperature below -15 °C
gave the best yield in our hands of 32% for 3aa (entry 7).
The use of NaH instead of t-BuOK led to similar result
(entry 8). The addition to reaction mixture of strong
oxidant DDQ did not improve but even decreased yield of
3aa (entry 9). In the presence of CAN, we did not detect
3aa at all (entry 10). To our surprise, the removal of any
oxidant including dioxygen from reaction and keeping
other conditions optimal still resulted in the product
with moderate yield of 25% (entry 11), suggesting
4-nitrophtalonitrile 1a to be not only the substrate but the
oxidant too, by analogy with known data [56–58].
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PHTHALOCYANINES WITH PHOSPHONATE MOIETY VIA C-NUCLEOPHILIC SUBSTITUTION IN PHTHALONITRILES
5
Scheme 2. Oxidative substitution of 4-nitrophthalonitrile 1a with phosphonates 2a–2c
Scheme 3. Regioselective substitution in tetrachlorophthalo-
nitrile 1c
of this mixture and all signals in 1H NMR spectrum were
found also.
Reaction of phosphonoacetate 2a with 3,5-dinitro-
phthalonitrile [49] proceeds even at -78 °C but we failed
to identify any products in very complicated reaction
mixture. Almost the same result we obtained with
4-bromo-5-nitrophthalonitrile [50] with an exception
Fig. 2. Evolution of UV-vis spectrum of 3aa in EtOH under
addition of t-BuOK
that 4-hydroxy-5-nitrophthalonitrile [53] was isolated
with negligible yield, probably due to the presence of
water traces. Indeed, the same reaction in the presence of
stoichiometric quantities of water using DMF as solvent
and K2CO3 as base led to isolation of only 4-hydroxy-5-
nitrophthalonitrile with 22% yield.
In analogous conditions, the reaction of tetrachloro-
phthalonitrile (1c) with phosphonoacetate 2a resulted in
isolation of the product of one chlorine atom substitution
with 27% yield. This reaction proceeds regioselectively
and only one of the two possible isomers was detected
in reaction mixture. Analogously to reaction with diethyl
malonate [62], isolated product was assumed to be triethyl
(2,3,6-trichloro-4,5-dicyanophenyl)phosphonoacetate
(3ca; Scheme 3).
were detected by LC-MS (m/z 349; calcd. for [M –
H]+ 349).
All phthalonitriles 3aa–3bd under basic conditions
change the color of their solutions from light yellow or
orange to deep red or burgundy. In UV-vis spectra intense
absorption with the maximum at ~370 nm replaces weak
absorption ~300 nm, and new absorption band at ~500 nm
appears (an example of this change is shown in the Fig. 2).
These changes are reversible, and in acidic medium spectra
returned to their initial state.
We suggest that these color changes correspond to acid-
base equilibrium of 3aa–3bd due to the presence of rather
acidicmethineproton.Itseliminationunderbaseconditions
leads to formation of carbanion which participates in
conjugation with benzene ring, and, as a result, a new
chromofore is formed consisting of extended ortho-
quinoid double bonds system with auxochromic groups
at the ends (Scheme 4). Moreover, cyanophosphonate 3ab
In contrast, no product was isolated in the reaction of
2a with 4-bromophthalonitrile, only traces of the pro-
duct of halogen ipso-substitution by phosphonocetate
Scheme 4. Acid-base equilibrium of 3aa–3bd
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6
V. NEGRIMOVSKY ET AL.
Scheme 5. Synthesis and acid-base equilibrium of phthalocyanines 4a and 4b
have a red color without a base, suggesting this compound
to exist as ortho-quionoid tautomer even in neutral state.
4-Hydroxy-5-nitrophthalonitrile (X-C-Y = O) also
takes part in acid-base interaction but correponding anion
maxima in UV-vis spectrum are located much shorter
(~340 and ~430 nm) than for 3aa–3bd.
Having in hand the new phthalonitriles with phospho-
nate group(s) we used them for synthesis of corresponding
phthalocyanines. At first we tried to obtain metal-free
phthalocyanines but failed both in classical conditions
usingDBUorN,N-dimethylaminoethanolinalcoholsorby
heating with lithium methoxide [63]. Possibly, this failure
is the consequence of acid-base equilibrium discussed
elsewhere: non-benzoid anion does not participate in
tetramerization with phthalocyanine formation.
Fig. 3. UV-vis spectra of 4a in DMF upon the addition of DBU
Thenwetriedtosynthesizeseveralzincphthalocyanines
avoidingtheuseofbasesorpolarsolventtopreventacid-base
equilibrium of starting phthalonitriles. The reaction of 3aa
with zinc acetate in the presence of ammonium molybdate
without solvent started at ~100°C; full conversion
was achieved at 120°C in one hour and tetraphosphonate
complex 4a was isolated with yield of 7%. The use of
1,2,4-trichlorobenzene as solvent required temperature
~120 °C for starting the complex formation, and at 140°C
reaction finished in two hours with yield of 4a higher than
40%, but above 150°C the product underwent complete
decomposition in 10 min. In nitrobenzene as solvent at
140 °C reaction proceeds slower and starting material was
detected even after 6 h.
In optimal conditions, dinitrile 3ac led to corresponding
octaphosphonate complex 4b though with lower yield
of 20–30%. No conditions were found for synthesis of
complex from cyanophosphonate 3ab, obviously, because
of its above-mentioned the ortho-quinoid state.
Both obtained complexes are green solids, rather soluble
in most organic solvents such as alcohols, dichloromethane,
acetone, ethyl acetate, DMF, etc. Their UV-vis spectra are
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J. Porphyrins Phthalocyanines 2013; 17: 6–9

PHTHALOCYANINES WITH PHOSPHONATE MOIETY VIA C-NUCLEOPHILIC SUBSTITUTION IN PHTHALONITRILES
7
typical for phthalocyanines in non-aggregated state: sharp
Q-band (maximum at ~700 nm) and its satellite (maximum
~630 nm) in long wavelength region, and wide splitted
band in short wavelength region.
Supporting information
Crystallographic data (excluding structure factors)
and details of the refinement for the structure 3aa have
been deposited at the Cambridge Crystallographic Data
Centre (CCDC) under number CCDC-914453. Copies
can be obtained on request, free of charge, via www.
ccdc.cam.ac.uk/data_request/cif or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK (fax: +44 1223-336-033 or email: deposit@
ccdc.cam.ac.uk).
It was intriguing if observed acid-base properties
of starting phthalonitriles will affect the properties of
corresponding phthalocyanines, particularly absorption
spectra. In fact, addition of different bases (K2CO3,
triethylamine, DBU, t-BuOK) to solutions of 4a or 4b led
to decrease of Q-band intensity and appearance of large
diffuse absorption from 500 to 950 nm with a maximum
at ~815 nm; simultaneously absorption with a maximum
~370 nm appeared in short wavelength region (Fig. 3).
Further addition of bases did not lead to principal changes
in character of spectra but maxima of both bands were red
shifted to ~870 and ~390 nm, respectively. These spectral
changes are reversible, and in acidic medium spectra
returned to their initial state as for parent phthalonitriles.
Such large shift of Q-band to near IR region during
interaction with a base is unprecedented for phthalo-
cyanines. In order to explain this shift we assume that it is
caused by formation of local ortho-quinoid chromophores
which include benzene ring bearing ortho-located
methine and nitro groups like in parent phthalonitriles.
Deprotonation of one methine group changes the
phthalocyanine aromatic system to tetraazachlorine-
like one, deprotonation of two groups leads to tetraaza-
bacteriochlorin- and/or tetraazaisobacteriochlorin-like
aromatic systems (Scheme 5), which absorb in near
IR region [64]. Absence of isosbestic points during an
evolution of spectra, possibly, is explained by the presence
of all anionic particles due to equilibrium existing in
solution till full transformation in dianions only.
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