Novel metal-free, metallophthalocyanines and their quaternized derivatives: Synthesis, spectroscopic characterization and catalytic activity of cobalt phthalocyanine in 4-nitrophenol oxidation

Article abstract of DOI:10.1016/j.poly.2012.11.032

Novel metal-free, Zn and Co phthalocyanines substituted with four 4-[4-((E)-{[4-(dimethylamino)phenyl]imino}methyl)phenoxy] substituents at peripheral positions have been synthesized. Quaternization of the dimethylamino functionality produced quaternized cationic metal-free, Zn and Co phthalocyanines which were soluble in DMF, DMSO and pyridine. The aggregation behavior of these compounds was investigated in different concentrations of chloroform for the metal-free, Zn and Co phthalocyanines, and DMF for the quaternized metal-free, Zn and Co phthalocyanines. The effect of solvents on the absorption spectra was studied in various organic solvents. Cobalt phthalocyanine complex 6 was tested as a catalyst for the oxidation of 4-nitrophenol with different oxidants, such as tert-butylhydroperoxide (TBHP), m-chloroperoxybenzoic acid (m-CPBA) and hydrogen peroxide (H₂O ₂), in organic solvent. The novel compounds were characterized using IR, ¹H NMR, ¹³C NMR, UV-Vis, MS spectral data and elemental analysis.

Full text of DOI:10.1016/j.poly.2012.11.032

Polyhedron 50 (2013) 345–353
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Polyhedron
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Novel metal-free, metallophthalocyanines and their quaternized derivatives:
Synthesis, spectroscopic characterization and catalytic activity of cobalt
phthalocyanine in 4-nitrophenol oxidation
a
Irfan Acar b, Rıza Bayrak a, Ece Tug˘ba Saka a, Zekeriya Bıyıklıog˘lu a, , Halit Kantekin
⇑
a Department of Chemistry, Faculty of Sciences, Karadeniz Technical University, 61080 Trabzon, Turkey
b Department of Woodworking Industry Engineering, Faculty of Technology, Karadeniz Technical University, 61830 Trabzon, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel metal-free, Zn and Co phthalocyanines substituted with four 4-[4-((E)-{[4-(dimethylamino)
phenyl]imino}methyl)phenoxy] substituents at peripheral positions have been synthesized. Quaterniza-
tion of the dimethylamino functionality produced quaternized cationic metal-free, Zn and Co phthalocy-
anines which were soluble in DMF, DMSO and pyridine. The aggregation behavior of these compounds
was investigated in different concentrations of chloroform for the metal-free, Zn and Co phthalocyanines,
and DMF for the quaternized metal-free, Zn and Co phthalocyanines. The effect of solvents on the absorp-
tion spectra was studied in various organic solvents. Cobalt phthalocyanine complex 6 was tested as a
catalyst for the oxidation of 4-nitrophenol with different oxidants, such as tert-butylhydroperoxide
(TBHP), m-chloroperoxybenzoic acid (m-CPBA) and hydrogen peroxide (H2O2), in organic solvent. The
novel compounds were characterized using IR, 1H NMR, 13C NMR, UV–Vis, MS spectral data and elemental
analysis.
Received 21 September 2012
Accepted 9 November 2012
Available online 29 November 2012
Keywords:
Phthalocyanine
Schiff base
Cationic
Cobalt
Catalyst
Oxidation
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
various solvents. Whereas peripheral substitution with bulky or
long-chain hydrophobic moieties leads to phthalocyanine deriva-
Although more than a century has passed since the discovery of
the first phthalocyanine (Pc) compound, they are still very popular
for many investigators due to their superlative properties [1,2]. Pcs
are highly stable and are capable of including more than 70 metal-
lic and non-metallic ions in the ring cavity, called metallophthalo-
cyanines (MPc). These remarkable macrocyclic compounds possess
magnificent physical and chemical properties [3]. Beyond utiliza-
tion as dyes and pigments, Pcs are used in many fields, such as
electrophotography, photovoltaic and solar cells, molecular elec-
tronics, Langmuir–Blodgett films, electrochromic display devices,
gas sensors, non-linear optics (NLO), optical discs and sensitizers
in the photodynamic therapy of cancer (PDT) [4].
A major disadvantage of phthalocyanines, because they are
planar macrocyclic systems, is their tendency to aggregate, which
results in low solubility, difficulties during purification and charac-
terization. To overcome this complication, several approaches were
made; introduction of bulky substituents, charged substituents or
monomerizing solvents are widely reported in the literature
[5–9]. Because of the insolubility of Pcs in organic and/or inorganic
solvents, one of the most important aims of researches on the
chemistry of phthalocyanines is to enhance their solubility in
tives soluble in organic solvents, on the contrary, tertiary-amino,
sulfo or carboxyl groups result in water-soluble materials
[10–13]. Cationic-pc derivatives also present a large and expanding
class of compounds which have applications in biology, catalysis
and materials [14–17]. Furthermore quaternized amino group con-
taining Pcs are useful in achieving solubility within a wide pH
range of aqueous solutions [18–20]. Metallophthalocyanine com-
plexes, especially Co(II) phthalocyanines, are readily available oxi-
dation catalysts and are found to transfer oxygen from various
oxygen donors to alkanes, alkenes, phenols and thiols in numerous
studies [21,22].
4-Nitrophenol (4-NP) is a toxic and bio-refractory pollutant
which can cause considerable damage to the ecosystem and
human health. It can damage the central nervous system, liver,
kidney and blood of humans and animals. 4-NP and its derivatives
are used in the production of pesticides, and as insecticides and
herbicides [23]. Nitroaromatics are used in the production of
explosives and 4-NP is used in the production of many synthetic
dyes [24]. Therefore, 4-NP and its derivatives are common pollu-
tants in many natural waters and in industrial wastewater [25].
Recently, Gül and co-workers have reported phthalocyanines
with unsaturated cinnamaldiamine moieties attached to the inner
core through phenoxy-bridges and containing Schiff’s base groups
⇑
Corresponding author. Tel.: +90 462 377 76 39; fax: +90 462 325 31 96.
E-mail address: zekeriya_61@yahoo.com (Z. Bıyıklıog˘lu).
[26,27]. This paper reports
a convenient procedure for the
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.11.032

346
I. Acar et al. / Polyhedron 50 (2013) 345–353
synthesis of novel metal-free and metallophthalocyanines and
their quaternized derivatives which contain four conjugated
Schiff’s base groups on peripheral positions in the phthalocyanine
framework. Also, the aggregation behavior of the synthesized
metal-free, metallophthalocyanines and their quaternized deriva-
tives are investigated in different solvents. In addition, the search
for a catalyst that can degrade 4-nitrophenol to products of re-
duced toxicity led to the use, in this work, of a phthalocyanine
complex containing a paramagnetic central metal: CoPc.
2.3.2. Synthesis of metal-free phthalocyanine (4)
4-[4-((E)-{[4-(Dimethylamino)phenyl]imino}methyl)phenoxy]
phthalonitrile 3 (0.3 g, 0.82 Â 10À3 mol), 1.8-diazabicyclo[5.4.0]
undec-7-ene (DBU) (3 drop) and dry n-pentanol (0.003 L) were
added to a Schlenk tube and then were heated and stirred at
160 °C for 24 h under N2. After cooling to room temperature, the
reaction mixture was refluxed with ethanol (0.05 L) to precipitate
the product, which was filtered off. The green solid product was
washed with hot ethanol, diethyl ether and dried in vacuo. The ob-
tained green solid product was purified by column chromatography
(aluminum oxide) using chloroform:methanol (100:4) as the sol-
vent system. Yield: 0.1 g (33%). IR (KBr pellet), m
max/cmÀ1: 3289
2. Experimental
(N–H), 3078 (Ar–H), 2918–2849 (Aliph. C–H), 1619 (C@N), 1600,
1514, 1469, 1419, 1395, 1344, 1228, 1159, 1090, 1006, 938, 884,
819, 742, 542. 1H NMR. (CDCl3), (d, ppm): 8.40 (m, 4H, @C–H),
7.94 (m, 8H, Ar–H), 7.29–7.03 (m, 28H, Ar–H), 6.70 (m, 8H, Ar–H),
2.1. Materials
All reagents and solvents were of reagent grade quality and
were obtained from commercial suppliers. All solvents were
dried and purified as described by Perrin and Armarego [28].
4-((E)-{[4-(Dimethylamino)phenyl]imino}methyl)phenol
and 4-nitrophthalonitrile 2 [30] were synthesized and purified
2.98 (s, 24H, CH3). UV–Vis (chloroform) kmax, nm (log
e): 702
(4.82), 666 (4.75), 640 (4.36), 607 (4.17), 351 (4.71), 285 (4.66).
MS (ES+), (m/z): 1465 [MÀ2H]+. Anal. Calc. for C92H74N16O4: C,
75.29; H, 5.08; N, 15.27. Found: C, 75.76; H, 4.76; N, 14.78%.
1
[29]
according to well known literature procedures.
2.3.3. Synthesis of zinc (II) phthalocyanine (5)
4-[4-((E)-{[4-(Dimethylamino)phenyl]imino}methyl)phenoxy]
phthalonitrile 3 (0.3 g, 0.82 Â 10À3 mol), anhydrous Zn(CH3 COO)2
(0.075 g, 0.41 Â 10À3 mol) and 0.003 L of n-pentanol were placed
in a standard Schlenk tube in the presence of 1,8-diazabicy-
clo[5.4.0]undec-7-ene (DBU) (3 drops) under a nitrogen atmo-
sphere and held at reflux temperature for 24 h. After cooling to
room temperature, the reaction mixture was refluxed with ethanol
(0.05 L) to precipitate the product, which was filtered off. The crude
product was collected by filtration and washed with water, ethanol
and ether, and then dried. The obtained green solid product was
purified by column chromatography (silica gel) with chloroform:
methanol (100:5) as the solvent system. Yield: 0.140 g (45%). IR
2.2. Equipment
The IR spectra were recorded on a Perkin Elmer 1600 FT-IR
spectrophotometer using KBr pellets. 1H and 13C NMR spectra
were recorded on a Varian Mercury 200 MHz spectrometer in
CDCl3 and DMSO-d6. Chemical shifts were reported (d) relative
to Me4Si as an internal standard. Mass spectra were measured
on a Micromass Quatro LC/ULTIMA LC–MS/MS spectrometer. The
elemental analyses were performed on a Costech ECS 4010 instru-
ment. GC Agilent Technologies 7820A equipment (30 m  0.32
mm  0.50
lm DB Wax capillary column, FID detector) was used
(KBr pellet),
m
max/cmÀ1: 3080 (Ar–H), 2918–2844 (Aliph. C–H),
for GC measurements. Optical spectra in the UV–Vis region were
recorded with a Perkin Elmer Lambda 25 spectrophotometer.
Melting points were measured on an electrothermal apparatus
and are uncorrected.
1617 (C@N), 1600, 1511, 1466, 1393, 1335, 1228, 1157, 1116,
1088, 1043, 944, 886, 817, 746, 540. 1H NMR. (CDCl3), (d, ppm):
8.51 (m, 4H, @C–H), 7.88 (m, 8H, Ar–H), 7.29–7.05 (m, 28H, Ar–
H), 6.71 (m, 8H, Ar–H), 2.94 (s, 24H, CH3). UV–Vis (chloroform) kmax
,
nm (log e
): 684 (4.97), 617 (4.29), 360 (4.84), 280 (4.77). MS (ES+),
2.3. Synthesis
(m/z): 1532 [M+H]+. Anal. Calc. for C92 H72N16O4Zn: C, 72.17; H,
4.74; N, 14.64. Found: C, 72.58; H, 5.06; N, 14.24%.
2.3.1. Synthesis of 4-[4-((E)-{[4-(dimethylamino)phenyl]imino}
methyl)phenoxy]phthalonitrile (3)
2.3.4. Synthesis of cobalt (II) phthalocyanine (6)
4-((E)-{[4-(Dimethylamino)phenyl]imino}methyl)phenol 1 (1.5 g,
6.25 Â 10À3 mol) was dissolved in dry dimethyl formamide (DMF)
(0.03 L) under a N2 atmosphere and 4-nitrophthalonitrile 2 (1.1 g,
6.25 Â 10À3 mol) was added to the solution. After stirring for 10 min,
finely ground anhydrous potassium carbonate (K2CO3) (2.6 g,
18.75 Â 10À3 mol) was added portionwise over 2 h with efficient stir-
ring. The reactionmixturewasstirred underN2 at 50 °C for 3 days. Then
the solution was poured into ice-water (100 g). The precipitate that
formed was filtered off, washed first with water until the filtrate was
neutral and then with diethyl ether and dried in vacuo over phosphorus
pentoxide (P2O5). The crude product was crystallized from tetrahydro-
furan (THF). Yield: 1.55 g (67%), mp: 184–185 °C. IR (KBr pellet),
4-[4-((E)-{[4-(Dimethylamino)phenyl]imino}methyl)phenoxy]
phthalonitrile
3
(0.25 g, 0.68 Â 10À3 mol), anhydrous CoCl2
(0.044 g, 0.34 Â 10À3 mol) and 0.0025 L of n-pentanol were placed
in a standard Schlenk tube in the presence of 1,8-diazabicy-
clo[5.4.0]undec-7-ene (DBU) (3 drops) under
a
nitrogen
atmosphere and held at reflux temperature for 24 h. After cooling
to room temperature, the reaction mixture was refluxed with eth-
anol (0.05 L) to precipitate the product, which was filtered off. The
crude product was collected by filtration and washed with water,
ethanol and ether, and then dried. The obtained green solid prod-
uct was purified by column chromatography (aluminum oxide)
using chloroform:methanol (100:4) as the solvent system. Yield:
m
max/cmÀ1: 3080 (Ar–H), 2925–2896 (Aliph. C–H), 2225 (C°N), 1621
0.080 g (31%). IR (KBr pellet), m
max/cmÀ1: 3076 (Ar–H), 2920–
(C@N), 1591, 1561, 1514, 1481, 1359, 1290, 1245, 1206, 1163, 1088,
1062, 1013, 948, 884, 817, 538. 1H NMR. (DMSO-d6), (d, ppm): 8.65
(s, 1H, @C–H), 8.13 (d, 1H, Ar–H), 7.99 (d, 2H, Ar–H), 7.86 (s, 1H,
Ar–H), 7.48 (d, 1H, Ar–H), 7.28 (d, 4H, Ar–H), 6.75 (d, 2H, Ar–H), 2.92
(s, 6H, CH3). 13C NMR. (DMSO-d6), (d, ppm): 161.14, 156.30, 154.61,
150.11, 140.23, 137.05, 134.85, 130.94, 123.91, 123.31, 123.09,
120.99, 117.47, 116.58, 116.07, 113.25, 109.36, 40.90. MS (ES+),
(m/z): 367 [M+H]+. Anal. Calc. for C23H18N4O: C, 75.39; H, 4.95; N,
15.29. Found: C, 75.92; H, 5.31; N, 14.88%.
2853 (Aliph. C–H), 1618 (C@N), 1597, 1514, 1469, 1408, 1355,
1232, 1157, 1116, 1094, 1058, 946, 882, 821, 753. UV–Vis (chloro-
form) kmax, nm (log e): 673 (4.46), 611 (4.08), 376 (4.70), 282
(4.84). MS (ES+), (m/z): 1524 [M]+. Anal. Calc. for C92H72N16O4Co:
C, 72.48; H, 4.76; N, 14.70. Found: C, 72.80; H, 5.12; N, 14.30%.
2.3.5. Synthesis of quaternized metal-free phthalocyanine (4a)
Metal-free phthalocyanine 4 (0.035 g, 0.024 Â 10À3 mol) was
dissolved in 0.003 L of chloroform and excess methyl iodide

I. Acar et al. / Polyhedron 50 (2013) 345–353
347
(0.0019 L) was added to this solution. The reaction mixture was
stirred at room temperature for 24 h. After cooling to room tem-
perature, the green precipitate that formed was filtered off, washed
with chloroform, acetone, diethyl ether and then dried. Yield:
phthalocyanine 5 (0.05 g, 0.032 Â 10À3 mol), excess methyl iodide
(0.002 L) in CHCl3 (0.004 L). Yield: 0.045 g (66%). IR (KBr pellet)
m
max/cmÀ1: 3015 (Ar–H), 2932–2863 (Aliph. C–H), 1619, 1595,
1505, 1488, 1469, 1393, 1333, 1232, 1157, 1116, 1092, 1045,
0.035 g (72%). IR (KBr pellet)
m
max/cmÀ1
:
3297 (N–H), 3012
944, 890, 748. UV–Vis (DMF) kmax, nm (log e): 677 (5.16), 610
(Ar–H), 2928–2856 (Aliph. C–H), 1618, 1593, 1516, 1501, 1471,
1419, 1395, 1309, 1234, 1155, 1112, 1090, 1008, 927, 828, 742.
(4.42), 355 (4.83). MS (ES+), (m/z): 1546 [MÀ4IÀ3CH3]+. Anal. Calc.
for C96H84N16O4I4Zn: C, 54.94; H, 4.03; N, 10.68. Found: C, 55.21; H,
4.44; N, 10.96%.
UV–Vis (DMF) kmax, nm (log e): 697 (4.67), 665 (4.66), 637 (4.33),
609 (4.21), 339 (4.61). MS (ES+), (m/z): 1525 [MÀ4IÀ2H]+. Anal.
Calc. for C96H86N16O4I4: C, 56.65; H, 4.26; N, 11.01. Found: C,
56.90; H, 4.03; N, 11.32%.
2.3.7. Synthesis of quaternized cobalt (II) phthalocyanine (6a)
Synthesis and purification was as outlined for 4a except cobalt
phthalocyanine 6 instead of metal-free phthalocyanine 4 was em-
ployed. The amounts of reagents employed were: Cobalt phthalo-
2.3.6. Synthesis of quaternized zinc (II) phthalocyanine (5a)
The synthesis and purification was as outlined for 4a, except
cyanine
6
(0.042 g, 0.027 Â 10À3 mol), excess methyl iodide
zinc phthalocyanine
5
was employed instead of metal-free
(0.0021 L) in CHCl3 (0.0035 L). Yield: 0.030 g (50%). IR (KBr pellet)
phthalocyanine 4. The amounts of reagents employed were: zinc
m
max/cmÀ1: 3018 (Ar–H), 2931–2865 (Aliph. C–H), 1618, 1594,
CN
OH
N
N
O2N
CN
2
1
50 ºC
dry K2CO3
dry DMF
O
CN
CN
N
N
3
350 W
175 ºC
DMAE
CoCl2
Zn(CH3COO)2
DBU
n-pentanol
160 ºC
N
N
N
N
O
O
N
N
N
N
M
N
N
N
N
O
O
N
N
4
Compound
M
5
6
N
Zn
2H
Co
N
Fig. 1. The synthesis of the metal-free and metallophthalocyanines.

348
I. Acar et al. / Polyhedron 50 (2013) 345–353
4+
RO
R'O
OR
OR'
N
N
N
N
N
N
N
N
N
N
CH3-I
4I-
N
N
M
N
M
N
RT, CHCl3
N
N
RO
R =
R'O
OR
OR'
N
N
N
N
R' =
4
5
6
Compound
M
4a 5a
Compound
M
6a
2H
Zn Co
2H
Zn Co
Fig. 2. The synthesis of the quaternized metal-free and metallophthalocyanines.
1507, 1489, 1469, 13,383, 1230, 1160, 1113, 1090, 948, 896, 748.
plished through the usual cyclotetramerization reactions in the
presence of the metal salts (Zn(CH3COO)2 and CoCl2), with n-pent-
anol as the solvent. Quaternization of the metal-free and metall-
ophthalocyanine complexes was achieved by reaction with
excess methyl iodide as a quaternization agent in CHCl3 at room
temperature. The yields of the products were 72% for 4a, 66% for
5a and 50% for 6a. All the phthalocyanines are new compounds.
All the new compounds were characterized by means of IR, UV–
Vis, MS spectral data and elemental analysis, all of which were
compatible with the proposed structures.
In the IR spectrum of compound 3, stretching vibrations of C°N
(2225 cmÀ1) and aliphatic CH (2925–2896 cmÀ1) appeared at the
expected frequencies. In the 1H NMR spectrum of 3, the OH group
of compound 1 disappeared, as expected. In the 13C NMR spectrum
of 3, the presence of nitrile carbon atoms was indicated, with peaks
at d 116.07 and 113.25 ppm. In the mass spectrum of compound 3,
the presence of a molecular ion peak at m/z = 367 [M+H]+ con-
firmed the proposed structures.
UV–Vis (DMF): kmax, nm (log
e): 662 (4.70), 603 (4.23), 335
(4.86). MS (ES+), (m/z): 1584 [MÀ4I]+. Anal. Calc. for C96H84N16O4I4-
Co: C, 55.11; H, 4.05; N, 10.71. Found: C, 55.34; H, 3.88; N, 11.05%.
2.3.8. General procedure for the oxidation of 4-nitrophenol
Experiments were carried out in a thermostated Schlenk vessel
equipped with a condenser and stirrer. A solution of 4-nitrophenol
and catalyst (cobalt complex 6) in solvent was purified with nitro-
gen to remove oxygen. A mixture of 4-nitrophenol (1.32 Â 10À3
-
mol), catalyst (cobalt complex 6) (3.28 Â 10À6 mol) and DMF as
solvent (0.01 L) was stirred in a Schlenk vessel for few minutes at
room temperature. The oxidant tert-butylhydroperoxide (TBHP),
m-chloroperoxybenzoic acid (m-CPBA) or hydrogen peroxide
(H2O2) (1.64 Â 10À3 mol) was then added and the reaction mixture
was stirred for the desired time. After certain time intervals, sam-
ples (0.0005 L) were taken. Each sample was injected in the GC
twice, 1 ll each time. Formation of products and consumption of
substrates were monitored by gas chromatography.
The sharp peak in the IR spectrum for the CNN vibration of pht-
halonitrile 3 at 2225 cmÀ1 disappeared after conversion into the
metal-free phthalocyanine, indicative of metal-free phthalocya-
nine formation. The IR band characteristic of the metal-free phtha-
locyanine ring is an N–H stretching at 3289 cmÀ1. The IR spectra of
metal-free 4 and metallophthalocyanines 5 and 6 are very similar,
3. Results and discussion
3.1. Syntheses and characterization
except for the m(NH) vibrations of the inner phthalocyanine core in
Starting from 4-((E)-{[4-(dimethylamino)phenyl]imino}methyl)
phenol (1) and 4-nitrophthalonitrile (2), a general synthetic route
for the synthesis of new phthalocyanines and their quaternized
derivatives is given in Figs. 1 and 2. The first step in the synthetic
procedure was to obtain 4-[4-((E)-{[4-(dimethylamino)phenyl]
the metal-free molecule. The NH protons of compound 4 could not
be observed owing to the probable strong aggregation of the mol-
ecules [34,35]. The 1H NMR spectrum of 4 indicated characteristic
imino}methyl)phenoxy]phthalonitrile.
4-[4-((E)-{[4-(Dimethyl-
amino)phenyl]imino}methyl)phenoxy]phthalonitrile was synthe-
sized by heating 4-((E)-{[4-(dimethylamino)phenyl]imino} methyl)
phenol 1 and 4-nitrophthalonitrile 2 in the presence of K2CO3 as
a base in dry DMF at 50 °C for 72 h. The electron-withdrawing
capability of dinitrile functionalities makes 4-nitrophthalonitrile
susceptible to nucleophilic attack [31–33]. The base catalyzed
nucleophilic substitution of the nitro group was performed in dry
DMF at 50 °C under an inert nitrogen atmosphere. The self-conden-
sation of the dicyano compound 3 in a high-boiling solvent in the
presence of a few drops 1,8-diazabicyclo[5.4.0] undec-7-ene (DBU)
as a strong base at reflux temperature under a nitrogen atmo-
sphere afforded the metal-free phthalocyanine 4 as a green solid
after purification by column chromatography (aluminum oxide)
using CHCl3:CH3OH (100:4) as the solvent system. Conversion of
3 into the metallophthalocyanine derivatives 5 and 6 was accom-
Fig. 3. UV–Vis spectra of 4, 5 and 6 in CHCl3.

I. Acar et al. / Polyhedron 50 (2013) 345–353
349
Table 1
UV–Vis spectral data for Pcs 4a, 5a and 6a in various solvents at a concentration of 10 Â 10À6 mol dmÀ3
.
Solvent
Pcs
Q-Band, kmax, (nm)
Log
e
B-Band, kmax, (nm)
Log
e
DMF
4a
4a
4a
5a
5a
5a
6a
6a
6a
697, 665, 637, 609
699, 665, 632, 610
700, 667, 636, 604
677, 610
678, 609
679, 612
662, 603
658, 599
658, 597
4.67, 4.66, 4.33, 4.21
4.56, 4.60, 4.49, 4.43
4.89, 4.86, 4.43, 4.26
5.16, 4.42
5.24, 4.50
5.20, 4.50
4.70, 4.23
4.59, 4.11
4.57, 4.11
339
330
345
355
352
353
335
325
339
4.61
4.73
4.64
4.83
4.92
4.90
4.86
4.77
4.75
DMSO
Pyridine
DMF
DMSO
Pyridine
DMF
DMSO
Pyridine
protons at 8.40 (m, 4H, @C–H), 7.94 (m, 8H, Ar–H), 7.29–7.03
(m, 28H, Ar–H), 6.70 (m, 8H, Ar–H) and 2.98 (s, 24H, CH3) ppm.
In the mass spectrum of compound 4, the presence of the charac-
teristic molecular ion peak at m/z = 1465 [MÀ2H]+ confirmed the
proposed structure.
The IR spectra of the zinc phthalocyanine 5 and cobalt phthalo-
cyanine 6 clearly indicate the cyclotetramerization of the phthalo-
nitrile derivative 3, with the disappearance of the C°N peaks at
2225 cmÀ1. In the 1H NMR spectrum of compound 5, the aromatic
protons appeared at 8.51, 7.88, 7.29–7.05 and 6.71 ppm, and the
aliphatic CH3 protons appeared at 2.94 ppm. 1H NMR measure-
ment of the cobalt phthalocyanine 6 was precluded owing to its
paramagnetic nature. The mass spectra of the tetra-substituted
phthalocyanines 5 and 6 confirmed the proposed structures, with
the molecular ion being easily identified at 1532 [M+H]+ and
1524 [M]+, respectively.
Chloroform
DCM
THF
Pyridine
DMF
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
300
400
500
600
700
800
Wavelength (nm)
Fig. 4. UV–Vis spectra of cobalt phthalocyanine
(Concentration = 10 Â 10À6 mol dmÀ3).
6 in different solvents
Quaternized tetra-substituted metal-free 4a and metallopht-
halocyanines 5a and 6a are very soluble in pyridine, DMF and
DMSO, as expected. Then tetracationic metal-free and metallopht-
halocyanines (4a, 5a and 6a) were obtained from the reaction of
the corresponding phthalocyanines (4, 5 and 6) with methyl iodide
in chloroform. No major change was found in the IR spectra of 4, 5
and 6 after quaternization. The MS spectra of compound 4a, 5a and
6a, which show
a
peak at m/z = 1525 [MÀ4IÀ2H]+, 1546
[MÀ4IÀ3CH3]+ and 1584 [MÀ4I]+, respectively, support the
proposed formula for these compounds.
The UV–Vis spectra of the phthalocyanine complexes exhibit
characteristic Q and B bands. Two principle
are seen for phthalocyanines: a Q-band, which is a
P ?
P⁄ transitions
P
?
P⁄ transi-
tion from the highest occupied molecular orbital (HOMO) to the
lowest unoccupied molecular orbital (LUMO) of the complexes
and B bands were observed in the 300–350 nm region [36,37].
The ground state electronic spectra of the compounds showed
characteristic absorptions in the Q band region at 702/666 nm for
compound 4, 684 nm for compound 5 and 673 nm for compound
6 in CHCl3. B band absorptions of the metal-free and metallopht-
halocyanines 4–6 were observed at (351, 285), (360, 280) and
(376, 282) nm, respectively (Fig. 3).
Wavelength (nm)
Fig. 5. Absorption spectra of zinc phthalocyanine 5 in chloroform at different
concentrations, 14 Â 10À6, 12 Â 10À6, 10 Â 10À6, 8 Â 10À6, 6 Â 10À6 mol dmÀ3
.
The ground state electronic spectra of the quaternized tetra-
substituted metal-free 4a and metallophthalocyanines 5a and 6a
showed characteristic absorptions in the Q band region at 697/
665 nm for 4a, 677 nm for 5a, 662 nm for 6a in DMF. The B band
region was observed around 335–355 nm in DMF. The shoulder
of quaternized metal-free 4a, zinc(II) 5a and cobalt(II) 6a phthalo-
cyanines registered at 637/609, 610 and 603 nm, respectively
(Table 1).
physical, photochemical and electrochemical properties. Generally,
aggregation is highly dependent on concentration, temperature,
nature of the substituents, nature of solvents and complexed metal
ions [38–42]. Phthalocyanine molecules can form two types of
aggregates in solution called H- and J-type [43,44], depending on
the nature and position of the substituents. Generally, phthalocya-
nine molecules form H-type aggregates in solution. J-type aggrega-
tion is rarely observed for phthalocyanine molecules. In this study,
the aggregation behavior of the metal-free 4 and zinc(II) and
cobalt(II) phthalocyanine complexes 5 and 6 was investigated in
different solvents (chloroform, dichloromethane, THF, DMF,
pyridine and DMSO) (see Fig. 4 for complex 6). The metal-free
phthalocyanine 4 did not show any aggregation in chloroform,
dichloromethane, THF or pyridine (Table 2). Also, the zinc(II)
3.2. Aggregation studies
Phthalocyanine compounds have a high aggregation tendency
due to the interactions between their 18
p-electron systems and
the aggregation decreases the solubility of these compounds in
many solvents. It also seriously affects their spectroscopic, photo-

350
I. Acar et al. / Polyhedron 50 (2013) 345–353
Table 2
UV–Vis spectral data for Pcs 4, 5 and 6 in various solvents at a concentration of 10 Â 10À6 mol dmÀ3
.
Solvent
Pcs
Q-Band, kmax, (nm)
Log
e
B-Band, kmax, (nm)
Log e
CHCl3
CH2Cl2
THF
Pyridine
CHCl3
CH2Cl2
THF
4
4
4
4
5
5
5
5
5
6
6
6
6
6
702, 666, 640, 607
699, 665, 635, 605
699, 664, 634, 604
702, 669, 638, 608
685, 617
683, 617
674, 607
677, 609
679, 611
673, 611
665, 603
665, 600
664, 599
4.82, 4.75, 4.36, 4.17
4.72, 4.70, 4.41, 4.24
4.80, 4.78, 4.45, 4.30
4.81, 4.78, 4.38, 4.23
4.97, 4.29
4.89, 4.30
5.17, 4.42
5.14, 4.41
5.09, 4.38
4.46, 4.08
4.48, 4.00
4.58, 3.95
4.58, 4.09
351, 285
377
373
378
360, 280
356
354
359
360
376, 282
323
4.71, 4.66
4.75
4.80
4.81
4.84, 4.77
4.83
4.94
4.92
4.90
4.70, 4.84
4.55
DMF
DMSO
CHCl3
CH2Cl2
THF
DMF
Pyridine
362
372
377
4.73
4.74
4.73
662, 596
4.58, 4.11
DMF
DMSO
Pyridine
DMF
DMSO
Pyridine
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
300
400
500
600
700
800
0
300
400
500
600
700
800
Wavelength (nm)
Wavelength (nm)
Fig. 6. UV–Vis spectra of quaternized metal-free phthalocyanine 4a in different
solvents. (Concentration = 10 Â 10À6 mol dmÀ3).
Fig. 8. UV–Vis spectra of quaternized cobalt phthalocyanine 6a in different
solvents. (Concentration = 10 Â 10À6 mol dmÀ3).
complex 5). The Beer–Lambert law was obeyed for all of the
compounds in concentrations ranging from 14 Â 10À6 to 6 Â
10À6 mol dmÀ3
.
Also, the aggregation behavior of the quaternized metal-free 4a
and quaternized zinc(II) and cobalt(II) phthalocyanine complexes
5a and 6a was investigated in different solvents (DMF, pyridine
and DMSO) (see Fig. 6 for quaternized metal-free Pc, Fig. 7 for com-
plex 5a and Fig. 8 for complex 6a). The quaternized metal-free
phthalocyanine 4a did not show any aggregation in DMF or pyri-
dine, but this compound showed aggregation in DMSO due to the
coordinating ability of these solvents. On the other hand, quatern-
ized zinc(II) and cobalt(II) phthalocyanine complexes 5a and 6a did
not show any aggregation in DMF, pyridine or DMSO.
In addition, the aggregation behavior of the quaternized metal-
free 4a and metallophthalocyanines 5a, 6a was also investigated at
different concentrations in DMF. In DMF, as the concentration was
increased, the intensity of absorption of the Q band also increased
and there were no new bands (normally blue shifted) due to aggre-
gated species for all the quaternized phthalocyanines. The Beer–
Lambert law was obeyed for all of the compounds in concentra-
Fig. 7. UV–Vis spectra of quaternized zinc phthalocyanine 5a in different solvents.
(Concentration = 10 Â 10À6 mol dmÀ3.)
phthalocyanine 5 did not show any aggregation in chloroform,
dichloromethane, THF, DMF, DMSO or pyridine. On the other hand,
the cobalt(II) phthalocyanine 6 did not show any aggregation in
chloroform, dichloromethane or THF but this compound showed
a small amount of aggregation in pyridine and DMF.
tions ranging from 14 Â 10À6 to 6 Â 10À6 mol dmÀ3
.
3.3. Catalytic studies
The aggregation behavior of the metal-free 4 and metallopht-
halocyanines 5 and 6 was also investigated at different concentra-
tions in chloroform. In chloroform, as the concentration was
increased, the intensity of the absorption of the Q band also in-
creased and there were no new bands (normally blue shifted)
due to aggregated species for all phthalocyanines (see Fig. 5 for
3.3.1. Oxidation of 4-nitrophenol with complex 6
Complex 6 has been used as a catalyst for the oxidation of
4-nitrophenol in DMF (90 °C, oxidant/substrate/cat = 500/200/1).
In a typical catalytic reaction, The Schlenk tube was charged with
4-nitrophenol (0.65 Â 10À3 mol), cobalt complex 6 (3.28 Â 10À6

I. Acar et al. / Polyhedron 50 (2013) 345–353
351
Table 3
The experimental results of 4-nitrophenol oxidation with cobalt complex 6.
Substrate (substrate/cat)
4-Nitrophenol (200/1)
Oxidant
TBHP
T (°C)
t (h)
Total conv. (%)
96
TON
190
TOF (hÀ1
63
)
Hydroquinone selectivity (%)
92
Productsa (%)
90
3
88.4 (hydroquinone)
7.6 (benzoquinone)
73.1 (hydroquinone)
6.9 (benzoquinone)
60 (hydroquinone)
8 (benzoquinone)
54 (hydroquinone)
7 (benzoquinone)
28.4 (hydroquinone)
9.6 (benzoquinone)
4-Nitrophenol (400/1)
4-Nitrophenol (600/1)
4-Nitrophenol (800/1)
4-Nitrophenol (1000/1)
TBHP
TBHP
TBHP
TBHP
90
90
90
90
3
3
3
3
80
68
61
38
317
404
483
376
105
134
161
125
91
88
88
74
Reaction conditions: 1.64 Â 10À3 mol TBHP, 3.28 Â 10À6 mol cobalt complex 6 in 0.01 L DMF.
a
Conversion was determined by GC.
Table 4
The experimental results of 4-nitrophenol oxidation with cobalt complex 6.
Entry
1
Substrate (substrate/cat)
4-nitrophenol (200/1)
Oxidant
TBHP
T (°C)
t (h)
Total conv. (%)
96
TON
190
Hydroquinone selectivity (%)
92
Productsa (%)
90
3
88.4 (hydroquinone)
7.6 (benzoquinone)
79.7 (hydroquinone)
7.3 (benzoquinone)
57 (hydroquinone)
8 (benzoquinone)
49 (hydroquinone)
8 (benzoquinone)
63 (hydroquinone)
4 (benzoquinone)
29 (hydroquinone)
8 (benzoquinone)
2
3
4
5
6
4-nitrophenol (200/1)
4-nitrophenol (200/1)
4-nitrophenol (200/1)
4-nitrophenol (200/1)
4-nitrophenol (200/1)
TBHP
TBHP
TBHP
H2O2
70
50
25
90
90
3
3
3
3
3
87
65
57
67
37
172
128
112
132
73
91
87
85
94
78
m-CPBA
Reaction conditions: 0.65 Â 10À3 mol 4-nitrophenol, 1.64 Â 10À3 mol TBHP, 3.28 Â 10À6 mol cobalt complex 6 in 0.01 L DMF.
a
Conversion was determined by GC.
increases. 4-Nitrophenol was converted to hydroquinone (88.4%)
and benzoquinone (7.6%) [45,46] with a TON of 190 by catalyst 6
in DMF after 3 h at 90 °C (Table 3).
4-Nitrophenol
Hydroquinone
Benzoquinone
100
90
80
70
60
50
40
30
20
10
0
To compare the oxidant effect, experiments were carried out
using TBHP, m-CPBA and H2O2 separately under similar reaction
conditions for cobalt complex 6. The results presented here show
that of the three oxidants, TBHP is the most efficient oxygen source
for the catalyst, in terms of giving higher yields of the products (Ta-
ble 4, entry 1). When m-CPBA was employed as an oxidant, total
destruction of the phthalocyanine ring was observed without for-
mation of the intermediate Co(III) phthalocyanine species. Thus,
the lowest activity was observed for the oxidation of 4-nitrophe-
nol, which proceeded with 37% yield over 3 h with a TON of 73
when using m-CPBA in DMF for the catalyst (cobalt complex 6)
(Table 4, entry 6). Table 4 (entry 5) also shows that even though
the product yields using H2O2 as the oxidant were lower than those
for TBHP, a higher selectivity for one of the products (hydroqui-
none) was obtained with H2O2 as the oxidant compared to TBHP
in DMF.
0
50
100
Time (min)
150
200
Fig. 9. Time-dependent conversion of 4-nitrophenol oxidation. Reaction conditions:
1.32 Â 10À3 mol 4-nitrophenol, 1.64 Â 10À3 mol TBHP, 3.28 Â 10À6 mol cobalt
complex 6 in 10 ml DMF.
The time dependence of the catalytic oxidation of 4-nitrophenol
for the catalyst (cobalt complex 6) was studied with TBHP at 90 °C
with a relative ratio of oxidant/substrate/cat of 500/400/1. The re-
sult is presented in Fig 9. An initiation period was not observed for
catalyst, the 4-nitrophenol conversion increased as the reaction
time was prolonged. Selectivity of the products was not signifi-
cantly changed on increasing the reaction time. The presence of
electron withdrawing ring substituent groups on the phthalocya-
nine complexes did not affect the rate of formation of active inter-
mediates with the Co–Pc complex, and the rates of oxidation, in
terms of conversion, are very close to each other.
mol) and TBHP (1.64 Â 10À3 mol) in DMF (0.01 L) and refluxed at
90 °C with 900 rpm stirring. Control experiments showed that
4-nitrophenol oxidation with tert-butylhydroperoxide (TBHP),
m-chloroperoxybenzoic acid (m-CPBA), hydrogen peroxide (H2O2)
did not occur in the absence of the catalyst under the same reac-
tion conditions, confirming that the catalyst plays a prominent role
in the oxidation process.
To examine the effect of the substrate to cobalt, the molar ratio
was varied over the range 200–1000, while other parameters were
kept constant. The experimental conditions were 90 °C,
1.64 Â 10À3 mol TBHP, 0.01 L DMF for 3 h. The results are expected,
as the substrate catalyst molar ratio decreases, the reaction rate
The oxidation system was further examined by UV–Vis spec-
troscopy during the reaction in order to investigate the catalytic

352
I. Acar et al. / Polyhedron 50 (2013) 345–353
dichloromethane, THF, pyridine, DMF and DMSO. On the other
hand, cobalt(II) phthalocyanine 6 was found to be monomeric
in chloroform, dichloromethane and THF, but this compound
showed a little aggregation in DMF and pyridine. Quaternized
metal-free phthalocyanine 4a did not show any aggregation in
DMF or pyridine, but this compound showed aggregation in
DMSO. In contrast, the quaternized zinc(II) and cobalt(II) phtha-
locyanine complexes 5a and 6a did not show any aggregation
in DMF, pyridine or DMSO. Also, we have studied the aggregation
behavior of these new metal-free, metallophthalocyanines 4–6
and their quaternized derivatives 4a–6a in different concentra-
tions in chloroform and DMF, respectively. No aggregation was
demonstrated in chloroform or DMF for concentration between
14 Â 10À6 and 6 Â 10À6 mol dmÀ3. The results show that 4-nitro-
phenol was converted to products (hydroquinone and benzoqui-
none) in 96% conversion with cobalt complex 6, within 3 h with
TBHP in DMF at 90 °C. Control experiments performed without
catalyst and using the corresponding metal salt as a catalyst pro-
duced no product. Mild reaction conditions, high yields of the
products, short reaction time and inexpensive reagents make this
catalytic system a useful oxidation method for 4-nitrophenol.
Fig. 10. Time-dependent changes in the visible spectra of the oxidized cobalt
complex 6 observed on addition of TBHP (1.64 Â 10À3 mol) to a reaction mixture
containing 1.32 Â 10À3 mol 4-nitrophenol and 3.28 Â 10À6 mol cobalt complex 6
catalyst in 10 ml DMF: (b) 60 min; (c) 120 min; (d) 180 min; min after addition of
TBHP. All spectra for the oxidized cobalt complex 6 were taken after sixfold dilution
with DMF. (a) The visible spectrum of the non-oxidized cobalt complex 6.
Acknowledgement
mechanism for the Co-catalyzed 4-nitrophenol oxidation. The
spectrum of cobalt(II) phthalocyanine 6 has been a subject several
reports [47,48]. The spectra of MPc complexes are well known and
consist of an intense band called the Q band in the visible region
[49]. The spectrum (a) in Fig. 10 is typical spectrum for a mono-
meric form of cobalt complex 6, with a Q band at 661 nm. Fig. 10
shows the spectral changes observed for the Co–Pc complex by
addition of TBHP to the solution during the catalytic process. For
cobalt complex 6, there was a shift in the Q band from 661 to
667 nm, and a decrease in the intensity of the Q band without
any new bands being formed. The shift in the Q band is consistent
with metal oxidation of CoII–Pc to CoIII–Pc [50]. There was no peak
around 596 nm, which suggests ring oxidation. Thus addition of
TBHP to solutions of Co–Pc resulted in only metal and not ring oxi-
dation of the Co–Pc. As the catalysis progressed, there was a grad-
ual decrease in the intensity of the Q band of the Co–Pc catalyst,
suggesting catalyst degradation, as is typical [22] of MPc catalysts
in homogeneous catalysis. The decomposition of the phthalocya-
nine complex during the oxidation of 4-nitrophenol is probably
the result of the attack of the phthalocyanine ring by ROÅ and ROOÅ
radicals. The color of the solution changed from green to light
yellow as the catalysis progressed. However, the reaction products
continued to form even after the catalyst had turned colorless, sug-
gesting that once reaction intermediates are formed, the reaction
can still proceed in the presence or absence of the original form
of the catalyst.
This study was supported by the Research Fund of Karadeniz
Technical University (Project No: 8202).
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