DBU-catalyzed condensation of metal free and metallophthalocyanines containing thiazole and azine moieties: Synthesis, characterization and electrochemical properties

Article abstract of DOI:10.1016/j.jorganchem.2013.04.043

Abstract Schiff base that contains carbothioamide moiety, substituted thiazole derivative, novel phthalonitrile compound and its corresponding metal free and metal phthalocyanines (Zn(II), Ni(II), Co(II) and Cu(II)) were synthesized and characterized for

Full text of DOI:10.1016/j.jorganchem.2013.04.043

Journal of Organometallic Chemistry 740 (2013) 70e77
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
DBU-catalyzed condensation of metal free and
metallophthalocyanines containing thiazole and azine moieties:
Synthesis, characterization and electrochemical properties
a
b
c
d
b,
*
_
ꢀ
ꢀ
Gökhan Dede , Rıza Bayrak , Mustafa Er , Ali Rıza Özkaya , Ismail Degirmencioglu
a Institute for Graduate Studies in Pure and Applied Sciences, Marmara University, Göztepe, Kadıköy, Istanbul 34722, Turkey
b Department of Chemistry, Faculty of Sciences, Karadeniz Technical University, Kanuni Kampüsü, 61080 Trabzon, Turkey
c Department of Chemistry, Karabük University, 78050 Karabük, Turkey
d Department of Chemistry, Marmara University, Göztepe, Kadıköy, Istanbul 34722, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Schiff base that contains carbothioamide moiety, substituted thiazole derivative, novel phthalonitrile
compound and its corresponding metal free and metal phthalocyanines (Zn(II), Ni(II), Co(II) and Cu(II))
were synthesized and characterized for the first time. The solubility of these novel phthalocyanines were
high in organic solvents and they did not aggregate in chloroform within the concentration range of
1.6 ꢀ 10ꢁ5e4 ꢀ 10ꢁ6 M. Electrochemical properties of the phthalocyanines have been examined by cyclic
voltammetry, square wave voltammetry and in situ UVevis spectroelectrochemistry on Pt in dime-
thylsulfoxide/tetrabutylammonium perchlorate. These measurements suggested that the compounds
display subsequent ligand- and/or metal-based one-electron reduction and oxidation processes. Cobalt
complex showed both metal-based and ring-based one-electron redox processes, while the other
complexes displayed only ring-based one-electron couples. It was observed that the redox processes of
metal free, Zn(II), Ni(II) and Cu(II) phthalocyanines are coupled by aggregation phenomenon, whereas
those CoPc are not, probably due to the difference in their axial coordinating properties.
Ó 2013 Elsevier B.V. All rights reserved.
Received 12 March 2013
Received in revised form
24 April 2013
Accepted 26 April 2013
Keywords:
Phthalocyanine
Thiazole
Azine
Electrochemistry
Synthesis
1. Introduction
biocides, fungicides, dyes, treatment of inflammation, hypertension,
bacterial and HIV infections [6e9].
Phthalocyanines (Pcs), blue to green colored pigments, combine
four iminoisoindoline units and thus, have 18 -electron hetero-
Both in heterocyclic and in acyclic chemistry term of azine is
used. While six-membered rings (pyrazines, pyrimidines) are
called as azines in heterocyclic chemistry, in acyclic chemistry, the
product of the reaction between one molecule hydrazine hydrate
and two molecules of carbonyl compounds are called azine too
[10,11]. Azines, biologically active compounds, have antitumor [12],
antibacterial [13] and antifungal activity [14].
The redox properties and industrial applications of the Pcs are
related to each other. Changing the substituent, central metal ion or
axial ligand may notably affect their redox properties [15e20]. The
redox properties of Pcs are generally determined by voltammetric
methods such as cyclic voltammetry, differential pulse voltamme-
try and square wave voltammetry. However, the voltammetry may
not be enough for distinguishing the type of redox process and in
such cases in situ spectroelectrochemical measurements which is a
combination of spectroscopic and electrochemical techniques may
be used [21].
p
cyclic aromatic system. This high delocalization makes them usable
in many technological applications such as infrared ray absorbents,
ink jet inks, data storage, electrophotographic photoreceptors, non-
linear optical devices and photosensitizers in photodynamic ther-
apy [1e3]. Different metallophthalocyanines (MPc) that have metal
element at the center can be prepared and different substituents
can be placed to the peripheral or non-peripheral positions [4,5].
Heterocyclic compounds such as imidazoles, oxazoles, oxadia-
zoles, triazoles etc., have been synthesized due to their wide
biological activities. Thiazole or 1,3-thiazole is a heterocyclic com-
pound that contains both sulfur and nitrogen and represents an
important part of vitamin B1 (thiamine). These type of aromatic
heterocyclic compounds containing nitrogen and sulfur have
important industrial and pharmaceutical uses such as manufacturing
To the best of our knowledge, there are only a few literature about
the synthesis of metal free (H2Pc) and MPcs containing thiazole and
* Corresponding author. Tel.: þ90 4623772525; fax: þ90 4623253196.
_
ꢀ
ꢀ
E-mail address: ismail61@ktu.edu.tr (I. Degirmencioglu).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.04.043

G. Dede et al. / Journal of Organometallic Chemistry 740 (2013) 70e77
71
Schiff moieties on peripheral positions that belongs to our group but
there is no any report on their electrochemical properties [22].
Therefore, the strategy of this study has focused on combining
thiazole, Schiff base and Pc into a single compound to obtain metal
free, Zn(II), Ni(II), Co(II) and Cu(II) Pcs and investigate their electro-
chemical properties. To this end, firstly the Schiff base moiety
bearing active carbothioamide group (1) has been prepared. Sec-
ondly, thiazole fragment of the target material has been created (2),
then the new phthalonitrile derivative (3) having azine and thiazole
groups was synthesized and characterized. At the final stage, Pcs
(4e8) have been prepared and electrochemical properties of these
Pcs have been studied via cyclic voltammetry, square wave voltam-
metry and in situ UVevis spectroelectrochemistry on Pt in dime-
thylsulfoxide (DMSO)/tetrabutylammonium perchlorate (TBAP).
dropped into the suspension in 30 min. The reaction mixture was
refluxed for 3 days and the cream color of the mixture turned to
yellow. The crude product was filtrated, washed with water, ethyl
alcohol and diethyl ether and crystallized in DMF:ethyl alcohol
(3:1) solvent system. Yield: 24.2 g (% 92.6). M.p.: 228e229 ꢂC. Anal.
Calc. for C17H21N3O5S: C 53.81, H 5.58, N 11.07; found: C 53.78, H
5.67, N 10.98. IR [(KBr) nmax/cmꢁ1]: 3416
2937 (Aliph. CH), 1685 (C]O), 1584 (CH]N), 1271e1246
OeC), 1087 (CeOeC), 848 : ppm):
(CH). 1H NMR (DMSO-d6), (
n
(eOH), 3122
n
(AreCH),
(Ce
n
n
n
n
d
d
d
8.88 (s, 1H/OH), 8.21 (s, 1H/CH]N), 7.02 (s, 2H/AreH), 4.16e4.23 (q,
2H/CH2), 3.81 (s, 6H/OeCH3), 3.37 (s, 3H/NeCH3), 2.50 (s, 3H/CH3),
1.22e1.27 (t, 3H/CH3CH2). 13C NMR (DMSO-d6), (
d: ppm): 165.05
(C]O), 161.36, 153.25 (CH]N), 148.28, 147.95, 137.74, 124.96,
104.68, 100.81, 60.27 (CH2), 55.86 (OCH3), 31.36 (NeCH3), 14.17
(CH3), 12.54 (CH3CH2). MS (ESI), (m/z): calculated: 379.12; found:
380.14 [M þ H]þ.
2. Experimental
2.1. Synthesis and characterization
2.1.3.3. (E)-Ethyl 2-((E)-(4-(3,4-dicyanophenoxy)-3,5-dimethoxy-
benzylidene)hydrazono)-3,4-dimethyl-2,3-dihydrothiazole-5-
2.1.1. Materials
carboxylate (3). Compound 2 (3.79 g, 0.01 mol) and 4-
All reactions were carried out under N2 atmosphere by Schlenk
techniques. All solvents were desiccated and refined according to
Perrin and Armarego’s method [23].1,8-Diazabicyclo[5.4.0]undec-7-
ene (DBU), syringaldehyde and 4-methyl-3-thiosemicarbazide were
provided from their commercial suppliers and 4-nitrophthalonitrile
were obtained according to the literature procedure [24].
nitrophthalonitrile (1.73 g, 0.01 mol) were dissolved in dry DMF
(50 mL) and the solution was stirred vigorously at 55e60 ꢂC. Then,
dry K2CO3 (1.38 g, 0.01 mol) was added into this solution in eight
equal portions at 15 min intervals. The system was stirred at same
temperature for 5 days. Then the solution was poured into ice water
(300 mL). The precipitated crude product was filtered and crys-
tallized in ethyl acetate. Yield: 3.64 g, (72%), mp: 171e172 ꢂC. Anal.
Calc. for C25H23N5O5S: C 59.39, H 4.59, N 13.85; found: C 59.36, H
2.1.2. Equipment
1H NMR and 13C NMR spectra were recorded on a Varian XL-200
NMR spectrophotometer in CDCl3 and DMSO-d6, and chemical
4.63, N 13.88. IR [(KBr) nmax/cmꢁ1]: 3092
(Aliph. CH), 2227 (C^N), 1621e1603 (C]C), 1568e1553
N), 1278e1250 (CeOeC)/(CeN), 1145 (CeN), 1092e1013
C), 985 : ppm): 8.33 (s, 1H/CH]N), 7.71e
(CH). 1H NMR (CDCl3), (
n
(AreCH), 2921e2874
(CH]
(CeOe
n
n
n
shifts were reported (
d
) relative to Me4Si as internal standard. IR
n
d
d
spectra were recorded on a PerkineElmer Spectrum FT-IR spec-
trometer using KBr pellets. The mass spectra were measured with a
Micromass Quattro LC/ULTIMA LC-MS/MS spectrometer using
chloroformemethanol solvent system. All experiments were per-
formed in the positive ion mode. Elemental analyses were per-
formed on a Costech ECS 4010 instrument and the obtained values
agreed with the calculated ones. UVevis spectra were recorded by
Unicam UV2-100 using 1 cm pathlength cuvettes at room tem-
perature. Melting points were measured on an electrothermal
apparatus and are uncorrected.
d
d
7.63 (d, 1H/AreH), 7.22e7.18 (d, 2H/AreH), 7.08e7.04 (d, 2H/AreH),
4.33e4.25 (q, 2H/CH2), 3.86 (s, 6H/OeCH3), 3.53 (s, 3H/NeCH3),
2.61 (s, 3H/CH3), 1.38e1.27 (t, 3H/CH3CH2). 13C NMR (CDCl3), (
d:
ppm): 165.11, 163.28, 161.74, 159.78, 152.90, 152.12, 146.82, 135.89,
135.40, 134.43, 133.63, 120.36, 117.56, 115.92, 115.44, 108.63, 106.14,
104.31, 61.23, 56.50, 32.05, 14.68, 13.22. MS (ESI), (m/z): calculated:
505.14; found: 506.23 [M þ H]þ.
2.1.3.4. The general procedure for synthesis of metal-free (4) metal-
lophthalocyanines (5e8). Substituted phthalonitrile (3) (0.2 g,
3,96 ꢀ 10ꢁ4 mol) and for metallophthalocyanines corresponding
anhydrous metal salts Zn(Ac)2 (0.018 g, 9.90 ꢀ 10ꢁ5 mol); Ni(Ac)2
(0.017 g, 9.90 ꢀ 10ꢁ5 mol); CoCl2 (0.013 g, 9.90 ꢀ 10ꢁ5 mol); CuCl2
(0.013 g, 9.90 ꢀ 10ꢁ5 mol) were dissolved in 4 mL of dry n-pentanol.
After increasing the temperature to 90 ꢂC, DBU (3 drops) was added
to the media. Thereafter the temperature was raised to 160 ꢂC and
stirred for 24 h under nitrogen atmosphere. After cooling, the so-
lutions were dropped to ethyl alcohol (40 mL) and the solid raw
products were filtrated and washed with hot ethanol, methanol, n-
hexane and diethyl ether. The pure green colored products were
isolated through silica gel column. Spectral data of these products
are given below.
2.1.3. Compounds
2.1.3.1. (E)-2-(4-Hydroxy-3,5-dimethoxybenzylidene)-N-methylhy-
drazinecarbothioamide (1). In a round-bottomed flask, syringalde-
hyde (13.65 g, 0.075 mol) and 4-methyl-3-thiosemicarbazide
(11.81 g, 0,1125 mol) heated to 140 ꢂC for 3 h and then heated to
160 ꢂC for 1 h under reflux with no solvent. The resulting residue
was washed with water, filtrated and crystallized in DMF:ethyl
alcohol (1:1) solvent system. Yield: 19.1 g (% 94.4). M.p.: 233e
234 ꢂC. Anal. Calc. for C11H15N3O3S: C 49.06, H 5.61, N 15.60; found:
C 49.13, H 5.54, N 15.71. IR [(KBr) nmax/cmꢁ1]: 3331
n
(eOH), 3147
(CH]N), 1553
: ppm): 11.32 (s, 1H/NH),
n
(eNH), 3001
n(AreCH), 2937 n(Aliph. CH), 1583 n
n
(C]C), 853, 828. 1H NMR (DMSO-d6), (
d
8.79 (bs, 1H/OH), 8.36 (s, 1H/NH(CH3)), 7.94 (s, 1H/CH]N), 7.04 (s,
2.1.3.4.1. Metal-free phthalocyanine (4). The used solvent sys-
tem during column chromatography: chloroform. Yield: 0.033 g,
(16.5%), mp >300 ꢂC. Anal. Calc. for C100H94N20O20S4: C 59.34, H
4.68, N 13.84; found: C 59.40, H 4.71, N 13.77. IR [(KBr) nmax/cmꢁ1]:
2H/AreH), 3.81 (s, 6H/OeCH3), 3.05e3.03 (d, 3H/NeCH3). 13C NMR
(DMSO-d6), (d: ppm): 177.24 (C]S), 147.98, 142.46 (CH]N), 137.64,
124.29, 104.87, 56.05 (OCH3), 30.68 (NeCH3). MS (ESI), (m/z):
calculated: 269.08; found: 269.96 [M þ H]þ.
3279 (eNH), 3093
(C]C), 1565e1544
(CeN), 1091e1012
n
(AreCH), 2915e2875
(CH]N), 1279e1262
(CeOeC), 980 d:
(CH). 1H NMR (CDCl3), (
n
(Aliph. CH), 1621e1603
n
n
n(CeOeC)/(CeN), 1144
2.1.3.2. (E)-Ethyl-2-((E)-(4-hydroxy-3,5-dimethoxy
hydrazono)-3,4-dimethyl-2,3-dihydro-thiazole-5-carboxylate
benzylidene)
(2).
d
d
d
ppm): 8.27 (s, 4H/CH]N), 7.70e7.58 (d, 4H/AreH), 7.14e7.02 (bd,
16H/AreH) 4.26e4.15 (q, 8H/CH2), 3.78 (s, 24H/OeCH3), 3.49 (s,
12H/NeCH3), 2.60 (s, 12H/CH3), 1.31e1.20 (t, 12H/CH3). UVevis
(CHCl3): lmax/nm: [(10ꢁ5 log ε dm3 molꢁ1 cmꢁ1)]: 708 (4.68), 673
In a two-necked flask, compound 1 (18.45 g, 0.069 mol) was sus-
pended in absolute ethanol. Then the solution of ethyl-2-
chloroacetoacetate (11.29 g, 0.069 mol) in ethyl alcohol was

72
G. Dede et al. / Journal of Organometallic Chemistry 740 (2013) 70e77
(4.67), 644 (4.34), 611 (4.08), 384 (5.00). MS (ESI), (m/z): calculated:
2023.59; found: 2024.86 [M þ H]þ.
of the solution by a double bridge. High purity of N2 was used for
deoxygenating the solution at least 15 min prior to each run and
to maintain a nitrogen blanket during the measurements. Ferro-
cene was used as an internal reference, but the potentials were
presented as the ones versus SCE. The spectroelectrochemical
measurements were carried out by utilizing a three-electrode
configuration of thin-layer quartz spectroelectrochemical cell at
25 ꢂC. The working electrode was transparent Pt gauze. Pt wire
counter electrode separated by a glass bridge and a SCE reference
electrode separated from the bulk of the solution by a double
bridge were used.
2.1.3.4.2. Zn(II) phthalocyanine (5). The used solvent system
during column chromatography: chloroform:methanol (100:9).
Yield: 0.028 g, (13.5%), mp >300 ꢂC. Anal. Calc. for
C100H92N20O20S4Zn: C 57.53, H 4.44, N 13.42; found: C 57.40, H 4.60,
N 13.32. IR [(KBr) nmax/cmꢁ1]: 3085
CH), 1618e1609 (C]C), 1560e1547
C)/(CeN), 1140 (CeN), 1090e1015
(CDCl3), ( : ppm): 8.32 (s, 4H/CH]N), 7.72e7.59 (d, 4H/AreH),
n
(AreCH), 2915e2870
(CH]N), 1270e1263
(CeOeC), 981
(CH). 1H NMR
n
(Aliph.
n
n
n(CeOe
d
d
d
d
7.12e6.98 (bd, 16H/AreH) 4.28e4.18 (q, 8H/CH2), 3.82 (s, 24H/Oe
CH3), 3.55 (s, 12H/NeCH3), 2.62 (s, 12H/CH3), 1.30e1.22 (t, 12H/
CH3). UVevis (CHCl3): lmax/nm: [(10ꢁ5 log ε dm3 molꢁ1 cmꢁ1)]: 684
(5.10), 617 (4.48), 384 (4.98). MS (ESI), (m/z): calculated: 2085.50;
found: 2086.91 [M þ H]þ.
3. Results and discussion
3.1. Outlook of the synthesized compounds
2.1.3.4.3. Ni(II) phthalocyanine (6). The used solvent system
during column chromatography: chloroform:methanol (100:15).
Yield: 0.042 g, (20.4%), mp >300 ꢂC. Anal. Calc. for
C100H92N20O20S4Ni: C 57.72, H 4.46, N 13.46; found: C 57.61, H 4.51,
The synthesis route of new Schiff base (1) derived from the re-
action between syringaldehyde and 4-methyl-3-thiosemicarbazide,
thiazole containing Schiff base (2), substituted phthalonitrile (3) and
target metal-free (4) and MPcs (5, 6, 7 and 8) is shown in Fig. 1. The
structures of novel compounds have been characterized by a com-
bination of 1H and 13C NMR, IR, UVevis spectroscopy, elemental
analysis and mass spectral data.
N 13.59. IR [(KBr) nmax/cmꢁ1]: 3089
CH), 1625e1612 (C]C), 1565e1549
C)/(CeN), 1144 (CeN), 1095e1017
(CDCl3), ( : ppm): 8.30 (bs, 4H/CH]N), 7.70e7.63 (d, 4H/AreH),
n
(AreCH), 2918e2871
(CH]N), 1271e1265
(CeOeC), 983
(CH). 1H NMR
n
(Aliph.
n
n
n(CeOe
d
d
d
d
7.15e7.01 (bd, 16H/AreH) 4.35e4.16 (q, 8H/CH2), 3.80 (s, 24H/Oe
CH3), 3.50 (s,12H/NeCH3), 2.65 (s,12H/CH3),1.32e1.21 (t,12H/CH3).
UVevis (CHCl3): lmax/nm: [(10ꢁ5 log ε dm3 molꢁ1 cmꢁ1)]: 672
(4.86), 607 (4.32), 334 (4.76). MS (ESI), (m/z): calculated: 2079.51;
found: 2102.78 [M þ Na]þ.
3.1.1. Synthesis of compounds 1, 2 and 3
1,3-Thiazoles derivatives can be prepared from the reactions
between substituted hydrazinecarbothioamides and ethyl
2-chloroacetoacetate [22]. Therefore at the first stage we have
prepared the Schiff base containing active hydrazinecarbothioa-
mide moiety (1) from the reaction between syringaldehyde and
4-methyl-3-thiosemicarbazide. From the IR data of the compound
1, the absence of the vibration of carbonyl group of syringaldehyde
and vibration of eNH2 group of 4-methyl-3-thiosemicarbazide and
presence of new absorption at 1583 cmꢁ1 belonging to (CH]N)
supported that the Schiff base (1) has been successfully prepared.
The structure of the compound 1 has been identified by the help of
NMR spectroscopy, too. In the 1H NMR data of 1, the signals of the
aldehyde proton of syringaldehyde and NH2 proton of 4-methyl-3-
thiosemicarbazide disappeared and a new signal at 7.94 ppm be-
longs to proton of CH]N group appeared. Furthermore, in its 13C
NMR data, the signal of the carbon of the carbonyl group of syrin-
galdehyde disappeared and a new signal at 142.46 ppm that be-
longs to the iminic carbon appeared. On the other hand, in the mass
spectrum of compound 1, molecular ion peak at m/z: 269.96
[M þ H]þ and elemental analysis data also supported the structure
of the product.
At the second step, the thiazole moiety of the target material
was obtained from the condensation of compound 1 and ethyl-2-
chloro-acetoacetate at 1:1 ratio in absolute ethanol in high yield.
The absence of the absorptions of eNH groups of compound 1 in
the IR spectra of compound 2, confirmed the realization of the re-
action. Furthermore, the absence of the eNH signals and the
presence of the new methyl and ethoxy group signals at 2.50, 4.16e
4.23 (for OCH2) and 1.22e1.27 ppm (for CH3 of ethoxy group),
respectively, in the 1H NMR spectra of compound 2 also supported
the proposed structure. 13C NMR spectrum of 2 also provided
satisfactory data for its characterization. The signal of the thione
group (C]S) of the compound 1 disappeared and new signals at
60.27 (OCH2), 14.17 (CH3), 12.54 (CH3CH2O) appeared. On the other
hand, the molecular ion peak at m/z: 380.14 [M þ H]þ in the mass
spectrum of 2 and the elemental analysis data also proved the
reaction.
2.1.3.4.4. Co(II) phthalocyanine (7). The used solvent system
during column chromatography: chloroform:methanol (100:17).
Yield: 0.046 g, (22.3%), mp >300 ꢂC. Anal. Calc. for
C100H92N20O20S4Co: C 57.71, H 4.46, N 13.46; found: C 57.82, H 4.58,
N 13.36. IR [(KBr) nmax/cmꢁ1]: 3086
n
(AreCH), 2923e2882
(CH]N), 1273e1260
(CeOeC), 980
n
(Aliph.
(CeOe
d(CH). UVevis
CH), 1623e1612
C)/(CeN), 1144
n
(C]C), 1562e1546
n
n
d(CeN), 1091e1015
d
(CHCl3): lmax/nm: [(10ꢁ5 log ε dm3 molꢁ1 cmꢁ1)]: 682 (4.57), 614
(4.08), 388 (4.81). MS (ESI), (m/z): calculated: 2080.50; found:
2081.44 [M þ H]þ.
2.1.3.4.5. Cu(II) phthalocyanine (8). The used solvent system
during column chromatography: chloroform:methanol (100:15).
Yield: 0.039 g, (18.9%), mp >300 ꢂC. Anal. Calc. for C100H92N20O20
-
S4Cu: C 57.59, H 4.45, N 13.43; found: C 57.66, H 4.52, N 13.28. IR
[(KBr) nmax/cmꢁ1]: 3087
n
(AreCH), 2916e2872
(CH]N), 1272e1261
(CeOeC), 984 (CH). UVevis (CHCl3):
n
(Aliph. CH), 1628e
1611
1143
n
(C]C), 1562e1545
(CeN), 1090e1012
n
n
(CeOeC)/(CeN),
d
d
d
lmax/nm: [(10ꢁ5 log ε dm3 molꢁ1 cmꢁ1)]: 682 (4.89), 621 (4.51), 368
(4.20). MS (ESI), (m/z): calculated: 2085.50; found: 2086.77
[M þ H]þ.
2.2. Electrochemical and in situ spectroelectrochemical
measurements
The electrochemical and in situ spectroelectrochemical mea-
surements were monitored using
a Gamry Reference 600
potentiostat/galvanostat controlled by an external PC and utiliz-
ing a three-electrode configuration at 25 ꢂC. UVevis absorption
spectra were recorded by an Agilent 8453 diode array spectro-
photometer equipped with the potentiostat/galvanostat. The
electrochemical measurements were carried in extra pure DMSO
containing electrochemical grade TBAP as the supporting elec-
trolyte at a concentration of 0.10 mol dmꢁ3. For cyclic voltam-
metry (CV) and square wave voltammetry (SWV) measurements,
the working electrode was a Pt plate. A Pt spiral wire served as
the counter electrode. Saturated calomel electrode (SCE) was
employed as the reference electrode and separated from the bulk
The preparation of the phthalonitrile derivative (3) was ach-
ieved by the nucleophilic aromatic substitution of the nitro group of
4-nitrophthalonitrile by compound 2 in the presence of anhydrous

G. Dede et al. / Journal of Organometallic Chemistry 740 (2013) 70e77
73
Fig. 1. Synthetic scheme of the novel compounds.
K2CO3 in DMF [25e27]. The structure of the compound was
confirmed by spectral investigation. In the IR spectrum, the for-
mation of compound 3 was clearly defined by the disappearance of
eOH absorption of compound 2, NO2 stretching of the 4-nitro-
phthalonitrile and the appearance of C^N absorption band at
2227 cmꢁ1. Its 1H NMR spectrum was also in good agreement with
the structure of the synthesized compound. Phenolic eOH signal
disappeared after condensation. The integral ratios of aromatic
and aliphatic proton signals are obtained as expected. In proton-
decoupled 13C NMR spectrum, the signals at 115.92 and
115.44 ppm indicated the presence of nitrile carbons for compound
3. Additionally, the mass spectrum of 3 showed molecular ion peak
at m/z ¼ 506.23 [M þ H]þ, supporting the proposed formula for this
compound. Furthermore the results of the elemental analysis
report were satisfactory.
3.1.2. Syntheses of metal free (4) and metallophthalocyanines (5e8)
The preparation of the metal-free Pc (4) was achieved by
cyclotetramerization of compound 3 in n-pentanol by the catalyst
of DBU at 160 ꢂC for 24 h. Similarly, as a result of the cyclo-
tetramerization of compound 3 in the presence of the corre-
sponding metal salts and at the same conditions as mentioned
above for metal free Pc (4) the tetra-substituted metal-
lophthalocyanines (5e8) were obtained.
Fig. 2. Absorption spectra of compounds 4 and 7 in CHCl3 at 1 ꢀ 10ꢁ5 M.
Fig. 3. Absorption spectra of compounds 5, 6 and 8 in CHCl3 at 1 ꢀ 10ꢁ5 M.

74
G. Dede et al. / Journal of Organometallic Chemistry 740 (2013) 70e77
Fig. 4. Absorption spectra of metal free Pc (4) in chloroform at different concentrations.
The characterization of the structure of the Pcs were accom-
The metal-free Pc (4) and MPcs (5e8) show two strong ab-
sorption regions in their electronic spectra. The first one e called as
“B” or Soret band e is observed at around 300 nm because of the
plished by 1H NMR, IR, UV/vis and mass spectral investigations.
Cyclotetramerization of compound 3 to metal-free Pc (4) was
confirmed by the disappearance of the C^N vibration at
2227 cmꢁ1 in its IR spectrum. Furthermore, in the IR spectrum of
the metal-free Pc (4) general inner core eNH absorption was
observed at 3279 cmꢁ1, that is characteristic for metal-free Pcs.
The rest of the spectrum of 4 was similar to that of substituted
phthalonitrile (3). In the 1H NMR spectrum of compound 4,
shielded inner core eNH protons could not be observed, probably
due to the aggregation [27]. The signals corresponding to aromatic
and aliphatic protons of 4 represent the significant absorbance
characteristics of the proposed structure. Furthermore, the ESI
mass spectrum of compound 4 showed a molecular ion peak at
m/z ¼ 2024.86 [M þ H]þ. In addition, elemental analysis values
were also satisfactory.
transitions from deeper
the second one is e called as “Q” band e observed at around
600e750 nm due to transitions from -HOMO to *-LUMO energy
p-HOMO to n*-LUMO energy levels and
p
p
levels [29]. One of the best indicators of the formation of Pcs is their
UVevis spectra in dilute (w1 ꢀ10ꢁ5 M) solution. The Q band of the
metal-free Pc (4) was observed as splitted two bands due to D2h
symmetry, as Qx and Qy bands [30]. The electronic absorption
spectrum of the metal free Pc (4) in chloroform at 1 ꢀ 10ꢁ5
M
concentration at room temperature is shown in Fig. 2. The splitting
Q band was observed at lmax 708 and 673 nm, indicating the
structure with non-degenerate D2h symmetry.
Differently from metal free Pc (4), the Q bands of the MPcs (5e8)
are observed as singlet due to their D4h symmetry (Figs. 2 and 3).
The UVevis absorption spectra of MPcs in chloroform show intense
Q absorption bands between 684 and 672 nm with shoulders at
around 615 nm and B bands at ca. 360 nm. The sharpness of the
observed bands in Figs. 2 and 3 are evidence of the presence of non-
aggregated species at 1 ꢀ 10ꢁ5 M concentration in chloroform. For
further investigation of aggregation behaviors of all novel phtha-
locyanines, absorption spectral changes were investigated in
chloroform at 1.6 ꢀ 10ꢁ5e4 ꢀ 10ꢁ6 M concentration range. At these
concentrations, all phthalocyanines showed monomeric behavior
(Fig. 4 as an example for metal free Pc (4)).
The disappearance of the C^N vibration of compound 3 at
2227 cmꢁ1 in the IR spectra of MPcs (5e8) proves the formation of
these Pcs. The 1H NMR spectra of Co(II)Pc and Cu(II)Pc (7 and 8)
could not be determined because of the presence of paramagnetic
cobalt and copper atoms in the Pc core [28]. The 1H NMR spectra of
the Zn(II)Pc and Ni(II)Pc (5 and 6) were similar to those of the
metal-free Pc (4). In the mass spectra of compounds 5e8, the
parent molecular ion peaks were observed at m/z ¼ 2086.91
[M þ H]þ for 5, 2102.78 [M þ Na]þ for 6, 2081.44 [M þ H]þ for 7 and
2086.77 [M þ H]þ for 8, and confirmed the proposed structures.
Table 1
Voltammetric data for the Pc compounds 4e8.
MII/MIII
MII/MI
Ring reductions
DE1/2
c
Complex
Ring oxidations
4 (H2Pc) in DMSO/TBAP)
E1/2 (V)a
Ep (V)b
E1/2 (V)a
Ep (mV)b
E1/2 (V)a
Ep (mV)b
E1/2 (V)a
Ep (mV)b
E1/2 (V)a
Ep (mV)b
0.68
e
ꢁ0.64
0.080
ꢁ0.57
e
ꢁ1.04
0.060
ꢁ0.84
0.060
ꢁ0.90
0.14
1.32
1.02
1.16
1.52
0.84
D
e
5 (ZnPc) in DMSO/TBAP)
6 (NiPc) in DMSO/TBAP)
8 (CuPc) in DMSO/TBAP)
7 (CoPc) in DMSO/TBAP)
0.68
0.060
0.45
0.060
0.62
e
ꢁ1.32
e
D
ꢁ0.54
e
ꢁ1.21
0.100
ꢁ1.45
D
0.65
e
ꢁ0.87
0.160
ꢁ1.39
0.060
ꢁ1.17
D
0.060
0.42
0.06
ꢁ0.42
D
0.080
a
E1/2 ¼ (Epa þ Epc)/2 at 0.050 V sꢁ1
.
b
c
D
D
Ep ¼ Epa þ Epc at 0.050 V sꢁ1
.
E1/2 ¼ E1/2 (first oxidation) ꢁ E1/2 (first reduction).

G. Dede et al. / Journal of Organometallic Chemistry 740 (2013) 70e77
75
Fig. 5 shows cyclic and square wave (inset) voltammograms of
metal-free Pc 4. The cyclic voltammogram involves only two one-
electron reduction processes. However, the square wave voltamme-
tryenabled us to record also the one-electron oxidationprocess of the
compound. All redox processes in Fig. 5 are ring-based since com-
pound 4 isa metal-free Pc. The broad cyclic voltammetry signals point
out that compound 4 may form aggregated species in DMSO/TBAP.
Voltammetric measurements suggested that the general voltam-
metric behavior of 5 (ZnPc), 6 (NiPc) and 8 (CuPc) is similar to each
other and that of 4 (H2Pc), in terms of the positions of voltammetric
signals on the voltage scale (Table 1). The similarity in general redox
behavior between metal-free and metal Pcs probably suggests that
Zn(II), Ni(II) and Cu(II) behave as redox-inactive metal centers [31,32].
On the other hand, the differences between the E1/2 values and the
number and shapes of the voltammetric signals can be attributed to
the different polarizing powers of central atoms and different ag-
gregation effects. While compound 4 displayed broad cyclic voltam-
metry signals, the splitting into two waves was observed for the first
reduction process of 5, 6 and 8, and also for the first oxidation couple
of 5. Fig. 6A shows cyclic and squarewave (inset) voltammograms of 5
as example. The redox processes in the MPcs are located at the ring
and at the metal center, [21,33e39]. Moreover, it appears that a gen-
eral trend for some Pc compounds in this study is their aggregation
character implied by splitting or broadening of the redox waves. In
most cases, it was not possible to identify the nature of redox pro-
cesses and also to understand possible aggregation effects on these
processes with great detail on the basis of electrochemical measure-
ments alone. For this reason, in situ spectroelectrochemical mea-
surements during the controlled-potential electrolysis of the
Fig. 5. Cyclic and square wave (inset) voltammograms of 4 at 0.050 V sꢁ1 scan rate in
DMSO/TBAP.
3.2. Electrochemistry and in situ spectroelectrochemistry
Redox properties of the Pc compounds (4e8) were studied by
cyclic voltammetry and square wave voltammetry on platinum
working electrode in DMSO/TBAP. Table 1 lists the half-peak po-
tentials (E1/2), the peak to peak potential separations (
difference between the first oxidation and reduction processes
E1/2). Pc compounds undergo one-electron reduction and one-
electron oxidation to yield the anion and cation radicals.
DEp), and the
(D
Fig. 6. Cyclic and square wave (inset) voltammograms of 5.0 ꢀ 10ꢁ4 M 5 in DMSO/TBAP (A) and in situ UVevis spectral changes monitored during the controlled-potential
electrolysis of 5 in DMSO/TBAP at (B) ꢁ0.95 V, (C) ꢁ1.25 V and (D) 0.85 V vs. SCE.

76
G. Dede et al. / Journal of Organometallic Chemistry 740 (2013) 70e77
complexes at suitable potentials were also carried out to provide
additional support for the assignment of redox processes and the
identification of possible aggregation effects.
around 542 nm appears (Fig. 6C). These spectral changes, accom-
panied by the formation of well-defined isosbestic points, corre-
spond to the second ring reduction with the formation of [Zn(II)
Pc(ꢁ4)]2ꢁ dianion species. During the oxidation at 0.85 V vs. SCE,
the absorption of all bands decreases without formation of a new
band which is attributed to the decomposition of the complex
immediately after the ring oxidation (Fig. 6D). This is an expected
observation due to the high positive oxidation potential.
Although the shape of the voltammetric peaks of 5 in Fig. 6A
appears as if the redox processes are associated with the aggrega-
tion phenomenon, our observations during in situ spectroelec-
trochemical measurements did not indicate the coupling of the
redox processes by aggregationedeaggregation transformations
(Fig. 6BeD). This can be attributed to the fact that in situ UVevis
spectroelectrochemical measurements was carried out relatively
dilute solutions, in comparison with the voltammetric measure-
ments. The spectral changes observed when the working electrode
was polarized at ꢁ0.95 V vs. SCE are shown in Fig. 6B. The sharp Q-
band absorption at 684 nm in the spectrum monitored at the
beginning of the electrolysis at the constant potential is indicative
of the absence of aggregated species. During the first reduction
process, the Q band absorption at 684 nm, and the broad B band
absorption at about 375 nm decreases while a new absorption band
appears at 580 nm. These spectral changes, accompanied by the
formation of well-defined isosbestic points can be attributed to the
Fig. 7A shows the cyclic voltammogram of CoPc (7). The complex
gives two one-electron reductions and a one-electron oxidation.
The DEp parameter of the redox couples takes the values within the
range of 0.060e0.080 V at 0.050 V sꢁ1 scan rate, indicating
reversible or quasi-reversible character of electron transfer pro-
cesses. The unity of the peak current ratios (Ipa/Ipc for reductions
and Ipc/Ipa for oxidation) with the scan rate and linear changes of
peak currents with the square root of scan rate for the redox cou-
ples indicated purely diffusion-controlled electron transfer mech-
anism for these processes. Metal center in 7 probably prefers six-
coordination and thus binds donor DMSO molecules. It is known
that six coordinate MPc species generally do not aggregate since
they are kept apart by the axially bound ligands [31]. Redox po-
tentials of 7 are considerably different as compared with those of
ring-based reduction of disaggregated species of
5 [40e43].
Therefore, the R10 and R1 couples of 5 in Fig. 6A can be attributed to
the Pc ligand-based reduction processes. During the second
reduction with ꢁ1.25 V potential application, the absorption of the
main Q band continues to decrease without shift, while a new band
the other Pc compounds (Table 1). DE1/2 value of 7, 0.84 V, is low in
comparison with those of 4, 5, 6, and 8. Thus, it is reduced and
oxidized more easily than the others. This distinctive behavior of 7
Fig. 7. Cyclic and square wave (inset) voltammograms of 5.0 ꢀ 10ꢁ4 M 7 in DMSO/TBAP (A) and in situ UVevis spectral changes monitored during the controlled-potential
electrolysis of 7 in DMSO/TBAP at (B) ꢁ0.53 V, (C) ꢁ1.50 V and (D) 0.50 V vs. SCE.

G. Dede et al. / Journal of Organometallic Chemistry 740 (2013) 70e77
77
can be attributed to the fact that Co(II) center has accessible
d orbital levels lying between the HOMO and LUMO gap of the Pc
species, then metal center can be oxidized and reduced before the
ring-based redox processes. However, this type of Pc complexes can
vary their electrochemical behavior according to their environ-
ment, depending on whether there are any available coordinating
species that would stabilize the Co(II) center. The main difference
lies in whether the metal or the ring is oxidized first. Donor solvents
strongly favor Co(III)Pc(ꢁ2) by coordinating along the axis to form
six coordinate species. If such donor solvents are absent, then
oxidation to Co(III) is inhibited and ring oxidation occurs first. Thus,
the first oxidation and the first reduction processes of 7 are prob-
ably metal-based and correspond to Co(II)Pc(ꢁ2)/[Co(III)Pc(ꢁ2)]þ
and Co(II)Pc(ꢁ2)/[Co(I)Pc(ꢁ2)]ꢁ redox couples, respectively, since
the voltammetric measurements were carried out in DMSO/TBAP.
On the other hand, it is also well known from the literature that the
other reduction processes and the second oxidation process are
ring-based [31,32]. Spectroelectrochemical measurements were
also carried out to assign especially the first reduction and the first
oxidation processes of 7 certainly. Fig. 7B represents in situ UVevis
spectral changes during the first reduction of 7 at ꢁ0.53 V vs. SCE,
corresponding to the redox process labeled R1 in Fig. 7A. The Q
band at 669 nm shifts to 710 nm, while new band at 476 nm ap-
pears. The spectral changes have well-defined isosbestic points at
415, 561 and 695 nm. The band at 476 nm and the shifting of the Q
band indicate the formation of [Co(I)Pc(ꢁ2)]ꢁ species, confirming
the CV assignment of the couple R1 to Co(II)Pc(ꢁ2)/[Co(I)Pc(ꢁ2)]ꢁ
process [33e36,42e45]. During the second reduction at ꢁ1.50 V vs.
SCE, the Q band at 710 nm decreases without shift and the ab-
sorption between 500 and 600 nm increases (Fig. 7C). These
spectral changes at the potential of the couple R2 are characteristics
for a ring-based reduction in Co(II)Pc complex and confirm the
voltammetric assignment of this process to [Co(I)Pc(ꢁ2)]ꢁ/[Co(I)
Pc(ꢁ3)]2ꢁ. Fig. 7D displays in situ UVevis spectral changes during
the first oxidation process. The Q band at 669 nm increases in in-
tensity with red shift to 676 nm. The increase of the Q band with
red shift is typical of a metal-based oxidation in CoPc complexes
and thus, confirms the CV assignment of Co(II)Pc(ꢁ2)/[Co(III)
Pc(ꢁ2)]þ for couple O1 of 7 in Fig. 7A [33e36,42e45].
University Scientific Research Project Coordination Unit (BAPKO)
(Project No: FEN-C-YLP-050413-0035) and The Turkish Academy of
Sciences (TUBA) for their financial support.
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Acknowledgments
The authors thank to The Research Fund of Karadeniz Technical
University, Project 2010.111.002.8. (Trabzon/Turkey), Marmara