Synthesis, characterization and catalytic activity of peripherally tetra-substituted Co(II) phthalocyanines for cyclohexene oxidation

Article abstract of DOI:10.1002/aoc.2939

New 3,3-diphenylpropoxyphthalonitrile (5) was obtained from 3,3-diphenylpropanol (3) and 4-nitrophthalonitrile (4) with K₂CO ₃ in DMF at 50 °C. The novel cobalt(II) phthalocyanine complexes, tetrakis-[2-(1,4-dioxa-8-azaspiro[4.5]dec-

Full text of DOI:10.1002/aoc.2939

Full Paper
Received: 15 August 2012
Revised: 12 September 2012
Accepted: 1 October 2012
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.2939
Synthesis, characterization and catalytic
activity of peripherally tetra-substituted Co(II)
phthalocyanines for cyclohexene oxidation
Ece Tugba Sakaa, Zekeriya Biyiklioglua, Halit Kantekina* and İbrahim Kanib
New 3,3-diphenylpropoxyphthalonitrile (5) was obtained from 3,3-diphenylpropanol (3) and 4-nitrophthalonitrile (4) with
K2CO3 in DMF at 50 ꢀC. The novel cobalt(II) phthalocyanine complexes, tetrakis-[2-(1,4-dioxa-8-azaspiro[4.5]dec-8-yl)ethoxy]
phthalocyaninato cobalt(II) (2) and tetrakis-(3,3-diphenylpropoxy)phthalocyaninato cobalt(II) (6) were prepared by the reac-
tion of the phthalonitrile derivatives 1 and 5 with CoCl2 by microwave irradiation in 2-(dimethylamino)ethanol for at
175 ꢀC, 350 W for 7 and 10 min, respectively. These new cobalt(II)phthalocyanine complexes were characterized by spectro-
scopic methods (IR, UV–visible and mass spectroscopy) as well as elemental analysis. Complexes 2 and 6 are employed as
catalyst for the oxidation of cyclohexene using tert-butyl hydroperoxide (TBHP), m-chloroperoxybenzoic acid (m-CPBA),
aerobic oxygen and hydrogen peroxide (H2O2) as oxidant. It is observed that both complexes can selectively oxidize cyclohex-
ene to give 2-cyclohexene-1-ol as major product, and 2-cyclohexen-1-one and cyclohexene oxide as minor products. TBHP was
found to be the best oxidant since minimal destruction of the catalyst, higher selectivity and conversion were observed in the
products. Copyright © 2012 John Wiley & Sons, Ltd.
Keywords: phthalocyanine; cobalt; phthalonitrile; cyclohexene; oxidation; tert-butyl hydroperoxide
Of the variety of ligands employed so far, noteworthy examples
Introduction
include porphyrin derivatives, macrocyclic compounds, phthalocya-
nine, and Schiff base.[12–15] Among these substrates, phthalocyanine
Metalloporphyrin complexes are well known for their ability to
transition metal complexes are attractive oxidation catalysts and
can be prepared simply and cheaply for industrial applications. The
catalytic oxidation of cyclohexene is attracting attention because its
oxidation products (e.g. 2-cyclohexen-1-one, 2-cyclohexen-1-ol, ep-
oxide) are very useful synthetic intermediates.[16] Synthetic metallo-
porphyrins, which are used as models of cytochrome P-450, are
highly efficient homogeneous and heterogeneous catalysts for
cyclohexene oxidation by various oxidants such as iodosylben-
zene,[17] hydrogen peroxide and tert-butyl hydroperoxide.[18] The
aerobic oxidation of olefins catalyzed by metalloporphyrins and
metallophthalocyanines is gaining interest from economic and envi-
ronmental viewpoints.[19] Additionally, cobalt(II) phthalocyanine
complexes have been applied as catalysts for selective oxidation of
olefins.[20] The oxidation of products such as aldehyde, ketones and
alcohols is widely used in chemical industries and in the academic
field. The oxidation products of cyclohexene studied in this work
are 2-cyclohexen-1-one, 2-cyclohexene-1-ol and cyclohexene ox-
ide. These products are of great importance to industrial processes
as well as fine chemical syntheses. Phthalocyanines with different
peripheral groups (especially electron-attracting groups such as halo-
genated, phenyl groups) have been largely studied for their ability in
oxidation of cyclohexene.[21]
actualize a wide range of oxidation reactions in homogeneous
systems. These complexes, acting like cytochrome P-450 depen-
dent monooxygenases, catalyze the oxidation of the relatively inert
carbon–hydrogen bond under mild conditions.[1–4] Catalytic activi-
ties of metallophthalocyanines derived from their structural similar-
ity to metallo-porphyrin complexes have been widely studied
because of their rather cheap and facile preparation on a large scale
and their chemical and thermal stability. Metallophthalocyanines
exhibit a wide range of applications in various areas such as semi-
conductors, nonlinear optics, electrochromic display devices and
liquid crystals.[5]
In particular, cobalt(II) phthalocyanines (CoPc) are habitually
utilized in the fields of gas and radiation sensors, optoelectronics,
oxidation processes and in medical applications. At the present
time, CoPc is regarded as an object for the development of
low-dimensional molecular magnets. Molecular magnets are
regarded as possible candidates for potential applications in
high-density information storage and quantum computers. Such
prospective applications give a strong motivation to characterize
and study the electronic structure and morphology of cobalt(II)
phthalocyanine thin films since these determine the performance
of devices. Moreover, the accurate assignment of the valance
band and empty-state electronic features is of central importance
for the profound understanding of this material and its interfaces
with different substances.[6–10]
*
Correspondence to: H. Kantekin, Department of Chemistry, Karadeniz Technical
University, 61080 Trabzon, Turkey. E-mail: halit@ktu.edu.tr
Transition metal complexes as catalysts for the oxidation of
cyclohexene have attracted much attention in recent years, mainly
for the oxidation products of cyclohexene, and the derivatives pres-
ent highly reactive carbonyl groups in cycloaddition reactions.[11]
a Department of Chemistry, Karadeniz Technical University, 61080Trabzon, Turkey
b Department of Chemistry, Anadolu University, 26470Eskişehir, Turkey
Appl. Organometal. Chem. 2013, 27, 59–67
Copyright © 2012 John Wiley & Sons, Ltd.

E. T. Saka et al.
Co(II) phthalocyanines are readily available oxidation catalysts
and found to transfer oxygen from various oxygen donors to
alkanes, alkenes, phenols and thiols in numerous studies.[15,22–33]
Herein we report the synthesis and characterization of 4-[2-
(1,4-dioxa-8-azaspiro[4.5]dec-8-yl)ethoxy] and 3,3-diphenylpropoxy
group-substituted Co(II) phthalocyanines 2 and 6. We also report
on the use of complexes 2 and 6 as catalysts for the oxidation of
cyclohexene, with the aim of improving product selectivity and
increasing the range of products, and compare their catalytic activity.
(Ar&bond;C3), 116.01 C14&tbond;N, 115.54 C15&tbond;N, 107.40
(Ar&bond;C4), 67.52 (C7), 47.36 (C9), 34.59 (C8). MS (ES+), (m/z): 380
[M+ Na + H2O + H]+. C23H18N2O: calcd C 81.63; H 5.36; N 8.28 %;
found C 82.01; H 5.61; N 8.91.
Tetrakis-(3.3-diphenylpropoxy)phthalocyaninato cobalt(II) (6)
4-(3,3-Diphenylpropoxy)phthalonitrile (5) (0.3 g, 0.88 mol) and
anhydrous CoCl2 (0.057 g, 0.44 ꢁ 10ꢂ3 mol) were added in
2-(dimethylamino)ethanol (DMAE) (0.003L). The mixture was then
irradiated in a microwave oven at 175ꢀC, 350 W, for 10 min. After
cooling to room temperature the reaction mixture was refluxed
with ethanol (0.04 L) to precipitate the product, which was filtered
off. The dark-blue solid product was washed with hot ethanol,
diethyl ether and dried in vacuo. The blue crude product was
purified by column chromatography on aluminium oxide using
CHCl3:CH3OH (8:2) as eluent. The obtained solid was dried under
vacuum over P2O5. Yield 0.160 g (48%); m.p. > 300 ꢀC. IR (KBr tablet)
Experimental
Materials
All reactions were carried out under a dry nitrogen atmosphere using
standard Schlenk techniques. All chemicals, solvents and reagents
were of reagent grade quality and were used as purchased from
commercial sources. All solvents were dried and purified as
described by a reported procedure.[34] 4-Nitrophthalonitrile,[35]
3,3-diphenylpropanol (3)[36] and 4-[2-(1,4-dioxa-8-azaspiro[4.5]
dec-8-yl)ethoxy]phthalonitrile (1)[37] were synthesized according to
the literature.
n
max/cmꢂ1: 3058 (Ar&bond;H), 2924–2850 (aliph. C&bond;H), 1606,
1523, 1489, 1463, 1410, 1342, 1279, 1229, 1185, 1059, 1020, 958,
844, 821. UV–visible (DMF), lmaks (log e)nm: 329 (4.99), 607 (4.52),
667 (5.04). MS (ES+); (m/z): 1518 [M + K + 3Na]+. C92H72N8O4Co:
calcd C 78.23; H 5.14; N 7.93 %; found C 77.90; H 5.49; N 8.17.
Tetrakis-[2-(1,4-dioxa-8-azaspiro[4.5]dec-8-yl)ethoxy]phthalocyaninatocobalt(II) (2)
Equipment
4-[2-(1,4-Dioxa-8-azaspiro[4.5]dec-8-yl)ethoxy]phthalonitrile (1)
(0.6g, 1.91 mol) and anhydrous CoCl2 (0.124g, 0.95 ꢁ 10ꢂ3 mol)
were added to 2-(dimethylamino)ethanol (DMAE) (0.006 L). The
mixture was then irradiated by microwave oven at 175ꢀC, 350W,
for 7 min. After cooling to room temperature the reaction mixture
was refluxed with ethanol (0.04 L) to precipitate the product, which
was filtered off. The dark-blue solid product was washed with
hot ethanol and diethyl ether and dried in vacuo. The blue crude
product was purified by column chromatography on aluminium
oxide using CHCl3:CH3OH (9:1) as eluent. The obtained solid was
dried under vacuum over P2O5. Yield 0.27 g (45%); m.p. > 300 ꢀC.
IR (KBr tablet) nmax/cmꢂ1: 3044 (Ar&bond;H), 2926–2878 (aliph.
C&bond;H), 1607, 1522, 1466, 1408, 1339, 1310, 1281, 1233, 1142,
1125, 1090, 963, 911, 820, 750, 666. UV–visible (DMF), lmaks (log e)
nm: 326 (4.94), 608 (4.54), 664 (5.04). MS (ES+); (m/z): 1312 [M]+.
C68H76N12O12Co: calcd C 62.24; H 5.84; N 12.81 %; found C 61.77;
H 5.39; N 11.83.
FT-IR spectra were obtained on a PerkinElmer 1600 FT-IR spectropho-
tometer with the samples prepared as KBr pellets. Optical spectra in
the UV–visible region were recorded with a PerkinElmer Lambda 25
spectrophotometer. 1 H and 13C NMR spectra were recorded on a
Varian Mercury 200 MHz spectrometer in CDCl3, and chemical shifts
were reported (d) relative to Me4Si as internal standard. Mass spectra
were recorded on a Micromass Quatro LC/ULTIMA LC-MS/MS
spectrometer. Elemental analyses were performed on a Costech
ECS 4010 instrument. Melting points were measured on an electro
thermal apparatus. A domestic microwave oven was used for all syn-
theses of phthalocyanines. Agilent Technologies 7820A equipment
(30 m ꢁ 0.32 mm ꢁ 0.50 mm DB Wax capillary column, FID detector)
was used for gas chromatographic measurements.
Synthesis
4-(3,3-Diphenylpropoxy)phthalonitrile (5)
General procedure for the oxidation of cyclohexene
3,3-Diphenylpropanol (3) (1g, 4.71 ꢁ 10ꢂ3 mol) was dissolved in
dry DMF (0.04 L) under N2 atmosphere and 4-nitrophthalonitrile
(4) (0.816 g, 4.71 ꢁ 10ꢂ3 mol) was added to the solution. After
stirring for 10 min, finely ground anhydrous K2CO3 (1.94 g,
0.12 mol) was added portion-wise within 2 h with efficient stirring.
The reaction mixture was stirred under N2 at 50 ꢀC for 3 days. The
solution was then poured into ice-water (0.1L). The precipitate
formed was filtered off, washed first with water until the filtrate
was neutral and then with diethyl ether and dried under vacuum
over P2O5. The crude product was recrystallized from methanol.
Experiments were carried out in a thermostated Schlenk vessel
equipped with a condenser and stirrer. The solution of cyclohexene
and catalyst in solvent was purified with bubbling nitrogen gas to
remove the oxygen. A mixture of cyclohexene (0.76 ꢁ 10ꢂ3 mol),
catalyst (3.81ꢁ 10ꢂ6 mol) and solvent (0.01L) was stirred in a
Schlenk vessel for few minutes at room temperature. The oxidant
TBHP (1.90 ꢁ 10ꢂ3 mol) was then added and the reaction mixture
was stirred for the desired time. The samples (0.005 L) were taken
at certain time intervals. Each sample was injected at least
twice in the gas chromatograph, 1 mL each time. Formation of
products and consumption of substrates were monitored by gas
chromatography (GC).
Yield 1.20 g (75%); m.p. 134–135 ꢀC. IR (KBr tablet) nmax/cmꢂ1
:
3056 (Ar&bond;H), 2943–2870 (aliph. C&bond;H), 2227 (C&tbond;
N), 1598, 1503, 1473, 1453, 1395, 1320, 1256, 1206, 1168, 1088,
1018, 942, 852, 829, 754, 696, 572, 524. 1 H NMR (CDCl3), (d: ppm):
7.70 (d, 1 H, J = 8.5Hz, Ar&bond;H5), 7.30–7.10 (m, 12 H, Ar&bond;
H), 4.23 (t, 1 H, J = 7.8Hz, CH&bond;CH2), 4.00 (t, 2 H, J = 6.3Hz,
CH2&bond;O), 2.62 (m, 2 H, CH2&bond;CH2). 13C NMR. (CDCl3),
(d: ppm): 162.18 (Ar&bond;C1), 143.77 (Ar&bond;C10), 135.45
(Ar&bond;C5), 129.01 (Ar&bond;C12), 128.00 (Ar&bond;C11), 126.96
(Ar&bond;C13), 119.78 (Ar&bond;C6), 119.59 (Ar&bond;C2), 117.62
Results and Discussion
Synthesis and Characterization
The synthetic routes to novel peripherally tetra-substituted cobalt(II)
phthalocyanines 2 and 6 are shown in Figs 1 and 2. The phthalonitrile
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Copyright © 2012 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2013, 27, 59–67

Synthesis and catalytic activity of cobalt phthalocyanines
CN
CN
CN
CN
O
O
O
i
OH
O
O
N
N
1
O2N
ii
O
O
O
O
N
N
O
O
N
N
N
N
Co
N
N
N
N
O
2
O
N
N
O
O
O
O
Figure 1. Synthesis of cobalt(II) phthalocyanine 2. (i) Dry K2CO3, dry DMF, 50 ꢀC. (ii) 2-(Dimethylamino)ethanol, microwave oven (MW), 175ꢀC, 350W, CoCl2
derivatives 1[37] and 5 were obtained via a based-catalyzed (K2CO3)
nucleophilic aromatic substitution reaction. Cyclotetramerization
of 1 and 5 occurred in the presence of CoCl2 to form the desired
complexes: 2 and 6, respectively. All of these new cobalt phthalocya-
nines were purified by column chromatography with aluminum
oxide as adsorbent. They were obtained in a yield of 48% for 2 and
45% for 6 and were characterized by spectral data (IR, UV–visible
spectroscopy, mass spectral data and elemental analysis). The
characterization data of the new compounds are consistent with
the assigned formula.
The IR spectra clearly indicate the formation of compound 5 with
the appearance of absorption bands at 2227 cmꢂ1 (C&tbond;N). In
the 1 H NMR spectra of compound 5 aromatic protons appear at
7.70 (d, 1 H, J = 8.5Hz, Ar&bond;H5), 7.30–7.10 (m, 12 H, Ar&bond;
H), and aliphatic protons appear at 4.23 (t, 1 H, J = 7.8 Hz,
CH&bond;CH2), 4.00 (t, 2 H, J = 6.3Hz, CH2&bond;O), 2.62 (m, 2 H,
CH2&bond;CH2) ppm. The 13C NMR spectra of compound 5 indicated
aromatic carbon atoms between 162.18 and 107.40 ppm. Also nitrile
carbon atoms for compound 5 were observed (116.01, 115.54 ppm).
In the mass spectra of compound 5 the presence of molecular ion
peak at m/z= 380 [M+Na+H2O+H]+ confirmed the proposed
structures. The results of elemental analysis also confirmed the
structure of compound 5.
of molecular ion peaks at m/z 1312 [M]+ and 1518 [M + K + 3Na]+,
respectively, confirmed the proposed structures. The results of ele-
mental analysis also confirmed the structure of complexes 2 and 6.
The metallophthalocyanines display typical electronic spectra
with two strong absorption regions: one of them in the UV region
at about 300–350 nm (B band) and the other in the visible region
at 600–700 nm (Q band).[38] The electronic absorption spectra of
cobalt phthalocyanines 2 and 6 in DMF at room temperature
are shown in Fig. 3. UV–visible spectra of cobalt phthalocyanine
2 (in DMF) split Q bands appeared at 664 and 608 nm, while
the split B band remained at 326 nm. UV–visible spectra of cobalt
phthalocyanine 6 (in DMF) exhibited an intense single Q band
absorption of p ! p* transitions around 667–607 nm and B band
in the UV region around 329 nm.[39]
Catalytic Studies
Oxidation of cyclohexene with 2 and 6
The catalytic activity and selectivity of 2 and 6 have been studied
for the oxidation of cyclohexene with TBHP as the model com-
pound under similar experimental conditions in DMF (Tables 1–4).
In a typical catalytic reaction, a Schlenk tube was charged with
cyclohexene (0.76ꢁ 10ꢂ3 mol), complex 2 (3.81 ꢁ 10ꢂ6 mol) or
complex 6 (3.53 ꢁ 10ꢂ6 mol) and TBHP (1.90 ꢁ 10ꢂ3 mol) in DMF
(0.01 L) and refluxed at 90ꢀC with 900 rpm stirring. Control experi-
ments show that cyclohexene oxidation with TBHP, m-CPBA
and H2O2 did not occur in the absence of catalyst under the same
reaction conditions, confirming that the catalyst plays a prominent
After conversion into cobalt phthalocyanine derivatives, the char-
acteristic C&tbond;N stretch at 2231 cmꢂ1 for 1 and 2227 cmꢂ1 for
5 disappeared in the IR spectra, indicative of metallophthalocyanine
formation. The 1 H NMR spectra of cobalt phthalocyanines 2 and 6
could not be taken due to the paramagnetic cobalt(II) centers. In
the mass spectrum of cobalt phthalocyanines 2 and 6, the presence
Appl. Organometal. Chem. 2013, 27, 59–67
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E. T. Saka et al.
14
CN
5
4
15
CN
13
11
6
3
1
12
2
7
CN
CN
O
i
10
OH
9
8
5
O2N
4
3
ii
O
O
N
N
N
N
N
Co
N
N
N
O
6
O
Figure 2. Synthesis of cobalt(II) phthalocyanine 6. (i) Dry K2CO3, dry DMF, 50 ꢀC. (ii) 2-(Dimethylamino)ethanol, MW, 175 ꢀC, 350 W, CoCl2
which are evidently identified using GC by both spiking and
comparison with standards (Fig. 4). In order to obtain maximum
conversion of cyclohexene, the catalytic reactions were carried
out varying the reaction temperature, time and different oxidants
and substrate/catalyst ratio.
The results of the catalytic oxidation of cyclohexene by TBHP in
the presence of 2 and 6 are shown in Fig. 5(a) and (b), respec-
tively, which shows the variation of product yield with reaction
time. A higher yield was obtained for cyclohexenol than
cyclohexenone and cyclohexene epoxide for both catalysts. The
yields for cyclohexenone and cyclohexene epoxide were similar
for catalysts 2 and 6. The yield of the three products increased,
but leveled off with time. This level-off was most likely due to
the degradation of the CoPc catalyst by oxidant with time.
To examine the effect of substrate to cobalt, the molar ratio
was carried out in the range of 200–800, while other parameters
Figure 3. UV–visible spectrum in DMF for complexes 2 and 6
were kept constant. The experimental conditions were 90 ꢀC,
1.90 ꢁ 10ꢂ3 mol TBHP and 0.01 L DMF for 3 h. The results are
role in the oxidation process. As shown in Tables 1–4, comparative
studies of the catalytic activity of 2 and 6 for oxidation of cyclohex-
ene revealed that both complexes are active catalysts in DMF. The
oxidation reactions gave cyclohexenol as the main product and
2-cyclohexen-1-one and cyclohexene epoxide in small yields,
shown in Table 1. As expected, with a decrease of the substrate
catalyst molar ratio the reaction rate increased. At each different
substrate/catalyst ratio the oxidation of cyclohexene gave the
same main product (2-cyclohexene-1-ol) with a selectivity of
~60% and 65% for 2 and 6, respectively.
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Synthesis and catalytic activity of cobalt phthalocyanines
Table 1. Effect of amount of substrate on cyclohexene oxidation with complexes 2 and 6
Catalyst
Subs./cat.
200/1
Alcohola
Ketoneb
Epoxidec
Tot. conv. (%)
TONd
TOFe (hꢂ1
)
2
6
2
6
2
6
2
6
2
6
2
6
55
67
53
60
48
56
46
52
39
38
28
24
16
15
24
15
22
15
20
15
17
12
12
10
11
15
11
14
11
14
11
14
9
92
98
88
90
81
85
77
81
65
63
47
45
179
184
257
255
315
319
374
378
388
376
375
358
71
73
300/1
400/1
500/1
600/1
800/1
102
102
126
127
149
151
129
125
125
119
13
7
11
a2-Cyclohexen-1-ol.
b2-Cyclohexen-1-one.
cCyclolohexene oxide.
dTON, moles of product/moles of catalyst.
eTOF, moles of product/moles of catalyst ꢁ time.
Conversion was determined by GC.
Table 2. Effect of different oxidants on cyclohexene oxidation with complex 2
Catalyst
Oxidant
TBHP
Alcohola
Ketoneb
Epoxidec
Total conv. (%)
TONd
TOFe (hꢂ1
)
2
6
2
6
2
6
2
6
53
67
46
39
49
18
—
—
24
16
15
20
19
16
—
—
11
15
7
88
90
68
73
80
45
—
—
263
270
203
219
239
135
—
87
90
67
73
79
45
—
—
H2O2
14
12
11
—
—
m-CPBA
Free oxidant
—
a2-Cyclohexen-1-ol.
b2-Cyclohexen-1-one.
cCyclolohexene oxide.
dTON, moles of product/moles of catalyst.
eTOF, moles of product/moles of catalyst ꢁ time.
Conversion was determined by GC.
The effect of oxygen source on the reaction rate of cyclohexene
oxidation was investigated for TBHP, m-CPBA, aerobic oxygen
and H2O2. With the exception of the oxidant, all experimental
conditions were kept constant for the catalytic reactions. The
data are given in Table 2 and Fig. 6. There was no conversion
for both complexes when the aerobic oxygen was used as
oxidant. The results showed that 2 and 6 exhibit significantly
higher activity with TBHP than with the other studied oxidants.
The control experiment showed that the cyclohexene was not
oxidized in the absence of oxidant. We observed that the
selectivity of 2-catalyzed oxidation was not dependent on the
nature of the oxidant, but in the case of 6 the selectivity of
alcohol decreased while the selectivity of epoxide increased.
The substrate-to-oxidant ratio is another important parameter
influencing the results of this oxidation reaction. The effect of
oxidant/catalyst ratio on the rate of cyclohexene was also
studied in the range of 300/1–900/1 (Table 3). The rate of the
reaction increased with increasing oxidant/catalyst ratio up to
500/1. Further increase in this ratio led to decreased conversion.
It is difficult to explain the oxidant effect at this stage, but it is
possible that the coordination around the cobalt ion may
change and produce inactive intermediate species.
Investigation into the effect of the reaction temperature on the
oxidation of cyclohexene with 2 and 6 showed that as the reac-
tion temperature was raised the catalyst activity increased, but
2-cyclohexen-1-ol selectivity was barely affected. The experi-
ments were conducted in the temperature range 25–90 ꢀC, with
oxidant/substrate/catalyst = 500/200/1 and TBHP, in DMF, over
3 h (Table 4). The overall conversion was increased 50% when
the temperature was raised from 25 to 90 ꢀC. The highest conver-
sion (92%) was obtained with TOF = 72 for complex 2 and (98%)
and with TOF = 64 for complex 6 at 90 ꢀC.
Appl. Organometal. Chem. 2013, 27, 59–67
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E. T. Saka et al.
Table 3. Effect of amount of oxidant on cyclohexene oxidation with complexes 2 and 6
Catalyst
Oxidant/catalyst
300/1
Alcohola
Ketoneb
Epoxidec
Tot. conv. (%)
TONd
TOFe (h-1)
2
6
2
6
2
6
2
6
2
6
43
51
46
53
53
60
45
50
29
39
16
15
18
16
24
15
22
20
19
17
8
12
9
67
78
72
82
88
90
79
80
58
65
200
231
215
243
263
264
236
234
173
195
66
92
71
81
87
88
78
78
28
65
400/1
500/1
600/1
900/1
13
11
14
12
10
10
9
a2-Cyclohexen-1-ol.
b2-Cyclohexen-1-one.
cCyclolohexene oxide.
dTON, moles of product/moles of catalyst.
eTOF, moles of product/moles of catalyst ꢁ time.
Conversion was determined by GC.
Table 4. Effect of temperature on cyclohexene oxidation with complexes 2 and 6
Catalyst
T (ꢀC)
Alcohola
Ketoneb
Epoxidec
Tot. conv. (%)
TONd
TOFe (hꢂ1
)
2
6
2
6
2
6
2
6
25
29
27
52
53
53
64
55
67
19
13
25
13
26
16
26
16
3
9
51
49
86
78
90
95
92
98
89
97
35
32
59
51
63
63
72
64
50
70
90
9
149
154
159
188
181
194
12
11
15
11
15
a2-Cyclohexen-1-ol.
b2-Cyclohexen-1- one.
cCyclolohexene oxide.
dTON, moles of product/moles of catalyst.
eTOF, moles of product/moles of catalyst ꢁ time.
Conversion was determined by GC.
O
OH
Oxidant
Catalyst (MPc)
O
Cyclohexene
cyclohexene oxide
2-cyclohexen-1-one
2-cyclohexen-1-ol
Figure 4. Product formed through oxidation of cyclohexene by TBHP, m-CPBA and H2O2 in the presence of complexes 2 and 6
As shown in Table 5, the performance of the Co-Pc catalysts 2 and
6 towards the cyclohexene oxidation was better compared to some
other MPc and M-porphyrin catalysts (like Fe, Zn, Cu and Mn). We
obtained the best reported results in terms of TOF in the literature
for homogeneous oxidation of cyclohexene with TBHP in the pres-
ence of Co-Pc.
catalytic mechanism for the Co-catalyzed cyclohexene oxidation.
The spectra of cobalt(II) phthalocyanines has been the subject of
several reports.[15,40–50] The spectrum of metal–phthalocyanine
(MPc) complexes is well known and consists of an intense band,
called the Q band, in the visible region.[51] The spectrum in Figs 7
and 8 show the typical spectrum of monomeric form of CoPc with
a Q band at 664 (for 2) and 667nm (for 6) and also the electronic
spectral changes of both catalysts during the course of the catalytic
The oxidation system was further examined by UV–visible
spectroscopy during the processes in order to investigate the
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Appl. Organometal. Chem. 2013, 27, 59–67

Synthesis and catalytic activity of cobalt phthalocyanines
Figure 5. Time-dependent conversion of cyclohexene oxidation with TBHP as an oxidant (a) for catalyst 2 and (b) for catalyst 6
MPc catalysts in homogeneous catalysis. The decomposition of
the phthalocyanine complex during the oxidation of cyclohexene
is probably a result of the attack of the phthalocyanine ring by
the ROꢃ and ROOꢃ radicals which are produced from TBHP. The
color of the solution changed from blue to green as catalysis pro-
gressed. However, the reaction products continued to form even
after the catalyst had turned yellow, suggesting that once
reaction intermediates are formed the reaction can still proceed
in the presence or absence of the original form of the catalyst.
Conclusion
We have presented the synthesis and characterization of new
peripherally tetra-substituted Co(II) phthalocyanines 2 and 6
using spectroscopic methods. The target symmetrical Co(II)
phthalocyanines 2 and 6 were separated by column chromatog-
raphy and characterized by a combination of UV–visible, IR,
1 H NMR, 13C NMR, mass spectroscopic data and elemental analy-
sis. This work has determined catalytic activities of Co(II) phthalo-
cyanines 2 and 6 on cyclohexene oxidation. There are few reports
about catalytic studies for Co(II) phthalocyanines. The results
show that cyclohexene was converted to 2-cyclohexene-1-ol as
a major product, and 2-cyclohexen-1-one and cyclohexene oxide
as minor products, with 92% and 98% with 2 and 6 respectively,
within 3 h with TBHP in DMF at 90 ꢀC. The most promising obser-
vation is that cyclohexenol is found to be the major product in all
Figure 6. Oxidant effect on cyclohexene oxidation
reaction in the presence of TBHP. The Q band shifted to 672 and
671 nm for complexes 2 and 6, respectively, with a decrease in
intensity of the Q band without any new band being formed. The
shift in the Q band is consistent with metal oxidation of Co(II)-Pc
to Co(III)-Pc.[30] There is no peak around 480 nm, suggesting ring
oxidation. Thus addition of TBHP to solutions of Co-Pc resulted in
only metal and not ring oxidation of Co-Pc. As catalysis progressed
there was a gradual decrease in the intensity of the Q band of the
Co-Pc catalyst, suggesting catalyst degradation, as is typical[22] of
Appl. Organometal. Chem. 2013, 27, 59–67
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E. T. Saka et al.
Table 5. Catalytic activities towards the homogeneous oxidation of cyclohexene of some previously reported catalysts
Catalyst
Relaxation time (h)
24
Relaxation temp. (ꢀC)
rtg
Oxidant
O2
Conv. (%)
Ref.
52
a
Mn(tbpcH2
)
~45
~55
~30
89
a
Fe(tbpcH2
)
a
Co(tbpcH2
Fe(TMPb)Cl
Mn(PFTDCPPc)
MnTMpyP
FeTMpyP
)
10 min
25
nrh
rtg
m-CPBA
PhIO
53
54
55
3
93
16
PhIO
28
29
MoTMpyP
MnTTAPP
0
39
Cl16FePcd
8
nrh
75
TBHP
45.3
22
FePcd
CoPcd
Co[N^O]2 Cu[N^Oe]2
8
24
8
H2O2
O2
27.6
43.50
60
56
57
58
Cu(II)(L-prolinate)2
22
40
40
20
f
[Mn(Me2salpnMe2 )]
TBHP
50.9
42.7
36.9
23.8
91
f
[Co(Me2salpnMe2 )]
f
[Cu(Me2salpnMe2 )]
f
[Ni(Me2salpnMe2 )]
Co(salen)–POM
6
60
H2O2
59
atbpcH2, tetra-tert-butylphthalocyanine.
bTMP, meso-tetramesitylporphyrin.
cPFTDCPP, 5-(pentaflorophenyl)-10,15-20-tri(2,6-dichlorophenyl)porphyrin.
dPc, phthalocyanine.
eN^O, 2-pyrazinecarboxylic acid.
fMe2salpnMe2, N,N-bis-(a-methylsalicylidene)-2,2-dimethylpropane-1.
grt, room temperature.
hnr, not reported.
Figure 7. Time-dependent changes in the visible spectrum of the oxidized
complex 2 observed on addition of TBHP (1.90 ꢁ 10ꢂ3 mol) to a reaction
mixture containing 0.76 ꢁ 10ꢂ3 mol cyclohexene and 3.81ꢁ 10ꢂ6 mol
complex 2 catalyst in 10 ml: (b) 45 min; (c) 90min; (d) 135min; (e) 180min
after addition of TBHP. All spectra for the oxidized complex 2 were taken
after sixfold dilution with DMF. (a) Visible spectrum of (non-oxidized)
complex 2
Figure 8. Time-dependent changes in the visible spectrum of the oxidized
complex 6 observed on addition of TBHP (1.76ꢁ 10ꢂ3 mol) to a reaction
mixture containing 0.70ꢁ 10ꢂ3 mol cyclohexene and 3.53 ꢁ 10ꢂ6 mol
complex 6 catalyst in 10 ml: (b) 45min; (c) 90 min; (d) 135 min; (e) 180 min
after addition of TBHP. All spectra for the oxidized complex 6 were taken
after sixfold dilution with DMF. (a) Visible spectrum of (non-oxidized)
complex 6
of the catalytic tests. Substrate effect, temperature effect and
oxidant effect were also discussed in this work. Control experi-
ments performed without catalyst and the corresponding metal
salt as catalyst produced no products in the reaction mixture.
Mild reaction conditions, high yields of the products, short reac-
tion time and inexpensive reagents make this catalytic system a
useful oxidation method for cyclohexene.
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Synthesis and catalytic activity of cobalt phthalocyanines
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