New peripherally tetra-[trans-3,7-dimethyl-2,6-octadien-1-ol] substituted metallophthalocyanines: synthesis, characterization and catalytic activity studies on the oxidation of phenolic compounds

Article abstract of DOI:10.1080/00958972.2018.1423560

In this paper, we elucidated the synthesis, characterization, and investigation of catalytic activity studies of new metallophthalocyanines 4 and 5 as the catalyst for phenolic compounds oxidation by trying different types of oxygen sources. The structural characterization of the products was made by a combination of elemental analysis, FT-IR, LC-MS/MS (for phthalonitrile derivative?3), MALDI-TOF mass spectral data (for metallophthalocyanines 4–7), UV–vis spectroscopy (for metallophthalocyanines 4–7), ¹H NMR and ¹³C NMR spectroscopies (for compounds 3 and 6). The synthetic routes for the (trans-3,7-dimethyl-2,6-octadien-1-ol) substituted phthalonitrile derivative 3 and corresponding metallophthalocyanines 4–7 are outlined in Scheme 1. The MPc complexes 4–7 were synthesized via cyclotetramerization of compound 3 in the presence of the corresponding anhydrous metal salts (CoCl₂ for 4, CuCl₂ for 5, Zn(CH₃COO)₂ for 6 and MnCl₂ for 7) in dry n-pentanol as solvent and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as strong base at reflux temperature under nitrogen gas. Phthalocyanines and their metal complexes, in general, display poor solubility in most of the organic solvents, however, the synthesized metallophthalocyanine complexes 4–7 were highly soluble in common organic solvents because of the introduction of the methyl groups on alkyl chains of peripheral arms. The catalytic activity of compounds 4 and 5 was evaluated for the oxidation of phenolic compounds such as 4-nitrophenol, o-chlorophenol, 2,3-dichlorophenol, and p-methoxyphenol. CoPc 4 displayed good catalytic performance with a full oxidation of 4-nitrophenol into the corresponding benzoquinone and hydroquinone with the highest TON and TOF values within 3?h.

Full text of DOI:10.1080/00958972.2018.1423560

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
New peripherally tetra-[trans-3,7-
dimethyl-2,6-octadien-1-ol] substituted
metallophthalocyanines: Synthesis,
characterization and catalytic activity studies on
the oxidation of phenolic compounds
Halit Kantekin, Ece Tuğba Saka, Beytullah Ertem, Miraç Nedim Mısır, Halise
Yalazan & Gülbınar Sarkı
To cite this article: Halit Kantekin, Ece Tuğba Saka, Beytullah Ertem, Miraç Nedim Mısır, Halise
Yalazan & Gülbınar Sarkı (2018): New peripherally tetra-[trans-3,7-dimethyl-2,6-octadien-1-
ol] substituted metallophthalocyanines: Synthesis, characterization and catalytic activity
studies on the oxidation of phenolic compounds, Journal of Coordination Chemistry, DOI:
10.1080/00958972.2018.1423560
To link to this article: https://doi.org/10.1080/00958972.2018.1423560
Accepted author version posted online: 04
Jan 2018.
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Date: 07 January 2018, At: 06:49

Publisher: Taylor & Francis
Journal: Journal of Coordination Chemistry
DOI: http://doi.org/10.1080/00958972.2018.1423560
New peripherally tetra-[trans-3,7-dimethyl-2,6-octadien-1-ol] substituted
metallophthalocyanines: Synthesis, characterization and catalytic activity
studies on the oxidation of phenolic compounds
HALİT KANTEKİN†, ECE TUĞBA SAKA†, BEYTULLAH ERTEM*‡, MİRAÇ NEDİM MISIR†,
HALİSE YALAZAN† and GÜLBINAR SARKI†
†Department of Chemistry, Karadeniz Technical University, 61080, Trabzon, Turkey
‡Vocational School of Health Services, Karadeniz Technical University, 61080, Trabzon, Turkey
In this paper, we elucidated the synthesis, characterization, and investigation of catalytic activity
studies of new metallophthalocyanines 4 and 5 as the catalyst for phenolic compounds oxidation
by trying different types of oxygen sources. The structural characterization of the products was
made by a combination of elemental analysis, FT-IR, LC-MS/MS (for phthalonitrile
derivative 3), MALDI-TOF mass spectral data (for metallophthalocyanines 4-7), UV-vis
spectroscopy (for metallophthalocyanines 4-7), 1H NMR and 13C NMR spectroscopies (for
compounds 3 and 6). The synthetic routes for the (trans-3,7-dimethyl-2,6-octadien-1-ol)
substituted phthalonitrile derivative 3 and corresponding metallophthalocyanines 4-7 are outlined
in scheme 1. The MPc complexes 4-7 were synthesized via cyclotetramerization of compound 3
in the presence of the corresponding anhydrous metal salts (CoCl2 for 4, CuCl2 for 5,
Zn(CH3COO)2 for 6 and MnCl2 for 7) in dry n-pentanol as solvent and
1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as strong base at reflux temperature under nitrogen
gas. Phthalocyanines and their metal complexes, in general, display poor solubility in most of the
organic solvents, however, the synthesized metallophthalocyanine complexes 4-7 were highly
soluble in common organic solvents because of the introduction of the methyl groups on alkyl
chains of peripheral arms. The catalytic activity of compounds 4 and 5 was evaluated for the
oxidation of phenolic compounds such as 4-nitrophenol, o-chlorophenol, 2,3-dichlorophenol and
p-methoxyphenol. CoPc 4 displayed good catalytic performance with a full oxidation of
*Corresponding author. Email: bertem@ktu.edu.tr
1

4-nitrophenol into the corresponding benzoquinone and hydroquinone with the highest TON and
TOF values within 3 h.
Keywords: Synthesis; 4-Nitrophenol oxidation; Manganese(III) chloride phthalocyanine;
Catalyst; Cobalt; Phenolic compounds
1. Introduction
Phthalocyanines (Pcs) are well established, versatile and stable macrocyclic compounds [1, 2]. A
Pc molecule is composed of four isoindole units connected by azomethine bridges to form an
18-π aromatic macrocycle [3, 4]. The term "phthalocyanine" was used for the first time by
Linstead in 1933 to describe the new class of organic compounds [5], after their accidental
discovery by Braun and Tcherniac in 1907 [6, 7]. Since then, many scientific types of research
have been carried out and devoted to the exploration of their synthesis and properties [8, 9]. Pcs
and their metal complexes (MPcs) have found extensive applications in biomedical and industrial
fields [1] depending upon their chemical, physical, and optical properties which vary with the
central metal ion, its axial coordination or peripheral functionalities [2, 10-12]. These tunable
options, 18 π-electronic structure, high thermal and optical properties make Pcs and MPcs
promising materials in important scientific areas such as sensors [7, 13, 14], semiconductors
[15], dye based solar cells and molecular electronics [16, 17], liquid crystals [11], laser dyes [4],
electrochromic systems [2], non-linear optical materials [18], photosensitizers for photodynamic
therapy of cancer [19-21], organic field effect transistors [22] and catalysts [23-25].
As it is known, phenolic compounds show high toxicity even at low concentrations.
Phenolic compounds are generally found in the effluents of industrial wastewater from assorted
activities in diverse industrial sectors such as pesticide productions, resin manufacturing,
pharmaceuticals, textile, coking operations, wood products, electrolytic strip tin coating, oil
refining, explosive, plastics, coffee, paint, ceramic, paper and pulp [26-30]. Practically, two
kinds of technological methods (i.e. conventional and advanced methods) are utilized in order to
remove phenolic compounds and their effluents from the environment and industrial wastewater.
Steam distillation, liquid-liquid extraction, adsorption, catalytic wet air oxidation, ion exchange,
solid-phase extraction, wet air oxidation, and biodegradation processes are classified as
conventional methods [26]. Advanced technologies for removal of phenols contain
2

electrochemical oxidation, photo-oxidation, ozonation, UV/H2O2, Fenton and Fenton-like
treatment, membrane processes (membrane distillation; hollow fiber membranes and extractive
membrane bioreactors; photocatalytic membrane reactors; high-pressure membrane processes
such as reverse osmosis, pervaporation and nanofiltration) [26, 30-32] and biological treatment
(phenol-degrading microorganisms are used to transform phenolic solutions into simple end
products [33]; enzymatic treatment that uses an enzyme and a biocatalyst to transform phenolic
compounds into harmless or less harmful products from wastewater [34]).
Due to the extensive usage of the precursor for the production of 4-aminophenol as
intermediate in the hair-dyeing agent [34], antipyretic drugs [36], photographic developers [37],
the catalytic reduction of 4-nitrophenol to 4-aminophenol [38, 39], dyes [40], pesticides [40] and
anticorrosion-lubricant [41], 4-nitrophenol (4-NP) is one of the most common pollutant and toxic
chemical intermediate that is extensively found in wastewater at the end of the manufacturing
processes of agricultural and industrial products [42, 43]. Recently, 4-NP and its derivatives pose
some important threat to human health and the ecosystem by causing damage to the central
nervous system, kidney, liver, and blood of animals and human beings [44, 45]. According to the
United States Environmental Protection Agency (USEPA), nitrophenols are listed as one of the
top-114 organic pollutants among various nitroaromatic compounds which remarkably threaten
human health and ecological environment owing to bioaccumulation, high toxicity, difficulty in
biochemical degradation of carcinogenesis, mutagenesis, and teratogenesis [46, 47].
Geraniol (GE) is a kind of acyclic monoterpene alcohol and largely abundant in some
essential oils such as lemon, ginger, orange, rose and lavender. Since it has a pleasant fragrance,
GE is substantially employed in a range of flavoring agents in many foods and beverages,
cosmetics, perfumes [48, 49] and cleansing materials [48]. Some papers revealed that GE
demonstrates anti-tumor activity against various cancer cells [50], insecticidal, antimicrobial,
anti-inflammatory properties [48, 51] and remarkable antioxidant effect in various metabolic
disorders [52-54].
To the best of our knowledge, numerous reports exist with respect to the antioxidant,
anti-inflammatory and anti-tumor studies of GE [55-57], but there is no scientific article related
with the catalytic oxidation of phenolic compounds by means of peripherally tetra-substituted
GE metallophthalocyanine derivatives. The main purpose of this study is to explore the catalytic
activity of the novel synthesized compounds bearing GE units 4 and 5 and to provide the
3

possibility for these metal complexes as the catalyst. In this context, we have synthesized new
tetra-substituted Co(II)Pc, Cu(II)Pc, Zn(II)Pc and Mn(III)C1Pc fused trans-3,7-dimethyl-2,6-
octadien-1-ol at peripheral positions and investigated the catalytic activity studies of products 4
and 5 as the catalyst on different phenolic compounds oxidation to prevent toxic and harmful
effects to the ecosystem and human health. Under the framework of this study, it has been
announced the successful application of CoPc and CuPc as being oxidation catalysts for
oxidation of 4-nitrophenol, 2-chlorophenol, 2,3-dichlorophenol and 4-methoxyphenol using
different oxygen sources.
2. Experimental
2.1. Materials
All reactions were carried out under dry nitrogen atmosphere and compounds 4-7 were
synthesized by using standard Schlenk techniques. 4-Nitrophthalonitrile 2 was synthesized as
described by literature procedure [58]. All chemicals and reagents were of reagent grade quality
and used as purchased from commercial sources. DMF and n-pentanol were dried and purified in
accordance with methods in the reported procedure [59]. Column chromatography was carried
out on aluminum oxide 90 active basic alumina columns with the indicated eluents. All reactions
were monitored by thin layer chromatography (TLC) using 0.25 mm silica gel plates with UV
indicator (60 F254).
2.2. Equipment
1H and 13C NMR spectra were recorded on a Bruker Ascend 400 NMR spectrometer with CDCl3
(deuterated chloroform) as the NMR solvent and chemical shifts were reported (δ) relative to
Me4Si (tetramethylsilane) as the internal standard. Mass spectra were recorded on Bruker
Microflex LT MALDI-TOF-MS and Micromass Quattro LC-MS/MS spectrometers. All mass
analyses were conducted in positive ion mode using chloroform as the solvent for the mass
analyses. FT-IR spectrum was recorded on a Perkin-Elmer Spectrum One FT-IR spectrometer
(ATR sampling accessory). The electronic absorption spectrum (Ultraviolet-Visible
spectroscopy) was obtained on a Perkin-Elmer Lambda 25 UV/Vis spectrophotometer using a
1 cm path length cuvette at room temperature. Melting points were determined by an
electrothermal apparatus. GC Agilent Technologies 7820A equipment (30m×0.32mm×0.50m
4

DB Wax capillary column, FID detector) was used for gas chromatography (GC) measurements.
2.3. Electrochemical measurements
All electrochemical measurements were carried out with a Gamry Interface 1000
potentiostat/galvanostat utilizing a three-electrode configuration at 25 C. The working electrode
was a Pt disc. A Pt wire served as the counter electrode and saturated calomel electrode (SCE)
was employed as the reference electrode and separated from the bulk of the solution by a double
bridge. Electrochemical grade tetrabutylammonium perchlorate (TBAP) in extra pure
dichloromethane (DCM) was employed as the supporting electrolyte at a concentration of
0.10 M.
2.4. General procedure for the oxidation of phenolic compounds
Experiments were performed in a thermostated Schlenk vessel equipped with a condenser and
stirrer. The solution of phenolic compounds and catalyst in the solvent was purified by bubbling
nitrogen gas to remove the oxygen. At room temperature, a mixture of phenolic compounds
(2.12×10-3 mol), catalyst (4.23×10-6 mol) and solvent (0.01 L) was stirred in a Schlenk vessel for
few minutes. Afterwards, the oxidant tert-butyl hydroperoxide (TBHP) (3.38×10-3 mol) was
added and the reaction mixture was stirred for the desired time. The samples (0.0005 L) were
taken at certain time intervals. Each sample was injected at least twice in the gas chromatography
(GC), 1 µL each time. The formation of the oxidative products and the consumption of substrates
were monitored by gas chromatography. Each run was repeated three or four times. The structure
of the oxidation reaction products was verified with 1H NMR spectroscopy.
Temperature program for Analysis of Phenolic Compounds oxidation:
Temperature of Injection Unit: 200 C
Temperature of Detector Unit: 250 C
Temperature program:
40o
s
s
1
1
1 s
20oC
s
C /
s
/
o
o
o
o
o
o
120 C
120 C
280 C
280 C
60
60
C
C
Carrier Gas: Helium
Flow of carrier gas: 1.5 mL/dk
Sample volume: 1 µL
5

Split ratio: 1/20
2.5. Synthesis
2.5.1. (E)-4-((3,7-dimethylocta-2,6-dien-1-yl)oxy)phthalonitrile (3). 4-Nitrophthalonitrile 2
(1.122 g, 6.48 mmol) was added to a solution of geraniol 1 (1.0 g, 6.48 mmol) in dry DMF
(10 mL) and the mixture was heated to 55 C. After stirring for 15 min at the same temperature,
finely ground anhydrous K2CO3 (3.13 g, 22.65 mmol) was added in small portions over 2 h with
efficient stirring and degassed several times. The mixture was stirred at 55 C under a nitrogen
stream for 6 days. Afterwards, the mixture was poured into 200 g of a crushed ice-water mixture
and stirred for 2 h. The resulting brown solid was collected by filtration and washed with ethyl
alcohol and water in turn, and subsequently dried in vacuo. Yield: 1.0 g (55%), m.p. 40-44 C.
Elemental analysis: Calc. (%) for C18H20N2O: C, 77.11; H, 7.19; N, 9.99, Found (%) C, 76.43; H,
7.32; N, 9.62. FT–IR, vmax (cm-1): 3131/3105/3077 (C-H aromatic), 2973/2928/2863 (CH2, CH3),
2228 (C≡N), 1599 (C=C), 1561, 1488, 1472, 1383, 1343, 1290/1252/1092 (C-O-C), 983, 826,
637. 1H NMR in CDCl3, δ(ppm): 7.73-7.70 (d, 1H, Ar-H), 7.28-7.26 (s, 1H, Ar-H), 7.21-7.18 (d,
1H, Ar-H), 5.48-5.43 (t, 1H, CH3-C=CH-CH2-O), 5.07 (t, 1H, [(CH3)2-C=CH-CH2]), 4.66-4.64
(d, 2H, Ar-O-CH2), 2.13 (s, 4H, CH2), 1.84-1.77 (s, 3H, CH3), 1.69-1.62 (s, 6H, CH3). 13C NMR
in CDCl3, δ(ppm): 161.98, 143.72, 136.14, 132.17, 123.62, 123.39, 119.79, 118.38, 117.36,
115.79 (C≡N), 115.37 (C≡N), 107.00, 65.92, 39.47 (CH2), 26.15 (CH2), 25.71 (CH3), 17.74
(CH3), 16.93 (CH3). LC-MS/MS (ES+) m/z: Calculated: 280.36, Found: 198.00 [M-C6H10]+,
321.00 [M+K+2H]+.
2.5.2. General procedure for the syntheses of MPcs (4-7). The phthalonitrile derivative 3
(0.1 g, 0.357 mmol) was dissolved in 3 mL of dry n-pentanol under a blanket of nitrogen gas in a
well-stopped Schlenk tube. Catalytic amount of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and
anhydrous metal salts (0.178 mmol) [CoCl2, 23.0 mg; CuCl2, 24.0 mg; Zn(CH3COO)2, 33.0 mg;
MnCl2, 22.0 mg] were subsequently added into the solution and the reaction mixture was
refluxed at 160 C for 4 h. After cooling to room temperature, the reaction mixture was diluted
and the product was precipitated by adding 10 mL of ethanol. The resulting precipitate was
filtered off, washed with EtOH and H2O separately and dried in vacuo. The crude products were
purified by column chromatography on aluminum oxide 90 active basic alumina. Scheme 1
6

displays the synthetic route for MPcs 4-7.
CN
OH
+
O2N
CN
CoPc
4
1
2
K2CO3
N2 (g)
DBU anhydrous CoCI2
N2 (g) dry n-Pentanol
160 ºC 11.4%
dry DMF 55%
55 ºC
CN
CN
dry n-Pentanol, DBU, N2 (g)
5
CuPc
anhydrous CuCI , 21.8%,
160 ºC
2
O
dry n-Pentanol
N2 (g)
3
73.7% DBU
160 ºC anhydrous Zn(Ac)2
dry n-Pentanol N2 (g)
DBU
27.8%
anhydrous MnCI2 160 ºC
6
ZnPc
O
Cl
N
N
N
N
O
O
Mn
N
N
N
N
O
7
MnIIICIPc
Scheme 1. Synthesis of precursor phthalonitrile compound 3 and MPcs 4-7.
7

2.5.2.1. 2(3),9(10),16(17),23(24)-Tetrakis-((3,7-dimethylocta-2,6-dien-1-yl)oxy)-
phthalocyaninato cobalt(II) (4). MPc 4 was synthesized by following the aforementioned general
procedure for MPcs. The crude blue product was purified by column chromatography on basic
alumina using chloroform:ethanol (100:1) as eluent. The extract was evaporated to dryness and
dried under vacuum to give blue solid product 4. Yield: 12.0 mg (11.4%), m.p. >300 C.
Elemental analysis: Calc. (%) for C72H80N8O4Co: C, 73.26; H, 6.83; N, 9.49, Found (%) C,
72.44; H, 6.12; N, 9.73. FT-IR, vmax (cm-1): 3183/3066 (C-H aromatic), 2963/2915/2850 (CH2,
CH3), 1639 (C=N), 1609 (C=C), 1523, 1487, 1472, 1380, 1364, 1230-1097-1056 (C-O-C), 997,
820, 749 (Pc skeleton). UV-vis (chloroform), λmax (in nm) (logε): 326 (4.24), 381 (4.24), 613
(3.88), 675 (4.30). MALDI-TOF-MS m/z: Calculated: 1180.39, Found: 1180.20 [M]+.
2.5.2.2. 2(3),9(10),16(17),23(24)-Tetrakis-((3,7-dimethylocta-2,6-dien-1-yl)oxy)-
phthalocyaninato copper(II) (5). Phthalocyaninato copper(II) derivative 5 was synthesized by
following the aforementioned general procedure for MPcs. The crude blue product was purified
by column chromatography on basic alumina using chloroform as eluent. The extract was
evaporated to dryness and dried under vacuum to give blue solid 5. Yield: 23.0 mg (21.8%), m.p.
>300 C. Elemental analysis: Calc. (%) for C72H80N8O4Cu: C, 72.98; H, 6.80; N, 9.46, Found
(%) C, 71.47; H, 6.62; N, 9.69. FT-IR, vmax (cm-1): 2956/2916/2849 (CH2, CH3), 1641 (C=N),
1608 (C=C), 1507, 1483, 1462, 1379, 1343, 1235/1118/1096/1053 (C-O-C), 997, 820, 746 (Pc
skeleton). UV-vis (chloroform), λmax (in nm) (logε): 338 (4.07), 384 (3.76), 617 (3.85), 683
(4.31). MALDI-TOF-MS m/z: Calculated: 1185.00, Found: 1185.13 [M]+.
2.5.2.3. 2(3),9(10),16(17),23(24)-Tetrakis-((3,7-dimethylocta-2,6-dien-1-yl)oxy)-
phthalocyaninato zinc(II) (6). MPc 6 was synthesized by following the aforementioned general
procedure for MPcs. The crude green product was purified by column chromatography on basic
alumina using chloroform as eluent. The extract was evaporated to dryness and dried under
vacuum to give green compound 6. Yield: 78.0 mg (73.7%), m.p. >300 C. Elemental analysis:
Calc. (%) for C72H80N8O4Zn: C, 72.86; H, 6.79; N, 9.44, Found (%) C, 71.32; H, 6.82; N, 9.60.
FT-IR, vmax (cm-1): 2923/2854 (CH2, CH3), 1638 (C=N), 1603 (C=C), 1507, 1485, 1445, 1377,
1317, 1221/1085/1044 (C-O-C), 991, 825, 748 (Pc skeleton). 1H NMR in CDCl3, δ(ppm): 7.80
(s, 4H, Ar-H), 7.38-7.34 (d, 8H, Ar-H), 5.20 (s, 4H, CH3-C=CH-CH2-O), 5.07-4.91 (s, br, 4H,
8

[(CH3)2-C=CH-CH2]), 4.70 (s, 8H, Ar-O-CH2), 2.10-2.07 (s, 16H, CH2), 1.85-1.60 (s, br, 12H,
CH3), 1.43-1.40 (s, 12H, CH3), 1.36-1.28 (s, 12H, CH3). 13C NMR in CDCl3, δ(ppm): 161.37,
144.19, 137.19, 131.97, 123.91, 119.52, 118.97, 117.71, 106.37, 65.92, 65.77, 62.94, 42.84,
39.80, 39.57, 37.20, 36.63, 26.48, 25.76, 17.02, 16.80, 15.31, 14.11. UV-vis (chloroform), λmax
nm (logε): 357 (4.06), 617 (3.67) and 685 (4.29). MALDI-TOF-MS m/z: Calculated: 1186.84,
Found: 1186.57 [M]+.
,
2.5.2.4. 2(3),9(10),16(17),23(24)-Tetrakis-((3,7-dimethylocta-2,6-dien-1-yl)oxy)-
phthalocyaninato manganese(III) chloride (7). Phthalocyaninato manganese(III) chloride 7 was
synthesized by following the aforementioned general procedure for MPcs. The crude product
was purified by column chromatography on basic alumina using chloroform:ethanol (100:1) as
eluent. The extract was evaporated to dryness and dried under vacuum to give dark brown-
reddish product 7. Yield: 30.0 mg (27.8%), m.p. >300 C. Elemental analysis: Calc. (%) for
C72H80N8O4MnCl: C, 71.36; H, 6.65; N, 9.25, Found (%) C, 70.37; H, 6.43; N, 8.98. FT-IR, vmax
(cm-1): 3056 (C-H aromatic), 2958/2914-2850 (CH2, CH3), 1641 (C=N), 1603 (C=C), 1505,
1483, 1456, 1381, 1341, 1225/1118/1071 (C-O-C), 983, 822, 744 (Pc skeleton). UV-vis
(chloroform), λmax (in nm) (logε): 376 (4.85), 527 (4.54), 675 (4.65), 736 (4.99). UV-vis (DMF),
λmax, nm (logε): 370 (4.95), 497 (4.59), 659 (4.60) and 731 (5.09). MALDI-TOF-MS m/z:
Calculated: 1211.84, Found: 1175.97 [M-Cl]+.
3. Results and discussion
3.1. Synthesis and characterization
The synthetic pathways for geraniol-substituted phthalonitrile derivative 3 and corresponding
metallophthalocyanines 4-7 are demonstrated in scheme 1. Herein, we notified the synthesis,
characterization, and investigation of catalytic activity of new metallophthalocyanines 4 and 5 as
the catalysts for the oxidation of phenolic compounds by using different types of oxidants. The
synthesized new compounds 3-7 were verified using UV-vis (for metallophthalocyanines 4-7),
1H NMR and 13C NMR spectroscopies (for compounds 3 and 6), LC-MS/MS (for phthalonitrile
derivative 3), MALDI-TOF-MS data (for metallophthalocyanines 4-7) and FT-IR, as well as
elemental analysis. All results with reference to compounds 3-7 were consistent with the
assigned formulations in scheme 1.
9

The new precursor dicyano derivative 3, (E)-4-((3,7-dimethylocta-2,6-dien-1-
yl)oxy)phthalonitrile, was synthesized with 55% yield through reaction of trans-3,7-dimethyl-
2,6-octadien-1-ol 1 with 4-nitrophthalonitrile 2 in the presence of K2CO3 in dry DMF at 55 C
under a nitrogen stream for 6 days through base-catalyzed nucleophilic aromatic displacement
reaction of nitro-group for 4-nitrophthalonitrile. MPc complexes 4-7 were synthesized via
cyclotetramerization of compound 3 in the presence of the corresponding anhydrous metal salts
(CoCl2 for 4, CuCl2 for 5, Zn(CH3COO)2 for 6 and MnCl2 for 7) in dry n-pentanol as solvent and
1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as strong base at 160 °C under nitrogen atmosphere.
These newly prepared products 4-7 were purified by column chromatography on basic alumina
as the column material. The synthesized metallophthalocyanine complexes 4-7 were highly
soluble in most of common organic solvents such as THF, ethyl acetate, CH2Cl2, CHCl3, DMF,
diethyl ether, ethyl alcohol, DMSO and acetonitrile due to the methyl groups on alkyl chains of
peripheral arms.
3.2. Spectroscopic characterization
The synthesis of compound 3 was achieved in 55% yield through base-catalyzed aromatic nitro
displacement reaction of 4-nitrophthalonitrile 2 with (E)-3,7-dimethyl-2,6-octadien-1-ol 1 in dry
DMF by using anhydrous K2CO3 as the base. After synthesis of precursor phthalonitrile product
3, the peak in the vibrational spectra of compound 1 for the v(O-H) vibration at 3655 cm-1
disappeared and a new vibration was observed at 2228 cm-1 belonging to the C≡N functionality,
indicative of the formation of targeted molecule 3. Other characteristic vibrations corresponding
to v(C-H)aromatic at 3131/3105/3077 cm-1, v(C-H)aliphatic at 2973/2928/2863 cm-1 and v(C-O-C)ether
at 1290/1252/1092 cm-1 are consistent with the assigned formulation. In the 1H NMR spectrum
of 3, the signal associated with the O-H group disappeared and new signals of the aromatic ring
protons at δ = 7.73-7.70, 7.28-7.26 and 7.21-7.18 ppm were observed for compound 3. Other
1H NMR signals are almost identical with compound 1. Besides, the presence of signals at δ =
115.79-115.37 ppm (C≡N) in the 13C NMR spectrum of 3 proved the proposed structure. The
mass spectrum of 3 was measured with electrospray ionization technique (ES+) and obtained
with some reasonable parent ion peaks at m/z: 198.00 [M-C6H10]+ and 321.00 [M+K+2H]+.
The disappearance of the v(C≡N) vibration at 2228 cm-1 approved the
cyclotetramerization reactions of phthalonitrile 3 into metallophthalocyanines 4-7. Another
10

notable difference was the presence of v(C=N) vibrations of the inner core of
metallophthalocyanine molecules 4-7 appearing at 1639 cm-1 for 4, 1638 cm-1 for 6 and
1641 cm-1 for both 5 and 7. The characteristic v(C-O-C) of ether group were seen at
1230/1097/1056 cm-1 for 4, 1235/1118/1096/1053 cm-1 for 5, 1221/1085/1044 cm-1 for 6 and
1225/1118/1071 cm-1 for 7. Owing to the paramagnetic nature of the central transition metal ions
(Co+2, Cu+2 and Mn+3), 1H and 13C NMR measurements of the cobalt(II) 4, copper(II) 5 and
manganese(III) chloride 7 phthalocyanine derivatives were precluded. Aromatic ring protons of
product 6 were measured at δ = 7.80 and 7.38-7.34 ppm as singlet and doublet peaks,
respectively. Other 1H NMR chemical shift values of zinc(II) phthalocyanine 6 were almost
identical with precursor compound 3 except some little changes. In addition to the elemental
analyses data, the mass spectral results for the newly synthesized phthalocyanine complexes 4-7
were consistent with the assigned formulations. The mass spectra of 4-7 were measured with
MALDI-TOF-MS and were in a good accordance with the proposed structures. The molecular
ion peaks were observed at m/z = 1180.20 [M]+ for 4, 1185.13 [M]+ for 5, 1186.57 [M]+ for 6
and 1175.97 [M-Cl]+ for 7 (figure 1), respectively.
The electronic spectra of phthalocyanine compounds 4-7 displayed the best indications
concerning the characteristic B and Q bands of typical MPcs. The electronic absorption spectra
of 4-6 were measured in chloroform and demonstrated in figure 2(a). Metallophthalocyanine
derivatives 4-6 showed B bands at 326 nm (logε = 4.24) and 381 nm (logε = 3.86) for 4, 338 nm
(logε = 4.07) and 384 nm (logε = 3.76) for 5 and 357 nm (logε = 4.06) for 6, and intense single Q
bands with lower wavelength shoulders at 613 nm (logε = 3.88) and 675 nm (logε = 4.30) for 4,
617 nm (logε = 3.85) and 683 nm (logε = 4.31) for 5 and 617 nm (logε = 3.67) and 685 nm (logε
= 4.29) for 6. These results are in accordance with the relating MPcs in the literature.
The UV-vis spectra of compound 7 were measured in chloroform and in DMF
(figure 2(b)). MnPc complex 7 exhibited B band at 376 nm (logε = 4.85) and Q band at 736 nm
(logε = 4.99) with a shoulder at 675 nm (logε = 4.65) in chloroform, and B band at 370 nm (logε
= 4.95) and Q band at 731 nm (logε = 5.09) with a shoulder at 659 nm (logε = 4.60) in DMF. The
Q-band absorption of product 7 in chloroform (at 736 nm) and in DMF (at 731 nm) was red-
shifted with respect to those of complexes 4-6 in the electronic absorption spectra (figure 2(a)
and 2(b)). This result is typical of manganese phthalocyanine complexes [60]. It has been
suggested [61, 62] that several equilibria exist between MnPc species in air and in DMF
11

according to Eqs. (1)-(5):
PcMnII + O2
PcMnIII(O2)
(1)
PcMnIII(O2) + PcMnII
PcMnIII-O2-MnIIIPc
2PcMnIVO + 2PcMnII
PcMnIII-O2-MnIIIPc
2PcMnIVO (3)
(2)
(4)
2PcMnIII-O-MnIIIPc
4PcMnII + O2
2PcMnIII-O-MnIIIPc
(Net equation) (5)
Although manganese(II) chloride was employed for the synthesis of the MnPc, the
negative redox potential of the MnIII/MnII species makes it air-sensitive and facilitates the
formation of MnIIIPc species during the synthesis and purification (taking place in aerobic
conditions) [63]. Multiple Q bands might be observed because of the presence of μ-oxo MnPc,
MnIIPc and MnIIIPc species in DMF under air in the ground state electronic absorption spectrum
of MnPc complexes. In the UV-vis spectrum of MnPc complexes in DMF, μ-oxo MnPc, MnIIPc
and MnIIIPc species are generally seen at around 620-630 nm, 680-690 nm and near 750 nm,
respectively [64-66]. The electronic absorption spectrum of manganese phthalocyanine
complex 7 indicated the presence of MnIIIPc and MnIIPc species by taking into account the
positions of the Q-bands in chloroform and DMF. Compound 7 exists mainly as the MnIIIPc
complex in chloroform and DMF. On the other hand, we performed a cyclic voltammetry (CV)
study to explain different oxidation states of compound 7. Basic electrochemical parameters, the
assignments of the redox couples and estimated electrochemical parameters including the half-
wave potentials (E1/2), peak-to-peak potential separations (Ep), and difference between the first
oxidation and reduction processes (E1/2), were derived from the analyses of complex 7 and
these data are tabulated in table 1. In figure 3, CV responses of MnIIIClPc 7 in DCM/TBAP is
displayed. MnIIIClPc gave two quasi-reversible reduction processes at -0.29 V R1 (∆Ep =
165 mV) and -1.15 V R2 (∆Ep = 125 mV), respectively. Also, during the cathodic scan,
MnIIIClPc gave one quasi-reversible oxidation O1 at 1.04 V within the potential window of
DCM/TBAP electrolyte system (∆Ep = 170 mV). R1 and R2 reduction processes and oxidation
process O1 were quasi-reversible characters with respect to Ep values. Depending upon the
positions of the redox processes, two redox couples (R1 at -0.29 V and R2 at -1.15 V) were
proposed to the reduction of MnIII to MnII and then MnII to MnI oxidation states. Quasi-reversible
12

oxidation O1 at 1.04 V was proposed to Pc based process. These assignments are in agreement
with the MnPcs in the literature [67-70]. We also observed absorption bands between 500 and
600 nm in the UV-vis spectrum of complex 7 at 527 nm (logε = 4.54) in chloroform and at
497 nm (logε = 4.59) in DMF. These bands are generally associated with charge transfer in
MnPc complexes owing to partially-filled d orbitals in MnPc complexes [64, 70-74]. Q bands of
7 were observed at 736 and 675 nm in chloroform and were red-shifted compared to the
spectrum in DMF (at 731 and 659 nm) (figure 2(b)). Positions of Q bands of the spectra of 7 are
closely related to the refractive indices of the solvents used for the measurement of the UV-vis
spectra. The higher the refractive index of the solvent, the more red-shifted the Q band of the
MPc complex concerned. CHCl3 has a refractive index of 1.438, compared to 1.430 for DMF,
justifying the red-shift in Q band of the manganese phthalocyanine complexes in CHCl3, relative
to that in DMF [64, 75].
3.3. Catalytic studies
The main product was determined as benzoquinone and the side product was determined as
hydroquinone in the oxidation of 4-nitrophenol oxidation reaction (figure 4). 4-Nitrophenol
oxidation proceeds by initial aromatic hydroxyl oxidative attack (similar to phenol oxidation)
followed by oxidative fragmentation, with the release of nitrates, as confirmed by the
identification of p-nitrocatechol, hydroquinone, benzoquinone, and catechol. 4-Nitrocatechol and
catechol were found as trace amounts (lower 8%) in this work. It is well known that the reaction
mechanism of HO• radicals with aromatic compounds proceeds mainly through an electrophilic
addition to the aromatic ring [76-79]. The phenolic -OH group is electron-donating for the
electrophilic aromatic substitution, thus increasing the electron density both in the ortho- and in
the para-positions [76]. Furthermore, the -NO2 group is electron-withdrawing, thus being meta-
directing [76]. In the particular case of 4-nitrophenol (i.e., in the presence of both substituents),
the electrophilic attack will occur at the ortho-position in respect to the -OH group, leading to the
formation of p-nitrocatechol, an aromatic substitution of the -NO2 group may occur due to an
attack of the radical HO• at the para-position in respect to the -OH group, hydroquinone being
obtained [77, 78]. These preliminary results exhibited that only one complex (CoPc 4) could
facilitate the oxidation of 4-nitrophenol and serve as an efficient and selective catalyst.
Unfortunately, when Cu(II) phthalocyanine 5 was used as the catalyst, no conversion was
13

observed. All substrate, catalysts and obtained results within the oxidation processes are
demonstrated in table 2. According to the results of this table, Co(II) phthalocyanine 4
demonstrated the highest activity producing benzoquinone as the major product in the
4-nitrophenol oxidation reaction.
Subsequently, optimization of the reaction conditions was performed by selectively
evaluating effects of different 4-nitrophenol:catalysts molar ratios, oxidant:catalysts molar ratios,
the oxidant and temperature used. In addition, in the blank reactions (without catalysts or
oxidants) there were no products detectable. It is proved that presence of the catalyst and oxidant
is essential for the oxidation (table 3). As the other parameters were kept constant, the molar
ratio was carried out from 300-1000 to determine the influence of substrate on metal ions. The
reaction rate increased with decreasing of the substrate:catalyst molar ratio (table 3) as expected.
Substrate:catalyst ratio of the oxidation course gave the same main product with TON and TOF
values (496 and 165 for Co complex 4).
To determine oxygen source effect, H2O2, tert-butyl hydroperoxide (TBHP),
m-chloroperoxybenzoic acid (m-CPBA) and air oxygen were used as the oxidant. The results in
table 3 showed that H2O2 was the best oxidant for 4-nitrophenol oxidation in the presence of
CoPc 4. Moreover, TBHP and m-CPBA can serve as an oxidant but the low conversion was
observed for both CoPc 4 and CuPc 5. The reaction color changed from blue to brown when we
added H2O2 or m-CPBA in the reaction media. This clue explains that complex 4 was degraded
immediately with H2O2 or m-CPBA [80]. The results of catalytic activity study for CoPc 4 and
CuPc 5 using air oxygen displayed that there was no formation of products during the oxidation
process (figure 5). Another important parameter is oxidant:catalyst ratio to find the optimal
conditions of 4-nitrophenol oxidation. When the oxidant/catalyst ratio was increased from 500:1
to 800:1, the rate of the reaction increased. In contrast, while the catalytic oxidation was
processing from 800:1 to 1200:1, the conversion (benzoquinone:hydroquinone ratio) inclined to
decrease. At this stage, it is possible that the coordination around the cobalt ion can change and
produce inactive intermediate species [81].
The results in table 3 showed that as the reaction temperature was upgraded from 50 °C
to 90 °C, the catalytic activity of CoPc 4 did not change. When the temperature was fixed to
50 °C, the maximum total conversion was obtained (99%) with cobalt(II) phthalocyanine 4.
Therefore, 50 °C is the optimum temperature of 4-nitrophenol oxidation for product 4 with H2O2
14

in 3 h. We focused on these catalytic studies and the nature of the introduced transition metals.
Although metallophthalocyanines are representatives for flat, π-conjugated carbon systems, their
electronic properties are determined to a large extent by the central metal atom. The electronic
configuration of the central metal atom can change the catalytic activity of phthalocyanine. The
activity of metallophthalocyanines in oxidation reaction follows the order CoPc > CuPc. It is
known that the catalytic performance of transition metal species depends on the outer d-electron
density [25, 82].
Table 4 indicates catalytic activity studies to the homogeneous oxidation of phenolic
compounds of some previously reported catalyst. Different peripherally units substituted
cobalt(II), iron(II), manganese(III), copper(II) phthalocyanines were investigated on 2,6-di-tert-
butylphenol, 2,4,6-trichlorophenol, 2,4,5-trichlorophenol, 2,3,6-trimethylphenol and
4-nitrophenol oxidation [76, 83-92]. By comparing the catalysts in the literature, it is inferred
that compound 4 will be interesting catalyst in 4-nitrophenol, o-chlorophenol, 2,3-dichlorophenol
and p-methoxyphenol oxidation. In the literature, tetrasubstituted Co(II) and Fe(II)
phthalocyanine complexes were studied as the catalyst for the oxidation of phenolic compounds
[88-90]. The results of our previous papers [91, 92] were valuable because of the high
conversion and selectivity of Co(II) phthalocyanine. But in this research, we achieved to reach
the highest product conversion and selectivity with Co(II) phthalocyanine at lower temperature
(50 °C).
4. Conclusion
Four new transition metal ion inserted tetra-substituted phthalocyanine complexes 4-7 bearing
geraniol units were designed and synthesized. In order to verify these novel products 3-7, a
combination of spectral techniques such as MALDI-TOF-MS data, UV-vis, FT-IR, 1H NMR and
13C NMR was used. Because of the MnIII metal ion center, manganese phthalocyanine complex 7
demonstrated red-shifted Q band relative to those of the other analogs 4-6. It is well known that
most of the metal-free and metallophthalocyanine derivatives exhibit low solubility in most
common organic solvents. This main disadvantage leads to limitations of their applications in
various scientific, technological and industrial fields. Therefore, it is very significant to obtain
organo-soluble phthalocyanines (both Pcs and MPcs) that are potentially useful materials for
assorted applications. MPcs 4-7 are highly soluble in most of the organic solvents and these new
15

organo-soluble products 4-7 are favorable for further scientific studies as well. 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 [23, 93, 94].
The catalytic activity of CoPc 4 was examined for the oxidation of 4-nitrophenol using different
oxygen sources. The results indicated that the catalyst exhibited satisfactory activity for the
oxidation of 4-nitrophenol to the corresponding benzoquinone in 3 h at 50 °C. The optimal
conditions were also determined in 4-nitrophenol oxidation with CoPc 4. All the results indicate
that CoPc 4 is an efficient and cleaning technology with cost-efficient, easy-applicable and
energy-saving for the toxic and refractory industrial wastewater. Converting from
environmentally harmful phenolic compounds into less harmful oxidation products by new CoPc
4 derivative makes this study attractive and useful. On the other hand, newly synthesized CoPc 4
would be a beneficial catalyst for oxidation of thiols, alkenes, and alkanes as well.
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[92] E.T. Saka, G. Sarkı, H. Kantekin. J. Coord. Chem., 68, 1132 (2015).
[93] H. Turk, Y. Cimen. J. Mol. Catal. A: Chem., 234, 19 (2005).
[94] Y. Cimen, H. Türk. Appl. Catal. A, 340, 52 (2008).
20

Figure 1. MALDI-TOF mass spectral data of compounds 4-7.
21

Figure 2. UV-vis spectra of 1.00×10-5 M of complexes. (a) Co(II)Pc (blue solid), Cu(II)Pc (red
dashed) and Zn(II)Pc (green dotted) in CHC13. (b) Mn(III)C1Pc in CHC13 (blue solid) and DMF
(red dotted).
22

Figure 3. CV of MnC1Pc (7) at 100 mV·s-1 scan rate on a Pt working electrode in
dichloromethane (DCM)/tetrabutylammonium perchlorate (TBAP) electrolyte system.
23

HO
NO2
+OH.
NO2
+OH.
NO2
4-Nitrophenol
O
O
HO
OH
Hydroquinone
Benzoquinone
Figure 4. The oxidation products of 4-nitrophenol.
24

Figure 5. The oxidant effect on 4-nitrophenol oxidation [reaction conditions: 4-nitrophenol
(2.12×10-3 mol), Co(II)Pc and Cu(II)Pc (4.23×10-6 mol), oxidant (3.38×10-3 mol), DMF (0.01 L),
3 h and 50 °C].
25

Table 1. Cyclic voltammetry data of MnC1Pc (7). All voltammetric data are given versus SCE.
bEp (mV)
cE1/2
Complex
Redox processes
a E1/2
R1[Cl-MnIIIPc-2] / [Cl-MnIIPc-2]-1
R2[MnIIPc-2] / [MnIPc-2]-1
-0.29 165
-1.15 125
MnClPc
1.33
O1[Cl-MnIIIPc-2] / [Cl-MnIIIPc-1]+1
1.04
170
a E1/2 = (Epa + Epc)/2 are given versus SCE at 0.100 Vs-1 scan rate. b ∆Ep = Epa - Epc at 0.100 Vs-1
scan rate. c ∆E1/2 = E1/2 (first oxidation) - E1/2 (first reduction).
26

Table 2. Oxidation of substituted phenols catalyzed by complexes 4 and 5.
Total
conversion (%)
Product
selectivity (%)
TON
TOF (h-1)
Substrate
Major product
4
5
4
5
4
5
4
5
O
OH
99
21
99
42
496
350
105
165
35
30
NO2
OH
O
O
Cl
Cl
70
18
87
60
90
116
O
O
OH
Cl
Cl
51
37
12
20
74
74
40
50
60
349
100
85
61
20
33
Cl
Cl
O
O
OH
185
O
OCH3
OCH3
TON = mole of product/mole of catalyst. TOF = mole of product/mole of catalyst × time. The conversion was
determined by gas chromatography (GC). Catalyst/substrate/oxidant ratio = 1/500/800; reaction time = 3 h.
27

Table 3. Selective oxidation of 4-nitrophenol with catalysts 4 and 5 using different oxidant and temperature.
Conversion (%)
Selectivitya (%)
TON
TOF (h-1)
Subs./Ox./Cat
Oxidant
Temperature (°C)
4
5
4
5
4
5
4
5
300/800/1
500/800/1
800/800/1
1000/800/1
500/500/1
500/1000/1
500/1200/1
500/800/1
500/800/1
500/800/1
500/800/1
500/800/1
500/800/1
500/800/free cat.
500/free ox./1
H2O2
50
50
50
50
50
50
50
50
50
50
75
90
25
50
50
54
99
68
60
45
80
49
44
38
-
12
21
15
15
12
18
16
12
14
-
77
99
85
85
75
94
81
73
76
-
50
42
37
37
34
45
40
30
35
-
162
496
545
601
225
400
245
220
190
-
36
105
50
150
60
90
80
60
70
-
54
165
181
299
75
133
81
73
63
-
12
35
16
50
20
30
26
20
23
-
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
m-CPBA
TBHP
Air oxygen
H2O2
99
99
75
-
20
18
17
-
99
99
88
-
50
45
42
-
496
496
496
-
100
90
85
-
165
165
165
-
33
30
28
-
H2O2
H2O2
H2O2
H2O2
-
-
-
-
-
-
-
-
TON = mole of product/mole of catalyst. TOF = mole of product/mole of catalyst × time. The conversion was determined by
gas chromatography (GC). Reaction conditions: 500/800/1: 2.12×10-3 mol)/3.38×10-3 mol/4.23×10-6 mol. a Selectivity of
TMHQ. Reaction time = 3 h. m-CPBA = m-chloroperoxybenzoic acid. TBHP = tert-butyl hydroperoxide.
28

Table 4. Catalytic activities towards the homogeneous oxidation of phenolic compounds of some previously
reported catalysts.
Catalyst
Substrate
Rxn Time (h)
Oxidant Conv. (%)
Ref.
Rxn temp. (C)
CoPcTsa
FePce
DTBP
TCP
24
24
70
nrı
O2
66
85
[83]
KHSO5
[84, 85]
CoPcd
CoPcTsa
FePcTsb
CoPcd
2,4,5-TCP
TMP
24
2
75
nr j
90
75
H2O2
O2
67
77
96
61
39
05
93
-
[87]
[87]
[88]
[89]
4-Nitrophenol
DTBP
3
TBHP
TBHP
CoPcTsa
FePcTsb
CuPcTsc
CoPcd
2
DTBP
3
30
TBHP
[90]
FePce
MnPcf
97
-
CuPcg
FePcTsb
FePcOCh
CoPcı
TCP
24
25
25
90
H2O2
H2O2
TBHP
24
6
[91]
[76]
[92]
TCP
10 min
3
4-Nitrophenol
97
75
FePcı
a CoPcTs = Tetrasulphonated cobalt phthalocyanine. b FePcTs = Tetrasulphonated iron phthalocyanine.
c CuPcTs = Tetrasulphonated copper phthalocyanine. d CoPc = Substituted cobalt phthalocyanine. e FePc =
Substituted iron phthalocyanine. f MnPc = Substituted manganese phthalocyanine. g CuPcg = Substituted copper
phthalocyanine. h FePcOC = Octa cationic iron phthalocyanine. j nr = not reported. DTBP = Di-tert-butyl
peroxide. TCP = 2,4,6-Trichlorophenol. 2,4,5-TCP = 2,4,5-Trichlorophenol. TMP = 2,3,6-Trimethylphenol.
29