Oxidation of benzyl alcohol by novel peripherally and non-peripherally modular C2-symmetric diol substituted cobalt (II) phthalocyanines

Article abstract of DOI:10.1002/aoc.5669

In this study, a modular ligand structure was designed by altering the binding position of the phenyl group at backbone of hydrobenzoin. A series of regio isomeric substituted phthalonitriles derived from this modular C₂-symmetric ligand was sy

Full text of DOI:10.1002/aoc.5669

Received: 13 January 2020
DOI: 10.1002/aoc.5669
Revised: 5 March 2020
Accepted: 8 March 2020
F U L L P A P E R
Oxidation of benzyl alcohol by novel peripherally and non-
peripherally modular C2-symmetric diol substituted cobalt
(II) phthalocyanines
Halil Zeki Gök1
| Yas¸ar Gök1
| Mustafa Kemal Yılmaz2
1Department of Biomedical Engineering,
Bucak Faculty of Technology, Burdur
Mehmet Akif Ersoy University,
In this study, a modular ligand structure was designed by altering the binding
position of the phenyl group at backbone of hydrobenzoin. A series of regio
isomeric substituted phthalonitriles derived from this modular C2-symmetric
ligand was synthesized and characterized. Then, eight cobalt
(II) phthalocyanines (CoPc) were obtained from the reaction of phthalonitrile
derivatives with cobalt (II) chloride. The catalytic activities of synthesized
cobalt (II) phthalocyanines were tested for benzyl alcohol oxidation in acetoni-
trile using tert-butylhydroperoxide as the oxygen source and in the presence of
Bucak/Burdur, 15300, Turkey
2Department of Chemistry, Faculty of Arts
and Sciences, Mersin University, Mersin,
33343, Turkey
Correspondence
Halil Zeki Gök, Department of Biomedical
Engineering, Bucak Faculty of
Technology, Burdur Mehmet Akif Ersoy
University, 15300, Bucak/Burdur, Turkey.
Email: halilzekigok@gmail.com
ꢀ
N-bromosuccinimide as an additive at 80 C for 5 hr of the reaction. In this
sense, the effect of substrate to catalyst ratio and oxidant to catalyst ratio have
been studied in detail for getting the highest benzaldehyde selectivity (up to
83%). The effect of structural design of substituents at peripheral or non-
peripheral positions of phthalocyanine skeleton on the catalytic activity perfor-
mance of cobalt (II) phthalocyanines in benzyl alcohol oxidation was also clar-
Funding information
TÜrkiye Bilimsel ve Teknolojik Aras¸tırma
Kurumu, Grant/Award Number: MAG-
115R015
1
ified. All newly synthesized compounds are characterized by FT-IR, H NMR,
IR, UV–Vis and MALDI-TOF MS spectral data.
K E Y W O R D S
benzyl alcohol, C2-symmetric-diol, oxidation, phthalocyanine, synthesis
1 | INTRODUCTION
Many researchers directed their effort to reveal mecha-
nism of dioxygen activation of cytochrome P-450.[3] In
The researches on the activation of C-H bonds such as in
alkane and alcohol are very important for the develop-
ment of clean oxidation process from the point of view of
chemistry and industry.[1] The activation of a bond in a
chemical reaction are mostly performed by a catalyst
which is capable of driving the chemical reaction under
mild condition. Numerous biochemical reactions in liv-
ing cells are being come true every day, and these reac-
tions are operated by enzymes which are very attractive
biocatalysts. The catalytic oxidation of steroids, fatty
acids, and the synthesis and breakdown of some of hor-
mone in mammals are operated by cytochrome P-450.[2]
those studies, metalloporphyrins have been investigated
extensively for the elucidating the activity of cytochrome
P-450 due to their closely relevant catalytic chemistry to
cytochrome P-450.[4, 5] Therefore, the chemistry of por-
phyrins has been well documented in numerous research
article, reviews and books.[6–9] Development of efficient
catalysts for the activation of C-H bonds in this manner
can be achieved by mimicking the active sites of
biocatalysts and natural products such as cytochrome P-
450 and porphyrin, respectively. At this point, phthalocy-
anines have been synthesized by bioinspired approach
and studied for a long time as the analogues of porphyrin
Appl Organomet Chem. 2020;e5669.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5669

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GÖK ET AL.
molecules.[10] The structure of metallophthalocyanines is
very similar to the structure of porphyrin but former have
high chemical and thermal stability in contrast to natu-
rally occurring porphyrins.[11–13] Not only because of the
chemical and thermal stability of phthalocyanines but
also due to their cost-efficient synthesis on large scales in
terms of ease accessibility and cheap precursors make the
phthalocyanines very attractive compounds as catalysts.
On account of the unique properties of
phthalocyanines above mentioned, they have been
applied widely in advanced technologies such as molecu-
2 | EXPERIMENTAL SECTION
2.1 | Materials and equipment
(R,R)-hydrobenzoin 4[29] and its derivatives 1–3,[30]
3-nitrophthalonitrile,[31] 4-nitrophthalonitrile,[32] C2-
symmetric diol substituted phthalonitriles 6, 10 and 8, 12,
and cobalt (II) phthalocyanines 16, 20[33] and 14, 18[34]
were synthesized according to the published literatures.
All reagents and solvents were reagent grade quality and
were obtained from commercial suppliers. All solvents
were dried and purified as described by Perrin and
Armarego.[35] Column chromatography was carried out
on silica gel (Merck, Kieselgel 60, 400–630 mesh).
FTIR spectra were measured on a Perkin Elmer Spec-
trum 65 spectrometer using potassium bromide (KBr)
pellets. 1H and 13C NMR spectra were recorded on a Var-
ian Mercury 400 MHz spectrometer using deutero-
chloroform (CDCl3) and deuterated tetrahyrofuran (THF-
d8, 99.95%). Mass spectra were measured on a Micromass
Quatro LC/ULTIMA LC–MS/MS and a Bruker Daltonics
MALDI-TOF spectrometer. Optical spectra were recorded
in the UV–Vis region with a PG-T80+ spectrophotometer
using 1 cm path length cuvettes at room temperature.
The catalytic reactions were monitored by GC-FID chro-
matography equipped with a 30 m × 0.25 μm × 0.25 μm
capillary column (Rxi-5 ms, 95% diphenyl, 95% dimethyl
polysiloxane) by comparison standards (benzaldehyde,
benzoic acid and 1,4-benzoquinone). Elemental analyses
were obtained with a LECO Elemental Analyser (CHNS
0932) spectrophotometer. Melting points were deter-
mined with an electrothermal apparatus and are
uncorrected.
lar photovoltaics,[14] electro-catalysts,[15] thin-film
18]
transistors,[16] solar cell material,[17,
optical
imaging,[19] photodynamic therapy[20] and as catalysts for
the oxidation of alkane,[21] olefins,[22] phenols,[23] alco-
hols[24] and sulfur compounds[25] in homogenous and
heterogenous catalytic reactions. The catalytic oxidation
of above-mentioned chemicals by phthalocyanine com-
plexes is very important for industry to prepare valuable
chemicals and also an attractive topic for research. The
catalytic activity of metallophthalocyanines depends on
the substituents attached to phthalocyanines and the
metal in its center.[1] The solubility of meta-
llophthalocyanines is also another important factor for
the catalytic activity, especially in homogenous catalysis.
To overcome the solubility problem of meta-
llophthalocyanines, the nature and the position of the
substituents are the key in the design of phthalocyanines.
Therefore, incorporation of electron donating or electron
withdrawing substituents to the peripheral and non-
peripheral position of phthalocyanine skeleton is a fruit-
ful approach for not only obtaining the desired solubility
properties of metallophthalocyanines but also tuning the
catalytic properties of them.[26–28]
Although more than 70 different metals located in the
center cavity of metallophthalocyanines have been
described, metallophthalocyanines with metals such as
Co, Fe, Ru, Mn and Cr are the most studied class of
phthalocyanines for the catalytic oxidation process due to
the redox activity of those metal ions. While inserting the
redox active metal ion in the center of phthalocyanines is
the necessity for the catalytic steps which are taking
places at the metal site, substitution of peripheral or non-
peripheral positions of phthalocyanine with bulky groups
improves the solubility and decrease the tendency to
aggregate in solution which limits the application of
phthalocyanines.
In this study, we report the synthesis and characteri-
zation of eight cobalt (II) phthalocyanines bearing posi-
tional isomers of phenyl substituted hydrobenzoin at
peripheral and non-peripheral positions of phthalocya-
nine skeleton as bulky groups, and investigation of their
catalytic activity in the oxidation of benzyl alcohol.
2.2 | Synthesis
2.2.1 | General procedure for the
synthesis of phenyl-substituted
hydrobenzoin derived 3- or 4-phthalonitrile
(5, 7, 9 and 11, Scheme 1)
3-nitrophthalonitrile or 4-nitrophthalonitrile (1.0 mmol,
1.0 equiv.) were added at once into two-necked flask con-
taining a stirring solution of phenyl-substituted hydro-
benzoin derivatives (1 or 3, 1.0 mmol, 1.0 equiv.) in 4 mL
of dimethyl sulfoxide (DMSO) under inert atmosphere at
room temperature. Then, the mixture was kept 15 min
stirred. At the end of this period, to the reaction mixture
was added 1.0 equivalent of finely ground anhydrous
potassium carbonate (K2CO3) and stirred further 2 hr.
The formation of product was evaluated by thin layer
chromatography. The reaction was kept stirring till the

GÖK ET AL.
3 of 14
consumption of one of the reactants. Then, the reaction
mixture was poured into ice-water (3:1 v/v) to assist the
precipitation of the crude product. The filtration of the
solution afforded the crude product as light-yellow pre-
cipitate which was then dissolved in dichloromethane.
The organic phase was washed twice with a portion of
50 mL of water and then dried over anhydrous sodium
sulfate (Na2SO4). The organic solvent was evaporated
under reduced pressure in order to obtain the crude prod-
uct which was finally purified by silica gel flash column
chromatography. The elution was carried out with dic-
hloromethane (DCM)-ethylacetate (EtOAc) (95:5).
(100 MHz, CDCl3, ppm) δ: 160.8, 141.9, 141.4, 140.4,
139.9, 137.0, 135.2, 133.8, 128.9, 127.8, 127.7, 127.5, 127.4,
127.0, 126.9, 121.1, 120.6, 117.4, 115.4, 115.1, 108.1, 86.1,
76.1; MS (ESI−) MS calculated [M
C34H24N2O2Cl: 527.1 found: 527.1.
+
Cl]− for
3-((10R,20R)-20 - hydroxy-10,20-di(200-phenylphenyl)
ethoxy) phthalonitrile (9)
Synthesis of 9 was performed by following the general
procedure by using 3-nitrophthalonitrile (0.181 g,
1.04 mmol), 1 (0.384 g, 1.04 mmol) and K2CO3 (0.144 g,
1.04 mmol). The product was obtained as a white solid.
Yield: 0.376 g, (74%); mp: 202–203 ꢀC. Found: C,
4-((10R,20R)-20- hydroxy-10,20-di(200-phenylphenyl)ethoxy)
phthalonitrile (5)
82.58; H, 4.67; N, 5.52%; 'molecular formula C34H24N2O2
0
20
requires C, 82.94; H, 4.91; N, 5.69%. ½αꢁD
=
+65.94
Synthesis of 5 was performed by following the general
procedure by using 4-nitrophthalonitrile (0.181 g,
1.04 mmol), 1 (0.384 g, 1.04 mmol) and K2CO3 (0.144 g,
1.04 mmol). The product was obꢀtained as a white solid.
Yield: 0.325 g, (64%); mp: 80–81 C. Found: C, 82.54; H,
(c = 1, CHCl3); retention time 7.63 min, Chiral ART
Amylose-C, 30:70 n-hexane-iPrOH, flow rate of
0.5 mL/min, 254 nm, t = 40 ꢀC; IR (KBr disc) vmax/cm−1
:
3465 (OH), 3088, 2932, 2232 (C ꢂ N), 1580, 1465, 1281,
1029, 761, 700; 1H-NMR (400 MHz, CDCl3, ppm) δ:
7.58–7.56 (m, H), 7.39–7.17 (m, 13H), 7.10–7.00 (m, 4H),
6.96 (dd, J = 7.5 Hz, J = 0.8 Hz, H), 6.79 (d, J = 8.3 Hz,
H), 6.30 (br, s, H), 5.59 (d, J = 8.5 Hz, H), 5.33 (d,
J = 8.3 Hz, H), 3.04 (br, OH); 13C-NMR (100 MHz,
CDCl3, ppm) δ: 160.1, 142.3, 141.8, 140.4, 139.8, 135.5,
133.8, 132.1, 130.3, 130.1, 129.1,129.0, 128.4, 128.3, 128.2,
128.2, 128.1, 127.9, 126.9, 125.8, 119.9, 116.8, 115.1, 113.0,
83.7, 73.1; MS (ESI−) MS calculated [M + Cl]− for
C34H24N2O2Cl: 527.1 found: 527.1.
0
4.98; N, 5.32%; 'molecular formula C34H24N2O2
20
requires C, 82.94; H, 4.91; N, 5.69%. ½αꢁD
=
+21.98
(c = 1, CHCl3); retention time 8.84 min, Chiral ART
Amylose-C, 30:70 n-hexane-iPrOH, flow rate of
0.5 mL/min, 254 nm, t = 40 ꢀC; IR (KBr disc) vmax/cm−1:
3439 (OH), 3035, 2952, 2231 (C ꢂ N), 1597, 1486, 1315,
1250, 1059, 751, 703; 1H-NMR (400 MHz, CDCl3, ppm) δ:
7.6 (dd, J = 7.2 Hz, J = 2.0 Hz, H), 7.51 (d, J = 9.0 Hz, H),
7.42–7.25 (m, 10H), 7.20 (dt, J = 7.5 Hz, J = 1.5 Hz, H),
7.12–7.09 (m, H), 7.01–6.87 (m, 6H), 6.36 (br, s, H), 5.57
(d, J = 8.0 Hz, H), 5.23 (d, J = 8.0 Hz, H), 2.89 (br, OH);
13C-NMR (100 MHz, CDCl3, ppm) δ: 160.5, 142.2, 140.5,
139.7, 135.5, 134.8, 132.1, 130.4, 130.2, 129.3, 129.1, 128.4,
128.3, 128.2, 128.1, 128.0, 127.9, 126.9, 121.5, 120.7, 117.2,
115.5, 114.9, 107.9, 82.5, 73.2; MS (ESI−) MS calculated
[M + Cl]− for C34H24N2O2Cl: 527.1 found: 527.1.
3-((10R,20R)-20 - hydroxy-10,20-di(400-phenylphenyl)
ethoxy) phthalonitrile (11)
Synthesis of 11 was performed by following the general
procedure by using 3-nitrophthalonitrile (0.34 g;
1.98 mmol), 3 (0.73 g, 1.98 mmol) and K2CO3 (0.27 g;
1.98 mmol). The product was obtained as a white solid.
ꢀ
Yield: 0.79 g, (81%); mp: 93–95 C. Found: C, 82.15; H,
4-((10R,20R)-20 - hydroxy-10,20-di(400-phenylphenyl)
ethoxy) phthalonitrile (7)
5.09; N, 5.79%; 'molecular formula C34H24N2O2
requires C, 82.94; H, 4.91; N, 5.69%. ½αꢁD
0
20
= +325.49
Synthesis of 7 was performed by following the general
procedure by using 4-nitrophthalonitrile (0.36 g,
2.11 mmol), 3 (0.77 g, 2.11 mmol) and K2CO3 (0.29 g,
2.11 mmol). The product was obꢀtained as a white solid.
Yield: 0.745 g, (72%); mp: 87–89 C. Found: C, 82.28; H,
(c = 1, CHCl3); retention time 26.34 min, Chiral ART
Amylose-C, 30:70 n-hexane-iPrOH, flow rate of
0.5 mL/min, 254 nm, t = 40 ꢀC; IR (KBr disc) vmax/cm−1
:
3465 (OH), 3030, 2921, 2231 (C ꢂ N), 1579, 1463, 1282,
1042, 761, 696; 1H-NMR (400 MHz, CDCl3, ppm) δ:
7.58–7.40 (m, 14H), 7.36–7.30 (m, 2H), 7.24 (d,
J = 8.2 Hz, 2H), 7.17 (d, J = 8.2 Hz, 2H), 7.10 (d,
J = 8.2 Hz, 2H), 5.36 (d, J = 7.3 Hz, H), 5.19 (d,
J = 7.3 Hz, H), 3.16 (s, OH); 13C-NMR (100 MHz, CDCl3,
ppm) δ: 160.39, 141.8, 141.2, 140.7, 136.9, 134.3, 133.9,
128.9, 128.8, 127.8, 127.6, 127.5, 127.4, 127.1, 127.0, 126.9,
125.8, 119.0, 117.1, 115.2, 113.2, 105.9, 87.1, 77.7; MS
(ESI−) MS calculated [M + Cl]− for C34H24N2O2Cl: 527.1
found: 527.1.
0
4.68; N, 5.01%; 'molecular formula C34H24N2O2
20
requires C, 82.94; H, 4.91; N, 5.69%. ½αꢁD
=
+79.88
(c = 1, CHCl3); retention time 23.50 min, Chiral ART
Amylose-C, 30:70 n-hexane-iPrOH, flow rate of
0.5 mL/min, 254 nm, t = 40 ꢀC; IR (KBr disc) vmax/cm−1:
3465 (OH), 3031, 2954, 2918, 2871, 2231 (C ꢂ N), 1597,
1488, 1313, 1249, 1092, 837, 696; 1H-NMR (400 MHz,
CDCl3, ppm) δ: 7.62–7.12 (m, 21H), 5.30 (d, J = 7.3 Hz,
H), 5.10 (d, J = 7.3 Hz, H), 2.95 (br, OH); 13C-NMR

4 of 14
GÖK ET AL.
2.2.2 | General procedure for the
synthesis of cobalt (II) phthalocyanines
(13, 15, 17 and 19)
1(4),8(11),15(18),22(25)-Tetrakis-{((10R,20R)-20-hydroxy-
10,20-di(200-phenylphenyl)ethoxy)} phthalocyaninato
cobalt (II) (17)
According to the general procedure of the synthesis of
cobalt (II) phthalocyanines, 3-((10R,20R)-20-hydroxy-10,20-
Cobalt (II) phthalocyanines 13, 15, 17 and 19 were
synthesized by the reaction of anhydrous CoCl2
(0.5 mmol, 0.5 equiv.) with the corresponding
phthꢀalonitrile derivatives in 2.5 mL of n-pentanol at
140 C for 24 hr in a Schlenk tube under inert atmo-
sphere in the presence of catalytic amount of
1,8-diazabicyclo(5.4.0) undec-7-ene (DBU). Then, the
resulting reaction mixture was cooled to the room tem-
perature. The solvent of the reaction mixture was
removed under reduced pressure. The remaining crude
product was purified by chromatography over silica gel
column with a solvent mixture hexane-diethyl ether
(7:3) followed by methanol and chloroform solvents as
eluents.
di(200-phenylphenyl)ethoxy phthalonitrile
9
(0.4 g;
0.81 mmol) and CoCl2 (0.053 g; 0.41 mmol) gave a green
solid cobalt (II) phthalocyanine 17. The yield was 0.045 g
(11%). mp: 246–247 ꢀC. Found: C, 79.03; H, 4.26; N,
5.09%; 'molecular formula C136H96N8O8Co' requires C,
80.50; H, 4.77; N, 5.52%. IR (KBr disc) νmax/cm−1: 3383
(OH), 3057, 2925, 1597, 1481, 1330, 1145, 1092, 746, 701;
UV–Vis (DMF): λmax, nm (log ε): 312 (4.74), 632 (4.44),
694 (4.96); MS (MALDI-TOF) (m/z): calculated [M]+ for
C136H96N8O8Co: 2027.6 found: 2027.9 [M]+.
1(4),8(11),15(18),22(25)-Tetrakis-{((10R,20R)-20-hydroxy-
10,20-di(400-phenylphenyl)ethoxy)} phthalocyaninato
cobalt (II) (19)
2(3),9(10),16(17),23(24)-Tetrakis-{((10R,20R)-20-hydroxy-
10,20-di(200-phenylphenyl)ethoxy)} phthalocyaninato
cobalt (II) (13)
According to the general procedure of the synthesis of
cobalt (II) phthalocyanines, 3-((10R,20R)-20-hydroxy-10,20-
di(400-phenylphenyl)ethoxy phthalonitrile 11 (0.42 g;
0.85 mmol) and CoCl2 (0.055 g; 0.42 mmol) gave a green
solid cobalt (II) phthalocyanine 19. The yield was 0.027 g
(6%). mp: 237–238 ꢀC. Found: C, 79.36; H, 4.18; N, 5.49%;
'molecular formula C136H96N8O8Co' requires C, 80.50; H,
4.77; N, 5.52%. IR (KBr disc) νmax/cm−1: 3352 (OH), 3059,
3030, 2923, 2854,1599, 1485, 1330, 1263, 1091, 762, 737,
694; UV–Vis (DMF): λmax, nm (log ε): 314 (4.86),
638 (4.22), 702 (4.64); MS (MALDI-TOF) (m/z): calcu-
lated [M]+ for C136H96N8O8Co: 2027.6 found: 2033.6
[M + 6H]+.
According to the general procedure of the synthesis of
cobalt (II) phthalocyanines, 4-((10R,20R)-20-hydroxy-10,20-
di(200-phenylphenyl)ethoxy phthalonitrile
5 (0.47 g;
0.95 mmol) and CoCl2 (0.062 g; 0.48 mmol) gave a blue
solid cobalt (II) phthalocyanine 13. The yield was 0.085 g
(17%). mp: 268–270 ꢀC. Found: C, 79.22; H, 4.41; N,
5.61%; 'molecular formula C136H96N8O8Co' requires C,
80.50; H, 4.77; N, 5.52%. IR (KBr disc) νmax/cm−1: 3547,
3453 (OH), 3058, 2927, 1656, 1612, 1476, 1410, 1230,
1096, 750, 702; UV–Vis (DMF): λmax, nm (log ε):
330 (4.96), 610 (4.59), 672 (5.18); MS (MALDI-TOF)
(m/z): calculated [M]+ for C136H96N8O8Co: 2027.6 found:
2027.4 [M]+.
3 | RESULTS AND DISCUSSION
3.1 | Synthesis and characterization
2(3),9(10),16(17),23(24)-Tetrakis-{((10R,20R)-20-hydroxy-
10,20-di(400-phenylphenyl)ethoxy)} phthalocyaninato
cobalt (II) (15)
The synthesis of optically active chiral phthalonitriles
5–12 and their cobalt (II) phthalocyanine derivatives
13–20 was illustrated in Scheme 1. The synthesis of four
According to the general procedure of the synthesis of
cobalt (II) phthalocyanines, 4-((10R,20R)-20-hydroxy-10,20-
phthalonitriles among them was reported before in litera-
34]
di(400-phenylphenyl)ethoxy phthalonitrile
7
(0.37 g;
ture.[33,
The syntheses of new phthalonitriles 5, 7,
0.74 mmol) and CoCl2 (0.049 g; 0.37 mmol) gave a green
solid cobalt (II) phthalocyanine 15. The yield was 0.088 g
(22%). mp: 261–262 ꢀC. Found: C, 80.13; H, 4.81; N,
5.08%; 'molecular formula C136H96N8O8Co' requires C,
80.50; H, 4.77; N, 5.52%. IR (KBr disc) νmax/cm−1: 3553,
3416 (OH), 3059, 3030, 2901, 1610, 1520, 1482, 1407,
1230, 1098, 1068, 835, 755, 696; UV–Vis (DMF): λmax, nm
(log ε): 326 (4.93), 610 (4.51), 672 (5.00); MS (MALDI-
TOF) (m/z): calculated [M]+ for C136H96N8O8Co: 2027.6
found: 2027.9 [M]+.
9
and 11 were performed by the reaction of
3-nitrophthalonitrile or 4-nitrophthalonitrile with the
corresponding phenyl-substituted C2 symmetric diol in
the presence of potassium carbonate in DMSO at room
temperature. These reactions gave the desired
phthalonitriles 5, 7, 9 and 11 with the yield of around
70%.
To characterize the phthalonitriles 5, 7, 9 and 11, a
combination of spectroscopic techniques such as FT-IR,
1H and 13C NMR and mass analyses was applied (see

GÖK ET AL.
5 of 14
SCHEME 1 Syntheses of phthalonitrile derivatives (5-12) and metallophthalocyanines (13-20). Reagents and conditions: (i) DMSO,
K2CO3, rt; (ii) CoCl2, n-pentanol, DBU, 140 ꢀC
Supporting Information). The FT-IR measurements of
optically active phthalonitriles 5, 7, 9 and 11 were per-
formed by using KBr pellet technique. The appearances
of strong intense stretching vibration band at around
2230 cm−1 due to the C ꢂ N group for all the
phthalonitriles in their FT-IR spectra are in good agree-
ment with the proposed structures. In addition to that,
the observation of a broad vibrational band at around
3400 cm−1 corresponding to the -OH group in the FT-IR
spectra of phthalonitriles 5, 7, 9 and 11 also confirmed
the formation of desired phthalonitriles. Acquiring the
1H and 13C NMR in CDCl3 allow us to determine the
exact structures of phthalonitriles. It was expected to
obtain very similar NMR spectra for all phthalonitriles
since phthalonitriles 5, 7, 9 and 11 were isomers and have
the same number of protons and carbons in their struc-
tures. The only difference between the spectra was the
small change in chemical shift values. The common point
phthalonitriles were observed in aromatic region as
expected. In the 13C NMR spectra of 5, 7, 9 and 11, the
specific carbon resonances such as aliphatic -CH carbons
bounded to the oxygen atom and hydroxyl group
appeared as two different carbon signals in a region of
δ = 75–85 ppm as expected. The existence of C ꢂ N group
in the case of phthalonitriles was characterized carbon
resonances at around δ = 115.00 ppm.[33] The observation
of two carbon resonances at around δ = 115.00 ppm for
all the synthesized phthalonitriles in their 13C NMR spec-
tra is consistent with the general expectation for the
structures of 5, 7, 9 and 11. The rest of the aromatic car-
bons was observed between δ = 105–160 ppm. The last
measurement for the phthalonitriles to confirm their
structures was mass analyses. The mass measurements of
phthalonitriles on a LC–MS system gave the same molec-
ular ion peaks at m/z = 527.1 [M + Cl]− as expected due
to the isomeric nature of the phthalonitriles 5, 7, 9 and
11. In addition to the mass analyses, the results of found
and calculated elemental analyses values were consistent,
which confirmed the successive synthesis of the desired
phthalonitriles.
1
of H NMR spectra for all phthalonitriles is the observa-
tion of two doublets with the same coupling constant
value between 5–6 ppm for the aliphatic -CH protons due
to the C1 symmetry of chiral phthalonitriles 5, 7, 9 and
11. Additionally, the observation of a broad singlet peak
at around δ = 3.00 ppm for the proton of -OH group in
As the last step of the synthetic pathway, the desired
cobalt (II) phthalocyanines 13–20 were synthesized from
the corresponding phthalonitriles 5–12 by the reaction of
phthalonitrile derivative with cobalt (II) chloride in the
1
the H NMR spectra of 5, 7, 9 and 11 confirmed the pro-
posed structures. The rest of the protons for the

6 of 14
GÖK ET AL.
presence of catalytic amount of DBU in 2.5 mL of n-
pentanol at 140 ꢀC for 24 hr in a Schlenk tube under inert
atmosphere. The new four cobalt (II) phthalocyanines 13,
15, 17 and 19 were purified by flash silica gel column
chromatography and characterized by FT-IR, UV–Vis
and mass measurements (see Supporting Information).
By taking account of the FT-IR measurements of cobalt
(II) phthalocyanines 13, 15, 17 and 19, we can conclude
that the synthesis of desired cobalt (II) phthalocyanines
was performed successfully due to the disappearance of
C ꢂ N group in their FT-IR spectra. The presence of a
vibrational band at around 3400 cm−1 attributed to the -
OH group of phthalocyanines can be also taken as clear
evidence for the formation of cobalt (II) phthalocyanines
13, 15, 17 and 19. The 1H NMR spectra of cobalt
(II) phthalocyanines could not be acquired due to the
paramagnetic nature of cobalt (II) ion.[33] The mass ana-
lyses of newly synthesized cobalt (II) phthalocyanines
were performed on a Bruker Daltonics MALDI-TOF spec-
trometer. The observation of molecular ion peaks at
m/z = 2027 [M + H]+ for regio isomer cobalt
(II) phthalocyanines 13, 15, 17 and 19 confirmed the pro-
posed structures of the phthalocyanines.
phthalocyanines give the two splitted Q band due to
their D2h symmetry.[10] The UV–Vis spectra of all cobalt
(II) phthalocyanines recorded in THF were given in
Figure 1. As seen from Figure 1, all phthalocyanines
gave two main absorptions bands as expected. The UV–
Vis absorption spectra of peripherally substituted CoPc
13–16 showed the main Q absorption band at around
λmax = 670 with the shoulder at around 610 nm while
the
Q absorption band was observed at around
λmax = 700 with the shoulder at around 640 for the
non-peripherally substituted CoPc 17–20. It was also
noted that the main Q absorption band of the non-
peripheral substituted CoPc 17–20 was seen in red-
shifted compared to that of peripherally substituted of
CoPc 13–16. This is well known as the effect of α-
substitution of phthalocyanine skeleton. The substitu-
tion at non-peripheral positions of phthalocyanine cau-
ses the electron density enhancement and resulted in
red shifting of spectra of metallophthalocyanines.[36, 37]
3.2 | Catalytic studies
Phthalocyanines have characteristic UV–Vis absorp-
tion spectra with two bands in the spectral window
between 300–800 nm.[10] One of these absorption bands
is called as B band and it was expected to observe at
around 300 nm. The other absorption band appeared
between 600–800 nm and is called as the Q band.[10]
The appearance of the Q band varies depending on
whether there is a metal in the center of phthalocya-
nine compound. In general, the phthalocyanines con-
taining a metal in their center give an unsplitted Q
band due to their D4h symmetry whereas metal-free
The catalytic activities of cobalt (II) phthalocyanines 13,
15 and 17, 19 were examined for the selective oxidation
of benzyl alcohol to benzaldehyde together with their
regio-isomers (14 and 18) as we have previously
reported.[34] In all catalytic experiments, benzaldehyde
was obtained as the main product and the other oxida-
tion products (1,4-benzoquinone and benzoic acid) were
formed very little or trace amount and yields were deter-
mined by gas chromatography analyses using the stan-
dards of these compounds (Scheme 2).
FIGURE 1 UV–Vis spectra of cobalt(II)
phthalocyanines 13-20 in tetrahydrofuran
[Colour figure can be viewed at
wileyonlinelibrary.com]

GÖK ET AL.
7 of 14
SCHEME 2 Oxidation of benzyl alcohol using
cobalt(II)phthalocyanines 13-15 and 17-20 as catalysts
One of the most important factors for the perfor-
mance of cobalt (II) phthalocyanines on the oxidation of
benzyl alcohol in homogenous catalysis is their solubility
in reaction solvent. The solubility of phthalocyanine com-
pounds can be improved by incorporation of various sub-
stituents to the either non–peripheral or peripheral
positions of phthalocyanine skeleton.[1, 10, 27, 28, 33, 34] We
have recently focused on synthesizing of phthalocyanines
with bulky C2-symmetric diols either peripheral or non-
peripheral positions of phthalocyanine skeleton to over-
found that the reaction gave the best conversion (94%)
and benzaldehyde selectivity (82%) for both non-
substituted catalysts (16 and 20) in the presence of the
catalytic amount of NBS as an additive with TBHP as the
ꢀ
source of oxidant in ACN solvent at 80 C. It should also
be noted that no oxidation product was observed in the
blank experiment which was carried out in the absence
of any catalyst under optimized conditions. So, to evalu-
ate the catalytic activity of each novel cobalt
(II) phthalocyanine complexes having phenyl substituted
hydrobenzoin units at peripheral and non-peripheral
positions, oxidant amount and substrate to catalyst ratio
were determined under certain conditions[33] for selective
oxidation of benzyl alcohol to benzaldehyde.
come the solubility and aggregation problems of phthalo-
34]
cyanines.[33,
The results showed that the
phthalocyanines substituted with C2-symmteric diols
have good solubility in common organic solvents such as
diethyl ether, chloroform, dichloromethane, tetrahydro-
furan, acetonitrile etc.
The efficiency of cobalt (II) phthalocyanine com-
plexes 13–15 and 17–19 in the oxidation of benzyl alcohol
to corresponding products was studied by varying the oxi-
dant to catalyst ratio from 100/1 to 900/1 (increasing by
100 units) for the reaction period of 5 hr and conse-
quently the highest percentage conversion and benzalde-
hyde selectivity was determined for each catalyst. Results
were presented in Table 1. For all peripheral and non-
peripheral substituted cobalt (II) phthalocyanine com-
plexes, full or higher conversions (≥84%) were obtained
in every case but benzaldehyde selectivity of the reaction
was decreased with depending on the rising concentra-
tion of oxidant. Maximal benzaldehyde selectivity
(ca 58%) was obtained when using 100/1 oxidant to cata-
lyst ratio with catalyst 13 (Table 1, entry 1). A slightly
decrease of the benzaldehyde selectivity (43–54%) was
observed with other catalysts in the presence of the same
amount of TBHP (Table 1, entries 7, 13, 19, 25, and 31).
However, a significant decrease (to 18%) was determined
for the benzaldehyde selectivity with an increasing oxi-
dant ratio due to the generation of nonactive species
around the cobalt ion depending on the excess amount of
oxidant during the catalytic cycle.[33, 40–44]
Substrate to catalyst ratio is another important factor
effecting the total conversion and benzaldehyde selectiv-
ity for the oxidation of benzaldehyde. So, the effect of the
substrate concentration was next examined for our cobalt
(II) phthalocyanine complexes and related results are
illustrated in Table 2. The results show that the conver-
sion of benzyl alcohol decreased with an increasing
amount of substrate until the minimum conversion of
9–22% when 2000/1 substrate to catalyst ratio was used
(Table 2, entries 7 and 14). Whereas increasing ratio
beyond 2000/1, the selectivity of benzaldehyde generally
The effectiveness of a metal complex in catalysis var-
ies depending on the interaction between the metal in
the center and the ligand coordinated to the metal center.
The ligand structure coordinated around the metal center
directly affects the reactivity and selectivity of the metal
complex. As a traditional approach for catalysis reactions,
performance of the catalyst can be tuned by changing the
steric and electronic properties of the ligand coordinated
to the metal center.[38] Studies have demonstrated that
the catalytic activity of the metal ion is directly related to
the number of electrons in the d shell.[39] 1st, 2nd and
3rd order transition metals are used as metal centers in
catalytic reactions due to their unfilled d shells. 1st order
transition metals are more preferred in catalyst synthesis
since they are cheaper and less toxic than 2nd and 3rd
order transition metals.[1, 38]
Very
recently,
we
reported
two
cobalt
(II) phthalocyanine complexes having both non-
substituted hydrobenzoin moieties at the peripheral (16)
and non-peripheral (20) positions and the catalytic activ-
ity of these complexes for the selective oxidation of ben-
zyl alcohol to benzaldehyde were studied in detail.[33] For
this purpose, we made a conscious effort to optimize the
selective oxidation process of benzyl alcohol and the effi-
ciency of several oxidants (tertiary butyl hydroperoxide;
TBHP, m-chloroperoxybenzoic acid; m-CPBA, and hydro-
gen peroxide; H2O2), solvents (dimethylformamide;
DMF and ꢀ acetonitrile; ACN), reaction temperature
(25 and 80 C) and the effect of using an additive (potas-
sium bromide; KBr, N-bromosuccinimide; NBS and
tetrabutylammonium bromide; Bu4NBr) on the catalyst
activity was explored for 5 hours of the reaction. We

8 of 14
GÖK ET AL.

GÖK ET AL.
9 of 14

10 of 14
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GÖK ET AL.
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GÖK ET AL.
remained steady for peripherally substituted catalyst 18
and non-peripherally substituted catalysts 14 and 15
(entries; 8–21 and 29–35). On the other hand, for cata-
lysts 13, 17 and 19, benzaldehyde selectivity was posi-
tively affected (from 68 to 83%) by increasing amount of
substrate (2000/1) in spite of the fact that conversion is
low (≤22%). However, conversion of benzyl alcohol
inclined to decrease while substrate to catalyst ratio was
processing from 300/1 to 2000/1 and the best conversion
was obtained at 115/1 substrate/catalyst ratio for all cata-
lysts (entries, 1, 8, 15, 22, 29, and 36).
Another purpose of this study is to explore the effects
of the substituent patterns on benzyl alcohol oxidation by
comparing other results obtained from our previously
synthesized hydrobenzoin (16, 20) and hydronaphtoin
(21) substituted cobalt (II) phthalocyanines. It is notewor-
thy, however, that our newly examined cobalt
(II) phthalocyanines 13–15 and 17–19 having phenyl
substituted on hydrobenzoin units at different positions
gave better benzaldehyde selectivity when compared to
the non-substituted analogues 16 and 20. We could not
conclude a direct comparison with the results obtained
with binding position of the phenyl substituents on
hydrobenzoin skeleton, since in every situation that we
reported in this paper there is no distinct differences in
conversion and selectivity been quoted. The best catalytic
structure of 21, but quite similar to that of 21. The gen-
eral structures for C2-symmetric diol substituted phthalo-
cyanine 13–21 are given in Scheme 3. The only difference
between the structures of 13–15, 17–19 and 21 is the pat-
tern of substituents. In the case of 21, the phenyl ring
was fused with the phenyl of hydrobenzoin unit to form
the naphthyl pattern while the same phenyl group was
bounded to the 2, 3 or 4-position of phenyl of hydro-
benzoin unit in the structures of 13–15 and 17–19. The
detailed catalytic activity studies of closely related struc-
tures 13–15, 17–19 and 21 in the oxidation of benzyl alco-
hol showed that the catalytic activity of the
phthalocyanine molecule can be affected by a very small
modification in molecule such as fusing a phenyl ring
with the phenyl ring of hydrobenzoin unit to form the
naphthyl pattern instead of binding of the phenyl ring to
the hydrobenzoin structure at 2, 3 or 4-position. From
these experimental results, we can conclude that the
structural design of R group covalently bounded to the
peripheral or non-peripheral position of phthalocyanine
skeleton can play a crucial role in the catalytic activity of
cobalt (II) phthalocyanines.
Previously published oxidation studies were listed in
Table 3 and the results that we noted on this paper are
considered together. Our cobalt (II) phthalocyanine com-
plexes which have phenyl substituted hydrobenzoin units
at peripheral and non-peripheral positions on
phthalonitrile skeleton were active, selective, robust and
suitable catalysts for the oxidation of benzyl alcohol.
Although the mechanism of this selective oxidation of
benzyl alcohol has not been studied in detail, this
probably proceeds over the formation of PcCoIII-O-O-tBu
complex in the first step interacting tertiary butyl
hydroperoxide (TBHP) with Co (II)-Pc catalyst
(Scheme 4). During the catalysis process, the attack of
the RO. and ROO. radicals, which are derived from
TBHP, on the Pc ring probably leads to the decomposi-
tion of the phthalocyanine complex, resulting in the
solution color turns from blue to green. However, the
continuation of the catalysis process, even when the
reaction medium turns yellow, gives the impression that
once the catalytically active species have been formed,
the reaction can continue, whether the original form of
Co (II)-Pc catalysts is in the reaction medium or
not.[41–43]
activity
among
the
synthesized
cobalt
(II) phthalocyanines (13–21) was observed in the case of
hydronaphtoin substituted cobalt (II) phthalocyanines 21
which converts benzyl alcohol to benzaldehyde by a con-
version of 99% with selectivity of 100% at room tempera-
ture in
1
hr.[40] The common point of the
phthalocyanines 13–21 are O-R groups at either periph-
eral or non-peripheral positions of phthalocyanine struc-
ture and cobalt (II) ion as center metal. It is noted that
the structures of 13–15 and 17–19 are not same as the
4 | CONCLUSIONS
A series of cobalt (II) phthalocyanines was synthesized
by introduction of phenyl-substituted hydrobenzoin moi-
eties to the peripheral and non-peripheral positions of
phthalocyanine and inserting cobalt ion as redox active
SCHEME 3 The structures of C2-symmetric diol substituted
cobalt(II) phthalocyanines 13-21.[33, 34, 40]

GÖK ET AL.
13 of 14
TABLE 3
Catalytic activities towards the homogeneous oxidation of benzyl alcohol and cyclohexene of some previously reported CoPc
catalysts
Catalyst
CoPca
CoPcb
CoPcc
CoPcd
Substrate
Time (h)
Temp. (ꢀC)
Oxidant
Conv. (%)
Selectivity (%)
Ref.
cyclohexene
3
90
TBHP
92
98
99
90
30
97
89
91
27
60j
68j
[45]
benzyl alcohol
benzyl alcohol
cyclohexene
1
25
90
25
50
70
90
70
TBHP
TBHP
O2
100k
80k
nr
86k
78k
82k
91k
[38]
[46]
[47]
[41]
[48]
[49]
[50]
3
Co (tbpcH2)
CoPce
CoPcf
CoPcg
CoPch
24
3
benzyl alcohol
benzyl alcohol
benzyl alcohol
benzyl alcohol
TBHP
TBHP
TBHP
TBHP
3
3
5.5
tbpcH2: tetra-tert-butylphthalocyanine, For Pcs;
atetrakis-[2-(1,4-dioxa-8-azaspiro[4.5]dec-8-yl)ethoxy]phthalocyanine,
btetrakis-(3,3-diphenylpropoxy)phthalocyanine,
c{1,2-di (naphthalene-1-yl)ethane-1,2-diol}phthalonitrile,
d(2-{2-[3-(trifluoromethyl)phenoxy]ethoxy} ethoxy),
e{2-[2-(2,3,5,6-Tetrafluorophenoxy)ethoxy]ethoxy},
f(2-{2-[3-(diethylamino) phenoxy]ethoxy}ethoxy),
g2-(2-(4-allyl-2-methoxyphenoxy)ethoxy)ethoxy,
h4-(Heptadeca fluorononyloxy).
jfor 2-cyclohexene-1-ol,
kfor benzaldehyde, nr: not reported.
with hydrobenzoin units at different positions. But, the
structural design of R group covalently bounded to the
peripheral or non-peripheral position of phthalocyanine
skeleton can play a crucial role in the oxidation of benzyl
alcohol when compare the results in this study with our
previous studies.[33, 40] In conclusion, we have shown the
importance of structural design of R group substituted to
phthalocyanine skeleton for high conversion efficiency in
the oxidation of benzyl alcohol.
SCHEME 4 Proposed reaction mechanism for the formation
of active species from Co(II)-Pc and TBHP
ACKNOWLEDGMENTS
metal to the center of phthalocyanine. Novel cobalt
(II) phthalocyanines were characterized and investigated
their catalytic activity in oxidation of benzyl alcohol. The
better benzaldehyde selectivity were obtained in the pres-
ence of phenyl ring on hydrobenzoin in case cobalt
(II) phthalocyanines 13–15 and 17–19 compared to cobalt
(II) phthalocyanines 16 and 20 containing non-
substituted hydrobenzoin at peripheral or non-peripheral
positions, respectively. According to experimental results,
changing the binding positions of phenyl ring on hydro-
benzoin did not affect the conversion and selectivity of
benzyl alcohol to benzaldehyde indicating that the posi-
tional isomerism has no critical effect on the oxidation of
benzyl alcohol. Hence, it can be said that structural isom-
erism has no critical effect on the oxidation of benzyl
alcohol in the case of phthalocyanine ring substituted
This study was supported by Türkiye Bilimsel ve
Teknolojik Aras¸tırma Kurumu (TUBITAK)(Project No:
_
ꢀ
MAG-115R015). Ilker Ümit Karayigit and Seda Kıl-
ıçarslan (Department of Chemistry, Osmaniye Korkut
Ata University) are gratefully acknowledged for their
assistance.
DISCLOSURE STATEMENT
There is no conflict of interest between the authors.
ORCID
Halil Zeki Gök https://orcid.org/0000-0001-7641-2683
Yas¸ar Gök https://orcid.org/0000-0003-3134-7560
Mustafa Kemal Yılmaz https://orcid.org/0000-0002-
9969-3956

14 of 14
GÖK ET AL.
[29] K. B. Sharpless, W. Amberg, Y. L. Bennani, G. A. Crispino,
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SUPPORTING INFORMATION
Additional supporting information may be found online
in the Supporting Information section at the end of this
article.
How to cite this article: Gök HZ, Gök Y,
Yılmaz MK. Oxidation of benzyl alcohol by novel
peripherally and non-peripherally modular C2-
symmetric diol substituted cobalt (II)
phthalocyanines. Appl Organomet Chem. 2020;
e5669. https://doi.org/10.1002/aoc.5669