Synthesis of carbazole-derived ligands and their metal complexes: characterization, thermal, catalytic, and electrochemical features

Article abstract of DOI:10.1007/s00706-016-1756-0

Abstract: Heading from N-ethylcarbazole, two novel carbazole-derived imine compounds and their copper, cobalt, and nickel complexes have been synthesized. Their open structures have been proposed on the basis of various spectroscopic analyses. All the synthesized compounds have also been examined for their catalytic, thermal, and electronic features. Good or moderate results have been obtained for the catalytic activities of the synthesized complexes. Thermal features showed that the coordination compounds can be used in many organic reactions like oxidation reactions depending on high temperatures. Electronic features of these newly synthesized compounds have also been reported for the first time with this paper. Graphical abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s00706-016-1756-0

Monatsh Chem
DOI 10.1007/s00706-016-1756-0
ORIGINAL PAPER
Synthesis of carbazole-derived ligands and their metal complexes:
characterization, thermal, catalytic, and electrochemical features
Selma Bal1 Süleyman Köytepe2 Joseph D. Connolly3
·
·
Received: 18 November 2015 / Accepted: 7 April 2016
© Springer-Verlag Wien 2016
Abstract Heading from N-ethylcarbazole, two novel
carbazole-derived imine compounds and their copper,
cobalt, and nickel complexes have been synthesized. Their
open structures have been proposed on the basis of various
spectroscopic analyses. All the synthesized compounds
have also been examined for their catalytic, thermal, and
electronic features. Good or moderate results have been
obtained for the catalytic activities of the synthesized
complexes. Thermal features showed that the coordination
compounds can be used in many organic reactions like
oxidation reactions depending on high temperatures.
Electronic features of these newly synthesized compounds
have also been reported for the first time with this paper.
Graphical abstract
Keywords Catalysis · Organometallic ·
Electrochemical · Ligand · Thermal
Introduction
Schiff base ligands and their metal complexes have been
studied and are still being studied extensively for years due
to their synthetic flexibilities. They have captured much
attention in the fields relating antimicrobial activity and
catalytic activity especially in the reactions including alkene
epoxidations [1–6] and epoxide ring openings [7–9]. Epox-
ides are the cyclic ethers produced by oxidation reactions of
alkenes. An important method for preparing epoxides is by
reaction with peroxyacids. In the literature, various oxida-
tion reagents have been used in many oxidation reactions of
different alkenes. However, it is important that the reagents
used are cheap and environmentally friendly and this is why
hydrogen peroxide is generally preferred as oxidating agent
in these kinds of reactions. Epoxidation of alkenes is also an
important biochemical reaction. For example, epoxidation of
an alkene group in a precursor molecule called squalene is a
key step in the pathway by which our bodies synthesize
Electronic supplementary material The online version of this
article (doi:10.1007/s00706-016-1756-0) contains supplementary
material, which is available to authorized users.
& Selma Bal
selmadagli9@hotmail.com
1
Chemistry Department, Science and Art Faculty,
Kahramanmaras¸ Sutcu Imam University, Avsar Campus,
46050 Kahramanmaras, Turkey
2
˙ ¨
¨ ¨
Kimya Bolumu, Fen Edebiyat Fakultesi, Inonu Universitesi,
Merkez Kampu¨su¨, 44280 Malatya, Turkey
¨ ¨
¨
¨
3
Chemistry Department, University of Glasgow, Joseph Black
Building, Glasgow G12 8QQ, UK
123

S. Bal et al.
cholesterol. Among alkene epoxidation reactions, styrene
and cyclohexene oxidation reactions captured quite high
attention due to their versatile usage as starting materials in
many synthetic organic reactions. In the literature, we have
previously synthesized some carbazole-derived Schiff bases
and examined their catalytic activity toward the oxidation
reactions of both cyclohexene and styrene [10]. Schiff base
complexes were and are still being examined for their cat-
alytic activities toward many different organic reactions
[11–15]. Literature survey also shows that imines and their
complexes have been extensively studied for their antibac-
terial, antifungal, antitumor, and anticancer activities [16–
19]. Many studies [20, 21] have shown the relationships
between the metal ions and their metal complexes as
antibacterial agents, which is a subject of great interest. This
work, first of all, deals with the synthesis and purification of
9-ethyl-3-carbazolecarboxaldehyde from N-ethylcarbazole.
Then, it moves on to the synthesis and characterization of
the two novel Schiff bases and their copper(II), cobalt(II),
and nickel(II) coordination compounds. Fully characterized
new coordination compounds were used as catalysts in the
epoxidation reactions of styrene and cyclohexene, which are
important intermediates in the synthetic routes of different
organic chemicals. In addition to their catalytic activities,
thermal and electronic features of the newly synthesized
compounds have also been explained for the first time.
overlapped doublet at 7.09 ppm. Both ligands showed the
hydroxyl proton at 10.1 ppm as a weak singlet. 13C NMR
spectra of the ligands revealed the imine carbon signals at
157.8 ppm for L1 and at 158.2 ppm for L2. The ethyl group
on the carbazole unit was seen at 37.8 and 13.8 ppm for
both ligands. For ligand L1, the methyl group on the phe-
nolic ring was at 20.9 ppm. The rest of the aromatic
carbons were seen between 100 and 150 ppm.
In the IR spectra of the ligands L1 and L2, we were able
to see weak signals at 1628 and 1622 cm−1, respectively,
corresponding the imine stretching frequency. This vibra-
tion was red-shifted in its complexes. Aromatic C–H
vibrations were seen at around 3050 cm−1 and the aliphatic
vibrations were between 2918 and 2973 cm−1. Although
the NMR spectrum of the ligands gave hydroxyl signals at
10.1 ppm, the IR spectrum of them gave weak broad peak
at around 3350 and 3374 cm−1; however, many sharper
peaks were observed at 1262 and 1328 cm−1 for O–H
bendings. In all of their complexes, hydroxyl stretchings
were also observed above 3200 cm−1. However, this time,
the hydroxyl stretchings were somewhat shifted than those
of the ligands, which proves the chelation between the
metals and the hydroxyls present on the phenolic rings. In
the IR spectra of the ligands and their complexes, we were
also able to observe some out-of-plane C–H bending
vibration, which tells us about the substitution patterns of
the benzene rings. In our compounds, we have three aro-
matic rings and the weak vibrations seen at 839 (L1), at
901 cm−1 (L1-Co and L1-Cu), and at 888 cm−1 (L1-Ni)
correspond our two meta-substituted benzene ring con-
taining one isolated hydrogen. The sharp signals at
745 cm−1 (L1), 747 cm−1 (L1-Co and L1-Cu), and 746 cm−1
(L1-Ni) proves that we have one ortho-substituted benzene
ring. Similar values were seen in the IR spectra of ligand
L2 and its complexes. IR spectra of all coordination com-
pounds showed M–N stretching frequencies between 536
and 539 cm−1. We were able to observe M–O stretching
frequencies both as asymmetric and as symmetric in the
ranges 611–613 and 583–589 cm−1, respectively [24].
Other than the sharp peak at around 747 cm−1, corre-
sponding to the ortho-substituted benzene ring, IR spectra
of all the complexes gave three intense bands belonging
to asymmetric and symmetric carboxylate stretchings,
which proves the chelation of the carboxyls with metals.
It is known that there are three possible carboxylate
coordination modes: unidentate, bidentate, and bridging.
And the splitting value of carboxylate stretching bands
(Δ = Ѵas − Ѵs) is frequently used to attempt to distinguish
between the three carboxylate coordination modes [25].
Deacon and Phillips [26] sought to correlate the differ-
ence, Δ, between the asymmetric and symmetric
stretchings of carboxylates in a number of acetate and
trifluoroacetate complexes. They concluded that
Results and discussion
Spectral analysis
Proton NMR spectra of the synthesized ligands (Scheme 1)
gave quite similar signals. For example, we can see the
ethyl group attached to nitrogen on the carbazole unit at
around 4.4 ppm (2H-14) as quarted (J = 7.2 Hz) and at
1.5 ppm (3H-15) as triplet (J = 7.2 Hz). The imine protons
for the ligands L1 and L2 were seen at 8.84 and 8.85 ppm,
respectively. Among the carbazole aromatic ring protons in
ligand L1, next to the imine proton signal, the doublet at
8.61 ppm (d, J = 1.2 Hz) belongs to H-4 and the two
signals appearing next to H-4 belongs to H-1 (8.2 ppm, d,
J = 8.6 Hz) and H-2 (8.1 ppm, dd, J = 8.6 Hz, 1.5 Hz). We
can see the other aromatic protons between 6.5 and
7.8 ppm for both ligands. We could clearly see the phenolic
aromatic protons H-19 and H-20, belonging L1, at
6.97 ppm (d, J = 8.1 Hz) and at 7.04 ppm (dd, J = 7 Hz,
0.5 Hz). The broad singlet seen at 7.2 ppm belongs to H-22.
The methyl protons on the phenolic ring in the same ligand
(L1) appeared as a sharp singlet at 2.4 ppm. As for the
ligand L2, we could see the phenolic aromatic protons H-20
and H-21 as doublet of triplets at 6.97 and 7.22 ppm. The
other two aromatic protons on the same ring gave
123

Synthesis of carbazole-derived ligands and their metal complexes: characterization, thermal…
Scheme 1
unidentate acetate coordination is generally associated
with Δ values higher than 200 cm−1, bridging coordina-
tion shows lower Δ values than 150 cm−1, and the
compounds with very low Δ values (≪150 cm−1) are
generally indicative of bidentate acetate chelation. In all
of our synthesized complexes, these Δ values were cal-
culated (Table 1) and they were found to be much higher
than 200 cm−1, which proves unidentate chelating of
acetates.
spectra of the complexes showed some bands in the high-
energy region at 309–332 nm which can be assigned to
charge transfer L-M bands [27, 28]. The complex com-
pounds showed d–d transitions between 423 and 434 nm.
The EDAX spectra of all the coordination compounds
showed characteristic Kα and Lα values for all the coordi-
nated metals. In addition to the energy dispersive X-ray
analysis (EDAX), scanning electron microscopy (SEM)
images of all complexes provided valuable information
concerning surface morphology. While the EDAX images
confirm the existence of the metals and the purity of the
UV–Vis spectra of the ligands and the complexes
showed absorption bands between 208 and 434 nm. The
123

S. Bal et al.
given in Table 2 and they are in good agreement with the
calculated values.
Table 1 Asymmetric and symmetric IR values of carboxylate coor-
dinations and the difference between them
Mass spectra of the synthesized ligands and their com-
plexes showed parent ion peaks as well as some other peaks
belonging to different fragments suitable to the proposed
structures. For example, the mass spectra of all the coordi-
nation compounds of L1 showed a mass peak at m/z = 327
corresponding to the ligand itself (C22H20N2O). And since
there are two of L1 in the complexes, another peak at around
m/z = 654 was also seen in the mass spectra of Co(II) and
Cu(II) coordination compounds of this ligand. For all the
complexes of L2, the mass peaks for the two phenolic groups
were clearly observed at around m/z = 186.
Magnetic susceptibility studies revealed the geometries of
all the complexes to be octahedral. For the copper com-
plexes, the magnetic moments were calculated as 2.03 and
1.91 B.M. [32]. The cobalt complexes gave these values as
5.08 and 4.98 B.M [33]. The nickel complexes also revealed
their characteristic magnetic moment values as 3.4 and 4.1
B.M., suggesting octahedral geometry [33, 34]. Molar con-
ductivities of the ligands and their coordination compounds
were between 1.5 and 25.4 Ω−1 cm2 mol−1, which proves
their nonelectrolite features [35].
Complex
Ѵasymmetric
Ѵsymmetric
Δ (Ѵasym − Ѵsym)
Co(L1H)2(OAc)2
Cu(L1H)2(OAc)2
Ni(L1H)2(OAc)2
Co(L2H)2(OAc)2
Cu(L2H)2(OAc)2
Ni(L2H)2(OAc)2
1681, 1579
1680, 1579
1680, 1567
1681, 1574
1681, 1574
1679, 1575
1232
1232
1229
1234
1232
1230
449, 347
448, 347
451, 338
447, 340
449, 342
449, 345
complexes, SEM photographs display uniform and homo-
geneous matrixes of the synthesized complexes. SEM
photographs and EDAX graphics of coordination com-
pounds Co(L1H)2(OAc)2 and Cu(L2H)2(OAc)2 are given in
Figs. 1 and 2.
Additionally, spectrochemical analyses by energy dis-
persive X-ray fluorescence (EDXRF) were performed on
all the coordination compounds to detect the presence of
metals in them. As it is known, this technique is based on
the fact that the chemical elements emit characteristic
radiation when subjected to appropriate excitation [29, 30].
The inner shell vacancies in the atoms of elements, created
by excitation, are filled by transition of electrons from
outer orbitals leading to emission of characteristic X-rays
[31]. The energy spectra of characteristic X-rays are
measured by a high-resolution Si(Li) detector. The con-
centration values were calculated using the net area under
the Kα peaks of cobalt, copper, and nickel. The results are
Thermal analysis
Thermal analysis of the Schiff base ligands and their
complexes was studied from ambient temperature to 800 °C
in nitrogen atmosphere. Thermal analysis of the ligands
gave two degradation steps, and between two Schiff bases,
Fig. 1 EDAX spectrum of complex Co(L1H)2(OAc)2 and its SEM photograph
123

Synthesis of carbazole-derived ligands and their metal complexes: characterization, thermal…
Fig. 2 EDAX spectrum of complex Cu(L2H)2(OAc)2 and its SEM photograph
Table 2 Metal percentages estimated by EDXRF
groups on the two carbazole units. Finally, the carbazole
unit (2 9 C12H7N) losses were observed between 420 and
625 °C with a total mass loss of 39.1 % (calc. 39.7 %). The
residual parts of the coordination compounds of L1 revealed
the two imine groups (2 9 CH=N) and the oxidized metals;
however, in addition to these parts, cobalt complex of L1
showed the two acetates as one of its residuals too. Ligand
L1 was more temperature resistant than its complexes.
TG graphics of L2 and its complexes revealed mass
losses in two degradation steps, and among the complexes
of L2, cobalt and copper complexes were slightly more
stable toward temperature than the ligand itself and nickel
complex of it. The first degradation steps of nickel and
copper complexes of L2 gave mass losses of 43.9 % (calc.
44.3 %) and 51.8 % (calc. 51.2 %), respectively, corre-
sponding to phenolic groups with imines attached, two
acetates, and the ethyl groups on carbazoles. However, the
mass loss for the two ethyl groups for the nickel complex
of L2 was calculated in the residual part. Generally, all the
complexes of this ligand gave similar patterns in their
thermal graphics, and only the cobalt complex of L2
revealed the biggest mass loss of 69.8 % (calc. 70.6 %)
attributed to two carbazoles (2 9 C12H7N) and two phe-
nolic groups with imines in the temperature range 260–
600 °C. And we could see the metallic cobalt for this
complex in the residual part with a percentage of 7.4 %
(calc. 7.3 %). The loss of carbazole units was calculated
and found around 40 % in TG graphics of all the coordi-
nation compounds and they were generally observed in the
second degradation part of all the TG graphics (Figs. 3, 4).
Compound
Chemical
formula
Calculated
value/%
Experimental
values
(EDXRF)/%
Co(L1H)2(OAc)2
Cu(L1H)2(OAc)2
Ni(L1H)2(OAc)2
Co(L2H)2(OAc)2
Cu(L2H)2(OAc)2
Ni(L2H)2(OAc)2
C48H44CoN4O6
C48H44CuN4O6
C48H44N4NiO6
C46H40CoN4O6
C46H40CuN4O6
C46H40N4NiO6
7.08
7.6
7
8
7
7
8
7
0.3
0.3
0.3
0.3
0.3
0.3
7.06
7.33
7.86
7.3
L1 was the most stable ligand with a degradation starting
temperature of 200 °C. While L1 gives the loss of phenolic
group, which has the imine group attached, in the first half
of the degradation, L2 gives this loss in the second half of
its thermal graphic. Carbazole losses were also observed as
vice versa in the thermal graphics of L1 and L2. Residual
part of L1 gave the ethyl group on the carbazole unit;
however, for L2, the calculations for the residual part
corresponded only the methyl part in the ethyl group.
Overall, the degradation of the two ligands was happened
in a total mass loss of 100 %.
All coordination compounds, except Ni(L1)2(AcO)2,
showed two degradation steps in their TG graphics. Nickel
(II) complex of L1 gave somewhat distorted three degrada-
tion steps, the first one happens between 130 and 325 °C
with a mass loss of 25.4 % (calc. 25.7 %) attributed to two
phenolic groups (2 9 C7H7O). The second loss with 20.9 %
(calc. 21.2 %) corresponds to the two acetates and the ethyl
123

S. Bal et al.
Fig. 3 TGA graphics of L1 and
its complexes
Fig. 4 TGA graphics of L2 and
its complexes
complex of L1 and Co(II) complex of L2, 71.2 and 68.7 %,
respectively. Therefore, styrene oxide selectivities for these
complexes were also slightly higher compared with the
other coordination compounds. The lowest styrene oxide
selectivity with 27.5 % belongs to Co(II) complex of L1. In
the cyclohexene oxidation reactions, all the coordination
compounds gave moderately good selectivities for
Catalytic activity
In both styrene and cyclohexene oxidation reactions, all
synthesized complexes showed good performances as cat-
alysts. In the styrene oxidation reaction, generally we
obtained high percentages for styrene conversion. The
highest ones among these percentages belong to Ni(II)
123

Synthesis of carbazole-derived ligands and their metal complexes: characterization, thermal…
Table 3 Styrene oxidation
results
Entry Catalyst
Styrene conversion/% Selectivity/%
Styrene oxide Benzaldehyde Benzoic acid Others
1
2
3
4
5
6
Ni(L1)2(OAc)2 71.2
43.3
40.1
27.5
33.9
36.2
39.4
46.7
44.6
62.5
51.1
46.8
45.4
6.4
10.3
5.7
3.6
5.0
4.3
6.1
5.8
4.9
Cu(L1)2(OAc)2 66.4
Co(L1)2(OAc)2 35.5
Ni(L2)2(OAc)2 41.4
Cu(L2)2(OAc)2 56.4
Co(L2)2(OAc)2 68.7
8.9
11.2
10.3
Others: phenylacetaldehyde, 1-phenylethane-1,2-diol
Reaction temperature: 80 °C (353.15 K)
Solvent: acetonitrile
Table 4 Cyclohexene oxidation
results
Entry Catalyst
Cyclohexene conversion/% Selectivity/%
Cyclohexene oxide 2-Cyclohexene-1-ol Others
1
2
3
4
5
6
Ni(L1)2(OAc)2 43.1
31.1
28.4
25.7
23.2
27.7
28.3
10.7
14.3
19.8
21.6
18.5
20.9
58.2
57.3
54.5
55.2
53.8
50.8
Cu(L1)2(OAc)2 40.8
Co(L1)2(OAc)2 32.1
Ni(L2)2(OAc)2 35.4
Cu(L2)2(OAc)2 39.7
Co(L2)2(OAc)2 38.3
Others: 2-cyclohexene-1-one, 2-cyclohexene-1-hydroperoxide
Reaction temperature: 80 °C (353.15 K)
Solvent: acetonitrile
cyclohexene oxide. The highest cyclohexene conversions
were obtained for Ni(II) and Co(II) complex of L1 with
percentages of 43.1 and 40.8, respectively. In general, Ni
(II) complex of both ligands showed good catalytic activity
in the oxidation reactions of both styrene and cyclohexene.
The results for these reactions can be seen in Tables 3 and
4, and the oxidation reaction schemes are given in
Scheme 2.
0.56 V for the anodic peaks and −0.17 and 0.51 V for the
cathodic peaks, the value between the anodic and cathodic
potentials was calculated near 1. Similar potentials were
recorded for this ligand in its 500 mV s−1 scan rate
(Fig. 5a). For 750 and 1000 mV s−1 scan rates, same ligand
gave quasi-reversible processes. Cobalt complex of ligand
L1 gave both reversible and irreversible potentials in all of
its scan rates. Nickel complex of the same ligand, also,
gave reversible redoxes in all of its scan rates except the
scan rate 100 mV s−1. Figure 6a shows CV graphics for Ni
(L1H)2(OAc)2 at 500 and 750 mV s−1 scan rates. Copper
complex of the same ligand also gave well-defined rever-
sible processes for the scan rates 100, 250, and
1000 mV s−1. For this complex, irreversible processes were
recorded for the other scan rates.
Electronic graphics of L2 revealed irreversible redox
processes in 100 and 1000 mV s−1; however, it showed Epa
values at 0.56, 0.67 V and Epc values at 0.59, 0.63 V for
scan rates 250 and 500, respectively, whose Ipa: Ipc values
equaled 1, proving their reversibility (Fig. 5b). Among the
coordination compounds of ligand L2, only the copper and
cobalt complexes revealed well-defined reversible pro-
cesses in most of their scan rates, and only the scan rates
100 and 250 mV s−1, for these complexes, showed irre-
versible or pseudo-reversible redoxes. Nickel complex of
Cyclic voltammetry analysis
Cyclic voltammograms of the ligands and their complexes
were run in DMF—0.1 M Bu4NBF4 and CH3CN—0.1 M
Bu4NBF4 as supporting electrolyte at 293 K. All potentials
quoted refer to measurements run at a scan rates (Ѵ) of 100,
250, 500, 750, and 1000 mV s−1 and against an internal
ferrocene–ferrocenium standard, unless otherwise stated.
For the scan rates 100, 250, and 500 mV s−1, our ligand L1
showed reversible redox processes, e.g., for the scan rate
100 mV s−1, anodic peak potential was recorded as 0.56 V
and the reverse scan gave the cathodic peak at 0.58 V. The
ratio between the anodic and cathodic peak potentials was
calculated as I = Ipa:Ipc = 0.97 (1), proving the reversible
process. Also, for the same ligand, the scan rate
250 mV s−1 gave two reversible peak potentials; −0.21 and
123

S. Bal et al.
Scheme 2
(a)
(b)
Fig. 5 CV graphics of L1 (a) and L2 (b) for scan rates 250 and 500 mV s−1
Fig. 6 CV graphics of Ni(L1)2(OAc)2 (a) and Co(L2)2(OAc)2 (b) for scan rates 500 and 750 mV s−1
123

Synthesis of carbazole-derived ligands and their metal complexes: characterization, thermal…
this ligand, however, mostly revealed irreversible or semi-
reversible redox procedures for all of its scan rates. For the
cobalt complex of L2, the CV graphics for the scan rates
500 and 750 mV s−1 are given in Fig. 6b.
electron beam energies from 3 to 30 keV had been used. In
all cases, the beam was at normal incidence to the sample
surface and the measurement time was 100 s. All the
EDAX spectra were corrected by using the ZAF correction,
which takes into account the influence of the matrix
material on the obtained spectra. Further, the presence of
metals in the complexes was detected by an energy dis-
persive X-ray fluorescence (EDXRF) spectrometer and its
percentage is estimated using CATXRF Program. Thermal
analyses of synthesized ligand and its metal complexes
were carried out on a PerkinElmer Thermogravimetric
Analyzer TG/DTA 6300 instrument under nitrogen atmo-
sphere between the temperature range 30 and 800 °C at a
heating rate of 10 °C/min. Magnetic measurements were
carried out by the Gouy method using Hg[Co(SCN)4] as
calibrant. Molar conductances of the Schiff base ligands
and their transition metal complexes were determined in
MeOH (ca. 10−3 M) at room temperature using a Jenway
Model 4070 conductivity meter.
Conclusion
The present work describes the synthesis and characteri-
zation of two carbazole-derived Schiff bases and their
copper(II), cobalt(II), and nickel(II) coordination com-
pounds. All spectral data and the thermal analysis
supported the proposed structures of the newly synthesized
compounds. Magnetic moment values strongly suggested
the geometries of the coordination compounds to be octa-
hedral. In thermal analysis, the coordination compounds of
L2, especially the copper(II) and cobalt(II) complexes,
were the most stable coordination compounds, compared
with the others. However, as for the ligands, L1 was much
more temperature resistant than L2. As a catalyst, nickel(II)
coordination compound of L1 showed higher conversion
percentages in the oxidation reactions of styrene and
cyclohexene compared with the other coordination com-
pounds that we have synthesized.
Synthesis of the ligands
Formylation of 9-ethylcarbazole was done by using
Vilsmeier formylating agent DMF and POCl3 [10, 22,
23]. The monoaldehyde was separated by flash chromatog-
raphy with ethyl acetate/hexane (1:10) as eluent. N-
Ethylcarbazole-3-carbaldehyde (1 mmol) was then reacted
with 1 mmol 2-amino-4-methylphenol to give (E)-2-[(9-
ethyl-9H-carbazol-3-yl)methyleneamino]-4-methylphenol
(L1) and with 1 mmol 2-aminophenol to give (E)-2-[(9-
ethyl-9H-carbazol-3-yl)methyleneamino]phenol. Reactions
were carried out in 30 cm3 ethanol under reflux for 9 h. The
resulting precipitates were recrystallized from methanol.
Experimental
9-Ethylcarbazole, phosphorus(V) oxychloride, 2-amino-4-
methylphenol, 2-aminophenol, acetate salts of copper(II),
cobalt(II), and nickel(II) were purchased from Sigma-
Aldrich. Nuclear magnetic resonance spectra were recor-
ded on a Bruker AV 400 MHz spectrometer in the solvent
CDCl3. Infrared spectra were obtained using KBr disks on
a Shimadzu 8300 FT-IR spectrophotometer in the region of
400–4000 cm−1. Ultraviolet spectra were run in ethanol on
a Schimadzu UV-160 A spectrophotometer. Mass spectra
of the ligand and the complexes were recorded on a LC/MS
APCI AGILENT 1100 MSD spectrophotometer. The oxi-
dation products were analyzed with a gas chromatograph
(Shimadzu, GC-14B) equipped with a SAB-5 capillary
column and a flame ionization detector. Elemental analyses
were performed on a LECO CHNS 932 elemental analyzer,
and the metal analyses were carried out on an Ati Unicam
929 Model AA Spectrometer in solutions prepared by
decomposing the compounds in aqua regia and subse-
quently digesting them in conc. HCl. Chemical
composition analysis by EDAX was performed with an
(E)-2-[[(9-Ethyl-9H-carbazol-3-yl)methylene]amino]-4-
methylphenol (L1, C22H20N2O)
Yield 2.7 g (80 %); m.p.: 177 °C; H NMR (400 MHz,
1
CDCl3): δ = 10.1 (s, OH), 8.84 (s, H-16), 8.61 (d,
J = 1.2 Hz, H-4), 8.20 (d, J = 8.6 Hz, H-1), 8.10 (dd,
J = 8.6, 1.5 Hz, H-2), 7.55 (ddd, J = 8.0, 7.0, 1.2 Hz, H-7),
7.45 (d, J = 7.4 Hz, H-5 overlapped with H-8), 7.45 (d,
J = 8 Hz, H-8 overlapped with H-5), 7.34 (ddd, J = 7.6,
7.1, 1.2 Hz, H-6), 7.20 (brs, H-22), 7.04 (dd, J = 7.0,
0.5 Hz, H-20), 6.97 (d, J = 8.1 Hz, H-19), 4.42 (q,
J = 7.2 Hz, 2H-14), 2.40 (s, 3H-23), 1.50 (t, J = 7.2 Hz,
3H-15) ppm; 13C NMR (100 MHz, CDCl3): δ = 157.8 (C-
16), 149.8 (C-18), 142.0 (C-10), 140.5 (C-13), 135.9 (C-
17), 129.3 (C-22), 128.5 (C-3), 127.4 (C-1), 126.4 (C-2),
123.3 (C-4), 123 (C-11), 122.3 (C-12), 120.7 (C-5), 119.8
(C-6), 116.4 (C-20), 114.4 (C-19), 108.8 (C-7), 108.9 (C-
8), 37.8 (C-14), 20.9 (C-23), 13.8 (C-15) ppm; FT-IR
(KBr): v = 3350 (OH), 3047 (C–HAr), 2973, 2920 (C–H),
1628 (CH=N), 1596 (C=CAr), 1328, 1262 (OH bending)
cm−1; UV–Vis (ethanol): λmax = 231, 274, 300, 331 nm;
MS: m/z = 328.2 (M+); ΛM = 1.9 Ω−1 cm2 mol−1.
¨
EDAX; Ronteck xflash detector analyzer was associated
with a scanning electron microscope (SEM, Leo-Evo
40xVP). The energy spectrum of characteristic X-rays is
measured with Bruker energy dispersive X-ray spectro-
scope (EDX) by a high-resolution Si(Li) detector. Incident
123

S. Bal et al.
(E)-2-[[(9-Ethyl-9H-carbazol-3-yl)methylene]amino]-
613 (νas, M–O), 587 (νs, M–O), 539 (M–N) cm−1; UV–Vis
(ethanol): λmax = 234, 276, 290, 332, 423 nm; MS (70 eV):
m/z = 833.0 (M+); ΛM = 17.1 Ω−1 cm2 mol−1; μeff = 3.4 B.
M.
phenol (L2, C21H18N2O)
1
Yield 2.1 g (76 %); m.p.: 191.2 °C; H NMR (400 MHz,
CDCl3): δ = 10.1 (s, OH), 8.85 (s, H-16), 8.62 (d,
J = 1.3 Hz, H-4), 8.20 (d, J = 8.0 Hz, H-1), 8.12 (dd,
J = 8.5, 1.4 Hz, H-2), 7.55 (dt, J = 8.2, 1.2 Hz, H-7), 7.46
(d, J = 8.5 Hz, H-5 overlapped with H-8), 7.46 (d,
J = 8.5 Hz, H-8 overlapped with H-5), 7.35 (dt, J = 7.5,
1.1 Hz, H-6), 7.22 (dt, J = 8.0, 1.4 Hz, H-21), 7.09 (d,
J = 8.0, 1.2 Hz, H-19 overlapped with H-22), 7.09 (dd,
J = 8.0, 1.2 Hz, H-22), 6.97 (dt, J = 7.4, 1.4 Hz, H-20),
4.41 (q, J = 7.2 Hz, 2H-14), 1.50 (t, J = 7.3 Hz, 3H-15)
ppm; 13C NMR (100 MHz, CDCl3): δ = 158.2 (C-16),
152.1 (C-18), 142.2 (C-10), 140.6 (C-13), 136.3 (C-17),
128.0 (C-3), 127.2 (C-1), 126.4 (C-2), 123.3 (C-4), 123.1
(C-11), 122.4 (C-12), 120.8 (C-5), 120.1 (C-21), 120.1 (C-
22), 119.9 (C-6), 115.9 (C-20), 114.8 (C-19), 109.0 (C-8),
108.8 (C-7), 37.8 (C-14), 13.8 (C-15) ppm; FT-IR (KBr):
v = 3374 (OH), 3047 (C–HAr), 2970, 2918 (C–H), 1622
(CH=N), 1583 (C = CAr), 1323, 1282 (OH bending) cm−1;
UV–Vis (ethanol): λmax = 209, 234, 292, 331 nm; MS:
m/z = 314.1 (M+); ΛM = 1.5 Ω−1 cm2 mol−1.
Di[(E)-2-[[(9-ethyl-9H-carbazol-3-yl)methylene]amino]-
phenol]cobalt(II) acetate (C46H42CoN4O6)
Yield 1.65 g (72 %); m.p.: 208.5 °C; IR (KBr): v = 3323
(OH), 3051 (C–HAr), 2918, 2850 (C–H), 1620 (CH=N),
1584 (C=CAr), 1681, 1574 (νas, COO−), 1234 (νs, COO−),
613 (νas, M–O), 583 (νs, M–O), 538 (M–N) cm−1; UV–Vis
(ethanol): λmax = 235, 276, 291, 332, 434 nm; MS (70 eV):
m/z = 803.1 ([M-2H]+); ΛM = 25.4 Ω−1 cm2 mol−1; μeff-
= 4.98 B.M.
Di[(E)-2-[[(9-ethyl-9H-carbazol-3-yl)methylene]amino]-
phenol]copper(II) acetate (C46H42CuN4O6)
Yield 1.44 g (62 %); m.p.: 222.2 °C; IR (KBr): v = 3327
(OH), 3051 (C–HAr), 2919, 2853 (C–H), 1618 (CH=N),
1585 (C=CAr), 1681, 1574 (νas, COO−), 1232 (νs, COO−),
612 (νas, M–O), 583 (νs, M–O), 536 (M–N) cm−1; UV–Vis
(ethanol): λmax = 235, 277, 291, 331, 433 nm; MS:
m/z = 811.8 ([M + H]+); ΛM = 20.3 Ω−1 cm2 mol−1;
μeff = 1.91 B.M.
Synthesis of the complexes
The ligand L1 or L2 (2 mmol) was taken into a 100-cm3
round-bottomed flask and dissolved in 20 cm3 ethanol.
Over this solution, 1 mmol of the acetate salt of the desired
metal dissolved in 25 cm3 ethanol was poured. The mixture
was left stirring under reflux for 24 h. The resulted
precipitates were then recrystallised from methanol/ethanol
(1:1) mixture.
Di[(E)-2-[[(9-ethyl-9H-carbazol-3-yl)methylene]amino]-
phenol]nickel(II) acetate (C46H42N4NiO6)
Yield 1.2 g (65 %); m.p.: 211.0 °C; IR (KBr): v = 3324
(OH), 3050 (C–HAr), 2974, 2919 (C–H), 1618 (CH=N),
1586 (C=CAr), 1679, 1575 (νas, COO−), 1230 (νs, COO−),
611 (νas, M–O), 583 (νs, M–O), 538 (M–N) cm−1; UV–Vis
(ethanol): λmax = 208, 238, 276, 332, 434 nm; MS:
m/z = 803.0 ([M-2H]+); ΛM = 16.1 Ω−1 cm2 mol−1; μeff-
= 4.1 B.M.
Di[(E)-2-[[(9-ethyl-9H-carbazol-3-yl)methylene]amino]-4-
methylphenol]cobalt(II) acetate (C48H46CoN4O6)
Yield 1.6 g (70 %); m.p.: 201 °C; IR (KBr): v = 3320 (OH),
3051 (C–HAr), 2973, 2920 (C–H), 1621 (CH=N), 1588
(C=CAr), 1681, 1579 (νas, COO−), 1232 (νs, COO−), 613 (νas,
M–O), 589 (νs, M–O), 538 (M–N) cm−1; UV–Vis (ethanol):
Oxidation procedure
A mixture of 1 9 10−3 mol catalyst, 20 cm3 solvent
(CH3CN), and 10 mmol cyclohexene/styrene was stirred
under nitrogen atmosphere in a 50-cm3 round-bottomed
flask. Then, 20 mmol of hydrogen peroxide (30 % in water)
was added dropwise. The resulting mixture was vigorously
stirred for 8 h at 80 °C. After filtration and washing with
solvent, the filtrate was concentrated and then subjected to
GC analysis. The yields were recorded as the GC yield
based on the starting styrene or cyclohexene. The identity
of the oxidation products was confirmed by GC–MS.
λ
max = 234, 274, 290, 331, 430 nm; MS: m/z = 832.0 ([M-
H]+); ΛM = 23.1 Ω−1 cm2 mol−1; μeff = 5.08 B.M.
Di[(E)-2-[[(9-ethyl-9H-carbazol-3-yl)methylene]amino]-4-
methylphenol]copper(II) acetate (C48H46CuN4O6)
Yield 1.67 g (73 %); m.p.: 210 °C; IR (KBr): v = 3318 (OH),
3053 (C–HAr), 2918, 2850 (C–H), 1620 (CH=N), 1588
(C=CAr), 1680, 1579 (νas, COO−), 1232 (νs, COO−), 613 (νas,
M–O), 589 (νs, M–O), 538 (M–N) cm−1; UV–Vis (ethanol):
λ
Λ
max = 234, 274, 291, 331, 429 nm; MS: m/z = 837.2 (M+);
M = 15.6 Ω−1 cm2 mol−1; μeff = 2.03 B.M.
References
Di[(E)-2-[[(9-ethyl-9H-carbazol-3-yl)methylene]amino]-4-
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Yield 1.55 g (68 %); m.p.: 205 °C; IR (KBr): v = 3321
(OH), 3047 (C–HAr), 2971, 2919 (C–H), 1618 (CH=N),
1587 (C=CAr), 1680, 1567 (νas, COO−), 1229 (νs, COO−),
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