Dicobaloxime/organodicobaloximes bridged by different axial groups: Synthesis, characterization, spectroscopy, and catalysis

Article abstract of DOI:10.1007/s11696-017-0165-0

In this study, the various ligands axially coordinated to two cobalt center bound to the N₄-oxime core in 12 new dicobaloxime/organodicobaloxime (1-12) complexes have been synthesized and characterized by NMR (¹H and ¹³C), UV-Visible, FT-IR, LC-MS, molar conductivity analysis, melting point, and magnetic susceptibility experiments with elemental analysis. These spectroscopic results indicate that the formation of new dicobaloxime/organodicobaloxime (1-12) complexes. The (C=N-OH) peaks disappeared in the ¹H-NMR spectrum of dicobaloxime/organodicobaloxime (1-12) complexes, while new peaks were observed at range 20.18-18.33 ppm, indicating that the groups of ligands have been transformed to intramolecular H-bridge (O-H?O). The dicobaloxime (1-6) species give a better cyclic voltammogram as compared to its organodicobaloxime derivatives (7-12) due to cyclic voltammograms of the organodicobaloximes (7-12) were poor. This is possibly due to the enhanced σ donation by R groups in the organocobaloximes which are substantially stabilized. The organodicobaloxime (10) showed much better catalytic activity compared to the other cobaoxime complexes. Graphical Abstract: The different dicobaloxime (1-6) and organodicobaloximes (7-12) have been synthesized for the first time. Their redox properties were investigated using cyclic voltammetric (CV) techniques in a DMSO solution. These dicobaloximes/organodicobaloximes have been used as homogeneous catalyst for synthesis of cyclic carbonates presence of DMAP as co-catalyst.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s11696-017-0165-0

Chem. Pap.
DOI 10.1007/s11696-017-0165-0
ORIGINAL PAPER
Dicobaloxime/organodicobaloximes bridged by different axial
groups: synthesis, characterization, spectroscopy, and catalysis
Ahmet Kilic1 Hamza Fırat1 Emine Aytar1 Mustafa Durgun1
•
•
•
•
Aysegul Kutluay Baytak1 Mehmet Aslanoglu1 Mahmut Ulusoy1
•
•
Received: 14 July 2016 / Accepted: 23 March 2017
Ó Institute of Chemistry, Slovak Academy of Sciences 2017
Abstract In this study, the various ligands axially coor-
dinated to two cobalt center bound to the N4-oxime core in
12 new dicobaloxime/organodicobaloxime (1–12) com-
plexes have been synthesized and characterized by NMR
(1H and 13C), UV–Visible, FT-IR, LC–MS, molar con-
ductivity analysis, melting point, and magnetic suscepti-
bility experiments with elemental analysis. These
spectroscopic results indicate that the formation of new
dicobaloxime/organodicobaloxime (1–12) complexes. The
(C=N–OH) peaks disappeared in the 1H-NMR spectrum of
dicobaloxime/organodicobaloxime (1–12) complexes,
while new peaks were observed at range 20.18–18.33 ppm,
indicating that the groups of ligands have been transformed
to intramolecular H-bridge (O–H_O). The dicobaloxime
(1–6) species give a better cyclic voltammogram as com-
pared to its organodicobaloxime derivatives (7–12) due to
cyclic voltammograms of the organodicobaloximes (7–12)
were poor. This is possibly due to the enhanced r donation
by R groups in the organocobaloximes which are sub-
stantially stabilized. The organodicobaloxime (10) showed
much better catalytic activity compared to the other
cobaoxime complexes.
Graphical Abstract The different dicobaloxime (1–6) and
organodicobaloximes (7–12) have been synthesized for the
first time. Their redox properties were investigated using
cyclic voltammetric (CV) techniques in a DMSO solution.
These dicobaloximes/organodicobaloximes have been used
as homogeneous catalyst for synthesis of cyclic carbonates
presence of DMAP as co-catalyst.
Keywords Co(III) complexes Á Dicobaloxime Á
Organodicobaloxime Á Cyclic voltammetry Á Cyclic
carbonates Á CO2 fixation Á Reaction parameters
Introduction
As inspired by models of Vit B12 co-enzyme in various
metabolisms, the different structures of cobaloxime or
organocobaloximes have been synthesized (Nayak et al.
2003; Schrauzer and Kohnle 1964; Cini et al. 1998;
Stolzenberg et al. 2007; Lawrence et al. 2016) and used in
various field by scientists due to great interest in
& Ahmet Kilic
kilica63@harran.edu.tr; kilica63@hotmail.com
1
Department of Chemistry, Faculty of Arts and Sciences,
Harran University, 63190 S¸anlıurfa, Turkey
123

Chem. Pap.
coordination chemistry and broad-scope potential applica-
tions as homogeneous catalysts in synthetic chemistry
reaction (Xiang et al. 2015; Yilmaz et al. 2008; Razavet
et al. 2005; Du et al. 2008; Kilic et al. 2015) in polymer
chemistry (Roberts et al. 2000), in liquid crystal behavior
(Alici and Karatas 2016), in EPR and DFT studies (Tiede
et al. 2012) and as other many areas. Besides, the coba-
loxime molecules made of earth-abundant, easy-to-handle
and inexpensive elements (e.g. Co elements) as homoge-
neous catalysts are of great potential and practical signifi-
cance for artificial photosynthesis and the effective
conversion of CO2 into valuable compounds under suit-
able conditions, because of their earth-abundant resources,
an alternate to the scarce, designable geometry, and regu-
latable electrochemical properties (Wang et al. 2015; Kilic
et al. 2013a; 2014). Up to now, the literature research shows
that numerous mononuclear Co(III) cobaloximes have been
synthesized and described, whereas reports on the structure
of Co(III) dicobaloximes examples are rather rare (Brown
1972; Herlinger and Ramakrishna 1985; Randaccio 1999;
Dreos et al. 2010). Most of the homoaxial or heteroaxial
ligand bridged dicobaloxime complexes reported to date
contains pyrazine or similar groups as the bridging ligand
(Dutta et al. 2015; Kumar and Seidel 2013). However,
research on the structure of the chloro or benzyl groups and
neutral diamine containing bridged dicobaloxime/organodi-
cobaloxime complexes is rather rare.
of CO2 through the assistance of axial ligand-bridged
dicobaloxime and organodicobaloximes as homogeneous
catalysts. The dicobaloxime or organodicobaloximes are
stable-air, low-cost, high activity and easily obtained as
compared to the other class metal complexes are surpris-
ingly remained unexplored as catalysts for the transfor-
mation of CO2 to value-added chemicals. These complexes
(1–12) have been characterized by various spectroscopic
methods such as NMR (1H and 13C) spectroscopy, UV–
Visible spectroscopy, FT-IR spectroscopy, Mass spec-
troscopy, molar conductivity analysis, melting point, and
magnetic susceptibility experiments with elemental analy-
sis. Also, the redox studies were discussed on a glassy
carbon electrode in DMSO in the presence of 0.1 M
n-Bu4NClO4 as the supporting electrolyte using cyclic
voltammety (CV) methods.
Experimental
General considerations
All chemicals and solvents commercially available were
purchased from commercial sources and without the spe-
cial requirement of any additional chemical process used as
received. The NMR (1H and 13C) spectra were recorded in
5 mm tubes at 25 °C with a Bruker Avance 300 NMR at
1
A number of studied catalytic systems containing
equivalent homoaxial or non-equivalent heteroaxial
bridging ligands have been shown to affect the geometry of
the complex and redox properties of the Co(III) center of
cobaloximes (Serroni et al. 1996). From recent reports,
different design of cobaloxime or cobalt oxime catalysts
that have been utilized in electrocatalytic and photocat-
alytic water splitting have been described in detail, and the
mechanisms of the catalysis of hydrogen production from
water have been analyzed based on most recent studies
(Eckenhoff et al. 2013; Dempsey et al. 2009; Connolly and
Espenson 1986; Artero et al. 2011). In contrast, to the best
of our knowledge, there were not many reports in the lit-
erature dealing with the dicobaloxime or organodi-
cobaloxime catalysts for chemical fixation of CO2 to
synthesize value-added chemicals. There are several pos-
sible approaches for catalytic conversion of CO2 into
desirable products in view of resource utilization and
reduce the levels of CO2 in the atmosphere. One of the
most promising strategies in this field has been the syn-
thesis of cyclic carbonates from CO2 and various epoxides
(Anastas and Lankey 2000; Darensbourg and Holtcamp
1996; Cuesta-Aluja et al. 2016; Al-Qaisi et al. 2016;
Martinez et al. 2015).
300 MHz for H and 75 MHz for 13C, respectively. The
NMR chemical shifts were referenced to the residual sol-
vent as determined relative to TMS (d = 0 ppm); coupling
constants (J) are in Hertz with chemical shifts given in ppm
at 25 °C. Elemental analyses (C, H, and N) were performed
on an LECO CHNS model 932 elemental analyzer. Infra-
red spectra were obtained on a Perkin-Elmer Two ATR
Fourier transform spectrometer in the range of
400–4000 cm-1. UV–Visible spectra were obtained using
quartz cells at 25 °C in a Perkin-Elmer model Lambda 25
spectrophotometer in the range of 200–1100 nm and
C2H5OH with CH2Cl2 was used as solvents. Magnetic
susceptibilities are measured by the Gouy methods and the
experimental results were obtained on a Sherwood Scien-
tific Magnetic Susceptibility Balance (Model MK1) at
25 °C. The compound Hg[Co(SCN)4] has been preferred as
a calibrant and diamagnetic corrections were calculated
from Pascal’s constants. Melting points of all compounds
have been determined in open capillary tubes with an
Electrothermal 9100 melting point apparatus and are
uncorrected. Molar conductivities (KM) measurements
were performed on an Inolab Terminal 740 WTW Series in
DMF solvent. The mass spectra (LC–MS) were obtained
using an Agilent LC–MS/MS spectrometer. The redox
studies were recorded using an EcoChemie Autolab
PGSTAT 12 potentiostat/galvanostat (Utrecht, The
Here, our aim is to draw attention to the organic solvent-
free synthesis of cyclic carbonates from chemical fixation
123

Chem. Pap.
(a)
(b)
Scheme 1 Synthesis of dioxime ligands (L1H2) and (L2H2); a n-C4H9ONO, C2H5ONa, -5 °C, b CH3COONa, NH2OH.HCl, EtOH, reflux
temperature
Netherlands) with the electrochemical software package
4.9. As the electrode system, 3 mm a GCE working elec-
trode (Bioanalytical Systems, Lafayette, USA), a Pt wire as
counter electrode and and an Ag/AgCl as reference elec-
trode (Metrohm, Switzerland). Catalytic tests were per-
formed in a PARR 4560 50 mL stainless pressure reactor.
Gas chromatography was performed on an Agilent 7820A
GC system with nitrogen as the carrier gas. The ligands
(L1H2) and (L2H2) were synthesized following the proce-
dure with some modifications (Kilic et al. 2013b, 2014) and
briefly the syntheses are given in Scheme 1.
2952-2856 t(Aliph-CH), 1603 t(C=N), 1557-1446
t(C=C), 1266 t(N–O) and 501 t(Co–N). 1H-NMR
(DMSO-d6, TMS, 300 MHz, d ppm): 18.62 (d, 4H,
J = 8.5 Hz, O–H_O), 7.57-6.86 (m, 16H, Ar–CH), 2.77
(s, 12H, Ar-CH3), 2.42 (s, 12H, C-CH3) and 2.33-1.24 (m,
16H, NH2 and Aliph-CH2). 13C-NMR (DMSO-d6, TMS,
75 MHz, d ppm): 150.05 (C1 of oxime), 142.83 (C2 of
oxime), 139.09 and 138.88 (C6 of Ar), 130.72 and 129.72,
(C3 of Ar), 128.96 (C4 of Ar), 128.17 (C5 of Ar), 31.12
(DAH-CH2), 21.51 (Ar-CH3) and 14.72 (CH3C = NOH).
UV–Vis (kmax/nm (loge), * = shoulder peak): 253 (4.65),
320 (4.36), 603* and 869* (in C2H5OH); 254 (4.58), 324
(4.12), 586 (2.58) and 879* (in CH2Cl2).
Synthesis of the dicobaloxime complexes (1-6)
The dioxime ligands (L1H2) or (L2H2) (2.30 g,
12.0 mmol) and CoCl2.6H2O (1.43 g, 6.0 mmol) were
dissolved in 100 mL of 96% ethanol and stirred for 40 min
with occasional swirling under a nitrogen atmosphere. The
mixtures turned green immediately. The green reaction
mixtures were gradually heated to reflux temperature and
maintained at this temperature for 2–3 h. After the green
mixtures were allowed to cool to room temperature and
1,6-diaminohexane (DAH), 4,40-bipyridine (4,40-bpy) or
2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-dipropanamine
(TUPA) (3.0 mmol) was added to mixture as axial-bridged
ligand and air was passed through the solution for about
5 h. A desired product was formed as brown precipitate
after water (10 mL) addition. Recrystallization from CH2-
Cl2/C2H5OH by slow evaporation afforded pure com-
pounds obtained. The obtained compounds were washed
successively with small amounts of water, and diethyl ether
and finally air-dried.
[(L2H)2CoCl-(DAH)-CoCl(L2H)2] (2)
Color: brown, yield: 79%, m.p: 189 °C, Anal. Calc. for
[C46H60N10O8Cl2Co2] (F.W: 1069.8 g/mol): C, 51.64; H,
5.65; N, 13.09. Found: C, 51.59; H, 5.58; N, 13.13%.
KM = 18 X-1cm2 mol-1 (in DMF), leff = Dia, LC–MS
(Scan ES?): m/z (%) 1069.5 (20) [M]?. FT-IR (KBr pellet,
t
max/cm-1): 3543-3104 t(O–H_O/NH2), 3026 t(Ar–CH),
2963-2870 t(Aliph-CH), 1601 t(C=N), 1551-1456
t(C=C), 1270 t(N–O) and 512 t(Co–N). 1H-NMR
(DMSO-d6, TMS, 300 MHz, d ppm): 20.18 (d, 4H,
J = 7.5 Hz, O–H_O), 8.45 (s, 4H, CH=N), 7.48 (d, 8H,
J = 8.0 Hz, Ar–CH), 7.23 (d, 8H, J = 8.0 Hz, Ar–CH),
2.67–2.56 (q, 8H, CH3–CH2) and 1.25-0.84 (m, 28H, CH3–
CH2, NH2 and Aliph-CH2). 13C-NMR (DMSO-d6, TMS,
75 MHz, d ppm): 151.24 (C1 of oxime) and 145.01 (C2 of
oxime), 141.27 (C6 of Ar), 131.90 (C3 of Ar), 128.21 (C4 of
Ar) and 127.72 (C5 of Ar), 31.13 (DAH-CH2), 28.39 (CH3–
CH2) and 15.97 (CH3-CH2). UV–Vis [kmax/nm (loge)]: 238
(4.80) and 266 (3.93) (in C2H5OH); 221 (4.56) and 259
(3.86) (in CH2Cl2).
[(L1H)2CoCl-(DAH)-CoCl(L1H)2] (1)
Color: brown, yield: 77%, m.p: 185 °C, Anal. Calc. for
[C46H60N10O8Cl2Co2] (F.W: 1069.8 g/mol): C, 51.64; H,
5.65; N, 13.09. Found: C, 51.60; H, 5.58; N, 13.04%.
KM = 16 X-1cm2 mol-1 (in DMF), leff = Dia, LC–MS
(Scan ES?): m/z (%) 1069.3 (20) [M]?. FT-IR (KBr pellet,
[(L1H)2CoCl-(4,40-bpy)-CoCl(L1H)2] (3)
Color: brown, yield: 78%, m.p: 189 °C, Anal. Calc. for
[C50H52N10O8Cl2Co2] (F.W: 1109.8 g/mol): C, 54.11; H,
4.72; N, 12.62. Found: C, 54.07; H, 4.68; N, 12.58%.
t
max/cm-1): 3582–3108 t(O–H_O/NH2), 3027 t(Ar–CH),
123

Chem. Pap.
KM = 11 X-1cm2 mol-1 (in DMF), leff = Dia, LC–MS
oxime), 139.70 and 139.13 (C6 of Ar), 130.73 and 129.62,
(C3 of Ar), 129.30 and 128.30 (C4 of Ar), 127.42 (C5 of
Ar), 101.38 (O–CH), 69.83 (O–CH2), 42.50 (NH2–CH2),
32.32 (C–CH2), 31.40 (CH–CH2), 24.02 (CH2–CH2–CH2),
(Scan ES?): m/z (%) 1109.7 (20) [M]?. FT-IR (KBr pellet,
t
max/cm-1): 3552-3178 t(O–H_O), 3082 t(Ar–CH),
2964-2869 t(Aliph-CH), 1604 t(C=N), 1542-1447
t(C=C), 1267 t(N–O) and 515 t(Co–N). 1H-NMR
(DMSO-d6, TMS, 300 MHz, d ppm): 18.36 (s, 4H, O–
H_O), 8.27 (s, 4H, Ar–CH), 7.06 (s, 4H, Ar–CH), 7.93 (d,
8H, J = 8.5 Hz, Ar–CH), 7.73 (d, 8H, J = 8.5 Hz, Ar–
CH), 2.33 (s, 12H, Ar-CH3) and 2.20 (s, 12H, C–CH3).
13C-NMR (DMSO-d6, TMS, 75 MHz, d ppm): 155.47 (C1
of oxime) and 153.83 (C2 of oxime), 152.99 and 152.47
(ortho C of 4,40-bpy), 151.13 (para C of 4,40-bpy), 140.27
(C6 of Ar), 130.74 (C3 of Ar), 129.47 (C4 of Ar), 128.22
(C5 of Ar), 126.72 (meta C of 4,40-bpy), 21.54 (Ar-CH3)
and 14.76 (CH3C=NOH). UV–Vis (kmax/nm (loge),
* = shoulder peak): 253 (4.76) and 323 (4.51) (in
C2H5OH); 234 (4.63), 255 (4.32) and 328* (in CH2Cl2).
21.51 (Ar-CH3) and 14.54 (CH3C=NOH). UV–Vis (kmax
/
nm (loge), * = shoulder peak): 251 (4.62), 324 (4.21) and
394* (in C2H5OH); 254 (4.43), 330 (4.03) and 407* (in
CH2Cl2).
[(L2H)2CoCl-(TUPA)-CoCl(L2H)2] (6)
Color: brown, yield: 80%, m.p: 197 °C, Anal. Calc. for
[C53H70N10O12Cl2Co2] (F.W: 1228.0 g/mol): C, 51.84; H,
5.75; N, 11.41. Found: C, 51.82; H, 5.77; N, 11.39%.
KM = 15 X-1cm2 mol-1 (in DMF) leff = Dia, LC–MS
(Scan ES?): m/z (%) 1228.2 (25) [M]?. FT-IR (KBr pellet,
t
max/cm-1): 3553-3121 t(O–H_O/NH2), 3030 t(Ar–CH),
2963-2871 t(Aliph-CH), 1604 t(C=N), 1513–1456
t(C = C), 1271 t(N–O) and 512 t(Co–N). 1H-NMR
(DMSO-d6, TMS, 300 MHz, d ppm): 20.02 and 19.98 (s,
4H, O–H_O), 8.45 (s, 4H, CH=N), 7.47 (d, 8H,
J = 8.1 Hz, Ar–CH), 7.22 (d, 8H, J = 8.1 Hz, Ar–CH),
4.42 (s, 2H, O–CH), 4.16 (d, 8H, J = 8.6 Hz, O–CH2),
2.76–2.55 (m, 20H, Aliph-CH2) and 1.24–1.06 (m, 16H,
NH2 and Aliph-CH3). 13C-NMR (DMSO-d6, TMS,
75 MHz, d ppm): 151.22 (C1 of oxime), 149.99 (C2 of
oxime), 141.25 (C6 of Ar), 128.92 and 128.55, (C3 of Ar),
128.32 and 128.18 (C4 of Ar), 127.72 (C5 of Ar), 101.73
(O–CH), 69.92 (O–CH2), 56.03 (NH2–CH2), 31.72 (C–
CH2), 31.14 (CH–CH2), 28.56 (CH3–CH2), 22.02 (CH2–
CH2–CH2) and 15.97 (CH3–CH2). UV–Vis (kmax/nm
(loge), * = shoulder peak): 239 (4.60), 264 (4.31) and
381* (3.88) (in C2H5OH); 259 (4.42), 341* and 419 (3.74)
(in CH2Cl2).
[(L2H)2CoCl-(4,40-bpy)-CoCl(L2H)2] (4)
Color: brown, yield: 80%, m.p: 166 °C, Anal. Calc. for
[C50H52N10O8Cl2Co2] (F.W: 1109.8 g/mol): C, 54.11; H,
4.72; N, 12.62. Found: C, 54.04; H, 4.64; N, 12.70%.
KM = 16 X-1cm2 mol-1 (in DMF), leff = Dia, LC–MS
(Scan ES?): m/z (%) 1109.9 (15) [M]?. FT-IR (KBr pellet,
t
max/cm-1): 3552-3113 t(O–H_O), 3059 t(Ar–CH),
2964-2872 t(Aliph-CH), 1605 t(C=N), 1534-1456
t(C=C), 1272 t(N–O) and 498 t(Co–N). 1H-NMR
(DMSO-d6, TMS, 300 MHz, d ppm): 19.02 and 18.83 (s,
4H, O–H_O), 8.44 (s, 4H, CH=N), 8.36-8.13 (m, 8H, Ar–
CH), 7.47-7.20 (m, 16H, Ar–CH), 2.70-2.51 (q, 8H, CH3–
CH2) and 1.24-1.15 (m, 12H, CH3-CH2), UV–Vis (kmax/nm
(loge), * = shoulder peak): 237 (4.23), 262 (4.08) and
345* (in C2H5OH); 224 (4.33), 255 (4.11), 338* and 409
(3.04) (in CH2Cl2).
Synthesis of the organodicobaloxime complexes
(7–12)
[(L1H)2CoCl-(TUPA)-CoCl(L1H)2] (5)
Color: brown, yield: 78%, m.p: 178 °C, Anal. Calc. for
[C53H70N10O12Cl2Co2] (F.W: 1228.0 g/mol): C, 51.84; H,
5.75; N, 11.41. Found: C, 51.78; H, 5.64; N, 11.37%.
KM = 13 X-1cm2 mol-1 (in DMF), leff = Dia, LC–MS
(Scan ES?): m/z (%) 1228.1 (20) [M]?. FT-IR (KBr pellet,
To a stirred solution of dicobaloxime (1–6) complexes
(3.0 mmol) in absolute ethanol (100 mL), NaOH (1.0 g,
25.0 mmol) dissolved in water (10 mL) was then added
dropwise at 0 °C with stirring for 20 min. under a N2
atmosphere. Then, sodium borohydride (NaBH4) (1.90 g,
4.0 mmol) dissolved in water (10 mL) was added to the
mixture by dropping cone. During this period, the reaction
mixture turned from brown to dark blue, followed by its
immediately turning orange on the addition of benzyl
bromide (4.26 g, 24.8 mmol). The reaction mixture was
stirred at 0 °C for 4 h, and then the solutions were removed
under N2 atmosphere. The reaction mixture was opened to
air and acetone (10 mL) with water (10 mL) was added to
dropwise. The volume of the reaction mixture was reduced
10 mL by evaporation and then poured into 40 mL of
t
max/cm-1): 3621-3242 t(O–H_O/NH2), 3027 t(Ar–CH),
2953-2854 t(Aliph-CH), 1601 t(C=N), 1552-1455
t(C=C), 1268 t(N–O) and 502 t(Co–N). 1H-NMR
(DMSO-d6, TMS, 300 MHz, d ppm): 18.73 and 18.34 (s,
4H, O–H_O for cis isomer), 18.62 (d, 4H, J = 8.8 Hz, O–
H_O for trans isomer), 7.59-7.07 (m, 16H, Ar–CH), 4.34
(s, 2H, O–CH), 4.19 (t, 8H, J = 6.0 Hz, O–CH2), 2.78 (s,
12H, Ar-CH3), 2.27 (s, 12H, C–CH3) and 1.74-0.86 (m,
16H, NH2 and Aliph-CH2). 13C-NMR (DMSO-d6, TMS,
75 MHz, d ppm): 153.37 (C1 of oxime), 151.97 (C2 of
123

Chem. Pap.
water. The solution was concentrated, filtered and washed
with hexane and diethyl ether, and dried. The obtained pure
compounds were recrystallized from CHCl3/C2H5OH (1:2)
solution and finally dried in vacuo.
CH), 2956–2865 t(Aliph-CH), 1603 t(C=N), 1536–1456
t(C=C), 1264 t(N–O) and 502 t(Co–N). 1H-NMR
(DMSO-d6, TMS, 300 MHz, d ppm): 18.80 and 18.48 (s,
4H, O–H_O), 8.56 (s, 4H, Ar–CH), 8.05 (s, 4H, Ar–CH),
7.93 (d, 8H, J = 7.5 Hz, Ar–CH), 7.72 (d, 8H, J = 7.5 Hz,
Ar–CH), 7.32–7.06 (m, 10H, Ar–CH), 5.13 (s, 4H, Ph-
CH2), 2.42 (s, 12H, Ar-CH3) and 2.32 (s, 12H, C–CH3).
13C-NMR (DMSO-d6, TMS, 75 MHz, d ppm): 158.41 (C1
of oxime) and 155.88 (C2 of oxime), 154.09 (ortho C of
4,40-bpy), 153.37 (para C of 4,40-bpy), 150.48 (C6 of Ar),
140.11 (C1 of phenyl), 132.18 (ortho C of phenyl), 130.74
(C3 of Ar), 130.63 (para C of phenyl), 129.96 and 129.64
(C4 of Ar), 129.11 and 128.59 (C5 of Ar), 126.88 (meta
C of 4,40-bpy), 126.08 (meta C of phenyl), 78.16 (Ph-CH2),
[(L1H)2PhCH2Co-(DAH)-CoCH2Ph(L1H)2] (7)
Color: gold yellow, yield (%): 68, m.p: 140 °C, Anal. Calc.
for [C60H74N10O8Co2] (F.W: 1181.2 g/mol): C, 61.01; H,
6.32; N, 11.86 Found: C, 60.93; H, 6.26; N, 11.79%.
KM = 17 X-1cm2 mol-1 (in DMF), leff = Dia, LC–MS
(Scan ES?): m/z (%) 1181.5 (20) [M?]. FT-IR (KBr pellet,
t
max/cm-1): 3552-3160 t(O–H_O/NH2), 3060 and 3030
t(Ar–CH), 2960-2865 t(Aliph-CH), 1601 t(C=N),
1
1537–1455 t(C=C), 1262 t(N–O) and 498 t(Co–N). H-
21.46 (Ar-CH3) and 15.64 (CH3C=NOH). UV–Vis (kmax/
NMR (DMSO-d6, TMS, 300 MHz, d ppm): 7.72-6.96 (m,
26H, Ar–CH), 5.16 (s, 4H, Ph-CH2), 2.37 (s, 12H, Ar-
CH3), 2.14 (s, 12H, C–CH3) and 1.73-0.87 (m, 16H, NH2
and Aliph-CH2). UV–Vis (kmax/nm (loge), * = shoulder
peak): 250 (4.83), 320 (4.26) and 428* (in C2H5OH); 251
(4.76), 324 (4.23) and 435* (in CH2Cl2).
nm (loge), * = shoulder peak): 254 (3.94) and 358* (in
C2H5OH); 234 (4.53), 255 (3.92) and 358* (in CH2Cl2).
[(L2H)2PhCH2Co-(4,40-bpy)-CoCH2Ph(L2H)2] (10)
Color: gold yellow, yield (%): 68, m.p: [ 300 °C, Anal.
Calc. for [C64H66N10O8Co2] (F.W: 1221.1 g/mol): C,
62.95; H, 5.45; N, 11.47 Found: C, 62.86; H, 5.34; N,
11.42%. KM = 11 X-1cm2 mol-1 (in DMF), leff = Dia,
LC–MS (Scan ES?): m/z (%) 1221.1 (25) [M?]. FT-IR
(KBr pellet, tmax/cm-1): 3539–3160 t(O–H_O), 3029
t(Ar–CH), 2963-2871 t(Aliph-CH), 1598 t(C=N),
[(L2H)2PhCH2Co-(DAH)-CoCH2Ph(L2H)2] (8)
Color: gold yellow, yield (%): 72, m.p: 149 °C, Anal. Calc.
for [C60H74N10O8Co2] (F.W: 1181.2 g/mol): C, 61.01; H,
6.32; N, 11.86 Found: C, 60.92; H, 6.20; N, 11.78%.
KM = 13 X-1cm2 mol-1 (in DMF), leff = Dia, LC–MS
(Scan ES?): m/z (%) 1182.2 (17) [M ? H?]. FT-IR (KBr
pellet, tmax/cm-1): 3539-3152 t(O–H_O/NH2), 3056 and
3029 t(Ar–CH), 2962–2871 t(Aliph-CH), 1602 t(C=N),
1
1534-1457 t(C=C), 1270 t(N–O) and 508 t(Co–N). H-
NMR (DMSO-d6, TMS, 300 MHz, d ppm): 18.42 and
18.13 (s, 4H, O–H_O), 10.03 (s, 4H, CH=N), 8.34 (s, 4H,
Ar–CH), 7.93 (d, 8H, J = 7.2 Hz, Ar–CH), 7.72 (d, 8H,
J = 7.2 Hz, Ar–CH), 7.62 (t, 8H, J = 7.1 Hz, Ar–CH),
7.25 (s, 4H, Ar–CH), 7.17 (s, 2H, Ar–CH), 5.51 (s, 4H, Ph-
CH2), 1.25-1.08 (m, 8H, CH3–CH2) and 0.87 (s, 12H,
CH3–CH2), UV–Vis (kmax/nm (loge), * = shoulder peak):
243 (4.86), 272 (3.87) and 381* (in C2H5OH); 248 (4.49),
269 (3.96) and 384* (in CH2Cl2).
1
1559–1454 t(C=C), 1269 t(N–O) and 508 t(Co–N). H-
NMR (DMSO-d6, TMS, 300 MHz, d ppm): 8.55 (s, 4H,
CH=N), 7.47–7.26 (m, 26H, Ar–CH), 5.18 (s, 4H, Ph-
CH2), 2.65-2.61 (q, 8H, CH3–CH2) and 1.39-0.86 (m, 28H,
CH3–CH2, NH2 and Aliph-CH2), 13C-NMR (DMSO-d6,
TMS, 75 MHz, d ppm): 150.00 (C1 of oxime) and 145.23
(C2 of oxime), 141.92 (C6 of Ar), 140.91 (C1 of phenyl),
137.63 (ortho C of phenyl), 136. 08(C3 of Ar), 130.89 (para
C of phenyl), 128.83 (C4 of Ar), 128.87 (C5 of Ar), 127.44
(meta C of phenyl), 77.34 (Ph-CH2), 31.70 (DAH-CH2),
[(L1H)2PhCH2Co-(TUPA)-CoCH2Ph(L1H)2] (11)
Color: gold yellow, yield (%): 70, m.p: [ 300 °C, Anal.
Calc. for [C67H84N10O12Co2] (F.W: 1339.3 g/mol): C,
60.08; H, 6.32; N, 10.46 Found: C, 60.02; H, 6.25; N,
10.38%. KM = 14 X-1cm2 mol-1 (in DMF), leff = Dia,
LC–MS (Scan ES?): m/z (%) 1339.4 (25) [M?]. FT-IR
(KBr pellet, tmax/cm-1): 3517–3126 t(O–H_O/NH2),
3060 and 3030 t(Ar–CH), 2952-2859 t(Aliph-CH), 1601
t(C=N), 1557–1454 t(C=C), 1262 t(N–O) and 500 t(Co–
N). 1H-NMR (DMSO-d6, TMS, 300 MHz, d ppm):
7.70–6.73 (m, 26H, Ar–CH), 5.15 (s, 4H, Ph-CH2), 4.31 (s,
2H, O–CH), 4.22 (t, 8H, J = 6.2 Hz, O–CH2), 2.67 (s,
12H, Ar-CH3), 2.33 (s, 12H, C–CH3) and 2.12-0.87 (m,
16H, NH2 and Aliph-CH2). 13C-NMR (DMSO-d6, TMS,
28.37 (CH3–CH2) and 15.91 (CH3–CH2). UV–Vis (kmax
/
nm (loge), * = shoulder peak): 264 (4.48) and 382* (in
C2H5OH); 266 (4.58) and 385* (in CH2Cl2).
[(L1H)2PhCH2Co-(4,40-bpy)-CoCH2Ph(L1H)2] (9)
Color: gold yellow, yield (%): 69, m.p: 129 °C, Anal. Calc.
for [C64H66N10O8Co2] (F.W: 1221.1 g/mol): C, 62.95; H,
5.45; N, 11.47 Found: C, 62.88; H, 5.38; N, 11.40%.
KM = 14 X-1cm2 mol-1 (in DMF), leff = Dia, LC–MS
(Scan ES?): m/z (%) 1221.3 (15) [M?]. FT-IR (KBr pellet,
t
max/cm-1): 3576-3160 t(O–H_O), 3056 and 3031 t(Ar–
123

Chem. Pap.
75 MHz, d ppm): 155.23 (C1 of oxime), 154.51 (C2 of
oxime), 153.08 (ortho C of phenyl), 151.14 (para C of
phenyl), 141.32 (C1 of phenyl), 138.93 (C6 of Ar), 131.86
and 130.53, (C3 of Ar), 129.78 (C4 of Ar), 128.46 (C5 of
Ar), 126.32 (meta C of phenyl), 101.12 (O–CH), 77.26 (Ph-
CH2), 68.58 (O–CH2), 42.58 (NH2–CH2), 32.13 (C–CH2),
29.75 (CH–CH2), 24.21 (CH2–CH2-CH2), 21.54 (Ar-CH3)
and 14.48 (CH3C=NOH). UV–Vis (kmax/nm (loge),
* = shoulder peak): 251 (4.72), 323 (4.53) and 432* (in
C2H5OH), 252 (4.41), 315 (4.13) and 438* (in CH2Cl2).
epoxide. The obtained cyclic carbonate in DMSO-d6 was
1
analyzed by H-NMR and FT-IR spectra. These spectral
results show that any polycarbonate, epoxides, DMAP (4-
dimethylamino pyridine) or other by-products were not
formed significant amounts. Besides, a detailed FT-IR
survey shows that the peak at around 1795 cm-1 was
attributed to the carbonyl group in cyclic carbonate. Also,
no peak at 1749 cm-1 was detected, which was attributed
to the carbonyl group in polycarbonate (Wang et al. 2015).
[(L2H)2PhCH2Co-(TUPA)-CoCH2Ph(L2H)2] (12)
Results and discussion
Color: gold yellow, yield (%): 64, m.p: 189 °C, Anal. Calc.
for [C67H84N10O12Co2] (F.W: 1339.3 g/mol): C, 60.08; H,
6.32; N, 10.46 Found: C, 60.03; H, 6.24; N, 10.52%.
KM = 12 X-1cm2 mol-1 (in DMF), leff = Dia, LC–MS
(Scan ES?): m/z (%) 1339.2 (25) [M?]. FT-IR (KBr pellet,
Herein, first we reported the synthesis of the two dioxime
ligands (L1H2 and L2H2) from various ketones skeletons
are outlined in Scheme 1. As shown in Scheme 2, the
dicobaloxime/organodicobaloxime (1–12) complexes were
obtained at reflux temperature and under the basic condi-
tions. Dicobaloxime complexes (1–6) have been synthe-
sized by treating dioxime ligands (L1H2 and L2H2) with
CoCl2.6H2O in the presence of O2 and various diamines
under an inert atmosphere. In contrast, organodi-
cobaloxime complexes (7–12) synthesized by treating
dicobaloxime complexes (1–6) with benzyl bromide in the
presence of NaBH4 and NaOH in EtOH solvent under an
inert atmosphere. These Co(III) complexes (1–12) were
successfully synthesized and characterized by various
spectroscopic methods such as NMR (1H and 13C) spec-
troscopy, UV–Visible spectroscopy, FT-IR spectroscopy,
Mass spectroscopy, molar conductivity analysis, melting
point, and magnetic susceptibility experiments with ele-
mental analysis and cyclic voltammetry (CV). We have
attempted to prepare single crystals of dicobaloxime/
organodicobaloximes (1–12) complexes in various sol-
vents, but unfortunately we could not obtain single crystals
suitable for X-ray diffraction studies for all dicobaloxime/
organodicobaloximes (1–12) complexes.
t
max/cm-1): 3534-3151 t(O–H_O/NH2), 3029 t(Ar–CH),
2964-2871 t(Aliph-CH), 1607 t(C=N), 1511-1455
t(C=C), 1270 t(N–O) and 511 t(Co–N). 1H-NMR
(DMSO-d6, TMS, 300 MHz, d ppm): 8.52 (s, 4H,
CH = N), 7.36-7.18 (m, 26H, Ar–CH), 5.24 (s, 4H, Ph-
CH2), 4.28 (s, 2H, O–CH), 4.17 (d, 8H, J = 11.7 Hz, O–
CH2), 2.62–2.33 (m, 20H, Aliph-CH2) and 1.48-0.86 (m,
16H, NH2 and Aliph-CH3). 13C-NMR (DMSO-d6, TMS,
75 MHz, d ppm): 148.44 (C1 of oxime), 145.76 (C2 of
oxime), 141.93 (ortho C of phenyl), 140.98 (para C of
phenyl), 141.32 (C1 of phenyl), 130.42 (C6 of Ar), 129.91
and 129.48 (C3 of Ar), 128.96 and 128.87 (C4 of Ar),
127.14 (C5 of Ar), 102.39 (O–CH), 77.41 (Ph-CH2), 70.07
(O–CH2), 58.16 (NH2–CH2), 31.95 (C–CH2), 30.94 (CH–
CH2), 28.76 (CH3–CH2), 21.01 (CH2–CH2–CH2) and 15.41
(CH3–CH2). UV–Vis (kmax/nm (loge), * = shoulder peak):
265 (4.48) and 381* (in C2H5OH); 268 (4.32) and 389* (in
CH2Cl2).
General procedure of coupling reaction of epoxides
and CO2
Spectroscopic properties
In a 50-mL stainless-steel autoclave with a magnetic stir-
ring bar in the absence of a solvent and a presence Lewis
base (9.0 9 10-5 mol) under CO2 pressure, with a
4.5 9 10-5 mol dicobaloxime or organodicobaloxime
complexes and 4.5 9 10-2 mol epoxide was added. The
mixture was injected into the reactor which was dried
before use. The reaction was carried out under a constant
pressure of carbon dioxide and the reaction mixture was
stirred at 100 °C for the desired time under an atmosphere
of CO2 (99.999%). After the reaction, the mixture was
cooled to room temperature and ethylene glycol dibutyl
ether added as internal standard for GC (Agilent 7820A)
analysis yield determination. All the yields were based on
The FT-IR spectra of the dicobaloxime/organodi-
cobaloximes (1–12) complexes are compared with those of
the free dioxime ligands (L1H2) and (L2H2) and their rel-
ative frequency and also the assignments are consistent
with reported compounds (Figs. 1, 2). In the FT-IR of the
dicobaloxime/organodicobaloxime (1–12) complexes, the
main stretching vibration for intermolecular H-bond (O–
HÁÁÁO), which on an encapsulation of the NH2 groups are
observed at 3621–3104 cm-1, provided the first evidence
of successful complexation on the Co(III) center in N4-
oxime core. The other important peak due to azomethine
t(C=N) groups were observed at 1611–1609 cm-1 in the
FT-IR spectra of the dioxime ligands (L1H2) and (L2H2),
123

Chem. Pap.
Scheme 2 The structure of the proposed dicobaloxime/organodicobaloximes (1–12) complexes
123

Chem. Pap.
Fig. 1 The FT-IR spectra of dicobaloxime (6) complex
Fig. 2 The FT-IR spectra of organodicobaloxime (7) complex
whereas in the FT-IR of dicobaloxime/organodi-
according to the stretching vibration of ligands (Wani et al.
2016). This a small frequency shift in its position may be
because of the formation of Co(III) / N dative bond in
cobaloximes
(1–12),
this
band
observed
at
1605-1598 cm-1 a small frequency shift in its position
123

Chem. Pap.
these complexes as expected. The infrared spectra show
that the typical characteristic t(N–O) stretches at about
*1285 cm-1 in ligands (L1H2) and (L2H2) a small low-
frequency shift upon treatment with Co3? ions, supporting
the formation of dicobaloxime/organodicobaloximes (1–
12) complexes. The coordination mode of the ligands
(L1H2) and (L2H2) are further supported by new frequen-
cies occurring in the range 515–498 cm-1 due to t(Co /
N) stretching vibrations that are not observed in the FT-IR
of the ligands (L1H2) and (L2H2).
The electronic absorption spectra of the ligands (L1H2)
and (L2H2) and their dicobaloxime/organodicobaloxime
(1–12) complexes obey well Lambert–Beer’s law in the
concentration range studied (2.10-6–2.10-8 mol L-1) in
C2H5OH and CH2Cl2 solution and recorded in the range
200–1100 nm at room temperature, suggesting that no
other chemical event occurs within this concentration range
in C2H5OH and CH2Cl2. The UV–Vis absorption bands of
the examples (L1H2) and (L2H2) and their dicobaloxime/
organodicobaloximes (1–12) indicate similar features for
p ? p* or n ? p* transitions of the chromophoric groups
present in the structure of the ligands. The ligands (L1H2)
and (L2H2) and their complexes (1–12) show sharp and
strong absorption bands under 382 nm in C2H5OH and
under 385 nm in CH2Cl2 are assumed to be probably intra
ligand property and can be assigned to the p ? p* or
n ? p* transitions localized on the conjugated aromatic
rings and functional azomethine (C=N) groups, considering
their intense and structured absorption band. Another
decisive evident bands for the formation of these com-
plexes (1–12) observed at 438–394 nm can be presumably
ascribed to the intermolecular transition from the ligand
compounds to the vacant orbitals localized on the coordi-
nated cobaloxime center. One of the most important
absorption bands for such molecules is d–d transition in the
visible region. But we did not observe these transitions in
the all dicobaloxime and organocobaloximes probably due
to their very low molar absorption coefficient. However,
the dicobaloxime complex (1) at high concentrations of
showed d–d transitions in the region 586–879 nm due to
Co3? metal center of cobaloximes (Lever 1968; Moore and
Janes 2004).
Fig. 3 The 1H-NMR spectra of dicobaloxime (1) complex in DMSO
Fig. 4 The 13C-NMR spectra of dicobaloxime (1) complex in DMSO
1
The H and 13C-NMR chemical results for the ligands
(L1H2) and (L2H2) and their dicobaloxime/organodi-
cobaloxime (1–12) complexes are given in the experi-
1
Fig. 5 The H-NMR spectra of organodicobaloxime (9) complex in
DMSO
1
mental section and Figs. 3, 4, 5 and 6. The H and 13C-
NMR values are in good agreement with those obtained
for the ligands (L1H2) and (L2H2) and their cobaloxime
complexes (1–12). In the 1H NMR spectra of dioxime
ligand (L1H2) and (L2H2), the D2O-exchangeable protons
of the (C=N–OH) groups show chemical shifts at
11.45 ppm as singlet for ligand (L1H2) and at 11.86 ppm
(trans isomer) and 11.69 with 11.47 ppm (cis isomer) as
singlet for ligand (L2H2), consecutively. This peak dis-
appeared in the 1H-NMR spectrum of dicobaloxime/
organodicobaloxime (1–12) complexes, while new peaks
were observed and identified as two singlet or doublet
peaks at range 20.18-18.33 ppm for cis/trans isomer,
indicating that the (C=N–OH) groups of dioxime ligands
123

Chem. Pap.
between 154.99 and 126.08 ppm assigned to ortho, para
or meta –C of axial 4,40-bpy ligand, and at between
102.39 and 21.01 ppm assigned to carbon resonance of
axial TUPA ligand, respectively.
The LC–MS spectra for the dioxime (L1H2) and (L2H2)
ligands and their dicobaloxime/organodicobaloxime (1–12)
complexes were investigated. The Mass (LC–MS) spectral
data of all compounds (ligands and complexes) supported
the proposed structures due to the molecular ion peaks
consistent with the molecular weight of the compounds.
The designated results for peak positions and the isotopic
distributions are given in the experimental part (Kilic et al.
2013b; Ruchi 2013). The values are in the range *18–11
X-1 cm2 mol-1 in DMF), suggesting a non-electrolytic
nature for the dicobaloxime/organodicobaloxime (1–12)
complexes, and there is no counter ion present outside their
coordination sphere. The measurements of magnetic
moments of the dicobaloxime/organodicobaloxime (1–12)
complexes were performed at 25 °C and in the solid state.
These magnetic values show that the dicobaloxime/organ-
odicobaloxime (1–12) complexes are diamagnetic form
and the low-spin (S = 0) octahedral d6-systems due to the
complete spin pairing as expected. Also, these magnetic
results indicate that the cobalt center of cobaloximes is in
the ?3 oxidation state.
Fig. 6 The 13C-NMR spectra of organodicobaloxime (9) complex in
DMSO
have been transformed to intramolecular D2O-exchange-
able H-bridge (O–H_O), supporting the formation of the
dicobaloxime/organodicobaloximes (1–12) (Mirra et al.
2016). The NMR spectra of dicobaloxime (1–6) com-
plexes compared with organodicobaloxime (7–12) com-
plexes were found major differences was the presence of
a benzyl group connecting instead of a chlorine atom as
axial ligand in the organodicobaloxime (7–12) complexes.
The conversions of the dicobaloxime (1–6) complexes to
the organodicobaloxime (7–12) complexes were con-
firmed by the changes observed in the NMR spectra and
by the appearance of a characteristic singlet resonance at
Electrochemical properties
Redox properties of the dicobaloxime and organodi-
cobaloxime (1–12) complexes were studied on a glassy
carbon electrode in DMSO containing 0.1 M n-Bu4NClO4
as the supporting electrolyte (Figs. 7, 8, 9, 10, 11). Table 1
summarizes the electrode potentials for the dicobaloxime
and organodicobaloxime (1–12) complexes in DMSO. The
cyclic voltammograms of the dicobaloxime (1–6) and
organodicobaloxime (7–12) complexes is not well resolved
1
range 5.24–5.13 ppm in the H NMR spectra and also at
range 78.16–77.26 ppm in the 13C NMR spectra attributed
to the Ph-CH2 of the benzyl group as axial ligand.
Another decisive event, the signals of the azomethine
carbon (C=N) are observed at between 158.41 and
142.83 ppm for the complexes (1–12), while this carbon
peak is observed at 155.59–145.02 ppm for the dioxime
ligand (L1H2) and (L2H2) (Yamuna et al., 2016). For
corroborate the proposed dimeric cobaloxime structures,
The 1H NMR resonance of axial-bridged ligands (1,6-
diaminohexane (DAH), 4,40-bipyridine (4,40-bpy) and
2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-dipropanamine
(TUPA) were located at range 2.33–1.24 ppm assigned to
the NH2 and Aliph-CH2 of axial DAH ligand, at range
2.33–0.84 ppm assigned to the NH2 and Aliph-CH2 of
axial DAH ligand, at range 8.63–7.93 ppm assigned to the
Ar–CH of axial 4,40-bpy ligand and at range 4.42-
4.28 ppm assigned to the O–CH, at range 4.22-4.16 ppm
assigned to the O–CH2 and at range 2.62–0.86 ppm
assigned to the NH2 and Aliph-CH2 of axial TUPA
ligand, respectively. Besides, 13C NMR resonance of
axial-bridged ligands were detected at between 31.70 and
31.12 ppm assigned to –CH2 of axial DAH ligand, at
20
15
10
5
0
-1.7
-1.2
-0.7
-0.2
0.3
0.8
-5
E (V) vs Ag/AgCl
-10
-15
-20
-25
Fig. 7 A cyclic voltammogram of cobaloxime (3) complex in DMSO
containing 0.1 M n-Bu4NClO4 as supporting electrolyte. Scan rate
100 mV/s
123

Chem. Pap.
50
40
10
5
30
20
10
0
-0.2
0
-1.7
-1.2
-0.7
0.3
0.8
-1.5
-1.1
-0.7
-0.3
0.1
0.5
0.9
-10
-20
-30
-40
-50
E (V) vs Ag/AgCl
E (V) vs AgAg/Cl
-5
-10
Fig. 10 A cyclic voltammogram of cobaloxime (5) complex in
DMSO containing 0.1 M n-Bu4NClO4 as supporting electrolyte. Scan
rate 100 mV/s
Fig. 8 Cyclic voltammogram of cobaloxime (3) complex in DMSO
containing 0.1 M n-Bu4NClO4 as supporting electrolyte. Scan rates
increasing from 100 to 500 mV/s
10
8
15
10
5
6
4
2
0
0
-2
-1.5
-1
-0.5
0
0.5
1
1.5
-1.2
-0.7
-0.2
0.3
0.8
-2
E (V) vs Ag/AgCl
-5
-10
-15
E (V) vs Ag/AgCl
-4
-6
-8
-10
Fig. 11 A cyclic voltammogram of cobaloxime (6) complex in
DMSO containing 0.1 M n-Bu4NClO4 as supporting electrolyte. Scan
rate 100 mV/s
Fig. 9 A cyclic voltammogram of cobaloxime (4) complex in DMSO
containing 0.1 M n-Bu4NClO4 as supporting electrolyte. Scan rate
100 mV/s
wave potentials can provide a rough evaluation of the
degree of the reversibility of one-electron transfer process.
The evaluation of cyclic voltammetric data with the scan
rate varying 100–500 mV/s gives the evidence for a quasi-
reversible one electron oxidation (Fig. 8). The ratio of
reduction to oxidation wave height was less than one.
However, the wave current increases with the increase of
the square root of the scan rate. The Ip/v1/2 value is almost
constant for all scan rates. This establishes the electrode
process as diffusion controlled (Bard and Faulkner 2001).
The separation in wave potentials increases at higher scan
rates. These characteristic features are consistent with the
quasi-reversibility of Co(III)/Co(II) redox couple. Since the
molecule is symmetrical both the cobalt centers behave
similarly. This might be due to electron delocalization
that probably the change in coordination number of cobalt
center during reduction and oxidation process (Dutta and
Gupta 2011). Among them, dicobaloxime (1–6) species
give a better cyclic voltammogram as compared to its
organodicobaloxime derivatives (7–12). Cyclic waves of
the dicobaloxime (3) complex exhibits a quasi-reversible
wave versus an Ag/AgCl which can be assigned to Co(III)/
Co(II) couples. As shown in Fig. 7, the dicobaloxime (3)
complex showed an oxidation peak at Epa = -0.647 V
with a corresponding reduction peak at Epc = -0.831 V.
The peak separation for this couple (DEp) is 184 mV. The
most significant feature of the formation Co(III)/Co(II)
redox couple is the one-electron transfer via electrochem-
ical process. The difference between anodic and cathodic
123

Chem. Pap.
between two cobalt centers by a substantial overlap of
cobalt and axial ligand orbitals. The dicobaloxime (3)
complex also shows another quasi-reversible redox wave
(Epa = 0.116 V and Epc = -0.079 V) followed by an
irreversible reduction peak at -0.501 V corresponding to
the ligand moiety of the complex. The cyclic voltammo-
gram of the dicobaloxime (4) complex (Fig. 9) shows an
oxidation peak at Epa = -0.581 V with a corresponding
reduction peak at Epc = -0.706 V which can be ascribed
to Co(III)/Co(II) couples. The peak separation for this
couple (DEp) is 125 mV. The dicobaloxime (4) complex
also shows one irreversible oxidation peak at Epa =
0.028 V and one reduction peak at Epc = -0.347 V cor-
responding to the ligand moiety of the complex. The
dicobaloxime (5) complex exhibits an oxidation peak at
Epa = -0.689 V with a corresponding reduction peak at
Epc = -0.762 V which can be ascribed to Co(III)/Co(II)
couples (Fig. 10). However, the irreversible reduction peak
at -1.146 V may be ascribed to the formation of
Co(I) species. The rest of oxidation and reduction peaks are
possibly due to the oxime moiety of the complex. The
dicobaloxime (6) complex exhibits only one oxidation peak
at 0.903 V corresponding to the oxidation of ligand moiety
and one reduction peak at -1.534 V corresponding to the
formation of Co(I) as shown in Fig. 11. Cyclic voltammo-
grams of the organodicobaloximes were poor. This is pos-
sibly due to the enhanced r donation by R groups in the
organocobaloximes which are substantially stabilized. In
other words, in the organodicobaloximes redox processes are
considerably cathodically shifted. Due to this, redox process
is further cathodically shifted and therefore not observed in
the accessible solvent window (Dutta et al. 2015).
conditions. The catalytic tests were performed at optimized
conditions, which were defined in our last studies (Kilic
et al. 2013b; Ulusoy et al. 2011a, b). The dicobaloxime and
organodicobaloxime compounds (1–12) showed good cat-
alytic activity and selectivity for the transformation of CO2
into cyclic carbonates using epoxide derivatives and pres-
ence of DMAP (4-dimethylamino pyridine) as Lewis base.
Among the cobaloxime complexes, the organodi-
cobaloxime (10) complex showed good catalytic activity
and selectivity for the coupling of CO2 and epichlorohydrin
in the presence of DMAP as co-catalysts. (Table 2, entries
1–12). In this catalytic system, regarding reaction mecha-
nism one Co(III) center was proposed to serve as Lewis
acid for epoxide activation and another as a counterion for
the nucleophile. In other words, for the understanding of
reaction mechanism, the amine-based co-catalyst is nec-
essary for the reaction in several different ways (first,
DMAP acts as a Lewis base to attack the sterically less
hindered carbon atom to open the epoxide ring, while the
role of Co(III) is of a Lewis acid and activates the epoxide
upon binding, and the generated oxyanion species then
react with CO2 to give the cyclic carbonate, and the cycle
goes on) (Kilic et al. 2016). Here, two structurally different
types of cobaloxime compounds were investigated. Type
one is the dicobaloximes (1–6) and the other is the
organometallic forms of cobalt (7–12) complexes (called
organodicobaloxime). The organodicobaloxime (10) com-
plex bearing Ph-CH2- substituent to metal center indicated
the best catalytic performance (Table 2) with epichloro-
hydrin as substrate. The main reason for the better catalytic
efficiencies of the organodicobaloxime (10) complex may
be the reaction media, where the differences between
compounds, substrates and the purity of CO2 could play a
role. However, the high conversion was attributed to good
diffusion and high miscibility of epichlorohydrin in CO2
under studies conditions. Consequently, the organodi-
cobaloxime (10) showed high conversion (78.0%) and
selectivity (98%) (entry 10) compared to the other coba-
loxime complexes, which may be attributed to the more
Lewis acidic octahedral Co(III) centers in organodi-
cobaloxime (7–12) complexes due to the presence of a
benzyl group connecting instead of a electron-withdrawing
Catalytic properties
The chemical fixation of CO2 to synthesize useful chemi-
cals in the presence of 0.1% dicobaloximes or organodi-
cobaloximes (1–12) complexes was preferred as a model
reaction for testing and the results are given in the Table 2.
The cycloaddition of CO2 and various epoxides catalyzed
by dicobaloxime (1–6) and organodicobaloxime (7–12)
complexes was investigated under adopted reaction
Table 1 Voltammetric data for
cobaloximes (3–6) complexes
Complex
Metal centered
Ligand based oxidation/reduction
Epa (V)
Epc (V)
(DEp)(mV)
Epc (V)
Epa (V)
Epc (V)
Epc (V)
3
4
5
6
-0.647
-0.581
-0.689
-0.831
-0.706
-0.762
184
125
73
0.116
0.028
–
-0.079
-0.347
-0.501
-1.146
-1.534
0.903
Supporting electrolyte = 0.1 M n-Bu4ClO4, scan rate = 100 mV/s
123

Chem. Pap.
Table 2 Synthesis of ECHC [4-(chloromethyl)-1,3-dioxalan-2-one] from ECH [2-(chloromethyl)oxirane] and CO2 catalyzed by cobaloxime
complexes
Entry (%)
Cat.
Conversiona (%)
Selectivitya
TONb
TOFc (h-1
)
1
1
61
59
44
65
56
60
68
53
59
78
62
62
99
98
98
98
98
99
99
98
98
98
99
98
606
593
443
653
556
595
682
530
588
780
617
618
303
297
222
327
278
298
341
265
294
390
309
309
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
10
11
12
a
10
11
12
Conversion and selectivity of epichlorohydrin to corresponding Epichlorohydrin carbonate were determined by GC
Moles of cyclic carbonate produced per mole of catalyst
The rate is expressed in terms of the turnover frequency {TOF [mol of product (mol of catalyst h)-1] = turnovers/h}
b
c
chlorine atom as axial ligand. However, we have carried
The results of optimization conditions such as reaction
temperature, epoxide, time and CO2 pressure were very
similar to those of homogeneous and heterogeneous sys-
tems previously reported (Ulusoy et al. 2009; Kilic et al.
2010). In addition, the DMAP, KOH, Na2CO3, Na2SO4 and
Cs2CO3 were tested for comparison of base effect. The
necessity of a base was observed as shown in Fig. 13.
Interestingly, the use of Cs2CO3 resulted in a yield of 19%,
and the yield remarkably increased 78% when DMAP was
used as the base (Fig. 13) in high selectivity (Ulusoy et al.
2011a, b). These results showed that organic base showed a
better activity than from the inorganic bases.
out the blank reaction without catalyst. To ascertain the
activity of DMAP alone in this reaction under the given
conditions the catalytic blank-run without Co(III) catalyst
was done and found to be 5% conversion.
We have executed similar catalytic tests changing the
reaction time, reaction temperature, ambient pressure,
various base and different epoxide to find the better reac-
tion conditions. In the beginning, the studies of cyclohex-
ene oxide (CHO), styrene oxide (SO), epichlorohydrin
(ECH), propylene oxide (PO), and 1, 2-epoxybutane (EB)
as substrates with CO2 to synthesize the corresponding
cyclic carbonates were investigated. As shown in Fig. 12,
among them epichlorohydrin was found to be the most
reactive epoxide compared to the other epoxides whose
propylene epoxide exhibited the lowest activity. It was
found that epichlorohydrin (ECH) was the most reactive
one (due to the fact that the electron-withdrawing chlor-
omethyl group of epichlorohydrin could assist the breaking
of C–O bond of the epoxide, thus favouring the subsequent
CO2 addition to the opened epoxy), while cyclohexene
oxide (CHO) exhibited the lowest activity. Also, the
internal epoxide, cyclohexene oxide is converted to the
corresponding cyclic carbonate with low yield presumably
due to the high steric hindrance (Bai et al. 2013).
It is generally adopted that reaction parameters such as
reaction time, temperature and initial CO2 pressure have a
significant effect on the catalytic activity of conversion of
ECH to its related cyclic organic carbonate (Fig. 14) using
the organodicobaloxime (10) as a catalyst. As shown in
Fig. 14a, when the temperature rises from 75 to 125 °C, [4-
(chloromethyl)-1,3-dioxolan-2-one]
(ECHC)
yield
increased sharply from 20 to 96%. These results show that
the temperature rise has an apparent positive effect on the
transformation of ECH to its related cyclic organic car-
bonate. However, the temperature rises from 125 to
150 °C, ECHC yield slight decreased from 96 to 93%
(Fig. 14a). Therefore, from a practical viewpoint, the
123

Chem. Pap.
Fig. 12 The conversion of
various epoxides to
corresponding cyclic carbonates
at the same catalytic conditions
with organocobaloxime (10) as
catalyst
80
60
40
20
0
yield (%)
selecꢀvity (%)
EB
ECH
PO
SO
CHO
Epoxides
Fig. 13 Conversion and
selectivity of 2-(chloromethyl)
oxirane as effect the
transformation of base at the
same catalytic conditions with
organocobaloxime (10) as
catalyst
80
60
40
20
0
yield (%)
selecꢀvity (%)
Bases
Conclusion
optimal reaction temperature has been accepted as 100 °C
for adopted catalytic conditions. As shown in Fig. 14b, in
the low-pressure range (0.5–1.6 MPa), there is rise of [4-
(chloromethyl)-1,3-dioxolan-2-one] (ECHC) yield (from
70 to 78%) with increase of initial CO2 pressure, but fur-
ther rise of pressure to 2.5 MPa results in moderate
decrease of ECHC yield. The reason for these results, a
higher initial CO2 pressure can effectively increase the
solubility of CO2 in epichlorohydrin (ECH), permitting the
reaction equilibrium to shift toward carbonate formation.
However, when the initial CO2 pressure reached 2.5 MPa,
this high CO2 pressure may have retarded the interaction
between ECH and catalysts, resulting in a decrease in the
transformation of ECH to its related cyclic organic car-
bonate. A similar effect was reported in our previous paper
(Ulusoy et al. 2009). As shown in Fig. 14c, the cycload-
dition reaction proceeds rapidly within the first 2 h,
In summary, the different substituted axial diamine-bridged
dicobaloxime and organodicobaloximes have been syn-
thesized for the first time. These Co(III) complexes (1–12)
were successfully characterized by various spectroscopic
methods such as NMR (1H and 13C) spectroscopy, UV–
Visible spectroscopy, FT-IR spectroscopy, Mass spec-
troscopy, molar conductivity analysis, melting point, and
magnetic susceptibility experiments with elemental analy-
sis and cyclic voltammetry (CV). The cyclic voltammo-
grams of the organodicobaloximes were poor. This is
possibly due to the enhanced r donation by R groups in the
organodicobaloximes which are substantially stabilized.
These obtained complexes also were used for conversion of
carbon dioxide to cyclic carbonates as homogeneous cat-
alysts under mild conditions. The best active catalyst
organodicobaloxime (10) complex was not effective in
epoxides (EB, SO, PO and CHO). Whereas using the
epichlorohydrin (ECH) as epoxide, good conversion and
selectivity were achieved at the same catalytic conditions.
reaching
an
[4-(chloromethyl)-1,3-dioxolan-2-one]
(ECHC) yield of 78%. With the increase of reaction time
from 0.5 h to 4 h, ECHC yield increased sharply from 40%
to 89%.
123

Chem. Pap.
100
80
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