Synthesis of the Multinuclear Cobaloxime Complexes via Click Chemistry as Catalysts for the Formation of Cyclic Carbonates from Carbon Dioxide and Epoxides

Article abstract of DOI:10.1007/s12039-015-0932-9

In this study, the structurally similar multinuclear cobaloxime complexes based on dioxime ligands were synthesized and characterized as trinuclear complexes with respect to varied axial groups. The multinuclear cobaloxime complexes were characterized by ¹H, ¹³C-NMR, FT-IR, UV-Vis, LC-MS spectra, melting point and magnetic susceptibility measurements. These multinuclear cobaloxime complexes have been successfully applied to the synthesis of cyclic carbonates from CO₂ and epoxides under optimized conditions and without using any solvent. All multinuclear cobaloxime complexes obtained by click chemistry are good catalysts for the cycloaddition of CO₂ to different epoxides in the presence of pyridine as a co-catalyst. Additionally, the effects of epoxides, bases, temperature, pressure, and time on the yield of cyclic carbonates were investigated.

Full text of DOI:10.1007/s12039-015-0932-9

c
J. Chem. Sci. Vol. 127, No. 9, September 2015, pp. 1665–1674. ꢀ Indian Academy of Sciences.
DOI 10.1007/s12039-015-0932-9
Synthesis of the Multinuclear Cobaloxime Complexes via Click
Chemistry as Catalysts for the Formation of Cyclic Carbonates from
Carbon Dioxide and Epoxides
AHMET KILIC∗, ARMAGAN KELES, EMINE AYTAR, MUSTAFA DURGUN and
MAHMUT ULUSOY
Chemistry Department, Harran University, 63190, Osmanbey Campus, Sanliurfa, Turkey
e-mail: kilica63@harran.edu.tr
MS received 6 May 2015; revised 25 June 2015; accepted 29 June 2015
Abstract. In this study, the structurally similar multinuclear cobaloxime complexes based on dioxime ligands
were synthesized and characterized as trinuclear complexes with respect to varied axial groups. The multin-
1
uclear cobaloxime complexes were characterized by H, 13C-NMR, FT-IR, UV-Vis, LC-MS spectra, melting
point and magnetic susceptibility measurements. These multinuclear cobaloxime complexes have been success-
fully applied to the synthesis of cyclic carbonates from CO2 and epoxides under optimized conditions and with-
out using any solvent. All multinuclear cobaloxime complexes obtained by click chemistry are good catalysts
for the cycloaddition of CO2 to different epoxides in the presence of pyridine as a co-catalyst. Additionally, the
effects of epoxides, bases, temperature, pressure, and time on the yield of cyclic carbonates were investigated.
Keywords. Click chemistry; multinuclear cobaloxime complexes; carbon dioxide; epoxides;
cyclic carbonate.
1. Introduction
For the synthesis of cyclic carbonates from car-
bon dioxide and epoxides, many efficient and cost
effective homogeneous catalytic systems with differ-
ent yields and turnover frequencies (TOFs) have been
developed by the academia and industry. These include
metal salts, metallic complexes, ionic liquids, metal-
organic frameworks, organocatalysts, and N-heterocyclic
carbenes.10
Over the past several decades, the average atmospheric
concentration of CO2 has increased from 280 ppm to
400 ppm (summer of 2013) and as a result, the aver-
age temperature has increased between 0.6◦C and 1◦C
in the same period.1,2 As a solution to such a serious
problem, carbon dioxide conversion to important chem-
icals and materials is needed. However, carbon dioxide
capture and utilization used in conjunction with carbon
storage not only can provide an alternative and renew-
able feedstock for the chemical industry but also can
generate revenue to offset the cost of carbon capture
and storage.3 In this regard, one of the most common
ways in chemical industry has been the synthesis of
five-membered cyclic carbonates via coupling of carbon
dioxide and epoxides for effective utilization of CO2, as
shown in scheme 1.
The synthesized five-membered cyclic organic car-
bonates are used both in industrial chemistry and in
academic chemistry studies as monomers, aprotic polar
solvents and pharmaceutical/fine chemical intermedi-
ates, in many biomedical applications,4,5 as electrolytes
for secondary batteries,6 and as starting materials for
polycarbonates,7 enantiopure aminoalcohols,8 and ther-
mosetting coatings.9
Although many efficient and cost effective homo-
geneous catalytic systems have been proposed for
the synthesis of cyclic organic carbonates, the search
for new homogeneous or heterogeneous catalytic sys-
tems still remains an exciting topic. To the best of
our knowledge, there are not many reports using
multinuclear cobaloxime complexes as homogeneous
catalysts for the conversion of carbon dioxide to cyclic
carbonates. Thus, in the present paper we report prepa-
ration and characterization of a new series multinu-
clear cobaloxime complexes obtained by click chemistry.
Further, these complexes were used as homogeneous
catalytic systems for conversion of carbon dioxide to a
five-membered cyclic organic carbonate. Additionally,
the effects of reaction temperature, pressure, and time
on the yield of cyclic carbonate were investigated. The
multinuclear cobaloxime complexes were character-
ized by 1H and 13C-NMR spectra, FT-IR, UV-Vis, LC-
MS spectra, melting point and magnetic susceptibility
measurements.
∗For correspondence
1665

1666
Ahmet Kilic et al.
LC-MS/MS spectrometer. Catalytic tests were per-
O
C
formed in a PARR 4560 50 mL stainless pressure reac-
tor. Gas chromatography was performed on an Agilent
7820A GC system with nitrogen as the carrier gas.
O
Catalysts
CO2
O
O
+
R
R
2.2 Synthesis of the ligand (L3H2)
Scheme 1. The synthesis of cyclic organic carbonate from
CO2 and epoxides.
The ligands (L1H2) and (L2H2) were synthesized
according to the literature method.12,13 However, the
ligand (L3H2) was synthesized by a similar procedure
as new product. The synthesis details are given briefly
in scheme 2.
2. Experimental
2.1 Chemicals and measurements
All chemicals and solvents were purchased from com-
mercial suppliers and were used as received without
2.2a (L3H2) ligand: Color: Pale yellow, yield: 82%,
M.p.: 182◦C, Anal. Calc. (%) for [C12H15N3O3] (F.W:
249.3 g/mol): C, 57.82; H, 6.07; N, 16.86. Found:
C, 57.72; H, 6.00; N, 16.75 %. LC-MS (Scan ES+):
m/z (%) 249.2 (35) [M]+, FT-IR (KBr pellets,
υmax/cm−1): 3357-3086 υ(O-H), 3038 υ(Ar-CH),
2967-2859 υ(Aliph-CH), 1656 υ(C=N), 1465-1417
υ(C=C) and 1270 υ(N-O). 1H-NMR (DMSO-d6, TMS,
400 MHz, δ ppm): 10.88 (s, 2H, C=N-OH), 8.04 (s, 1H,
HC=N), 7.54 (d, 2H, J = 8.8 Hz, Ar-CH), 6.95 (d, 2H,
J = 8.8 Hz, Ar-CH), 3.75 (t, 4H, J = 4.8 Hz, O-CH2),
and 3.15 (t, 4H, N-CH2). 13C-NMR (DMSO-d6, TMS,
100 MHz, δ ppm): 155.42 and 148.68 (C=NOH), 142.
01, 133.41, 130.12, 115.36 and 113.93 (Ar-CH), 66.82
(O-CH2) and 47.65 (N-CH2). UV-Vis (λmax/nm): 233,
297 and 353 (in CH3OH); 232, 256, 305, and 356 (in
CH2Cl2).
1
any further treatment. H and 13C-NMR spectra were
recorded in 5-mm tubes at room temperature with a
Bruker Avance 300 NMR or an Agilent-VNMRS-400
NMR at 400 MHz. All chemical shifts are reported in
δ units with reference to the residual protons of the
deuterated solvents for proton chemical shifts. Signals
are quoted relative to tetramethylsilane (δ = 0.00 ppm)
and coupling constants (J) are in hertz. Elemental
analyses (C, H and N) were performed on a LECO
CHNS model 932 elemental analyzer. Infrared spec-
tra were obtained from KBr pellets (3 mg sample in
300 mg KBr) on a Perkin Elmer Spectrum Two FT-IR
Fourier Transform spectrometer (4000–400 cm−1). UV-
Vis spectra were obtained on a Perkin-Elmer Lambda
25 spectrophotometer in the wavelength range from 200
to 1100 nm in CH3OH and CH2Cl2 solvents. Magnetic
Susceptibilities were determined on a Sherwood Sci-
entific Magnetic Susceptibility Balance (Model MK1)
at room temperature (25◦C) using Hg[Co(SCN)4] as a
calibrant; diamagnetic corrections were calculated from
2.3 Synthesis of the multinuclear cobaloxime
complexes (1-3)
Pascal’s constants.11 Melting points were measured In a two-necked, 100 mL round-bottom flask and
in open capillary tubes with an Electrothermal 9100 equipped with a blanket of argon (Ar) was placed 50 mL
melting point apparatus and are uncorrected. LC-MS of 96% EtOH. To this solution, CoCl2.6H2O (1.19 g,
spectra results were recorded on an Agilent LC/MSD 5.0 mmol) was added slowly at room temperature under
R1
OH
O
C
O
C
OH
N
C
C
N
(b)
(a)
R1
CH2
R2
R1
C
N
R2
R2
OH
R1 = CH3 and R2 = CH3 for ligand (L1H2)
R1 = CH3-CH2 and R2 = H for ligand (L2H2)
Ligands (L(1-3)H2)
R1= O
N
and R2 = H for ligand (L3H2)
Scheme 2. Synthesis of the dioxime ligands (L1−3H2); (a) n-C4H9ONO,
C2H5ONa, -5◦C; (b) CH3COONa, NH2OH.HCl, EtOH, reflux temperature.

Synthesis of the Multinuclear Cobaloxime Complexes
1667
argon atmosphere and with vigorous mechanical stir- O−H· · · O), 18.84 (d, 3H, J = 6.0 Hz, O−H· · · O),
ring. Then, the solution of dioxime ligand (L1H2) 8.22 (s, 6H, CH=N), 7.40-6.90 (m, 24H, Ar-CH), 2.70
(1.92 g, 10.0 mmol), (L2H2) (1.92 g, 10.0 mmol) and (d, 12H, J = 7.2 Hz, CH3-CH2), 2.10-1.85 (m, 12H,
(L3H2) (2.49 g, 10.0 mmol) was quickly injected into C-CH2 and N-CH2), and 1.23-0.93 (m, 24H, CH3-CH2,
the reaction mixture in one portion. The mixtures were and CH2-NH2). 13C-NMR (DMSO-d6, TMS, 75 MHz,
vigorously strirred for 40 min with occasional swirling, δ ppm): 147.70 and 147.01 (C=NOH), 143.41, 142.61,
during which the solution turned green, and the mix- 129.42, 128.92, 128.55, 128.23, 127.57 and 126.28
tures were again heated for 3 h at reflux temperature. (Ar-CH), 61.14 (N-CH2), 45.56 (C-CH2), 28.50 (CH3-
Later the mixtures were allowed to cool to room tem- CH2) and 15.99 (CH3-CH2). UV-Vis (λmax/nm, * =
perature and then 1.70 mmol tris (2-aminoethyl) amine shoulder peak): 261, 337* and 836* (in CH3OH); 253,
(TAEA) was added to mixture as axial base and a very 270 and 312* (in CH2Cl2).
gentle stream of air was passed through the solution for
about 6 h. After completion of the reaction, 5 mL water
2.3c [(L3H)6Cl3Co3(TAEA)] (3): Color: Brown,
was added to get the desired product and the crude prod-
yield: 68%, M.p.: 217◦C, Anal. Calc. (%) for
uct obtained was recrystallized from CH2Cl2/C2H5OH.
[C78H102Cl3Co3N22O18] (F.W: 1918.9 g/mol): C, 48.82;
The mixtures were set aside for 5 h, after which the
H, 5.36; N, 16.06. Found: C, 48.74; H, 5.28; N, 15.96%.
product was collected on sintered glass and washed suc-
cessively with small amounts of water, and diethyl ether
and finally air-dried.
μeff = Dia, LC-MS (Scan ES+): m/z (%) 1918.8
(15) [M]+. FT-IR (KBr pellet, υmax/cm−1): 3548-3297
υ(O−H· · · O), 3233 and 3146 υ(NH2), 3070 υ(Ar-
CH), 2963-2851 υ(Aliph-CH), 1605 υ(C=N), 1521-
1
2.3a [(L1H)6Cl3Co3(TAEA)] (1): Color: Brown,
1446 υ(C=C), 1266 υ(N-O) and 513 υ(Co-N). H-
yield: 62%, M.p.: 223◦C, Anal. Calc. (%) for
NMR (DMSO-d6, TMS, 300 MHz, δ ppm): 19.92 (s,
[C66H84Cl3Co3N16O12] (F.W: 1576.6 g/mol): C, 50.28;
6H, O−H· · · O), 8.23 (s, 6H, HC=N), 8.02-6.95 (m,
H, 5.37; N, 14.21. Found: C, 50.19; H, 5.24; N,
14.14 %. μeff = Dia, LC-MS (Scan ES+): m/z (%)
1576.7 (18) [M]+. FT-IR (KBr pellet, υmax/cm−1): 3540-
3301 υ(O−H· · · O), 3221 and 3130 υ(NH2), 3030
υ(Ar-CH), 2954-2863 υ(Aliph-CH), 1616 υ(C=N),
1553-1445 υ(C=C), 1264 υ(N-O) and 502 υ(Co-
24H, Ar-CH), 3.73 (s, 24H, Ar-O-CH2), 3.46 (s, 24H,
Ar-N-CH2). 3.18-2.95 (m, 6H, Aliph-N-CH2), 2.10 (s,
6H, Aliph-C-CH2) and 1.16 (t, 6H, J = 7.2 Hz, CH2-
NH2). 13C-NMR (DMSO-d6, TMS, 75 MHz, δ ppm):
155.30 and 151.64 (C=NOH), 138.85, 131.88, 131.30,
126.79, 122.34, 114.85 and 113.38 (Ar-CH), 66.20 (Ar-
O-CH2), 48.40 (Ar-N-CH2), 46.74 (Aliph-N-CH2), and
46.27 (Aliph-CH2). UV-Vis (λmax/nm, * = shoulder
peak): 223*, 294 and 456 (in CH3OH); 231, 280 and
452 (in CH2Cl2).
1
N). H-NMR (DMSO-d6, TMS, 300 MHz, δ ppm):
18.74 (d, 3H, J = 6.0 Hz, O−H · · · O), 18.60 (s, 3H,
O−H · · · O), 7.59-7.06 (m, 24H, Ar-CH), 2.40 (s, 18H,
Ar-CH3), 2.31 (s, 18H, C-CH3), 2.28 (d, 6H, J =
6.0 Hz, C-CH2), 2.06 (s, 6H, N-CH2), and 1.09-1.04 (m,
6H, CH2-NH2). 13C-NMR (DMSO-d6, TMS, 75 MHz,
δ ppm): 155.58 and 149.78 (C=NOH), 143.25, 140.19,
139.21, 137.33, 130.74, 129.53, 128.57, 128.42 and
128.08 (Ar-CH), 56.52 (N-CH2), 36.93 (C-CH2), 21.48
(Ar-CH3) and 14.94 (CH3C=NOH). UV-Vis (λmax/nm,
* = shoulder peak): 251, 314*, and 835* (in CH3OH);
250, 268*, and 315 (in CH2Cl2).
2.4 Synthesis of the azido-functionalized
multinuclear cobaloxime complexes (4-6)
The azido-functionalized multinuclear cobaloxime
complexes (4-6) were synthesized according to the
literature method.14 In a two-necked, 100 mL round-
bottom flask and equipped with a blanket of argon
(Ar) was placed 10 mL of CH3CN. To this solution
2.3b [(L2H)6Cl3Co3(TAEA)] (2): Color: Dark was added 0.5 mmol of [(L1-3H)6Cl3Co3(TAEA)] (1-
brown, yield: 64%, M.p.: 235◦C, Anal. Calc. (%) for 3) cobaloxime complexes slowly at room temperature
[C66H84Cl3Co3N16O12] (F.W: 1576.6 g/mol): C, 51.28; under argon atmosphere and with vigorous mechan-
H, 5.37; N, 14.21. Found: C, 51.19; H, 5.29; N, 14.13 ical stirring. In another a two-necked round-bottom
%. μeff = Dia, LC-MS (Scan ES+): m/z (%) 1576.5 flask, 1.50 mmol of AgClO4 was dissolved in an equal
(20) [M]+. FT-IR (KBr pellet, υmax/cm−1): 3569-3329 volume of CH3CN. The [(L1-3H)6Cl3Co3(TAEA)] (1-
υ(O−H· · · O), 3220 and 3122 υ(NH2), 3027 υ(Ar-CH), 3) solution was then cannulated into the silver per-
2967-2867 υ(Aliph-CH), 1608 υ(C=N), 1545-1453 chlorate solution. Immediate precipitation of AgCl
1
υ(C=C), 1266 υ(N-O) and 505 υ(Co-N). H-NMR was observed, and the reaction was stirred overnight.
(DMSO-d6, TMS, 300 MHz, δ ppm): 19.03 (s, 3H, 4.5 mmol of NaN3 was added, keeping exposure to

1668
Ahmet Kilic et al.
air at a minimum. The reaction was stirred for an 2.4c [(L3H)6(N3)3Co3(TAEA)] (6): Color: Dark
additional 24 h. The mixture was diluted with distilled brown, yield: 64%, M.p.: >300◦C, Anal. Calc. for
diethyl ether and the organic portion washed with water [C78H102Co3N31O18] (F.W: 1938.6 g/mol): C, 48.32; H,
to remove NaClO4 and excess NaN3, then dried with 5.30; N, 22.40%. Found: C, 48.23; H, 5.29; N, 22.31%.
Na2SO4 and the solvent removed in vacuo and finally μeff = Dia, LC-MS (Scan ES+): m/z (%) 1938.5
the products was dried in vacuo.
(10) [M]+. FT-IR (KBr pellet, υmax/cm−1): 3596-3263
υ(O−H· · · O), 3210 and 3129 υ(NH2), 3072 υ(Ar-CH),
2966-2849 υ(Aliph-CH), 2035 υ(N3), 1603 υ(C=N),
1548-1444 υ(C=C), 1264 υ(N-O) and 512 υ(Co-N).
1H-NMR (DMSO-d6, TMS, 400 MHz, δ ppm): 19.98
(s, 6H, O−H· · · O), 8.20 (s, 6H, HC=N), 7.98 (d,
12H, J = 5.2 Hz, Ar-CH), 7.00 (d, 12H, J = 5.2 Hz,
Ar-CH), 3.70 (s, 24H, Ar-O-CH2), 3.40 (s, 24H, Ar-
N-CH2), 3.12-3.00 (m, 6H, Aliph-N-CH2), 2.48 (s,
6H, Aliph-C-CH2), and 1.23 (s, 6H, CH2-NH2). 13C-
NMR (DMSO-d6, TMS, 100 MHz, δ ppm): 154.20
and 151.62 (C=NOH), 137.78, 130.77, 130.12, 126.71,
121.29, 114.13 and 112.28 (Ar-CH), 65.12 (Ar-O-
CH2), 48.32 (Ar-N-CH2), 47.60 (Aliph-N-CH2), and
45.66 (Aliph-CH2). UV-Vis (λmax/nm, * = shoulder
peak): 225*, 274 and 464 (in CH3OH); 276, 397* and
460 (in CH2Cl2).
2.4a [(L1H)6(N3)3Co3(TAEA)] (4): Color: Dark
brown, yield: 60%, M.p.: >300◦C, Anal. Calc. for
[C66H84Co3N25O12] (F.W: 1596.3 g/mol): C, 49.66; H,
5.30; N, 21.94. Found: C, 49.56; H, 5.24; N, 21.86
%. μeff = Dia, LC-MS (Scan ES+): m/z (%) 1596.4
+
(12) [M] . FT-IR (KBr pellet, υmax/cm−1): 3544-3327
υ(O−H· · · O), 3253 and 3139 υ(NH2), 3031 υ(Ar-CH),
2956-2856 υ(Aliph-CH), 2021 υ(N3), 1610 υ(C=N),
1554-1447 υ(C=C), 1270 υ(N-O) and 506 υ(Co-
1
N). H-NMR (DMSO-d6, TMS, 400 MHz, δ ppm):
18.71 (d, 3H, J = 6.0 Hz, O−H· · · O), 18.45 (s, 3H,
O−H· · · O), 7.60-7.04 (m, 24H, Ar-CH), 2.39 (s, 18H,
Ar-CH3), 2.34 (d, 6H, J = 6.0 Hz, C-CH2), 2.28 (s,
18H, C-CH3), 2.06 (s, 6H, N-CH2), and 1.28-1.03 (m,
6H, CH2-NH2). 13C-NMR (DMSO-d6, TMS, 100 MHz,
δ ppm): 154.31 and 149.28 (C=NOH), 139.37, 139.19,
137.27, 130.29, 129.83, 129.52, 128.40 and 127.55 (Ar-
CH), 56.48 (N-CH2), 36.95 (C-CH2), 21.51 (Ar-CH3)
and 14.32 (CH3C=NOH). UV-Vis (λmax/nm, * = shoul-
der peak): 246, and 317* (in CH3OH); 248 and 324* (in
CH2Cl2).
2.5 Procedure for click reaction to form 1,2,3-triazole
containing multinuclear cobaloxime complexes (7-9)
The 1,2,3-triazole containing multinuclear cobaloxime
complexes (7-9) were synthesized via click reaction
according to the literature method.15 The azido-functio-
nalized cobaloxime complex (4) (0.5 g, 0.31 mmol),
complex (5) (0.5 g, 0.31 mmol), complex (6) (0.5 g,
0.26 mmol) and excess quantity of propargyl alcohol
(0.08 g, 1.35 mmol) were dissolved in 1:1 (30:30 mL)
mixture of THF and water solvent mixture in a round-
bottom flask. To the reaction mixture, CuSO4 (0.08 g,
dissolved in 2 mL water) was added followed by freshly
prepared sodium ascorbate solution (0.06 g, dissolved
in 2 mL water) dropwise. The reaction mixture was
stirred for 18 h at room temperature. After removal of
the THF under vacuum, dichloromethane (15 mL) and
conc. NH3 (3 mL) were added to the solution, which
was allowed to stir for a further 1 h at room tempera-
ture. The dichloromethane solution was dried over mag-
nesium sulfate and crude compounds were collected
after evaporating the solvent. Finally the products was
recrystallized from dichloromethane and hexane.
2.4b [(L2H)6(N3)3Co3(TAEA)] (5): Color: Dark
brown, yield: 62%, M.p.: >300◦C, Anal. Calc. for
[C66H84Co3N25O12] (F.W: 1596.3 g/mol): C, 49.66; H,
5.30; N, 21.94%. Found: C, 49.52; H, 5.23; N, 21.86%.
μeff = Dia, LC-MS (Scan ES+): m/z (%) 1596.2
(16) [M]+. FT-IR (KBr pellet, υmax/cm−1): 3577-3341
υ(O−H· · · O), 3235 and 3129 υ(NH2), 3047 υ(Ar-CH),
2966-2870 υ(Aliph-CH), 2017 υ(N3), 1607 υ(C=N),
1568-1455 υ(C=C), 1270 υ(N-O) and 513 υ(Co-
1
N). H-NMR (DMSO-d6, TMS, 400 MHz, δ ppm):
18.53 (s, 3H, O−H· · · O), 18.41 (d, 3H, J = 6.0 Hz,
O−H· · · O), 8.57 (s, 6H, CH=N), 8.19-7.25 (m, 24H,
Ar-CH), 2.68 (d, 12H, J = 7.2 Hz, CH3-CH2), 2.63-
2.59 (m, 12H, C-CH2 and N-CH2), and 1.23-1.05 (m,
24H, CH3-CH2, and CH2-NH2). 13C-NMR (DMSO-
d6, TMS, 100 MHz, δ ppm): 147.49 and 146.51
(C=NOH), 142.39, 142.71, 141.71, 131.93, 128.98,
128.89, 128.28, 127.74, 127.38, 126.61 and 126.30 (Ar- 2.5a [(L1H)6(triazole)3Co3(TAEA)]
(7): Color:
CH), 61.18 (N-CH2), 45.73 (C-CH2), 28.53 (CH3-CH2) Brown, yield: 80%, M.p.: 215◦C, Anal. Calc. for
and 15.89 (CH3-CH2). UV-Vis (λmax/nm, * = shoulder [C75H96Co3N25O15] (F.W: 1764.5 g/mol): C, 51.05; H,
peak): 260 and 346* (in CH3OH); 253, 262 and 348* 5.48; N, 19.85%. Found: C, 50.98; H, 5.41; N, 19.76%.
(in CH2Cl2).
μeff = Dia, LC-MS (Scan ES+): m/z (%) 1764.6

Synthesis of the Multinuclear Cobaloxime Complexes
1669
(12) [M]+. FT-IR (KBr pellet, υmax/cm−1): 3539-3312
2.6 General procedure of coupling reaction of
epoxides and CO2
υ(O−H· · · O), 3249 and 3150 υ(NH2), 3026 υ(Ar-
CH), 2959-2856 υ(Aliph-CH), 1650 υ(triazole), 1607
υ(C=N), 1522-1446 υ(C=C), 1267 υ(N-O) and 499
υ(Co-N). 1H-NMR (DMSO-d6, TMS, 300 MHz, δ
ppm): 18.68 (d, 3H, J = 6.0 Hz, O−H· · · O), 18.49 (s,
3H, O−H· · · O), 8.18 (s, 3H, triazole-CH), 7.63-7.01
(m, 24H, Ar-CH), 4.52 (br., s, 3H, CH2-OH), 3.25 (s,
6H, CH2-OH), 2.36 (s, 18H, Ar-CH3), 2.30 (d, 6H, J
= 6.0 Hz, C-CH2), 2.16 (s, 18H, C-CH3), 2.03 (s, 6H,
N-CH2), and 1.21-0.99 (m, 6H, CH2-NH2). 13C-NMR
(DMSO-d6, TMS, 75 MHz, δ ppm): 155.32 and 148.56
(C=NOH), 146.77 (triazole CH), 139.33, 139.07,
137.18, 130.30, 129.86, 129.62, 128.49 and 127.71
(Ar-CH), 123.32 (triazole C-CH2OH), 56.48 (N-CH2),
55.16 (triazole-CH2-OH), 37.08 (C-CH2), 21.32 (Ar-
CH3) and 14.28 (CH3C=NOH). UV-Vis (λmax/nm, * =
shoulder peak): 251, and 319* (in CH3OH); 256 and
328* (in CH2Cl2).
All the coupling reactions were performed in a 50 mL
stainless steel autoclave equipped with a mechanical
stirring. The autoclave reactor was successively charged
with multinuclear cobaloxime complexes obtained by
click chemistry (4.5 × 10−5 mol), epoxide (4.5 ×
10−2 mol) and DMAP (9.0 × 10−5 mol). The reaction
vessel was placed under a constant pressure of carbon
dioxide for 2 min to allow the system to equilibrate
and CO2 was charged into the autoclave at the desired
pressure; then it was heated and stirred at the desired
reaction temperature. The pressure was kept constant
during the reaction. When the pressure of CO2 fell to 1–
3 atm, the reactor was cooled quickly to 5–10◦C in an
ice bath after the expiration of the desired reaction time.
The pressure was released, and then the excess gases
were vented. The crude product in DMSO-d6 was ana-
lyzed by 1H-NMR spectroscopy and FT-IR to determine
if any polycarbonate, epoxides, DMAP or other by-
products were present. Also, aliquot of the crude prod-
uct was taken from the reaction mixture and injected
directly without further purification for the by GC (Agi-
lent 7820A) analysis. Ethylene glycol dibutyl ether was
used as the internal standard.
2.5b [(L2H)6(triazole)3Co3(TAEA)]
(8): Color:
Brown, yield: 78%, m.p: 125◦C, Anal. Calc. for
[C75H96Co3N25O15] (F.W: 1764.5 g/mol): C, 51.05;
H, 5.48; N, 19.85%. Found: C, 50.92; H, 5.39; N,
19.77%. μeff = Dia, LC-MS (Scan ES+): m/z (%)
1764.3 (12) [M]+. FT-IR (KBr pellet, υmax/cm−1):
3557-3097 υ(O−H· · · O/NH2), 3032 υ(Ar-CH), 2964-
2867 υ(Aliph-CH), 1646 υ(triazole), 1610 υ(C=N),
1546-1454 υ(C=C), 1273 υ(N-O) and 516 υ(Co-
3. Results and Discussion
3.1 Synthesis
1
N). H-NMR (DMSO-d6, TMS, 300 MHz, δ ppm):
18.62 (s, 3H, O−H· · · O), 18.43 (d, 3H, J = 6.0 Hz,
O−H· · · O), 8.46 (s, 6H, CH=N), 8.19 (s, 3H, triazole-
CH), 7.65-7.15 (m, 24H, Ar-CH), 4.51 (br., s, 3H,
CH2-OH), 3.36 (s, 6H, CH2-OH), 2.67 (d, 12H, J
= 3.9 Hz, CH3-CH2), 2.65-2.54 (m, 12H, C-CH2
and N-CH2), and 1.23-1.18 (m, 24H, CH3-CH2, and
CH2-NH2). 13C-NMR (DMSO-d6, TMS, 75 MHz, δ
ppm): 150.16 and 146.98 (C=NOH), 143.93 (triazole
CH), 142.86, 142.73, 140.17, 130.87, 128.58, 128.12,
127.88, 127.31, 126.66, 126.46 and 126.36 (Ar-CH),
124.94 (triazole C-CH2OH), 67.88 (N-CH2), 58.27
(triazole-CH2-OH), 45.78 (C-CH2), 27.59 (CH3-CH2)
and 15.93 (CH3-CH2). UV-Vis (λmax/nm, * = shoulder
peak): 262 and 411* (in CH3OH); 234, 261 and 380*
(in CH2Cl2).
In this paper, we introduce a simple and rapid two-
step method for the synthesis of the three dissymmet-
rical dioxime ligands (L(1,2)H2) from various ketones
as described previously by our group.12,13 However,
the ligand (L3H2) was synthesized by a similar pro-
cedure as new compounds (scheme 2). Then, using
these ligands and tris (2-aminoethyl) amine (TAEA)
as axial base, multinuclear cobaloxime complexes (1-
3) were obtained at reflux temperature and under
the basic conditions (scheme 3). The synthesis of
the new azido-functionalized multinuclear cobaloxime
complexes (4-6) were achieved by a one-pot reac-
tion involving azide substitution of chlorine groups
in multinuclear cobaloxime complexes (1-3) using
NaN3 in CH3CN through nucleophilic substitution reac-
tion (scheme 3). The azido-functionalized multinuclear
2.5c [(L3H)6(triazole)3Co3(TAEA)] (9): Although cobaloxime complexes (4-6) and excess quantity of
much effort was made to clarify the structure of the propargyl alcohol were performed using CuSO4/sodium
[(L3H)6(triazole)3Co3(TAEA)] (9) complex, we failed ascorbate as the catalyst system in THF/H2O at 30◦C,
to isolate their crystals. Thus, the structure of the for 18 h to obtain a well-defined 1,2,3-triazole contain-
[(L3H)6(triazole)3Co3(TAEA)] (9) complex has not ing multinuclear cobaloxime complexes (7-9), as seen
been evaluated through spectroscopic techniques.
in scheme 3. As an exception, although much effort

1670
Ahmet Kilic et al.
R1
OH
N
C
C
H2N
N
N
R2
OH
Ligands (L(1-3)H2)
CoCl2.6H2O, EtOH
Reflux, O2
NH2
H2N
+
H2N
H
R1
O
O
N
R2
C
C
N
C
Co
Cl
N
N
O
N
O
C
R2
NH2
H2N
R1
H
tris (2-aminoethyl) amine (TAEA)
(1-3)
NaN
AgC
lO
, CH
3CN
4
3, Ar
H2N
H2N
N
1) THF/H2O
2) propargyl alcohol
N
NH2
NH2
H2N
H2N
3) CuSO4
4) sodium ascorbate
H
H
R1
R1
O
N
O
N
O
O
N
R2
R2
C
C
C
C
C
N
C
C
Co
N
Co
N
O
N
C
N
O
N
O
N3
N
R2
R2
N
H
O
R1
R1
H
HO
(7-9)
(4-6)
Scheme 3. The structure of the proposed multinuclear cobaloxime complexes (1-9).
was made to clarify the structure of this complex (9), 3.2 Spectroscopic characterization
we failed to isolate their crystals. In continuation of
In the present investigation, FT-IR spectra showed
this work, the catalytic efficiency of the multinuclear
cobaloxime complexes were obtained by click chem-
istry have been successfully applied to the synthesis of
a five-membered cyclic organic carbonates from CO2
and epoxides under optimally conditions and without
using any solvent. To the best of our knowledge, the
multinuclear cobaloxime complexes have not been used
as a catalyst system for conversion of carbon dioxide
to a five-membered cyclic organic carbonate. Although
much effort was made to clarify the structure of the
multinuclear cobaloxime complexes, we failed to iso-
late their single crystals. However, the spectroscopic
data 1H and 13C-NMR, FT-IR, UV-Vis spectra, elemen-
tal analysis, melting point measurements, LC-MS spec-
tra, and magnetic susceptibility techniques showed high
probability that these compounds have the proposed
structures.
that the formation of three dioxime ligands and
their multinuclear cobaloxime complexes (1-3), azido-
functionalized multinuclear cobaloxime complexes (4-
6) and triazole containing multinuclear cobaloxime
complexes (7 and 8) as new compounds (figure S1).
The FT-IR of the multinuclear cobaloxime complexes
are compared with those of the free dioxime lig-
ands (L(1−3)H2) in order to determine the coordina-
tion sites that may be involved in chelation. Forma-
tion of the multinuclear cobaloxime complexes (1-
8) was established by disappearance of the υ(O-H)
peaks around 3505-3086 cm−1 and also the appear-
ance of the intermolecular H-bond υ(O-H· · · O) stretch-
ing are observed at 3596-3263 cm−1.16 In the FT-IR
spectra of the dioxime ligands and their multinuclear
cobaloxime complexes, the characteristic absorption

Synthesis of the Multinuclear Cobaloxime Complexes
1671
band of the imine υ(C=N) groups were observed at the imine (C=N) carbon signals of dioxime ligands
1656-1603 cm−1. The FT-IR spectra of the multinu- (L(1−3)H2) were significantly different field shift com-
clear cobaloxime (1-8) complexes were compared with pared to the multinuclear cobaloxime complexes (1-
those of the free dioxime (L(1−3)H2) ligands in order to 8), which is powerful evidence to the formation of
monitor the change in the vibration frequency of the the multinuclear cobaloxime complexes (1-8) and con-
coordination sites, which a small frequency shift in its firm the complex formation via imine nitrogen coor-
position may be because of the formation of Co(III)←N dination to Co(III) ion. Analysis of 1,2,3-triazole con-
or Co(III)←NH2 dative bonds in these complexes, as taining multinuclear cobaloxime complexes (7 and 8)
1
expected.17 Next, the powerful evidence for the trans- by H and 13C NMR spectra revealed that presence
formation of chlorine to azido group could be seen in of the peaks corresponding to the methine proton in
the FT-IR spectra of the azido-functionalized multinu- 1,2,3-triazole ring at 8.18 ppm for complex (7) and
1
clear cobaloxime complexes (4-6) and the characteris- at 8.19 ppm for complex (8) in H NMR spectra and
tic absorption band of the azido groups were observed methine carbon in 1,2,3-triazole ring at 146.77 ppm
at 2021 cm−1 for complex (4), at 2017 cm−1 for com- for complex (7) and at 143.93 ppm for complex (8) in
plex (5) (figure S1b) and at 2035 cm−1 for complex 13C NMR spectra. These chemical shift results indi-
(6) as very strong peaks, consecutively. The click reac- cate the occurrence of the click cyclization reaction
tion between azidated multinuclear cobaloxime com- and formation of 1,2,3-triazole containing multinuclear
plexes (4-6) and propargyl alcohol was proven by the cobaloxime complexes (7 and 8). Another evidence
disappearance of the azide peak at 2035-2017 cm−1 that 1,2,3-triazole containing multinuclear cobaloxime
(figure S1b) and presence of the aromatic triazole ring complexes (7 and 8) are formed was the new peaks
stretching peak at about ∼1650 cm−1 (figure S1c) as at 4.52 and 3.37 ppm for complex (7) and at 4.51 and
new peak in the final FT-IR spectra of triazole con- 3.36 ppm for complex (8) belonging to the CH2-OH and
taining multinuclear cobaloxime complexes (7 and 8), the CH2-OH protons of 1,2,3-triazole group, respec-
1
which support the formation of the 1,2,3-triazole con- tively, in the H NMR spectra. Also, other proton and
taining multinuclear cobaloxime complexes (7 and 8) carbon NMR shifts of the dioxime ligands (L(1−3)H2)
(figure S1c) by the click cyclization reaction. Addi- and their multinuclear cobaloxime complexes (1-8)
tionally, the observed absorption bands at range 516– indicate the formation of all compounds.
499 cm−1 due to Co(III)←N or Co(III)←NH2 stretch-
The UV-Vis spectra of the dioxime ligands
ing vibrations that are not observed in the FT-IR spectra (L(1−3)H2) and their multinuclear cobaloxime com-
of the dioxime ligands (L(1−3)H2) indicates the forma- plexes (1-8) obey well with Lambert-Beer’s law in the
tion of multinuclear cobaloxime complexes (1-8).18
concentration range studied (2.10−5–2.10−8 mol L−1)
1
The H and 13C-NMR spectra for three dioxime in two solvents (CH3OH and CH2Cl2). The results
ligands (L(1−3)H2) and their multinuclear cobaloxime are summarized in experimental part. As expected
complexes (1-8) obtained by click chemistry were in for the eight multinuclear cobaloxime complexes (1-
good agreement with the structure of the newly formed 8) in octahedral environment, the UV-Vis spectrum
1
compound. Detailed assignments of H and 13C NMR showed Co(III) d–d transitions at about ∼835 nm
spectra along with coupling constants of the signals for complexes (1) and (2). In the other multinuclear
for dioxime ligands (L(1−3)H2) and their multinuclear cobaloxime complexes, this characteristic Co(III) d-d
cobaloxime complexes (1-8) have been presented in transition in the visible region was not observed, most
experimental section. In the 1H NMR spectra in DMSO- probably owing to their very low molar absorption
d6, the formation of the multinuclear cobaloxime com- coefficient. The sharp and strong absorption bands at
plexes (1-8) obtained by click chemistry was confirmed 353 nm in CH3OH and at 380 nm in CH2Cl2 for both
by the disappearance of peaks related to the deuterium- the dioxime ligands (L(1−3)H2) and their multinuclear
exchangeable protons of the (C=N–OH) groups of the cobaloxime complexes (1-8) display similar features
dioxime ligands (L(1−3)H2) at range 11.69-10.88 ppm for π → π* or n → π* transitions due to the presence
1
in H NMR spectra. Another result that supports for- of aromatic rings and functional imine (C=N) groups
mation of the multinuclear cobaloxime complexes (1- in the structure of the dioxime ligands. In addition, the
8) was new peaks observed, identified as singlet or absorption spectra of the dioxime ligands (L(1−3)H2)
doublet peaks in range 19.98–18.41 ppm, indicating and their multinuclear cobaloxime complexes (1-8)
that the (C=N-OH) groups of three dioxime ligands showed a characteristic strong band corresponding
(L(1−3)H2) have been transformed to intramolecular to the intermolecular transition from the dioxime
D2O exchangeable H-bridge (O−H· · · O), as expected. ligand molecules to the vacant orbitals localized
However, in the 13C NMR spectra in DMSO-d6, on the coordinated Co(III) metal ion in the region

1672
Ahmet Kilic et al.
cyclic organic carbonate at 1795 cm−1 were monitored
during the reaction of CO2 and different epoxides for all
eight cobaloxime catalysts (1-8).20 However, no peak
at 1749 cm−1 was detected, which was attributed to the
carbonyl group in polycarbonate.21 The multinuclear
cobaloxime complexes (1-8), using 4-(dimethylamino)
pyridine (DMAP) as co-catalyst, showed high cat-
alytic activity and selectivity for the conversion of CO2
into cyclic carbonates using the epichlorohydrin (ECH)
which served as substrate and solvent. Catalytic exper-
iments were carried out at optimized conditions, which
were determined in previous studies.13,17,22,23 To opti-
mize the reaction conditions for the ECH/CO2 cycload-
dition reactions, different parameters (epoxide, base,
reaction time, and temperature and CO2 pressure) were
investigated, in which DMAP was used as a co-catalyst.
The results are summarized in table S1.
The high activity of the cobaloxime complex (1) cat-
alyst relative to the other cobaloxime catalysts can be
explained by the electron-withdrawing property of the
chloro substituents as axial groups on the Co(III) cen-
ter. Whereas, in the azido-functionalized multinuclear
cobaloxime complexes (4-6) and 1,2,3-triazole con-
taining multinuclear cobaloxime complexes (7-9) the
catalytic activity is low, due to the chloro groups trans-
formation to azido or 1,2,3-triazole groups. Due to the
Lewis acidity of the Co(III) center in the cobaloxime
complex (1) catalyts and its analogue, the epichloro-
hydrin (ECH) or other epoxides are coordinated more
strongly to the Co(III) centers. For the investigation of
the efficiency of the catalytic system, different epox-
ides (propylene oxide (PO), 1, 2-epoxybutane (EB),
epichlorohydrin (ECH), styrene oxide (SO) and cyclo-
hexene oxide (CHO)) were used as both solvent and
substrate under the optimized reaction conditions. The
cobaloxime complex (1) catalyst is also an efficient
catalyst for the cycloaddition of CO2 with epichloro-
hydrin (ECH). As shown in figure S4, epichlorohy-
drin (ECH) was found to be the most reactive epoxide,
while styrene oxide exhibited the lowest activity among
the epoxides surveyed. This result may be due to the
higher electron donating substituents linked to C2-atom
of these epoxides (PO, EB, SO and CHO) which could
be coordinately bonded to the metal centre and could
be responsible for the catalyst poisoning. Similar effect
was observed in our previous studies.13,17,22
464-411 nm which was clearly separated from the main
transition.
The molecular weights of the dioxime ligands
(L(1−3)H2) and their multinuclear cobaloxime com-
plexes (1-8) were analyzed from LC-MS analysis. The
peak positions and the isotopic distributions have been
well assigned and the results are summarized in experi-
mental section and figures S2 and S3. From the LC-MS
plots, it is seen that the molecular weight correspond-
ing to the highly intense peak in the spectrum has good
agreement with theoretical molecular weight which is
also verified by elemental analyses and the other spec-
troscopic analysis. The highest mass peak is detected
for the molecular ion peak at m/z = 249.2 for ligand
(L3H2), corresponding to the [M]+ peak. The molecular
ion peaks at m/z = 1576.7 for complex (1), 1576.5 for
complex (2), 1918.8 for complex (3), 1596.4 for com-
plex (4), 1576.2 for complex (5), 1938.5 for complex
(6), 1764.6 for complex (7), and 1764.4 for complex (8)
correspond to the [M]+ peak, which could be attributed
to the trimeric structures of the cobaloxime complexes
(1-8).19
The molar magnetic susceptibility (μeff) of the mult-
inuclear cobaloxime complexes (1-8) in the solid state
was measured at room temperature and found to be dia-
magnetic in character due to the complete spin pairing
as expected, indicating low-spin (S=0) octahedral d6-
systems. Furthermore, the magnetic susceptibility mea-
surement confirms the presence of cobalt centers in the
+3 oxidation state, which indicates the formation of the
three types multinuclear cobaloxime complexes (1-8).
The change in the % C, H, N content of the dioxime
ligands (L(1−3)H2) and their three types of multinu-
clear cobaloxime complexes (1-8), as summarized in
the experimental section, suggest the formation of all
compounds.
3.3 Catalytic properties
In the presence of a series of multinuclear cobaloxime
complexes (1-8), the coupling reaction of epichloro-
hydrin (ECH) and carbon dioxide to form 4-
(chloromethyl)-1,3-dioxolan-2-one (ECHC) was car-
ried out under identical reaction conditions (cata-
lyst loading 0.1% (1-8), 0.2% DMAP, CO2 pressure,
1.6 MPa, 100◦C, 2 h) and the corresponding results
were summarized in table S1 (see Supplementary Infor-
mation). In an in situ ATR-IR, which can be recorded
for continuous monitoring using an attenuated total
reflectance probe in FT-IR, the decrease of the stretch-
ing carbonyl vibration of carbon dioxide at 2350
cm−1 and the increase of the carbonyl vibration of
In addition to DMAP (4-(dimethylamino) pyridine),
CH3CN (acetonitrile), C5H5N (pyridine), NEt3 (triethy-
lamine) and PPh3 (triphenylphosphine) were tested to
expand the range of the co-catalysts with the coba-
loxime complex (1) as catalyst (figure S5). This showed
that C5H5N (pyridine) was the best co-catalyst for this
system with a yield of 90% of 4-(chloromethyl)-1,

Synthesis of the Multinuclear Cobaloxime Complexes
1673
3-dioxolan-2-one (ECHC) in high selectivity. In con- increase of time from 0.5 to 4 h, ECHC yield increased
trast to C5H5N (pyridine), the use of DMAP (4- from 89 to 96%. This result suggested that the CO2 fix-
(dimethylamino) pyridine), CH3CN (acetonitrile), NEt3 ation on epichlorohydrin (ECH) was completed within
(triethylamine) or PPh3 (triphenylphosphine) as co- 4 h. Similar effects of temperature, CO2 pressure and
catalyst led only to a low yield of ECHC) (figure S5), time on catalytic activity were observed in previous
probably due to the formation of a stable [Co-co- studies.10,12,16,21
catalyst] complex as already suggested by the teams of
Rieger,24 Lu25 and Zevaco26 for related systems.
4. Conclusions
It is generally accepted that reaction parameters such
as temperature, CO2 pressure and time have an effect
on product yield. We adopted the cobaloxime complex
(1) catalyst to investigate the effects of reaction param-
eters because of its good activity. The effect of the
reaction temperature on the cycloaddition reaction was
studied with the cobaloxime complex (1) as catalyst at
1.6 MPa CO2 pressure, 2 h, epichlorohydrin (ECH) as
substrate and C5H5N as base, and the results are shown
In conclusion, three dioxime ligands (L(1−3)H2) and
their three types of multinuclear cobaloxime complexes
(1-8) were synthesized and fully characterized by dif-
ferent spectroscopic techniques. Experimental results
indicated trimeric nature for these three types multin-
uclear cobaloxime complexes (1-8). The multinuclear
cobaloxime complexes (1-8) have been successfully
used for the synthesis of five-membered cyclic organic
in figure S6(a). It can be seen that temperature has a
carbonates from CO2 and epoxides under optimized
strong effect on the epichlorohydrin (ECH) conversion.
conditions and without using any solvent. The syn-
The reaction was carried out at different reaction tem-
thesized homogeneous catalysts are inexpensive, easily
peratures ranging from 75, 100, 125 and 150◦C. With
synthesized and stable or robust catalytic systems for
increase of temperature from 75 to 125◦C, yield of 4-
synthesizing a five-membered cyclic organic carbonates
(chloromethyl)-1,3-dioxolan-2-one (ECHC) increased
from CO2 and different epoxides. The cobaloxime com-
sharply from 31 to 96%. With increase of temperature
plex (1) catalyst and DMAP as the co-catalyst showed
good catalytic activity and selectivity for the coupling
from 125 to 150◦C, yield of ECHC decreased from 96
to 92%. A decrease in the catalytic activity, is possibly
of CO2 and epichlorohydrin (ECH). The high activity of
due to more side-products formed at the higher tem-
the cobaloxime complex (1) catalyst relative to the other
cobaloxime catalysts can be explained by the electron-
perature, such as, 1-chloroethane-1,2-diol. Thus, 125◦C
was considered to be the optimum reaction temperature.
withdrawing property of the chloro substituents as axial
The effect of CO2 pressure on the cycloaddition reac-
groups on the Co(III) center. Investigation of a range
tion was studied (figure S6(b)). The reaction was con-
of molecules as co-catalysts showed that pyridine is the
ducted at 125◦C, 2 h, C5H5N as co-catalyst, epichloro-
best co-catalyst for this system.
hydrin (ECH) as substrate and the cobaloxime complex
(1) as catalyst. As shown in figure S6(b), there is a rise
in yield of ECHC (from 94 to 96%) with increase of
CO2 pressure (from 0.5 to 1.6 MPa). Further increase
Supplementary Information
of pressure to 2.5 MPa results ied a moderate decrease
of ECHC yield (94%). In the 0.5-2.5 MPa range, ECHC
selectivity is over 95%. This can be explained quali-
tatively by the effect of pressure on the concentration
of CO2 and epoxide in the two phases in the reaction
system.27 The upper phase is the vapor phase, and bot-
tom phase is the liquid phase. The reaction took place
mainly in the liquid phase because the catalyst was
dispersed only in the liquid phase. When the pressure
was higher than 2.5 MPa, the CO2 concentration was
too high and inhibited the contact of epichlorohydrin
(ECH) with the catalyst by a dilution effect.28,29
The catalytic results and spectral data are given as
table S1 and figures S1–S6 which are available at www.
ias.ac.in/chemsci.
Acknowledgements
This work was supported by the Technological and Sci-
entific Research Council of Turkey TUBITAK (TBAG
Project No: 111T944) and the Research Fund of Har-
ran University (HUBAK Projects No: 13107, Sanliurfa,
Turkey).
As shown in figure S6(c), the effect of the reaction
time on the ECHC yield was investigated. The reac-
tion was conducted at 125◦C, 1.6 MPa CO2 pressure,
C5H5N as co-catalyst, epichlorohydrin (ECH) as sub-
strate and the cobaloxime complex (1) as catalyst. With
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