The coupling of carbon dioxide and epoxides by phenanthroline derivatives containing different Cu(II) complexes as catalyst

Article abstract of DOI:10.1016/j.saa.2013.04.124

(Chemical Equation Presented) A series of the mononuclear Cu(II) metal complexes containing the ligand Bdppz [(9a,13a-dihydro-4,5,9,14-tetraaza- benzo[b]triphenylene-11-yl)-phenyl-methanone] (L₁) and Aqphen [(12,17-dihydronaphthol[2,3-h]dipyrido[3,2-a:2′,3′-c]-phenazine-12, 17-dione)] (L₂) were synthesized and used as catalyst for the coupling of carbon dioxide (CO₂) and liquid epoxide which served as both reactant and solvent. Dimethylamino pyridine (DMAP) was used as co-catalyst. The yields of epoxides to corresponding cyclic carbonates were determined by comparing the ratio of product to substrate in the ¹H NMR spectrum of an aliquot of the reaction mixture. The mononuclear Cu(II) complexes of these ligands were synthesized by treating an ethanol solvent of the appropriate ligand with a different molar amount of CuCl₂· 2H₂O. The Cu(II) complexes were characterized by FT-IR, UV-Vis, elemental analysis, melting point analysis, mass spectra, molar conductivity measurements and magnetic susceptibility techniques. The reaction of the Bdppz and Aqphen ligands in a 1:1, 1:2 or 1:3 mole ratio with CuCl₂· 2H₂O afforded ionic Cu(II) complexes in the presence of Et ₃N.

Full text of DOI:10.1016/j.saa.2013.04.124

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 432–438
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
The coupling of carbon dioxide and epoxides by phenanthroline
derivatives containing different Cu(II) complexes as catalyst
a
a
b
a
Ahmet Kilic a, , Ahmet Arif Palali , Mustafa Durgun , Zeynep Tasci , Mahmut Ulusoy
⇑
a Department of Chemistry, University of Harran, 63190 Osmanbey Campus, Sanliurfa, Turkey
b Department of Chemistry, University of Mugla, 4800, Mugla, Turkey
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
A series of the mononuclear Cu(II) metal complexes containing the ligand Bdppz [(9a,13a-dihydro-
4,5,9,14-tetraaza-benzo[b]triphenylene-11-yl)-phenyl-methanone] (L1) and Aqphen [(12,17-dihydro-
naphthol[2,3-h]dipyrido[3,2-a:20,30-c]-phenazine-12,17-dione)] (L2) were synthesized and used as
catalyst for the coupling of carbondioxide and liquid epoxide which served as both reactant and solvent.
The Cu(II) complexes were characterized by FT-IR, UV–Vis, elemental analysis, melting point, mass spec-
tra, molar conductivity measurements and magnetic susceptibility techniques. The reaction of the Bdppz
(L1) and Aqphen (L2) ligands in a 1:1, 1:2 or 1:3 mole ratio with CuCl2ꢁ2H2O afforded ionic Cu(II) com-
plexes in the presence of Et3N. The catalytic results shown that the mononuclear complex [Cu(L2)Cl2]
(6) has the best effective activities than the other mononuclear Cu(II) complexes for the formation of cyc-
lic organic carbonates from carbon dioxide.
ꢀ
The two ligand and its mononuclear
Cu(II) complexes have been
synthesized.
The Cu(II) complexes were
synthesized for the coupling of
carbon dioxide and epoxide.
Dimethylamino pyridine (DMAP) was
used as co-catalyst.
ꢀ
ꢀ
ꢀ
A high selective conversion rate was
obtained using catalyst and
epichlorohydrine as the substrate.
O
O
O
0.1 % cat., 0.2 % DMAP
2 h, 100 oC, 1.5 MPa
O
CO2
+
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of the mononuclear Cu(II) metal complexes containing the ligand Bdppz [(9a,13a-dihydro-
4,5,9,14-tetraaza-benzo[b]triphenylene-11-yl)-phenyl-methanone] (L1) and Aqphen [(12,17-dihydro-
naphthol[2,3-h]dipyrido[3,2-a:20,30-c]-phenazine-12,17-dione)] (L2) were synthesized and used as cata-
lyst for the coupling of carbon dioxide (CO2) and liquid epoxide which served as both reactant and
solvent. Dimethylamino pyridine (DMAP) was used as co-catalyst. The yields of epoxides to correspond-
ing cyclic carbonates were determined by comparing the ratio of product to substrate in the 1H NMR
spectrum of an aliquot of the reaction mixture. The mononuclear Cu(II) complexes of these ligands were
synthesized by treating an ethanol solvent of the appropriate ligand with a different molar amount of
CuCl2ꢁ2H2O. The Cu(II) complexes were characterized by FT-IR, UV–Vis, elemental analysis, melting point
analysis, mass spectra, molar conductivity measurements and magnetic susceptibility techniques. The
reaction of the Bdppz and Aqphen ligands in a 1:1, 1:2 or 1:3 mole ratio with CuCl2ꢁ2H2O afforded ionic
Cu(II) complexes in the presence of Et3N.
Received 19 November 2012
Received in revised form 24 April 2013
Accepted 29 April 2013
Available online 16 May 2013
Keywords:
Cu(II) complexes
Spectroscopy
Mass spectra
Carbon dioxide
Cyclic carbonate
Ó 2013 Elsevier B.V. All rights reserved.
⇑
Corresponding author. Tel.: +90 4143183587; fax: +90 4143183541.
E-mail address: kilica63@harran.edu.tr (A. Kilic).
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.04.124

A. Kilic et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 432–438
433
analysis was carried out on a LECO CHNS model 932 elemental ana-
lyzer. Forcatalytic measurements, 1H NMRspectra were recorded on
a Varian AS-400 MHz instrument at room temperature for catalytic
measurements. FT-IR spectra were recorded on a Perkin Elmer Spec-
trum RXI FT-IR Spectrometer as KBr pellets in the wavenumber
range of 4000–400 cmꢂ1. Magnetic Susceptibilities were deter-
mined on a Sherwood Scientific Magnetic Susceptibility Balance
(Model MK1) at room temperature (20 °C) using Hg[Co(SCN)4] as a
calibrant; diamagnetic corrections were calculated from Pascal’s
constants [16,17]. Electronic spectral studies were conducted on a
Perkin–Elmer model Lambda 25 UV–Vis spectrophotometer in the
wavelength range from 200 to 1100 nm. Melting points were mea-
sured in open capillary tubes with an Electrothermal 9100 melting
Introduction
Nitrogen-donor ligands play crucial biological roles in the bind-
ing of essential metal ions to proteins. Their synthetic analogs,
which have an extensive general coordination chemistry (that in-
cludes different phenanthroline derivatives and ligands) in partic-
ular, have been the subject of numerous investigations on their
possible applications not only in medicinal field but also in cataly-
sis and materials science [1]. In the family of polypyridine ligands,
different phenanthroline derivatives containing ligands are of spe-
cial interest because of both its relatively easy synthesis with a
wide range of additional functionalities and its ability to form
highly stable complexes without necessarily occupying all the
coordination sites of a metal [2]. However, the investigation on
the derivatives of 1,10-phenanthroline has attracted much atten-
tion because they play important roles in synthesizing various
metal complexes and coordination polymers with luminescent
p-conjugated groups [3]. The [Cu(NAN)X2], [Cu(NAN)2X]X or
[Cu(NAN)3]X2 compounds may occur either in octahedral geome-
try, or in a tetrahedral geometry without space in inner sphere
for X ligands, and also in a five-coordinate geometry with one X
ligand in second coordination sphere. Furthermore, in dependence
of steric demand of substituents of the phenanthroline rings,
different coordination ability of the counter anions
(NOꢂ3 ; NOꢂ2 ; Clꢂ and ClOꢂ4 ) towards copper (II) has been observed
[4]. Like phenanthroline and bipyridine, phenanthroline derivates
containing ligands can also provide two nitrogen atoms to act as
bidentate chelating ligands in the reactions with transition-metal
cations exhibiting as catalysts in transformation of carbon dioxide
to cyclic carbonates.
In the current global climate, with high oil prices and increasing
concern over global warming, and consumption petroleum re-
sources, the development of renewable carbon sources is of the ut-
most importance. CO2 is a particularly an attractive alternative
feedstock as it is inexpensive, naturally abundant, and the byproduct
of many industrial processes, including combustion [5]. The reac-
tions of CO2 with metal complexes have been extensively studied,
revealing potential pathways for catalytic reactions [6–11]. A major-
ity of these publications involve the reaction of CO2 with epoxides to
generate polycarbonates and–or cyclic carbonates. Cyclic carbon-
ates are used industrially as polar aprotic solvents, substrates for
small molecule synthesis, additives, antifoam agents for antifreeze,
and plasticizers [12,13]. Due to such uses, a number of syntheses of
cyclic carbonates have been described over the last 30 years. As ob-
served in early studies, only a few metals are active for the coupling
of epoxides and CO2, including Al, Cr, Co, Mg, Li, Zn, Cu, and Cd
[6,14,15]. Studies have shown that large differences in catalytic effi-
ciency result from the organic frameworks surrounding these met-
als. Accordingly, subsequent studies have largely focused on
empirical modification of ligands to generate improved catalysts.
In this paper, we report synthesis, characterization, and
spectroscopic properties of six new mononuclear Cu(II) complexes
having Bdppz [(9a,13a-dihydro-4,5,9,14-tetraaza-benzo[b]triphen-
ylene-11-yl)-phenyl-methanone] (L1) and Aqphen (12,17-dihydro-
naphthol[2,3-h]dipyrido[3,2-a:20,30-c]-phenazine-12,17-dione) (L2)
ligands with 1:1, 1:2, and 1:3 molar ratios of metal and ligand
(Scheme 1). We also report the catalytic activity of Bdppz and Aq-
phen Cu(II) metal complexes as catalyst in transformation of car-
bon dioxide to cyclic carbonates.
point apparatus and are uncorrected. Molar conductivities (KM
)
were recorded on a Inolab Terminal 740 WTW Series. Mass Spectra
results were recorded on a Micromass Quatro LC/ULTIMA LC–MS/
MS spectrometer. Catalytic tests were performed in a PARR 4843
50 mL stainless pressure reactor. The ligands Bdppz [(9a,13a-dihy-
dro-4,5,9,14-tetraaza-benzo[b]triphenylene-11-yl)-phenyl-metha-
none] (L1) and Aqphen (12,17-dihydronaphthol[2,3-h]dipyrido[3,
2-a:20,30-c]-phenazine-12,17-dione) (L2) were synthesized follow-
ing procedures with some modifications [10,18].
Synthesis of mononuclear Cu(II) complexes
The mononuclear Cu(II) complexes were synthesized according
to the reported procedure with some modifications [19]. The
syntheses of the complexes [Cu(Ln)3]Cl2 (n = 1 or 2) were carried
out by using three equivalents of the ligands Bdppz [(9a,13a-dihy-
dro-4,5,9,14-tetraaza-benzo[b]triphenylene-11-yl)-phenyl-metha-
none] (L1) or Aqphen [(12,17-dihydronaphthol[2,3-h]dipyrido[3,
2-a:20,30-c]-phenazine-12,17-dione)] (L2) in 70 mL of absolute
ethanol to one equivalent of CuCl2ꢁ2H2O in 20 mL of absolute
ethanol–water. In a glass flask, the ligand solution was added drop-
wise to the metal salt solution under Ar atmosphere with continu-
ous stirring and to this mixture was added a few drops of Et3N
while stirring. The stirred mixture was then heated to the reflux
temperature for 4 h. The mixture then was allowed to cool down
to room temperature and was stirred for 1 h additionally at room
temperature. After 30 min a precipitate was formed. The solvent
was evaporated slowly at room temperature and Cu(II) complexes
were collected, then washed with cold ethanol–water and dried in
air. The Cu(II) complexes [Cu(Ln)2Cl]Cl (n = 1 or 2) and [Cu(Ln)Cl2]
(n = 1 or 2) were synthesized as described above for [Cu(Ln)3]Cl2
(n = 1 or 2), with ligands:salt ratio of 2:1 and 1:1, respectively.
For [Cu(L1)3]Cl2 (1) Color: Green; m.p: 205 °C; Yield (%): 58;
Anal. Calc. for [C75H42N12O3Cl2Cu] (F.W: 1293.7 g/mol): C, 69.63;
H, 3.27; N, 12.99. Found: C, 70.04; H, 3.15; N, 12.86%. KM = 219 -
X
ꢂ1 cm2 molꢂ1 max/cmꢂ1):
, leff = 1.75 [B.M]. FT-IR (KBr pellets, t
3058
1447
t
(ArACH), 1661
t
(C@O), 1594 and 1578
t
(C@N), 1493–
ꢃ
t(C@C), 715 (CuACl), 488
t
t
(CuAN). UV–Vis (kmax, nm,
-
= shoulder peak): 284, 366, 385, 532ꢃ and 728 (in C2H5OH); 286,
369, 388, and 735ꢃ (in CHCl3). MS (LSI, Scan ES+): m/z (%) 1294
(16) [M]+, 1097 (82), 1054 (100), 779 (26), 716 (53), 422 (18) and
141 (20).
For [Cu(L1)2Cl]Cl (2) Color: Green; m.p: >300 °C; Yield (%): 61;
Anal. Calc. for [C50H28N8O2Cl2Cu] (F.W: 907.3 g/mol): C, 66.19; H,
3.11; N, 12.35. Found: C, 66.11; H, 3.08; N, 12.29%. KM = 74 Xꢂ1
-
cm2 molꢂ1
,
l
eff = 1.81 [B.M]. FT-IR (KBr pellets,
(ArACH), 1662 (C@O), 1595 and 1578 (C@N), 1494–1446
(C@C), 716 (CuACl), 487
(CuAN). UV–Vis (kmax, nm, ꢃ = shoul-
t
max/cmꢂ1): 3060
t
t
t
t
Experimental
t
t
der peak): 290, 354ꢃ, 365, 384 (in C2H5OH); 288, 351ꢃ, 368 and
386 (in CHCl3). MS (LSI, Scan ES+): m/z (%) 872 (82) [MꢂCl+1]+,
870 (100), 835 (28), 484 (84), 372 (26) and 105 (63).
Materials and measurements
All reagents and solvents were of reagent-grade quality and ob-
tained from commercial suppliers (Aldrich or Merch). Elemental
For [Cu(L1)Cl2] (3) Color: Dark green; m.p: >300 °C; Yield (%):
63; Anal. Calc. for [C25H14N4OCl2Cu] (F.W: 520.8 g/mol): C, 57.65;

434
A. Kilic et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 432–438
Scheme 1. The structure of the proposed ligands and their Cu(II) complexes.
H, 2.71; N, 10.76. Found: C, 57.58; H, 2.78; N, 10.73 KM = 29 Xꢂ1
cm2 molꢂ1 max/cmꢂ1): 3059
eff = 1.74 [B.M]. FT-IR (KBr pellets,
(ArACH), 1660 (C@O), 1594 and 1584 (C@N), 1496–1446
(C@C), 716 (CuACl), 482
(CuAN). UV–Vis (kmax, nm, ꢃ = shoul-
-
353ꢃ, 368 and 387 (in CHCl3). MS (LSI, Scan ES+): m/z (%) 924 (16)
[MꢂCl+1]+, 872 (23), 835 (28), 387 (100), 263 (14) and 104 (16).
For [Cu(L2)Cl2] (6) Color: Dark brown; m.p: >300 °C; Yield (%):
63; Anal. Calc. for [C26H12N4O2Cl2Cu] (F.W: 546.8 g/mol): C,
57.11; H, 2.21; N, 10.25. Found: C, 57.17; H, 2.18; N, 10.19
,
l
t
t
t
t
t
t
t
der peak): 239ꢃ, 281, 382, 422 (in C2H5OH); 287, 334ꢃ, 366, 385
and 431 (in CHCl3). MS (LSI, Scan ES+): m/z (%) 519 (10) [Mꢂ1]+,
484 (100), 453 (18), 237 (16), 228 (45) and 148 (19).
KM = 32
cmꢂ1): 3067
1495–1467
X
ꢂ1 cm2 molꢂ1
(ArACH), 1671
(C@C), 720 (CuACl), 478
, leff = 1.85 [B.M]. FT-IR (KBr pellets, tmax/
t
t(C@O), 1588 and 1537
t
(C@N),
For [Cu(L2)3]Cl2ꢁH2O (4) Color: Dark-Red; m.p: >300 °C; Yield
(%): 66; Anal. Calc. for [C78H38N12O7Cl2Cu] (F.W: 1389.7 g/mol):
C, 67.42; H, 2.76; N, 12.01. Found: C, 67.34; H, 2.68; N, 12.06%.
t
t
t(CuAN). UV–Vis (Kmax,
nm, ꢃ = shoulder peak): 243, 275, 474ꢃ (in C2H5OH); 248, 287,
334, 366, 385 and 429ꢃ (in CHCl3). MS (LSI, Scan ES+): m/z (%)
547 (8) [M+1]+, 418 (16), 387 (100), 263 (14) and 104 (12).
KM = 213
cmꢂ1): 3383–3258
and 1537 (C@N), 1495–1478
X
ꢂ1 cm2 molꢂ1
(H2O), 3067
t
,
l
eff = 1.80 [B.M]. FT-IR (KBr pellets, tmax
(ArACH), 1671 (C@O), 1588
(C@C), 719 (CuACl), 476
/
t
t
t
t
t
General procedure for the cycloaddition of epoxides to CO2
t
(CuAN). UV–Vis (kmax, nm, ꢃ = shoulder peak): 245ꢃ, 269, 398
and 542ꢃ (in C2H5OH); 260, 281, 398 and 503ꢃ (in CHCl3). MS
(LSI, Scan ES+): m/z (%) 1387 (8) [M]+, 1097 (82), 707 (20), 330
(23), 270 (35), 187 (33) and 135 (100).
A 50 mL stainless pressure reactor was charged with Cu(II)
(1.125 ꢄ 10ꢂ5 mol), epoxide (1.125 ꢄ 10ꢂ2 mol), and DMAP
(2.25 ꢄ 10ꢂ5 mol). The reaction vessel was placed under a constant
pressure of carbon dioxide for 2 min to allow the system to equil-
ibrate and CO2 was charged into the autoclave with desired pres-
sure then heated to the desired temperature. The pressure was
kept constant during the reaction. The vessel was then cooled to
5–10 °C in an ice bath after the expiration of the desired time of
reaction. The pressure was released, then, the excess gases were
vented. The yields of epoxides to corresponding cyclic carbonates
For [Cu(L2)2Cl]Cl (5) Color: Dark brown; m.p: >300 °C; Yield
(%): 63; Anal. Calc. for [C52H24N8O4Cl2Cu] (F.W: 959.3 g/mol): C,
65.11; H, 2.52; N, 11.68. Found: C, 65.08; H, 2.46; N, 11.54%.
KM = 72
cmꢂ1): 3064
1495–1441
X
ꢂ1 cm2 molꢂ1
(ArACH), 1670
(C@C), 719 (CuACl) and 465
, leff = 1.79 [B.M]. FT-IR (KBr pellets, tmax/
t
t(C@O), 1587 and 1538
t(C@N),
t
t
t
(CuAN). UV–Vis (kmax,
nm, ꢃ = shoulder peak): 246, 268, 387ꢃ and 537ꢃ (in C2H5OH); 287,

A. Kilic et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 432–438
435
were determined by comparing the ratio of product to substrate in
the 1H NMR spectrum of an aliquot of the reaction mixture.
upon chelation. Coordination of the hindered ligands (L1) and
(L2) to the Cu(II) metal through the nitrogen atom is expected to
reduce the electron density in the azomethine link and lower the
t
(C@N) absorption frequency. The very strong and sharp bands lo-
cated at 1595–1578 and 1588–1537 cmꢂ1 are assigned to the
(C@N) stretching vibrations of the azomethine of the mononu-
Results and discussion
t
Synthesis and spectral properties
clear Cu(II) complexes. These FT-IR spectra are located different
wavenumber for free ligands. So, these shifts to different wave-
numbers suggest the participation of the azomethine group of
these ligands in binding to the Cu(II) ion [24]. A strong peak ob-
served at range 1671–1660 cmꢂ1 in the mononuclear Cu(II) com-
The ligands (L1) and (L2) were prepared in moderate yields by
refluxing the 1,10-phenantroline-5,6-dione with 3,4-diaminoben-
zophenone or 1,2-diamino antraquinone (one equivalent ratio) in
absolute ethanol (Scheme 1), following procedures with some mod-
ifications [10,18]. The mononuclear Cu(II) complexes (Scheme 1)
were synthesized by treating CuCl2ꢁ2H2O with one, two or three
equivalents of the corresponding ligands in absolute ethanol–water
at reflux temperature. To confirm the identity of the pre-catalysts
prepared in the present work, a variety of techniques including
FT-IR, UV–Vis, elemental analysis, melting point, mass spectra,
molar conductivity measurements and magnetic susceptibility
techniques determination for the [Cu(Ln)3]Cl2, [Cu(Ln)2Cl]Cl or
[Cu(Ln)Cl2] (in here n = 1 or 2) complexes have been utilized. The
metal to ligand ratios in the mononuclear Cu(II) complexes were
found to be 1:1, 1:2 or 1:3 (Scheme 1). It is reported, for complexes
number (1) and (4), that copper is hexacoordinated and has an octa-
hedral arrangement with six CuAN bonds. In addition to the copper
coordinated cation, there are two chloride ions [20,21]. In (2) and
(5), copper is pentacoordinated and presents trigonal bipyramidal
geometry [20,22], while in complexes (3) and (6) copper is probably
tetracoordinated with a ligand (L1 or L2), and two chlorines in a
plane [20,23]. The mononuclear Cu(II) complexes are paramagnetic,
thus their NMR spectra could not be obtained. The other results are
presented in the ‘Experimental’ section.
plexes has been assigned to
t(C@O) stretching vibrations. The
coordination mode of the ligands (L1) and (L2) are further sup-
ported by new frequencies occurring in the range 488–465 cmꢂ1
due to
t
(Cu N) stretching vibrations that are not observed in
the infrared spectra of the ligands[25,26]. Also, the coordination
mode of the ligands (L1) and (L2) are further supported by new fre-
quencies occurring in the range 720–715 cmꢂ1 due to
t(CuACl)
stretching vibrations that are not observed in the infrared spectra
of the ligands. These remain almost unchanged in the spectra of
complexes, indicating that chlorines in a plane and absence in
coordination. These values are in good agreement with those for
mononuclear Cu(II) complexes (1–6).
Electronic spectra of mononuclear Cu(II) complexes (1–6) have
been recorded in the 200–1100 nm range in C2H5OH and CHCl3 sol-
vents and their corresponding data are given in experimental part.
The electronic spectra of mononuclear Cu(II) complexes (1–6)
recorded in C2H5OH and CHCl3 solutions showed an intense energy
charge-transfer absorption band in the UV–Vis region (in ‘Experi-
mental’ section). The position of this band was strongly influenced
by the structure of the compounds, such as by the length of the
p-conjugated bridge, by the electronic nature of the ligands, and
The IR spectra of the mononuclear Cu(II) complexes (1–6) were
carried out in the range 4000–400 cmꢂ1. The FT-IR spectra of the
Cu(II) complexes (1–6) are compared with those of the free ligands
in order to determine the coordination sites that may be involved
in chelation. There are some guide peaks in the spectra of the
ligands, which are of good help for achieving this goal. The position
and/or the intensities of these peaks are expected to be changed
also by the number of the phenanthroline moieties substituted
on the conjugated system of ligand [27]. The reflectance UV–Vis
spectra of the complexes (1–6) contain bands in the 239–474 nm
region which are attributable to ligand-to-Cu(II) metal CT transi-
tion and the electronic transitions of the organic ligands, as
expected from the higher aromaticity of the ligands which eases
delocalization of electron density. However, the absorption shift
Table 1
Synthesis of styrene carbonate from styrene oxide and CO2 catalyzed by Cu(II) complexes (1–6).
DMAP
MPa
Entries
Catalysts
Yielda
TONb
TOFc (hꢂ1
)
1.
2.
3.
4.
5.
6.
7.
8.
9.
[Cu(L1)3]Cl2 (1)
[Cu(L1)2Cl]Cl (2)
[Cu(L1)Cl2] (3)
[Cu(L2)3]Cl2 (4)
[Cu(L2)2Cl]Cl (5)
[Cu(L2)Cl2] (6)
–
64
53
32
72
39
75
5d
640
530
320
720
390
750
50
320
265
160
360
195
375
25
[Cu(L2)Cl2] (6)
[Cu(L2)3]Cl2 (4)
16e
14e
160
140
80
70
Catalyst (1.125 ꢄ l0ꢂ5 mol), DMAP (2.25 ꢄ l0ꢂ5 mol), epoxide (1.125 ꢄ l0ꢂ2 mol), CO2 (1.5 MPa), 2 h.
a
Yield of epoxides to corresponding cyclic carbonates was determined by comparing the ratio of product to substrate in the 1H NMR spectrum of an aliquot of the reaction
mixture.
b
c
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)ꢂ1) = turnovers/h.
Only DMAP used as catalyst.
d
e
Only catalyst used (without DMAP).

436
A. Kilic et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 432–438
Table 2
solubility. They provide a method of testing the degree of ioniza-
tion of the complexes, the more molecular ions that a complex lib-
erates in solution (in case of presence of anions outside the
coordination sphere), the higher will be its molar conductivity
and vice versa. The molar conductivity values indicate that the an-
ions may be present outside the coordination sphere or inside or
absent [31]. With a view to studying the electrolytic nature of
the mononuclear Cu(II) complexes, their molar conductivities were
measured in DMF (10ꢂ3 M). The molar conductivity (KM) values of
the mononuclear Cu(II) complexes (3) and (6) are in the range of
Coupling of CO2 and various epoxides catalyzed by complex [Cu(L2)Cl2] (6).
Entries
1.
Product
Yield (%)
75
TON
750
TOF (hꢂ1
375
)
O
O
O
O
29–32
X
ꢂ1 cm2 molꢂ1 at room temperature [32,33], indicating
2.
35
350
175
O
their almost non-electrolytic nature. The results indicate that these
Cu(II) complexes are poor in molar conductivity due to the non-
free ions in Cu(II) complexes (3) and (6). The molar conductivities
O
(
KM) values of these Cu(II) complexes (2) and (5) are in the range of
72–74
ꢂ1 cm2 molꢂ1 at room temperature, indicating 1:1 electro-
lytes or presence of two ionic species in solution, whereas the com-
plexes (1) and (4) are in the range of 213–219
ꢂ1 cm2 molꢂ1 at
room temperature, indicating 1:2 electrolytes or existence of three
ionic species in solution [34,35].
CH
Cl
3
X
3.
4.
95
52
950
520
475
260
O
O
X
O
O
O
The results of mass spectra of the mononuclear Cu(II) com-
plexes are taken as evidence for the formation of the proposed
structures. The values of molecular weights by mass spectrometer
are presented in the ‘Experimental’ section. The spectrums show
the molecular ion peak at m/z = 1294 [M]+ for (1), 872 [MꢂCl+1]+
for (2), 519 [Mꢂ1]+ for (3), 1387 [M]+ for (4), 924 [MꢂCl+1]+ for
(5), and 547 [M+1]+ for (6) which are consistent with the suggested
structure as well as the theoretical molecular weight. The spectra
show some prominent peaks corresponding to the various frag-
ments of the Cu(II) complexes. The appearance of many peaks is
due to the presence of isotopic atoms in the compounds. However,
the mass spectrum of the complexes (2) and (5) does not display a
peak refers to molecular ion peak. This may reflecting the sudden
fragmentation during the evaporation process. We think a cleavage
happened to an organic part surrounds the Cu(II) metal ion.
O
CH
3
Reaction conditions: [Cu(L2)Cl2] (6) (1.125 ꢄ l0ꢂ5 mol), DMAP (2.25 ꢄ l0ꢂ5 mol),
epoxide (1.125 ꢄ l0ꢂ2 mol), CO2 (1.5 MPa), 100 °C, 2 h.
and intensity change in the spectra of the mononuclear Cu(II)
complexes most likely originated from the metallation, increased
the conjugation and delocalization of the whole electronic system
and resulted in the energy change of the
p ?
pꢃ and n ? pꢃ
transitions of the conjugated chromophore [28,29]. The new broad
bands of the lowest energies and in lower intensities at between
503 and 735 are assignable to d–d transitions (dxy ? dx2–y2 or
dz2 ? dx2–y2), seems to be little influenced by the different substi-
tutions on the ligands, suggesting that the coordination geometry
at the metal ion could be probably a distorted octahedron for com-
plexes (1) and (4) and five-coordinate geometry for complex (5) in
C2H5OH or CHCl3 solvents. These modifications in shifts and inten-
sity for the absorption bands support that coordination of the li-
gands to the central Cu(II) ion occurred. Whereas, these
absorption band (d–d transitions) could not be observed in the
UV–Vis spectra for complexes (2), (3) and (6), due to forbidden
transition rules. The energy of the band assigned to d–d transitions
provides a rough estimate of the ligand field strength, since one of
the electronic transitions comprised in the band envelope is
dx2–y2 ? dxy and the energy associated with this transition is
10Dq-C [30].
Catalytic properties
The coupling of carbon dioxide and epoxides catalyzed by
mononuclear Cu(II) complexes (Scheme 1) was investigated under
different reaction conditions. The results were shown in Tables 1
and 2. Lewis base and Lewis acid work together to open the epoxy
ring and then CO2 react with this intermediate to give the corre-
sponding cyclic carbonate via a recyclization step. In our previous
study [10], [Ru(L1)3](PF6)2 complex has been synthesized and used
as catalyst at the identical conditions (1.6 MPa, 2 h, 0.02 mol%
DMAP, 0.01 mol% cat, 100 °C). When compared [Cu(L1)3]Cl2 and
[Ru(L1)3](PF6)2 complexes, the yield of SC were almostly the same,
yields were 64 and 62.7 respectively.
It should be noted that all of the mononuclear Cu(II) complexes
are air-stable and robust. The yields of epoxides to corresponding
cyclic carbonates were determined by comparing the ratio of prod-
uct to substrate in the 1H NMR spectrum of an aliquot of the reac-
tion mixture. It can be seen that the catalyst of [Cu(L2)Cl2] (6) have
better effective than the other mononuclear Cu(II) complexes in
the formation of cyclic organic carbonates from carbon dioxide
(Fig. 1). A very high selective conversion rate was obtained using
this catalyst [Cu(L2)Cl2] (6) and epichlorohydrine as the substrate.
In general, differences in the ligand substitution pattern in the phe-
nanthroline derivatives containing mononuclear Cu(II) complexes
do not have a great effect on the catalytic activity. This suggests
that the overall coordination sphere in these phenanthroline deriv-
atives containing catalyst precursors is favorable for the efficient
coupling reaction and the nature and size of ligand substituents
in the series have a minor influence on the course of the reaction
[36].
Magnetic susceptibility measurements provide sufficient data
to characterize the structure of the metal complexes. Magnetic mo-
ments measurements of compounds were carried out at room tem-
perature. The room temperature effective magnetic moments (leff
)
of all the complexes were measured on samples after necessary
diamagnetic corrections were done using Pascal’s table. The ob-
served effective magnetic moments: 1.75
1.74 B (3), 1.80 B (4), 1.79 B (5) and 1.85
to the expected spin-only value (1.73 B) for one unpaired electron
lB (1), 1.81
lB (2),
l
l
l
lB (6) are comparable
l
and confirm the formal +2 oxidation state of the copper centers. It
is obvious that the mononuclear Cu(II) complexes do not possess
anti-ferromagnetic properties at room temperature [9,30].
The conductivity measurements have frequently been used in
structural elucidation of metal chelates within the limits of their

A. Kilic et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 432–438
437
Fig. 1. Conversion of styrene oxide as a function of (a) time, (b) pressure and (c) temperature with [Cu(L2)Cl2] (6) as catalyst.
The catalysts [Cu(L2)3]Cl2 (4) and [Cu(L2)Cl2] (6) show low activ-
ity without additive (DMAP). The catalytic run blank without Cu(II)
catalyst to ascertain the activity of DMAP alone under the given
conditions was done and found to be 5% SC conversion. Similarly,
when metal catalysts [Cu(L2)3]Cl2 (4) and [Cu(L2)Cl2] (6) used
alone, SC conversion were 14% and 16% respectively (Table 1). As
a conclusion, it can be said that both a metal catalyst and a co-cat-
alyst must be used together. Similar results have been reported
elsewhere [37–40].
The CO2 pressure has also an important effect on the yield of SC.
Between 0.5 and 2.5 MPa CO2 pressure, SC yield was proportional
to the pressure. In the higher pressures than 2.5 MPa, it was found
that there was an inverse proportion between pressure and SC
yield (Fig. 1b). The effect of temperature has also been investigated.
While the reaction did not occur at 50 °C, the SC yield has increased
suddenly at the region of 75–125 °C. However, at higher tempera-
tures than 125 °C, SC yield has decreased rapidly (Fig. 1c).
It can be seen from Table 2 that the electron withdrawing
groups at the 2-position of the epoxide activate the substrate,
while electron donating substituents deactivated the epoxide.
Epichlorohydrine was found to be the most reactive epoxide, while
1,2-epoxy butane exhibited the lowest activity of the epoxides
surveyed. The reaction time was shown to have an influence on
the catalytic activity of transformation of SO to its related cyclic
carbonate using [Cu(L2)Cl2] (6) as catalyst. The influence of time
on the yield of styrene carbonate (SC) was investigated at CO2
pressures of 1.5 MPa and 100 °C. The yield increased with increas-
ing the catalytic reaction time (Fig. 1a).
Conclusion
A series of the mononuclear Cu(II) metal complexes containing
the ligand Bdppz [(9a,13a-dihydro-4,5,9,14-tetraaza-benzo[b]
triphenylene-11-yl)-phenyl-methanone] (L1) and Aqphen [(12,17-
dihydronaphthol[2,3-h]dipyrido[3,2-a:20,30-c]-phenazine-12,17-
dione)] (L2) as catalyst were synthesized for the coupling of
carbon dioxide and liquid epoxide which served as both reactant
and solvent. Besides the classical methods such as FT-IR, UV–Vis,
elemental analysis, melting point, mass spectra, and molar con-
ductivity measurements for structural determination in addition

438
A. Kilic et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 113 (2013) 432–438
[12] G. Shaikh, Chem. Rev. 96 (1996) 951–976.
[13] J.H. Clements, Ind. Eng. Chem. Res. 42 (2003) 663–676.
[14] S. Inoue, ChemTech 6 (1976) 588–594.
[15] W. Kuran, Prog. Polym. Sci. 23 (1998) 919–992.
[16] A. Earnshaw, Introduction to Magnetochemistry, Academic Press, London,
1968. pp. 4.
[17] I. Yilmaz, S. Ilhan, H. Temel, A. Kilic, J. Incl. Phenom. Macrocycl. Chem. 63
(2009) 163–169.
[18] R. Lopez, B. Loeb, T. Boussie, T.J. Meyer, Tetrahedron Lett. 37 (1996) 5437–
5440.
[19] F.P. Canhota, G.C. Salomao, N.M.F. Carvalho, O.A.C. Antunes, Catal. Commun. 9
(2008) 182–185.
to magnetic susceptibility techniques were also employed for
structural characterization. The results agree with the expected
structure. The reaction of the Bdppz (L1) and Aqphen(L2) ligands
in a 1:1, 1:2 or 1:3 mole ratio with CuCl2ꢁ2H2O afforded ionic
Cu(II) complexes in the presence of Et3N. The catalytic results
shown that the mononuclear complex [Cu(L2)Cl2] (6) has better
effective activities than the other mononuclear Cu(II) complexes
in the formation of cyclic organic carbonates from carbon
dioxide.
[20] C. Detoni, N.M.F. Carvalho, Rodrigo O.M.A. de Souza, Donato A.G. Aranda, O.A.C.
Antunes, Catal. Lett. 129 (2009) 79–84.
[21] F.F. Jian, J.H. Lin, S.S. Zhang, Chin. J. Chem. 19 (2001) 772–777.
[22] G. Murphy, C. O’Sullivan, B. Murphy, B. Hathaway, Inorg. Chem. 37 (1998)
240–248.
[23] G.H. Faye, Can. J. Chem. 44 (1966) 2165–2171.
[24] N. Gokhale, S. Padhye, D. Rathbone, D. Billington, P. Lowe, C. Schwalbe, C.
Newton, Inorg. Chem. Commun. 4 (2001) 26–29.
[25] S. Shit, J. Chakraborty, B. Samanta, A.M.Z. Slawin, V. Gramlich, S. Mitra, Struct.
Chem. 20 (2009) 633–642.
Acknowledgements
This research was supported by the Technological and Scientific
Research Council of Turkey TUBITAK (TBAG Project No:111T944 and
110T655) and the Research Fund of Harran University (HUBAK
Projects No: 1042, Sanliurfa, Turkey). We would like to thank Prof.
Dr. H. KANTEKIN from the Karadeniz Technical University
Trabzon/Turkey for recording the mass spectra.
[26] M. Ulusoy, O. Sahin, A. Kilic, O. Buyukgungor, Catal. Lett. 141 (2011) 717–725.
[27] R.M.F. Batista, S.P.G. Costa, M. Belsley, C. Lodeiro, M. Manuela, M. Raposo,
Tetrahedron 64 (2008) 9230–9238.
[28] Z. Chen, Y. Wu, D. Gu, F. Gan, Spectrochim. Acta A 68 (2007) 918–926.
[29] A.Z. El-Sonbati, M.A. Diab, A.A. El-Bindary, M.I. Abou-Dobara, H.A. Seyam,
Spectrochim. Acta A 104 (2013) 213–221.
[30] G. Maki, J. Chem. Phys. 28 (1958) 651–662.
[31] M.S. Refat, J. Mol. Struct. 742 (2007) 24–37.
References
[1] S. Brooker, J.A. Kitchen, J. Chem. Soc. Dalton (2009) 7331–7340.
[2] M. Walesa-Chorab, A.R. Stefankiewicz, A. Gorczynski, Polyhedron 30 (2011)
233–240.
[3] F. Xu, B. Hu, T. Tao, W. Huang, Struct. Chem. 22 (2011) 123–133.
[4] B. Machura, J.G. Malecki, A. Switlicka, I. Nawrot, R. Kruszynski, Polyhedron 30
(2011) 864–872.
[5] M.R. Kember, A.J.P. White, C.K. Williams, Inorg. Chem. 48 (2009) 9535–9542.
[6] G.W. Coates, D.R. Moore, Angew. Chem. Int. Ed. 43 (2004) 6618–6639.
[7] D.J. Darensbourg, M. Ulusoy, O. Karronnirun, R.R. Poland, J.H. Reibenspies, B.
Cetinkaya, Macromolecules 42 (2009) 6992–6998.
[32] R.L. Dutta, Inorganic Chemistry Part II, second ed., The New Book Stall,
Calcutta, 1981. p. 386.
[33] A. Kilic, E. Tas, I. Yilmaz, J. Chem. Sci. 121 (1) (2009) 43–56.
[34] S. Ilhan, H. Temel, I. Yilmaz, A. Kilic, Trans. Metal. Chem. 32 (2007) 344–349.
[35] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81–122.
[36] A. Sibaouih, P. Ryan, K.V. Axenov, M.R. Sundberg, M. Leskel, T. Repo, J. Mol.
Catal. A: Chem. 312 (2009) 87–91.
[37] A. Sibaouih, P. Ryan, M. Leskel, B. Rieger, T. Repo, Appl. Catal. A 365 (2009)
194–198.
[38] K. Mori, Y. Mitani, T. Hara, T. Mizugaki, K. Ebitani, K. Kaneda, Chem. Commun.
(2005) 3331–3333.
[8] D.H. Gibson, Chem. Rev. 96 (1996) 2063–2095.
[9] A. Kilic, M. Durgun, M. Ulusoy, E. Tas, J. Chem. Res. 11 (2011) 622–626.
[10] A. Kilic, M. Ulusoy, M. Durgun, Z. Tasci, I. Yilmaz, B. Cetinkaya, E. Tas, Appl.
Organomet. Chem. 24 (2010) 446–453.
[11] M. Ulusoy, A. Kilic, M. Durgun, Z. Tasci, B. Cetinkaya, J. Organomet. Chem. 696
(2011) 1372–1379.
[39] F. Li, C. Xia, L. Xu, W. Sun, G. Chen, Chem. Commun. (2003) 2042–2043.
[40] R.L. Paddock, S.T. Nguyen, J. Am. Chem. Soc. 123 (2001) 11498–11499.