Synthesis and characterization of four new complexes of Cu(I), Cu(II), Ir(III) and Pd(II) formed by CS2 insertion in L2MXn (L = PPh3 and imidazole, X = Cl, n = 2,3)

Article abstract of DOI:10.14233/ajchem.2018.21449

Four new complexes [L2Cu(S2COC2H5)] {L=PPh3 (A), C3H4N2 (B)}, [L2IrCl2(S2COC2H5)] (L=PPh3) (C) and [L2Pd(S2COC2H5)] (L=PPh3) (D) have been synthesized by the insertion of CS2 in L2CuCl2, L3IrCl3 and L2PdCl2, respectively in mixed solvent of dichloromethane and ethanol at room temperature. The complexes have been characterized by FTIR, UV-visible and ESR spectroscopy. All the complexes have been found to be air-stable. Complexes (A), (B) and (D) are distorted square planar while complex (C) is of distorted octahedral geometry.

Full text of DOI:10.14233/ajchem.2018.21449

Asian Journal of Chemistry; Vol. 30, No. 10 (2018), 2285-2288
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2018.21449
Synthesis and Characterization of Four New Complexes of Cu(I), Cu(II), Ir(III) and Pd(II)
Formed by CS2 Insertion in L2MXn (L = PPh3 and Imidazole, X = Cl, n = 2,3)
*
SAMIM SULTANA and PRADIP K. GOGOI
Department of Chemistry, Dibrugarh University, Dibrugarh-786 004, India
*Corresponding author: E-mail: dr.pradip54@gmail.com
Received: 17 May 2018;
Accepted: 14 June 2018;
Published online: 31 August 2018;
AJC-19059
Four new complexes [L2Cu(S2COC2H5)] {L=PPh3 (A), C3H4N2 (B)}, [L2IrCl2(S2COC2H5)] (L=PPh3) (C) and [L2Pd(S2COC2H5)] (L=PPh3)
(D) have been synthesized by the insertion of CS2 in L2CuCl2, L3IrCl3 and L2PdCl2, respectively in mixed solvent of dichloromethane and
ethanol at room temperature. The complexes have been characterized by FTIR, UV-visible and ESR spectroscopy. All the complexes have
been found to be air-stable. Complexes (A), (B) and (D) are distorted square planar while complex (C) is of distorted octahedral geometry.
Keywords: Metal complexes, Cu(I,II), Ir(III), Pd(II), Imidazole, Triphenylphosphine.
1
2
2
as η -end on, η -bridging and η -side on coordination modes
(Fig. 1), which can be distinguished from FTIR spectra and
therefore has versatile coordination chemistry which provides
an attractive entry into the chemistry of sulphur containing
coordinated ligands. Some examples of CS2 insertion reaction
INTRODUCTION
Carbon disulphide, a versatile ligand with the potential to
form complexes with most of the transition metals have the
ability to insert into a variety of M-X bonds (X = H, C, N, P, S,
Cl or O), of which its insertion into M-O bonds of alkoxides is
specific leading to the formation of metal O-alkyl thiocarbo-
nates or dithiocarbonates [1]. Insertion of carbon disulphide
into M-H and M-P bonds leading to the formation of dithioformate
and phosphoniodithiocarboxylate ligands is common [2]. The
complexation of transition metals with σ-donors like phosp-
hines, arsine and stibines having empty d-orbitals of proper
symmetry is also known [3]. Moreover, in recent years, research
in the area of carbon rich ligands with appreciable π-electron
density are gaining more attention because of their good opto-
electronic property which take an active part in tuning the elect-
ronic properties and stabilizing the complexes. The antioxidant
and biological activities of transition metal compounds with
dithio-ligands are also known, which can be synthesized by
insertion of CS2 into transition metal centers containing carbonyls,
arsine, phosphine and cyclopentadienyls. CS2, being an unsatu-
rated electrophile and an abundant source of C1 chemistry, is
a useful reagent for insertion into transition metal complexes
in presence of other donor ligands producing new and exciting
derivatives. It can bond to metal centres in various modes such
3
yielding η -S2CR ligand systems also exist. The insertion of
CS2 generally takes place to a metal in a low valency state [3,4].
S
S
S
M
M C SR
M S C R
C R
S
η1-end on
η2-bridging
η2-side on
Fig. 1. Various bonding modes of CS2 to metal centre
Triphenylphosphine (PPh3) receives wide attention as a
ligand due to its good σ-donating and π-accepting nature. It
can also bind strongly to transition metals with low oxidation
state and can stabilize organometallic and hydride derivative
of the elements [5]. Moreover, imidazole derivatives play signi-
ficant role in medicinal chemistry such as antifungal, anti-
bacterial, anti-inflammatory, analgesic, antitubercular, anti-
depressant, anticancer, antiviral and antileishmanial activities
[6]. It can function as both an acid and as a base and hence is
amphoteric. Many studies on insertion of CS2 have been reported
so far using various transition metals complexes such as Ru
This is an open access journal, and articles are distributed under the terms of the Creative CommonsAttribution-NonCommercial 4.0 International
(CC BY-NC 4.0) License, which allows others to copy and redistribute the material in any medium or format, remix, transform, and build upon
the material, as long as appropriate credit is given and the new creations are licensed under the identical terms.

2286 Sultana et al.
Asian J. Chem.
[4,7], Cu [5], Mn, Re [8], Ni [9], Pt, Pd [10], Rh, Ir [10-12],
Au [13], U [14], etc.All these transition metals are remarkable
in the sense that they display several oxidation states.
Herein, we reported the synthesis and characterization of
four new complexes formed by insertion of CS2 into CuL2Cl2
(L = PPh3 and imidazole), IrL3Cl3 and PdL2Cl2 (L = PPh3) in mixed
solvent of dichloromethane and ethanol at room temperature.
air at room temperature for slow evaporation to reduce its volume
to 10-15 mL. Brownish green precipitate of [(C3H4N2)2Cu(S2
COC2H5)] wasformedwhichwasfilteredoff, washedwithamixture
of C2H5OH:H2O (2:1), recrystallized from CH2Cl2:C2H5OH (1:1)
and then dried.The compound is air-stable, soluble in dimethyl
sulphoxide but sparingly soluble in dichloromethane.Yield: 76.92
%; Elemental analysis (%) calcd. for [(C3H4N2)2Cu (S2COC2H5)]:
C, 33.6899; H, 4.0841; N, 17.4617; S, 19.966; Cu, 19.7908.
Found: C, 33.5991; H, 4.0798; N, 17.5121; S, 20.11; Cu, 19.8101.
IR (KBr, νmax, cm-1): 1499, 1424, 1067 (C-S), 1172, 1258 (C-O),
441 (Cu-N), 310, 326 (Cu-S).
Synthesis of [(PPh3)2IrCl2(S2COC2H5)] (C):The digested
IrCl3·3H2O (0.571 g, 1.91 mmol) was dissolved in CH2Cl2,
ethanol and DMSO (3:1:1) to which triphenylphosphine (1.503
g, 5.73 mmol) dissolved in 30 mL dichloromethane was added
dropwise with constant stirring.After stirring about 2 h, brown
precipitate of (PPh3)3IrCl3 was observed. It was filtered off,
washed with ethanol, recrystallized with CH2Cl2:CHCl3 (1:1)
and then dried. The (PPh3)3IrCl3 (2 g, 1.84 mmol) was added
to a mixture of CH2Cl2 and ethanol (2:1) followed by the drop-
wise addition of 1 mL of CS2. The resulting mixture was stirred
for more than 2 days at room temperature and then exposed to
air for slow evaporation at room temperature to reduce the
volume upto 10-15 mL. Brown precipitate of [(PPh3)2IrCl2(S2
COC2H5)] was formed which was filtered off, washed with a
mixtureofC2H5OH:H2O(2:1), recrystallizedfromCH2Cl2:C2H5OH
(1:1) and then dried.The compound is air-stable and soluble
in dimethyl sulphoxide.Yield: 56.64 %. Elemental analysis (%)
calcd. for [(PPh3)2IrCl2(S2COC2H5)]: C, 51.5364; H, 3.8816;
S, 7.05; Ir, 21.1482. Found: C, 51.7435; H, 3.7981; S, 7.15;
Ir, 21.0213. IR (KBr, νmax, cm-1): 3060 (C-H), 1480, 1431, 1099
(C-S), 1321 (C-O), 320, 329 (Ir-P), 300 (Ir-S).
Synthesis of [(PPh3)2Pd(S2COC2H5)] (D): The digested
PdCl2·2H2O (0.532g, 3 mmol) was dissolved in a mixture of
ethanol and dichloromethane (1:1) to which triphenylphosphine
(1.574 g, 6 mmol) dissolved in a mixture of ethanol and dichloro-
methane (1:1) was added dropwise with constant stirring.After
stirring about 2 h, brownish yellow coloured precipitate of
(PPh3)2PdCl2 was observed. It was filtered off, washed with
ethanol, recrystallized with CH2Cl2:CHCl3 (1:1) and then dried.
The (PPh3)2PdCl2 (2 g, 2.849 mmol) was added to a mixture of
CH2Cl2 and ethanol (2:1). CS2 (1 mL) was added dropwise and
the resulting mixture was stirred for more than 2 days at room
temperature. It was then exposed to air at room temperature
for slow evaporation to reduce the volume to 10-15 mL. Brownish
yellow precipitate of [(PPh3)2Pd(S2COC2H5)] was formed which
was filtered off, washed with a mixture of ethanol:water (2:1)
and recrystallized from dichloromethane:ethanol (1:1) and then
dried.The compound is air-stable and soluble in benzene, ethanol,
dichloromethane and dimethylsulphoxide. Yield: 73.91 %.
Elemental analysis (%) calcd. for [(PPh3)2Pd(S2COC2H5)]: C,
62.2728; H, 4.6902; S, 8.51; Pd, 14.1478. Found: C, 62.4102;
H, 4.722; S, 8.68, Pd, 14.1321. IR (KBr, νmax, cm-1): 3057 (C-
H), 1307 (C-O), 1096 (C-S), 324, 361 (Pd-P), 270 (Pd-S).
EXPERIMENTAL
The chemicals used for the synthesis were mostly of AR
grade (Ranbaxy) and procured from Sigma-Aldrich and Fluka.
Carbon disulphide (CS2) was purchased from E. Merck. Cupric
chloride pentahydrate (CuCl2·5H2O, FlukaA.G. grade), iridium
chloride trihydrate (IrCl3·3H2O, Arora Mathey Ltd., Kolkata)
and palladium chloride dihydrate (PdCl2·2H2O,Arora Mathey
Ltd. Kolkata) were digested with conc. HCl for several times
before use. The complexes were synthesized according to the
literature method [4].
The FTIR spectra (4000-250 cm-1) of the complexes were
obtained as KBr disc using Shimadzu-Prestige-21 FTIR spectro-
meter. Electronic spectra (250-1100 nm) of the complexes were
obtained by using Shimadzu-Graphicord UV-1700 spectro-
meter with 1 cm3 quartz cell. ESR spectrum at liquid N2 temperature
in DMSO was recorded at SAIF, IIT Bombay, India on E-112
ESR spectrometer.
Synthesis of [(PPh3)2Cu(S2COC2H5)] (A): The digested
CuCl2·5H2O (4.417 g , 25.91 mmol) was dissolved in a mixture
of ethanol and dichloromethane (1:1) to which triphenylphos-
phine (13.591 g, 51.82 mmol) dissolved in a mixture of ethanol
and dichloromethane (1:1) was added dropwise with constant
stirring.After 2 h, white precipitate of (PPh3)2CuCl2 was observed.
It was filtered off, washed with ethanol, recrystallized with
CH2Cl2:CHCl3 (1:1) and then dried. The (PPh3)2CuCl2 (3 g,
4.55 mmol) was added to a mixture of CH2Cl2 and ethanol (2:1).
CS2 (1 mL) was added dropwise and the mixture was stirred for
more than 2 days at room temperature. The resulting mixture
was exposed to air at room temperature for slow evaporation
to reduce the volume upto 10-15 mL.White precipitate of complex
(PPh3)2Cu(S2COC2H5) was formed. It was then filtered off, washed
with a mixture of ethanol:water (2:1), recrystallized from
CH2Cl2:C2H5OH (1:1) and then dried.The compound was air-
stable, soluble in chloroform and dichloromethane but sparingly
soluble in dimethyl sulphoxide. Yield: 73.43 %. Elemental
analysis (%) calcd. for [(PPh3)2Cu(S2COC2H5)]: C, 66.0410; H,
4.974; S, 9.025; Cu, 8.9527. Found: C, 66.1101; H, 4.0901; S,
9.205; Cu, 9.0012. IR (KBr, νmax, cm-1): 3057 (C-H), 1185 (C-O),
1097 (C-S), 287 (Cu-S), 280 (Cu-P).
Synthesis of [(C3H4N2)2Cu(S2COC2H5)] (B):The digested
CuCl2·5H2O (4.092 g , 24 mmol) was dissolved in a mixture of
ethanol and dichloromethane (1:1) to which imidazole (3.268 g,
48 mmol) dissolved in 20 mL ethanol was added dropwise with
constant stirring. After stirring about 2 h, green precipitate of
(C3H4N2)2CuCl2 was observed. It was filtered off, washed with
ethanol, recrystallized with CH2Cl2:CHCl3 (1:1) and dried. The
(C3H4N2)2CuCl2 (3.5 g, 12.94 mmol) was added to a mixture of
CH2Cl2 and ethanol (2:1) followed by the dropwise addition
of 1 mL of CS2 and the resulting mixture was stirred continuously
at room temperature for more than 2 days. It was exposed to
RESULTS AND DISCUSSION
At room temperature, reaction of CS2 with the compounds
[(PPh3)2CuCl2] (I), [(C3H4N2)2CuCl2] (II), [(PPh3)3IrCl3] (III)

Vol. 30, No. 10 (2018)
Synthesis and Characterization of Four New Complexes 2287
and [(PPh3)2PdCl2] (IV) in mixed solvent of dichloromethane
and ethanol results in the formation of new compounds [(PPh3)2
Cu(S2COC2H5)] (A), [(C3H4N2)2Cu(S2COC2H5)] (B), [(PPh3)2
IrCl2(S2COC2H5)] (C) and [(PPh3)2Pd(S2COC2H5)] (D), respec-
tively as shown in Scheme-I.
Since triphenylphosphine is a strong σ-donor and hence
more basic than imidazole it stabilizes low oxidation state;
therefore, Cu in complex (A) is in +1 oxidation state while
with imidazole in complex (B) is in +2 state. Moreover, ESR
spectrum of compound (B) at liquid nitrogen temperature
shows that compound has characteristic of tetragonal distortion
(Fig. 2) showing two g-values (g|| = 2.20 and g⊥ = 2.04) with
hyperfine coupling constant (A = 160 G). Hence, Cu metal in
this complex is in +2 state with ground state term symbol is
2D5/2. In the electronic spectrum of compound (C), the broad
peak at around 888 nm shows that Ir metal is in +3 oxidation
state while in compound (D), the weak peak at around 360
nm of wavelength indicates L→M charge transfer transition
with Pd in +2 oxidation state [15,16].
Ph3P
Ph3P Cl
Cu
S
ethanol
Cu
C O C2H5
+
CS2
S
Ph3P
Cl
Ph3P
(A)
N
N
S
N
Cl
N
Cu C O C2H5
S
H
ethanol
H
Cu
+
CS2
Cl
N
N
N
H
N
H
(B)
Cl
Ir
Cl
Ph3P
Ph3P
Ph3P Cl
Ir
S
ethanol
ethanol
+
CS2
CS2
C O C2H5
S
Ph3P Cl
Cl
PPh3
(C)
Ph3P
Cl
Ph3P
Pd
Ph3P
S
S
Pd
Ph3P Cl
+
C O C2H5
(D)
Scheme-I: Synthetic route of the complexes [(PPh3)2Cu(S2COC2H5)] (A),
[(C3H4N2)2Cu(S2COC2H5)] (B), [(PPh3)2IrCl2(S2COC2H5)] (C)
and [(PPh3)2Pd(S2COC2H5)] (D)
The FTIR spectrum of compound (A) shows a sharp bands
at 1097.54 and 3057.30 cm-1 due to stretching frequency of
ν(C-S) and aromatic ν(C-H) stretching frequency, respectively.
A weak band at 1185.31 cm-1 due to ν(C-O) stretching frequency
is also observed. Other sharp bands at 747.45 and 287.41 cm-1
due to aromatic C-H bending frequency and ν(Cu-S) stretching
frequency, respectively and a weak band at about 280 cm-1 is
due to ν(Cu-P) stretching vibration. For compound (B), the
FTIR spectrum shows sharp peaks at 1067.65, 1499.72, 1424.49
cm-1 and a weak peak at 1172.77 cm-1 due to ν(C-S) stretching
frequency. The sharp peak at 1258.61 cm-1 and a weak peak at
1172.77 cm-1 is due to ν(C-O) stretching frequency. Two sharp
peaks were observed at about 310 and 326.95 cm-1 due to ν(Cu-S)
stretching vibration, and a medium peak at 441.72 cm-1 is due
to ν(Cu-N) stretching vibration. In the compound (C), it shows
broad peak at 1099.47cm-1, two sharp peaks at 1431.24 cm-1 and
1480.43 cm-1 are due to ν(C-S) stretching vibration. The sharp
peak at 3060.20 cm-1 is due to aromatic C-H stretching vibration.
The broad peak at 1321.30 cm-1 is due to ν(C-O) stretching
vibration. A sharp peak at 747.45 cm-1 is due to aromatic C-H
bending vibration. The sharp peak at 300 cm-1 corresponds to
ν(Ir-S) stretching vibration and two sharp peaks at about 320
and 329.84 cm-1 are due to ν(Ir-P) stretching vibration. For
compound (D), FTIR spectra shows sharp peak at 1096.58
cm-1 is due to ν(C-S) stretching frequency. A sharp peak at
3057.30 cm-1 is due to aromatic ν(C-H) stretching vibration.
A broad peak at 1307.79 cm-1 is due to ν(C-O) stretching vibra-
tion. The sharp peak at 748.41 cm-1 is due to aromatic ν(C-H)
bending vibration. A sharp peak at about 270 cm-1 is due to
ν(Pd-S) stretching vibration and two sharp peaks at 324.05
and 361.67 cm-1 are due to ν(Pd-P) stretching vibration.
5000 G
3000 G
Scan range
Fig. 2. ESR spectrum of the compound [(C3H4N2)2Cu(S2COC2H5)] (B)
The tentative structures of the complexes have shown
below:
N
S
S
N
C O C2H5
Cu
H
Ph3P
S
N
N
Cu C O C2H5
S
Ph3P
A
B
( )
( )
H
Ph3P
Cl
Ph3P
S
S
Pd C O C2H5
S
Ir
C O C2H5
Ph3P
Ph3P
S
Cl
(C)
(D)
ACKNOWLEDGEMENTS
The authors thank to SAIF, IIT Bombay for ESR analysis
facilities. S. Sultana thanks UGC-Maulana Azad National
Fellowship, New Delhi for financial support.
CONFLICT OF INTEREST
The authors declare that there is no conflict of interests
regarding the publication of this article.

2288 Sultana et al.
Asian J. Chem.
10. M.C. Baird and G. Wilkinson, J. Chem. Soc. A, 865 (1967);
REFERENCES
https://doi.org/10.1039/j19670000865.
11. M. Baird, G. Hartwell Jr., R. Mason, A.I.M. Rae and G. Wilkinson,
Chem. Commun., 92 (1967);
1. I.K. Bezougli, A. Bashall, M. McPartlin and D.M.P. Mingos, J. Chem. Soc.,
Dalton Trans., 2671 (1998);
https://doi.org/10.1039/c19670000092.
https://doi.org/10.1039/a802681e.
12. M.C. Baird, G. Hartwell and G. Wilkinson, J. Chem. Soc. A, 2037 (1967);
https://doi.org/10.1039/j19670002037.
2. M.R. Torres, A. Perales and J. Ros, Organometallics, 7, 1223 (1988);
https://doi.org/10.1021/om00095a033.
13. A.C. Lane, C.L. Barnes, M.V. Vollmer and J. R. Walensky, Inorganics,
2, 540 (2014);
3. P.K. Gogoi, D.K. Bhuyan and N. Gogoi, Asian J. Chem., 29, 657 (2017);
https://doi.org/10.14233/ajchem.2017.20295.
https://doi.org/10.3390/inorganics2040540.
14. O.P. Lam, L. Castro, B. Kosog, F.W. Heinemann, L. Maron and K.
Meyer, Inorg. Chem., 51, 781 (2012);
4. P.K. Gogoi, G. Borah, N. Bharali and D. Saikia, Indian J. Chem., 46A,
1113 (2007).
5. Z. Dong, L. Guanliang, Z. Liang and Z. Chuanjan, Indian J. Chem., 42A,
1102 (2004).
https://doi.org/10.1021/ic202535e.
15. A.B.P. Lever, Inorganic Electronic Spectroscopy, Elsevier Science
Publishing Company Inc., edn 2, p. 341 and 547 (1986).
16. A.F. Hill, ed.: E.W. Abel, Co-Ligands in Organotransition Metal
Chemistry, In: Organotransition Metal Chemistry, The Royal Society
of Chemistry, pp. 22-41 (2002).
6. K. Shalini, P.K. Sharma and N. Kumar, Der Chem. Sinica, 1, 36 (2010).
7. B. Buriez, D.J. Cook, K.J. Harlow, A.F. Hill, T. Welton, A.J.P. White, D.J.
Williams and J.D.E.T. Wilton-Ely, J. Organomet. Chem., 578, 264 (1999);
https://doi.org/10.1016/S0022-328X(98)01130-9.
8. E. Lindner, R. Grimmer and H. Weber, Angew. Chem., 82, 639 (1970);
https://doi.org/10.1002/ange.19700821517.
9. B.J. McCormick, R.I. Kaplan and B.P. Stormer, Can. J. Chem., 49, 699
(1971);
https://doi.org/10.1139/v71-117.