Synthesis and characterization of some copper(I) complexes formed by the insertion of carbon disulfide in L2CuCl (L = PPh3, AsPh3 and SbPh3)

Article abstract of DOI:10.14233/ajchem.2017.20295

Insertion reaction of carbon disulfide with bis(triphenyl phosphine), bis(triphenyl arsine) or bis(triphenyl stibine) copper(I) chloride in a mixed solvent of dichloromethane and ethanol results in the formation of new class of copper (I) complexes of the type [L₂Cu(S₂COEt)] (L = PPh₃, AsPh₃ and SbPh₃). These three new complexes have been characterized by chemical analysis, DTA, TGA and infrared spectroscopic method. The molar conductances of these complexes are measured in dichloromethane (10^-3 M) at room temperature.

Full text of DOI:10.14233/ajchem.2017.20295

Asian Journal of Chemistry; Vol. 29, No. 3 (2017), 657-660
A
SIAN
J
OURNAL OF HEMISTRY
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https://doi.org/10.14233/ajchem.2017.20295
Synthesis and Characterization of Some Copper(I) Complexes Formed by the
Insertion of Carbon Disulfide in L2CuCl (L = PPh3, AsPh3 and SbPh3)
*
P.K. GOGOI , D.K. BHUYAN and NIBEDITA GOGOI
Department of Chemistry, Dibrugarh University, Dibrugarh-786 004, India
*Corresponding author: E-mail: dr.pradip54@gmail.com
Received: 8 September 2016;
Accepted: 14 December 2016;
Published online: 30 December 2016;
AJC-18221
Insertion reaction of carbon disulfide with bis(triphenyl phosphine), bis(triphenyl arsine) or bis(triphenyl stibine) copper(I) chloride in a
mixed solvent of dichloromethane and ethanol results in the formation of new class of copper (I) complexes of the type [L2Cu(S2COEt)]
(L = PPh3, AsPh3 and SbPh3). These three new complexes have been characterized by chemical analysis, DTA, TGA and infrared
spectroscopic method. The molar conductances of these complexes are measured in dichloromethane (10-3 M) at room temperature.
Keywords: Carbon disulphide, Insertion, Copper complexes, Ligand, Coordination compound.
ligand. They bind strongly to many transition metals in low
oxidation state and are used to stabilize organometallic and
hydride derivative of the elements, either in isolated comp-
ounds or as intermediate in homogeneous catalytic reaction.
Dong et al. [2] and Gogoi et al. [4] reported the synthesis and
X-ray structure of [(PPh3)2CuS2COMe]. Similarly, another few
reports are available in this regard [5-10]. In particular, the
complexes of the type [L2CuCl] (L = PPh3, AsPh3 and SbPh3)
are excellent starting material for the synthesis of new Cu(I)
complexes of the type [L2Cu(S2COEt)] (L = PPh3, AsPh3 and
SbPh3) which are obtained by treating L2CuCl and with CS2 in
a mixed solvent of CH2Cl2 and C2H5OH at room temperature.
In this report, we describe the synthesis and characteriza-
tion of three new Cu(I) complexes of the type [L2Cu(S2COEt)]
(L = PPh3,AsPh3 and SbPh3) where L act as monodentate ligand
and EtOCS2- anion acts as bidentate ligand. A study of their
thermal stability as well as spectroscopic properties has been
described through this article.
INTRODUCTION
Insertion reactions are of profound interest because of
their major role in synthetic chemistry. A number of insertion
reactions show promising importance in catalytic system
involving transition metal-carbon bond. As an unsaturated
electrophile and potentially a most abundant source of C1
chemistry, carbon disulphide has proved to be a significant
tool for insertion reactions of transition metal complexes [1],
leading to a new class of compounds, often called organo-
metalllic compound. Carbon disulfide has rather versatile coordi-
nation chemistry with a number of bonding modes to metal
1
2
centres. It is widely accepted that CS2 bonds in η -end on, η -side
on and bridging coordination modes.
Besides, there exist some examples of CS2 insertion
3
reactions yielding η -S2CR ligand system. Carbon disulfide
inserts readily to a transition metal in low valency state. Dong
et al. [2] have reported insertion reaction of CS2 into a Cu(I)
compound [(PPh3)2CuNO3] in a mixed solvent of CH2Cl2 and
CH3OH at room temperature. Copper(I) is found to display
wide diversity in structural chemistry, the coordination number
ranging from 2 to 6. The Cu(I) complexes with d10 configuration
provide no optical absorption band. Copper(I) complexes are
important in coordination chemistry and catalytic reactions.
They are of significant importance in oxygen transfer oxidative
addition and homogeneous hydrogenation.
EXPERIMENTAL
All the chemicals used in the synthesis of the complexes
were ofAR grade (Ranbaxy, India) and used as such. Triphenyl
phosphine, triphenyl arsine and triphenyl stibine were of Fluka
A. G. made. Carbon disulphide was of E. Merck (India) made.
Synthesis of [(PPh3)2Cu(S2COEt)]: The compound
(PPh3)2CuCl was prepared by treating CuCl (0.5 g, 5.05 mmol)
and triphenyl phosphine (2.6 g, 9.9 mmol) in dichloromethane
at room temperature. 0.5 g of (PPh3)2CuCl (0.8 mmol) was added
to a mixture of CH2Cl2 (20 mL), CS2 (1.2 mL) and ethanol (10
There is an extensive chemistry of Cu(I) complexes with
PPh3 ligand [3]. In modern co-ordination chemistry, PPh3,AsPh3
and SbPh3 ligands have aroused great attention as π-acceptor

658 Gogoi et al.
Asian J. Chem.
TABLE-1
ELEMENTAL ANALYSIS DATA OF THREE COMPLEXES
Elemental analysis (%): Found (calcd.)
Compound
Cu
S
C
H
[(PPh3)2Cu(S2COEt)]
[(AsPh3)2Cu(S2COEt)]
[(SbPh3)2Cu(S2COEt)]
9.17 (8.96)
8.10 (7.97)
6.90 (7.11)
8.91 (9.03)
8.13 (8.02)
7.03 (7.17)
69.65 (71.07)
59.77 (58.71)
51.91 (52.48)
4.48 (4.93)
3.87 (4.39)
3.38 (3.92)
mL). The mixture was stirred for 24 h at room temperature.
The resulting solution was exposed to air for evaporation at room
temperature to 10-15 mL, yellow crystals of [(PPh3)2Cu(S2COEt)]
was precipitated. It was filtered off, washed with ethanol and
dried. It is air stable, yellow crystalline material, insoluble in
water, chloroform, ether, slightly soluble in ethanol, toluene
and readily soluble in dichloromethane, acetonitrile, dimethyl
sulphoxide and benzene.
RESULTS AND DISCUSSION
At room temperature, reaction of CS2 with the compounds
of the type [L2CuCl] (L = PPh3,AsPh3, SbPh3) in mixed solvent
of dichloromethane and ethanol results in the formation of
a new series of the compounds of the type [L2Cu(S2COEt)]
(L = PPh3, AsPh3, SbPh3). The mechanism of the reaction is
attributed to the insertion of CS2 in the O-H bond of ethanol to
give HS2COEt which in a subsequent reaction with [L2CuCl]
results in a mononuclear copper(I) complex [L2Cu(S2COEt)].
The reaction can be depicted as:
Synthesis of [(AsPh3)2Cu(S2COEt)]: 0.5 g of CuCl (5.05
mmol) was treated with 3.09 g of triphenyl arsine (10.09 mmol)
in dichloromethane solvent at room temperature to give
(AsPh3)2CuCl. 0.861 g of (AsPh3)2CuCl (1.2 mmol) was added
to a mixture of CH2Cl2 (20 mL), CS2 (1.2 mL) and ethanol
(10 mL). The mixture was stirred for 24 h at room temperature.
When the resulting mixture was exposed to air for evaporation
to 10-15 mL, yellowish white crystals of [(AsPh3)2Cu(S2COEt)]
was precipitated. It was filtered off, washed with ethanol and
dried. It is slightly soluble in chloroform, toluene, ethanol, but
readily soluble in dichloromethane and dimethyl sulphoxide.
It is insoluble in water, benzene and not very stable in air.
Synthesis of [(SbPh3)2Cu(S2COEt)]: The compound
(SbPh3)2CuCl was prepared by adding CuCl (1 g, 10.1 mmol)
to triphenyl stibine (7.13 g, 20.1 mmol) in dichloromethane
solvent at room temperature. (SbPh3)2CuCl (2.578 g, 3.2 mmol)
was added to a mixture of CH2Cl2 (20 mL), CS2 (1.2 mL)
and ethanol (10 mL). The mixture was stirred for 24 h at
room temperature. When the resulting solution was allowed
for evaporation to 10-15 mL, yellowish white crystals of
[(SbPh3)2Cu(S2COEt)] was obtained. It was filtered off, washed
with ethanol and dried. It is slightly soluble in chloroform,
ethanol etc., but readily soluble in dichloromethane and
dimethyl sulphoxide. It is insoluble in water and benzene and
not very stable in air.
The IR spectra of these compounds were recorded in a
Perkin-Elmer spectrophotometer (Model No. 883) in the
Department of Chemistry, Dibrugarh University. The molar
conductivity measurement was carried out in 10-3 M CH2Cl2
solution at 25 °C using a digital conductance bridge, (Model:
180). The melting point of the compounds was determined on an
electro thermal apparatus (Model: Raaga). Thermal gravimetric
analysis (TGA) and differential thermal analysis (DTA) of the
compounds were performed in Department of Chemistry,
Dibrugarh University by using Perkin Elmer DTA-TGA
instrument (Model: Pyris Diamond). The chemical analysis of
the compounds was expressed in terms of weight percentages
of C, H, Cu and S. Copper and sulphur were analyzed as per
known procedure. Copper was estimated iodometrically and
sulphur was estimated gravimetrically. Carbon and hydrogen
were analyzed at Central Drug Research Institute (CDRI),
Lucknow.
L2CuCl + CS2 + EtOH → [L2Cu(S2COEt)] + HCl
where L = PPh3, AsPh3 and SbPh3.
Chemical analysis: The data of chemical analysis for the
compounds are listed in the Table-1.
From the elemental analysis, it is seen that the compounds
give satisfactory C, H, Cu and S analysis. Thus, the chemical
analysis agrees well with their formulation. The melting point
data shows that the stability of the compounds decreases in
the order of the ligands: PPh3 > AsPh3 > SbPh3.
The molar conductance data of the compounds in 10-3 M
CH2Cl2 solution show them to be non-electrolyte in the view
of established ranges for such compounds. The non-electrolyte
behaviour of the compounds confirms their mononuclear
nature and co-ordination character of the ligands PPh3, AsPh3
and SbPh3. The molar conductivity and melting point data are
shown in Table-2.
TABLE-2
MOLAR CONDUCTIVITY AND MELTING
POINT DATA OF THE THREE COMPLEXES
Molar conductivity
Compound
m.p. (°C)
(S mol-1 cm2)
[(PPh3)2Cu(S2COEt)]
[(AsPh3)2Cu(S2COEt)]
[(SbPh3)2Cu(S2COEt)]
4.6
5.4
3.8
155
145
141
An important characteristic of this compound is that they
exhibit photoluminescence behaviour at room temperature.
When the compounds were irradiated with an ultraviolet radia-
tion source, they exhibit photoluminescence of the following
types (Table-3).
TABLE-3
PHOTOLUMINESCENCE DATA OF THREE COMPLEXES
[(PPh3)2Cu(S2COEt)]
Light green luminescence in short wave
region (intense)
[(AsPh3)2Cu(S2COEt)] Violet luminescence in short wave region
(less intense)
[(SbPh3)2Cu(S2COEt)] Red-pink luminescence in long wave region
(most intense)

Vol. 29, No. 3 (2017)
Synthesis of Some Cu(I) Complexes Formed by Insertion of CS2 in L2CuCl (L = PPh3, AsPh3 and SbPh3) 659
Infrared spectral analysis: The IR absorption spectrum
of the compound [(PPh3)2Cu(S2COEt)] consist of a strong
peak at 519 cm-1 corresponds to Cu-S asymmetric stretching
vibration, while a weak IR absorption band at 1095 cm-1 is
due to C-S stretching vibration. The spectrum also shows a
weak absorption band at 3056 cm-1 owing to aromatic C-H
stretching vibration. The strong peak at 743 cm-1 is due to
aromatic C-H bending vibration.
Similarly, IRspectrumofthecompound[(AsPh3)2Cu(S2COEt)]
consist of a strong peak at 489 cm-1 which corresponds to Cu-S
stretching vibration and a weak peak at 1080 cm-1 indicates
C-S stretching vibration. The absorption band of 738 cm-1 is
due to aromatic C-H bending vibration.
In the IR spectrum of the compound [(SbPh3)2Cu(S2COEt)],
we observe a weak absorption band at 480 cm-1 which corres-
ponds to the Cu-S stretching vibration and another weak
absorption band at 1070 cm-1 arises from C-S stretching vibra-
tion. The weak absorption band at 3051 cm-1 is characteristic
of aromatic C-H stretching vibration. The spectrum shows a
strong band at 750 cm-1 owing to aromatic C-H bending vibra-
tion.
At 419.96 °C, there was a weight loss of 84.4 %, corresponding
to removal of two PPh3 ligands and removal of CS2 ligand. A
weak exothermic peak in the DTA curve at 419.96 °C corro-
borates this decomposition and indicates the formation of CuO
and some other products which is the final product of thermal
decomposition of the sample (weight loss found = 84.4 %
calculated = 91.03 %).
From TGA-DTA study of [(AsPh3)2Cu(S2COEt)],
(Fig. 1b) it is seen that weight loss started at 149.41 °C and
continues upto 496.91 °C. between 149.4-496.91 °C, there
was a 81.66 % of weight loss. The first endothermic peak at
155 °C in the DTA curve shows 0.5 % weight loss, which
corresponds to adsorbed moisture from the compound. The
TGA curve shows 6 % weight loss at 230 °C. This corresponds
to an exothermic peak between 220-260 °C, confirming the
dissociation of O-C2H5 group (weight loss found = 6 % calcu-
lated = 5.6 %). At 496.91 °C, there was a weight loss of 81.77
%, corresponding to the removal of two AsPh3 ligands and
removal of CS2 ligand (weight loss found = 81.77 % calculated
= 92.02 %). This weight loss is indicative of formation of CuO
and some other products.
The IR spectral data shown in Table-4 indicated that the
ν(Cu-S) and ν(C-S) decreases on going from PPh3 to SbPh3
derivatives in agreement with decreasing σ-donating capa-
city of the series in the order PPh3 > AsPh3 > SbPh3. As the
σ-donating capacity decreases there is corresponding decrease
in the electron delocalization of the chelate ring (as shown
below) with consequent decrease in the Cu-S and S-C force
constant. Stronger the σ-donation, more prominent will be the
partial double bond character of Cu-S and S-C bond.
Similarly TGA-DTA study of [(SbPh3)2Cu(S2COEt] shows
(Fig. 1a) that the weight loss started at 148.84 °C and it
continues up to 327.59 °C. Within the reported temperature
82.69 % of weight loss takes place. The first endothermic peak
at 165 °C in the DTA curve is accompanied by 1.2 % weight
loss, which indicates the loss of adsorbed moisture from the
compound.
TGA
c
100
a
b
S
c
σ
80
60
40
20
b
a
Cu
C
OR
DTA
σ
S
The above trend is also reflected in the thermal stability
of the complexes as obtained from DTA/TGA studies, which
indicated the thermal stability order as PPh3 > AsPh3 > SbPh3.
Thermal gravimetric analysis (TGA) and differential
thermalanalysis(DTA):TGA-DTAstudiesof[(PPh3)2Cu(S2COEt)]
shows (Fig. 1c) that the weight loss started at 160.18 °C and
there is a gradual decline till 419.96 °C, indicating a continuous
weight loss of the sample. Within the reported temperature
range, 83.78 % of weight loss takes place. The first endo-
thermic peak at 160.18 °C in the DTA curve is accompanied
by 1.1 % weight loss, which indicates the loss of adsorbed
moisture from the compound. The TGA thermogram shows 7
% weight loss at 250 °C, corresponds to an exothermic DTA
peak between 225 and 305 °C, confirming the dissociation of
O-C2H5 group (weight loss found = 7 % calculated = 6.345 %).
100
200
300
400
500
Temperature (°C)
Fig. 1. TGA-DTA curve of (a) [(SbPh3)2Cu(S2COEt] (b)
[(AsPh3)2Cu(S2COEt)] (c) [(PPh3)2Cu(S2COEt)]
The TGA thermogram shows the weight loss (4.8 %) at
210 °C. This corresponds to an endothermic peak between
190 °C-220 °C, confirming the dissociation of O-C2H5 group
(weight loss found = 4.8 % calculated = 5.04 %).At 327.59 °C,
there was a weight loss of 83.3 %, corresponding to the removal
of two SbPh3 ligands and removal of CS2 ligand. A weak
exothermic peak in the DTA curve at 327.59 °C corroborates
TABLE-4
IR SPECTRAL DATA OF THE COMPLEXES
Compounds
[(PPh3)2Cu(S2COEt)]
519(s)
[(AsPh3)2Cu(S2COEt)]
489(w)
[(SbPh3)2Cu(S2COEt)]
480(w)
Assignment
Cu-S asymm. Stretching vibration
C-S Stretching vibration
Aromatic C-H Stretching vibration
Aromatic C-H bending vibration
1095(w)
3056(w)
743(s)
1080(w)
3040(w)
738(w)
1070(w)
3051(w)
750(s)
Frequency (cm-1)

660 Gogoi et al.
Asian J. Chem.
this decomposition and indicates the formation of CuO and
some other products like in earlier cases.
The thermal characteristics of PPh3, AsPh3 and SbPh3
derivatives have been studied by thermal gravimetric analysis
and differential thermal analysis and it is found that PPh3
derivatives is the most stable and stability trend is PPh3 >AsPh3
> SbPh3. This trend can be explained from the σ-donor and
π-acceptor property of the ligands corroborating the IR spectral
results discussed earlier.
Conclusions
In coordination chemistry, because of their π-acceptor
character the ligands PPh3,AsPh3 and SbPh3 stabilize transition
metals in lower oxidation state. Phosphorus, arsenic and anti-
mony have empty d-orbital which are of proper symmetry to
overlap with the metal orbital. The overlap facilities shift of
electron density from the filled metal orbital to the ligand empty
d-orbital through dπ-dπ back bonding. The π-acidic character
of the ligands decreases in the order PPh3 > AsPh3 > SbPh3.
This order indicate that the smaller P-atom can participate more
effectively in dπ-dπ back bonding.
The triaryl derivatives of P,As and Sb are stable with Cu(I)
oxidation state (HSAB principle). The triaryls of P, As and Sb
possess strong σ-donor capacity which decreases in the order
P > As > Sb. The more σ-donor capacity, more stable is Cu(I)
oxidation state. The stability of PPh3, AsPh3 and SbPh3 deri-
vatives follow the trend PPh3 > AsPh3 > SbPh3. The PPh3-
derivative is found to be more stable than other two derivatives
ofAs and Sb. It can also be visually noticed that comparatively
less stable compounds of As and Sb are easily oxidized to
blue colour in air.
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