Copper(I) complexes of N-(2-quinolynylmethylene)-1H-benzimidazole and triphenylphosphine: Synthesis, characterization, luminescence and catalytic properties

Article abstract of DOI:10.1016/j.ica.2017.05.076

Copper(I) complexes of the type [Cu(L)(PPh₃)₂]X (1–4) [where L?=?N-(2-quinolynylmethylene)-1H-benzimidazole; PPh₃?=?triphenylphosphine, X?=?NO₃(1), ClO₄(2), BF₄(3) and PF₆(4)] were prepared by the condensation of 2-aminobenzimidazole with 2-quinolinecarboxaldehyde followed by reaction with [Cu(CH₃CN)₄]NO₃, [Cu(CH₃CN)₄]ClO₄, [Cu(CH₃CN)₄]BF_4, [Cu(CH₃CN)₄]PF₆ in presence of triphenylphosphine as a coligand. The single crystal X-ray diffraction study of representative complex [Cu(L)(PPh₃)₂]⁺ (3) reveals a distorted tetrahedral geometry around copper(I). Cyclic voltammogram of complexes 1–4 displayed quasireversible redox behavior corresponding to Cu(I)/Cu(II) couple. All complexes show red emission as a result of ligand to ligand charge transfer (LLCT) or intra-ligand charge transfer (ILCT) or admixture of them. The catalytic efficiency of the complexes 1–4 was tested and it was found that all the complexes worked as an effective catalyst for the Sonogashira coupling of phenylacetylene with different aryl halides in good yield at 90?°C.

Full text of DOI:10.1016/j.ica.2017.05.076

Inorganica Chimica Acta 466 (2017) 122–129
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Research paper
Copper(I) complexes of N-(2-quinolynylmethylene)-1H-benzimidazole
and triphenylphosphine: Synthesis, characterization, luminescence and
catalytic properties
⇑
S.S. Devkule, S.S. Chavan
Department of Chemistry, Shivaji University, Kolhapur, MS-416004, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Copper(I) complexes of the type [Cu(L)(PPh3)2]X (1–4) [where L = N-(2-quinolynylmethylene)-1H-benz-
imidazole; PPh3 = triphenylphosphine, X = NO3(1), ClO4(2), BF4(3) and PF6(4)] were prepared by the con-
densation of 2-aminobenzimidazole with 2-quinolinecarboxaldehyde followed by reaction with [Cu
(CH3CN)4]NO3, [Cu(CH3CN)4]ClO4, [Cu(CH3CN)4]BF4, [Cu(CH3CN)4]PF6 in presence of triphenylphosphine
as a coligand. The single crystal X-ray diffraction study of representative complex [Cu(L)(PPh3)2]+ (3)
reveals a distorted tetrahedral geometry around copper(I). Cyclic voltammogram of complexes 1–4 dis-
played quasireversible redox behavior corresponding to Cu(I)/Cu(II) couple. All complexes show red
emission as a result of ligand to ligand charge transfer (LLCT) or intra-ligand charge transfer (ILCT) or
admixture of them. The catalytic efficiency of the complexes 1–4 was tested and it was found that all
the complexes worked as an effective catalyst for the Sonogashira coupling of phenylacetylene with dif-
ferent aryl halides in good yield at 90 °C.
Received 27 March 2017
Received in revised form 22 May 2017
Accepted 31 May 2017
Available online 1 June 2017
Keywords:
Copper(I) complexes
Crystal structure
Luminescence
Catalysis
Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction
More recently considerable interest has been paid on N-hetero-
cyclic system especially benzimidazole and their derivatives which
The monovalent copper(I) complexes with tetrahedral coordi-
nation geometry have received special attention due to its low tox-
icity, low cost advantage and relatively abundant resource
compared to more precious metal systems such as Re(I) [1], Ir(III)
[2], Pt(IV) [3] and Au(I) [4]. These obvious advantages make cop-
per(I) compounds excellent candidates for their potential applica-
tions such as photosensitizers (PS) for solar energy conversion,
dye-sensitized solar cells (DSSCs), organic light emitting diodes
(OLEDs), light emitting electrochemical cells (LEECs), supramolec-
ular devices, catalysis and biological relevance [5–9]. The combina-
tion of the electron rich copper(I) center, conjugated organic ligand
and high degree of inherent covalence in soft acid-soft base bond-
ing can produce low energy electronic interactions between metal
center and the ligand and resulting compound possesses interest-
ing optical and electronic properties [10,11]. Moreover, the steric,
electronic and conformational effects imparted by the coordinated
ligands play an essential role in stabilizing the copper(I) state and
modifying the physical and chemical properties of the prepared
complexes. Hence careful choice of ligand is of significant impor-
tance which will tune the properties of the resulting compound.
are reported to exhibit remarkable features like ease of prepara-
tion, electrochemical behavior, light absorption in the visible
region, characteristic structural flexibility, supramolecular archi-
tecture, long-lived electronically excited states and intense lumi-
nescence [12–15]. Because of having high thermal stability, good
catalytic performance and superior optical properties, metal com-
plexes with benzimidazole ligands are important. An important
feature of these system is the structural modifications which
causes a large p-delocalization over the N-heterocyclic ligand than
that of the regular complexes. The copper(I) complexes with phos-
phorous containing ligands are of great important to carry wide
range organic transformations such as allylic amination, hydro-
genation, copolymerization, cross coupling reactions etc. [16–19].
The steric crowding and
p-acidic character imparted by these
ligands are most important prerequisites for stabilizing the cop-
per(I) complexes and their redox, photophysical and catalytic
behavior.
In this paper we report synthesis of some mixed ligand copper
(I) complexes (1–4) derived by the reaction of N-(2-quinolynyl-
methylene)-1H-benzimidazole (L) with [Cu(CH3CN)4]NO3 [Cu(CH3-
CN)4]ClO4, [Cu(CH3CN)4]BF4 and [Cu(CH3CN)4]PF6 in presence of
triphenylphosphine as coligand. All the complexes were
characterized by elemental analysis, spectroscopic techniques
⇑
Corresponding author.
E-mail address: sanjaycha2@rediffmail.com (S.S. Chavan).
http://dx.doi.org/10.1016/j.ica.2017.05.076
0020-1693/Ó 2017 Elsevier B.V. All rights reserved.

S.S. Devkule, S.S. Chavan / Inorganica Chimica Acta 466 (2017) 122–129
123
and representative complex 3 by X-ray crystallography analysis.
The luminescent behavior and catalytic performance of all com-
plexes for the Sonogashira coupling of phenylacetylene with aryl
halides have also been reported.
10 ml of dichloromethane and stirred for 2 h at room temperature.
The volume of solvent reduced under vacuum and the solid pro-
duct was produced by diffusion of diethyl ether into the filtrate.
Yield: 82% (0.642 g, 0.701 mmol); Elemental analyses (C, H, N,
wt%) Anal. Calc. for C53H42N5O3P2Cu: C, 69.01; H, 4.59, N, 7.59;
found: C, 68.96; H, 4.49, N, 7.68%; IR (KBr; cmÀ1); 3362,
1587, (HC@N), 1384, (C–N); 3066, (Ar–CH); 488
1482, 1436, 695, 518, (PPh3); 1375, 821, (NO3): UV–Vis (CH2Cl2)
kmax (nm) (
/MÀ1 cmÀ1): 294 (75,000), 352 (35,000), 458 (7000);
t
(NH),
2. Experimental
t
t
t(Cu–N);
t
t
2.1. Materials and methods
e
1H NMR (CDCl3; 300 MHz); d 11.03 (s, 1H, NH), d 9.48 (s, 1H,
HC@N), d 7.12–8.46 (m, 10H, Ar–H); 13C NMR (CDCl3; 300 MHz) d
160.3 (N@CN), 150.7 (quin-C), 146.1 (HC@N), 138.9 (benzi-C),
133.4 (ph-C), 132.1 (quin-C), 130.3 (ph-C), 130.2 (ph-C), 129.5
(quin-C), 128.5 (ph-C), 128.1 (ph-C), 127.9 (quin-C), 126.5 (quin-
C), 125.7 (quin-C), 125.1 (quin-C), 122.5 (quin-C), 119.4 (benzi-
C), 112.5 (benzi-C); ESI (MS): 859 [MÀNO3]+.
The reagent used in synthesis of copper(I) complexes are 2-
quinolinecarboxaldehyde (Alfa Aesar), 2-aminobenzimidazole
(Aldrich, USA), triphenylphosphine were of reagent grade and used
without further purification. Other reagents included iodobenzene,
4-iodoaniline, 1-bromo-4-iodobenzene, phenylacetylene and
potassium carbonate. The copper(I) compounds Cu(CH3CN)4]NO3
[20], Cu(CH3CN)4]ClO4 [21], [Cu(CH3CN)4]BF4 [21] and [Cu(CH3-
CN)4]PF6 [22] were prepared according to the literature procedure.
Elemental analyses (C, H and N) of the copper(I) complexes were
conducted on Thermo Finnegan FLASH EA-1112 CHNS analyzer. IR
spectra were recorded on a Perkin-Elmer-100 FTIR Spectrometer,
1H NMR and 13C NMR spectra of the samples dissolved in
CDCl3 were measured on Bruker 300 MHz instrument using TMS
[(CH3)4Si] as an internal standard of chemical shifts (ppm).
Electronic spectra were recorded in dichloromethane (10À5 M)
Shimadzu 3600 UV–Vis-NIR spectrophotometer. Emission spectra
were recorded using a Perkin-Elmer LS 55 spectrofluorometer
equipped with quartz cuvette of 1 cm path length at room temper-
ature. ESI mass spectra were recorded using a Bruker Apex3.
Luminescence lifetime measurements were carried out by using
time-correlated single photon counting from HORIBA JobinYvon.
Cyclic voltammetry measurements were performed with a CH-400
electrochemical analyzer. Tetrabutyl ammonium perchlorate
(TBAP) was used as the supporting electrolyte and ferrocene was
used as an internal reference. All measurements were carried out
in CH2Cl2 solution at room temperature with scan rate 50 mV sÀ1
2.2.3. Synthesis of [Cu(L)(PPh3)2]ClO4 (2)
Complex 2 was prepared by a procedure similar to that used for
the preparation of 1 except that, [Cu(CH3CN)4]NO3 was replaced by
[Cu(CH3CN)4]ClO4 (0.300 g, 0.918 mmol).
Yield: 87% (0.717 g); Elemental analyses (C, H, N, wt%) Anal.
Calc. for C53H42N4P2O4ClCu: C, 66.32; H, 4.41, N, 5.84; found: C,
66.21; H, 4.33, N, 5.95%; IR (KBr; cmÀ1); 3362,
t
(NH), 1588,
(Cu–N); 1482, 1436,
(ClO4); UV–Vis (CH2Cl2) kmax (nm)
e
/MÀ1 cmÀ1): 292 (71,000), 349 (33,000), 451 (8000); 1H NMR
t
(HC@N), 1384,
t(C–N); 3065, (Ar–CH); 488 t
695, 518, (PPh3); 1097, 622,
t
t
(
(CDCl3; 300 MHz): d 11.04 (s, 1H, NH), d 9.47 (s, 1H, HC@N), d
7.11–8.49; 13C NMR (CDCl3; 300 MHz): d 160.2 (N@CN), 150.7
(quin-C), 145.9 (HC@N), 139.0 (benzi-C), 133.4 (ph-C), 132.2
(quin-C), 130.3 (ph-C), 130.2 (ph-C), 129.5 (quin-C), 128.5 (ph-C),
128.1 (ph-C), 127.7 (quin-C), 126.9 (quin-C), 125.6 (quin-C),
125.2 (quin-C), 122.6 (quin-C), 119.5 (benzi-C), 112.4 (benzi-C);
ESI (MS): 859 [MÀClO4]+.
2.2.4. Synthesis of [Cu(L)(PPh3)2]BF4 (3)
Complex 3 was prepared by a procedure similar to that used for
the preparation of 1 except that, [Cu(CH3CN)4]NO3 was replaced by
[Cu(CH3CN)4] BF4 (0.289 g, 0.918 mmol).
2.2. Synthesis
2.2.1. Synthesis of ligand (L)
Yield: 88% (0.902 g); Elemental analyses (C, H, N, wt%) Anal.
Calc. for C53H42N4P2F4BCu: C, 67.20; H, 4.47, N, 5.91; found: C,
N-(2-quinolynylmethylene)-1H-benzimidazole (L) was pre-
pared by adopting and modifying the method described in the lit-
erature [23]. To a solution of 2-aminobenzimidazole (0.800 g,
6.010 mmol) in ethanol (10 ml) a solution of 2-quinolinecarbox-
aldehyde (0.944 g, 6.010 mmol) in EtOH (10 ml) was added drop
wise with constant stirring. The resulting reaction mixture was
refluxed at about 82 °C until the completion of reaction (checked
by TLC). On partial removal of solvent the product obtained was fil-
tered, washed with ethanol and dried in vacuo.
67.11; H, 4.38, N, 5.99%; IR (KBr; cmÀ1); 3363,
t
(NH), 1585,
(Cu–N); 1482, 1436,
(BF4); UV–Vis (CH2Cl2) kmax (nm) (
t
(HC@N), 1384,
t(C–N); 3066, (Ar–CH); 488 t
695, 518, (PPh3); 1058
t
t
e/
MÀ1 cmÀ1): 291(69,000), 346 (33,000), 454 (9000); 1H NMR
(CDCl3; 300 MHz): d 11.03 (s, 1H, NH), d 9.48 (s, 1H, HC@N), d
7.12–8.46; 13C NMR (CDCl3; 300 MHz): d 160.2 (N@CN), 150.7
(quin-C), 146.2 (HC@N), 138.9 (benzi-C), 133.4 (ph-C), 132.1
(quin-C), 130.3 (ph-C), 130.2 (ph-C), 129.6 (quin-C), 128.5 (ph-C),
128.4 (ph-C), 127.9 (quin-C), 126.4 (quin-C), 125.8 (quin-C),
125.2 (quin-C), 122.5 (quin-C), 119.4 (benzi-C), 112.1 (benzi-C);
ESI (MS): 859 [MÀBF4]+.
Yield: 89% (1.560 g, 3.107 mmol); Elemental analyses (C, H and
N, wt%) Anal. Calc. for C17H12N4: C, 78.98; H, 4.44; N, 20.58; found:
C, 78.89; H, 4.40; N, 20.67%; IR (KBr; cmÀ1); 3365,
t
(NH), 1618,
t
(HC@N); 1381,
t(C–N); 3056, t
(Ar–CH); 1H NMR (CDCl3;
300 MHz): d 10.26 (s, 1H, NH), d 9.31 (s, 1H, HC@N), d 7.29–8.35
(m, 10H, Ar–H); 13C NMR (CDCl3); 300 MHz: d 161.4 (N@CN),
152.9 (quin-C), 146.9 (HC@N), 139.9 (benzi-C), 132.6 (quin-C),
131.6 (quin-C), 129.9 (quin-C), 129.7 (quin-C), 128.8 (quin-C),
127.1 (quin-C), 126.9 (quin-C), 123.8 (quin-C), 120.9 (benzi-C),
113.7 (benzi-C); ESI (MS): 272 [M]+.
2.2.5. Synthesis of [Cu(L)(PPh3)2]PF6 (4)
Complex 4 was prepared by a procedure similar to that used for
the preparation of 1 except that, [Cu(CH3CN)4]NO3 was replaced by
[Cu(CH3CN)4]PF6 (0.342 g, 0.918 mmol).
Yield: 84% (0.911 g); Elemental analyses (C, H, N, wt%) Anal.
Calc. for C53H42N4P3F6Cu: C, 63.32; H, 4.21, N, 5.57; found: C,
63.22; H, 4.13, N, 5.69%; IR (KBr; cmÀ1); 3362,
t
(NH), 1589,
(Cu–N); 1482, 1436,
(PF6) UV–Vis (CH2Cl2) kmax (nm) (
t
2.2.2. Synthesis of [Cu(L)(PPh3)2]NO3 (1)
(HC@N), 1384,
t(C–N); 3066, (Ar–CH); 488 t
To a 10 ml acetonitrile solution of [Cu(CH3CN)4]NO3 (0.266 g,
695, 518, (PPh3); 842,562
t
t
e/
0.918 mmol),
2
equivalent of triphenylphosphine (0.481 g,
MÀ1 cmÀ1): 292 (62,000), 351 (29,000), 456 (11,000): 1H NMR
(CDCl3; 300 MHz): d 11.04 (s, 1H, NH), d 9.48 (s, 1H, HC@N), d
7.12–8.46; 13C NMR (CDCl3; 300 MHz): d 160.3 (N@CN), 150.7
(quin-C), 146.1 (HC@N), 139.0 (benzi-C), 133.5 (ph-C), 132.2
1.836 mmol) were added and the solution was stirred for 30 min.
The crystalline product [Cu(CH3CN)2(PPh3)2]NO3 obtained was
added to a stirring solution of ligand L (0.250 m, 0.918 mmol) in

124
S.S. Devkule, S.S. Chavan / Inorganica Chimica Acta 466 (2017) 122–129
(quin-C), 130.3 (ph-C), 130.2 (ph-C), 129.5 (quin-C), 128.5 (ph-C),
128.1 (ph-C), 127.8 (quin-C), 126.9 (quin-C), 125.7 (quin-C),
125.1 (quin-C), 122.6 (quin-C), 119.5 (benzi-C), 112.5 (benzi-C);
ESI (MS): 859 [MÀPF6]+.
3. Result and discussion
N-(2-quinolynylmethylene)-1H-bezimidazole (L) was synthe-
sized by the reaction of 2-amino benzimidazole with 2-quino-
linecarboxaldehyde. The obtained spectral data, elemental
analysis and mass spectra confirm the formation of L. The mononu-
clear copper(I) complexes 1–4 possessing L and phosphine ligands
were prepared (Scheme 1) via two simple steps. The complexes [Cu
(L)(PPh3)2]X (X = NO3, ClO4, BF4 and PF6) were firstly afforded by
the treatment of [Cu(CH3CN)4]X (X = NO3, ClO4, BF4 and PF6) with
two equivalent of PPh3 then one equivalent of L was slowly added.
The complexes prepared show a good thermal stability and are sol-
uble in common organic solvents such as dichloromethane, chloro-
form, acetonitrile, THF, methanol, ethanol etc. Composition and
identity of all the complexes were deduced from the satisfactory
elemental analysis, FTIR, UV–Visible, 1H NMR and 13C NMR spectra
and complex 3 by a single crystal X-ray diffraction study. Molar
conductivity values of all the complexes in 10À3 M solution of CH2-
Cl2 suggest that, they are 1:1 electrolytes indicating anions are not
coordinated to the central copper(I) atom. At room temperature all
the complexes are diamagnetic which is characteristic of presence
of copper(I) (d10).
2.3. X-ray crystallography
A single crystal of [(Cu(L)(PPh3)2]BF4ÁCH2Cl2 (3) suitable for X-
ray analysis was obtained by slow diffusion of diethyl ether in
dichloromethane solution. X-ray study performed on a Bruker
KAPPA Apex-II diffractometer. Data were collected in omega and
phi scan modes, MoKa = 0.71073 Å at room temperature with scan
width of 0.3° at h (0°, 90° and 180°) by keeping distance at 40 mm
between sample and fixed detector at 24°. The X-ray generator was
operated at 50 kV and 30 mA. The details of crystal data, data col-
lection and the refinement are given in Table 1. The X-ray data col-
lection was monitored by SMART program (Bruker, 2003). All the
data were collected using SAINT and SADABS programs (Bruker,
2003). SHELXL-2014 was used for the solution of the structure
and full matrix least-squares refinement on F2 [24]. Molecular
and packing diagrams were generated using ORTEP-3 [25] and
Mercury-3 [26].
3.1. Spectral characterization
2.4. Catalytic activity for the Sonogashira coupling of phenylacetylene
with aryl halides
The IR spectra of free ligand L exhibit a band at 3365 cmÀ1 is
due to ʋ(N–H). No significant shift in ʋ(NH) stretching were
observed in the infrared spectra of 1–4 in comparison with the free
ligand L feature non-involvement of the benzimidazole N–H in a
possible complexation to the metal ion [27]. On the other hand,
the band at 1618 cmÀ1 in the spectrum of L which is characteristic
The Sonogashira coupling reaction of phenylacetylene with dif-
ferent aryl halides catalyzed by copper(I) complexes was carried
out according to the procedure: 10 mol% of copper(I) catalyst
was added to 2 mmol of respective aryl halide, 2.5 mmol of pheny-
lacetylene, 2 mmol of K2CO3 in toluene and the reaction mixture
was stirred for 16 h at 90° under nitrogen. The reaction mixture
was then cooled to room temperature and the solution was filtered
to remove the precipitated base. The filtrate was concentrated and
crude product was purified by column chromatography using
ether:chloroform (9:1). The purified product obtained was charac-
terized by elemental analyses, IR, 1H NMR and mass spectral
studies.
of
1–4 indicative of
t
(HC@N) vibration shifted to lower frequency by 29–33 cmÀ1 in
p
-back bonding from the electron rich copper(I)
ion to vacant p⁄-orbital of the ligand [28]. The IR spectra of all cop-
per(I) complexes 1–4 exhibit an expected band due to the PPh3
ligand at 1482,1436,695 and 518 cmÀ1
. The strong band at
1375 cmÀ1 and medium intensity band at 821 cmÀ1 in the spec-
trum of 1 assigned for presence of ionic nitrate in the complexes.
The perchlorate complex 2 exhibit a broad band at 1097 (ʋ3) and
strong band at 622 (ʋ4) suggesting stretching vibration of non-
coordinated ClO4 ion in the complex [29]. A broad band at
1058 cmÀ1 in 3 corresponds to presence of antisymmetric ʋ(B-F)
stretching mode [30]. However, the strong band at 842 cmÀ1 and
562 cmÀ1 in 4 are consistent with presence of PFÀ6 anion in the
complex [31].
Table 1
Crystal data and structure refinements details for[(Cu(L)(PPh3)2]BF4ÁCH2Cl2 (3).
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C53H42CuN4P2, BF4, CH2Cl2
1032.12
Triclinic
The UV–Vis absorption spectra of the complexes were recorded
in CH2Cl2 solution (10À5 M) at room temperature and are shown in
Fig. 1. The free ligand L exhibit high energy bands at kmax 282 and
P-1
10.8832(6)
12.7145(8)
18.0915(11)
85.378(3)
81.531(3)
86.740(3)
2465.5(3)
2
b (Å)
c (Å)
336 nm assigned to
complexes 1–4 exhibited intense high energy absorption bands
at 291–294 and 346–352 nm are likely arise due to
p⁄ (benzim-
idazoline) and
p⁄(phosphine) intra-ligand (IL) transitions. The
red shift of
p⁄ transitions in 1–4 compare to free ligand L indicat-
p-
p⁄ transitions inside L. While the copper(I)
a
(°)
b (°)
p-
c
(°)
p-
V (A3)
p-
Z
Density (mg/m3)
1.390
0.673
ing involvement of imine and quinolynyl nitrogen in coordination
with copper(I) ion. In addition to these bands, the low energy
broad absorption bands observed in all copper(I) complexes at
451–458. This band remain absent in L and is assigned to the metal
l
(MoK ) (mmÀ1
)
a
F (000)
1060
Data collection
Temperature (K)
296(2)
to ligand charge transfer(MLCT) transition from d
p orbital of the
h mini.-maxi.(deg)
Data set [h, k, l]
Total, unique data, Rint
Observed data
2.28–24.11
copper(I) to the unoccupied p⁄ orbitals of ligand L [32]. The com-
plexes 1–4 are diamagnetic and hence provide no optical absorp-
tion band; no d-d transition is encountered for copper(I) with d10
configuration.
À12/12, À15/15, À21/21
[R(int) = 0.0656]
>2[spsbackslash]s(I)
Full-matrix least-squares on F2
8664/42/636
R1 = 0.0703, wR2 = 0.1813
R1 = 0.1208, wR2 = 0.2256
1.047
Refinement
Data/restraints/parameters
Final R indices [I > 2sigma(I)]
R indices (all data)
Goodness-of-fit
The 1H NMR spectra of copper(I) complexes 1–4 were recorded
in CDCl3 and analyzed on comparing with free ligand value. The
free ligand L displayed a singlet at d 9.31 ppm assigned to imine

S.S. Devkule, S.S. Chavan / Inorganica Chimica Acta 466 (2017) 122–129
125
H
N
H
N
CH3OH
NH2
+ OHC
N
N
Refluxed
N
N
N
L
[Cu(CH3CN)2(PPh3)2]X
CH2Cl2
H
N
N
N
X = NO3, ClO4, BF4 and PF6
N
Cu
PPh3
Ph3P
X-
1-4
Scheme 1. Synthetic route of L and its copper(I) complexes (1–4).
Fig. 1. UV–Visible absorption spectra of 1–4.
(HC@N) proton. In the spectra of 1–4, the signal of imine proton is
considerably deshielded and appears as a singlet at around d
9.48 ppm due to positive charge delocalization on the correspond-
ing C-atom through resonance resulting from the coordination of
ligand [33]. Benzimidazole N–H appears as
a singlet at
Fig. 2. Molecular structure of [Cu(L)(PPh3)2]BF4.CH2Cl2(3) showing 50% probability
ellipsoids. The hydrogen atoms, counter anion and solvent molecules have been
removed for clarity.
10.26 ppm in L is significantly shifted to downfield side at
ꢀ11.03 ppm in all copper(I) complexes. However, the broad multi-
plet appeared in the range d 7.11–8.49 ppm for 1–4 assigned to the
PPh3 protons together with ring protons of ligand L.
one CH2Cl2 molecule, and exhibit a highly distorted tetrahedral
geometry around the copper(I) with P2CuN2 coordination The dis-
3.2. X-ray structure of [(Cu(L)(PPh3)2]BF4ÁCH2Cl2 (3)
Table 2
Selected bond lengths (Ǻ) and bond angles (°) for 3.
The crystals of [(Cu(L)(PPh3)2]BF4ÁCH2Cl2 (3) were grown by
slow diffusion of diethyl ether into the solution of complex in
dichloromethane and its structure was determined by X-ray crys-
tallography. The molecular structure of 3 along with atom number-
ing scheme is illustrated in Fig. 2 and selected bond lengths and
bond angles are collected in Table 2. X-ray analysis reveals that
complex 3 crystallizes in triclinic space group with discrete [Cu
(L)(PPh3)2]+ cation and tetrafluroborate as counter anion with
Bond lengths
Bond Angles
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–P(1)
Cu(1)–P(2)
2.121(5)
2.105(5)
2.2707(15)
2.2659(16)
N(2)–Cu(1)–N(1)
N(2)–Cu(1)–P(2)
N(1)–Cu(1)–P(2)
N(2)–Cu(1)–P(1)
N(1)–Cu(1)–P(1)
P(2)–Cu(1)–P(1)
78.19(18)
113.41(14)
108.04(13)
110.95(13)
116.16(13)
121.95(6)

126
S.S. Devkule, S.S. Chavan / Inorganica Chimica Acta 466 (2017) 122–129
torted tetrahedral coordination geometry of copper(I) is completed
by imine nitrogen, quinolynyl nitrogen and two phosphorous
atoms from two PPh3 ligands. The largest deviation from the ideal
tetrahedral geometry is arises from the restricted bite angle of the
chelating ligand. The intra-ligand chelate angles N(2)–Cu(1)–N(1)
is much less than 109.4°, being 78.19(18)°. However, the P(2)–Cu
(1)–P(1) 121.95 (6) Å angle have open up due to the steric effects
from bulky PPh3 ligands. The average Cu–N and Cu–P bond lengths
are 2.113 and 2.2683 Å, respectively and are comparable to those
reported for [Cu(L)(PPh3)2]BF4Á2CH2Cl2 complexes [2.076 and
2.2591 Å] [34]. The Cu(1)–N(1) (Pyridyl bond length, 2.121(5)° is
longer than Cu(1)–N(2) (imine bond length, 2.105(5)°), which
means that the intermolecular attraction between Cu(I) center
and N(imine) is stronger than that between Cu(I) center and N(qui-
nolynyl) [35]. Torsion angles in the chelating ring are given in
Table 3. The chelating ring Cu(1)–N(1)–C(45)–C(44) and Cu(1)–N
(2)–C(44)–C(45) are 3.5(6)° and 2.0(7)°. The significant strain in
the chelate ring is observed by the deviations from 120° for the
angles about the N atom; Cu(1)–N(1)–C(45), Cu(1)–N(1)–C(53),
Cu(1)–N(2)–C(44) and Cu(1)–N(2)–C(43) are 112.7(4)°, 129.8(4)°,
113.6(4)° and 125.2(4)°.
Fig. 3. Perspective view of cell packing in the complex [Cu(L)(PPh3)2]BF4.CH2Cl2(3).
In the heteroatomic part of benzimidazoline, the angles N(4)–C
(43)–N(2), 126.1(6)°, N(3)–C(43)–N(2), 120.8(5)° and N(3)–C(43)–
N(4), 113.1(6)° indicate the sp3 hybridize state of the carbon atom
and the geometry around C(43) can be viewed in terms of a dis-
torted tetrahedral geometry. The two N–C(sp2) bond distances [N
(2)–C(44), 1.267(8)° and N(3)–C(43), 1.301(8)°] show double bond
character, while one N(4)–C(43), 1.359(7)° show single bond char-
acter. The bond angles around N(3) and N(4) are C(43)–N(3)–C(37),
104.7(5)° and C(43)–N(4)–C(42), 107.1(6)° respectivaly. Further,
the tortional angle of N(2)–C(43)–N(3)–C(37) is 179.1(5° indicating
an periplanar arrangement.
The crystal packing structure of [Cu(L)(PPh3)2]BF4. CH2Cl2 (3)
was given in Fig. 3. In the space packing of 3 there exist plenty of
weak H–F bonding between the F(1) atoms of BFÀ4 anion and the
hydrogen atoms of the phenyl rings of PPh3 to form supramolecu-
lar structure.
3.3. Photoluminescence
The photoluminescence property of ligand L and its copper(I)
complexes 1–4 were studied at room temperature in CH2Cl2 solu-
tion (10À5 M). The emission spectra of 1–4 are shown in Fig. 4 and
the data are summarized in Table 4. Free ligand L emits a green col-
our centered at kmax = 532 nm with an excitation at 280 nm attrib-
Fig. 4. Emission spectra of 1–4.
Table 4
Emission data of copper(I) complexes in CH2Cl2(10À5 M) (1–4).
uted to fluorescent emission from
a ligand centered p-
p⁄
Complex
kem (nm)
/
s
(ns)
Kr (sÀ1/107)
Knr (sÀ1/109)
transition. Upon excitation at ꢀ295 nm, complexes 1–4 show
steady state marked differences in emission behavior at kmax 706,
704, 702 and 711 nm with lifetime of 2.48, 2.51 2.54 and 2.60 ns,
respectively. The complexes do not show significant emission
when they are excited at their MLCT band maxima, hence the
emission band in 1–4 may be assigned to the ligand to ligand
charge transfer (LLCT) or intra-ligand charge transfer (ILCT) or
admixture of them. The enhancement of fluorescence efficiency
observed in 1–4 may be due to coordination of L and PPh3 ligands
to copper(I) ion, which effectively increases the rigidity to the
L
1
2
3
4
632
706
704
702
711
0.075
0.084
0.092
0.088
0.096
2.12
2.48
2.51
2.54
2.60
3.537
3.387
3.665
3.464
3.692
0.436
0.369
0.360
0.359
0.347
Table 5
Electrochemical data for copper(I) complexes (1–4).
Complex
Epa (V)
Epc (V)
D
Ep (mV)
E1/2 (V)
1
2
3
4
0.741
0.743
0.745
0.751
0.621
0.624
0.629
0.632
120
119
116
120
0.681
0.683
0.687
0.691
Table 3
Torsion angles for chelating ring.
Supporting electrolyte: n-Bu4NClO4 (0.05 M); complex: 0.01 M; solvent: CH2Cl2;
1/2 = 1/2(Epa + Epc); Scan rate: 50 mV sÀ1
Cu(1)–N(1)–C(45)–C(44)
Cu(1)–N(2)–C(44)–C(45)
Cu(1)–N(1)–C(53)–C(52)
Cu(1)–N(1)–C(53)–C(48)
Cu(1)–N(2)–C(43)–N(3)
Cu(1)–N(2)–C(43)–N(4)
3.5(6)
2.0(7)
À6.0(8)
172.9(4)
À14.5(8)
164.8(5)
E
.
structure of the complexes that restricts vibrational relaxation.
Moreover, intermolecular and intramolecular
in 1–4 along with a large P–Cu–P bite angle may also play a key
p
Á Á Áp⁄ interactions

S.S. Devkule, S.S. Chavan / Inorganica Chimica Acta 466 (2017) 122–129
127
Fig. 5. Cyclic voltammogram of 1–4.
Table 6
Sonogashira coupling reaction of phenylacetylene with aryl halides.
Entry
Phenylacetylene
Aryl halide
Product
Complex
% yield
1.
2.
3.
4.
1
2
3
4
71
80
76
83
I
5.
6.
7.
8.
1
2
3
4
77
84
80
91
NH2
I
I
NH2
9.
1
2
3
4
66
74
70
79
Br
Br
10.
11.
12.
Reaction conditions: phenylacetylene, 2.5 mmol; aryl halide, 2 mmol; copper(I) catalyst (10 mol%); K2CO3 (2 mmol); Toluene, 20 ml; temperature 90 °C; reaction time 16 h.
role for the enhancement of the luminescence behavior of the com-
plexes [36]. It is to be noted that the emission energies of all the
complexes (1–4) are sensitive to the size of the counter ion, follow-
ing the sequence PF6 > ClO4 > BF4 > NO3 [37]. These results could be
attributed to coordinating ability of the counterion as well as dif-
ferences in solubility of the complexes in CH2Cl2.
is not equal to 1, the values of
D
Ep
(
D
Ep = Epa À Epc) ranging
from 116 to 120 mV. These results confirm the quasire-
versible redox behavior of these complexes and are in good
agreement with the similar copper(I) complexes reported in
the literature [38].
The experimental measured
s and / values are used to calculate
3.5. Catalytic properties
the radiative kr and nonradiative knr rate constants. The knr values
of 1–4 show the marked decrease displaying that the rigidity and
the size of the counterion play a dominant role in CH2Cl2 solution.
The Pd-catalyzed Sonogashira cross-coupling reaction of termi-
nal alkyne with aryl halides is one of the most powerful and reli-
able tool for the synthesis of polyfunctional alkyne, which finds
extensive applications in pharmaceuticals, dyes, sensors, electron-
ics, polymers, guest-host constructs, natural products and hetero-
cycle synthesis [39–42]. Traditionally, such coupling reaction
have been performed with palladium complex catalyst such as
PdCl2(PPh3)2 or Pd(PPh3)4 [43]. However, the cost of reagents,
removal of trace palladium from late stage synthetic intermediate,
and difficulties in coupling of electron-rich or ortho-substituted
aryl halides are the drawbacks of this method. Copper-catalyzed
Sonogahira cross-coupling reaction is another choice of the reac-
tion for the production of alkyne due to their low cost advantage,
low toxicity and environmentally benign character. However, most
of the copper-catalyzed couplings reported so far are not well
defined [44], as they are generated in situ based on copper salt,
ligands and additives. Only few papers have been reported to use
3.4. Cyclic voltammetry
The electrochemical behavior of the copper(I) complexes 1–4
was examined cyclic voltammetrically in 0.01 M CH2Cl2 solution
and the results are displayed in Table 5. The cyclic voltammo-
gram of 1–4 are shown in Fig. 5. All copper(I) complexes 1–4
displayed oxidative response at 0.741–0.751 V (Epa) correspond-
ing to Cu(I)/Cu(II) oxidation, whilst the potential appeared in
the reverse scan at 0.621–0.632 V (Epc) is associated with reduc-
tion of Cu(II) to Cu(I). The Cu(I)/Cu(II) redox couple at
E
½
= 0.685 V for 1–4 is also supported by a comparison between
cyclic voltammetry experiments of ferrocene which involve Fe
(II)/Fe(III) couple occurs in very similar potential range at same
scan rate. The ratio of peak current (Ipc/Ipa) for complexes 1–4

128
S.S. Devkule, S.S. Chavan / Inorganica Chimica Acta 466 (2017) 122–129
Table 7
Microanalytical and spectral data of coupling product.
Compound
C, H, N found (calculated)
IR (cmÀ1
)
Mass
1H NMR (d ppm)
C
H
N
Diphenylacetylene
94.24
5.53
–
2156
m/z 178 [C6H5C„CC6H5]+, 77 [C6H5]+
d 7.43–7.56, (m, Ar-H)
(94.34)
86.86
(87.01)
65.29
(5.66)
5.68
(5.74)
3.48
–
4-Amino-
diphenylacetylene
4-Bromo-
7.34
(7.22)
–
3413, 3295,
2153
2156
m/z 193 [C6H5C„CC6H4NH2]+,
178 [C6H5C„CC6H5]+, 77 [C6H5]+
m/z 257 [C6H5C„CC6H4Br]+,
178 [C6H5C„CC6H5]+, 77 [C6H5]+
d 7.42–7.68, (m, Ar-H) d 3.83,
(s, 2 H, NH2)
d 7.43–7.56, (m, Ar-H)
diphenylacetylene
(65.40)
(3.53)
–
K2CO3
Cu(I) catalyst,
Toluene,
R
R
+
I
900C
p-substituted diphenylacetylene
R = H, NH 2 , Br
Scheme 2. Sonogashira coupling of phenylacetylene with aryl halides catalyzed by 1–4.
R1
R2
[Cu(L)(PPh3)2]+
R1
R1
significant electronic effect was observed for substituted aryl
halide containing electron donating group at para-position. It was
also observed that the copper(I) complexes with different counter
anions exhibit different activities. It is evident that the copper(I)
complex with PFÀ6 ion exhibit higher catalytic activities than the
complexes with ClOÀ4 , BF4À and NOÀ3 as their counter anions and fol-
low the sequence PF6À > ClO4À > BF4À > NOÀ3 . These results could be
attributed to difference in coordinating ability of counterion with
metal ion as well as difference in solubility of the complexes in sol-
vent during the reaction.
H
R1
H+
Cu(L)(PPh3)2
Cu(L)(PPh3)2
R1
R2
X
R2
KHCO3 + KX
The probable mechanism for the coupling of phenylacetylene
with aryl halides using present complexes 1–4 is illustrated in
Scheme 3. At first copper(I) complex activates C–H bond of the ter-
minal alkyne to form a copper-acetylide intermediate (species I),
which on oxidative addition of aryl halide leads to formation of
species II. The species II again activated in presence of base to give
species III which undergoes reductive elimination to give diphenyl-
acetylene and regenerate corresponding copper(I) catalyst.
Cu(L)(PPh3)2
K2CO3
R2
X
Scheme 3. Probable mechanistic route for Sonogashira coupling of phenylacetylene
with aryl halides using 1–4.
copper complex catalyst for this C–C bond formation process
[45,46]. In order to check the catalytic efficiency of copper(I) com-
plexes 1–4, the Sonogashira coupling reaction of phenylacetylene
with aryl halide was carried out using K2CO3 as a base and solvent
toluene at 90 °C (Scheme 2). Under these reaction conditions, cou-
pling reactions of phenylacetylene with aryl halides proceeded
very smoothly by attaining the desired diphenylacetylene product
in high yields. The isolated product was characterized by elemental
analysis, IR, 1H NMR and mass spectral studies (Table 7). When no
catalyst was added, the blank reaction in solvent toluene and
K2CO3 as base exhibited extremely low reactivity results into
decrease in yield of diphenylacetylene with many byproducts.
The catalytic efficiency of 1–4 was compared with the previously
reported [47] similar type of copper(I) complexes and it was found
that all reactions proceeded at relatively low temperature and
reached the yield of diphenylacetylene up to 66–91% (Table 6).
With iodobenzene the coupling yield reached up to 71–83%
(Table 6, entries 1–4). With 1-bromo-4-iodoaniline containing
electron withdrawing group at para position, the coupling yield
was observed up to 66–79% (Table 6, entries 9–12). However, with
4-iodoaniline containing electron donating NH2 group at para
position, the coupling reaction proceeds with considerable
increase in the yield up to 77–91% (Table 6, entries 5–8). These
results confirmed that the variety of functional groups such as
bromo and amino tolerated on aryl halide component and
4. Conclusion
In conclusion, a series of mixed ligand copper(I) complexes have
been prepared by the reaction of N-(2-quinolynylmethylene)-1H-
benzimidazole with [Cu(MeCN)2(PPh3)2]NO3, [Cu(MeCN)2(PPh3)2]
ClO4, [Cu(MeCN)2(PPh3)2]BF4, [Cu(MeCN)2(PPh3)2]PF6 and charac-
terized. Complex [Cu(L)(PPh3)2]BF4. CH2Cl2 (3) crystallizes in a tri-
clinic space group P-1 and show a distorted tetrahedral geometry
around copper(I). The quasireversible redox process (E1/2 = 0.685 V
versus Fc0/+) attributed to Cu(I)/Cu(II) couple. The complexes exhibit
red emission, and complex 4 shows highest emission intensity in
CH2Cl2 solition. The emission observed in all complexes primarily
related to ligand charge transfer (LLCT) or intra-ligand charge trans-
fer (ILCT) or mixture of them. These complexes have been success-
fully employed as a catalyst for the sonogashira coupling of
phenylacetylene with aryl halides at low temperature. The differ-
ences in size of the counterions in the complexes have a marked
effect on catalytic properties of the complexes.
Acknowledgement
We gratefully acknowledge Head, Sophisticated Analytical
Instrument Facility Center, IIT, Madras, India for providing single
crystal X-ray facilities.

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