Copper(I) complexes of 2-(benzen-1-yl)methyleneamino-3-aminomaleonitrile and triphenylphosphine ligands: synthesis, characterization, luminescence and catalytic properties

Article abstract of DOI:10.1007/s11243-017-0138-8

Some mixed ligand copper(I) complexes of general formula [Cu(L)(PPh₃)₃]X (X?=?Cl (1), ClO₄ (2), BF₄ (3) or PF₆ (4); L?=?2-(benzen-1-yl)methyleneamino-3-aminomaleonitrile) were prepared and characterized by physicochemical and spectroscopic methods. A single-crystal X-ray diffraction study of [Cu(L)(PPh₃)₃]CIO₄ (2) revealed that the copper atom is four coordinated in a distorted tetrahedral geometry. Electrochemical studies of complexes 1–4 show quasireversible redox behavior corresponding to the Cu(I)/Cu(II) couple. Room temperature luminescence is observed for all four complexes. These complexes proved to be effective catalysts for the Sonogashira coupling of terminal alkynes with aryl halides at 90?°C.

Full text of DOI:10.1007/s11243-017-0138-8

Transit Met Chem (2017) 42:347–356
DOI 10.1007/s11243-017-0138-8
Copper(I) complexes of 2-(benzen-1-yl)methyleneamino-
3-aminomaleonitrile and triphenylphosphine ligands: synthesis,
characterization, luminescence and catalytic properties
1
1
S. S. Devkule
•
S. S. Chavan
Received: 7 January 2017 / Accepted: 20 March 2017 / Published online: 30 March 2017
Ó Springer International Publishing Switzerland 2017
Abstract Some mixed ligand copper(I) complexes of
general formula [Cu(L)(PPh ) ]X (X = Cl (1), ClO (2),
BF (3) or PF (4); L = 2-(benzen-1-yl)methyleneamino-
aldehyde [7]. These compounds are important as synthetic
intermediates and also used in pharmacology [8], synthesis
of conjugate linear polymers [9] and in thermostable opti-
cal materials [10]. However, the coordination chemistry of
Schiff bases derived from DAMN is not well explored.
Meanwhile, copper(I) complexes of phosphorous-contain-
ing ligands have been used to carry out a wide range of
organic transformations such as allylic amination, hydro-
genation, copolymerization, and cross-coupling reactions
[11–14]. The steric crowding and p-acidic character
imparted by these ligands are important prerequisites for
stabilizing the copper(I) complexes and their redox, pho-
tophysical and catalytic behavior.
3
3
4
4
6
3
-aminomaleonitrile) were prepared and characterized by
physicochemical and spectroscopic methods. A single-
crystal X-ray diffraction study of [Cu(L)(PPh ) ]CIO (2)
3
3
4
revealed that the copper atom is four coordinated in a
distorted tetrahedral geometry. Electrochemical studies of
complexes 1–4 show quasireversible redox behavior cor-
responding to the Cu(I)/Cu(II) couple. Room temperature
luminescence is observed for all four complexes. These
complexes proved to be effective catalysts for the Sono-
gashira coupling of terminal alkynes with aryl halides at
9
0 °C.
In this context, we report here the ligational behavior of
2
-(benzen-1-yl)
L) with copper(I) in the presence of triphenylphosphine as
a coligand. The catalytic and luminescence behavior of the
complexes have been investigated. Complexes
[Cu(L)(PPh ) ]X (1–4) have been prepared and character-
methyleneamino-3-aminomaleonitrile
(
Introduction
Numerous mononuclear copper(I) complexes have been
reported in the literature. Their structures depend on the
nature of the ligands, metal-to-ligand ratio, reaction con-
ditions and metal–ligand interactions [1–5]. Diaminoma-
leonitrile (DAMN) acts as a symmetric ligand. It is known
as an unsaturated electron rich ligand, being a tetramer
resulting from the polymerization of HCN under basic
conditions [6]. The reaction of DAMN with aromatic
aldehydes is interesting as in every case the 1 ? 1 con-
densed Schiff base is obtained, even in presence of excess
3
3
ized by physicochemical and spectroscopic techniques and
additionally complex 2 by X-ray crystallography. The
luminescence behavior and thermal stabilities of the com-
plexes have been studied. The catalytic performance of the
complexes for the Sonogashira coupling of terminal alky-
nes with aryl halides is also reported.
Experimental
Materials and methods
&
S. S. Chavan
sanjaycha2@rediffmail.com
Benzaldehyde (Alfa Aesar), 2,3-diaminomaleonitrile
(Aldrich, USA), triphenylphosphine (Aldrich, USA) were
1
of reagent grade and used without further purification.
CuCl [15], Cu(CH CN) ]ClO [16], [Cu(CH CN) ]BF
4
Department of Chemistry, Shivaji University, Kolhapur,
MS 416004, India
3
4
4
3
4
123

3
48
Transit Met Chem (2017) 42:347–356
[
16] and [Cu(CH CN) ]PF [17] were prepared according
4
2 h at room temperature under nitrogen. The volume of the
solvent was reduced under vacuum, and the solid product
was precipitated by diffusion of diethyl ether into the filtrate.
Yield: 0.905 g (82%); Elemental analyses (C, H, N, wt%)
Anal. Calc. for C H N P ClCu: C, 72.1; H, 4.9, N, 5.1;
3
6
to the literature procedures.
Elemental analyses (C, H and N) were obtained on a
Thermo Finnegan FLASH EA-1112 CHNS analyzer. IR
spectra (KBr pellets) were recorded on a PerkinElmer-100
6
5 53 4 3
1
13
-1
FTIR spectrometer, H and C NMR spectra of the samples
found: C, 72.1; H, 4.9; N, 5.2%; IR (KBr, m/cm ); 3413 s,
3303 w, 2237 w, 2195 s, 1622 s, 1483 s, 1435 s, 694 s, 518 s;
dissolved in CDCl were recorded on a Bruker 300 MHz
3
6
-1
-1
instrument using TMS as an internal standard. Electronic
UV–Vis (CH Cl ) k
(nm) (e 910 , M cm ): 283
(0.81), 334 (0.39), 442 (0.08); H NMR (CDCl ; 300 MHz):
2
2
max
-6
1
spectra were recorded in dichloromethane (10 M) on a
Shimadzu 3600 UV–Vis–NIR spectrophotometer. Mass
spectra were measured on a GCMS Shimadzu-2010 instru-
3
d 8.19 (s, 1H, HC=N), d 7.42–7.87 (m, 50H, phenyl), d 7.39
1
3
(s, 2H, NH2); C NMR (CDCl ; 300 MHz): d 156.8
3
ment. Emission spectra were recorded using a PerkinElmer LS
3
(HC=N), d 134.75–128.96 (phenyl-C), d 127.14 (Cu–CN), d
115.88(CN), d 113.57 (HCNC=C), d 104.59 (CNC=C).
5
5 spectrofluorometer equipped with quartz cuvettes of 1 cm
path length at room temperature. Thermal analysis was carried
out on a PerkinElmer thermal analyzer in nitrogen atmosphere
at a heating rate of 10 °C/min. Cyclic voltammetry measure-
ments were taken with a CH-400A Electrochemical Analyzer.
A Standard three electrode system, consisting of a Pt disk
working electrode, Pt wire counter electrode and Ag/AgCl
reference electrode was used. Tetrabutyl ammonium per-
chlorate (TBAP) was used as the supporting electrolyte, and all
measurements were taken in CH Cl solution at room tem-
Synthesis of [Cu(L)(PPh ) ]CIO (2)
4
3
3
Complex 2 was prepared by a similar procedure to that
used for complex 1, except that CuCl was replaced by
[Cu(CH CN) ]ClO (0.334 g, 1.02 mmol).
3
4
4
Yield: 1.095 g (82%); Elemental analyses (C, H, N, wt%)
Anal. Calc. for C H O N P ClCu: C, 68.1; H, 4.6; N, 4.89;
6
5 53 4 4 3
-
1
found: C, 68.0; H, 4.63; N, 4.9%; IR (KBr, m/cm ); 3415 s,
3306, 2237 w, 2197 s, 1610 s, 1481 s, 1436 s, 693 s, 519 s,
2
2
1
-
perature with a scan rate 100 mV s .
6
1
094 b, 621 w; UV–Vis (CH Cl ) k
(nm) (e 910 ,
cm ): 280 (0.69), 332 (0.32), 438 (0.06); H NMR
2
2
max
-
1
-1
1
Synthesis of L
M
(
CDCl ; 300 MHz): d 8.20 (s, 1H, HC=N), d 7.42–7.88 (m,
3
1
3
2
-[(Benzen-1-yl)methyleneamino]-3-aminomaleonitrile
L) was prepared by a modification of the method described
in the literature [18]. To a solution of benzaldehyde (0.500 g,
.71 mmol) in methanol (10 ml), a solution of 2,3-di-
aminomaleonitrile (0.509 g, 4.71 mmol) in methanol
10 ml) was added dropwise with constant stirring. The
50H, phenyl), d 7.38 (s, 2H, NH2); C NMR (CDCl3;
300 MHz): d 156.59 (HC=N), d 134.78–128.93 (phenyl-C),
d 127.13 (Cu–CN), d 115.89 (CN), d 113.55 (HCNC=C), d
104.57 (CNC=C).
(
4
(
Synthesis of [Cu(L)(PPh ) ]BF (3)
3
3
4
resulting mixture was refluxed at about 80 °C for 5 h until
completion of the reaction (checked by TLC). The pro-
duct 2-[(benzen-1-yl)methyleneamino]-3-aminomaleonitrile
obtained was filtered off and purified by column chro-
matography (ether:dichloromethane) to afford a yellowish-
brown solid.
Complex 3 was prepared by a similar procedure to that
used for complex 1, except that CuCl was replaced by
[Cu(CH CN) ]BF (0.321 g, 1.02 mmol).
3
4
4
Yield: 1.058 g (80%); Elemental analyses (C, H, N,
wt%) Anal. Calc. for C H F N P BCu: C, 68.8; H, 4.7;
6
5 53 4 4 3
-
1
Yield: 0.847 g (84%); Elemental analyses (C, H and N,
wt%) Anal. Calc. for C H N : C, 67.3; H, 4.1, N, 28.5;
N, 4.9; found: C, 68.8; H, 4.6; N, 4.9%; IR (KBr, m/cm );
3413 s, 3304 w, 2237 w, 2195 s, 1620 s, 1482 s, 1435 s,
1
1 8 4
-1
6
found: C, 67.3; H, 4.09; N, 28.5%; IR (KBr, m/cm ): 3404 s,
694 s, 517 s, 1084 s; UV–Vis (CH Cl ) k
M
(nm) (e 910 ,
cm ): 283 (0.83), 334 (0.45), 432 (0.10); H NMR
2
2
max
1
298w, 2237w, 2204s, 1605s; HNMR(CDCl ; 300 MHz):
-1
-1
1
3
3
d 8.46 (s, 1H, HC=N), d 7.46–7.96 (m, 5H, phenyl), d 7.45 (s,
(CDCl ; 300 MHz): d 8.18 (s, 1H, HC=N), d 7.40–7.86 (m,
50H, phenyl), d 7.38 (s, 2H, NH2); C NMR (CDCl3;
300 MHz): d156.7(HC=N), d 134.79–128.92 (phenyl-C), d
127.16 (Cu–CN), d 115.89 (CN), d 113.57 (HCNC=C), d
3
1
3
13
2
1
1
H, NH ); C NMR (CDCl ; 300 MHz): d 156.61(HC=N), d
28.99–128.88 (phenyl-C), d 115.84 (CN), d 114.85 (CN), d
13.61 (HCNC=C), d 104.65 (CNC=C).
2
3
104.58 (CNC=C).
Synthesis of [(CuL)(PPh ) ]Cl (1)
3
3
Synthesis of [Cu(L)(PPh ) ]PF (4)
6
3
3
To a solution of CuCl (0.102 g, 1.02 mmol) in MeCN
10 ml), three equivalents of triphenylphosphine (0.802 g,
.06 mmol) and one equivalent of L (0.200 g, 1.020 mmol)
were added. The resulting reaction mixture was stirred for
(
Complex 4 was prepared by a similar procedure to that
used for complex 1, except that CuCl was replaced by
[Cu(CH CN) ]PF (0.379 g, 1.02 mmol).
3
3
4
6
1
23

Transit Met Chem (2017) 42:347–356
349
Yield: 1.118 g (81%); Elemental analyses (C, H, N, wt%)
Anal. Calc. for C H F N P Cu: C, 65.5; H, 4.4; N, 4.7%;
Table 1 Crystal data and structure refinements details for
[
3 3 4
Cu(L)(PPh ) ]ClO (2)
6
5
53
6
4
4
-
1
found: C, 65.4; H, 4.4; N, 4.8%; IR (KBr, m/cm ); 3418 s,
Empirical formula
Formula weight
Crystal system
Space group
65 4 4 3
C H53ClCuN O P
3
304 w, 2237 w, 2193 s, 1608 s, 1482 s, 1435 s, 694 s, 517 s,
6
1146.01
Monoclinic
P2(1)/n
12.2880 (7)
33.5542 (14)
13.9490 (7)
90.00
-1
8 (nm) (e 910 , M
cm ): 282 (0.64), 332 (0.35), 442 (0.08); H NMR (CDCl ;
41 s, 558 m; UV–Vis (CH Cl ) k
2
2
max
-
1
1
3
3
00 MHz): d 8.18 (s, 1H, HC=N), d 7.40–7.88 (m, 50H,
˚
a (A)
1
3
phenyl), d 7.39 (s, 2H, NH2); C NMR (CDCl ; 300 MHz):
˚
b (A)
3
d 156.8 (HC=N), d 134.78–128.96 (phenyl-C), d 127.16
˚
c (A)
(
Cu–CN), d 115.87(CN), d 113.57 (HCNC=C), d 104.58
a (°)
b (°)
c (°)
(
CNC=C).
91.225
90.00
Sonogashira coupling reactions
3
V (A )
5750.4 (5)
4
Z
The coupling of phenylacetylene with aryl halides cat-
alyzed by these copper(I) complexes was carried out
according to the following procedure: The copper(I) cata-
lyst (10 mol %) was added to the respective aryl halide
3
Density (mg/m )
1.324
-
1
l (M
F (000)
Data collection
K
0 a
) (mm
)
0.562
2376
(
(
2 mmol), phenylacetylene (2 mmol), and K CO3
2
Temperature (K)
h mini.-maxi. (°)
Data set [h, k, l]
123(2)
2 mmol) in toluene (10 ml), and the reaction mixture was
1.899–25.498
stirred for 16 h at 90 °C 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 to dryness, and the crude product
was purified by column chromatography using ether/chlo-
roform (9:1). The purified product was then characterized
-14/14, -40/40, -16/16
[R(int) = 0.0769]
Total, unique data, Rint
Observed data
[2\s(I)
Full-matrix least-squares on F
2
Refinement
No. of reflection, No. of
parameters
67,934/10,696 (Rint) = 0.0558
1
by elemental analyses, IR, H NMR and mass spectral
Final R indices [I [ 2r(I)]
R indices (all data)
Goodness-of-fit
R1-0.0663, wR2-0.1760
R1-0.0961, wR2-0.1564
1.023
studies.
X-ray crystallography
A single crystal of complex 2 suitable for X-ray analysis
was obtained by slow evaporation of a saturated solution of
the complex in methanol. The X-ray diffraction study was
performed on a Bruker Apex-II CCD diffractometer with
literature procedure. The obtained spectral data, elemental
analysis and mass spectra confirm the formation of L. The
mixed ligand copper(I) complexes [Cu(L)(PPh ) ]X were
3
3
prepared by the reactions of L with CuCl, [Cu(CH3-
CN) ]ClO , [Cu(CH CN) ]BF or [Cu(CH CN) ]PF in the
˚
graphite-monochromatized MoKa radiation (0.71073 A)
4
4
3
4
4
3
4
6
with scan width of 0.30 at h (0°, 90°, 180°). The X-ray
generator was operated at 50 kV and 30 mA. Details of the
crystal data, data collection and the refinement are given in
Table 1. The structure was solved by direct methods using
the SHELXS 93 program and refined using SHELXL-2014
software [19]. Molecular and packing diagrams were gen-
erated using ORTEP-3 [20] and Mercury [21].
presence of triphenylphosphine. The complexes show good
thermal stability and are stable to moisture, both in solution
and in the solid phase. They are soluble in common organic
solvents such as dichloromethane, chloroform, acetonitrile,
tetrahedrofuran, methanol and ethanol. The complexes
were characterized by elemental analysis, FTIR, UV–visi-
1
13
ble, H and C NMR spectra; in addition, the single-
crystal X-ray structure of complex 2 was obtained. Molar
-
conductivity values of 10 M solutions in CH Cl of each
3
2
2
Results and discussion
of the complexes suggest that they are 1:1 electrolytes,
indicating that the anions are not coordinated to the cop-
per(I) center. At room temperature, all the complexes are
diamagnetic, which is characteristic of copper(I).
Synthesis and characterization
The synthetic route to complexes 1–4 is shown in
Scheme 1. 2-[(Benzen-1-yl) methyleneamino]-3-amino-
maleonitrile (L) was synthesized by the reaction of 2,3-
diaminomaleonitrile with benzaldehyde according to the
The IR frequencies of selected features in the spectra of
the complexes are given in the experimental section. The
IR spectrum of free L exhibits two characteristic bands of
-
1
the nitrile t(C:N) group, at 2237 and 2204 cm . The
123

3
50
Transit Met Chem (2017) 42:347–356
Scheme 1 Synthetic route of
L and its copper(I) complexes
N
N
H
O
N
N
MeOH
N
NH2
+
H N
NH2
2
L
[
Cu(CH CN) ]X
CH Cl2
3 4
2
PPh3
Ph3P
PPh3
Cu
Ph3P
N
N
-
-
-
-
X= Cl , ClO , BF , PF
6
4
4
N
NH2
X
1-4
slight shifts of these bands toward lower frequency, at
-
7.45 ppm for free L, are shifted upfield to 7.38 ppm for the
complexes, indicating noninvolvement of NH2 in
coordination.
1
2
193–2197 cm
for complexes 1–4, are ascribed to
involvement of the nitrile group in coordination with the
-
1
metal atom [22]. A strong band at 1605 cm
in the
The UV–Vis absorption spectra of the complexes were
-
recorded in CH Cl solution (10 M) at room temperature
6
spectrum of the free ligand L corresponding to m(HC=N) is
shifted to higher frequency, appearing at 1608–1622 cm
2
2
-
1
and are shown in Fig. 1. The free ligand L displayed two
absorption bands at 274 and 338 nm, assigned to p–p*
transitions. Complexes 1–4 show an intense absorption
band at 280–344 nm, most likely originating from L and
in the spectra of the complexes; this suggests that the imine
group is not coordinated. The spectrum of L shows broad
-
1
bands at 3404 and 3298 cm
due to msym and masym
vibrations of NH which are also shifted to higher fre-
PPh . The red shifts in the p–p* absorptions of 1–4 com-
2
3
quency in the spectra of the complexes, suggesting that the
pared to free L indicate conjugation of L, resulting in a
smaller p–p* energy gap. In addition to the high energy
absorption, complexes 1–4 displayed a low energy weak
band at 448–456 nm corresponding to metal-to-ligand
charge transfer from the dp orbital of copper(I) to the
unoccupied p orbitals of L, probably mixed with some
intra-ligand charge transfer character [27].
NH groups are not involved in coordination. The presence
2
of the PPh ligand can be easily identified from the strong
3
-
bands at around 1482, 1436, 694 and 518 cm . The per-
1
-
1
chlorate complex 2 has a broad band at 1094 cm (m ) and
3
-
1
unsplit band at 621 cm (m ), assigned to the non-coor-
4
dinated ClO ion in this complex [23]. For the tetrafluo-
4
-
1
roborate complex 3, an intense band at 1084 cm
attributed to the antisymmetric t(B-F) stretching mode
is
X-ray crystal structure
-
24], while strong bands at 841 and 558 cm for complex
1
[
-
are consistent with the PF anion in this complex [25].
4
The single-crystal X-ray analysis of [Cu(L)(PPh ) ]ClO
4
6
3 3
1
The H NMR spectral data of the complexes in CDCl
(2) reveals that this complex crystallizes in monoclinic
space group P2(1)/n and consists of discrete
?
[Cu(L)(PPh3)3] cations and perchlorate anions. The
3
solution are given in the experimental section. The phenyl
protons of the coordinated PPh ligands overlap to some
3
extent with those of the phenyl hydrogen atoms of L and
are observed in the range of 7.40–7.88 ppm for all four
complexes. The imine proton appears as a singlet at around
d 8.19 ppm. The upfield shift of the imine proton in the
complexes relative to free L can be attributed to the
shielding effect resulting from coordination of the nitrile
molecular structure of 2 along with the atom numbering
scheme is illustrated in Fig. 2, and selected bond lengths
and angles are given in Table 2. The monomeric complex 2
exhibits a distorted tetrahedral geometry around copper(I),
provided by one nitrogen atom from L and three triph-
enylphosphine phosphorous atoms, giving P CuN coordi-
3
˚
nation. The Cu–N bond distance in 2 (2.056 A) is
group [26]. The NH protons, which appear as a singlet at d
2
1
23

Transit Met Chem (2017) 42:347–356
351
Cu(I) catalyst, K CO
2
3
+
I
R
R
Toluene, 90
C
0
p-substituted diphenylacetylene
Scheme 2 Sonogashira coupling of terminal alkynes with aryl halides catalyzed by 1-4
R = H, NH , Br
2
-
3
10
M CH Cl solution in the potential range -1.5 to
2 2
1.5 V verses the SCE electrode. The electrochemical data
are summarized in Table 3, and the cyclic voltammograms
are shown in Fig. 4. In each case, there is a well-defined
redox process on the positive potential side. A one electron
oxidation peak corresponding to oxidation of copper(I) to
copper(II) occurs in the potential range 0.512–0.578 (Epa),
while the reduction peak in the reverse scan falls within the
range of 0.372–0.446 V (E ). The copper(I)/copper(II)
pc
redox process at around E1/2 = 0.480 V for all complexes
is also supported by a comparison between cyclic
voltammetry experiments involving the Fe(II)/Fe(III) redox
-
1
couple (from ferrocene), at a potential range 100 mV s
.
The current values found for the well-established one
electron Fe(II)/Fe(III) redox process in the ferrocene/fer-
rocenium system are very similar to those observed for the
Cu(I)/Cu(II) process at the same scan rate. The ratio of
peak current (Ipc/Ipa) for complexes 1–4 is not equal to 1,
and DE = (|E - E |) is[60 mV. These results confirm
Fig. 1 UV–visible absorption spectra of 1–4
p
pa
pc
comparable to those reported for other pseudo-tetrahedral
complexes. All Cu–P bond lengths are as expected, i.e.,
˚
close to the average value (2.324 A) found in similar
that the quasireversible redox behavior of these complexes
is in good agreement with similar examples as reported in
the literature [29].
[
Cu(PPh ) (CH CN)]X complexes [28]. The intra-ligand
3 3 3
bond angles N(1)–Cu(1)–P(1), N(1)–Cu(1)–P(3) and N(1)–
Cu(1)–P(2) are much less than tetrahedral, being
Thermal studies and emission spectra
9
7.09(10)°, 104.37(10)° and 106.04(10)°, respectively.
However, the bond angles P(2)–Cu(1)–P(1), P(1)–Cu(1)–
The thermal stabilities of the complexes were studied by
thermogravimetric (TG) analysis between 25 and 800 °C
under a nitrogen atmosphere. The perchlorate complex 1 is
potentially explosive and hence not studied for safety
reasons. The other complexes showed two decomposition
stages. The first decomposition stage takes place in the
region 165–425 (1), 170–422 (3), 165–428 °C (4), corre-
sponding to mass losses of 72.80, 70.05 and 66.12,
respectively [theoretical values 72.78 (1), 69.47 (3) and
65.99% (4)], attributed to decomposition of the triph-
enylphosphine ligands. The DTA curve gives exothermic
peaks at 190, 196 and 192 for 1, 3 and 4, respectively. The
second consists of a continuous weight loss from 425 to
655, 422 to 656 and 428 to 660 °C along with strong
exothermic DTA peaks at 326, 320 and 324 °C, accom-
panied by mass losses of 18.25 (1), 17.40 (3), 16.56% (4).
This process is attributed to decomposition of L, leaving
CuCl, CuBF and CuPF as residues (theoretical mass loss
P(3) and P(2)–Cu(1)–P(3) are 124.67(4)°, 112.46(4)° and
1
09.29(4)°, closer to the tetrahedral value. These geomet-
rical parameters suggest that the copper(I) center in com-
plex 2 has a highly distorted tetrahedral geometry. The
distortion from ideal tetrahedral geometry in 2 is mainly
due to the restricted bite angle of the chelating nitrile
ligands, and steric hindrance of the phosphine ligands.
The crystal packing structure of 2 is given in Fig. 3. The
complex forms intramolecular p…p interactions between
the phenyl rings of PPh and the ClO anion. The ClO
4
3
4
anion is weakly interacting with phenyl-C–H groups, giv-
ing a loose supramolecular structure.
Cyclic voltammetry
In order to study their electron transfer properties, cyclic
4
6
voltammetry studies of complexes 1–4 were carried out in
18.21, 17.36 and 16.51%).
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3
52
Transit Met Chem (2017) 42:347–356
Fig. 2 Molecular structure of
Cu(L)(PPh ]ClO (2)
showing 50% probability
[
3
)
3
4
ellipsoids. The hydrogen atoms
have been removed for clarity
Table 2 Selected bond lengths
to coordination of L and triphenylphosphine ligands to
copper(I), which effectively increases the rigidity of the
ligands and so reduces the loss of energy via radiationless
decay [30]. The emission energies of the complexes are
sensitive to the size of the counterion, following the
´
˚
Cu(1)–N(1)
2.056(3)
(
A) and bond angles (°) for 2
Cu(1)–P(2)
2.304(11)
2.327(12)
2.342(12)
106.04(10)
97.09(10)
104.37(10)
124.67(4)
109.29(4)
112.46(4)
Cu(1)–P(1)
Cu(1)–P(3)
N(1)–Cu(1)–P(2)
N(1)–Cu(1)–P(1)
N(1)–Cu(1)–P(3)
P(2)–Cu(1)–P(1)
P(2)–Cu(1)–P(3)
P(1)–Cu(1)–P(3)
-
-
-
-
sequence PF6 [ ClO4 [ BF4 [ Cl . These results
could be attributed to the different coordinating abilities
of the anions, as well as the differences in solubility of
the complexes [31].
The emission quantum yields (/) of the complexes were
determined using quinine sulfate as a reference, with
known / of 0.52 at 298 K, giving values of 0.077–0.093
R
(
Table 4). The peak areas were integrated using software
The emission properties of L and complexes 1–4 were
-
3
studied at room temperature in CH Cl solution (10 M).
available on the instrument, and the quantum yields were
calculated according to the following equation;
2
2
The emission spectra are shown in Fig. 5, and the data are
summarized in Table 4. Free ligand L exhibits an emis-
sion in the violet–blue region centered at kmax = 426 nm
with an excitation at 324 nm assigned to a ligand centered
p–p* transition. In contrast, complexes 1–4 show marked
differences in emission behavior in dichloromethane
solution; their spectra show a broad emission band with
kmax at 462–475 nm, with excitation maxima at
2
S
/S ½A Š ½ðAbsÞ Š ½g Š
S
R
¼
2
R
/R ½A Š ½ðAbsÞ Š ½g Š
R
S
where / and / are the fluorescence quantum yields of
the sample and reference, respectively. A and A are the
S
S
R
R
areas under the fluorescence spectra of the sample and
reference, respectively, (Abs) and (Abs) are the respec-
S
R
tive optical densities of the sample and the reference
3
41–346 nm. The complexes do not show significant
solution at the wavelength of excitation, and g and g are
s
R
emission when they are excited at their MLCT band
maxima; hence, the emission can be attributed to p ? p*
intra-ligand charge transfer. The enhancement of fluores-
cence efficiency in all of the complexes can be attributed
the values of refractive index for the solvent used for the
sample and reference, respectively. The results obtained
are in good agreement with values reported in the literature
1
23

Transit Met Chem (2017) 42:347–356
353
-
4
Fig. 3 The p…p, C–H…p and hydrogen bonded ClO
3 3 4
in [Cu(L)(PPh ) ]ClO (2)
Table 3 Electrochemical data for copper(I) complexes (1–4)
Complex
E
pa (V)
E
pc (V)
DE
p
(mV)
E1/2 (V)
1
2
3
4
0.531
0.512
0.566
0.578
0.399
0.372
0.437
0.446
132
140
129
132
0.465
0.442
0.501
0.512
Fig. 5 Emission spectra of 1–4
[
32]. The lifetime data of the complexes were obtained
upon excitation at 320 nm and are summarized in Table 4.
The observed decay of each complex fits well to a single
exponential. The average lifetimes of the complexes follow
the same sequence described above with respect to
increasing size of the counterion [33].
Catalytic activity
The Sonogashira Pd-catalyzed cross-coupling reaction is an
important and powerful tool in organic synthesis. It
involves coupling of aryl, alkyl, heteroaryl or vinyl halides
with terminal acetylenes in the presence of a palladium
Fig. 4 Cyclic voltammogram of 1–4
123

3
54
Transit Met Chem (2017) 42:347–356
Table 4 Emission data of
copper(I) complexes in CH Cl
2 2
-1
(s /10 )
7
-1
Knr (s /10 )
9
Complex
k
ex (nm)
k
em (nm)
/
s (ns)
K
r
(
1–4)
L
1
2
3
4
324
341
342
344
346
426
462
473
469
475
0.069
0.077
0.087
0.082
0.093
2.32
2.59
2.72
2.65
2.83
2.974
2.972
3.198
3.094
3.286
0.4012
0.3563
0.3356
0.3463
0.3204
Table 5 Sonogashira coupling
reaction of terminal alkyne with
aryl halides
Entry
Phenylacetylene
Aryl halide
Product
Complex
% yield
1
2
3
4
5
6
7
8
9
1
1
1
.
1
2
3
4
1
2
3
4
1
2
3
4
72
77
75
79
78
84
80
86
68
72
71
76
I
.
.
.
.
I
NH
2
NH2
.
.
.
.
I
Br
Br
0.
1.
2.
Reaction conditions: phenylacetylene, 2.5 mmol; aryl halide, 2 mmol; copper(I) catalyst (10 mol %);
CO
(2 mmol); Toluene, 20 ml; temperature 90 °C; reaction time 16 h
K
2
3
Table 6 Microanalytical and spectral data of coupling product
-1
)
1
Compound
C, H, N found (calculated)
IR (cm
Mass
H NMR (d ppm)
C
H
N
–
?
] , 77 [C
?
Diphenylacetylene
94.30
(
5.48
2152
m/z 178 [C
6
H
5
C:CC
6
H
5
6 5
H ]
d 7.40–7.55, (m, Ar–H)
d 7.40–7.62, (m, Ar–H) d
94.34)
(5.66)
5.71
(5.74)
?
] , 178
4
-Amino-
diphenylacetylene
86.76
7.27
(7.22)
3411,
m/z 193 [C
[C
6
H
5
C:CC
6
H
4
NH
2
?
] , 77 [C
?
(87.01)
3292,
151
2152
6
H
5
C:CC
6
H
5
6
5
H ]
3.84, (s, 2H, NH
2
)
2
?
4
-Bromo-
diphenylacetylene
65.12
(65.40)
3.55
(3.53)
–
m/z 257 [C
6
H
5
6 4
C:CC H Br] , 178
d 7.41–7.58, (m, Ar–H)
?
?
[C C:CC H ] , 77 [C H ]
6 5 6 5
H
6 5
complex such as PdCl (PPh ) or Pd(PPh ) . Although Pd-
2
study the scope of copper(I) complexes 1–4 as catalysts for
Sonogashira coupling, reactions of phenylacetylene with
aryl halides were carried out using K CO as a base in
3 2
3 4
catalyzed coupling [34] has become the most important
method for laboratory scale synthesis, copper mediated
coupling [35] is also well established and attractive due to
low cost, non-toxicity and environmentally friendly nature.
However, most of the copper catalyzed couplings reported
so far are not well defined; the catalysts are generated
in situ based on copper salt, ligands and additives. Also,
they generally require prolonged reaction times, high
temperature and a large amount of copper reagent. There-
fore, it is necessary to develop well-defined and versatile
catalysts that are active under mild conditions. In order to
2
3
toluene at 90 °C (Scheme 2), with the results outlined in
Table 5. The isolated products were characterized by ele-
1
mental analyses, IR, H NMR and mass spectra (Table 6).
We found that these coupling reactions proceeded very
smoothly to afford the corresponding coupling products in
excellent yields. The catalytic efficiency was comparable
with previously reported copper(I) complexes [36, 37] and
all of the reactions proceeded smoothly at relatively low
temperature for 16 h, attaining coupling yields of up to
1
23

Transit Met Chem (2017) 42:347–356
355
R1
R2
observed for all four complexes corresponding to the Cu(I)/
Cu(II) couple. These complexes are effective catalysts for
the Sonogashira coupling of terminal alkynes with aryl
halides at low temperature. Further, the different counter
anions in the complexes have a marked effect on the yields
of the coupling products.
+
[
CuL(PPh ) ]
3 3
R1
H
R1
H+
III
CuL(PPh3)
R1
3
CuL(PPh3)3
X
R2
I
R2
R1
KHCO + KX
3
Supplementary data
CuL(PPh3)
3
CCDC 1434712 contains the supplementary crystallo-
K CO3
2
R2
graphic data for [Cu(L)(PPh ) ]ClO (2). Supplementary
3 3 4
II
data associated with this article can be found in the online
version.
X
Scheme 3 Probable mechanistic route for Sonogashira coupling of
terminal alkynes with aryl halides using 1–4
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