Synthesis, characterization, luminescence and catalytic properties of copper(I) complexes with N-(2-pyridylmethylene)-1,5-dimethyl-2-pyrazole-3-(2H)-one and triphenylphosphine as ligands

Article abstract of DOI:10.1016/j.ica.2016.10.024

A series of copper(I) complexes of the formula [Cu(L)(PPh₃)₂]X (1–4) [where L = N-(2-pyridylmethylene)-1,5-dimethyl-2-pyrazole-3-(2H)-one; PPh₃= triphenylphosphine, X = Cl(1), ClO₄(2), BF₄(3) and PF₆(4)] have been prepared by the condensation of 4-aminoantipyrine with pyridine-2-carboxaldehyde followed by reaction with CuCl, [Cu(MeCN)₄]ClO₄, [Cu(MeCN)₄]BF_4,[Cu(MeCN)₄]PF₆in presence of triphenylphosphine as a coligand. A single crystal X-ray diffraction study of the representative complex [Cu(L)(PPh₃)₂]BF₄(3) reveals a distorted tetrahedral geometry around Cu(I). Complexes 1–4 exhibit quasireversible redox behavior corresponding to a Cu(I)/Cu(II) couple. All complexes show orange-red emission as a result of fluorescence from an intra-ligand charge transition (ILCT) with some metal to ligand charge transfer (MLCT) character. Significant increase in size of the counter anion shows marked effect on quantum efficiency and lifetime of the complexes. The catalytic efficiency of the complexes was tested and it was found that all the complexes worked as an effective catalyst in the Sonogashira coupling of phenylacetylene with aryl halides in good yield.

Full text of DOI:10.1016/j.ica.2016.10.024

Accepted Manuscript
Research paper
Synthesis, characterization, luminescence and catalytic proper ties of cop
per(I) complexeswith N-(2-pyridylmethylene)-1,5-dimethyl-2-pyrazole-3-
(2H)-oneand triphenylphosphineasligands
S.S. Devkule, M.S. More, S.S. Chavan
PII:
S0020-1693(16)30725-3
http://dx.doi.org/10.1016/j.ica.2016.10.024
ICA 17317
DOI:
Reference:
Inorganica Chimica Acta
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Accepted Date:
11 September 2016
13 October 2016
19 October 2016
Please cite this article as: S.S. Devkule, M.S. More, S.S. Chavan, Synthesis, characterization, luminescence and
catalyticpropertiesof copper(I) complexeswith N-(2-pyridylmethylene)-1,5-dimethyl-2-pyrazole-3-(2H)-one
and triphenylphosphine as ligands, Inorganica Chimica Acta (2016), doi: http://dx.doi.org/10.1016/j.ica.
2016.10.024
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Synthesis, characterization, luminescence and catalytic properties of copper(I)
complexes with N-(2-pyridylmethylene)-1,5-dimethyl-2-pyrazole-3-(2H)-one and
triphenylphosphine as ligands
S. S. Devkule, M. S. More, S. S. Chavan*
Department of Chemistry, Shivaji University, Kolhapur(MS) India-416004
Abstract
A series of copper(I) complexes of the formula [Cu(L)(PPh3)2]X (1-4) [where L= N-(2-pyridyl
methylene)-1,5-dimethyl-2-pyrazole-3-(2H)-one; PPh3= triphenylphosphine, X= Cl(1), ClO4(2),
BF4(3) and PF6(4)] have been prepared by the condensation of 4-aminoantipyrine with pyridine-
2-carboxaldehyde followed by reaction with CuCl, [Cu(MeCN)4]ClO4, [Cu(MeCN)4]BF4,
[Cu(MeCN)4]PF6 in presence of triphenylphosphine as a coligand. A single crystal X-ray
diffraction study of the representative complex [Cu(L)(PPh3)2]BF4 (3) reveals a distorted
tetrahedral geometry around Cu(I). Complexes 1-4 exhibit quasireversible redox behaviour
corresponding to a Cu(I)/Cu(II) couple. All complexes show orange-red emission as a result of
fluorescence from an intra-ligand charge transition (ILCT) with some metal to ligand charge
transfer (MLCT) character. Significant increase in size of the counter anion shows marked effect
on quantum efficiency and lifetime of the complexes. The catalytic efficiency of the complexes
was tested and it was found that all the complexes worked as an effective catalyst in the
Sonogashira coupling of phenylacetylene with aryl halides in good yield.
.
Keywords: Copper(I) complexes; Crystal structure; Luminescence; Catalysis
Corresponding author: Tel.: +91 231 2609381; fax: +91 231 2691533.
E-mail: sanjaycha2@rediffmail.com

1. Introduction
The chemistry of copper(I) have drawn special attention because of its unusual structural
features, utility in solar energy and supramolecular devices, luminescent material, catalysis and
biological importance[1-4]. Due to favorable soft-acid and soft-base interaction this closed
shell (d10) metal ion can readily coordinate to halide, pseudohalides and N-containing ligands [5].
Additionally, the combination of electron rich metal centers, conjugated organic ligands and
high degree of inherient covalence in soft acid-base bonding can produce low energy electronic
interactions between the metal center and the ligands and resulting compound possesses
interesting optical and electronic properties. In recent years, the copper(I) complexes
containing N-donor ligands have drawn special attention due to their structural diversities and
rich photophysical properties as well as promising applications in numerous areas such as
catalysis, organic light-emitting devices(OLEDs), dye-sensitized solar cells(DSSCs), optics
and luminescent materials [6-9]. The formation of these complexes is always influenced by
experimental conditions of their synthesis, structure of ligand and also metal-ligand interaction.
Among various ligands pyrozolinone derivatives especially 4-aminoantipyrine derivatives
constitute an important class of organic compounds which possesses appreciable biological
activities. They exhibit remarkable properties like multi-site coordination [10], anti-oxidant [11],
anti-putrefactive [12] and optical characteristics [13]. The 4-aminoantipyrine derivatives and
their coordination complexes have been extensively investigated due to their biological,
clinical, pharmacological, analytical and material applications [14-16]. They are also known
for their variety of applications in the area of catalysis. However, only a few structurally
characterized metal complexes with 4-aminoantipyrine Schiff base derived ligands have
been reported and its coordination chemistry remains largely unexplored. The copper(I)
complexes with phosphorus containing ligands are used to carry wide range organic
transformations such as allylic amination, hydrogenation, copolymerization, cross coupling
reactions etc [17-20]. The steric crowding and π–acidic character imparted by these ligands
not only play an important role in stabilizing the copper(I) state but also possesses rich
photophysical and catalytic properties.

Influenced by these facts, it was considered worthwhile to undertake the synthesis of some copper(I)
complexes (1-4) derived by the reaction of N-(2-pyridylmethylene)-1,5-dimethyl-2-pyrazole-3-(2H)-
one with CuCl, [Cu(MeCN)4]ClO4, [Cu(MeCN)4]BF4 and [Cu(MeCN)4]PF6 in the presence of
triphenylphosphine as coligand. All the complexes were characterized by elemental analysis,
spectroscopic techniques and representative complex 3 by X-ray crystallography. The luminescent
behavior and catalytic performance of all complexes for the Sonogashira coupling of phenylacetylene
with aryl halides have also been reported.
2. Experimental
2.1 Materials and methods
The reagent used in synthesis of copper(I) complexes are pyridine-2-carboxaldehyde (Alfa
Aesar), 4-aminoantipyrine (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 CuCl [21],
Cu(MeCN)4]ClO4 [22], [Cu(MeCN)4]BF4 [22] and [Cu(MeCN)4]PF6 [23] 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
1
13
Spectrometer, H NMR and C 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 (10-4 M) Shimadzu 3600 UV-Vis-NIR
spectrophotometer. Emission spectra were recorded using a Perkin-Elmer LS 55 spectrofluorometer
equipped with quartz cuvette of 1 cm3 path length at room temperature. 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 all measurements
were carried out in CH2Cl2 solution at room temperature with scan rate 100 mVs-1

2.2. Synthesis
2.2.1. Synthesis of ligand (L)
N-(2-Pyridylmethylene)-1,5-dimethyl-2-pyrazol-3-(2H)-one (L) was prepared by adopting and
modifying the method described in the literature [24]. To a solution of 4-aminoantipyrine (0.7 g,
3.444 mmol) in ethanol (10 ml) a solution of Pyridine-2-carboxaldehyde (0.368 g, 3.444 mmol) in
EtOH (10 ml) was added drop wise with constant stirring. The resulting reaction mixture was
refluxed at about 80°C until the completion of reaction (checked by TLC). On partial removal of
solvent the product obtained was filtered, washed with ethanol and dried in vacuo.
Yield: 85% (0.908 g, 3.107 mmol); Elemental analyses (C, H and N, wt%) Anal.Calc. for
C17H16N4O: C, 69.85; H, 5.52; N, 19.17; found: C, 69.76; H, 5.45; N, 19.38%; IR (KBr; cm-1);
1
3054, υ(Ar-CH); 1643, υ(C=O), 1608, υ(HC=N); 1435, υ(N-CH3); 1380, υ(C-N); H NMR
(CDCl3; 300 MHz): δ 9.80 (s, 1H, HC=N), δ 7.25-8.71 (m, 9H, Ar-H), δ 3.20 (s, 3H, N-CH3),
13
δ 2.54 (s, 3H, C-CH3), C NMR (CDCl3; 300 MHz): 160.3 (>C=O), 156.6 (Py-C), 156.2 (Py-C),
152.4 (Py-C), 149.7 (HC=N), 136.2(Py-C), 134.6 (CH3C=CN), 129.2 (Py-C), 127.1 (Ph-C), 124.7
(Ph-C), 123.9 (Ph-C), 121.5 (Ph-C), 118.1 (NC=CCH3), 35.5 (-NCH3), 10.2 (-CH3); ESI(MS): m/z
314.07 [M+Na]+ (Calcd. m/z 314.13).
2.2.2. Synthesis of [Cu(L)(PPh3)2]Cl (1)
To a 10 ml acetonitrile solution of CuCl (0.846 g, 0.855 mmol), 2 equivalent of triphenylphosphine
(0.448 g, 1.710 mmol) were added and the solution was stirred for 30 min. The crystalline product
[Cu(MeCN)2(PPh3)2]Cl obtained was added to a stirring solution of ligand L (0.250 m, 0.855 mmol)
in 10 ml of dichloromethane and stirred for 2 h at room temperature. The volume of solvent reduced
under vaccum and the solid product was produced bydiffusion of diethyl ether into the filtrate.
Yield: 82% (0.642 g, 0.701 mmol); Elemental analyses (C, H, N, wt%) Anal. Calc. for
C53H46N4P2OClCu: C,69.50; H, 5.06, N, 6.12; found: C,69.41; H, 5.01; N, 6.21%; IR (KBr; cm-1);
3065, υ(Ar-CH); 1647, υ(C=O), 1587, υ(HC=N), 1437, υ(N-CH3); 1384, υ(C-N); 1481, 1436, 694,
518, υ(PPh3); 488 υ(Cu-N); UV-Vis (CH2Cl2) λmax (nm)(ε/M-1 cm-1): 232 (16400), 262 (10600), 392
(4400); 1H NMR (CDCl3; 300 MHz); δ 9.97 (s, 1H, HC=N), δ 7.17-7.78 (m, Ar-H), δ 3.19 (s, 3H, N-
CH3), δ 2.25 (s, 3H,C-CH3); 13C NMR (CDCl3; 300 MHz): 159.1 (>C=O), 151.6 (Py-C), 151.5 (Py-C),

149.2 (HC=N), 148.4 (Py-C), 138.5 (Py-C), 133.5 (CH3C=CN), 133.2 (PPh3-C), 131.5 (PPh3-C),
130.5 (PPh3-C), 129.6 (PPh3-C), 129.2 (PPh3-C), 128.3 (Ph-C), 127.7 (Ph-C), 126.4 (Ph-C), 125.8
(Py-C), 116.2 (NC=CCH3), 34.9 (-NCH3), 11.6 (C-CH3); ESI(MS): m/z 878.97 [M-Cl]+ (Calcd.
m/z 879.24).
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, CuCl was replaced by [Cu(MeCN)4]ClO4 (0.279 g, 0.855 mmol,).
Yield: 82% (0.802 g, 0.818 mmol); Elemental analyses (C, H, N, wt %) Anal. Calc. for
C53H46N4P2O5ClCu: C, 64.96; H, 4.73, N, 5.27; found: C, 64.83; H, 4.68; N, 5.38%; IR (KBr; cm-1);
3064, υ(Ar-CH); 1647, υ(C=O), 1588, υ(HC=N), 1434, υ(N-CH3); 1383, υ(C-N); 1481, 1436,
694, 518, υ(PPh3); 1097, 622, υ(ClO4); 487 υ(Cu-N); UV-Vis (CH2Cl2) λmax (nm)(ε /M-1 cm-1):234
1
(13900), 266 (11900), 396 (4500); H NMR (CDCl3; 300 MHz): δ 9.98 (s, 1H, HC=N), δ 7.15-
7.76 (m, Ar-H), δ 3.18 (s, 3H, N-CH3), 2.26 (s, 3H,C-CH3); 13C NMR (CDCl3; 300 MHz): 159.1
(>C=O), 154.9 (Py-C), 151.4 (Py-C), 149.2 (HC=N), 148.4 (Py-C), 138.4 (Py-C), 133.3
(CH3C=CN), 133.1 (PPh3-C), 131.5 (PPh3-C), 130.5 (PPh3-C), 129.5 (PPh3-C),129.1 (PPh3-C),
128.3 (Ph-C), 127.7 (Ph-C), 126.3 (Ph-C), 125.7 (Py-C), 116.1 (NC=CCH3), 34.9 (-NCH3), 11.6
(C-CH3); ESI(MS): m/z 878.99 [M-ClO4]+ (Calcd. m/z 879.24).
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
CuCl was replaced by [Cu(MeCN)4] BF4 (0.269 g, 0.855 mmol).
Yield: 86% (0.832 g, 0.860 mmol); Elemental analyses (C, H, N, wt%) Anal. Calc. for
C53H46N4P2OF4BCu: C,65.81; H, 4.79, N, 5.79; found: C, 65.58; H, 4.64; N, 5.87%; IR (KBr;
cm-1); 3066, υ(Ar-CH); 1648, υ(C=O), 1583, υ(HC=N), 1436, υ(N-CH3); 1385, υ(C-N); 1481,
1435, 694, 518, υ(PPh3); 1059 υ(BF4); 488, υ(Cu-N); UV-Vis (CH2Cl2) λmax (nm)(ε/M-1 cm-1):
1
234 (13900), 270 (10600), 394 (4300); H NMR (CDCl3; 300 MHz): δ 9.96 (s, 1H, HC=N),
δ 7.15-7.75 (m, Ar-H), δ 3.19 (s, 3H, N-CH3), 2.26 (s, 3H,C-CH3); 13C NMR (CDCl3; 300
MHz): 159.1 (>C=O), 156.2 (Py-C), 151.4 (Py-C), 149.2 (HC=N), 148.4 (Py-C), 138.5 (Py-C),

133.2 (CH3C=CN), 133.1 (PPh3-C), 131.5 (PPh3-C), 130.7 (PPh3-C), 129.5 (PPh3-C), 129.1 (PPh3-
C), 128.3 (Ph-C), 127.7 (Ph-C), 126.5 (Ph-C), 125.8 (Py-C), 116.1 (NC=CCH3), 34.9 (-NCH3),
11.6 (C-CH3); ESI(MS): m/z 878.98 [M-BF4]+ (Calcd. m/z 879.24).
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
CuCl was replaced by [Cu(MeCN)4]PF6 (0.318 g, 0.855 mmol).
Yield: 81% (0.823 g, 0.803 mmol); Elemental analyses (C, H, N, wt%) Anal. Calc. for
C53H46N4P3OF6Cu: C,62.08; H, 4.52, N, 5.46; found: C, 61.76; H, 4.38; N, 5.62%; IR (KBr; cm-1);
3061, υ(Ar-CH); 1648, υ(C=O), 1589, υ(HC=N), 1431, υ(N-CH3); 1385, υ(C-N); 1481, 1435,
694, 518, υ(PPh3); 842,560 υ(PF6); 488 υ(Cu-N); UV-Vis (CH2Cl2) λmax (nm)(ε/M-1 cm-1): 234
(13800), 265 (8800), 395 (3700): 1H NMR (CDCl3; 300 MHz): δ 9.97 (s, 1H, HC=N), δ 7.14- 7.79
(m, Ar-H), δ 3.19 (s, 3H, N-CH3), 2.26 (s, 3H,C-CH3); 13C NMR (CDCl3; 300 MHz): 159.1
(>C=O), 155.5 (Py-C), 151.4 (Py-C), 149.2 (HC=N), 148.4 (Py-C), 138.4 (Py-C), 133.3
(CH3C=CN), 133.1 (PPh3-C), 131.5 (PPh3-C), 130.5 (PPh3-C), 129.6 (PPh3-C),129.0 (PPh3-C),
128.3 (Ph-C), 127.7(Ph-C), 126.3 (Ph-C), 125.7 (Py-C), 116.0 (NC=CCH3), 34.9 (-NCH3), 11.6
(C-CH3); ESI(MS): m/z 878.97 [M-PF6]+ (Calcd. m/z 879.24).
2.3. X-ray crystallography
A single crystal of [(Cu(L)(PPh3)2]BF4.C5H12 (3) suitable for X-ray analysis was obtained by slow
diffusion of pentane in dichloromethane solution X-ray study performed on a Bruker KAPPA
Apex-II diffractometer. Data were collected in omega and phi scan modes, MoKα = 0.71073 Å at
room temperature with scan width of 0.3º at θ (0º, 90º and 180º) by keeping distance at 40 mm
between sample and fixed detector at 24º. The X-ray generator was operated at 50 kv and 30 mA.
The details of crystal data, data collection and the refinement are given in Table 1. The X-ray data
collection was monitored by SMART program (Bruker, 2003). All the data were collected using
SAINT and SADABS programs (Bruker, 2003). SHELXL 97 was used for the solution of the
structure and full matrix least-squares refinement on F2 [25]. Molecular and packing diagrams were
generated using ORTEP-3 and Mercury-3.

2.4. Catalytic activity for the Sonogashira coupling of phenylacetylene with aryl halides
The Sonogashira coupling reaction of phenylacetylene with aryl halides catalyzed by copper(I)
complexes was carried out according to the procedure (Scheme 1): 10 mol% of copper(I)
catalyst was added to 2 mmol of respective aryl halide, 2.5 mmol of phenylacetylene, 2 mmol
of K2CO3 in toluene and the reaction mixture was stirred for 16 h at 900 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 was then characterized by
elemental analyses, IR, 1H NMR and mass spectral studies.
3. Results and discussion
3.1. Synthesis of ligand and copper (I) complexes
The synthesis route to the formation of L and copper(I) complexes is shown in Scheme 2. N-(2-
Pyridylmethylene)-1,5-dimethyl-2-pyrazol-3-(2H)-one (L) was synthesized by the reaction of
4-aminoantipyrene with Pyridine-2-carboxaldehyde. The obtained spectral data, elemental
analysis and mass spectra confirm the formation of L. The mononuclear copper(I) complexes
1-4 possessing L and phosphine ligands were prepared via two simple steps. The complexes
[Cu(L)(PPh3)2]X (X= Cl, ClO4, BF4 and PF6) were firstly afforded by the treatment of
[Cu(MeCN)4]X (X= Cl, ClO4, BF4 and PF6) with two equivalent of PPh3 then one equivalent of
L was slowly added. The complexes obtained were microcrystalline solids that were soluble in
common organic solvents like dichloromethane, chloroform, acetonitrile, THF, methanol, ethanol,
etc. The results of elemental analyses (C, H and N) which are given in section 2 confirm the
assigned composition of the copper(I) complexes. At room temperature all the complexes are
diamagnetic which is characteristic of Cu(I)(d10).
3.2. Spectral characterization
The IR frequencies of selected groups in the spectra of all compounds are given in section 2.
The IR spectra of L exhibit a medium intensity band at 1643 cm-1 is due to ʋ(C=O). This band
shifted to higher frequency at ~1647 cm-1 in the spectra of 1-4 indicating noninvolvement of
carbonyl oxygen in coordination to the metal ion. The band at 1608 cm-1 in the spectrum of L

which is characteristic of υ(HC=N) vibration shifted to lower frequency by 19-25 cm-1 in 1-4
indicative of π-back bonding from the electron rich copper(I) center to vacant imine π*-orbital
[26]. Another characteristic band at 997 cm-1 in L is associated with pyridine ring breathing
mode of vibration. On complexation this band shifted to higher energy at 1021-1026 cm-1 in 1-
4 indicating copper-nitrogen bond formation. The spectra of all copper(I) complexes exhibit
the expected bands due to the PPh3 ligand at 1481,1435,694 and 518 cm-1. The perchlorate
complex 2 exhibit a broad band at 1097 (ʋ3) and strong band at 622(ʋ4) which is devoid of any
-
splitting suggesting ClO4 anion is not coordinated to the copper(I) [27]. A broad band at 1059
-
-
cm-1 in 3 corresponds to presence of BF4 anion in the complex [28]. The presence of PF6
anion in 4 is shown by medium intensity band at 842 cm-1 and 560 cm-1 [29].
The UV-Visible absorption spectra of L and complexes 1-4 were measured in CH2Cl2 (10-4 M).
The ligand L displayed two absorption bands at 230 and 265 nm assigned to π-π* and n-π*
transitions within L. All the copper(I) complexes exhibit multiple absorption peaks in the range
232-270 nm region most likely coming from ligand L and PPh3 (Fig. 2). The red shift of π-π* and
n-π* absorption of 1-4 is consistent with better conjugation of the ligands upon coordination
resulting in a smaller π-π* and n-π* energy gap. In addition to the high energy absorptions,
complexes 1-4 display a comparatively broad band with low energy absorption at 392-396 nm
which is absent in L. These can be assigned to metal to ligand charge transfer transitions (MLCT)
from the dπ orbital of the copper(I) center to the unoccupied π* orbital of the ligand L [30].
1
The H NMR spectra of free ligand L displayed a singlet at δ 9.80 ppm assigned to imine
(HC=N) proton. In the spectra of 1-4 signal of imine proton is considerably deshielded and
appear as a singlet at around δ 9.96 ppm due to positive charge delocalization on the
corresponding C-atom through resonance resulting from the coordination of ligand [31].
However, the broad multiplet observed in the range δ 7.14-7.79 ppm for 1-4 assigned to the
phenyl protons of phosphine ligand together with ring protons of L. In addition to these signals,
the complexes display two sharp signals at δ 2.26 and 3.19 ppm with an integration equivalent to
three protons attributed to the C-CH3 and N-CH3 groups in all complexes.

3.3. X-ray structure of [Cu(L)(PPh3)2]BF4.C5H12 (3)
The crystals of [Cu(L)(PPh3)2]BF4.C5H12(3) were grown by slow diffusion of pentane in
dichloromethane solution and structure was determined by X-ray crystallography. X-ray
analysis reveals that complex 3 crystallizes in triclinic space group P-1. The molecular
structure of 3 along with atom numbering scheme is illustrated in Fig.1 and selected bond lengths
and bond angles are collected in Table 2.
-
Complex 3 contains discrete [Cu(L)(PPh3)2]+ cation and BF4 as anion with highly distorted
tetrahedral geometry around copper(I) with P2CuN2 coordination. Ligand L is bonded to the
central copper ion in a bidentate manner through imine and pyridyl nitrogen to form a five
membered chelate ring. The distorted four coordinate geometry of copper(I) is completed by
imine, pyridyl nitrogen and phosphorous atoms of two triphenylphosphine groups. 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(1)-Cu(1)-N(4) and N(4)-Cu(1)-P(2) are
much less than 109.4°, being 79.21(13)° and 105.99(9)°,respectively. The average distance for
Cu-N (2.135 Å) and Cu-P (2.307 Å) are comparable to those reported for copper(I) complexes [32].
The Cu(1)-N(1) (Pyridyl bond length, 2.103(3)° is longer than Cu(1)-N(4) (imine bond length,
2.167(3)°), which means that the intermolecular attraction N(imine) is stronger than that
between Cu(I) center and N(pyridyl)[33].
Torsion angles in the chelating ring are given in Table 3. The chelating ring Cu(1)-N(4)-C(19)-
C(35) and Cu(1)-N(1)-C(35)-C(19) are -3.9(3)º and -8.7(5)º. The significant deviations from
120º for the angles about the N atom Cu(1)-N(4)-C(19), Cu(1)-N(4)-C(20), Cu(1)-N(1)-C(35)
and Cu(1)-N(1)-C(34) are 109.7(3)º, 131.7(2)º, 111.8(3)º and 130.6(3)º.
3.4. Emission behavior
The emission properties of L and copper(I) complexes 1-4 have been investigated at room
temperature in CH2Cl2 solution (10-4 M) and the data are displayed in Table 4. The ligand L
exhibit an emission in the green region centered at λmax= 530 nm with an excitation at 260 nm
attributed to the emission stemming from a ligand centered π→π* transition. In contrast,

complexes 1-4 show steady state marked differences in emission behavior in dichloromethane
solution. As shown in Fig. 3, the spectra of 1-4 exhibit a broad emission profile in degassed
CH2Cl2 at room temperature with λmax at around 651-656 nm upon excitation at 262-270 nm.
Thus emission observed in 1-4 can be attributed to π→π* intra-ligand charge transition (ILCT)
with some metal to ligand charge transfer (MLCT) character. The enhancement of fluorescence
efficiency in all the complexes can be attributed to coordination of the ligands to copper(I) ion
which effectively increases the rigidity of the ligands and reduced the loss of energy via
radiation less thermal vibration decay [34]. There is a significant increase in the emission
-
-
-
energy of 1-4 as size of the counter anion increases in the sequence PF6 > ClO4 > BF4 > Cl- as
their counter anion [35].
The emission quantum yields (ϕ) of all the complexes was determined by using quinine sulfate
as a reference with known ϕR of 0.52 at 298 K and appeared at 0.080-0.091 (Table 4). The area
of the emission spectrum was integrated using the software available on the instrument and the
quantum yields were calculated according to the following equation.
φS [AS ] [(Abs)R ] [ηS2 ]
=
X
X
φR [AR ] [(Abs)S ] [ηR2 ]
Here ϕS and ϕR are the fluorescence quantum yield of the sample and reference, respectively.
AS and AR are the areas under the fluorescence spectra of the sample and reference,
respectively, (Abs)S and (Abs)R are the respective optical densities of the sample and the
reference solution at the wavelength of excitation and ηs and ηR are the values of refractive
index for the respective solvent used for the sample and reference. The results obtained are in
good agreement with those values reported in the literature [36]. The lifetime data of the
complexes were obtained upon excitation at 320 nm and are summarized in Table 4. The
observed decay of the complexes fit well with single exponential decay. The average lifetime
of 1-4 follow the same sequence described above with respect to increase in size of the counter
anions in the complexes. These results could be attributed to decreased emission intensity of
-
-
-
the complexes in the order PF6 >ClO4 >BF4 >Cl- [37].

3.5. Cyclic Voltammetry
In order to study the electronic environment of the copper(I) ion the electrochemical behavior
of all the copper(I) complexes have been examined cyclic voltammetrically in 10-3 M CH2Cl2
solution in the potential range 1.5 V verses SCE electrode and are presented in Table 4. The
representative cyclic voltammogram of 2 is shown in Fig. 4. The electrochemical potential of 1-4
was characterized by a well defined redox process in the positive potential side. Complexes 1-4
display oxidative response at 0.721-0.782 V (Epa) which is attributed to Cu(I)/Cu(II) oxidation.
The potential appearing in the range 0.581-0.629 V (Epc) is associated with reduction of Cu(II)
to Cu(I). A quasireversible character is observed for all complexes with the values of ∆Ep
(∆Ep=Epa-Epc) ranging from 140-153 mV under the conditions of the measurements. These
results are in good agreement with those values reported in the literature [38].
3.6. Catalytic properties
A Sonogashira coupling is one of the most important and powerful tool in organic
synthesis. This method involves production of alkynes by coupling of aryl, heteroaryl or
vinyl halides with terminal acetylenes in presence of stoichiometric amount of transition
metal ion. This method has been widely applied in diverse areas such as synthesis of
natural products, agrochemicals, molecular materials, biological active molecules, non-
linear optical materials and molecular electronics, dendrimer and polymeric materials,
macrocycles with acetylene linkages and polyalkynated molecules [39, 40]. This wide
spread importance of coupling reaction has led to the development of many synthetic
methodologies. Amongst them, the copper mediated [41] coupling and the recently
developed Pd-catalyzed [42] aryl coupling are more commonly used methods. Although
the Pd-catalyzed coupling of aryl halide has recently become the most important method
for laboratory scale synthesis; the copper mediated coupling is still the reaction of choice
due to its cheap price and environmentally friendly nature. In order to study the scope of
copper(I) complexes 1-4 as a catalyst for the Sonogashira coupling reaction of phenylacetylene

with aryl halides was carried out by using K2CO3 as base in solvent toluene at 900C. Under this
experimental condition the purified product obtained was characterized by elemental analysis,
1
IR, H NMR and mass spectral studies (Table 7).With these optimized conditions it was
observed that copper(I) complexes 1-4 significantly enhance the reaction of phenylacetylene
with iodobenzene, 4-iodoaniline or 1-bromo-4-iodoaniline into desired diphenylacetylene
product in good yield. In order to check the catalytic effect of 1-4 it was observed that, when
no catalyst was added, the blank reaction with solvent toluene and K2CO3 as base exhibited
extremely very low reactivity towards the yield of diphenylacetylene. The catalytic efficiency
of 1-4 was compared with the previously reported similar type of copper(I) complexes [43] and
it was found that all reactions were smoothly carried out at relatively low temperature and
reached the yield of the diphenylacetylene product up to 63-87% (Table 6). It was observed that
the catalytic coupling of phenylacetylene with iodobenzene reached the coupling yield up to 72-78%
(Table 6, entries 1-4).With 4-iodoaniline containing electron donating NH2 group at para
position, the coupling yield was observed up to 75-87% (Table 6, entries 5-8). However, with
1-bromo-4-iodoaniline containing electron withdrawing group at para position, the coupling
reaction proceeds with considerable increase in the yield up to 63-75% (Table 6, entries 9-12).
These results confirmed that the variety of functional group such as amino or bromo group
tolerated on aryl halide component under the reaction conditions and significant electronic
effect was observed for substituted aryl halide containing electron donating group at para-
position. It was also observed that the efficiency of copper(I) catalyst with different counter
-
anions exhibit different activities. It is evident that the copper(I) complex catalyst with PF6
-
-
anion shows greater activities than the complexes with ClO4 , BF4 , Cl- and reached the
-
coupling yield up to 87%. The catalytic activity of these complexes decreases in order of PF6 >
-
-
ClO4 >BF4 >Cl- as their counter anions. These results might be due to difference in
-
-
-
coordinating ability of Cl-, ClO4 , BF4 and PF6 as anion with metal ion as well as difference in
solubility of the complexes in solvent during the reaction.
4. Conclusion

In conclusion, a series of copper(I) complexes featuring N-(2-pyridylmethylene)-1,5-dimethyl-2-
pyrazole-3-(2H)-one and triphenylphosphine have been prepared and characterized. It has been
demonstrated that the ligand L is coordinated to copper(I) by involvement of azomethine nitrogen
and pyridine ring nitrogen in coordination. Complex 3 crystallizes in triclinic space group P-1 and
assume distorted tetrahedral geometry around copper(I). Quasireversible redox behavior is
observed for all complexes corresponding to Cu(I)/Cu(II) couple. All complexes exhibit ogange-
red emission as a result of the fluorescence from π→π* intra-ligand charge transitions (ILCT) with
some metal-ligand charge transfer (MLCT) character. As the size of the counter anion increases, a
marked effect on the quantum efficiency (ϕ) and the lifetime decay (τ) of the complexes is
observed. The catalytic efficiency of the complexes was tested and it was found that all the
complexes worked as effective catalyst in the Sonogashira coupling of phenylacetylene with aryl
halides in good yield and markedly depend on size of the counter anions.
Acknowledgement
We gratefully acknowledge Head, Sophisticated Analytical Instrument Facility Center,
IIT, Madras, India for providing single crystal X-ray facilities.
Supplementary data
CCDC 1503577 contains the supplementary crystallographic data for [Cu(L)(PPh3)2]BF4. C5H12 (3)
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Figure captions:

Scheme 1: Synthetic route of L and its copper(I) complexes
Scheme 2: Sonogashira coupling reaction of phenylacetylene with aryl halides catalyzed by
Cu(I) complexes
Fig. 1: The crystal structure diagram of the cation in [Cu(L)(PPh3)2]BF4. C5H12 (3) showing
50% probability ellipsoids. The BF4 anion and solvent molecule have been removed for
clarity.
Fig. 2: UV-visible absorption spectra of 1-4
Fig. 3: Emission spectra of 1-4
Fig. 4: Cyclic voltammogram of [Cu(L)(PPh3)2]ClO4(2).

Fig. 1
Fig. 2

Fig. 3
Fig. 4

Scheme 1
CH3
N
CH3
N
CH3
N
CH3
NH2
MeOH
N
OHC
+
N
Refluxed
N
O
N
O
L
[Cu(CH3CN)2(PPh3)2]X
CH2Cl2
+
CH3
N
CH3
N
N
X = Cl, ClO4, BF4 and PF6
N
O
Cu
Ph3P
PPh3
X-
Scheme 2
K2CO3
Cu(I) catalyst,
Toluene,
R
R
+
I
900C
R = H, NH2 , Br
p-substituted diphenylacetylene

Table 1:Crystal data and structure refinements details for[(Cu(L)(PPh3)2]BF4.C5H12(3)
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C53H46CuN4OP2,BF4,C5H12
1039.37
Triclinic
P-1
10.1522(7)
14.8808(8)
20.2385(13)
98.124(3)
103.414(3)
108.683(3)
2739.1(3)
2
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (A3)
Z
Density (mg/m3)
µ (M0Kα)(mm-1)
F (000)
1.260
0.513
1084
Data collection
Temperature (K)
θ mini.-maxi.(deg)
Data set [h, k, l]
Total, unique data, Rint
Observed data
Refinement
296(2)
2.16 to 23.27
-12/12,-17/17,-24/24
[R(int) = 0.0833]
>2\s(I)
Full-matrix least-squares on F2
No of reflection, no of
parameters
59853 /10696(Rint) = 0.0714
R1, R1
0.0569, 0.1260
0.1495, 0.2011
1.060
wR2, wR2
Goodness-of-fit
Table 2: Selected bond lengths (Ǻ) and bond angles (°) for 3.
Bond lengths
Bond Angles

Cu(1)- N(1)
Cu(1)-N(4)
Cu(1)-P(1)
Cu(1)-P(2)
N(2)-N(3)
2.103(3)
2.167(3)
N(1)-Cu(1)-N(4)
N(1)-Cu(1)-P(1)
N(4)-Cu(1)-P(1)
N(1)-Cu(1)-P(2)
N(4)-Cu(1)-P(2)
P(1)-Cu(1)-P(2)
79.21(13)
104.69 (11)
118.14(9)
110.37(10)
105.99(9)
127.54(5)
2.2737(13)
2.2812(13)
1.398(5)
Table 3: Torsion angles for chelating ring
Cu(1)-N(1)-C(35)-C(31)
-172.2(4)
Cu(1)-N(1)-C(35)-C(19)
-8.7(5)
-3.9(6)
-7.3(6)
-3.9(6)
178.1(3)
Cu(1)-N(4)-C(19)-C(35)
Cu(1)-N(4)-C(20)-C(21)
Cu(1)-N(4)-C(20)-C(22)
Cu(1)-N(4)-C(20)-C(21)

Table 4: Emission data of copper(I) complexes in CH2Cl2 (1-4)
Complex
τ(ns)
Kr(s−1/107) Knr(s−1/109)
λex(nm)
260
λem(nm)
530
φ
0.072
0.080
0.086
0.083
0.091
2.10
2.46
2.52
2.50
2.59
3.428
3.252
3.412
3.320
3.513
0.441
0.373
0.362
0.366
0.350
L
1
2
3
4
262
651
266
654
270
652
265
656
Table 5: Electrochemical data for copper(I) complexes (1-4)
Complex
Epa(V)
0.782
0.771
0.721
0.734
Epc(V)
0.629
0.622
0.581
0.592
∆Ep (mV)
153
E1/2(V)
0.705
0.696
0.651
0.663.
1
2
3
4
149
140
142

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
72
76
75
78
I
5.
6.
7.
8.
1
2
3
4
75
82
80
87
NH2
I
NH2
9.
1
2
3
4
63
71
67
75
10.
11.
12.
Br
I
Br
Reaction conditions: phenylacetylene, 2.5 mmol; aryl halide, 2 mmol; copper(I) catalyst (10 mol%); K2CO3
(2 mmol); Toluene, 20 ml; temperature 900C; reaction time 16 h.

Table 7: Microanalytical and spectral data of coupling product
Compound
C, H, N
found
IR
Mass
1H
NMR
(cm-1)
(calculated)
(δ
ppm)
C
H
5.48
N
-
Diphenylacetylene 94.30
2152
m/z 178
δ
+
≡CC
[C6H5C
6H5] , 77 7.40-
7.55,
(m,
Ar -
H)
(94.34)
86.76
(5.66)
5.71
-
[C6H5]+
4- Amino-
diphenylacetylene
7.27
3411, m/z 193
δ
3292, [C6H5C≡CC6H4NH2]+, 7.40-
2151
7.62,
(m,
Ar-H)
6H5] , δ
3.84,
+
≡CC
(87.01)
65.12
(5.74) (7.22)
178 [C6H5C
77 [C6H5]+
(s,
2H,
NH2)
δ
7.41-
7.58,
(m,
Ar -
H)
4-Bromo-
diphenylacetylene
3.55
-
-
2152
m/z 257
[C6H5C
178
+
≡CC
6H4Br] ,
(65.40)
(3.53)
[C6H5C≡CC6H5]+, 77
[C6H5]+
24

Graphical Abstract Pictogram
25

Graphical Abstract
Synthesis, Characterization, Luminescence and Catalytic Properties of Copper(I)
Complexes with N-(2-pyridylmethylene)--1,5-dimethyl-2-pyrazole-3-(2H)-one
and Triphenylphosphine as Ligands
S. S. Devkule, M. S. More, S. S. Chavan*
Department of Chemistry, Shivaji University, Kolhapur (MS), India-416004
Abstract
Copper(I) complexes of the formula [Cu(L)(PPh3)2]X (1-4) [where L= N-(2-pyridylmethylene)-1,5-
dimethyl-2-pyrazole-3-(2H)-one; PPh3= triphenylphosphine, X= Cl (1), ClO4 (2), BF4 (3) and PF6 (4)]
have been prepared and characterized. Complex 3 crystallizes in triclinic space group P-1 and
assume distorted tetrahedral geometry around copper(I). Quasireversible redox behaviour is observed
for 1-4 corresponding to Cu(I)/Cu(II) couple. Room temperature luminescence is observed for all
complexes in dichloromethane solution. All complexes worked as effective catalyst for the
Sonogashira coupling of phenylacetylene with aryl halides in good yield.
Keywords: Copper(I) complexes; Crystal structure; Luminescence; Catalysis
Corresponding author Tel.: +91 231 2609381; fax: +91 231 2691533.
E-mail: sanjaycha2@rediffmail.com
26

Research Highlights
ꢀ Synthesis of copper(I) complexes.
ꢀ
ꢀ
ꢀ
Quasireversible redox behavior is observed for all complexes.
Complexes exhibit red emission in dichloromethane solution.
Complexes worked as effectivecatalyst for Sonogashira coupling.
27