Synthesis, X-ray crystal structures and catecholase activity investigation of new chalcone ligands

Article abstract of DOI:10.1016/j.molstruc.2015.08.071

The reaction of dehydroacetic acid DHA carboxaldehyde and RCHO derivatives (R = quinoleine-8-; indole-3-; pyrrol-2- and 4-(dimethylamino)phenyl - afforded four new chalcone ligands (4-hydroxy-6-methyl-3-[(2E)-3-quinolin-8-ylprop-2-enoyl]-2H-pyran-2-one) L

Full text of DOI:10.1016/j.molstruc.2015.08.071

Journal of Molecular Structure 1102 (2015) 295e301
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Synthesis, X-ray crystal structures and catecholase activity
investigation of new chalcone ligands
,
,
, f
Salima Thabti a b, Amel Djedouani c d, Samra Rahmouni b, Rachid Touzani e
,
b
c
,
d,
, d
*, Abdelhamid Mousser c
ꢀ
Abderrahmen Bendaas , Henia Mousser
Faculte des Sciences et Technologie, Universite Mohamed el Bachir El Ibrahimi, El Anasser, 34000, Bordj Bou Arreridj, Algeria
Laboratoire de Materiaux Moleculaires et Complexes, Universite Ferhat ABBAS, Setif, 19000, Algeria
Laboratoire de Physicochimie Analytique et Cristallochimie des Materiaux Organometalliques et Biomoleculaires, Universite Constantine 1, 25000,
a
ꢀ
ꢀ
ꢀ
b
c
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Constantine, Algeria
d
ꢀ
Ecole Normale Superieure de Constantine, Ville Universitaire Ali Mendjeli, 25000, Constantine, Algeria
e
ꢀ
ꢀ
ꢀ
Laboratoire de Chimie Appliquee et Environnement, LCAE-URAC18, COSTE, Faculte des Sciences, Universite Mohamed Premier, BP524, 60000, Oujda,
Morocco
f
ꢀ
Faculte Pluridisciplinaire Nador BP 300, Selouane, 62702, Nador, Morocco
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of dehydroacetic acid DHA carboxaldehyde and RCHO derivatives (R ¼ quinoleinee8e;
indolee3e; pyrrole2e and 4e(dimethylamino)phenyl e afforded four new chalcone ligands (4ehydroxy
e6emethyle3e[(2E)e3equinoline8eylprope2eenoyl]e2Hepyrane2eone) L1, (4ehydroxye3e[(2E)
e3e(1Heindole3eyl)prope2eenoyl]e6emethyle2Hepyrane2eone) L2, (4ehydroxye6emethyle3
e[(2E)e3e(1Hepyrrole2eyl)prope2eenoyl]e2Hepyran-2-one) L3, and (3e{(2E)e3e[4e(dimethyla-
mino)phenyl]prope2eenoyl}e4ehydroxye6emethyle2Hepyrane2eone) L4. L3 and L4 were charac-
terized by X-ray crystallography. Molecules crystallize with four and two molecules in the asymmetric
unit, respectively and adopt an E conformation about the C]C bond. Both structures are stabilized by an
extended network OeH … O. Furthermore, NeH … O and CeH … O hydrogen bonds are observed in L3
and L4 structures, respectively. The in situ generated copper (II) complexes of the four compounds L1, L2,
L3 and L4 were examined for their catalytic activities and were found to catalyze the oxidation reaction
of catechol to o-quinone under atmospheric dioxygen. The rates of this oxidation depend on three pa-
rameters: ligand, ion salts and solvent nature and the combination L2[Cu (CH3COO)2] leads to the faster
catalytic process.
Received 5 June 2015
Received in revised form
28 August 2015
Accepted 31 August 2015
Available online 4 September 2015
Keywords:
Synthesis
Chalcone
X-ray crystal structure
Oxidation
Transition metal
O2 activation
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
biological relevance was fully recognized only in the previous years
due to the development of its bioinorganic chemistry and suc-
The oxidation of organic substrates with molecular oxygen un-
der mild conditions is of great interest for industrial and synthetic
processes both from an economical and environmental point of
view [1,2]. The synthesis and investigation of functional model
complexes for metalloenzymes with oxidase or oxygenase activity
is therefore of great promise for the development of new and
efficient catalysts for oxidation reactions [3]. Copper has been
known as a bio-essential element for a long time [4], but its
cessful interaction between the chemistry complex models and
metal-protein biochemistry [4e12]. It is now well known that
proteins containing copper (metal-protein) play a very important
role in transport, activation, and metabolism of dioxygen in living
organisms [13]. Several catechol derivative substrates were used in
the literature to understand the mechanisms of oxidase enzyme
research [14]. Catechol oxidase (CO) are plant enzymes [15] which
catalyze the oxidation of a broad range of o-diphenols to o-qui-
nones in presence of dioxygen [14e16] through the four-electron
reduction of molecular oxygen to water [17e20]. It was observed
that the catalytic activities of the complexes are not only dependent
on the organic ligand but also on the type of inorganic anion co-
ordinated to the copper center [21]. In this paper, we report the
ꢀ
* Corresponding author. Ecole Normale Superieure de Constantine, Laboratoire
ꢀ
ꢀ
de Physicochimie Analytique et Cristallochimie des Materiaux Organometalliques
ꢀ
ꢀ
et Biomoleculaires, Universite Constantine 1, 25000, Constantine, Algeria.
E-mail address: bouzidi_henia@yahoo.fr (H. Mousser).
http://dx.doi.org/10.1016/j.molstruc.2015.08.071
0022-2860/© 2015 Elsevier B.V. All rights reserved.

296
S. Thabti et al. / Journal of Molecular Structure 1102 (2015) 295e301
synthesis of four new chalcone derivatives of dehydroacetic acid
(Scheme 1) and describe their in situ generated copper (II) com-
plexes catecholase activity.
A mixture of dehydroacetic acid (1.68 g; 0.01 mol) and R-carbox-
aldehyde (0.01 mol) were refluxed in 25 ml of chloroform con-
taining a few drops of piperidine. 5e7 ml of the chloroform-water
azeotrope mixture was removed by a simple distillation. The
product were obtained by slow evaporation of the remaining
chloroform and washed with ethyl acetate (2 ꢂ 5 ml). L3 and L4
were recrystalized from dichloromethane and a mixture of Ethanol
and a few drops of DMSO, respectively. Crystals were dried under
vaccum.
2. Experimental
2.1. Materials and physical measurements
All reagents and solvents were analytical grade and used
without further purification. Elemental analyses were carried out
by the service central of analyses (C.N.R.S. Vernaison, France) by
Std. meth.0804-ox, with K Factors calibration.
The melting points were determined with a Kofler bank and are
not corrected. The FT-IR spectra (4000e400 cmꢀ1) are recorded
from KBr disks using FT-IR-4000 (Shimadzu) spectrophotometer.
1HNMR (300 MHz) and 13C NMR (400 MHz) spectra were recorded
using CDCl3 and tetramethylsilane (TMS) was used as an internal
reference. The electronic spectra of the ligand and its metal com-
plexes were measured on a UV PROB SHIMADZU 1700 spectro-
photometer in the range of 200e900 nm.
2.4.1. 4-hydroxy-6-methyl-3-[(2E)-3-quinolin-8-ylprop-2-enoyl]-
2H-pyran-2-one (L1)
1H NMR(CDCl3):
d ppm: 2.18 (s, 3H, CH3); 5.99 (s, 1H, C]
CHeC¼CPyr); 7.48e7.93 (m, 3H, CHeCH¼CHAryl); 8.29 (dd, 2H,
CH¼CHEth); 8.59e9.38 (m, 3H, CHeCH¼CHQuin); 11.48 (s, 1H, OH).
13C RMN(CDCl3):
d ppm: 20.67 (CH3); 99.61 (N]CH); 102.61 (C]
CH); 121.68 (CeCQuin ¼ C); 124.55 (NeC¼CQuin); 126.40 (COeC ¼ );
128.47 (CHQuin); 128.61 (CHQuin); 130.96 (CQuin); 133.28 (CQuin);
136.29 (CHQuin); 142.62 (CQuin); 146.56 (CHQuin); 150.44
(CH¼CQuin); 161.41 (CO); 168.49 (CeCH3); 183.40 (CeOH);
192.83(CO). IR (KBr,
n
cmꢀ1): 3400 (OH, Pyr); 1650 (C]N, Quin);
1520 (C]C, Aryl); 1700 (C]O); 1000 (CeO, Pyr). [M]þ Calc.
2.2. X-ray crystallographic study
C
18H13NO4: m/z ¼ 307.0845; peaks selected for the internal cali-
bration are observed: m/z ¼ 300.2017 and m/z ¼ 327.2013,
X-ray single-crystal diffraction data were collected at 293 K on a
respectively.
ꢁ
ꢁ
Diffractometre Bruker-Nonius and goniometre Kappa CCD, equip-
ped with a graphite monochromator using Mo/K
a radiation
2.4.2. 4-hydroxy-3-[(2E)-3-(1H-indol-3-yl) prop-2-enoyl]-6-
ꢀ ^
(l
¼ 0.71073 Å) (Spectropole-RX, Campus Saint-Jerome, Service
methyl-2H-pyran-2-one: (L2)
ꢀ
D11, Aix-Marseille Universite). Structures were solved by direct
methods and refined on F2 by full-matrix least-squares method,
using SHELX97 package [22]. All non-H atoms were refined aniso-
tropically by the full matrix least squares method on F2 using
SHELXL [23] and the H atoms were included at the calculated po-
sitions and constrained to ride on their parent atoms.
1H NMR (CDCl3):
d ppm: 2,23 (s, 3H, CH3); 6.18 (s, 1HPyr);
7.28e7.96 (m, 4H, CH]CHeCH¼CHAryl); 8.16 (d, 1H, CHInd); 8.22 (d,
2H, CH¼CHEthyl); 8.33 (d, 1H, -NHInd); 12.19 (S, 1H, OH). 13C NMR
(DMSO)
113 (CeCHInd); 113.78 (CH
(CH]C)Ind
d
ppm: 19.93 (CH3); 97.97 (C¼CPyr); 102.62 (C¼CHPyreC);
¼ CeN); 114.65 (CH]C)Ind; 120.08
Ind
; 122.04 (CH]C)Ind; 123.42 (CHeCeCH)Ind; 124.66
(HCeN); 136.64 (CH]CH) Ethy; 137.98 (CeNH); 142.43 (CH]CH)E-
thy; 160.91, 168.5 (CeCH3); 183.49 (CeOH); 190.41 (CO). IR (KBr,
n
(C]O); 1000 (CeO, Pyr); 3100 (CeH). [M] Calc. C18H13NO4: m/
z ¼ 307.0845; peaks selected for the internal calibration are
observed: m/z ¼ 300.2017 and m/z ¼ 327.2013, respectively.
2.3. Catecholase activity measurements
cmꢀ1): 3400 (OH, Pyr); 1650 (C]N, Ind); 1þ520 (C]C, Aryl); 1700
Kinetic measurements were made spectrophotometrically on
UVeVis spectrophotometer, following the appearance of o-quinone
over time at 25 ꢁC (390 nm absorbance maximum,
ε ¼ 1600 L molꢀ1 cmꢀ1 in methanol [24]). The complexes were
prepared in situ by successively mixing 0.15 mL of a solution
(2 ꢂ 10ꢀ3 M) of CuX2, nH2O (X ¼ Cle, Bre, NOe3 , CH3COOe or SO24ꢀ),
with 0.15 mL of a solution (2 ꢂ 10ꢀ3 M) of ligand, then adding 2 mL
of a solution of catechol at a concentration of 10ꢀ1 M.
2.4.3. 4-hydroxy-6-methyl-3-[(2E)-3-(1H-pyrrol-2-yl) prop-2-
enoyl]-2H-pyran-2-one (L3)
1H NMR (CDCl3):
d ppm: 2,13 (s, 3H, CH3); 3.58 (d,1H, NeH); 5.72
(s, 1H, NeCHPyr); 6.18 (s, 1HPy); 6.54 (s, 2H, ¼CHPyr); 6.91 (s, CH ¼ );
7.29(s, ¼CH); 11.8 (s, OH). 13C NMR (DMSO):
d ppm: 21 (CH3); 101
(C¼CPyr); 102 (C¼CHPyreC); 108.3(C¼CPyr); 11.8(CH]CH); 118.3
2.4. Synthesis and characterization
(CH
¼ CeN); 129 (CH]CH)Ethy; 129.5 (HCeN); 143.5 (CH]
Pyr
All compounds were prepared as described elsewhere [25e28].
CH)Ethy; 162.6 (CeCH3); 163 (CO); 183.8 (CO); 191.1 (CeOH). IR (KBr,
n
cmꢀ1): 3400 (OH, Pyr); 3100 (NeH); 2850 (CeHAryl); 1700þ(C]O,
Pyr); 1650 (C]N); 1700 (C]O); 1000 (CeO, Pyr). [M]
Calc.
C
13H11O4N: m/z ¼ 245.1900; peaks selected for the internal cali-
bration are observed: m/z ¼ 245.2017 and m/z ¼ 245.2013,
respectively.
2.4.4. 3-{(2E)-3-[4-(dimethylamino)phenyl]prop-2-enoyl}-4-
hydroxy-6-methyl-2H-pyran-2-one (L4)
1H NMR (CDCl3):
d ppm: 2.18 (s, 3H, CH3); 3 (s, 6H, CH3eNeCH3);
5.83 (s, 1H, CHPyr); 6.60 (s, 1H, CHAryl); 6.63 (s, 1H, CHAryl); 7.53 (s,
1H, CHAryl); 7.55 (s, 1H, CHAryl); 7.93 (d, 1H, CH¼CHEthy, J ¼ 15.5 Hz);
8.05 (d, 1H, CH¼CHEthy, J ¼ 15.5 Hz). 13C NMR (DMSO):
d ppm: 20.53
(CH3); 40.12 (H3CeN); 98.98 (C]C); 103.19 (CeHPyr); 111.77
(CeHAryl); 116.40 (CH]CHeCAryl); 122.67 (CH]CH)Ethy; 131.81
(CHAryl); 148.32 (CH]CH)Ethy; 152.70 (CHAryleN); 161.61 (CO);
Scheme 1. .
167.38 (CeO) Pyr; 183.93 (CeOH); 191.93 (CO). IR (KBr, n
cmꢀ1):

S. Thabti et al. / Journal of Molecular Structure 1102 (2015) 295e301
297
3400 (OH, Pyr); 1700 (C]O, Pyr); 1650 (C]N); 1700 (C]O); 1000
(CeO, Pyr); [M] þ Calc. C17H17NO4: m/z ¼ 300.1229; peaks selected
for the internal calibration are observed m/z ¼ 309.2272 and m/
z ¼ 327.2013, respectively.
3. Results and discussion
3.1. Reaction of DHA with RCHO
Dehydroacetic acid reacted with four carboxaldehydes RCHO
(Scheme 1) and afforded four colored chalcones: L1 (80%); L2
(70%); L3 (75%) and L4 (80%). Obtained compound were fully
characterized by mass spectrometry and by spectroscopic methods.
In the other hand, L3 and L4 were characterized by X-ray crystal-
Fig. 1. Crystal structure and atoms numbering for L3.
lography. The formation of L(1e4) is the result of
a Clai-
atom pairs C06/C09, H07/H08 are all trans, shown by the value
of ꢀ3.51 (14)ꢁ for O04eC06eC07eC08 torsion angle.
seneSchmidt condensation of DHA and RCHO derivatives.
Elemental analyses are in good agreement with the experimental
result. The 1HNMR spectrums in CDCl3, with TMS as an internal
standard, showed a singlet between 2.13 and 2.23 ppm for methyl
group hydrogens attached to the DHA ring, a singlet between 5.83
and 6.18 ppm for hydrogen of the DHA ring, a singlet between 11.4
and 11.8 ppm for the phenolic hydrogen and a doublet between 7.2
and 7.9 ppm for the two olefinic protons. The IR spectra of ligands
show bands at 3400e3100, 1700, 1520e1550 and 1650e1675 cmꢀ1
The double-bond character of the bond between C07 and C08 is
deduced from the short bond distance 1.348 (3) Å (Table 3).
Structure of L4 is stabilized by five hydrogen bonds an intra-
molecular interaction: O02eH02 … O01 and four intermolecular H
bonds: C04eH04 … O02, C015eH015 … O01, C016eH018 … O03
and C017eH017 … O04 (Fig. 4, Table 4). The stacking of molecules
within the crystal lattice generates double zigzag planes parallel to
the plane (b, c) (Fig. 4).
assignable to
n(OH) (phenolic hydrogen bonded),
n(C]O) (lactone
All bond lengths and angles in L3 and L4 have normal values
[29]. The hydroxyl hydrogen, participates in a strong intramolecular
hydrogen bond with the carbonyl atom (Table 4) and generates an S
(6) ring motif [30]. Similar intramolecular hydrogen bonds were
reported in the above-mentioned zwitterionic phenolates [31]. This
six-membered pseudocycle is almost planar and the cohesion of
the two crystals is ensured by the presence of intermolecular
hydrogen bonds.
carbonyl), (CeO) (phenolic) and
stretching mode, respectively. Additional analytical data of L1, L2,
L3 and L4 are summarized in Table 1.
n
n
(C]O) (acetyl carbonyl)
3.2. Crystallographic studies
3.2.1. Crystal structure description of L3
Orange crystals of L3 were grown in ethanol. Crystals are
monoclinic with space group P21/n. Structure of L3 is illustrated in
Fig. 1. The main crystal parameters are reported in Table 2. The
molecule of L3 adopts E configuration with respect to the C7eC8
double bond. The molecule is quite planar and the angle between
the two ring planes is 4.71ꢁ. To the C7eC8 double bond, the atom
pairs C6/C9, H7/H8 are all trans, shown by the value of 2.38 (14)ꢁ for
O4eC6eC7eC8 torsion angle. The double-bond character of the
bond between C7 and C8 is deduced from the short bond distance
3.3. Catecholase studies
The progress of the catechol oxidation reaction is conveniently
followed by monitoring the strong absorbance peak of o-quinone in
the UV/Vis spectrophotometer (Scheme 2). The metal complex
solution and catechol reductant were added together in the spec-
trophotometric cell at 25 ꢁC [32e35] (1 equivalent of ligand for 1
equivalent of metallic salt). Formation of o-quinone was monitored
by the increase in absorbance at 390 nm as a function of time. In all
cases, catecholase activity was noted. Table 5 gives absorbances of
Cu(II) complexes generated in situ after 60 min by mixing metallic
salts Cu(CH3COO)2, Cu(Br)2, Cu(Cl)2, Cu(NO3)2 and CuSO4 and li-
gands L1eL4 (1/1) and catechol. The oxidation rates are shown in
Table 6.
ꢀ
1.344 (3) Å (Table 3). Molecules of L3 exhibit one intramolecular
hydrogen bonds O3eH3 … O4 and two intermolecular Hbonds
N1eH1 … O2 and C10eH10 … O4 (Fig. 2, Table 4). In the crystal,
molecules are aligned head to foot along b axis, forming layers that
extend in zigzag parallel to the plane (a, b), (Fig. 2).
3.2.2. Crystal structure description of L4
The main crystal parameters are reported in Table 2. The
molecule of L4 with numbering scheme is given in Fig. 3. The
compound exists in an E configuration with respect to the C7eC8
double bonds.
It appears clearly that catalytic activity varies from one complex
to another. All copper complexes, catalyze the oxidation reaction of
catechol to o-quinone, but with oxidation rate values ranging from
0.035
m
mol Lꢀ1 minꢀ1, for complex formed from L1 and metallic salt
The molecule is not planar and the angle between the two rings
CuCl2 (weak catalyst), to 31.78 m
mol Lꢀ1 minꢀ1, for complex formed
derived from DHA and phenyl is 11.83ꢁ. To the C07eC08 bond, the
from ligand L2 and metallic salt Cu(CH3COO)2 (best catalyst)
Table 1
Analytical data for the ligands L1, L2, L3 and L4.
Compound
FW (g/mol)
Color
MP (ꢁC)
Rdt
Found (calc)%
C
H
O
N
L1(C18H13 O4 N)
L2(C17H13 O4 N)
L3(C13H11O4N)
L4(C17H17O4N)
307.08
295.08
245
Olive powder
Orange Powder
Orange crystal
Red crystal
215
224.7
225
80
70
75
80
70.11 (70.33)
65.04 (69.15)
63.21 (63.67)
68.65 (68.22)
4.41 (4.23)
4.05 (4.74)
4.85 (4.48)
5.76 (5.98)
20.19 (20.84)
20.14 (21.69)
26.01 (26.12)
20.59 (21.40)
4.90 (4.55)
4.42 (4.47)
5.95 (5.71)
4.72 (4.68)
299
222

298
S. Thabti et al. / Journal of Molecular Structure 1102 (2015) 295e301
Table 2
Crystallographic data and structure refinement details for L3 and L4.
Name
L3
L4
Formula
C13H11NO4
245.23
Orange
P21/n
C17H17NO4
299.31
Red
P21
316
Formula weight
Crystal color
Space group
F (000)
512
Crystal system
Unit cell dimensions
a (Å)
Monoclinic
Monoclinic
8.96322 (15)
12.25193 (16)
10.37846 (2)
93.0584 (15)
1138.11 (3)
4
10.5409 (12)
4.02669 (7)
17.2101 (2)
97.0943 (11)
725.177 (18)
2
b (Å)
c (Å)
b
(ꢁ)
V (Å3)
Z
Temperature(K)
293 (2)
5.6e73.6ꢁ
293 (2)
4.2e73.6
q
Range for data
collection (ꢁ)
Crystal size (mm)
0.2 ꢂ 0.2 ꢂ 0.08
1.54184
1.431
0.2 ꢂ 0.16 ꢂ 0.14
1.54184
1.371
Fig. 2. Intermolecular hydrogen bonds in L3.
Wavelength ((Cu Ka) (Å)
Dcalc (g cmꢀ3
)
m
(mmꢀ1
hkl range
)
0.901
0.808
ꢀ10 ꢃ h ꢃ 11
ꢀ15 ꢃ h ꢃ 15
ꢀ12 ꢃ h ꢃ 12
17,895
ꢀ13 ꢃ h ꢃ 13
ꢀ4 ꢃ k ꢃ 413
ꢀ21 ꢃ l ꢃ 21
10,547
(0.63
m
mol Lꢀ1 minꢀ1), whereas, with the other ligands, the rate
values calculated are located in the same gap but are still very low
within the range of 0.035
mol Lꢀ1 minꢀ1 (L1) to
0.252
mol Lꢀ1 minꢀ1 (L4). Comparison between the catalytic ac-
Ref Nmb of reflections
measured
Number of independent
reflections (Rint)
Number of parameters
reflections with I > 2
Refinement method
m
m
2279
2739
tivity of the complexes of copper (II) and the four ligands L1, L2, L3
and L4 (Table 6) showed that Cu-L1 complexes were observed to be
the lowest active, except in the case of SO24ꢀ anion.
165
2039
Full-matrix least-
squares on F2
1.06
205
2666
Full-matrix least-
squares on F2
1.05
s
(I)
3.3.2. Effect of ligand concentration on the catecholase activity
Evolution of catechol oxidation into o-quinone is followed by
varying the ratio of equivalents ligand L2/metallic salt Cu(CH3
Goodness-of-fit (GOF) on
F2 (S)
R [F2 >2
wR(F2)
Rint
s
(F2)]
0.041
0.123
0.041
0.81
0. 033
0.090
0.023
0.90
0.12/-0.14
-
COO)2. Three tests were carried out in ratio: 1/1; 2/1 and 1/2.
The results indicate that the test with the ratio L2/
Cu(CH3COO)2 ¼ 1 leads to the higher oxidation rate value
Absorption coeff. (mmꢀ1
)
Max/min
d
p (e/Å3)
0.16/-0.18
(31,78
rate is 23.91
reached a maximum of 8.93
m
mol Lꢀ1 minꢀ1). For the ratio 2/1, the maximum value of the
m
mol Lꢀ1 minꢀ1. For the ratio 1/2, the rate value have
m
mol Lꢀ1 minꢀ1 after 25 mn before
(Table 6). The catalytic activity depends strongly on both the
structure of the ligand and the action of the anion. Indeed, most
ligands have a low absorbance with all the anions except in the case
of acetate anion where the values of the absorbance are high
(Table 5).
decreasing, probably due to complex precipitation in the cell
(Fig. 10).
3.3.3. Solvent effect
The effect of different solvents (MeOH, DMF and CH3CN) on the
oxidation reaction with the ligand L2 and the Cu(CH3COO)2 salt was
studied under the same thermodynamical conditions. The influ-
ence of polar solvents appears clearly through the rate values ob-
tained for the oxidation reaction and the UVevisible records
(Table 6; Figs. 11e13). Methanol which is a protic and polar solvent
seems to work better than the other two aprotic solvents: aceto-
3.3.1. 1. Effect of the nature of the anion and the ligand
In the CH3COOꢀ case (Fig. 5), L2, L3 and L4 show high values of
absorbance in time. However, from 40 min of reaction, the absor-
bance starts to decrease for L2 and L4 and precipitation of the
complex could be the reason for the decrease. In sulfates, nitrates,
chlorides and bromides (Figs. 6e9), Cu-L3 complex seams the best
nitrile and DMF with a maximal value of 31.78 m
mol Lꢀ1 minꢀ1 and
oxidation
catalyst
with
a
highest
value
of
rate
is in and in agreement with results obtained previously in the
literature [36e38] and confirmed that solvatation of copper, by the
Table 3
Selected bond lengths (Å) and angles (ꢁ) in L3 and L4.
Table 4
Bond lengths (Å)
Angles lengths (ꢁ)
Bond lengths (Å) of intermolecular hydrogen bonds in L3 and L4.
L3
Compound
Hydrogen bonds
Distance (Å)
Angles (ꢁ)
N1e C9 1.374 (16)
C6eC7 1.441 (18)
C7eC8 1.344 (18)
C8eC9 1.426 (18)
L4
C1eC6 1.444 (2)
C6eC7 1.440 (2)
C7eC8 1.348 (2)
C8eC9 1.439 (2)
C1eC6eC7 122.78 (11)
C6eC7eC8 122.08 (12)
C7eC8eC9 124.46 (12)
C8eC9eN1 121.53 (11)
L3
O3eH3 … O4
N1eH1 … O2
C10eH10 … O4
O02eH02 … O01
C04eH04 … O02
C015eH015c … O01
C016eH018a … O03
C017eH017 … O04
1.683 (2)
1.998 (3)
2.706 (3)
1.661 (2)
2.615 (5)
2.611 (4)
2.639 (12)
2.635 (9)
149.57 (2)
175.38 (2)
124.41 (3)
150.03
152.15 (2)
166.33 (1)
123.86 (2)
163.07 (1)
L4
C1eC6eC7 124.24 (16)
C6eC7eC8 120.39 (17)
C7eC8eC9 128.06 (17)
C8eC9eC10 124.18 (15)

S. Thabti et al. / Journal of Molecular Structure 1102 (2015) 295e301
299
Fig. 3. Crystal structure and atoms numbering for L4.
Fig. 4. Intermolecular hydrogen bonds in L4.
bond, and became moderately reactive.
4. Conclusion
We report here the synthesis of two new chalcone
a
,
b
ligands
L1{
4-hydroxy-6-methyl-3-[(2E)-3-quinolin-8-ylprop-2-enoyl]-
2H-pyran-2-one} and L2{ 4-hydroxy-3-[(2E)-3-(1H-indol-3-yl)
prop-2-enoyl]-6-methyl-2H-pyran-2-one} with good yields. The X-
ray structures of L3 and L4 have been investigated for the first time
herein. The oxidation reaction of catechol is very efficient to give o-
quinone by complexes of copper (II), obtained with the four ligands
(L1 e L4). Copper (II) complexes were generated in situ and the
results obtained show that all the complexes catalyze the aerobic
oxidation of catechol to the corresponding o-quinone. To under-
stand the parameters influencing the catalytic activity of the
studied complexes, the nature and concentration of the ligand and
the solvent effects are studied.
Scheme 2.
aprotic and polar solvents (DMF and CH3CN), slows the catalytic
activity of the metal cation in the oxidation reaction of catechol to
o-quinone.
The copper cations are also solvated by the electronegative pole
of the solvent but are weaker than the solvation by a hydrogen
Table 5
Absorbances of Cu(II) complexes generated in situ after 60 min by mixing metallic
salt and ligand L1eL4 (1/1) and catechol.
Table 6
Oxidation rate of catechol oxidation in methanol (m
mol Lꢀ1 minꢀ1).
Ligand/metallic
salt
Cu(CH3COO)2
CuSO4
Cu(NO3)2
CuCl2
CuBr2
Ligand/metallic salt
Cu(CH3COO)2
CuSO4
Cu(NO3)2
CuCl2
CuBr2
L1
L2
L3
L4
1,4369
3,0679
2.6128
2.0217
0,0058
0.0076
0.0443
0.1287
0,0463
0,0143
0.0618
0.1202
0,0128
0.236
0015
0.0229
0.0189
0.0115
0.1972
L1
L2
L3
L4
15.34
31.78
21.05
27.13
0.084
0.079
0.456
0.445
0.114
0.144
0.630
0.571
0.035
0.236
0.252
0.038
0.092
0.195
0.560
0.119
0.2297

300
S. Thabti et al. / Journal of Molecular Structure 1102 (2015) 295e301
Fig. 5. Oxidation of catechol in presence of Cu(CH3COO)2.
Fig. 8. Oxidation of catechol in presence of bromide.
Fig. 6. Oxidation of catechol in the presence of sulfate.
Fig. 9. Oxidation of catechol in presence of chloride.
Fig. 10. Catechol oxidation in methanol, in presence of formed L2 copper complexes
Fig. 7. Oxidation of catechol in presence of nitrate.
with different concentrations.

S. Thabti et al. / Journal of Molecular Structure 1102 (2015) 295e301
301
Acknowledgments
ꢁ
We are grateful to the Algerien Ministere de l’Enseignement
ꢀ
Superieur de la Recherche Scientifique (MESRS) and the Algerian
ꢀ ꢀ
Direction Generale de la Recherche Scientifique et du
ꢀ
Developpement Technologique (DGRSDT) for financial support and
ꢀ
to Dr. Jean-Luc Parrain, Dr. Michel Giorgi, Dr Valerie Monnier and
ꢀ
Christophe Chendo, from Aix-Marseille Universite Campus Saint-
ꢀ ^
Jerome, France for analyses.
Electronic supplementary material
CCDC 1000086 and 999631 contain the supplementary crys-
tallographic data for L3 (C17H17NO4) and L4 (C13H11NO4), respec-
tively. This data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
Fig. 11. Catechol oxidation in different solvents and in presence of formed L2 copper
Complexes (1 Equivalent of ligand for 1 Equivalent of metallic salt).
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