New palladium-oxazoline complexes: Synthesis and evaluation of the optical properties and the catalytic power during the oxidation of textile dyes

Article abstract of DOI:10.3762/bjoc.11.132

The present paper describes the synthesis of new palladium-oxazoline complexes in one step with good to high yields (68-95%). The oxazolines were prepared from enantiomerically pure α-aminoalcohols. The structures of the synthesized palladium complexes we

Full text of DOI:10.3762/bjoc.11.132

New palladium–oxazoline complexes: Synthesis and
evaluation of the optical properties and the catalytic power
during the oxidation of textile dyes
Rym Hassani1, Mahjoub Jabli1, Yakdhane Kacem1, Jérôme Marrot2, Damien Prim2
and Béchir Ben Hassine*1
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2015, 11, 1175–1186.
1Laboratoire de Synthèse Organique, Asymétrique et Catalyse
Homogène (11URES56), Faculté des sciences de Monastir, Avenue
de l’Environnement, 5019 Monastir, Tunisia, Tel: 0021673500279,
Fax: 0021673500278 and 2University of Versailles
Saint-Quentin-en-Yvelines, Institut Lavoisier de Versailles, UMR
CNRS 8180, 45, avenue des Etats-Unis, 78035 Versailles, France
doi:10.3762/bjoc.11.132
Received: 11 April 2015
Accepted: 25 June 2015
Published: 15 July 2015
Associate Editor: B. Stoltz
Email:
Béchir Ben Hassine* - bechirbenhassine@yahoo.fr
© 2015 Hassani et al; licensee Beilstein-Institut.
License and terms: see end of document.
* Corresponding author
Keywords:
aminoalcohols; catalysis; dye decolorization; optical properties;
oxazolines; palladium complexes
Abstract
The present paper describes the synthesis of new palladium–oxazoline complexes in one step with good to high yields (68–95%).
The oxazolines were prepared from enantiomerically pure α-aminoalcohols. The structures of the synthesized palladium complexes
were confirmed by NMR, FTIR, TOFMS, UV–visible spectroscopic analysis and X–ray diffraction. The optical properties of the
complexes were evaluated by the determination of the gap energy values (Eg) ranging between 2.34 and 3.21 eV. Their catalytic
activities were tested for the degradation of Eriochrome Blue Black B (a model of azo dyes) in the presence of an ecological
oxidant (H2O2). The efficiency of the decolorization has been confirmed via UV–visible spectroscopic analysis and the factors
affecting the degradation phenomenon have been studied. The removal of the Eriochrome reached high yields. We have found that
the complex 9 promoted 84% of color elimination within 5 min (C0 = 30 mg/L, T = 22 °C, pH 7, H2O2 = 0.5 mL) and the energetic
parameters have been also determined.
Introduction
Palladium complexes have been used as starting materials to total synthesis of natural products and nanocompounds [5]. It is
prepare polymers [1], agrochemicals [2], pharmaceuticals [3], only since 1986 that oxazoline-based ligands have been utilized
flavors and fragrances [4]. They have also been used for the in asymmetric catalysis. This initiated considerable research
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activity in this field and triggered the synthesis of numerous
chiral ligands containing at least one oxazoline ring [6].
Oxazoline units are expected to readily coordinate to a metal
center and have been shown to bind a wide range of transition
metals [7]. The wide variety of ligands with one or more
oxazoline rings incorporating different heteroatoms, additional
chiral groups, and specific structural features have been
used in diverse reactions [8]. The importance of these ligands
lies in the fact that the stereogenic centers are kept in close
proximity to the metal and thereby having a strong and direct
influence on the stereochemical course of the metal-catalyzed
process.
Figure 1: Structure of Eriochrome Blue Black B.
Results and Discussion
The use of oxazolines as ligands during the preparation of opti-
cally active cyclopalladated compounds can give rise to
different applications [24-28].
Oxazolines possess several interesting advantages: versatility of The compilation of the literature shows that the presence of
the ligand design, their straightforward synthesis from readily substituents on the ligand promotes the cyclopalladation.
available starting materials and variability of the chiral center, Smoliakova and co-workers performed the cyclopalladation of
which are located near the donor atoms. The oxazoline unit is tert-butyl-substituted phenyloxazoline by stirring the reaction
anticipated to increase the stability of a metal complex giving mixture at room temperature [29].
rise to more air- and possibly water-stable catalysts [9].
In the light of these results, we also attempted to carry out this
Commonly, difficulties arise when trying to treat waste waters process under milder conditions. When (S)-4-isopropyl-2-
containing dyes because the dyes are recalcitrant molecules, (naphthalen-1-yl)oxazoline (2) was added to an acetic acid solu-
often resistant to aerobic digestion, and stable to light, heat, and tion of Pd(OAc)2, a yellowish precipitate was obtained and
oxidizing agents [10,11]. Recently, the catalytic oxidation was identified as (S,S)-di-μ-acetatobis[1-(4-isopropyloxazolin-2-
recognized as an effective method to treat colored waters [12]. yl)naphthalen-2-yl-C,N]dipalladium(II) (3) (Scheme 1). Unfor-
tunately, complex dimer 3 was relatively unstable, so only its
In fact, the treatment of colored waters remains a serious envi- 1H NMR and FTIR data were performed. The metathesis of
ronmental topic. Many industries such as textile, leather and dimer 3 with lithium chloride in acetone afforded the more
paper discharge various dyes during their processing operations stable (S,S)-dimer 4 in which NMR analysis shows the pres-
[13,14]. These dyes are toxic, mutagenic, and carcinogenic ence of two dimeric forms. For better elucidation of their struc-
[15,16]. That’s why many unconventional methods and tech- tures, dimeric complexes 4 were transformed into their
niques have been investigated and a number of studies have mononuclear phosphane derivatives 5a and 5b using PPh3 in
been developed [17-19]. In particular, attention has been toluene. According to 1HNMR data, the mixture contains 5a
focused on the synthesis of supports having metal complexes in and 5b in the ratio of 4:1. Essays to separate the later regioiso-
their structures due to their capacities and efficiencies to treat mers by column chromatography or preparative TLC on silica
colored waters [20-22].
gel were unsuccessful.
Owing to the easy formation of palladium–oxazoline According to the literature, the PPh3 adducts of cyclopalladated
complexes, it was very interesting to investigate the ability of oxazolines have the trans (N,P) geometry [30,31]. In addition,
some synthetic dyes to coordinate to palladium complexes by the palladacycles with oxazoline ligands exists in endo and exo
developing binary systems. This was done by complexing oxa- regioisomers. Results obtained in the present study show that
zoline with PdII ions, leading to the adsorption of dyes. More- naphthyl-oxazoline has a tendency to form exclusively endo-
over, the decolorization of the solution by Pd and Pd complexes cyclic complexes with the C=N bond within a palladacycle.
has also been applied [23].
Furthermore, NMR data analyses demonstrate that the five-
membered palladacycle 5a was preferentially formed upon the
In this paper, we report the synthesis and characterization of six-membered 5b. Indeed, palladium insertion in the peri C–H
some new palladacycles. Optical properties were determined bond of the naphthyl-oxazoline will take place at high tempera-
and the catalytic activity of these complexes was evaluated for ture reactions [32].
the first time during the degradation of organic dyes such as
Eriochrome Blue Black B referred to as Erio which was chosen In order to investigate the effect of solvents on the isomeric
as an example of azo dyes (Figure 1).
ratio, cyclopalladation of oxazoline 2 was also carried out with
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Scheme 1: Cyclopalladation reactions of (S)-4-isopropyl-2-(naphthalen-1-yl)oxazoline.
Pd(OAc)2 in refluxing MeCN. After 3.5 h the reaction yielded The molecular structure is presented in Figure 2 (see Supporting
89% of the expected dimer. However, a significant change on Information File 1 for the cif of complex 8). The coordination
the isomer ratio was observed.
geometry of 8 is pseudo-square planar with the four coordina-
tion sites occupied by the two nitrogen donors and the two chlo-
In this work, we report one example related to the direct palla- rine atoms. The molecule possesses approximate C2 symmetry
dation of enantiopure bis-oxazoline 7 having a chiral center at and its chirality has been confirmed to be the (S,S)-isomer. The
the 4-position and the substituent at the 2-position of the hetero- Pd–N and the Pd–Cl distances (Pd–N16 distance (1.963 A°),
cycles. The addition of one equivalent of 7 to a methanolic solu- Pd–N1 distance (2.031 A°)) are almost the same (Pd–Cl1 dis-
tion of Na2PdCl4 gave the palladium complex 8 in 75% yield. tance (2.281 A°), the Pd–Cl2 distance (2.259 A°)).
The coordination sphere has two chlorine atoms bonding in a
cis configuration to the Pd center and the oxazoline ligand On the other hand, the addition of (S)-4-isopropyl-2-(naph-
chelating to the Pd center via the two nitrogen atoms to form a thalen-1-yl)oxazoline (2) and 3-[(4S)-4,5-dihydro-4-isopropyl-
planar palladium ring system (Scheme 2). Crystallization by 1,3-oxazol-2-yl]propanenitrile (11) to a methanolic solution of
slow diffusion of pentane into a solution of 8 in dichloro- Na2PdCl4 at room temperature gave the palladium complexes 9
methane gave suitable crystals for an X-ray diffraction study. and 12 in 85% and 68% yields, respectively (Scheme 3). The
Scheme 2: Synthesis of cyclopalladated complex from bis-oxazoline.
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Figure 2: ORTEP drawing of the complex 8.
Scheme 3: Synthesis of the bis(oxazoline) coordinated complexes.
two complexes are stable when exposed to air and water. The All the complexes prepared in this work were characterized by
single crystal X-ray model of complex 9 is depicted in Figure 3 IR, 1H, 13C, 2D NMR, X-ray diffraction (for 9 and 8) and
(see Supporting Information File 2 for the cif of complex 9). UV–visible spectroscopy. The characterized bands in the IR
This structure confirms the expected monomeric nature of the spectra of all complexes are given in Table 1.
complex and coordination of the oxazoline nitrogen to the palla-
dium atom. The Pd(II) unit is coordinated to two monodentate Optical properties
ligands with the two nitrogen and two chlorine atoms in equato- The gap energy values (Eg) of the complexes determined from
rial positions to complete the distorted tetragonal coordination the absorption edge of the solution spectra are given in Table 2.
sphere. The two ligands coordinate to the palladium center in a The gap energy was evaluated by the extrapolation of the
trans geometry with respect to each other.
tangent to the first inflexion point of the UV curve.
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Beilstein J. Org. Chem. 2015, 11, 1175–1186.
Figure 3: ORTEP drawing of the complex 9.
Table 1: The FTIR analysis of the complexes.
vibration
bands ν (cm−1)
attribution
3
4
5
8
9
12
ν(C–H)
ν(nitrile)
ν(C=N)
ν(C–N)
δ(CH3)
ν(P–C)
ν(C–O)
δ(C–H)
δ(Pd–N)
2956.4
–
2954.8
–
2956.7
–
2961.7
–
2957.8
–
2963.9
2250.8
1635.4
1545.2
1260.3
–
1645.4
1350.2
1205.2
–
1641.6
1355.3
1210.0
–
1637.4
1436.7
1201.0
1094.9
1011.0
692.3
513.4
1638.2
1345.7
–
1642.2
1377.8
1200.4
–
–
1016.1
760
1012.9
766.2
510.9
1023.2
773.6
525.2
1030.8
776.0
573
1018.8
–
–
–
Finally, we have studied the catalytic activities of the new
complexes during the decolorization of azo dyes in solutions
which are discharged in textile industry.
Table 2: Optical properties of the chiral complexes.
complexes
λmax (nm)
Eg (eV)
3
342
341
299
380
341
300
2.67
2.50
2.34
2.72
2.57
3.21
Oxidative degradation of dyes
4
Six complexes were checked for the oxidative degradation of
Eriochrome Blue Black B. The experimental results indicated
that the complexes have potential activities during the
degradation of the azo dyes in the aqueous medium and
in the presence of hydrogen peroxide. From the preliminary
data, it was found that all the prepared complexes have demon-
5
8
9
12
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strated a promising catalytic activity at the same conditions able to decompose the reaction products completely by the
(t = 10 min, C0 = 30 mg/L, 10 mg of the catalyst, amount of cleavage of the azo linkage (chromophore structure: –N=N–, re-
H2O2 = 0.5 mL). Among the six compounds, catalyst 9 was sponsible for the color) [33,34].
found to be the most active during this study because the corres-
ponding solution became almost colorless within five minutes
(Figure 4). As also clearly depicted in Figure 5, the complete
removal of Eriochrome was reached in 10 min for all samples
tested.
Figure 4: Change in color removal in the presence of different cata-
lysts within 10 min (before filtration). T: sample which contain only the
solution of dye and H2O2.
Figure 6: Evolution of the color degradation against time using
Eriochrome plus H2O2, the complex plus H2O2 or the complex alone.
Effect of the hydrogen peroxide concentration
As proved in the previous section, the action of H2O2 alone did
not show any degradation capacity for the studied dye solution,
although this agent is considered a relatively powerful oxidant.
In this section, we examine the effect of H2O2 dose on the rate
of dye removal for an initial dye concentration of 30 mg/L
using 10 mg of the catalyst. Data given by Figure 6 revealed
that the presence of the catalyst, with the increment in H2O2
concentration, significantly reduced the time necessary to decol-
orize the solution with high target removal. As an example, we
observe that after only a 5 min reaction and at the optimum
concentration of H2O2 (0.5 mL), the decolorization of the
Figure 5: Change in color removal in the presence of different cata-
lysts (after filtration over 10 min).
In attempts to check the efficiency of the prepared complex 9 Eriochrome solution reached 84% whereas the target removal is
concerning the degradation of Eriochrome Blue Black B, we about 18% for the studied catalyst in the same condition and
have discussed the results by varying the experimental condi- using 0.2 mL of H2O2. This means that the increase of the
tions (contact time, initial dye concentration, temperature and oxidant concentration generates more free-hydroxyl radicals,
H2O2 dose).
causing the dye decolorization. On the contrary, a slight
decrease of the decolorization process from 84% to 79% has
Figure 6 represents the evolution of the rate of the degradation occurred for a highest amount of H2O2 (0.7 mL) because the
of Eriochrome against time using H2O2, the complex 9 plus solution undergoes self-quenching (scavenger) of OH· radicals
H2O2 and the complex alone [18]. First, it can be registered that by adding amounts of H2O2 to produce HO2· radicals, according
the color solution remains persistent and stable in the presence to the following equations:
of H2O2 without the addition of any catalyst. However, it was
observed that the concentration of the dye declined sharply, in H2O2 + HO· → H2O + HO2·
the presence of the system catalyst/H2O2. Indeed, 84% of the
target was achieved in the presence of the prepared catalyst HO2·+ HO· → H2O2 + O2
after only 5 min of reaction time at 22 °C whereas the dye
removal does not exceed 14% using the complex alone. The We observe that all curves depicted in Figure 7 have a pseudo-
efficiency of the combination of catalysts/H2O2 for the degrad- first-order kinetics shape, suggesting, therefore, a first-order
ation of the studied azo dye is so confirmed and catalyst 9 is kinetics law.
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Figure 7: Change of the concentration of the Erio solution with the
Figure 8: Evolution of the color removal against initial dye concentra-
variation of H2O2 dose.
tion.
Effect of the initial dye concentration on the
decolorization process
The effect of the initial dye concentration on the decolorization
process was studied at a constant dose of H2O2 and at a
temperature of 22 °C. Data given in Figure 8 exhibited that the
percentage of color removal decreased with the increase of the
initial dye concentration. As an example, it decreased from 84%
(C = 30 mg/L) to 64% (C = 70 mg/L) for a reaction time of
5 min in the presence of the studied catalyst. This confirms the
fact that the decolorization process depends, on the concentra-
tion of H2O2 and the initial dye concentration. These trends
were in agreement with those observed in our laboratory during
the study of the degradation of azo dyes [18-20] and also with
literature [35,36].
Figure 9: Change of the color removal versus temperature.
Effect of the temperature on the decoloriza-
tion process of dyes
In this section, the effect of the temperature was studied at a Thermodynamic parameters
constant dose of H2O2 and an initial dye concentration of To better understand the degradation process, the pseudo first-
30 mg/L. The results shown in Figure 9 indicated that the order kinetic equation was used to determine the kinetic para-
removal of the color was enhanced when the temperature meters. The Arrhenius law was used to calculate the activation
increased. The target removal after 5 min of reaction at 22 °C energy (Ea). The determination of the entropy and the enthalpy
and 60 °C were, respectively, 84% and 94%, in the presence of of activations (ΔS* and ΔH*) were performed using the Eyring
the studied catalyst.
equation [37]. The results are summarized in Table 3.
Table 3: Calculation of the activation parameters for the dynamic process.
T (°C)
k0 (min−1)
Ea (kJ mol−1)
ΔS* (J mol−1 K−1)
−231.594
ΔH* (kJ mol−1)
ΔG*(kJ mol−1)
22
40
60
0.0167
0.0211
0.0363
82.385
86.553
91.185
16.669
14.065
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The activation energy (Ea) has been found to be low The reuse of the prepared catalysts is found to be possible after
(16.669 kJ mol−1) confirming that the complex 9 was very effi- separation and washing. The regenerated catalysts were also
cient for the degradation of azo dyes using H2O2.
characterized by FTIR analyses after each cycle, and no change
was observed.
Reuse of the catalysts
In this section, the reusability of the catalysts was considered. Suggested mechanism of decolorization
To do this, for example, the catalyst 9 was separated by filtra- On the evidence of the kinetic studies and the literature data, we
tion, washed with distilled water after each run, then dried and propose the mechanistic pathway depicted in Scheme 4. The
further subjected to subsequent runs under the same conditions. first step involves the complexation of the azo dye to
The data given in Figure 10 indicate that the regeneration palladium(II) hydroperoxide 13, followed by a peroxymetala-
process could be repeated for six cycles, without appreciable tion of the azo moiety. This then affords the pseudocyclic five
activity loss.
membered hydroperoxometallic intermediaite 15 which decom-
Figure 10: Recycling experiments for Erio removal (C0 = 30 ppm, 20 mL) in the presence of catalyst 9 at pH 7 and T = 22 °C.
Scheme 4: Proposed mechanism of decolorization.
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poses to azoxy product 16 and palladium hydroxide complex ligand 1,2-bis[(S)-4-phenyloxazoline]benzene (7) was synthe-
17. The degradation of the azoxy product 16 can afford sized from L-(α)-(+)-phenylglycinol under the same conditions
quinolinones and diazonium salts as it established by many of the reaction as described by B. Ben Hassine et al. [42]. The
authors [38-40].
third ligand 3-[(4S)-4,5-dihydro-4-isopropyl-1,3-oxazol-2-
yl]propanenitrile (11) was obtained using the reaction of
4-ethoxy-4-iminobutanenitrile monohydrochloride with
Conclusion
In summary, new palladium-complexes using oxazolines as L-valinol in high yield [43].
ligands were synthesized, characterized and tested for the
catalytic activity during the degradation of the dye Eriochrome Synthesis of the cyclopalladated complexes
Blue Black B. The variation of the experimental conditions Synthesis of (S)-chloro-[(4-isopropyloxazolinyl)-2-
exhibited that the degradation process is contact time, initial naphthyl](triphenylphosphine)palladium(II) (5): The com-
dye concentration, temperature and H2O2 dose-dependent. plex (3) was synthesized using two methods:
84% of target removal of Eriochrome Blue Black B was
reached within minutes, under some experimental conditions. Method A: A mixture of Pd(OAc)2 (50 mg, 0.22 mmol,
These new complexes prove to be active and also to be a 1 equiv), AcONa (18.3 mg, 0.22 mmol, 1 equiv) and (S)-4-iso-
reusable catalyst for the decolorization of Erio solutions in the propyl-2-(naphthalen-1-yl)oxazoline (2, 59 mg, 0.24 mmol,
presence of hydrogen peroxide. Further work is ongoing to 1.1 equiv) in acetic acid (3.0 mL) was heated in an oil bath at 80
apply the same strategy for the degradation of other organic °C for 3.5 h. Complex 3 was isolated in 90% yield.
pollutants.
Method B: Pd(OAc)2 (50 mg, 0.22 mmol) was added to an
Experimental
acetonitrile solution (3 mL) of oxazoline (2) and refluxed for
Analytical methods
3 h at 78 °C. The mixture was allowed to cool to rt and filtered
Unless otherwise noted, all starting materials were obtained through celite. The solvent was evaporated, and the crude prod-
from commercial suppliers and used without purification. NMR uct was recrystallized from ether/petroleum ether to obtain 3
spectra were recorded on a 300 MHz and 200 MHz Bruker (89%).
spectrometer. Chemical shifts were reported in ppm relative to
the residual solvent peak (7.27 ppm for CHCl3) for 1H spectra The metathesis of dimer 3 (0.196 mmol, 1 equiv) with LiCl
and (77.00 ppm for CDCl3) for 13C spectra. All chemical shifts (18.5 mg, 0.43 mmol, 2.2 equiv) in acetone (7.0 mL) at room
were reported as δ values (ppm) relative to internal tetramethyl- temperature for 24 h afforded dimer 4 in 91% yield. PPh3
silane. High resolution mass spectrometry data were recorded (94.4 mg, 0.36 mmol, 2 equiv) was added to a stirred solution of
on an Autospec Ultima (Waters/Micromass) device with a reso- the dimer 4 (138 mg, 0.18 mmol, 1 equiv) in toluene (10.0 mL).
lution of 5000 RP at 5%. Thin-layer chromatography (TLC) After 12 h, the solvent was evaporated to obtain a pale-yellow
was carried out on aluminium sheets precoated with silica gel solid, which was purified by trituration with petroleum ether or
60 F254. Microwave irradiations were realized using an Anton recrystallization from pentane/CH2Cl2 to afford pure 5 as a
Paar Monowave 300 apparatus. Microwave heating was yellow powder in 78% yield. [α]D −350 ± 36.9 (c 0.02, MeCN);
performed with a single mode cavity Discover Microwave 1H NMR (CDCl3, 300 MHz) δ 8.03 (dd, J = 7.2 Hz, J = 1.5 Hz,
Synthesizer, producing continuous irradiation with IR tempera- 1H), 7.80 (dd, J = 9.6 Hz, J = 1.2 Hz, 1H), 7.73–7.66 (m, 2H),
ture control. An ultraviolet–visible spectrophotometer (U-2000 7.48–7.42, 7.20–7.16 (m, 15H(PPh3)), 7.09 (d, 1H), 6.97 (t, 1H),
Hitachi), wavelengths of range 200–800 nm and a quartz cell 5.46 (dt, J = 9.6 Hz, J = 4.8 Hz, CH-N, 1H), 4.58 (m, J = 9.6
were employed for the absorbance measurements.
Hz, J = 8.7 Hz, 1H), 4.37 (m, J = 8.7 Hz, J = 5.4 Hz, 1H),
2.28–2.19 (m, 1H), 0.92 (d, J = 6.9 Hz, 3H), 0.71 (d, J 6.9 Hz,
3H); 13C NMR (CDCl3, 75 MHz) δ 163.1, 143.2–123.2
Synthesis of the ligands
The amino acids and (R)-2-aminobutan-1-ol were purchased (C(PPh3)), 134.8, 132.9, 131.7, 131.1, 129.9, 128.5, 128.0,
from Sigma-Aldrich. The other α-aminoalcohols were obtained 127.8, 124.8, 123.9, 70.2, 68.0, 31.3, 18.5, 15.9; 31P NMR
by the reduction of the corresponding amino acids using the (MeOD, 75 MHz) δ 36.0 ppm; TOF–MS (ES+) for
method developed by Meyers [41]. The ligands bis- and mono- (C34H31NOPPd): theoretical [M − Cl]+: 602.1199; measured
oxazolines were prepared from the available optically pure [M − Cl]+: 602.1201; FTIR (KBr pellets, cm−1): 2956.7,
α-aminoalcohols (derived from the corresponding amino acids). 1637.4, 1436.7, 1201.0, 1094.9, 1011.0, 692.3, 513.4.
(S)-4-Isopropyl-2-(naphthalen-1-yl)oxazoline (2) was isolated
in a moderate yield from the condensation of the L-valinol with Synthesis of dichloro-[1,2-bis((S)-4-phenyl-4,5-dihydro-
naphthonitrile under microwave irradiation, while the second oxazol-2-yl)benzene]palladium(II) (8): Complex 8 was
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Beilstein J. Org. Chem. 2015, 11, 1175–1186.
synthesized from 1,2-bis((S)-4-phenyl-4,5-dihydrooxazol-2- FTIR (KBr pellets, cm−1): 2963.9, 2250.8, 1635.4, 1545.2,
yl)benzene (7) (170 mg, 0.46 mmol, 1.01 equiv) and sodium 1260.3, 1018.8.
tetrachloropalladate(II) (134 mg, 0.45 mmol, 1 equiv) in freshly
distilled and thoroughly degassed methanol (5 mL). The red Oxidative degradation procedures of dyes
solution was allowed to stand for 1 h at room temperature. After All experiments were carried out in a batch system for a period
filtration, the solid was washed with methanol to afford the of time (sufficient to achieve equilibrium) and were uniformly
expected palladium(II) complex 8 (0.34 mmol) in 75% yield. agitated at a speed of 150 rpm. The pH of the solution was
1H NMR (CDCl3, 300 MHz) δ 7.99–7.96 (m, 4H), 7.65–7.58 adjusted to 7.0 (buffered aqueous solution). 0.2 mg of each
(m, 5H, Haromat), 7.31–7.04 (m, 5H, Haromat), 5.88 (dd, J = 10.2 catalyst were added to 20 mL of the dye solution
Hz, J = 5.7 Hz, 1H), 5.06 (t, J = 9.3 Hz, 1H), 4.89 (dd, J = 9.3 (C0 = 30 mg/L) followed by the addition of a calculated dose of
Hz, J = 5.7 Hz, 1H), 4.62 (t, J = 9.3 Hz, 1H), 4.51 (t, J = 9 Hz, H2O2. At the end of each contact time, the content of the flasks
1H), 4.10 (t, J = 9 Hz, 1H); 13C NMR (CDCl3, 75 MHz) δ was filtered using a Whatman No. 41 filter paper. The concen-
162.5, 142.9–124.4, 73.2, 70.5; TOF–MS (ES+) for tration of dye in each filtrate was determined at the maximum
(C24H20ClN2O2Pd): theoretical [M − Cl]+: 511.0202; measured wavelength (531 nm). Factors affecting the degradation of the
[M − Cl]+: 511.0201.
dyes such as H2O2 dose, initial concentration and temperature
were studied in the ranges 0–0.7 mL/L, 30–70 mg/L and
22–60 °C, respectively.
Synthesis of the bis(oxazoline) coordinated
complexes
Synthesis of dichlorobis[(4-isopropyl-2-naphthalen-1-yl)oxa-
zoline)]palladium(II) (9) and dichlorobis(4-isopropyl-2-(2-
cyanoethyl)oxazoline)palladium(II) (12): Complexes 9 and 12
were synthesized using the same procedure. A solution of
sodium tetrachloropalladate(II) Na2PdCl4 (0.34 mmol, 1 equiv)
in absolute MeOH (3 mL) was added to (0.75 mmol, 2.2 equiv)
of the ligand. A yellow precipitate was formed immediately.
The mixture was stirred for 24 h at room temperature. After
removal of the solvent under reduced pressure, the yellow solid
was washed with methanol, and recrystallized from CHCl3/
hexane. Yields of dichloro[bis(4-isopropyl-2-naphthalen-1-
yl)oxazoline]palladium(II) (9) and dichloro[bis(4-isopropyl-2-
(2-cyanoethyl)oxazoline)]palladium(II) (12) are 85% and 68%,
respectively.
Supporting Information
The electronic Supporting Information includes the X-ray
diffraction of the structures of complexes 8 and 9. The
crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data
Center, CCDC 1052659-1052660 for 8 and 9, respectively.
Crystallographic data associated with this article can be
obtained, free of charge, on application to CCDC, at
http://www.ccdc.cam.ac.uk/deposit/.
Supporting Information File 1
CIF file for complex 8.
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-11-132-S1.cif]
Complex 9: [α]D −113 ± 28 (c 0.1, MeCN); 1H NMR (CDCl3,
300 MHz) δ 8.49 (d, J = 6.9 Hz, 1H, H1), 8.00–7.97 (m, 2H,
H3,7), 7.90–7.87 (m, 1H, H5), 7.55–7.49 (m, 2H, H6,7), 7.43 (bs,
1H, H2), 4.58–4.50 (m, 1H, CH-N), 4.46–4.38 (m, 2H, CH2-O),
2.62 (m, 1H, CH(CH3)2), 0.99 (d, J = 6.9 Hz, 3H, CH3), 0.92
(d, J = 6 Hz, 3H, CH3); 13C NMR (CDCl3, 75 MHz) δ 168.9,
133.2, 132.0, 130.7, 130.0, 128.2, 127.1, 126.4, 125.8, 124.6,
124.2, 70.8, 69.3, 30.0, 19.1, 15.3; TOF–MS (ES+) for
(C18H29ClN4O2Pd): theoretical [M − Cl]+: 615.1365; measured
[M − Cl]+: 615.1361; FTIR (KBr pellets, cm−1): 2957.8,
1642.2, 1377.8, 1200.4, 1030.8, 776.0, 573.
Supporting Information File 2
CIF file for complex 9.
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-11-132-S2.cif]
Supporting Information File 3
Experimental procedures, spectroscopic and analytical data,
and copies of spectra of the products.
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-11-132-S3.pdf]
Complex 12: [α]D −5.7 ± 0.5 (c 0.94, CHCl3); 1H NMR
(MeOD, 300 MHz) δ 3.64–3.56 (m, 1H), 3.50–3.39 (m, 2H), Acknowledgements
2.66–2.45 (m, 1H), 1.83–1.73 (m, 1H), 0.88–0.80 (m, 6H); 13C The authors are grateful to the DGRS “Direction Generale de la
NMR (MeOD, 75 MHz) δ 173.0, 119.4, 64.0, 58.9, 33.1, 30.8, Recherche Scientifique” (Directorate General for Scientific
20.8, 19.6, 14.7; TOF–MS (ES+) for (C18H29Cl2N4O2Pd): theo- Research) of the Tunisian Ministry of Higher Education and
retical [M + H]+: 509.0594; measured [M + H]+: 509.0598; Scientific Research, the CNRS, the University of Versailles
1184

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