New palladium (II) complexes with Thiophene and furan bridged N-Acylbenzotriazole ligands: Synthesis, characterization and hydrogenation activity in ionic liquid

Article abstract of DOI:10.1016/j.molliq.2017.06.038

Palladium complexes of N-acylbenzotriazole derivative ligands were synthesized and characterized. The catalytic activities of complexes of ([PdL1(OAc)₂] and [PdL2(OAc)₂]) were investigated in relation to hydrogenation reactions of styrene, 1-octene and cyclohexene in [bmim][BF₄] as greener reaction media. 100% ethyl benzene conversion was obtained with both complexes in 1?h reaction time. Additionally, 100% 1-octene conversion was reached within the same period of time with [PdL2(OAc)₂] complex. In cyclohexene hydrogenation, product formation reached up to 67% at 363?K with [PdL1(OAc)₂] complex. Reusability tests were conducted under the highest product conversion conditions, and both catalysts were found to be efficient up to 5?cycles for all substrates. The other reaction parameters such as solvent effect, H₂ (g) pressure, n_s/n_c ratio were also investigated.

Full text of DOI:10.1016/j.molliq.2017.06.038

Accepted Manuscript
New palladium (II) complexes with Thiophene and furan bridged
N-Acylbenzotriazole ligands: Synthesis, characterization and
hydrogenation activity in ionic liquid
Hakan Ünver, Filiz Yilmaz
PII:
DOI:
Reference:
S0167-7322(17)30638-4
doi: 10.1016/j.molliq.2017.06.038
MOLLIQ 7484
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
11 February 2017
###REVISEDDATE###
6 June 2017
Please cite this article as: Hakan Ünver, Filiz Yilmaz , New palladium (II) complexes with
Thiophene and furan bridged N-Acylbenzotriazole ligands: Synthesis, characterization
and hydrogenation activity in ionic liquid, Journal of Molecular Liquids (2017), doi:
10.1016/j.molliq.2017.06.038
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ACCEPTED MANUSCRIPT
New Palladium (II) Complexes with Thiophene and Furan Bridged N-
Acylbenzotriazole Ligands: Synthesis, Characterization and Hydrogenation
Activity in Ionic Liquid
Hakan Ünvera, Filiz Yilmaz*,a
a. Anadolu University, Faculty of Science, Chemistry Department, 26470 Eskisehir,
Turkey.
Abstract: Palladium complexes of N-Acylbenzotriazole derivative ligands were
synthesized and characterized. The catalytic activities of complexes of ([PdL1(OAc)2]
and [PdL2(OAc)2]) were investigated in relation to hydrogenation reactions of styrene,
1-octene and cyclohexene in [bmim][BF4] as greener reaction media. 100% ethyl
benzene conversion was obtained with both complexes in 1h reaction time.
Additionally, 100% 1-octene conversion was reached within the same period of time
with [PdL2(OAc)2]) complex. In cyclohexene hydrogenation, product formation
reached up to 67% at 363 K with [PdL1(OAc)2] complex. Reusability tests were
conducted under the highest product conversion conditions, and both catalysts were
found to be efficient up to five cycles for all substrates. The other reaction parameters
such as solvent effect, H2 (g) pressure, ns/nc ratio were also investigated.
Keywords: N-Acylbenzotriazole, Palladium, Ionic Liquid, Hydrogenation
* Corresponding author. Tel.: +90 505 564 20 94
E-mail address: fyilmaz@anadolu.edu.tr
1. Introduction
The primary purpose of a chemical reaction is to achieve maximum product yield
and selectivity in a short period of time. Unfortunately, it is always not possible to
achieve 100% yield and selectivity for every chemical reaction. Catalysts help at this
point. Without using a suitable catalyst, reactions generally require much more time and
energy during the desired product formation and by-products are observed many times
as well. Organometallic compounds can behave as suitable catalysts for several
chemical reactions such as hydrogenation [1,2], hydroformylation [3,4], oxidation [5,6]
etc offering high product yields and selectivities. The common problems in catalytic
reactions are decomposition of expensive catalysts, laborious product isolation, low
activities and selectivities, poor reagent and catalyst solubility, and all these problems
force the chemists to search alternative solvent systems. ILs can solve not all but most
of these problems. Ionic liquids (ILs) are low-melting (<373 K) salts having numerous
specialities including thermal stability [7], low vapour pressure [8], non-toxic [9-11] and
non-flammability [12]. These specialities make them better alternatives to conventional
organic solvents [13,14]. They can solve several inorganic, organic, organometalic and
polymeric compounds.
N-heterocycles are important compounds thanks to their significant chemical,
biological and pharmacological activities [15]. One of these compounds, benzotriazole
(Bt) derivatives, has widespread research area for different industrial applications
including field-effect transistors [16], light emitting diodes [17], photovoltaic devices
[18], solar cells [19] synthetic products [20] and so on. Benzotriazole derivatives have
also drawn increasing attention in coordination chemistry due to excellent coordination
1

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capability. They are used as N-donor ligand. Most of the Bt derivatives are air and
moisture stable compounds, and they are thus preferred ligands for catalytic reactions.
For example, Hurtado, J., et al. reported 3,5-bis (benzotriazol-1-ylmethyl) toluene
ligand obtained between 3,5-bis (bromomethyl) toluene and benzotriazole reaction.
Synthesized ligand was then reacted with [PdCl2(cod)] (cod = 1,5-cyclooctadiene) to
form a new palladium complex catalyst for oxidative amination reactions [21].
Wangming, D. et al. synthesized several ruthenium(II) complexes with 2-
(benzimidazole-2-yl)-6-(benzotriazole-1-yl)pyridine ligand for examining its catalytic
effects on transfer hydrogenation reactions [22].
In this study, we prepared two N-Acyl-benzotriazole derivative ligands via
substitution reaction between 1H-benzotriazole and thiophene or furan-2,5-dicarboxylic
acid compounds in the presence of chlorinating agent (thionyl chloride), and the one
with thiophene-substituted benzotriazole ligand had been reported by our research
group23 before. Synthesized ligands were then reacted with palladium acetate precursor
to obtain two new palladium complexes. All the compounds were characterized with
1
FT-IR, H-NMR, 13C-NMR and elemental analysis techniques. Catalytic activity of
complexes was investigated in relation to hydrogenation reactions of some olefins
(styrene, 1-octene and cyclohexene) in 1-buthyl-3-methylimidazolium tetrafluoroborate
([bmim][BF4]).
2. Experimental
2.1. Materials
All the reagents were commercially obtained (Sigma-Aldrich and Merck) at highest
quality and used without further purification. 1-butyl-3-methylimidazolium
tetrafluoroborate, thiophene-2,5-dicarboxylic acid and palladium (II) acetate were
purchased from Aldrich Chemical Co. 1H-benzotriazole, styrene, 1-octene and
cyclohexene were obtained from Merck. Chemical syntheses were carried out under a
dry nitrogen atmosphere using standard Schlenk techniques unless otherwise noted.
2.2. Measurements
1H and 13C-NMR spectra were recorded on a Bruker (500 MHz) DPX FT
spectrometer, using the solvents of CDCl3 and DMSO-d6. Chemical shifts were
expressed in δ (ppm) using TMS as the internal standard. Elemental analysis was
conducted using Elementar Vario EL III microanalyzer. The magnetic susceptibility
was measured at room temperature (20-28 °C) with a Sherwood Scientific MX-I Model
magnetic balance. The melting points were determined on a capillary melting point
apparatus Stuart SMP30. FT-IR spectra were recorded with Perkin Elmer Spectrum 100
Spectrometer using KBr discs. Mass spectra were recorded on Agilent LC-MSD Trap
SL spectrophotometer. The conversions of products in catalytic hydrogenation reactions
were determined with Thermo Finnigan Trace GC using a Permabond SE-54-DF-0.25,
25 m x 0.32 mm ID column and using helium as carrier gas.
2.3. Synthesis of ([5-(Benzotriazole-1-carbonyl)-thiophen-2-yl]-benzotriazol-1-yl-
methanone) ligand (L1)
Ligand (L1) was synthesized as described previously [23] (Figure 1). The solution
of 1H-Benzotriazole (5.6 g, 0.047 mol) in THF was cooled to 273 K, and SOCl2 (1 mL,
0.013 mol) was added dropwise to the solution under nitrogen atmosphere. The solution
was mixed for 30 minutes, and then the solution of thiophene-2,5-dicarboxylic acid (1.0
g, 0.0058 mol) in THF was added. The mixture was stirred at room temperature for 24
2

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h. At the end of the reaction, the mixture was filtered, and the solvent was removed
under vacuum. The residue was dissolved in dichloromethane and extracted with 6 N
HCl (3 x 10 mL). The organic phase was dried over anhydrous MgSO4 and evaporated.
Ligand was obtained as a white solid. Yield: 82.2%, m.p.: 513 K. Anal. Calc. (%) for
C18H10N6O2S: C=57.8; H=2.7; S=8.6; N=22.5. Found: C=58.1; H=2.5; S=8.3; N=22.8.
1
FT-IR (cm-1): 1695, 1368, 1223. H-NMR: (500 MHz, CDCl3, δ ppm): 8.65 (2H, s),
8.46 (2H, d, J=8.25 Hz), 8.25 (2H, d, J=8.25 Hz), 7.78 (2H, t, J=7.46 Hz), 7.62 (2H, t,
J=7.46 Hz), 13C-NMR: (500 MHz, CDCl3, δ ppm): 159.02, 146.03, 141.72, 137.20,
131.98, 130.94, 126.84, 120.60, 114.83.
2.4. Synthesis of ([5-(Benzotriazole-1-carbonyl)-furan-2-yl]-benzotriazol-1-yl-
methanone) ligand (L2)
Ligand (L2) was synthesized from the reaction between furan-2,5-dicarboxylic
acid and 1H-benzotriazole according to the same procedure described for L1. White
solid. Yield: 70%, m.p.: 536 K. Anal. Calc. (%) for C18H10N6O3: C=60.3; H=2.8;
1
N=23.4. Found: C=59.4; H=2.5; N=23.2. FT-IR (cm-1): 1710, 1379, 1249. H-NMR:
3
3
(500 MHz, CDCl3, δ ppm): 8,48 (2H, d, J=8,27), 8,34 (2H, s), 8,24(2H, d, J=8,28),
7,78 (2H, t, J=7,33), 7,62 (2H, t, J=7,34). 13C-NMR:(500 MHz, CDCl3, δ ppm):
154,39 C(a), 147,66 C(b), 145,72 C(c), 131,98 C(d), 131,06 C(e), 126,90 C(f), 124,41
C(g), 120,52 C(h), 114,78 C(ı)
3
3
Figure 1: Synthesis procedure of L1 and L2 ligands
2.5. Synthesis of [PdL1(OAc)2]
Palladium acetate (100 mg, 0.45 mmol) was dissolved in 50 mL THF and added to
the ligand solution (180 mg, 0.48 mmol in 20 mL THF) at 323 K for 30 minutes. The
mixture was stirred at room temperature for 72 h under nitrogen atmosphere. The
precipitated brown solid was isolated by filtration and washed with THF (3 x 10 mL)
and then dried under vacuum (Scheme 2). Yield 42 %, (120 mg), m.p.: > 593 K
decomp. Anal. Calc. (%) for C22H16N6O6SPd: C=44.1; H=2.6; S=5.4; N=14.0. Found:
C=44.8; H=2.9; S=5.1; N=13.7. LC-MS, m/z (calc./found): 670.1/660.1 FT-IR (cm-1):
1
1695, 1508, 1368, 533, 427 H-NMR: (500 MHz, d6-DMSO, δ ppm): 8.65(2H, s), 8.40
(2H, d, J=8.23), 8.38(4H, dd, J1=12.3 Hz, J2=8.23 Hz), 7.89 (2H, t, J=7.50), 7.72 (2H, t,
J=7.70), 1.91 (3H, s) 13C-NMR: (500 MHz, d6-DMSO, δ ppm): 162.85, 140.24, 138.80,
134.88, 133.68, 114.95, 97.69, 84.81, 67.51, 66.26, 23.95
2.6. Synthesis of [PdL2(OAc)2]
[PdL2(OAc)2] was synthesized with the same procedure described above (Figure 2).
Dark brown solid. Yield 53 %, m.p.: > 593 K decomp. Anal. Calc. (%) for
C22H16N6O6SPd: C=45.3; H=2.7; N=14.4. Found: C=44.6; H=2.4; N=14.7. LC-MS, m/z
1
(calc./found): 654.1/661.3 FT-IR (cm-1): 1720, 1577, 1330, 523, 434 H-NMR: (500
3

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MHz, d6-DMSO, δ ppm): 8,15 (2H, s), 8,08 (2H, d, 3J=8,39), 7,92 (2H, d, 3J=8,34), 7,59
3
3
(2H, t, J=7,38), 7,45 (2H, t, J=7,56), 2,09 (3H, s, asetat). 13C-NMR: (500 MHz, d6-
DMSO, δ ppm): 202,2, 159,94, 148,24, 147,91, 118,51, 104,52, 97,67, 66,35, 33,76,
24,07, 21,73.
Figure 2: Synthesis and possible structures of complexes
2.5. Characterization of ligands and complexes
In this study, the ligands acting as a bidentate ligand and coordinates to the
palladium centre. Detailed description and characterization of L1 had been published
previously.
Therefore, we here explain [PdL1(OAc)2] characterization. In the IR spectrum of
[PdL1(OAc)2] complex, Pd-N and Pd-O (from acetate oxygen) peaks were observed at
533 cm-1 and 427 cm-1, respectively. Formation of the Pd-N bond indicates that ligand
coordinated to the metal center via nitrogen atoms (See Supplemantary Materials,
Figure S1). In the 1H-NMR spectra of the L1 ligand, the aromatic protons of the N-acyl
benzotriazole moiety appeared to be two triplet (7.62 ppm and 7.78 ppm) and two
doublet (8.25 ppm and 8.46 ppm), and the thiophene protons appeared to be a single
peak (8.65 ppm) because of the symmetrical nature of the ligand (See Supplemantary
1
Materials, Figure S2). In the H-NMR spectra of [PdL1(OAc)2] complex, benzotriazole
protons appeared to be doublet of doublets at 8.38 ppm and triplets at 7.89 and 7.72
ppm. Also, we noted the presence of a singlet at 1.91 ppm corresponding to CH3
protons of acetate ligand (See Supplemantary Materials, Figure S3). In the 13C-NMR
spectrum of the L1 ligand had nine signals between 159.02-114.83 ppm due to the
symmetrical nature of ligand. The signal located at 159.02 ppm corresponds to the
carbonyl group. The signals located at 146.03 and 137.2 ppm corresponding to
thiophene carbons. The carbons of benzotriazole ring appeared to be between 140.24-
66.26 ppm(See Supplemantary Materials, Figure S4). In 13C-NMR spectrum of
[PdL1(OAc)2] complex, carbon signal of C=O shifted to 162.85 ppm. The methyl
carbon of the acetate ligand appeared to be at 23.95 ppm (See Supplemantary Materials,
Figure S5).
In the IR spectrum of L2 ligand, the O-H stretching vibration of dicarboxylic acid
disappeared after benzotriazole substitution. Vibrations observed at 3176-3134 cm-1
were related to aromatic C-H bonds. Carbonyl stretching frequency shifted from 1689
cm-1 to 1710 cm-1 after substitution with benzotriazole. C-N stretching and bending
vibration peaks were observed at 1379 cm-1 and 1249-1212 cm-1, respectively (See
Supplemantary Materials, Figure S6). After the complex formation, peaks observed at
4

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1330 and 1223 cm-1 were dedicated to coordination which occurred via nitrogen atom of
L2 ligand. Eventually, frequency shifting for about 49 cm-1 value was observed. Pd-O
vibration of acetate ion was also observed at 434 cm-1 (See Supplemantary Materials,
Figure S7). In the 1H-NMR spectrum of L2 ligand, aromatic protons of benzotriazole
part were observed as two triplet (7.62-7.78 ppm) and two doublet (8.24-8.48 ppm)
signals. Singlet peak observed at 8.34 ppm was related to furan protons signal (See
Supplemantary Materials, Figure S8). In the [PdL2(OAc)2] complex spectrum, proton
signals of furan ring shifted from 8.34 ppm to 8.15 ppm. Additionally, two triplet peaks
of free ligand at 7.62 ppm and 7.78 ppm shifted to 7.45 ppm and 7.59 ppm. After the
complexation, two doublet proton peaks of benzotriazole ring at 8.24 ppm and 8.48 ppm
appeared at 7.62 ppm and 7.78 ppm respectively. The acetate group peaks were
13
observed at 2.09 ppm as singlet signal (See Supplemantary Materials, Figure S9). C-
NMR spectrum of L2 ligand contains nine carbon signals between 154.3-114.7 ppm.
The carbonyl (C=O) carbon signal was observed at 154.3 ppm. The carbon atoms of
furan ring were observed at 147.6 ppm and 124.4 ppm. The other carbon signals
between 145.7-114.7 ppm were related to benzotriazole group (See Supplemantary
13
Materials, Figure S10). In the C-NMR, the spectrum of [PdL2(OAc)2] complex was
observed to have eleven signals between 202.2-21.7 ppm values. The aromatic carbon
signals pf complex were observed between 159.9-104.5 ppm. The signals observed at
21.7 ppm and 202.2 ppm were associated with methyl and carbonyl carbon of complex
acetate ion (See Supplemantary Materials, Figure S11).
The UV-VIS spectrum of complexes and ligands were taken with DMSO solutions
between 200-800 nm range. For L1 ligand, π→π* and n→π* intra ligand transitions
were observed at 262, 281 and 335 nm. After the formation of [PdL1(OAc)2] complex,
these transitions shifted to lower wavelength (251 and 331 nm) (See Supplemantary
Materials, Figure S12). The transitions observed at 252, 279 and 333 nm for L2 ligand
shifted to 265 and 320 nm in the [PdL2(OAc)2] complex spectra (See Supplemantary
Materials, FigureS13). Any d-d transitions of both complexes were not observed from
spectra because of d8 electronic configurations of metal ions.
The mass spectra of [PdL1(OAc)2] complex showed the molecular ion peak at m/z
661.4. This value indicates that the solvent molecule tetrahydrofuran (THF) was trapped
in the complex structure (See Supplemantary Materials, Figure S14). The same situation
was observed also for [PdL2(OAc)2] complex with close m/z value as m/z 661.3 (See
Supplemantary Materials, Figure S15). The magnetic susceptibility measurement of
complexes was performed according to the method of Evans with a Gouy balance. The
experimental magnetic susceptibility values were equal to zero for both complexes. This
indicated that the complexes were diamagnetic with all electrons paired and that both of
the geometries were square planar. In line with all these characterization studies, the
proposed structures of complexes can be seen in Figure 2.
2.6. Catalytic studies
Catalytic hydrogenation experiments were carried out using a 100 mL stainless
steel high pressure reactor (Parr Inc. 4590 micro Bench Top with 4842 process
controller) containing a magnetic bar, temperature controller and sapphire window for
viewing. Before this, each experiment reactor was first cleaned, and substrate, catalyst
and ionic liquid were then placed into the reactor. The reactor was tightly closed and
flushed with nitrogen gas to displace any air inside. The reactor was heated to reaction
temperature, and hydrogen gas was introduced into the reactor. After the reaction ended,
5

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hydrogen gas was depressurized with valves and product(s) extracted with n-hexane
from ionic liquid media; then, the organic solution was directly analyzed by gas
chromatography.
We also investigated reusability of catalysts. For this purpose, when the main
reaction was completed, catalyst was removed from ionic liquid via extraction with
DMSO, filtered and washed with acetone and diethylether and dried at 333 K. Fresh
reactants and catalyst was added to reactor for the next reaction cycle.
2.7. Solubility Tests of Complexes in IL
Qualitative solubility of complex in [bmim][BF4] was investigated by visual
observation under different temperatures (303-383 K). For this purpose, 1 mL
[bmim][BF4] and 10 mg catalyst was placed in a test tube, mixed and heated to desired
temperature. The solution was stirred for one hour, and solubility was observed by
visual observation. Both complexes were found to be insoluble in [bmim][BF4] and to
act as a heterogeneous catalyst during the catalytic reactions.
3. Results and discussion
The objective of the catalytic study presented here was to develop an
environmentally friendly catalytic system for the hydrogenation of some olefins. For
this purpose, in this study, we synthesized two new Pd complexes for use as
hydrogenation catalysts. In addition, we also aimed at using ionic liquid as reaction
media. The results obtained are presented below.
3.1. Styrene hydrogenation in IL
The effects of various parameters such as temperature, H2(g) pressure, reaction
medium, catalyst amount and reaction time on the hydrogenation reactions of styrene
were investigated. We also investigated the reusability of the palladium catalysts. The
data obtained can be seen in Table 1 and Table 2.
Table 1. Hydrogenation of styrene by [PdL1(OAc)2] complex
Ent.
1
T(K)
313
323
333
343
353
323
323
353
353
353
353
353
353
353
353
PH2 (Bar)
t(h)
ns/nc Total Conv. (%) TON
TOF(h-1)
10
1
103
103
103
103
103
103
103
103
103
103
172
515
103
103
103
4
4
3.8
14.9
28.8
52.7
100
46.8
75.4
23.5
35.6
54.4
100
65
2
3
10
10
10
10
30
60
10
10
10
10
10
10
10
10
1
1
15
15
30
30
4
1
55
55
5
1
104
49
104
49
6
1
7
1
78
78
8
0.25
0.5
0.75
1
24
92
9
37
74
10
11
12
13b
14c
15d
57
75
172
338
104
104
94
172
338
104
104
94
1
1
100
100
90.1
1
1
a Reaction conditions: ncat. = 8.36x10−6 mol, nstyr. = 8.69x10−4 mol, Vsolv. = 0.5 mL, PH2 = 10 bar; b DMSO;
c Toluene; d cat.= [Pd(OAc)2].
6

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For [PdL1(OAc)2] complex, the effects of reaction temperature were investigated in
the range of 313 K to 353 K, and the other reaction parameters were kept constant
(PH2=10 bar, sub./cat.=103). It was observed that the conversion value reached from 3.8
% to 100 % with the increasing temperature in 1h (Entries 1-5). As a result of the
increasing reaction temperature, higher energizing molecules can easily exceed the
activation energy required to form the desired product and increase the product yield.
Hence, the optimal reaction temperature was found to be 353 K.
We studied four different reaction times to determine the optimal reaction time in the
hydrogenation of styrene (Entries 5, 8-10 ). 100 % ethylbenzene formation was obtained
in 1 h at 353 K. Hence, the remaining catalytic experiments were conducted in 1 hour
reaction time.
To investigate the effects of the hydrogen pressure, experiments were carried out at
10, 30 and 60 bar H2(g) pressures at 323 K in 1h. According to the results, the hydrogen
pressure had a strong effect on ethyl benzene conversion. TON value increased from 15
to 78 as shown in entries 2, 6 and 7. In order to determine the catalyst amount effect on
styrene hydrogenation reactions, three different ns/nc ratios were selected (Entries
5,11,12) at 393 K in 1h. The conversion of ethylbenzene increased from 65% to 100%
when the ns/nc ratio decreased from 515 to 172. Reusability and recovery of catalyst
from the reaction media are important issues for catalytic systems. The reusability of
[PdL1(OAc)2] complex was investigated for the five cycles under the optimal reaction
conditions (353 K, 10 bar H2 and 1 h), and catalyst activity retained over 96% without
observing significant deactivation for at least three cycles (Figure 1).
%100
%100
%96
%86,
100
80
60
40
20
0
%70,4
1
2
3
5
4
Cycle No
Fig 1. Reusability of [PdL1(OAc)2] catalyst in styrene hydrogenation. Reaction conditions: T = 353 K,
PH2= 10 bar, nsub. = 8.69 × 10−4, ncat. = 8.36 × 10−6 mol, ns/nc = 103, t = 1 h.
For [PdL2(OAc)2] complex, temperature effect was investigated between 313 K
to 363 K under constant hydrogen pressure (10 Bar), reaction time (1 h) and sub./cat.
ratio (100) (Entries 1-6). According to the results, ethylbenzene conversion increased
from 13.9% to 100% with the increasing reaction temperature. We determined the
optimal reaction temperature for [PdL2(OAc)2] complex as 363 K. H2 pressure effect
experiments were carried out at minimum conversion temperature as 323 K in order to
observe whether there was an increase in the conversion value of the desired product
with the rising hydrogen pressure. When the pressure increased from 10, 30 and finally
7

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60 bar, ethylbenzene conversion was found to increase from 28.4%, 93.7% and finally
to 100%, respectively (Entries 2,7,8).
Table 2. Hydrogenation of styrene by [PdL2(OAc)2] complex
Ent.
1
T(K)
313
323
333
343
353
363
323
323
353
353
363
363
363
PH2 (Bar)
t(h) ns/nc
Total Conv. (%)
TON
TOF(h-1)
10
1
1
1
1
1
1
1
1
1
1
1
1
1
100
100
100
100
100
100
100
100
167
500
100
100
100
14
14
13.9
28.4
38
2
3
10
10
10
10
10
30
60
10
10
10
10
10
29
38
29
38
4
44
44
43.6
74.6
100
93.7
100
73.4
45.6
100
100
92,7
5
75
75
6
101
95
101
95
7
8
101
124
230
101
101
93
101
124
230
101
101
93
9
10
11b
12c
13d
a Reaction conditions: ncat. = 8.59 × 10−6 mol, nstyr. = 8.69 × 10−4 mol, Vsolv. = 0.5 mL, b DMSO; c Toluene;
dcat.= [Pd(OAc)2].
In order to test the effect of ns/nc ratio on styrene hydrogenation reactions,
experiments were carried out with the ns/nc values of 100, 167 and 500. According to
the results, the highest TON value (TON=230) was obtained with ns/nc =500 at 353 K in
1h (Entries 5, 9, 10).
To test the effect of solvent type on catalytic reactions, toluene and DMSO were
selected as non-polar and polar solvents. The results indicated that catalytic cycle does
not depend on the solvent polarity under the same conditions (353 K, 10 bar H2 and 1h
reaction time) (Entries 6, 11, 12).
As for the testing of [PdL2(OAc)2] catalyst reusability, experiments were
conducted for five cycles with the same catalyst under optimal reaction conditions (363
K, 10 bar and 1 h). Catalyst was found to be effective over five cycles without loss of its
activity. Catalyst reusability results are given in Figure 2.
%100
%100
%100
%100
%100
100
80
60
40
20
0
1
4
5
2
3
Cycle No
8

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Fig 2. Reusability of [PdL2(OAc)2] catalyst in styrene hydrogenation. Reaction conditions: T = 363 K,
PH2= 10 bar, nsub. = 8.69 × 10−4, ncat. = 8.59 × 10−6 mol, ns/nc = 100, t = 1 h.
3.2. 1-Octene Hydrogenation in IL
1-octene was chosen as a terminal olefin in catalytic experiments. The results are
given in Table 2. n-octane is the desired hydrogenation product of 1-octene. Conversion
to internal alkenes as 2-octene and 3-octene (byproduct) was also observed in some
cases.
In order to study the effect of temperature on catalyst activity of [PdL1(OAc)2]
catalyst, the experiments were conducted at 4 different temperatures (333-363 K). The
catalyst activity was found to be very low at 333 K with only 2.4% n-octane formation.
Increasing reaction temperature from 343 to 363 K resulted in an increase in n-octane
selectivity from 10.9% to 86.7% and in an increase in the total conversion value.
Reusability tests of the same catalyst were performed at 363 K in 1h as shown in
Table 2. The conversion rate was found to be about 80% for the first four cycles and to
decrease to 65.7% at the last cycle.
Table 3. Hydrogenation of 1-octene by [PdL1(OAc)2] complex
Cycle Total Conv.
Ent.
T(K)
Products (%)
TON TOF (h-1)
No
(%)
(n-octane) (2-octene) (3-octene)
1
2
3
333
343
353
363
363
363
363
363
363
363
2.4
2.4
------
3.1
15.3
6.9
38.1
0
21.6
19.2
21.4
17.2
------
1.6
8.1
2.0
17.4
0
10.4
13.7
12.4
10.2
2
2
15.6
81.7
95.6
91.2
100
87.9
84.2
79.3
65.7
10.9
58.3
86.7
35.7
100
55.9
51.3
45.4
38.3
12
62
73
69
76
67
64
60
50
12
62
73
69
76
67
64
60
50
4
1
5b
6c
7
2
3
4
5
8
9
10
a Reaction conditions: ncat. = 8.36 × 10−6 mol, n1-oct. = 6.37 × 10−4 mol, ns/nc=76, Vsolv. = 0.5 mL, PH2 = 10
bar, t=1h, b DMSO, c Toluene.
To test the effectivity of [PdL2(OAc)2] catalyst on 1-octene hydrogenation,
experiments were conducted between 323 K - 353 K temperatures. Catalyst activity was
found to be lower at 323 K than at other temperatures (Entry 1). It was found that the
increasing reaction temperature had a positive effect on hydrogenation reactions under
the same conditions (10 Bar H2, 1 h reaction time). The highest conversion rate was
obtained at 353 K in 1 h reaction time with 100% n-octane formation (Entry 4).
Catalyst reusability was tested under 10 Bar H2(g) over five cycles at 353 K in 1 h
reaction time period. Approximately 30% catalyst activity loss was found for the last
cycle on 1-octene hydrogenation reaction (Entries 7-10).
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Table 4. Hydrogenation of 1-octene by [PdL2(OAc)2] complex
Total
Conv.
(%)
Cycle
No
Ent.
T(K)
Products (%)
TON TOF (h-1)
(n-octane) (2-octene) (3-octene)
1
2
3
323
333
343
353
353
353
353
353
353
353
16.5
21.8
61.1
100
56.7
100
100
100
100
95.7
12.5
16.6
51.4
98.2
29.0
69.9
98.7
99.0
95.7
85.7
2.6
3.1
6.3
1.5
2.1
3.2
0
9.7
6.3
0
0
1.5
2.6
12
16
45
74
42
74
74
74
74
71
12
16
45
74
42
74
74
74
74
71
4
1
1.8
5b
6c
7
17.9
23.8
1.3
1.0
2.8
2
3
4
5
8
9
10
7.4
a Reaction conditions: ncat. = 8.59 × 10−6 mol, n1-oct. = 6.37 × 10−4 mol, ns/nc= 74, Vsolv. = 0.5 mL, PH2 = 10
bar, t=1h
b DMSO; c Toluene.
3.3. Cyclohexene Hydrogenation in IL
Cyclohexene was hydrogenated to cyclohexane with [PdL1(OAc)2] complex in
catalytic conditions. The results obtained are given in Table 5. The catalytic efficiency
of complex on cyclohexene hydrogenation was investigated with temperatures ranging
from 333 K to 373 K (Entries 1-5). It was observed that the activity of catalyst increased
gradually to 363 K and then decreased at 373 K suddenly. The reason for the decrease
in activity is thought to be the decomposition of catalyst at higher temperatures. The
highest conversion value (TOF= 79) was observed at 363 K, under 10 Bar H2(g) in 1
hour reaction time (Entry 4).
Solvent effect of [PdL1(OAc)2] catalyst on 1-octene hydrogenation led to nearly
100% product formation in toluene when compared to polar DMSO with only 5.6%
product formation (Entries 6,7). This means DMSO molecules can coordinate to the
metal center and affect the catalytic cycle under these conditions.
Reusability of the same catalyst on cyclohexene hydrogenation was investigated at
363 K in 1 h reaction time (Table 5). It was found that catalyst activity decreased at
each cycle and conversion values decreased from 67.1% to 13.7% for the last cycle
(Entries 1, 8-11).
Table 5. Hydrogenation of cyclohexene by [PdL1(OAc)2] complex
Entry
T (K)
333
343
353
363
373
363
Cycle No
Conv. (%)
0
TON
0
TOF (h-1)
1
2
0
27
61
79
49
7
27
61
79
49
7
22.5
51.3
67.1
41.1
5.6
3
4
1
5
6b
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7c
8
116
116
45
363
98.1
37.8
26.7
16.9
13.7
2
3
45
32
363
363
363
363
9
32
10
11
4
5
20
16
20
16
a Reaction conditions: ncat. = 8.36 × 10−6 mol, ncyc. = 9.87× 10−4 mol, ns/nc=118, Vsolv. = 0.5 mL, PH2 = 10
bar, t=1h, b DMSO; c Toluene.
In order to evaluate the catalytic activity of [PdL2(OAc)2] complex on cyclohexene
hydrogenation, experiments were conducted between 333-383 K under 10 bar H2(g), in
1h reaction time. The results are given in Table 6. Catalyst activity was found to be
increase with reaction temperature, and the highest activity was obtained at 373 K as
42.5% rather than 383 K (Entry 5). The reason for the activity decrease at 383 K is
dedicated to degeneration of the structure of the complex. The highest TON value was
reached at 373 K in 6 hour reaction time as 73 (Entry 7). Considering the solvent effect,
catalyst is more effective in apolar toluene than DMSO media, and the conversion was
found to be 47.3% at 353 K in 1 hour in toluene.
Catalyst reusability was tested under the most productive conditions (373 K, 6 h),
and approximately 15% activity loss was found to be from 55.3% to 41.3% after five
cycles (Entries 7, 11-14).
Table 6. Hydrogenation of cyclohexene by [PdL2(OAc)2] complex
Entry
T (h)
T (K)
Cycle No
Conv. (%)
TON
12
21
31
42
49
33
73
3
TOF (h-1)
1
2
1
1
1
1
1
1
6
1
1
6
6
12
21
31
42
49
33
12
3
333
343
353
363
373
383
373
353
353
373
373
373
373
10.5
18.1
27.1
36.3
42.5
28.6
63.1
2.8
3
4
5
6
7
1
9b
10c
11
12
54
54
47.3
55.3
50.4
44.8
41.3
2
3
64
58
51
47
12
11
10
9
13
14
4
5
6
6
a Reaction conditions: ncat. = 8.59 × 10−6 mol, ncyc. = 9.87× 10−4 mol, ns/nc=115, Vsolv. = 0.5 mL, PH2 = 10
bar, b DMSO; c Toluene.
4. Conclusion
In this study, two new N-Acyl benzotriazole palladium complexes containing
thiophene and furan ring were synthesized and characterized. The activity of complexes
for some olefins hydrogenation reactions in [bmim][BF4] was investigated. The activity
of [PdL1(OAc)2] complex was found to be close to [PdL2(OAc)2] especially on styrene
hydrogenation under the same conditions. Little activity difference was observed on 1-
11

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octene and cyclohexene hydrogenations between two catalysts. Both catalysts can be
active in organic solvents besides green reaction media. Additionally, [PdL2(OAc)2]
catalyst can be reused up to five times on styrene hydrogenation reactions without loss
of its activity.
We also investigated the performance of metal precursor (Pd(OAc)2) in
[bmim][BF4]. For both complexes, lower TOF values were obtained with (Pd(OAc)2).
This indicates new ligands have a positive effect on the catalytic activity of metal.
Acknowledgements
The authors are grateful to Anadolu University, Plant, Drug and Scientific Research
Center (AUBIBAM) for NMR analyses and The Scientific And Technological Research
Council Of Turkey (TUBITAK) for 2211 grant program.
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Graphical abstract
13

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Highlights:
 New benzotriazole derived thiophene and furan ligands and their palladium
complexes has been synthesized and characterized.
 Catalytic activity of complexes was tested on some olefins hydrogenations and
100 % ethyl benzene formation was observed within 1 hour in [bmim][BF4] with
both complexes.
 [PdL2(OAc)2] complex can be reused up to five times on styrene hydrogenation
without loss of its activity.
14