Preparation and spectroscopic studies of Fe(II), Ru(II), Pd(II) and Zn(II) complexes of Schiff base containing terephthalaldehyde and their transfer hydrogenation and Suzuki-Miyaura coupling reaction

Article abstract of DOI:10.1515/chem-2019-0074

This study describes synthesis, spectroscopic characterization and catalytic activities of Fe(II), Ru(II), Pd(II) and Zn(II) complexes with a novel Schiff base ligand (L) derived from methyl 2-amino-5,5,7,7-tetramethyl-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylate and terephthalaldehyde. We used spectroscopic techniques including IR, UV-Vis, ¹H-NMR, ¹³C-NMR, elemental analysis and also mass analysis and magnetic susceptibility measurements to identify the products. The Pd(II) complex was used as a potential catalyst for Suzuki-Miyaura coupling reaction of some aryl halides under optimized conditions. The effect of various bases such as NaOH, KOH, and KOBu^t was investigated in transfer hydrogenation (TH) of ketones by isopropyl alcohol as the hydrogen source. Ru(II) and Pd(II) complexes showed catalytic activity while Zn(II) and Fe(II) metal complexes failed to do that.

Full text of DOI:10.1515/chem-2019-0074

Open Chem., 2019; 17: 571–580
Research Article
NPervienpTuaranr*a, Kteinoann Bualdnurduns, Npakei Çcotlarko, İssmcaoil Öpzidcemsirtudies of Fe(II),
Ru(II), Pd(II) and Zn(II) complexes of Schiff base
containing terephthalaldehyde and their transfer
hydrogenation and Suzuki-Miyaura coupling
reaction
https://doi.org/10.1515/chem-2019-0074
received February 12, 2018; accepted October 7, 2018.
1 Introduction
Abstract: This study describes synthesis, spectroscopic Schiff bases belong to a prominent class of compounds
characterization and catalytic activities of Fe(II), Ru(II), and they draw significant attention in many different
Pd(II) and Zn(II) complexes with a novel Schiff base fields because of their characteristic features [1]. The main
ligand (L) derived from methyl 2-amino-5,5,7,7-tetramethyl- advantagesofSchiffbasesaretheireaseofformationunder
4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylate and mild conditions and the linking of additional functional
terephthalaldehyde. We used spectroscopic techniques groups for developing new structures and chemo-physical
including IR, UV-Vis, 1H-NMR,13C-NMR, elemental analysis properties. They play an important role in inorganic
and also mass analysis and magnetic susceptibility chemistry since they can easily form stable complexes
measurements to identify the products. The Pd(II) with most transition metal ions. Metal complexes of Schiff
complex was used as a potential catalyst for Suzuki- bases possess a wide range of implementation such as
Miyaura coupling reaction of some aryl halides under catalysts, drugs and magnetic or luminescent materials
optimized conditions. The effect of various bases such [2-5].
as NaOH, KOH, and KOBut was investigated in transfer
The high thermal and moisture stabilities of Schiff
hydrogenation (TH) of ketones by isopropyl alcohol as base complexes render them valuable for applications like
the hydrogen source. Ru(II) and Pd(II) complexes showed catalysts in reactions at high temperatures. The activity
catalytic activity while Zn(II) and Fe(II) metal complexes of Schiff bases frequently increases by complexation.
failed to do that.
Therefore, a comprehensive understanding of the
properties of ligands and metal complexes may result
in the synthesis of highly active compounds. The most
important advantages of using Schiff base ligands in
metal complexes are that they include the hydrogenation
of olefins and carbonyl groups, the transfer of an amino
group and their capability to form complexes against toxic
metals and other applications [6-12].
Keywords: Catalysis; Metal complexes; Thiophene
carboxylate; Terephthalaldehyde; Schiff base.
Transition metal complexes, mainly those containing
ruthenium, are very significant catalyst precursors
[13]. The center of attraction in ruthenium complexes
containing Schiff bases remains unchanged owing to their
multi-electron transfer properties, their ability to exhibit
a large oxidation state, and their potential catalytic
activity [14-20]. Palladium-catalyzed Heck-Mizoroki or
Suzuki-Miyaura coupling reactions are important tools for
construction of aryl-carbon bond. Currently, researchers
*Corresponding author: Nevin Turan, Department of Chemistry,
Faculty of Arts and Sciences, Muş Alparslan University, 49250 Muş,
Turkey, E-mail: nevintrn@hotmail.com, n.turan@alparslan.edu.tr
Kenan Buldurun, Department of Chemistry, Faculty of Arts and
Sciences, Muş Alparslan University, 49250 Muş, Turkey
Naki Çolak, Department of Chemistry, Faculty of Arts and Sciences,
Hitit University, 19100 Çorum, Turkey
Kenan Buldurun, İsmail Özdemir, Catalysis Research and
Application Center, İnönü University, 44280 Malatya, Turkey
Open Access. © 2019 Nevin Turan et al., published by De Gruyter.
Attribution alone 4.0 License.
This work is licensed under the Creative Commons
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have focused on these coupling reactions using more 2.2 Synthesis and characterization of ligand
active catalysts or using ones that can be recycled. The
goal is to reduce the cost, produce higher purity products
and its complexes
and develop more productive and less wasteful processes Sulfur (0.32 g, 0.01 mol), triethylamine (1.01 g, 0.01
with more efficient methodologies for such coupling mol) and methyl-2-cyanoacetate (0.99 g, 0.01 mol)
reactions [21-29].
were put to 50 mL of ethyl alcohol in the presence of
The synthesis, spectroscopic and catalytic properties 3,3,5,5-tetramethylcyclohexanone (1.13 g, 0.01 mol). The
of the Schiff base ligand and its [Zn2L∙2Cl2∙2H2O], mixture was heated at 50°C under reflux for 3 h. Some
[Fe2L∙2Cl2∙2H2O]∙3H2O,
[Ru2Cl2(p-cymene)2L], water was added to precipitate the resulting solids in
[Pd2L∙2Cl2]∙4H2O complexes were described in this study. the mixture. Crystallization of filtrate with ethyl alcohol
The catalytic activities of the Pd(II) complex for Suzuki- afforded the starting material.
Miyaura coupling reactions were investigated. Further,
The terephthalaldehyde (0.01 mol) dissolved in
the transfer hydrogenation of acetophenone was carried ethanol (20 mL) was put to the solution of the starting
out by Ru(II) complex of reduced Schiff base ligand. material (0.02 mol) in ethanol (20 mL). The mixture was
The Ru(II) complex was found to be an active catalyst. refluxed for 10 h. Finally, the product was filtered off,
The Pd(II) complex showed efficient catalytic activity in washed with diethylether and dried at room temperature.
Suzuki-Miyaura cross-coupling reaction between various
aryl halides and aryl boronicacids.
Ligand: Yield: 78%. Anal. Calc. for C36H44N2O4S2
(formula weight 632.88 g/mol): C, 68.26; H, 6.95; N, 4.42;
S, 10.11. Found: C, 68.28; H, 6.90; N, 4.35; S, 10.23%. IR
(KBr, cm-1) ν:, 3100, 3000 (Ar–CH), 2903, 2831 (Aliph.–CH,
CH3), 1729 (C=O), 1605, 1602 (CH=N), 1579, 1562 (Ar–C=C),
777 (C–S–C). 1H-NMR (400 MHz, DMSO-d6): δ (ppm) = 8.55
(s, 2H, N=CH), 7.53-7.19 (m, 4H, Ar-H), 3.59 (s, 6H, –CO–O–
CH3), 2.52 (s, 4H, 2CH2), 1.48 (s, 4H, 2CH2), 1.48 (s, 6H, C–
2 Experimental
2.1 Materials and methods
13
(CH3)2), 1.34 (s, 6H, C–(CH3)2). C-NMR (400 MHz, DMSO-
Every chemicals used were of reagent grade. Solvents d6): δ (ppm) = 162.76 (2C=O), 158.85 (2CH=N), 141.23, 137.64
were purified and distilled for synthesis and physical (2Cthiophene), 133.17, 113.82 (Cbenzene), 53.50, 24.59 (Ccyclohexane),
measurements. The IR spectra were recorded in KBr 51.49 (O–CH3)2, 31.38, 29.38 (–8CH3). UV-Vis (λmax/nm,
discs in the wave number range of 4000-400 cm-1 on a (ε/L mol-1 cm-1)): π→π*, 204 (2400), 257 (3494); n→π*, 300
1
Perkin Elmer Model 65 FTIR Spectrophotometer. The H (361), 309 (387). Mass Spectrum [ESI]: m/z 631.88 (Calc.),
13
and C-NMR spectras were recorded in DMSO-d6 solvent 631.04 (Found) [L-H]-. Color: Pale Brown.
on Perkin Elmer 400 MHz NMR spectrometer using
The metal complexes were prepared adding
tetramethylsilane as the internal standard. Chemical stoichiometric proportion into a hot ethanol solution
shifts have been expressed in ppm. Electronic spectra were (20 mL) including 0.01 mol of ligand and a hot ethanol
recordedonaUV–VisibleShimadzu1800inthewavelength solution (20 mL) containing 0.02 mol metal chlorides
1100-190 nm. Mass spectra were recorded on Varian (ZnCl2 and FeCl2∙4H2O). The mixture was refluxed for 4 h.
Inc, Anadolu University made Liquid Chromatography- The precipitate was filtered off, washed with diethyl ether
Mass Spectrometer. Elemental analyses were performed three times and finally dried at air room temperature.
on a LECO 932 CHNS analyzer. Magnetic susceptibility
[Zn2L∙2Cl2∙2H2O] complex: Yield: 75%. IR (KBr,
measurements were carried out using Hg[Co(SCN)4] as cm-1) ν:, 3495, 3385 (OH), 3210, 3100 (Ar–CH), 2960, 2869
calibrant by Gouy balance. GC-MS measurements for (Aliph.–CH, CH3), 1690 (C=O), 1641, 1607 (CH=N), 1577,
catalytic experiments were applied using an Agilent 7890 1522 (Ar–C=C), 770 (C–S–C), 575, 535 (M–O), 480, 453
1
B GC and Agilent 5977 M MS (GC-MS) system by GC-FID (M–N). H-NMR (400 MHz, DMSO-d6): δ (ppm) = 8.59 (s,
with an HP-5 column of 30 m length, 0.32 mm diameter, 2H, 2N=CH), 7.55-7.19 (m, 4H, Ar-H), 4.26 (4H, 2H2O). Anal.
and 0.25 mm film thickness. The GC parameters were as Calc. for C36H48N2S2O6Cl4Zn2 (formula weight 941.54 g/mol):
follows: oven: 80°C (isothermal); carrier gas: He (Split C, 45.88; H, 5.10; N, 2.97; S, 6.80. Found: C, 45.87; H, 5.12; N,
ratio 1:10); flow rate: 4 mL/min; injector port temperature: 2.99; S, 6.83%. UV-Vis (λmax/nm, (ε/L mol-1 cm-1)): π → π*, 217
200°C; detector temperature: 260°C; injection volume: (868), 252 (284); n → π*, 299 (282), 349 (538), 364 (530); L →
2.0 μL.
M, 408 (547). MS [ES]: m/z 940.54 (Calc.), 940.00 (Found)
[M-H]-. Color: Orange.
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Figure 1: Synthesis scheme of dimethyl 2,2’-(1E-1’E)-(1,4-phenylenebis(methan-1-yl-1-ylidene))bis(azan-1-yl-1-ylidene)bis(5,5,7,7-tetramethyl-
4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylate (L).
[Fe2L∙2Cl2∙2H2O]∙3H2O complex: Yield: 80%. IR (KBr,
cm-1) ν:, 3487, 3343 (OH), 3180, 3032 (Ar–CH), 2956, 2876
(Alip–CH), 1725, 1694 (C=O), 1663, 1641 (CH=N), 1599 (Ar–
C=C)broad, 787 (C–S–C), 592, 561 (M–O), 482, 457 (M–N).
Anal. Calc. for C36H54N2S2O9Cl4Fe2 (formula weight 976.38
g/mol): C, 44.25; H, 5.53; N, 2.87; S, 6.55. Found: C, 44.27;
H, 5.53; N, 2.88; S, 6.54%. UV-Vis (λmax/nm, (ε/L mol-1 cm-1)):
π → π*, 203 (315), 218 (377); n → π*, 299 (117), 307 (107),
349 (258), 363 (257); L → M, 408 (272). MS [ES]: m/z 921.38
(Calc.), 921.77 (Found) [M-3H2O-H]-. Color: Black.
A toluene solution of ligand (0.01 mol) was mixed with
PdCl2(CH3CN)2, (0.02 mol) maintaining metal-ligand ratio
2:1. The mixture was refluxed for 8 h. The solid product,
Figure 2: Suggested structure of the [Zn2L∙2Cl2∙2H2O] complex.
precipitated after cooling, was collected through filtration,
washed with diethyl ether and recrystallized from
methylene chloride. Similar synthesis were conducted for
the Ru(II) complex using [RuCl2(p-cymene)]2, (0.01 mol).
[Ru2Cl2(p-cymene)2L] complex: Yield: 78%. IR (KBr,
cm-1) ν:, 3062, 3036 (Ar–CH), 2960, 2872 (Alip–CH), 1694
(C=O), 1643, 1600 (CH=N), 1571 (Ar-C=C), 1372, 1170 (Ru–
1
Cl), 776 (C-S-C), 576, 537 (M–O), 472, 453 (M–N). H-NMR
(400 MHz, DMSO-d6): δ (ppm) = 8.61 (s, 2H, 2N=CH),
7.58-7.20 (m, 4H, Ar–H), 2.30, 2.10 (m, H, –CH (p-cymene,
methine), 2.16 (s, 3H, (p-cymene, methyl), 1.20, 1.10 (d, 6H,
(CH3)2CH (p-cymene). Anal. Calc. for C56H72N2S2O4Cl2Ru2
(formula weight 1173.14 g/mol): C, 57.28; H, 6.13; N, 2.38;
S, 5.46. Found: C, 57.27; H, 6.12; N, 2.38; S, 5.48%. UV-Vis
(λmax/nm, (ε/L mol-1 cm-1)): π → π*, 216 (1813); n → π*, 293
(351), 307 (332), 346 (541); L → M, 407 (523). MS [ESI+]: m/z
Figure 3: Suggested structure of the [Fe2L∙2Cl2∙2H2O]∙3H2O
complex
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selected to be the model reaction, and all reactions were
conducted under aerobic conditions. After that, the
optimal parameters were investigated in order to have the
best reaction conditions (Table 3-5). The conversions were
collected at different times. The yields were recorded by
GC-MS analysis to examine the progress of the reaction.
2.4 General procedure for the transfer hyd-
rogenation reaction
The hydrogen transfer reaction was performed in a closed
Schlenk flask under argon atmosphere. Ketone (1 mmol),
catalyst Ru(II) complex (0.01 mmol), and isopropyl alcohol
(5 mL) were added into a Schlenk flask. KOH (2 mmol) was
then put into the obtained mixture, and it was heated at
80°C for 10 h. Then the solvent was evaporated at reduced
pressure. The precipitate was extracted by hexane/ethyl
acetate (2:4), filtered by a pad of silica gel with multiple
washings and purified by flash chromatography on silica
gel. The yields were recorded using 1H-NMR spectroscopy
and GC-MS.
Figure 4: Suggested structure of the [Ru2Cl2(p-cymene)2L] complex.
Ethical approval: The conducted research is not
related to either human or animal use.
3 Results and discussion
Figure 5: Suggested structure of the [Pd2L∙2Cl2]∙4H2O complex.
3.1 Spectroscopy analysis
1018.14 Calc.), 1018.68 (Found) [M-2Cl-2(-C3H7)]2+. Color: The characteristic absorption band 1729 cm-1 attribute to
Brown. C=O stretching frequency of the ester carbonyl [30], sharp
[Pd2L∙2Cl2]∙4H2O complex: Yield: 80%. IR (KBr, cm-1) CH=N bands seen were in the range of 1605, 1602 cm-1
ν:, 3567, 3457 (OH), 3062, 3036 (Ar–CH), 2956 (Alip-CH), [31]. We observed that the stretching frequency of CH=N
1722 (C=O), 1612 (CH=N), 1573 (Ar–C=C), 775 (C–S–C), 578, slightly shifted to lower or high wave numbers (1663-
540 (M–O), 504 (M–N). Anal. Calc. for C36H52N2S2O8Cl4Pd2 1600 cm-1), which suggests that the azomethine nitrogen
(formula weight 1059.48 g/mol): C, 40.77; H, 4.91; N, 2.64; was involved in coordination to the metal ion in all metal
S, 6.04. Found: C, 40.78; H, 4.93; N, 2.64; S, 6.05%. UV-Vis complexes. Thiophene C–S–C stretching vibration was
(λmax/nm, (ε/L mol-1 cm-1)): π → π*, 218 (607), 260 (335); n appeared at 777 cm-1 in the free ligand [32,33]. This band
→ π*, 347 (178); L → M, 403 (110). MS [ESI+]: m/z 1058.48 shifted to higher and lower stretching frequency (770-787
(Calc.), 1058.69 (Found) [M-H]-. Color: Black.
cm-1) in the Fe(II) and Zn(II) complexes. That revealed
the coordination of thiophene sulfur to the metal center
[34,35]. The new bands seen at 1690-1725 cm-1 in the
spectra of complexes were assigned to ester carbonyl
group, which indicated the joining of oxygen atom of
ester carbonyl group in coordination with metal ions [36].
2.3 General experimental procedure for
Suzuki-Miyaura coupling reaction
Pd(II) complex was utilized in a preliminary test to The two new bands appeared in the far infrared region at
have the best reaction conditions (i.e., temperature, 592-535 cm-1 and 504-453 cm-1 were attributed to ν(M–O)
base, solvent, amount of catalyst). The cross coupling and ν(M–N) respectively. This confirmed the attachment
of 4-bromoacetophenon and phenylboronic acid was of ligand to the center metal ions through the carbonyl
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Table 1: Effect of bases for transfer hydrogenation.
oxygen atoms and the azomethine nitrogen [37,38]. The
infrared broad bands (3567-3343 cm-1) of Fe(II), Zn(II) and
Pd(II) complexes assigned to bonding of water molecules
[39].
Entry
Base
Conversion (%)
1
2
3
4
5
6
KOH
84
55
51
42
37
-
Electronic spectra were taken in the 1100-190 nm
range and 1.0x10-4 mol/L in ethanol for all compounds.
The spectra of the ligand indicated four high-intensity
absorption bands: at 309, 300, 257 and 204 nm. These
bands were attributed to π→π* and n→π* transitions of
the ligand [40]. The spectra of the complexes showed four
bands at 203-260, 293-299 and 307-364 nm which were
assigned to the π→π* and n→π* transitions, respectively,
within the ligand. The spectra of the complexes showed
bands in the range of 403-408 nm, which might be
appointed to L→M charge transfer transitions [41-43].
NaOH
K2CO3
KOBut
NaOAc
none
aReaction conditions: Ketones (1 mmol), bases (2 mmol), isopropyl
alcohol (5 mL), stirring for 10 h, 80 °C. bYield is determined by
GC-MS.
The recorded magnetic moment value of Fe(II) this studies (Table 1), the KOH was the most suitable
complex was 4.92 B.M. and that confirmed octahedral base and the conversion of yield was increased to 100%
geometry of Fe(II) metal center [44]. Zn(II)) complex was (Table 2, entry 6). However, more time was needed for
diamagnetic and had an octahedral geometry [45]. The reasonable conversions. In the condition of not using a
structured absorption bands between 260 and 347-403 nm base, TH of the ketones was not seen (Table 1, entry 6).
1
1
for Pd(II) complex were assigned to A1g→1Bg and A1g→1Eg The TH reactions of a variety of substituted acetophenone
transitions, respectively in a square-planar configuration derivatives were applied with Ru(II) complex as the
[46]. And also, the other high-intensity bands in the model catalyst, using i-PrOH/KOH, and the results were
293-346 nm could be attributed to (1A1g→1T2g) and d→d given in Table 2. Corresponding alcohols were obtained
transition, occurring within ligand orbitals. The electronic with very good results by using various acetophenone
spectra was similar to that of Ru(II) octahedral complexes derivatives. The variety substituents present on the
[46,47].
acetophenone ring were seen that it didn’t influence on
1
13
The H and C NMR spectras of the ligand was given catalytic conversion.
in experimental section. The protons of HC=N group
The presence of an electron-withdrawing substituent
were observed at 8.55 ppm as singlet. The singlet peak of (bromo, chloro) on the aryl ring showed higher
azomethines in the ligand was shifted to lower value at 8.59 conversions (Table 2, entries 2, 3). When compared with
ppm in Zn(II) complex, which shows the participation of acetophenone (Table 2, entry 1), p-methoxyacetophenone
HC=N group in the complexation [48]. The signal showed and pentamethylacetophenone reacted very clearly and
at 4.26 ppm in Zn(II) assigned to two water molecules [49]. in good yields with isopropyl alcohol (Table 2, entries 4,
13
The C NMR spectra of the ligand showed a peak at 6). The maximum conversion to corresponding alcohol of
158.85 ppm because of characteristic azomethine carbons. 4-bromoacetophenone was accomplished over a period of
This signal shifted upfield in Zn(II) complex spectrum 10 hours (Table 2, entry 3). We also tested this reaction on
(148.70 ppm) which indicated the participation of HC=N benzophenone. As a result of this reaction, benzophenone
groups in complex formation. The ligand also showed had a high conversion ratio in comparison to the
signal at 162.76 ppm (2C=O). This signal was shifted acetophenone and methoxy group bearing p-position
to 158.10 ppm in Zn(II) complex spectrum because of acetophenone (Table 2, entries 1, 4, 5). For the substituted
bonding formation ester carbonyl oxygen. Based on the acetophenones, Ru(II) complex showed more conversion
above spectroscopic data, the structures were proposed than cyclicketones (Table 2, entries 1-7). Among the tested
for complexes, as shown in Figures 2-5.
substrates, the tertiary butylcyclohexanone used as a
ketone was observed to perform worse in TH (Table 2,
entry 7). Ru(II) complex was highly efficient in the TH.
This shows that air is not involved in the TH reaction and
arene Ru(II) complexes are air-stable [50].
3.2 Transfer hydrogenation of ketones
In this study, KOH, NaOH, NaOAc, KOBut and K2CO3 were
investigated in TH. Among the different bases used for reaction, 4-bromoacetophenone and phenylboronic acid
In the catalytic activity of Suzuki-Miyaura coupling
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Table 2: Catalytic activity for transfer hydrogenation of ketones catalyzed by Ru(II) complex.
OH
H
O
2a
X
2 mmol KOH
OH
O
X
+
+
80°C,10h
R
R
(5 mL)
X= H, Ph
R= H,CI, Br, OCH3
Cl
Ru
O
O
N
S
S
N
O
Ru
O
Cl
2a
Entry
Ketone
Alcohol
Catalyst
Base
Yield (%)b
OH
O
1
2a
KOH
84
C
H
CH3
OH
C CH3
2
3
4
5
6
2a
2a
2a
2a
2a
KOH
KOH
KOH
KOH
KOH
95
98
88
97
100
O
Cl
C CH3
H
Cl
C CH3
OH
O
C
Br
C CH3
H
Br
CH3
O
C
OH
H3CO
C
H
CH3
H3CO
CH3
O
C
OH
C
H
OH
O
C
H
CH3
C
CH3
7
2a
KOH
44
OH
O
aReaction conditions: Ketones (1 mmol), bases (2 mmol), isopropyl alcohol (5 mL), stirring for 10 h, 80 °C. bYield is determined by GC-MS.
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Table 3: Effect of bases for the Suzuki-Miyaura reaction.
80 °C, yield of product was not obtained in 20 h (Table 4,
entry 1). The best solvent was found to be ethanol solvent
with the highest yield, but DMF were obtained with the
lowest yield (Table 4, entries 2-7). This solvent is less
efficient to coordinate to the palladium center, because
the O-donor atoms in dioxane are harder base than the
N-donor atom in DMF and therefore catalyst performance
is poor [52]. Since N-donor atoms of DMF coordinate to
palladium ion, the catalyst activity of DMF is smaller than
in other solvents [53].
Table5maysuggestthatvariousarylhalides, likethose
containing –CH3, –OCH3, –COCH3 and –CHO substituent
group, reacted smoothly under optimized conditions and
provided the demanded products with quantitative yields.
Arylbromides with various functional groups reacted
efficiently with boronic acids (Table 5, entries 1-5) using
K2CO3 and 5 mL ethanol at reflux temperature in presence
of Pd(II) catalyst for 3 h to yield Suzuki-Miyaura products in
good conversions. The reaction of p-bromoacetophenone
with boronic acid showed a very high conversion (Table
5, entry 1, 92%). In p-bromotoluene, the conversions
were good in these conditions (Table 5, entry 2, 79%).
p-methoxy, p-benzaldehyde substrates also showed an
excellent conversion (Table 5, entries 3, 5, 82-86%). As
expected, p-bromobenzene showed a medium conversion
(Table 5, entry 4, 76%). Catalytic activity of Pd(II) depended
on electronic properties of arylbromide substituent used.
In the presence of electron withdrawing group on aryl ring
increase the yield [54].
Entry
Base
Time (h)
Conversion (%)
1
2
3
4
5
NaOH
Cs2CO3
Na2CO3
K2CO3
KOBut
3
3
3
3
3
52
42
19
90
12
Reaction conditions: 4-Bromoacetophenone (0.3 mmol),
phenylboronic acid (0.45 mmol), catalyst (0.001 mmol) and base (1.5
mmol), solvent (5 mL)
Table 4: Effect of solvents for the Suzuki-Miyaura reaction.
Entry
Solvents
H2O
Time (h)
Conversion (%)
1
2
3
4
5
6
7
8
9
20
3
-
Ethanol
Methanol
DMF
92
19
10
12
32
17
10
45
8
8
Toluen
Dioxane
THF
8
8
8
DMF+H2O
THF
8
8
Reaction conditions: 4-Bromoacetophenone (0.3 mmol),
phenylboronic acid (0.45 mmol), catalyst (0.001 mmol) and base (1.5
mmol), solvent (5 mL)
4 Conclusion
was chosen as a model substrate. Different parameters
examined and the results were summarized in Table 3, New ligand and its complexes were synthesized and
4. The cross-coupling of 4-bromoacetophenone with characterized. The bidentate or tridentate coordination
phenylboronic acid in ethanol medium under aerobic of ligand through carbonyl oxygen, azomethine nitrogen
condition was chosen as the model reaction. The impacts and thiophene sulfur was confirmed using spectral data
of the temperature and base on the reaction were also analysis. The metal complexes had octahedral geometry
examined. Various bases like K2CO3, Na2CO3, NaOH, KOBut, except for the palladium complex. The ruthenium
and Cs2CO3 were also examined. The results indicated complex was shown to be an effective catalyst for the
organic bases were less effective than inorganic bases transfer hydrogenation of the different aromatic ketones
such as KOBut (Table 3, entries 4, 5). Therefore, K2CO3, to their corresponding secondary alcohols. It was found
which was more cost-effective, was chosen as a base for that a series of electronically diversified, different aryl
Suzuki-Miyaura coupling reactions [51]. The results are halides of the Pd(II) complex was a highly effective
given in Table 3.
catalyst for Suzuki-Miyaura cross-coupling reaction with
Subsequently, the effects of solvents such as H2O, THF, phenylboronic acid. In conclusion, the catalytic activity of
EtOH, MeOH, dioxane, toluene and DMF were studied in palladium complex influenced the Suzuki-Miyaura cross-
the presence of Pd(II) complex (0.01 mmol) at 80 °C for 3 coupling reaction while ruthenium complex influenced
h. It is seen in Table 4 that when temperature increased to the transfer hydrogenation of ketones.
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578ꢀ
Nevin Turan et al.
Table 5: Suzuki-Miyaura reactions with different substituent catalyzed by Pd(II) complex under optimized reaction conditions.
K2CO3 / Pd comp
R
B(OH)2
R
Br
+
C2H5OH / Reflux
Entry
Catalyst
ArX
Time (h)
Yield(%)
1
4a
3
92
Br
COCH3
2
3
4
5
4a
4a
4a
4a
3
3
3
3
79
82
76
86
Br
Br
Br
Br
CH3
OCH3
CHO
Reaction conditions: R-C6H4Br-p(4-bromoacetophenone) (1 mmol), phenylboronicacid (1.5 mmol), K2CO3 (2 mmol), Pd(II) complexes (0.005
mmol), ethanol (3 mL), purity of compounds is checked by GC and NMR yields are based on p-arylbromide. All reactions were monitored by
GC-MS. Temperature 80 °C, 3 h.
[6] Henrici G., Olive S., The Chemistry of the Catalyzed
Acknowledgment: Thank to Scientific Research-
Hydrogenation of Carbon Monoxide, Springer, Berlin, 1984, pp.
Publications and Projects Research and Practice Center
152.
(BAYPUAM) under research project no MŞÜ15-FEF-G01 for [7] Manikandan R., Viswanathamurthi P., Muthukumar M.,
Ruthenium(II) hydrazone Schiff base complexes: Synthesis,
their support.
spectral study and catalytic applications, Spectrochim. Acta A
Mol. Biomol. Spectrosc., 2011, 83, 297-303.
Conflict of interest: Authors declare no conflict of
interest.
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[10] Buldurun K., Turan N., Savcı A., Çolak N., Synthesis, structural
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