Synthesis and catalytic activity of ionic palladium N-heterocyclic carbene complexes

Article abstract of DOI:10.3906/kim-1907-74

The synthesis of 3 benzimidazole-based ionic Pd(II)-NHC complexes (NHC: N -heterocyclic carbene) is presented. The structures of the complexes are as follows: [NHC-PdBr ₃ ] ^? [NHC] ⁺ . The ionic palladium(II)-NHC complexes were synthesized in high yields and were fully characterized by nuclear magnetic resonance spectroscopy, X-ray diffraction, LC-MS/MS, and elemental analysis. These complexes have been identified as active catalysts in Suzuki–Miyaura reactions in a solution of 2-propanol and water at room temperature for different aryl bromides.

Full text of DOI:10.3906/kim-1907-74

Turkish Journal of Chemistry
Turk J Chem
2019) 43: 1622 – 1633
TÜBİTAK
doi:10.3906/kim-1907-74
(
©
http://journals.tubitak.gov.tr/chem/
Research Article
Synthesis and catalytic activity of ionic palladium N-heterocyclic carbene
complexes
1
,∗
1
2
1
Sedat YAŞAR ,, Mitat AKKOÇ ,, Namık ÖZDEMİR ,, İsmail ÖZDEMİR ,
1
Department of Chemistry, Faculty of Science and Art, İnönü University, Malatya, Turkey
Department of Mathematics and Science Education, Faculty of Education, Ondokuz Mayıs University,
Samsun, Turkey
2
Received: 29.07.2019
•
Accepted/Published Online: 30.10.2019
•
Final Version: 09.12.2019
Abstract: The synthesis of 3 benzimidazole-based ionic Pd(II)-NHC complexes (NHC:N -heterocyclic carbene) is
presented. The structures of the complexes are as follows: [NHC-PdBr The ionic palladium(II)-NHC
]− [NHC]+
3
.
complexes were synthesized in high yields and were fully characterized by nuclear magnetic resonance spectroscopy,
X-ray diffraction, LC-MS/MS, and elemental analysis. These complexes have been identified as active catalysts in
Suzuki–Miyaura reactions in a solution of 2-propanol and water at room temperature for different aryl bromides.
Key words: Ionic palladium complex, N -heterocyclic carbene, C-C bond formation, anionic palladium species, Suzuki–
Miyaura cross-coupling reactions
1. Introduction
C-C bond formation reactions are the most useful reactions for the synthesis of very important unsymmetrical
biaryls in academic and industrial applications [1–4]. To achieve maximum benefit in C-C bond formation
reactions, many different types of ligands [5–11], as well as ligand-free catalytic systems [12], have been
investigated. When the history of the Suzuki–Miyaura [13] coupling reaction was examined in detail, it was seen
that phosphine-based ligands were commonly used [14]. Recently, the disadvantages of phosphine-based ligands,
such as toxicity and sensitivity to air and moisture, have led to the development of phosphine-free catalytic
systems in Suzuki–Miyaura cross-coupling reactions [15]. Since Arduengo isolated the first free NHC, imidazole,
imidazolidine, and benzimidazole-based Pd-NHC complexes have been reported and applied successfully as a
catalyst in Suzuki–Miyaura cross-coupling reactions [16,17].
In 2006, Huynh et al. reported the first example of a benzimidazole-based NHC-stabilized tribromo
palladium complex, containing an NHC-Pd(II)Br3 as an anion and a corresponding benzimidazolium as a
cation [18] (Scheme 1). A similar triiodo complex was reported by Herrmann et al. [19].
As additive, quaternary ammonium salts are often used in Heck-type C-C bond formation reactions
[20,21]. It is believed that these salts help to stabilize or maintain stable active species via the coordination or
formation of ion pairs [18,21]. Thus, the synthesis and investigation of catalytic activity of ionic type Pd(II)-
NHC complexes may be interesting and nice to compare with the catalytic activity of Pd(II)-NHC on Suzuki–
Miyaura reactions [22–24]. Our earlier investigations showed that neutral PdX2 (NHC)2 , PdX2 (NHC)pyridine
∗Correspondence: sedat.yasar@inonu.edu.tr
1
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This work is licensed under a Creative Commons Attribution 4.0 International License.

YAŞAR et al./Turk J Chem
Scheme 1. Our new ionic palladium complexes and those of Huynh.
complexes, which bear the same NHC ligands as the ionic Pd(II)-NHC complexes, are very active catalysts for
Suzuki–Miyaura reactions.
Taking these studies into account, we present the synthesis and catalytic activity of ionic palladium(II)
complexes in Suzuki–Miyaura reactions of aryl bromides.
2. Materials and methods
All reactions were carried out under normal atmospheric conditions. Pd(OAc)2 was purchased from Alfa-
Easer (Tewksbury, MA, USA) and used without any purification. Elemental analyses were performed using
1
the ElementarVario EL III Carlo Erba 1108 (Elemental Microanalysis Ltd., Okehampton Devon, UK). The
H
1
3
and C nuclear magnetic resonance (NMR) spectra were recorded in CDCl3 or DMSO-d6 solutions operating
on a Bruker Avance III HD 300 and 400 MHz NMR spectrometer (Billerica, MA, USA); chemical shifts were
1
13
reported relative to tetramethylsilane for H and C NMR spectra as the standard. Signals were quoted in
parts per million as δ downfield from tetramethylsilane (δ 0.00) as an internal standard. Coupling constants (J
values) were given in Hertz. NMR multiplicities were abbreviated as follows: singlet (s), doublet (d), doublet of
doublet (dd), triplet (t), and multiplet (m) signals. The LC-MS/MS (ESI) electrospray ionization mass spectra
were recorded on an Agilent LC-MS/MS spectrometer (Santa Clara, CA, USA) in CH3 OH. The solvent ratio
was given as v/v.
3. Results
In homogeneous catalysis systems, the solubility of catalysts and reagents in aqueous media is an important
parameter for the efficiency of the reaction. In this manner, to increase the solubility of catalyst precursors
in aqueous media, our strategy was based on the synthesis of ionic Pd(II)- NHC complexes (Scheme 1). With
this aim, we chose symmetrical 1,3-bisalkylbenzimidazolium precursors (1a–1c), which were previously used in
the synthesis of neutral Pd-NHC complexes [22–24]. These results may provide knowledge about the catalytic
activities of neutral and ionic Pd-NHC complexes, which bear the same NHC ligands.
1
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YAŞAR et al./Turk J Chem
A general method for the synthesis of ionic Pd(II)-NHC includes the reaction of 1 equiv. of Pd(OAc)2
with 1 equiv. of NHC salts and 5 equiv. of NaBr in DMSO; this produces the corresponding ionic Pd(II)-
N -heterocyclic carbene complex. A similar synthetic method for the synthesis of ionic palladium(II)-NHC
complexes was reported by Huynh [18]. With this method, the ionic palladium(II)-NHC complexes were obtained
in high yields of 80%–90% (Scheme 2).
Scheme 2. Synthesis method for the NHC-stabilized ionic palladium(II)-NHC complexes 2a–2c.
Due to the formation of black palladium, the quantity of Pd(OAc)2 decreases in reaction media and
the excess amounts of NHC ligands in the reaction medium cause cleavage of the dimeric palladium complex,
forming the ionic palladium complex. In our case, this reaction was carried out in normal DMSO under aerobic
reaction conditions without a significant loss of yield. Ionic Pd(II)-NHC complexes were isolated as an orange-
yellow solid that was soluble in the polar solvent. The formation of ionic Pd(II)-NHC complexes was confirmed
1
by H NMR spectroscopy, which showed the existence of the NCHN proton on the benzimidazolium cation.
Furthermore, a significant downfield shift signal of the coordinated NCN carbon of NHC ligands to palladium
1
3
metal and a slight downfield shift signal of NCHN emerging in one C NMR spectrum confirmed the formation
of ionic palladium complexes. The formation of 3 ionic Pd(II)-NHC complexes (2a–2c) was supported by LC-
MSMS (ESI) spectroscopy in negative mode, which showed an isotopic envelope centered at m/z = 813.8,
m/z = 1226.0, and m/z = 902.9, respectively, corresponding to the ionic complexes.
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YAŞAR et al./Turk J Chem
The ORTEP-3 view of 2a with the atom-labelling scheme is shown in Figure, while important bond
lengths and angles are listed in Table 1. The compound crystallized as salt and its asymmetric unit contained
a discrete complex anion and a benzimidazolium cation. The ionic complex consisted of a 5,6-dimethyl-1,3-
bis(2,3,4,5,6-pentamethylbenzyl)-2,3-dihydro-1H -benzo[d]imidazole with a Pd metal center and 3 bromide
ligands. The coordination around the Pd was a distorted square-planar with angles between adjacent ligands
◦
◦
◦
ranging from 86.32(15) to 95.00(3) . The 2 trans angles also deviated from the ideal value of 180 , being
1
71.34(3) for Br1|Pd1|Br3 and 176.22(15)◦ for Br2|Pd1|C1. The 4-coordinate geometry index for the
complex, τ4 [25], was 0.09 (where 0 would be perfectly square-planar, and 1 was perfectly tetrahedral).
◦
Figure 1. View of 2a showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability
level and H atoms have been omitted for clarity.
The Pd|C bond length amounted to 1.943(5) Å; this length is characteristic for Pd-NHC complexes
[
18,26]. Among the 3 Pd|Br bonds in the complex, the Pd|Br bond trans to the carbene ligand was notably
longer than the others due to the trans influence of the carbene, which had strong σ-donating and weak
π-acceptor ability; these data were consistent with those in the literature [18]. The carbene ring plane was
◦
oriented almost perpendicular to the PdBr3 coordination plane with a dihedral angle of 79.23(13) , which is
typical for NHC complexes to minimize steric hindrance [27]. Compared to the benzimidazolium cation, the
◦
Ccarbene|N1/N2 bond lengths had increased, which was accompanied by a decrease in the N|C|N angle at 4.8 .
Furthermore, the C1|N1|C10 and C1|N2|C22 angles contracted, while the C1|N1|C2 and C1|N2|C9 angles
1
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YAŞAR et al./Turk J Chem
Table 1. Selected geometric parameters for 2a.
−
+
−
+
Parameters
Bond lengths (Å)
Pd1|Br1
[NHCPdBr3]
X
Parameters [NHCPdBr3]
X
2.4410(8)
2.4975(8)
2.4429(8)
1.943(5)
1.363(6)
−
−
−
−
N1|C2
N1|C10
N2|C1
N2|C9
1.392(6)
1.482(6)
1.341(6)
1.409(6)
1.483(6)
1.394(6)
1.474(7)
1.317(7)
1.390(6)
1.464(6)
Pd1|Br2
Pd1|Br3
Pd1|C1
N1|C1
1.320(6) N2|C22
◦
Bond angles ( )
Br1|Pd1|Br2
Br1|Pd1|Br3
Br2|Pd1|Br3
Br1|Pd1|C1
Br2|Pd1|C1
Br3|Pd1|C1
N1|C1|N2
95.00(3)
171.34(3)
92.19(3)
86.79(15)
176.22(15)
86.32(15)
107.0(4)
−
C1|N1|C2
109.7(4)
C1|N1|C10 122.2(4)
107.0(5)
124.9(5)
128.0(5)
107.2(4)
123.7(4)
129.0(4)
−
−
C2|N1|C10 127.4(4)
−
C1|N2|C9
110.6(4)
−
C1|N2|C22 120.7(4)
−
C9|N2|C22 128.7(5)
111.8(5)
X: Corresponding benzimidazolium cation
expanded. Other parameters remained almost unchanged. In the ionic complex, the NHC ring made dihedral
◦
angles of 79.24(17) and 87.52(16) with the pentamethyl benzene rings. In the case of the benzimidazolium
◦
cation, the corresponding dihedral angles were 81.0(2) and 85.94(17) , respectively. In order to perform a better
comparison, we presented the crystallographic data obtained in Tables 1 and S2.
3.1. Catalysis
In preliminary studies [17,24], the Pd-PEPPSI complexes of NHC ligands used in this study were tested for the
Suzuki–Miyaura reaction of aryl halides. The reaction of 4-bromoanisole with phenylboronic acid was chosen
as a model reaction with which to compare our preliminary study with the published works on the Suzuki–
Miyaura reaction of aryl bromides [17,24]. The reaction conditions were optimized using complex 2a. The results
summarized in Table 2 indicated good catalytic activity of 2a in 2-propanol and water (1:2 v/v), in the presence
of K2 CO3 under aerobic conditions at room temperature with low catalyst loading (0.1 mol%), giving virtually
quantitative asymmetric-symmetric biaryl products. This catalysis system was especially important, since
coupling reactions in aqueous media usually require harsh reaction conditions, such as a higher temperature,
strong base, or higher catalyst loading [28–30]. This catalysis system was free of such harsh reaction conditions.
t
On the other hand, low yield with different types of bases, such as Na2 CO3 KO Bu, KOH, K3 PO4 , and
Cs2 CO3 , were also observed (Table 2, entries 1–5). Furthermore, the use of pure i-PrOH, H2 O, DMF, and
EtOH with K2 CO3 resulted in poor yields (Table 2, entries 12–17).
With the optimized reaction conditions in hand, the substrate scope was investigated. We focused on
the coupling of electronically and sterically different types of aryl bromides with different phenylboronic acids.
Different types of aryl bromides, such as electron-withdrawing and electron-donating functional groups, and
phenylboronic acids, were tolerated very well by this catalysis system (Table 3, entries 2, 5, and 6). Electron-
1
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YAŞAR et al./Turk J Chem
a
Table 2. Optimization of the reaction conditions .
a
b
Entry Solvent
Base
Yield (%)
74
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
i-PrOH/H2O(1:2, v/v) K2CO3
i-PrOH/H2O(1:2, v/v) Na2CO3 49
i-PrOH/H2O(1:2, v/v) Cs2CO3 28
i-PrOH/H2O(1:2, v/v) K3PO4
i-PrOH/H2O(1:2, v/v) KOH
i-PrOH/H2O(1:1, v/v) K2CO3
DMF/H2O(1:2, v/v)
EtOH/H2O(1:2, v/v)
MeOH/H2O(1:2, v/v)
53
39
68
36
60
49
70
58
50
5
K2CO3
K2CO3
K2CO3
0
1
2
3
4
5
6
7
i-PrOH/H2O(1:3, v/v) K2CO3
i-PrOH/H2O(1:4, v/v) K2CO3
i-PrOH
H2O
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
DMF
23
53
42
45
EtOH
MeOH
Acetone
a
Reaction condition: 1 mmol of 4-bromoanisole, 1.0 mmol of
phenylboronic acid, 1 mmol of base, 0.1 mol% 2a, 3 mL of solvent,
room temperature, 0.5 h. GC yields are the average of the 2 runs.
b
Yield was determined by GC with use of undecane as the internal standard.
−
1
withdrawing substrates were converted into the product in 1 min with high TOF values of 59,400 mol h
5
,
−
1
−1
7,831 mol h , and 56,024 mol h , respectively, for 2a–2c. On the other hand, 4-phenoxyboronic acid was
converted to the coupled product in very high yields, regardless of their electronic and steric situation (Table 3,
entries 7–11). Aryl bromides with steric hindrance required long reaction times to produce high yields (Table
3
, entries 12 and 14).
a
Table 3. Substrate scope in Suzuki–Miyaura reactions catalyzed by 2a–2c.
b
Cat/ %Yield
Entry Product
1
2c TOF (mol h 1)
−
2a
2b 2c Time
2a
2b
94 87 96 1 h
940
870
960
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YAŞAR et al./Turk J Chem
Table 3. continued
2
3
4
5
6
7
8
9
99 99 99 1 min
77 67 73 1 h
80 81 89 1 h
94 96 95 1 min
90 91 93 1 min
98 95 96 2 min
94 93 94 2 min
30 45 23 12 h
59400 59400 59400
770
800
670
810
730
890
56626 57831 57022
54021 54819 56024
29402 28528 28802
28228 27902 28202
25
37
19
1
1
0
1
95 88 85 6 h
37 30 35 6 h
158
61
146
50
141
58
1
1
2
3
15 11 12 12 h
12
9
10
70
86 88 84 12 h
71
45
73
1
1
4
5
55 45 52 12 h
37
43
c
99 99 99 10 min 5940
5940
5940
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YAŞAR et al./Turk J Chem
Table 3. continued
c
1
6
95 90 99 4 h
237
225
247
a
Reaction condition: 0.1 mol%[Cat.], 1 mmol substrate, 1.0 mmol phenylboronic acid, 1.0 mmol K2CO3, at room temperature.
￿
Yields are based on aryl bromides after the average of 2 runs.
b
Yield was determined by GC with use of undecane as the internal standard.
c
2
.0 mmol K2CO3.
When we compared the preliminary studies [17,18,24] with the current results, it can be seen that the
present study was more effective than the preliminary studies in many respects. However, it remains unclear
why the reaction times for the couplings of some aryl bromides were so different (Table 3, entries 9–14).
3
3
.2. Synthesis
.2.1. Synthesis of NHC precursors 1a–1c.
NHC precursors 1a–1c were synthesized according to the published procedure [22–24].
3.2.2. Synthesis of ionic Pd(II)-NHC complexes 2a–2c.
Ionic Pd(II)-NHC complexes 2a–2c were synthesized according to the published procedure [18].
3
.2.3. 1,3-Bis-(2,3,4,5,6-pentamethylbenzyl)-5,6-dimethylbenzimidazolium tribomo-(1,3-bis-(2,3,
,5,6-pentamethylbenzyl)-5,6-dimethylbenzimidazole-2-ylidene)palladate(II),(2a):
H NMR (400 MHz, CDCl3 , signals from the counter-cation are marked with an asterisk*): δ 9.23 (s, 1 H,
4
1
NCH *N), 7.06 (s, 2H, ArH*), 6,17, 6.09, 5.96, 5.89, 5.49 (bs, 10H, ArH , CH2 *-Ar, CH2 -Ar), 2.24–2.10 (m,
1
3
1
7
1
2H, Ar-CH3 *, Ar-CH3).
C{ H} NMR (100 MHz, CDCl3): 166.7 (s, NC N), 140.6 (s, NC *HN), 136.8,
35.3, 134.8, 134.6, 134.5, 133.9, 133.7, 133.6, 133.5, 132.9, 132.4, 130.4, 129.8, 128.3, 125.6, 113.5, 111.5, 111.4
(
(
Ar-C *, Ar-C), 52.4, 52.3, 52.1 (C H2 -Ar), 48.5 (C H2 *-Ar), 20.7, 20.2, 20.1, 17.9, 17.6, 17.4, 17.2, 17.1, 16.8
Ar-C H3∗, Ar-C H3). Anal. Calc for C66 H85 Br3 N4 Pd: C, 61.90; H, 6.69; N, 4.38. Found: C, 61.74; H, 6.73;
N, 4.34. LC-MSMS (ESI): for C33 H42 Br3 N2 Pd found m/z = 813.8 (100%) [M+H], Calcd. 814.0
3.2.4. 1,3-Bis-(2,3,4,5,6-pentamethylbenzyl)benzimidazolium tribomo(1,3- bis- (2,3,4,5,6-penta-
methylbenzyl)benzimidazole-2-ylidene)palladate(II), (2b):
1
H NMR (400 MHz, CDCl3 , signals from the counter-cation are marked with an asterisk*): δ 9.62 (s, 1H,
NCH *N), 7.29 (dd, 2H, Ar-H *), 7.23(dd, 2H, Ar-H *), 6.70, 6.48, 5.86 (m, 4H, Ar-H), 6.20 (m, 4H, CH2 *-Ar),
1
3
1
5
.94 (bs, 4H, CH2 -Ar), 2.23–2.10 (m, 60H, Ar-CH3 *, Ar-CH3). C{ H} NMR (100 MHz, CDCl3): 167.6 (s,
NC N), 135.9 (s, NC *HN), 134.4, 134.2, 133.7, 132.7, 132.5, 131.5, 130.9, 126.9, 125.8, 124.4, 120.5, 113.0, 109.9
Ar-C *, Ar-C), 54.4, 51.7, (C H2 -Ar), 48.5 (C H2 *-Ar), 16.6, 16.2, 15.9, 15.8 (Ar-C H3 *, Ar-C H3). Anal.
(
Calc for C62 H77 Br3 N4 Pd: C, 60.82; H, 6.34; N, 4.58. Found: C, 60.88; H, 6.38; N, 4.30. LC-MSMS (ESI) for
C62 H77 Br3 N4 Pd found m/z = 1226.0 [M+2H], Calcd. 1226.3; LC-MSMS (ESI) for C31 H38 Br3 N2 Pd found
m/z = 785.6 (100%) [M], Calcd. 785.0
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YAŞAR et al./Turk J Chem
3.2.5. 1,3-Bis-(2-methylbenzyl)-5,6-dimethylbenzimidazolium tribomo(1,3-bis- (2-methylbenzyl)-
5,6-dimethylbenzimidazole-2-ylidene)palladate(II), (2c):
1
H NMR (400 MHz, CDCl3 , signals from the counter-cation are marked with an asterisk*): δ 10.85 (s, 1H,
NCH *N), 7.17–6.94 and 6.45 (m, 20H, Ar-H * and Ar-H), 6.16–6.0 (m, 4H, CH2 *-Ar), 5.71 (bs, 4H, CH2 -Ar),
1
3
1
2
1
1
2
.34, 2.32, 2.26, 2.19, 2.02 (bs, 24H, Ar-CH3 *, Ar-CH3). C{ H} NMR (100 MHz, CDCl3): 165.6 (s, NC N),
43.4 (s, NC *HN), 137.0, 136.5, 135.1, 133.4, 133.3, 133.2, 131.9, 131.8, 131.1, 130.1, 130.0, 128.9, 128.0, 127.9,
27.8, 127.3, 126.6, 126.3, 126.2, 113.4, 111.4 (Ar-C * and Ar-C), 50.6, 50.4 (C H2 -Ar), 49.9 (C H2 *-Ar), 20.6,
0.1, 19.7, 19.6, 19.5 (Ar-C H3 *, Ar-C H3). Anal. Calc for C50 H53 Br3 N4 Pd: C, 56.86; H, 5.06; N, 5.30.
Found: C, 56.91; H, 5.09; N, 5.23; LC-MSMS (ESI) for C25 H26 Br2 N2 Pd found m/z = 616.6 (100%) [M-H],
Calcd. 616.9
3.3. X-ray diffraction analysis
The intensity data of 2a were collected on an STOE IPDS II diffractometer at room temperature using graphite-
monochromated Mo Kα radiation by applying the ω-scan method. Data collection and cell refinement were
carried out using X-AREA [31], while data reduction was applied using X-RED32 [31]. The structure was solved
2
by a dual-space algorithm using SHELXT-2014 [32] and refined with full-matrix least-squares calculations on F
using SHELXL-2018 [32] implemented in the WinGX [33] program suit. All carbon-bound H atoms were located
in different electron-density maps. Next, they were treated as riding atoms in geometrically idealized positions,
with C|H = 0.93 (aromatic), 0.97 (CH2), and 0.96 Å (CH3), and with Uiso (H) = kU eq (C), where k = 1.5
for the methyl groups and 1.2 for all other H atoms. The molecular graphic was drawn using ORTEP-3 [33].
Crystal data, data collection, and structure refinement details are summarized in Table S1 in the Supplemental
Information.
3.4. Suzuki–Miyaura cross-coupling reaction
In a typical run, in the air atmosphere, a reaction tube was charged with aryl halide (1.0 mmol), phenylboronic
acid (1.0 mmol), ionic Pd-NHC complex (0.001 mmol), and K2 CO3 (1 mmol). Solvent (2-propanol/H2 O, 1:2
v/v) (3 mL) was added to tube and the mixture was vigorously stirred at room temperature for a specific time.
After the desired reaction time, 5 mL of diethyl ether was added to the reaction mixture, and the organic phase
was extracted with the appropriate volume of water and dried over MgSO4 . Next, the organic phase (1 µL
)
was injected to GC. The reactions were monitored with a Shimadzu GC-2010 Plus (FID) (Kyoto, Japan).
The results were the average of the 2 runs. The yields were determined by GC with use of undecane as the
internal standard. All of the coupling products were previously reported. The turn over frequency (TOF) was
calculated using the following equations: TOF = TON/time of reaction and TON = moles of desired product
formed/moles of the catalyst.
4. Discussion
This study showed that ionic palladium-N -heterocyclic carbene complexes 2a–2c had high catalytic activity in
the Suzuki–Miyaura cross-coupling reactions of various aryl bromides and boronic acids, which was characterized
5
−1
by a TOF of up to 10
h
in aqueous media at room temperature, in a very short time with low catalyst
loading. We believe that the benzimidazolium cation on the ionic palladium complex contributed extra stability
to the active palladium catalyst and led to better solubility in aqueous media. This structural difference resulted
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YAŞAR et al./Turk J Chem
in better activity than neutral Pd-NHC complexes [17,24]. Wide substrate tolerance, short reaction times, and
moderate yields with easy reactions and work-up procedures rendered this catalytic system more attractive and
economically viable.
Appendix A. Supplementary data
CCDC 1816638 contains the supplementary crystallographic data for 2a (see Supplementary data). These
data can be obtained free of charge via http://www.ccdc.cam.ac.uk/data request/cif, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
Acknowledgments
This study was supported by Ondokuz Mayıs University (Project No: PYO.FEN.1906.19.001).
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Supplemental Information
Table S1. Crystal data and structure refinement parameters for 2a.
CCDC depository
Color/shape
1816638
Orange/prism
[PdBr3(C33H42N2)]¯•(C33H43N2)
1280.51
+
Chemical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
296
0.71073 Mo Kα
Monoclinic
P21/n (No. 14)
Unit cell parameters
a, b, c (Å)
α, β, γ ( )
Volume (Å )
Z
13.0856(7), 24.9258(9), 19.6128(10)
◦
90, 103.349(4), 90
6224.2(5)
4
1.366
2.265
3
3
Dcalc. (g/cm )
−
(
µ (mm
)
Absorption correction
Tmin., Tmax.
F000
Integration
0.4015, 0.7976
2640
3
Crystal size (mm )
0.66 × 0.22 × 0.11
Diffractometer/measurement method STOE IPDS II/rotation (ω scan)
Index ranges
θ range for data collection ( )
Reflections collected
−15
≤
h
≤ 16, −32 ≤
k
≤ 31, −25 ≤
l
≤ 25
◦
1.634 ≤
θ
≤ 27.171
40895
Independent/observed reflections
Rint.
13725/5770
0.0998
2
Refinement method
Data/restraints/parameters
Goodness-of-fit on F
Full-matrix least-squares on F
13725/0/688
0.834
2
Final R indices [I > 2σ(I)]
R1 = 0.0558, wR2 = 0.0763
R1 = 0.1666, wR2 = 0.0983
0.42, −.42,
R indices (all data)
3
∆
ρmax., ∆ρmin. (e/Å )
1

YAŞAR et al./Turk J Chem
Table S2. Comparison of the selected geometric parameters for 2a and published reference.
[
1] makale]
Parameters
Bond lengths (Å)
Pd1|Br1
2a
Huynh’s Comp.
2.4410(8)
2.4975(8)
2.4429(8)
1.943(5)
1.363(6)
2.4441(7)
2.5042(7)
2.4284(7)
1.951(5)
1.340(7)
Pd1|Br2
Pd1|Br3
Pd1|C1
N1|C1
◦
Bond angles ( )
Br1|Pd1|Br2
Br1|Pd1|Br3
Br2|Pd1|Br3
Br1|Pd1|C1
Br2|Pd1|C1
Br3|Pd1|C1
N1|C1|N2
95.00(3)
171.34(3)
92.19(3)
86.79(15)
176.22(15) 178.02(15)
86.32(15)
107.0(4)
94.01(2)
172.92(3)
93.06(3)
87.83(14)
85.11(14)
109.2(4)
2

YAŞAR et al./Turk J Chem
Figure S1. NMR spectra of 2a
3

YAŞAR et al./Turk J Chem
Figure S2. NMR spectra of 2b
4

YAŞAR et al./Turk J Chem
Figure S3. NMR spectra of 2c
5

YAŞAR et al./Turk J Chem
Figure S4. LC-MS/MS spectra of 2a
6

YAŞAR et al./Turk J Chem
Figure S5. LC-MS/MS spectra of 2b
7

YAŞAR et al./Turk J Chem
Figure S6. LC-MS/MS spectra of 2c
References
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1] Huynh HV, Han Y, Ho JH, Tan GK. Organometallics 2006; 25: 3267-3274.
8