Highly active Pd(II) catalysts with pyridylbenzoimidazole ligands for the Heck reaction

Article abstract of DOI:10.1016/j.jorganchem.2007.07.006

The air-, and thermo-stable palladium(II) complexes C1-C10 are prepared by the reaction of PdCl₂(CH₃CN)₂ with pyridylbenzoimidazole. With various substituents on the pyridine ring, palladium atom was coordinated by two pyridylbenzoimidazole molecules via nitrogen atoms of benzoimidazole. The structure of complexes C3, C4, C6, and C7 has been confirmed by X-ray diffraction analysis. Without substituents on the pyridine ring, palladium atom was directly coordinated with two nitrogen atoms of pyridine and benzoimidazole nitrogen via intramolecular chelation (C10). These complexes performed the Heck olefination of aryl bromides in a good to high yield under phosphine-free conditions.

Full text of DOI:10.1016/j.jorganchem.2007.07.006

Journal of Organometallic Chemistry 692 (2007) 4381–4388
www.elsevier.com/locate/jorganchem
Highly active Pd(II) catalysts with pyridylbenzoimidazole ligands
for the Heck reaction
*
Weixuan Chen, Chanjuan Xi , Yongwei Wu
Key Lab of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry,
Tsinghua University, Beijing 100084, China
Received 8 June 2007; received in revised form 7 July 2007; accepted 10 July 2007
Available online 13 July 2007
Abstract
The air-, and thermo-stable palladium(II) complexes C1–C10 are prepared by the reaction of PdCl
2 3 2
(CH CN) with pyridylbenzoim-
idazole. With various substituents on the pyridine ring, palladium atom was coordinated by two pyridylbenzoimidazole molecules via
nitrogen atoms of benzoimidazole. The structure of complexes C3, C4, C6, and C7 has been confirmed by X-ray diffraction analysis.
Without substituents on the pyridine ring, palladium atom was directly coordinated with two nitrogen atoms of pyridine and benzoim-
idazole nitrogen via intramolecular chelation (C10). These complexes performed the Heck olefination of aryl bromides in a good to high
yield under phosphine-free conditions.
ꢀ
2007 Elsevier B.V. All rights reserved.
Keywords: Heck reaction; Palladium; Pyridylbenzoimidazole; Catalysis
1
. Introduction
attracted the interests of synthetic organic chemists. As
examples, Hayashi et al. have reported the palladium-cata-
lyzed Heck reaction that involved the simple catalytic
Palladium-catalyzed olefination of aryl halides, known
as the Heck reaction, have become one of the most power-
ful methods for carbon–carbon bond formation in organic
synthesis [1,2]. The reactions are commonly carried out in
the presence of phosphine ligands such as the reported
works by the groups of Fu [3], Beller [4], and Hartwig [5]
who have made use of sterically demanded electron-rich
tertiary phosphines as catalyst modifiers as well as pallada-
system of PdCl -imidazole [11]. Mino et al. have reported
2
the catalytic behavior of Pd(II) complexes that featured
hydrazone on the Heck reaction [10]. Recently, we reported
2-iminopyridylpalladium dichloride as a highly active cata-
lyst for the Heck reaction [12]. In this paper, we would like
to report the synthesis of palladium(II) complexes from
pyridylbenzoimidazole derivatives and their catalytic activ-
ity for the Heck olefination of aryl bromides. The resulting
palladium(II) complexes are not only readily available, and
inexpensive, but also the pyridylbenzoimidazole moiety
allows the facile introduction of various substituents into
the benzimidazole framework and pyridine framework.
cycle formed by the reaction of Pd(OAc) and tris(o-tolyl)-
2
phosphine [6]. Considering the negative environmental
effect, air-sensitivity, and cost of phosphine ligands, the
development of phosphine-free catalysts for Heck reaction
would be an important subject regarding academic and
industrial application. Recently, some achievements have
appeared in literature [7]. Among them, the low toxicity
and stability of nitrogen-based ligands such as diimine
2. Results and discussion
[
8], dipyridine [9], hydrazone [10] and imidazole [11] have
2.1. Synthesis and spectroscopic characterization
*
All the pyridylbenzoimidazole ligands were prepared
according to the literature method [13–15]. Palladium(II)
Corresponding author. Tel.: +86 10 62782695.
E-mail address: cjxi@tsinghua.edu.cn (C. Xi).
0
022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.07.006

4382
W. Chen et al. / Journal of Organometallic Chemistry 692 (2007) 4381–4388
dichloride complexes C1–C7 were obtained by the reaction
of the corresponding ligands with PdCl (CH CN) in
2
3
2
dichloromethane at room temperature (Scheme 1). All
complexes tended to precipitate from the reaction solution,
and optimized yields were obtained by adding excessive
amount of Et O in the reaction solution. The complexes
2
C1–C7 are pale yellow solids. Comparing their IR spectra,
we noted that the palladium complexes C1–C7 showed the
suitable absorptions in the pyridine range, for example,
ꢀ
1
ꢀ1
ꢀ1
1
594 cm for C2, 1593 cm for C4, 1586 cm for C7,
which are similar to L2, L4, L7, respectively. That means
the pyridine did not have interaction with palladium. On
the other hand, reaction of PdCl (CH CN) with ligands
2
3
2
Fig. 1. Molecular structure of complex 3. Thermalellipsoids are shown at
30% probability. Hydrogen atoms and solvent molecules have been
omitted for clarity.
L8–L10 gave complexes C8–C10 (Scheme 2), which are
orange solids [16]. Comparing their IR spectra, we noted
that the complexes C8–C10 did not show the suitable
ꢀ1
absorptions in the pyridine range, such as 1604 cm for
C10. This observation is attributed to the infrared inactive
pyridine vibration in the palladium complexes C8–C10
1
[
12,17]. Moreover, the shifts of the H NMR peaks of the
palladium complex C10 tended to low field, which pro-
vided additional evidences for the existence of strong coor-
dination of pyridine nitrogen and benzimidazole nitrogen
to the palladium center. It is noteworthy that the reaction
of L4 with PdCl (CH CN) was treated in the 1:1 ratio
2
3
2
and C4 was obtained in 41% isolated yield, while the reac-
tion of L10 with PdCl (CH CN) was treated in 2:1 ratio,
2
3
2
about 50% of the starting L10 remained unreacted. These
results further indicated that effect of substitutent on the
pyridine led to formation of different type complexes. In
addition, these complexes are thermally stable. When the
complexes, such as C4 and C10, were refluxed in DMSO
for 1 h, respectively, the same NMR spectra were observed.
Fig. 2. Molecular structure of complex 4. Thermalellipsoids are shown at
3
0% probability. Hydrogen atoms and solvent molecules have been
omitted for clarity.
2
.2. Structural features
The single crystals of complexes C3, C4, C6, C7, and
C10 suitable for X-ray crystallography were grown by
corresponding bond lengths and angles in the coordination
palladium frame are shown in Table 1. As shown in Figs.
1–4, the palladium atom is coordinated by two benzimid-
azole molecules via their nitrogen atoms and two chloride
atoms. The ORTEP diagrams of the complex C10 is pre-
sented in Fig. 5 and its corresponding bond lengths and
angles in the coordination palladium frame were shown
in Table 2. The palladium atom was coordinated by pyri-
dine nitrogen and benzimidazole nitrogen via chelation,
which was different from complexes C1–C7. This result
may be attributed to effect of substitutent on the pyridine.
diffusing Et O into the DMF solution. The ORTEP dia-
2
grams of the complexes are presented in Figs. 1–4 and their
R2
N
1
.
R
R
R
R
R
R
R
1
1
1
1
1
1
1
= H, R2 = Me
R1
N
2
2.
3.
= Me, R = Me
R1
Cl
N Pd
2
PdCl
2
(CH
Cl
3
CN)
, rt
2
= Et,
R
= Me
N
N
4.
=
i-Pr, R =Me
2
CH
2
2
N
N
N
R1
Cl
5.
6.
= Me,
= Et,
R
2
= Ac
= Ac
R2
2
R
N
2
7.
= i-Pr, R = Ac
R2
2.3. Heck reaction
Scheme 1.
The complexes C1–C10 have been tested as catalysts in
the model Heck reaction of bromobenzene with n-butyl
acrylate under nitrogen atmosphere to ascertain the most
optimum conditions (Table 3). Although the catalysts
C1–C10 were all effective for the Heck reaction, the use
of C4 as catalyst led to higher yield for this reaction (entry
4). In general, the difference in reactivity of these palladium
R1
N
R1
N
R1 = H
1
PdCl
2
(CH
Cl
3
CN)
2
8
9
1
.
R = Me
CH
2
2
, rt
N
0. R1 = i-Pr
N
N
N
Pd
Cl Cl
Scheme 2.

W. Chen et al. / Journal of Organometallic Chemistry 692 (2007) 4381–4388
4383
Table 1
Selected bond lengths (A) and angles (ꢁ) for complexes C3, C4, C6, and C7
˚
C3 C4 C6 C7
Bond lengths
Pd1–N1
2.001(4)
2.035(4)
2.019(3)
2.013(2)
Pd1–N1A
Pd1–Cl1
Pd1–Cl1A
2.001(4)
2.2882(2)
2.2882(2)
2.035(4)
2.2840(1)
2.2840(1)
2.019(3)
2.2897(1)
2.2897(1)
2.013(2)
2.2981(1)
2.2981(1)
Bond angles
N1–Pd1–N1A
Cl1–Pd1–Cl1A
N1–Pd1–Cl1
N1–Pd1–Cl1A
N1A–Pd1–Cl1
N1A–Pd1–Cl1A
180.0
180.000(1)
180.00(8)
90.82(1)
89.18(1)
89.18(1)
90.82(1)
180.0
180.00(15)
180.00(5)
90.45(8)
89.55(8)
89.55(8)
90.45(8)
180.00(7)
91.20(1)
88.80(1)
88.80(1)
91.20(1)
180.00(7)
90.22(1)
89.78(1)
89.78(1)
90.22(1)
Fig. 3. Molecular structure of complex 6. Thermalellipsoids are shown at
0% probability. Hydrogen atoms and solvent molecules have been
3
omitted for clarity.
complexes can be attributed to the bulky effects of substitu-
ent of the nitrogen of benzimidazoles. In addition, it is no
remarkable difference in the reactivity between methyl
(
electron-donating group) and acetyl (electron-withdraw-
ing group) substitutent on pyridine ring. Without the sub-
stituent on the pyridine ring, the catalysts gave moderate
yields. An investigation of the influence of the base sug-
gested that K CO was the reagent of choice. K PO and
2
3
3
4
NaOAc also affect the Heck coupling of bromobenzene
with n-butylacrylate leading to low yields in 48 h (Table
3
, entries 11 and 12). Piperidine (Pip), Et N, and CsF
Fig. 5. Molecular structure of complex 10. Thermalellipsoids are shown at
0% probability. Hydrogen atoms have been omitted for clarity.
3
3
showed no activity under our conditions (Table 3, entries
Fig. 4. Molecular structure of complex 7. Thermalellipsoids are shown at 30% probability. Hydrogen atoms have been omitted for clarity.

4384
W. Chen et al. / Journal of Organometallic Chemistry 692 (2007) 4381–4388
Table 2
Selected bond lengths (A) and angles (ꢁ) for complex C10
lent yields of the desired products (entries 1 and 2). 4-
Vinylpyridine also gave high yield of the Heck reaction
product (entry 3). Using acrylate led to excellent yields
of the desired product (entries 4 and 5). The above men-
tioned reactions proved highly regioselective (>99:1 E
selectivity). This catalytic system was also active for sim-
ple linear alkenes such as oct-1-ene, although the yield
was low (entries 6). We next investigated the effect of neu-
tral and activated aryl bromides in the Heck reaction
using styrene as substrate (entries 7 and 8). It is notewor-
thy that using 2-methyl-benzene bromides also led to
excellent yields of the Heck reaction products (entry 7).
Using 1-bromonaphthalene resulted in good yield of the
desired product (entry 9).
˚
Bond lengths
Bond angles
Pd1–N1
Pd1–N2
Pd1–Cl2
Pd1–Cl1
N1–C7
C8–C7
2.021(5)
2.040(5)
2.2849(2)
2.2926(2)
1.337(7)
1.456(8)
1.388(8)
1.348(8)
N1–Pd1–N2
N1–Pd1–Cl2
N2–Pd1–Cl2
N1–Pd1–Cl1
N2–Pd1–Cl1
Cl2–Pd1–Cl1
79.6(2)
172.59(2)
94.07(2)
97.12(2)
176.67(2)
89.22(7)
C8–C9
C8–N2
Table 3
Optimization of reaction conditions on Heck reaction of bromobenzene
a
with butenyl acrylate
O
3. Conclusions
O
0
.1mol % Pd-Cat.
Ph Br
Entry
Ph
On-Bu
On-Bu Base, Solvent, 24h, N2
A series of palladium complexes containing pyr-
idylbenzoimidazole ligands have been synthesized and
characterized along with their single-crystal X-ray analysis.
With substitutent in the pyridine, the palladium atom is
coordinated by two benzimidazole molecules via their
nitrogen atoms and two chloride atoms. Without substitu-
tent in the pyridine, the palladium atom is coordinated by
pyridine nitrogen and benzimidazole nitrogen via chela-
tion. Both showed catalytic activity for Heck coupling
between aryl bromide and olefins. The investigation of
the reactivity of the resulting palladium(II) complexes
would provide a new catalyst system for the Heck reaction
under phosphine-free conditions.
b
Cat
Base
Solvent Temperature (ꢁC) Yield (%)
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
a
1
2
3
4
5
6
7
8
9
10
4
4
4
4
4
4
4
4
K
2
K
2
K
2
K
2
K
2
K
2
K
2
K
2
K
2
K
2
K
2
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
3
3
3
3
3
3
3
3
3
3
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
16
72
60
97
86
45
90
48
40
52
11
40
1
1
1
1
1
1
1
1
1
1
PO
4
NaOAc NMP
CsF
Pip
NMP
NMP
NMP
DMA
DMF
Trace
NR
NR
40
Trace
NR
Trace
K
2
K
2
K
2
K
2
K
2
CO
CO
CO
CO
CO
3
3
3
3
3
4. Experimental
4.1. General
Toluene 110
CH CN 50
4
3
All manipulations were conducted in Schlenk tube and
Reaction conditions: bromobenzene (1 mmol), butenyl acrylate
carried out under an atmosphere of nitrogen with a slightly
positive pressure. GC analyses were performed on a gas
chromatograph equipped with a flame ionization detector
using a capillary column (CBP1-M25-025). The NMR
yields were determined using mesitylene as an internal stan-
dard. Unless otherwise noted, all starting materials were
commercially available and were used without further puri-
(
2.5 mmol), base (1.1 mmol), solvent (3 mL), catalyst (0.001 mmol).
NMR yields.
b
1
3–15). In this reaction, several commonly used solvents
were tested (Table 3, entries 16–19). Solvents, such as
N,N -dimethylformamide (DMF), toluene, and CH CN,
were not effective (Table 3, entries 17–19) for this reaction.
Dimethylacetamide (DMA) was less effective (Table 3,
entry 16). Finally we found the optimized conditions as fol-
low: using the complex C4, the reaction proceeded with
0
3
1
13
fication. H NMR and C NMR spectra were recorded on
JOEL 300 NMR spectrometer with TMS as internal stan-
dard. Elemental analyses were performed on a Flash EA
1112 instrument. The IR spectra were obtained on a Per-
kin–Elmer FT-IR 2000 spectrophotometer by using the
9
7% in NMP (NMP = 1-methyl-2-pyrrolidinone) with
ꢀ
1
K CO at 140 ꢁC for 24 h under nitrogen atmosphere
(
KBr disc in the range of 4000–400 cm .
2
3
Table 3, entry 4).
Heck couplings were carried out with catalyst 4 between
aryl bromides and olefins. A summary of the results is
shown in Table 4.
4.2. General procedure for the synthesis of palladium
complexes 1–7
In the beginning, we investigated the activity of a
group of olefins in the Heck reaction using 1-bromoben-
zene as substrate under the optimized reaction conditions
All the benzimidazole based ligands were synthesized
according to the literature method [13–15], and all palla-
dium complexes were prepared by same procedure. Herein
only the synthesis of palladium complex 4 is described as
(
entries 1–6). Styrene or para-methyl styrene led to excel-

W. Chen et al. / Journal of Organometallic Chemistry 692 (2007) 4381–4388
4385
Table 4
Heck reaction of aryl bromide with olefin using 2-benzimidazolylpyridine based catalyst 4
a
b
c
Entry
1
Aryl bromide
Br
Olefin
Time (h)
12
Product
Yield (%)
TON
>99
990
2
Br
12
90
900
Me
Me
3
4
5
Br
Br
Br
Br
12
24
24
>99
990
970
970
N
N
MeO
97
O
O
MeO
O
O
BuO
Hex
97
BuO
6
7
24
12
32
99
320
990
Hex
Br
Me
Me
8
>99
Br
O
1
2
990
O
Me
Me
9
12
88
Br
8
80
a
Reaction conditions: aryl bromide (1 mmol), olefin (2.5 mmol), K
NMR yields.
TON = mol of product/mol of the catalyst.
2 3
CO (1.1 mmol), NMP (5 mL), catalyst 4 (0.001 mmol).
b
c

4386
W. Chen et al. / Journal of Organometallic Chemistry 692 (2007) 4381–4388
an example in detail. To ligand L4 (0.503 g, 2.0 mmol) and
4.2.4. Complex 5
1
PdCl (CH CN) (0.259 g, 1.0 mmol) was added 10 mL
Light yellow solid was produced in 88% yield H NMR
2
3
2
freshly distilled dichloromethane at room temperature
and stirred overnight. Then 10 mL diethyl ether was added
to precipitate the complex completely. Trans-di-[2-(1-iso-
propyl-2-benzimidazolyl)-6-methylpyridine]-dichloropalla-
dium(4) (0.633 g, 0.93 mmol) light yellow powder was
(300 MHz, ppm, DMSO-d ) d 8.62–8.59 (d, 1H, –Py),
8.30–8.25 (t, 1H, –Py), 8.13–8.11 (d, 1H, –Py), 7.86–7.83
6
(d, 2H, –Ph), 7.51–7.41 (m, 2H, –Ph), 4.37 (s, 3H, –CH ),
3
1
3
2.79 (s, 3H, –CH3); C NMR (75 MHz, ppm, DMSO-d6)
d 199.8, 153.2, 149.0, 147.9, 140.1, 139.7, 129.1, 125.3,
124.8, 123.0, 119.2, 113.1, 112.6, 34.2, 27.1. IR (KBr;
1
obtained in 93% yield. H NMR (300 MHz, ppm,
ꢀ1
DMSO-d ) d 8.38–8.36 (d, 1H, –Py), 8.10–7.98 (m, 4H,
cm ): 3387, 3063, 2947, 1703 (mC@O), 1587, 1481, 1435,
1406, 1354, 1295, 1262, 1226, 1158, 1112, 1078, 993, 954,
824, 748, 591. Anal. Calc. for C H Cl N O Pd Æ
6
Ar), 7.52–7.48 (m, 2H, –Ph), 5.30–5.25 (m, 1H, –CH–
(
CH ) ), 2.56 (s, 3H, –CH ), 1.74–1.72 (d, 6H, –CH );
3 2 3 3
30 26
2
6
2
1
3
C NMR (75 MHz, ppm, DMSO-d ) d 158.7, 150.7,
0.75CH Cl : C, 49.67; H, 3.73; N, 11.30. Found: C,
2 2
6
1
2
1
47.8, 140.2, 138.5, 133.0, 125.7–124.1, 120.2, 114.8, 50.9,
4.8, 21.3. IR (KBr; cm ): 3082, 2979, 1593, 1462, 1420,
302, 1248, 1203, 1139, 905, 815, 751. Anal. Calc. for
49.57; H, 3.80; N, 11.26%.
ꢀ
1
4.2.5. Complex 6
Light yellow solid was produced in 86% yield
1
C H Cl N Pd Æ 1.5H O: C, 54.36; H, 5.27; N, 11.89.
H
3
2
34
2
6
2
Found: C, 54.24; H, 5.11; N, 11.55%.
NMR (300 MHz, ppm, DMSO-d ) d 8.69–8.67 (d, 1H,
6
–Py), 8.39–8.33 (t, 1H, –Py), 8.22–8.20 (d, 1H, –Py),
4
.2.1. Complex 1
Orange powder was produced in 92% yield H NMR
300 MHz, ppm, DMSO-d ) d 10.5 (br, 1H, NH),
7.99–7.96 (d, 1H, –Ph), 7.92–7.90 (d, 1H, –Ph), 7.60–
1
7.53 (m, 2H, –Ph), 5.04–5.00 (q, 2H, –CH –), 2.57 (s,
2
1
3
(
3H, –CH3), 1.65–1.60 (t, 3H, –CH3);
C NMR
6
8
7
2
.59–8.56 (m, 1H, –Py), 8.18–8.16 (m, 1H, –Py), 7.65–
.61 (m, 2H, –Ph), 7.46–7.44 (m, 1H, –Py), 7.30–7.26 (m,
H, –Ph), 2.52 (s, 3H, –CH3); C NMR (75 MHz, ppm,
(75 MHz, ppm, DMSO-d ) d 199.6, 153.7, 147.3, 146.1,
6
140.6, 135.0, 126.5, 126.3, 124.0, 117.9, 113.3, 42.4,
1
3
ꢀ1
27.0, 16.1. IR (KBr; cm ): 3418, 3063, 2976, 1700
DMSO-d ) d 158.8, 151.4, 150.6, 141.8, 138.3, 133.4,
(mC@O), 1588, 1477, 1426, 1356, 1298, 1251, 1205, 1112,
824, 751, 594. Anal. Calc. for C H Cl N O Pd Æ 3H O:
C, 50.44; H, 4.76; N, 11.03. Found: C, 50.51; H, 4.38; N,
10.84%.
6
ꢀ
1
1
3
1
6
4
1
25.5–123.8, 119.6, 113.7, 24.7. IR (KBr; cm ): 3111,
053, 2976, 2928, 1597, 1510, 1471, 1438, 1396, 1341,
295, 1202, 1159, 1137, 1112, 1066, 1026, 835, 782, 745,
86, 423. Anal. Calc. for C H Cl N Pd Æ 2.5H O: C,
8.73; H, 4.25; N, 13.11. Found: C, 48.57; H, 3.95; N,
2.80%.
3
2
30
2
6
2
2
2
6
22
2
6
2
4.2.6. Complex 7
1
Light yellow solid was produced in 90% yield. H NMR
(
300 MHz, ppm, DMSO-d ) d 8.91–8.88 (d, 1H, –Py),
6
4
.2.2. Complex 2
Light yellow solid was produced in 90% yield H NMR
8.71–8.66 (t, 1H, –Py), 8.45–8.42 (d, 1H, –Py), 8.17–8.14
(d, 1H, –Ph), 8.04–8.01 (d, 1H, –Ph), 7.50–7.44 (m, 2H,
1
(
8
300 MHz, ppm, DMSO-d ) d 8.48–8.45 (t, 1H, –Py),
.24–8.22 (d, 1H, –Py), 7.95–7.93 (d, 1H, –Py), 7.80–7.77
–Ph), 5.94–5.90 (sep, 1H, –CH–(CH ) ), 2.48 (s, 3H,
–CH ), 1.69–1.66 (dd, 6H, –CH ); C NMR (75 MHz,
3 3
6
3 2
1
3
(
–
(
1
d, 1H, –Ph), 7.76–7.73 (d, 1H, –Ph), 7.51–7.44 (d, 2H,
ppm, DMSO-d ) d 196.5, 150.3, 147.4, 146.2, 136.7,
6
1
3
Ph), 4.30 (s, 3H, –CH ), 2.52 (s, 3H, –CH ); C NMR
131.6, 129.0, 127.2, 121.6, 120.8, 117.9, 111.9, 48.7, 23.8,
3
3
ꢀ
1
75 MHz, ppm, DMSO-d ) d 158.0, 150.3, 147.1, 142.6,
19.0. IR (KBr; cm ): 3427, 3072, 2978, 1698 (mC@O),
1586, 1458, 1423, 1357, 1297, 1248, 1203, 1163, 1136,
1112, 1062, 956, 818, 750, 598. Anal. Calc. for
C H Cl N O Pd Æ CH Cl : C, 51.21; H, 4.42; N, 10.24.
6
40.7, 137.6, 135.1, 125.5–123.9, 119.4, 112.0, 33.1, 24.7.
ꢀ
1
IR (KBr; cm ): 3053, 2953, 1594, 1571, 1483, 1436,
406, 1341, 1248, 1161, 1084, 1002, 813, 750. Anal. Calc.
for C H Cl N Pd Æ 1.5H O: C, 51.67; H, 4.49; N, 10.89.
1
3
4
34
2
6
2
2
2
Found: C, 51.47; H, 4.58; N, 10.25%.
2
8
26
2
6
2
Found: C, 51.49; H, 4.27; N, 12.75%.
4.3. General procedure for the synthesis of palladium
complexes 8–10
4
.2.3. Complex 3
Light yellow solid was produced in 92% yield H NMR
300 MHz, ppm, DMSO-d ) d 8.67–8.64 (d, 1H, –Py),
1
(
8
All the benzimidazole based ligands were synthesized
according to the literature method [14,15], and all palla-
dium complexes were prepared by same procedure. Herein
only the synthesis of palladium complex 10 is described as
an example in detail. To ligand L10 (0.237 g, 1.0 mmol)
and PdCl (CH CN) (0.259 g, 1.0 mmol) was added
6
.30–8.24 (t, 1H, –Py), 8.17–8.14 (d, 1H, –Py), 7.88–7.85
(
m, 2H, –Ph), 7.49–7.43 (m, 2H, –Ph), 5.02–4.95 (q, 2H,
1
3
–
CH –), 2.56 (s, 3H, –CH ), 1.61–1.57 (t, 3H, –CH );
C
2
3
3
NMR (75 MHz, ppm, DMSO-d ) d 159.0, 151.9, 147.1,
6
1
1
1
44.4, 139.5, 133.5, 128.6, 124.6, 123.9, 122.4, 119.5,
11.8, 41.1, 26.6, 16.0. IR (KBr; cm ): 3063, 2976, 1585,
475, 1426, 1354, 1298, 1255, 1081, 824, 747. Anal. Calc.
2
3
2
ꢀ1
10 mL freshly distilled dichloromethane at room tempera-
ture and stirred overnight. Then 10 mL diethyl ether was
added to precipitate the complex completely. (2-(Pyridin-
2-yl)-1H-benzo[d]imidazol-1-yl)praseodymium palladium
for C H Cl N Pd Æ 0.75CH Cl : C, 51.61; H, 4.44; N,
1
3
0
30
2
6
2
2
1.74. Found: C, 51.91; H, 4.33; N, 11.79%.

W. Chen et al. / Journal of Organometallic Chemistry 692 (2007) 4381–4388
4387
dichloride 10 (0.357 g, 0.86 mmol) orange powder was
obtained in 86% yield. H NMR (300 MHz, ppm,
4.3.2. Complex 9
Orange solid was produced in 90% yield. IR (KBr;
1
ꢀ1
DMSO-d ) d 9.24–9.22 (d, 1H, –Py), 8.87–8.84 (d, 1H,
cm ): 3133, 3044, 1608, 1531, 1485, 1456, 1410, 1350,
1224, 1170, 1028, 1015, 941, 829, 791, 760, 740. Anal. Calc.
for C H Cl N Pd: C, 40.39; H, 2.87; N, 10.87. Found: C,
6
–
7
5
Py), 8.33–8.32 (d, 2H, –Ph), 8.04–8.01 (d, 1H, –Py),
.81–7.76 (q, 1H, –Py), 7.45–7.34 (m, 2H, –Ph), 5.55–
1
3
11
2
3
1
3
.42 (sep, 1H, N–CH–), 1.75–1.72 (d, 6H, –CH3);
C
39.88; H, 2.89; N, 10.66%.
NMR (75 MHz, ppm, DMSO-d ) d 151.7, 147.9, 141.8,
6
1
40.8, 133.3, 127.5, 125.9, 125.7, 125.1, 120.0, 115.2. IR
4.4. Heck reaction
ꢀ1
(
KBr; cm ): 3405, 2976, 1604, 1510, 1471, 1438, 1396,
1
7
4
9
341, 1295, 1202, 1159, 1137, 1112, 1066, 1026, 835,
4.4.1. General procedure
Under nitrogen atmosphere, K CO (2.2 mmol), olefin
82, 745, 686. Anal. Calc. for C H Cl N Pd Æ H O: C,
1
5
15
2
3
2
2
3
1.64; H, 3.96; N, 9.71. Found: C, 41.75; H, 3.61; N,
.81%.
(5 mmol), aryl bromide (2 mmol), and NMP (5 mL) were
added in turn to a Schlenk tube equipped with a magnetic
stirring bar. A 20 lL NMP solution containing 0.002 mmol
of complex (about 1.1 mg) was added into the Schlenk
tube. The mixture was stirred at 140 ꢁC and monitored
by GC. After 12–24 h, the mixture was diluted with ether
and water. The organic layer was washed with brine, dried
over Na SO , and concentrated under reduced pressure.
4
.3.1. Complex 8
Orange solid was produced in 75% yield. IR (KBr;
ꢀ
1
cm ): 3161, 3092, 1611, 1590, 1542, 1482, 1459, 1447,
327, 1308, 1151, 990, 822, 751, 657. Anal. Calc. for
C H Cl N Pd Æ CH Cl : C, 34.13; H, 2.42; N, 9.19.
1
1
2
9
2
3
2
2
2
4
Found: C, 34.02; H, 2.39; N, 9.16%.
The residue was purified by flash chromatography on silica
Table 5
Crystal data and structure refinement for C3, C4, C6, C7, and C10
C3
C4
C6
C7
C10
Empirical formula
Formula weight
Crystal color
C
60
H
60Cl
4
2
N12Pd 2CH
3
CN
C
753.05
yellow
32
H
434Cl
2
N
6
PdDMF
C
854.13
yellow
32
H
30Cl
2
N
6
O
2
Pd2DMF
C
735.99
yellow
34
H
34Cl
2
N
6
O
2
Pd
15 2 3
C H15Cl N Pd
1385.95
yellow
414.6
red
Temperature (K)
293(2) K
0.71073
Triclinic
293(2) K
0.71073
293(2) K
0.71073
Triclinic
P1
9.3344(8)
9.9752(9)
12.6714(1)
110.525(5)
94.746(6)
110.388(6)
1007.14(2)
1
293(2) K
0.71073
Monoclinic
Pc
293(2) K
0.71073 A
˚
Wavelength (A)
Crystal system
Space group
Monoclinic
P2(1)/c
16.7341(4)
14.5875(4)
15.9854(4)
90
113.6640(1)
90
3574.06(2)
4
Monoclinic
P2(1)/n
11.2585(4)
10.2044(4)
13.6927(5)
90
93.427(2)
90
1570.29(10)
4
ꢀ
P1
˚
a (A)
9.4073(2)
11.658(2)
15.631(3)
100.63(3)
91.46(3)
94.57(3)
1678.1(5)
1
7.3122(2)
14.365(3)
17.246(3)
90.0
98.67(3)
90.0
1790.8(6)
2
1.365
˚
b (A)
˚
c (A)
a (deg)
b (deg)
c (deg)
˚
3
Volume (A )
Z
ꢀ3
D
calc (g cm
)
1.371
0.744
1.399
0.707
1.408
0.642
1.754
1.517
ꢀ
1
l (mm
)
0.705
F(000)
708
1552
440
752
824
Crystal size (mm)
h Range (ꢁ)
0.32 · 0.23 · 0.15
1.33–27.49
0.35 · 0.25 · 0.18
1.93–28.29
ꢀ18 6 h 6 22,
ꢀ16 6 k 6 19,
ꢀ21 6 l 6 20
28564
8844
99.5 (h = 28.29ꢁ)
Empirical
0.30· 0.20 · 0.10
3.29–28.37
ꢀ12 6 h 6 12,
ꢀ13 6 k 6 13,
ꢀ16 6 l 6 16
19520
4980
99.0 (h = 28.37ꢁ)
Empirical
0.35 · 0.25 · 0.18
1.85–27.47
ꢀ9 6 h 6 9,
ꢀ18 6 k 6 18,
ꢀ22 6 l 6 22
7469
0.35 · 0.25 · 0.10
1.81–28.30
ꢀ11 6 h 6 15,
ꢀ11 6 k 6 13,
ꢀ18 6 l 6 18
13370
3908
99.9 (h = 28.30ꢁ)
Empirical
Limiting indices
ꢀ12 6 h 6 12,
ꢀ
15 6 k 6 15,
20 6 l 6 20
ꢀ
Reflections collected
Unique reflections
Completeness to (%)
Absorption correction Empirical
Number of
12034
7473
97.0 (h = 27.49ꢁ)
4058
98.8 (h = 27.47ꢁ)
Empirical
208
382
418
241
190
parameters
Goodness-of-fit on F
Final R indices
2
1.109
1.055
1.024
1.155
1.216
R
1
= 0.0612, wR
2
2
= 0.1531
= 0.1672
R
1
= 0.0681,
wR = 0.1233
= 0.1410,
wR = 0.1500
0.553 and ꢀ0.521
R
1
= 0.0673,
wR = 0.1153
= 0.1037,
wR = 0.1297
0.654 and ꢀ0.513
R
1
= 0.0422,
wR = 0.1027
= 0.0635,
wR = 0.1174
0.468 and ꢀ0.630
R
1
= 0.0773,
wR = 0.1024
= 0.1071,
wR = 0.1099
0.499 and ꢀ1.241
[
I > 2r(I)]
2
2
2
2
R indices (all data)
R
1
= 0.0855, wR
R
1
R
1
R
1
R
1
2
2
2
2
Largest difference in
peak and hole
0.850 and ꢀ0.614
˚
ꢀ3
(
e A
)

4388
W. Chen et al. / Journal of Organometallic Chemistry 692 (2007) 4381–4388
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1
(
Acknowledgements
(
This work was supported by the National Natural Sci-
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