Aqueous-phase Suzuki-Miyaura cross-coupling reactions catalyzed by Pd-NHC complexes

Article abstract of DOI:10.1039/b907032j

Cleavage reactions of [PdBr₂(NHC)]₂ with two equiv. of pyridine derivatives (L), having one or two carboxylic acid groups [L = NC₅H₄-2-COOH, NC₅H₄-3-COOH, NC ₅H₄-4-COO

Full text of DOI:10.1039/b907032j

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www.rsc.org/dalton | Dalton Transactions
Aqueous-phase Suzuki–Miyaura cross-coupling reactions catalyzed by
Pd-NHC complexes
Hayati T u¨ rkmen, Rahime Can and Bekir C¸ etinkaya*
Received 7th April 2009, Accepted 28th May 2009
First published as an Advance Article on the web 13th July 2009
DOI: 10.1039/b907032j
Cleavage reactions of [PdBr
carboxylic acid groups [L = NC
NC -2,6-(COOH) in chloroform or DMSO, respectively, afforded the monomeric mixed ligand
complexes trans-[PdBr (NHC)L] (1–4) which, due to deprotonation of the carboxylic acid functionality,
2
(NHC)]
2
with two equiv. of pyridine derivatives (L), having one or two
5
H
4
-2-COOH, NC
5
H
4
-3-COOH, NC -4-COOH, or
5
H
4
5
H
3
2
2
are water soluble in KOH. The catalytic activity of complexes 1–4 in aqueous Suzuki–Miyaura
cross-coupling reactions were evaluated and compared. The dicarboxylic functionality enhances the
catalyst reactivity and stability and the carboxylate derived from 4 could be easily recovered and reused
for several cycles under the mild reaction conditions.
1
. Introduction
PEPPSI (PEPPSI = Pyridine Enhanced Precatalysts Preparation,
Stabilization and Initiation) and successfully applied as the cross-
The Suzuki–Miyaura reactions, catalyzed by palladium complexes
have been commonly employed to generate functionalized biaryls.
Since the first report in the early 1980s, a large number of sup-
porting ligands, such as phosphines and N-heterocyclic carbenes
9
coupling catalysts. However, to our knowledge no pyridine
derivatives containing carboxyl group, have been utilized as a
supporting ligand for the complexation, which will provide a
straightforward approach to water-soluble NHC complexes in
basic media.
(
NHCs) have been developed as good catalysts for various C–C
1,2
cross-coupling reactions.
Because they are stable towards air and moisture and tolerant
to a variety of functional groups, Pd(NHC) complexes are parti-
2
.1. Synthesis of Pd(II) complexes, 1–4
3,4
The dimeric complexes of the type [PdX (NHC)] can be readily
prepared and cleaved by various nucleophiles to give mixed
cularly useful catalysts for this purpose. In practice, the steric and
electronic properties of the NHC framework composed of two N
atoms and a hetero ring, can be tuned by altering the substituents
on either portion. Therefore, many reports have since 1995
2
2
10–15
[
Pd(NHC)(nuc)] complexes.
Therefore, we applied this con-
(NHC)L] (NHC =
cept to the dimer I to obtain trans-[PdBr
2
5
1,3-dialkylbenzimidazol-2-ylidene; L = pyridinecarboxylic acid)
complexes of the type. Scheme 1 shows the synthetic routes used
to prepare the desired complexes which have carboxylic acid(s)
groups on different position of the pyridine ring.
appeared describing studies of structurally varied complexes.
Although the C–C coupling reactions, catalyzed by the
Pd(NHC) complexes in organic solvents is well-developed, its
6
potential utility in water is largely limited. Water is an attrac-
tive replacement for organic solvents because it is inexpensive,
7
renewable, nontoxic, and nonflammable. Furthermore, the use of
water-soluble metal complexes allows an easy separation of the
catalyst and the organic reagents, and in principle, combines the
virtues of conventional homogeneous and heterogeneous systems.
The implementation of aqueous catalysis is due to lack of suitable
catalysts. To address this need we synthesized a series of new
palladium NHC complexes bearing pyridinecarboxylic acids
(
1–4) and we studied their application in Suzuki–Miyaura cross-
coupling reactions. The immediate goals of our studies were to
evaluate the effect of new monomeric catalysts on the reactivity
and to further determine the extent of their recovery and recycling
in water.
2
. Results and discussion
Meanwhile, the NHC ligand is widely utilized as an ancillary
8
ligand in coordination and organometallic complexes. Recently,
Organ and coworkers reported a combination of Pd(NHC) with
3
Scheme 1 Reagents and conditions: (i) pyridinecarboxylic acid, CHCl ,
◦
◦
Department of Chemistry, Ege University, 35100, Bornova-Izmir, Turkey
25 C, 24 h; (ii) pyridine-2,6-dicarboxylic acid, DMSO, 25 C, 24 h.
This journal is © The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7039–7044 | 7039

Table 1 Comparison of selected spectroscopic data of complexes, 1–4
Table 2 aEffect of temperature on the Suzuki coupling reaction catalyzed
by 2 or 4
13
IR(nC=O
,
NMR ( C,
C–Pd, ppm)
-1
Complex
n
O–H, cm )
UV-visible (nm)
1
1
1
2
2
2
3
3
3
4
4
4
a
b
c
a
b
c
a
b
c
a
b
c
1752, 3712
1735, 3650
1739, 3674
1752, 3712
1703, 3433
1731, 3423
1750, 3722
1759, 3712
1705, 3437
1740, 3498
1750, 3712
1742, 3502
161.1
161.2
161.3
162.4
162.6
162.6
163.5
163.1
163.1
160.5
160.6
160.9
231, 274, 280, 351
233, 270, 284, 350
230, 272, 279, 354
240, 273, 361
243, 246, 271, 361
234, 241, 244, 274, 361
235, 245, 274, 362
233, 242, 271, 362
233, 240, 242, 273, 362
240, 277, 2.80, 351
233, 272, 2.81, 352
239, 279, 2.83, 352
◦
Complex Temperature ( C) Conversion (%) II (%) III (%) IV (%)
2
2
2
2
2
2
a (4a)
b (4b)
c (4c)
a (4a)
b (4b)
c (4c)
25
25
25
50
50
50
80
80
80
80(83)
77(78)
82(81)
87(88)
80(85)
83(88)
88(89)
90(91)
93(94)
60(61) 14(11) 5(9)
57(59) 13(12) 4(5)
58 (63) 13(14) 8(3)
51(52) 27(30) 3(4)
55(58) 20(22) 5(3)
42(48) 32(34) 4(4)
20(21) 62(64) 4(2)
20(20) 67(66) 2(3)
13(12) 76(78) 3(3)
All new complexes have been isolated as yellow and air-
2a (4a)
2
2
2
2
b (4b)
c (4c)
a (4a)
b (4b)
stable solids. They are insoluble in nonpolar solvents such as
diethyl ether, hexane, pentane or toluene, but soluble in DMSO,
DMF, C
100
100
100
100(100)
100(100)
100(100)
04(05) 89(93)
05(03) 81(91)
03(01) 94(96)
—
—
—
2
H
5
OH and H O. The complexes were characterized
2
by elemental analysis, by their IR, NMR and UV-visible spec-
troscopy (Table 1 lists some selected data). The formation of
the metal complexes were evident from the distinctive Pd-Ccarbene
peak, appeared at ca. 160.5–163.5 ppm for 1–4. This data
suggests that the weakest s-donor leads to the most upfields
2c (4c)
a
Yields were determined by gas chromatography for an average of two
runs.
1
3
12,15
C chemical shift.
chemical shift to that of {[PdBr
ylidene)Py], Py = pyridine, 4,4¢-bipyridine, 4,4¢-bipridylethane,
,4¢-bipridylethylene}complexes clearly confirm the trans-
configuration proposed for 1–4. The IR spectra of compounds
Furthermore, a comparison of such
Table 3 The Suzuki coupling reaction of aryl chlorides with phenyl-
a
boronic acid
2
(1,3-diisopropylbenzimidazol-
4
12c
-
1
1
–4 displayed absorption bands at 1703–1759 cm due to n(COO),
Yield (%)
-
1
and broad bands between 3423 and 3722 cm due to n(O–H).
From the IR data we may infer that the COOH group(s) on the
pyridine ring were not involved in metal-bonding, at least under
neutral conditions. Whilst, the versatility of 2-pyridinecarboxylic
or 2,6-pyridinedicarboxylic acids as multidentate ligands is well
known.
The UV-visible absorption spectral data obtained for com-
plexes, 1–4, in CH Cl are summarized in Table 1. The mixed
Entry R¢¢
1a 1b 1c 2a 2b 2c 3a 3b 3c 4a 4b 4c
CO 92 90 93 89 81 94 87 85 88 93 91 96
1
3
2
4
CH
3
CHO
CH
CH
89 87 92 82 81 84 83 83 87 91 88 92
86 83 88 83 83 88 84 82 86 89 85 89
81 80 89 75 74 77 70 71 75 87 85 88
3
3
O
16
a
Yields was determined by gas chromatography for an average of two runs.
2
2
NHC/pyridinecarboxylic acid complexes, 1–4, showed weak ab-
In order to determine the influence of the ligands i.e. NHC and
sorption bands and 350–362 nm corresponding to the metal-to-
pyridinecarboxylic acids (L) on the Suzuki reaction in neat water,
the coupling reaction of p-chloroacetophenone and phenylboronic
acid was selected as a model reaction and KOH was used as the
base. The yield of unsymmetrical biaryls (III) ranged from 81% to
17
ligand charge transfer (MLCT). The absorbance maxima spectra
of complexes 1–4 exhibited at 240–283 nm, which are assigned to
intraligand p → p* transitions.
9
6% (Table 3, Entry 1). The activated and unactivated aryl chloride
substrates also were treated under identical conditions (Table 3,
Entries 2–4), to give good to excellent yields of the biaryls. The
similar reactivity trends with our previous report is in agreement
with the stronger donating ability of alkyl substituents, making the
donor atoms more electron-rich. Among the complexes tested, 1
and 4 gave the highest yield while complexes 2 and 3, with 3- and 4-
pyridinecarboxylic acids gave moderate or good yields. This result
implies that the COOH(K) functionality ortho to the N atom of
the pyridine has some influence on the stability of active species.
2
.2. Suzuki coupling of aryl halides and phenylboronic acid
We have found that the NHC ligands containing the asymmetric
substituents on the N atoms of the ring are more efficient than
11
11
the symmetrical ones for C–C coupling reactions. Therefore,
we have chosen the NHC substituents shown in Scheme 1.
First of all, we studied the influence of temperature on the
distribution of the possible coupling products (II–IV) formed from
p-chloroacetophenone-phenylboronic acid in the presence of (2)
and (4) and observed that as the temperature increased the yield
of desired product (III) also increased (Table 2).
At room temperature biphenyl formation from the homocou-
pling of phenylboronic acid is adominantreaction which gradually
subsides as the temperature rises. Therefore, we set to 100 C as
2.3 Catalyst recycling
The potential recyclability of the catalysts derived from the
4c system was explored in the model cross-coupling of 4-
chloroacetophenone and phenylboronic acid (Fig. 1). The reaction
◦
the standard temperature.
7
040 | Dalton Trans., 2009, 7039–7044
This journal is © The Royal Society of Chemistry 2009

1
13
spectrometer at 400 MHz ( H), 100.56 MHz ( C). Elemental
analyses were carried out by the analytical service of TUBITAK
with a Carlo Erba Strumentazione Model 1106 apparatus. The
yields of C–C coupling products were determined by using Trace
GC Ultra Thermo Al 3000.
General procedure for the Suzuki coupling reactions
A two-necked 25 mL flask fitted with a reflux condenser
was charged with aryl chlorides (1.0 mmol), 2 mmol KOH,
phenylboronic acid (1.5 mmol), diethyleneglycol-di-n-butylether
(
0.6 mmol, internal standard), then 1.0% 1–4 in 6 mL of H
2
O
◦
was added. The flask was placed in a preheated oil bath (100 C)
under air atmosphere, temperature 100 C, 4 h. The conversion
◦
was monitored by gas chromatography. Yields were determined
by gas chromatography for an average of two runs.
Fig. 1 Recycling of catalyst 4c.
Recycling of catalyst
◦
was carried out in water at 100 C without any additive. After
cooling to room temperature, the organic products were extracted
by dichloromethane and the yields were determined by GC. The
aqueous phase was then transferred to a new reaction flask for the
next cycle. It was shown that the coupling reaction using 1 mol%
catalyst could be reused by two cycles and the yield significantly
dropped to ca. 52% for the fourth cycle. On the other hand,
the experiments with the substrate 4-bromoacetophenone can be
recycled three times with 90% yield.
The flask was charged with catalyst 4c, 4-bromoacetophenone
(4-chloroacetophenone) (1.0 mmol), 2 mmol KOH, phenylboronic
acid (1.5 mmol), and diethyleneglycol-di-n-butylether (0.6 mmol,
internal standard). The reaction was carried out in water at
◦
100 C. After cooling to room temperature, the organic products
were extracted by dichloromethane. The aqueous phase was then
transferred to a new reaction flask for the next cycle. Yields were
determined by gas chromatography.
Precipitation of palladium black was observed during the
heating of reaction mixtures which may be the main reason for
the short cut in the recycling attempts. Therefore, efforts are
underway to use similar palladium complexes with increased steric
bulk around the metal center, which should increase the thermal
stability of the active species and activity of the precatalyst by
facilitating the reductive elimination step of the catalytic cycle.
General procedure for the preparation of the mixed
NHC/pyridine carboxylic acid complexes of palladium(II), 1–4.
A sample of dimeric complexes 1 (0.25 mmol) and pyridinecar-
boxylic acid, C
chloroform; in the case of pyridine-2,6-dicarboxylic acid, DMSO
15 mL) was used as solvent. The mixture was stirred at ambient
5
H
4
NCOOH (0.5 mmol) were dissolved in 15 mL of
(
temperature for 24 h. The solvent was removed in vacuo. The
solid residue obtained was dissolved in a few milliliters of ethanol,
and the solution was added dropwise to diethyl ether (30 mL). The
cream precipitate obtained was collected by filtration, washed with
3
. Conclusion
To render bromo bridged dimeric palladium-NHC complexes
I) water soluble, they were cleaved with pyridinecarboxylic
10 mL of diethyl ether, and dried in vacuo.
(
acids, since such catalysts have potential applications in industry.
The resulting monomeric complexes have been studied for their
catalytic properties in the Suzuki coupling reaction of aryl
chlorides and phenylboronic acid in neat water under ambient
atmosphere with low catalyst loading (1 mol%). The coupling of
{
N-(2,4,6-trimethylbenzyl)-N¢-(2-metoxyethyl)benzimidazoline-
2
1
-ylidene}(pyridine-2-carboxylic acid) palladium(II) dibromide,
1
a. Yield: 0.27 g, 78%. H NMR (400 MHz, DMSO-d
6
):
d 8.78 (d, 1H, J = 4.8 Hz, C
NCOOH), 7.90 (d, 1H, J = 7.62.0 Hz, Ar-H), 7.73 (m,
H, C
NCOOH), 7.50 (t, 1H, J = 7.6 Hz, Ar-H), 7.40 (t,
5
5
H NCOOH), 8.12 (m, 2H,
C
1
5
H
5
4
-bromoacetophenone with PhB(OH) gave yield and recyclibility.
2
5
H
5
In the case of aryl chlorides, higher temperatures were required. A
◦
1H, J = 7.6 Hz, Ar-H), 7.30 (d, 1H, J = 7.6 Hz, Ar-H), 7.02
temperature of 100 C decreased the formation of homo coupling
(
(
s, 2H, CH
t, 2H, J = 5.2 Hz, NCH
CH OCH ), 3.31 (s, 3H, NCH
(CH ), 2.23 (s, 6H, CH
100 MHz, DMSO-d ): d 166.1 (C
53.3, 149.2, 140.2, 138.9, 138.6, 135.7, 134.5, 133.0, 130.0,
NCOONa,
CH OCH ),
2
C
6
H
2
(CH
3
)
3
), 5.93 (s, 2H, CH
CH OCH
), 4.12 (t, 2H, J = 5.2 Hz,
CH OCH ), 2.36 (s, 3H,
(CH
NCOOH), 161.4 (C-Pd),
2
C
6
H
2
(CH
3
)
3
), 5.00
by-products to a negligible amount in neat water.
2
2
3
NCH
CH
2
2
3
2
2
3
4
. Experimental
13
2
C
6
H
2
3
)
3
2
C
6
H
2
3
3
) ). C NMR
(
1
6
5
H
5
General procedures
All reactions for the preparation of salts were carried out under
Ar in flame-dried glass-ware using standard Schlenk-type flasks.
Anhydrous solvents were either distilled from appropriate drying
agents or purchased from Merck and degassed prior to use by
purging with dry argon and kept over molecular sieves. NMR
spectra were recorded at 297 K on a Varian Mercury AS 400 NMR
129.5, 128.4, 125.6, 124.3, 112.4, 111.2 (Ar-C, C
(CH ), 71.2 (NCH CH OCH ), 59.0 (NCH
49.4 (CH ), 48.5 (NCH
(CH (CH Cl
5
H
5
C
6
H
2
3
)
3
2
2
3
2
2
3
2
C
6
H
2
(CH
3
)
3
2
CH
2
OCH
3
), 21.5, 21.0
-
1
-1
2
C
6
H
2
3
)
3
). IR(CH
2
2
): nC=O 1752 cm , nO–H 3712 cm .
Anal. Calc. for C26
N 6.88, Found C 44.71, H 4.11, N 6.97%.
H
29Br
2
N
3
3
O Pd (697.75): C 44.75, H 4.19,
This journal is © The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7039–7044 | 7041

{
N-(2,3,5,6-tetramethylbenzyl)-N¢-(2-metoxyethyl)benzimida-
{N-(2,3,5,6-tetramethylbenzyl)-N¢-(2-metoxyethyl)benzimida-
zoline-2-ylidene}(pyridine-2-carboxylic acid) palladium(II) dibro-
zoline-2-ylidene}(pyridine-3-carboxylic acid) palladium(II) dibro-
1
1
mide, 1b. Yield: 0.27 g, 75%. H NMR (400 MHz, DMSO-
mide, 2b. Yield: 0.28 g, 80%. H NMR (400 MHz, DMSO-d
6
):
d
C
6
): d 8.74 (d, 1H, J = 4.8 Hz, C
5
H
4
NCOOH), 8.11 (m, 2H,
NCOOH), 7.73
d 9.19 (s, 1H, C
(d, 1H, J = 6.4 Hz, C
Ar-H), 7.30 (t, 1H, J = 7.6 Hz, Ar-H), 7.18 (t, 1H, J = 7.6 Hz,
Ar-H), 7.11 (s, 1H, CH H(CH
), 7.04 (d, 1H, J = 7.6 Hz,
Ar-H), 5.93 (s, 2 H, CH H(CH
NCH CH OCH
), 4.18 (t, 2H, J = 5.6 Hz, NCH
3.28 (s, 3H, NCH CH OCH ), 2.17 (s, 6 H, CH H(CH
(s, 6H, CH H(CH ). C NMR (100 MHz, DMSO-d
(C NCOOH), 162.6 (C-Pd), 155.8, 153.3, 139.9, 135.4, 135.1,
135.0, 134.4, 132.7, 131.6, 128.4, 125.5, 123.8, 123.6, 112.4, 111.2
(Ar-C, C NCOOH, CH H(CH ), 71.3 (NCH CH OCH ),
59.1 (NCH CH OCH ), 49.7 (CH (CH ), 48.8 (NCH
). IR(CH Cl
5
H
4
NCOOH), 8.91 (b, 1H, C
5
H
4
NCOOH), 8.34
5
H
4
NCOOH), 7.77 (d, 1H, J = 4.7 Hz, C
5
H
4
5
H
4
NCOOH), 7.72 (b, 2H, C
5
H
4
NCOOH,
(
t, 1H, J = 7.6 Hz, Ar-H), 7.67 (d, 1H, J = 7.6 Hz, Ar-H),
7
6
4
5
2
.22 (t, 1H, J = 7.6 Hz, Ar-H), 7.14 (s, 1H, CH
2
C
6
H(CH
3
)
)
4
),
),
2
C
6
)
3 4
.85 (d, 1H, J = 7.6 Hz, Ar-H), 5.98 (s, 2H, CH
2
C
6
H(CH
3
4
2
C
6
3
)
4
), 5.02 (t, 2H, J = 5.2 Hz
.95 (t, 2H, J = 5.2 Hz NCH
2
CH
2
OCH
3
), 4.14 (t, 2H, J =
2
2
3
2
CH
2
OCH
3
),
.2 Hz, NCH
.22 (s, 6H, CH
2
CH
2
OCH
H(CH
C NMR (100 MHz, DMSO-d
3
), 3.27 (s, 3H, NCH
), 2.13 (s, 6H, CH
): d 166.0 (C
2
CH
2
OCH
3
),
).
2
2
3
2
C
6
3
)
4
), 2.12
1
3
2
C
6
3
)
4
2
C
6
H(CH
3
)
4
2
C
6
3
)
4
6
): d 165.5
1
3
6
5
H
4
NCOOH),
5
H
4
161.2 (C-Pd), 153.5, 149.0, 140.7, 139.9, 138.0, 13.1, 133.5,
133.9, 131.0, 128.5, 128.3, 125.2, 124.3, 111.9, 111.0 (Ar-C,
5
H
4
2
C
6
3
)
4
2
2
3
C
5
H
4
NCOOH, CH
(NCH CH OCH
CH OCH
2
C
6
H(CH
3
)
4
), 71.0 (NCH
(CH (CH
H(CH ). IR (CH
2
CH
2
OCH
48.6
Cl ):
Pd
3
),
2
2
3
2
C
6
H
2
3
)
3
2
-
58.9
2
2
3
), 49.9
2
C
6
H
2
3
)
3
),
CH
2
OCH
3
1
), 20.9, 17.1 (CH
2
C
6
H(CH
3
)
4
2
2
): nC=O
-
-1
(
NCH
2
2
3
), 20.9, 20.0 (CH
2
C
6
3
)
4
2
2
1703 cm , nO–H 3433 cm . Anal. Calc. for C27
H
31Br
2
N
3
3
O Pd
-
1
-1
n
C=O 1735 cm , nO–H 3650 cm . Anal. Calc. for C27
H
31Br
2
N
3
O
3
(711.78): C 45.56, H 4.39, N 5.90. Found C 45.48, H 5.83, N 5.97%.
(
711.78): C 45.56, H 4.39, N 5.90. Found C 45.50, H 4.41,
{
N-(pentamethylbenzyl)-N¢-(2-metoxyethyl)benzimidazoline-2-
N 5.97%.
ylidene}(pyridine-3-carboxylic acid) palladium(II) dibromide, 2c.
1
Yield: 0.31 g, 85%. H NMR (400 MHz, DMSO-d
H, C
Hz, C
6
): d 9.25 (s,
{N-(pentamethylbenzyl)-N¢-(2-metoxyethyl)benzimidazoline-2-
1
6
5
H
4
NCOOH), 8.94 (b, 1H, C
5
H
4
NCOOH), 8.44 (d, 1H, J =
ylidene}(pyridine-2-carboxylic acid) palladium(II) dibromide, 1c.
5
H
4
NCOOH), 7.70 (d, 2H, J = 8.4 Hz, C
5
H
4
NCOOH,
1
Yield: 0.28 g, 78%. H NMR (400 MHz, DMSO-d
6
): d 8.72 (d, 1H,
Ar-H), 7.27 (t, 1H, J = 7.8 Hz, Ar-H), 7.12 (t, 1H, J = 7.8 Hz, Ar-
(CH ),
), 4.18 (t, 2H, J =
), 3.28 (s, 3H, NCH CH OCH ), 2.27,
). C NMR (100 MHz, DMSO-d ):
NCOOH), 162.6 (C-Pd), 155.9, 153.3, 139.9,
35.9, 135.6, 134.9, 134.6, 133.3, 128.6, 128.5, 125.5, 123.8,
23.5, 112.4, 111.2 (Ar-C, C NCOOH, CH H(CH ),
1.3 (NCH CH OCH ), 59.1 (NCH CH OCH ), 50.8
(CH ), 48.7 (NCH CH OCH ), 18.1, 17.7, 17.4
(CH ). IR(CH Cl ): nC=O 1731 cm , nO–H 3423 cm .
Pd (725.81): C 46.33, H 4.58,
N 5.79. Found C 46.40, H 4.47, N 5.87%.
J = 5.2 Hz, C
5
H
4
NCOOH), 8.11 (m, 2H, C
H, J = 4.8 Hz, C NCOOH), 7.66 (d, 1H, J = 7.8 Hz, Ar-H),
.44 (t, 1 H, J = 7.8 Hz, Ar-H), 7. 28 (t, 1 H, J = 7.8 Hz, Ar-H),
.17 (d, 1H, J = 7.8 Hz, Ar-H), 5.91 (s, 2 H, CH (CH ),
.98 (t, 2H, J = 5.6 Hz NCH CH OH ), 4.11 (t, 2H, J =
.6 Hz, NCH CH OCH ), 3.33 (s, 3H, NCH CH OCH ), 2.20,
.17 (s, 15H, CH (CH ). C NMR (100 MHz, DMSO-d ):
NCOOH), 161.3 (C-Pd), 153.9, 147.9, 139.9,
36.5, 134.9, 133.2, 131.0, 130.3, 128.7, 128.5, 125.5, 123.8,
23.3, 112.0, 111.2 (Ar-C, C NCOOH, CH H(CH ),
0.9 (NCH CH OCH ), 59.0 (NCH CH OCH ), 49.8
(CH ), 48.5 (NCH CH OCH
(CH
5
H
4
NCOOH), 7.77 (d,
H), 6.83 (d, 1H, J = 6.4 Hz, Ar-H), 5.97 (s, 2 H, CH
2
C
6
)
3 5
1
7
7
4
5
2
5
H
4
5
5
2
.01 (t, 2H, J = 5.4 Hz NCH
.6 Hz, NCH CH OCH
.17 (s, 15H, CH (CH
2
CH
2
OCH
3
2
2
3
2
2
3
C
6
3
)
5
13
2
C
6
)
2
3
5
6
2
2
3
d 165.6 (C
H
5
4
2
2
3
2
2
3
1
1
7
(
(
1
3
2
C
6
3
)
5
6
H
C
)
3 4
5
4
2
6
d 166.0 (C
5
H
4
2
2
3
2
2
3
1
1
7
CH
CH
2
C
6
H
2
3
)
3
2
2
3
H
4
2
C
6
3
)
4
-1
-1
5
C
6
)
2
3
5
2
2
2
2
3
2
2
3
Anal. Calc. for C28
H
33Br
N
O
3
2
3
(
(
CH
2
C
6
H
2
3
)
3
2
2
3
), 20.1, 19.9, 17.7
-
1
-1
CH
2
C
6
3
)
5
). IR(Nujol): nC=O 1739 cm , nO–H 3674cm . Anal.
{
N-(2,4,6-trimethylbenzyl)-N¢-(2-metoxyethyl)benzimidazoline-
-ylidene}(pyridine-4-carboxylic acid) palladium(II) dibromide,
Calc. for C28
Found C 46.41, H 4.62, N 5.77%.
H
33Br
2
N
3
3
O Pd (725.81): C 46.33, H 4.58, N 5.79.
2
3
1
a. Yield: 0.27 g, 79%. H NMR (400 MHz, DMSO-d
6
): d 8.89
(
1
b, 2H, C
5
H
4
NCOOH), 7.92 (b, 2H, C
5
H NCOOH), 7.69 (d,
4
{
N-(2,4,6-trimethylbenzyl)-N¢-(2-metoxyethyl)benzimidazoline-
H, J = 8.4 Hz, Ar-H), 7.26 (t, 1H, J = 7.8 Hz, Ar-H), 7.12
2
-ylidene}(pyridine-3-carboxylic acid) palladium(II) dibromide, 2a.
(
(
(
(
(
1
1
C
5
t, 1 H, J = 7.8 Hz, Ar-H), 6.94 (s, 2H, CH
2
C
6
H
2
(CH
H(CH
CH
3
)
)
3
4
3
), 6.83
), 4.99
), 3.26
), 2.21
1
Yield: 0.24 g, 70%. H NMR (400 MHz, DMSO-d
H, C
.8 Hz, C
6
): d 9.21 (s,
d, 1H, J = 7.6 Hz, Ar-H), 5.90 (s, 2 H, CH
2
C
6
3
1
6
(
1
5
H
4
NCOOH), 8.95 (s, 1H, C
5
H
4
NCOOH), 8.41 (d, 1H, J =
b, 2H, NCH
2
CH
CH
(CH
NCOOH), 163.5 (C-Pd), 153.5, 148.5, 138.9, 138.4,
35.5, 134.7, 130.1, 128.6, 124.5, 123.8, 123.6, 112.5, 111.2 (Ar-C,
NCOOH, CH H(CH ), 71.4 (NCH CH OCH ),
(NCH CH OCH ), 49.7 (CH (CH ), 48.7
H(CH ). IR(CH Cl ):
Pd
2
OCH
3
), 4.17 (b, 2H, NCH
2
2
OCH
5
H
4
NCOOH), 7.69 (b, 2H, C
5
H
4
NCOOH, Ar-H), 7.27
s, 3H, NCH
s, 6H, CH
2
2
OCH
3
), 2.28 (s, 3 H, CH
). C NMR (100 MHz, DMSO-d ): d
2
C
6
H
2
(CH
3 3
)
t, 1H, J = 7.6 Hz, Ar-H), 7.14 (t, 1H, J = 7.6 Hz, Ar-H), 6.99 (d,
H, J = 8.0 Hz, Ar-H), 6.92 (s, 2H, CH (CH ), 5.87 (s, 2H,
CH (CH ), 5.00 (b, 2H, NCH CH OCH
), 4.16 (t, 2 H, J =
.2 Hz, NCH CH OCH ), 3.26 (s, 3 H, NCH CH OCH ), 2.26 (s,
H, CH (CH ), 2.21 (s, 6 H, CH (CH
): 165.5 (C NCOOH), 162.4 (C-Pd),
55.9, 153.3, 140.0, 138.7, 135.5, 134.9, 130.1, 128.8, 128.5,
25.6, 124.5, 123.8, 123.6, 112.5, 111.2 (Ar-C, C NCOOH,
(CH ), 71.4 (NCH CH OCH ), 59.1 (NCH CH OCH ),
9.2 (CH ), 48.7 (NCH
CH (CH Cl
13
2
C
6
H
2
3
)
3
6
2
C
6
H
2
)
3 3
65.9 (C
5
H
4
2
C
6
H
2
3
)
3
2
2
3
5
3
(
1
1
C
2
2
3
2
2
3
5
H
4
2
C
6
3
)
4
2
2
3
1
3
2
C
6
H
2
3
)
3
2
C
6
H
2
3
) ). C NMR
3
9.1
2
2
3
2
C
6
H
2
)
3 3
100 MHz, DMSO-d
6
5
H
4
(
n
(
NCH
2
CH
2
OCH
3
), 21.4, 21.3 (CH
2
C
6
3
)
4
2
2
-1
-1
C=O 1750 cm , nO–H 3722 cm . Anal. Calc. for C26
H
29Br
2
N
3
O
3
5
H
4
697.75): C 44.75, H 4.19, N 6.88. Found C 44.65, H 4.21,
6
H
2
3
)
3
2
2
3
2
2
3
N 6.90%.
4
(
2
C
6
H
2
(CH
3
)
3
2
CH
2
OCH
3
), 21.4, 21.3
-
1
-1
2
C
6
H
2
3
)
3
). IR(CH
2
2
): nC=O 1752 cm , nO–H 3712 cm .
{N-(2,3,5,6-tetramethylbenzyl)-N¢-(2-metoxyethyl)benzimida-
Anal. Calc. for C26
N 6.88. Found C 44.81, H 4.12, N 6.77%.
H
29Br
2
N
3
O
3
Pd (697.75): C 44.75, H 4.19,
zoline-2-ylidene}(pyridine-4-carboxylic acid) palladium(II) dibro-
1
mide, 3b. Yield: 0.29 g, 82%. H NMR (400 MHz, DMSO-d
6
):
7
042 | Dalton Trans., 2009, 7039–7044
This journal is © The Royal Society of Chemistry 2009

d 8.85 (b, 2H, C
5
H
4
NCOOH), 7.92 (b, 2H, C
5
H
4
NCOOH), 7.68
Ar-H), 5.93 (s, 2 H, CH
NCH CH OCH
3.24 (s, 3H, NCH
(s, 6H, CH H(CH
165.1 (C
134.6, 134.5, 132.9, 130.7, 128.1, 123.8, 123.6, 112.4, 111.2 (Ar-C,
N(COOH) CH H(CH ), 71.2 (NCH CH OCH ),
(NCH CH OCH ), 51.4 (CH (CH ), 48.6
CH OCH H(CH ). IR(CH Cl ):
Pd
2
C
6
H(CH
3
)
4
), 4.92 (t, 2H, J = 5.4 Hz
(
d, 1H, J = 8.00 Hz, Ar-H), 7.26 (t, 1H, J = 7.4 Hz, Ar-H),
2
2
3
), 4.10 (t, 2H, J = 5.8 Hz, NCH
2
CH
2
OCH
), 2.11
): d
), 160.6 (C-Pd), 148.8, 139.9, 135.6, 135.0,
3
),
7
6
4
3
.13 (t, 1 H, J = 6.00 Hz, Ar-H), 7.09 (s, 1H, CH
2
C
6
H(CH
3
)
)
4
4
3
),
),
),
2
CH
2
OCH
3
), 2.19 (s, 6H, CH
2
C
6
H(CH
3
)
4
1
3
.90 (d, 1H, J = 7.6 Hz, Ar-H), 5.93 (s, 2 H, CH
2
C
6
H(CH
3
2
C
6
3
)
4
). C NMR (100 MHz, DMSO-d
6
.99 (b, 2H, NCH
2
CH
2
OCH
3
), 4.16 (b, 2H, NCH
2
CH
2
OCH
5
H
3
N(COOH)
2
.26 (s, 3H, NCH
2
CH
2
OCH
3
), 2.17 (s, 6H, CH
2
C
6
H(CH
3
)
4
), 2.10
1
3
(
s, 6H, CH
2
C
6
H(CH
3
)
4
). C NMR (100 MHz, DMSO-d
6
): d
C
5
H
3
2
,
2
C
6
3
)
4
2
2
3
1
1
C
65.8 (C
34.9, 134.5, 132.8, 131.5, 124.5, 123.8, 123.6, 112.4, 111.2 (Ar-C,
NCOOH, CH H(CH ), 71.3 (NCH CH OCH ),
(NCH CH OCH ), 49.9 (CH (CH ), 48.7
CH OCH H(CH ). IR(CH Cl ):
Pd
5
H
4
NCOOH), 163.1 (C-Pd), 153.5, 140.8, 135.5, 135.0,
59.1
(NCH
2
2
3
2
C
6
H
2
)
3 3
2
2
3
), 20.9, 16.9 (CH
C=O 1750 cm , nO–H 3712 cm . Anal. Calc. for C28
2
C
6
3
)
4
2
2
-
1
-1
5
H
4
2
C
6
3
)
4
2
2
3
n
H
31Br
2
N
3
O
5
59.1
2
2
3
2
C
6
H
2
3
)
3
(755.79): C 44.50, H 4.13, N 5.56. Found C 44.51, H 4.21,
N 5.62%.
(
NCH
2
2
3
), 20.9, 17.1 (CH
2
C
6
3
)
4
2
2
-
1
-1
n
C=O 1759 cm , nO–H 3712 cm . Anal. Calc. for C27
H
31Br
2
N
3
O
3
(
711.78): C 45.56, H 4.39, N 5.90. Found C 45.40, H 4.49,
{N-(pentamethylbenzyl)-N¢-(2-metoxyethyl)benzimidazoline-2-
N 6.00%.
ylidene}(pyridine-2,6-dicarboxylic acid) palladium(II) dibromide,
1
4
c. Yield: 0.27 g, 71%. H NMR (400 MHz, DMSO-d
6
):
{
N-(pentamethylbenzyl)-N¢-(2-metoxyethyl)benzimidazoline-2-
ylidene}(pyridine-4-carboxylic acid) palladium(II) dibromide, 3c.
d 8.23-8.20 (m, 2H, C
N(COOH)
), 7.64 (d, 1H, J = 8.4 Hz, Ar-H), 7.19 (t, 1H,
J = 7.8 Hz, Ar-H), 6.99 (t, 1H, J = 7.8 Hz, Ar-H), 6.37 (d, 1H, J =
.6 Hz, Ar-H), 5.95 (s, 2H, CH (CH
NCH CH OCH
), 4.11 (t, 2H, J = 5.6 Hz, NCH
.25 (s, 3H, NCH CH OCH ), 2.24 (s, 3H, CH
.17 (s, 6H, CH (CH ), 2.14 (s, 6H, CH (CH
): d 164.3 (C N(COOH)
60.9 (C-Pd), 138.1, 134.4, 133.8, 132.8, 132.7, 131.5, 126.3,
5
H
3
N(COOH)
2
), 8.17-8.13 (m, 1H,
C
5
H
3
2
1
Yield: 0.29 g, 80%. H NMR (400 MHz, DMSO-d
6
): d 8.87 (b,
2
H, C
5
H
4
NCOOH), 7.91 (b, 2H, C
5
4
H NCOOH), 7.72 (d, 1H,
7
2
C
6
3
)
5
), 4.92 (t, 2H, J = 5.2 Hz,
J = 8.00 Hz, Ar-H), 7.24 (t, 1H, J = 7.6 Hz, Ar-H), 7.13 (t, 1
2
2
3
2
CH
2
OCH
(CH )
3
),
),
H, J = 7.2 Hz, Ar-H), 6.72 (d, 1H, J = 8.0 Hz, Ar-H), 5.97 (s,
3
2
2
2
3
2
C
6
3
13
5
2
H, CH
J = 5.0 Hz, NCH
.25 (s, 3H, CH
2
C
6
(CH
3
)
5
), 4.99 (b, 2H, NCH
2
CH
2
OCH
3
), 4.16 (t, 2H,
2
C
6
3
)
5
2
C
6
3
)
5
).
C
2
CH
(CH
C NMR (100 MHz, DMSO-d
63.1 (C-Pd), 153.5, 140.8, 135.9, 135.6, 134.6, 133.3, 128.6,
24.5, 123.8, 123.6, 123.6, 112.4, 111.2 (Ar-C, C NCOOH,
(CH ), 71.3 (NCH CH OCH ), 59.1 (NCH CH OCH ),
1.0 (CH (CH ), 48.7 (NCH CH
CH (CH ). IR(CH Cl
Anal. Calc. for C28
N 5.79. Found C 46.33, H 4.70, N 5.65%.
2
OCH
), 2.15 (s, 12H, CH
): d 165.8 (C
3
), 3.26 (s, 3H, NCH
2
CH
2
OCH
3
),
NMR (100 MHz, DMSO-d
H
),
6
5
3
2
2
2
C
6
3
)
5
2
C
6
(CH
3
)
5
).
1
1
CH
5
(
1
3
6
5
H
4
NCOOH),
26.1, 122.0, 121.7, 116.9, 110.5, 109.3 (Ar-C, C
(CH ), 69.3 (NCH CH OCH ), 57.2 (NCH
0.0 (CH (CH ), 46.7 (NCH CH
CH (CH ). IR(CH Cl
Anal. Calc. for C29
H
N(COOH)
,
5
3
2
1
1
CH
5
(
2
C
6
3
)
5
2
2
3
2
CH OCH ),
2
3
5
H
4
C
H
)
OCH
), 16.1, 15.9, 15.5
): nC=O 1742 cm , nO–H 3502 cm .
2
6
2
3
3
2
2
3
-1
C
6
3
)
5
2
2
3
2
2
3
-1
2
C
)
2
6
3
5
2
2
2
C
6
H
2
3
)
3
2
2
OCH
3
), 18.0, 17.7, 17.4
H
33Br
N
O
5
Pd (769.82): C 45.25, H 4.32,
2
3
-
1
-1
2
C
6
3
)
5
2
2
): nO–H 1705 cm , nC=O 3437 cm .
N 5.46. Found C 45.18, H 4.33, N 5.37%.
H
33Br
2
N
3
3
O Pd (725.81): C 46.33, H 4.58,
References
{
N-(2,4,6-trimethylbenzyl)-N¢-(2-metoxyethyl)benzimidazoline-
2
4
8
6
-ylidene}(pyridine-2,6-dicarboxylic acid) palladium(II) dibromide,
1
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(b) A. F. Littke and G. C. Fu, Angew. Chem., Int. Ed., 2002, 41, 4176–
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a. Yield: 0.28 g, 82%. H NMR (400 MHz, DMSO-d
6
): d
4
211; (c) D. Bourissou, O. Guerret, F. P. Gabba ¨ı and G. Bertrand, Chem.
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H
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N(COOH)
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5
H
3
2
), 7.69 (d, 1H, J = 8.4 Hz, Ar-H), 7.25
(
t, 1H, J = 8.0 Hz, Ar-H), 7.09 (t, 1H, J = 8.0 Hz, Ar-H),
6
5
4
2
.98 (s, 2H, CH
.86 (s, 2H, CH
.13 (b, 2H, NCH
.28 (s, 3H, CH
2
C
6
H
2
(CH
(CH
CH OCH
(CH
C NMR (100 MHz, DMSO-d
3
)
3
), 6.67 (d, 1H, J = 7.2 Hz, Ar-H),
2
C
6
H
2
3
)
3
), 4.94 (b, 2H, NCH
), 3.26 (s, 3H, NCH
), 2.21 (s, 6H, CH
): d 165.8 (C
2
CH
CH
2
OCH
3
3
3
2
),
),
).
),
2
2
3
2
2
OCH
2
C
6
H
2
3
)
3
2
C
6
H
2
(CH
3
)
1
3
6
5
H
3
N(COOH)
2
(a) N. Hadei, A. B. Kantchev, C. J. O’Brien and M. G. Organ, Org. Lett.,
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1
C
4
60.5 (C-Pd), 148.3, 139.8, 138.7, 138.6, 135.5, 134.5, 129.9,
2
005, 7, 1991–1994; (b) H. T u¨ rkmen and B. C¸ etinkaya, J. Organomet.
28.0,127.9, 123.6, 123.4, 112.2, 110.9 (Ar-C, C
(CH ), 71.1 (NCH CH OCH ), 58.7 (NCH
9.9 (CH ), 48.7 (NCH
CH (CH Cl
5
H
3
N(COOH)
2
,
Chem., 2006, 691, 3749–3759.
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6
H
2
3
)
3
2
2
3
2
CH OCH ),
2
3
2
2
C
6
H
2
(CH
3
)
3
2
CH
2
OCH
3
), 20.9, 20.7
¨
and S. D. Hofmann, Organometallics, 2007, 26, 626–632; (c) I. Ozdemir,
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-
1
-1
(
2
C
6
H
2
3
)
3
). IR(CH
2
2
): nC=O 1740 cm , nO–H 3498 cm .
Anal. Calc. for C27
N 5.66. Found C 43.71, H 4.01, N 5.77%.
H
29Br
2
N
3
5
O Pd (741.76): C 43.72, H 3.94,
¨
4
¨
Demir and N. G u¨ rb u¨ z, Catal. Lett., 2004, 97, 37–40; (c) H. T u¨ rkmen,
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{
N-(2,3,5,6-tetramethylbenzyl)-N¢-(2-metoxyethyl)benzimida-
zoline-2-ylidene}(pyridine-2,6-dicarboxylic acid) palladium(II)
4
915–4921.
1
dibromide, 4b. Yield: 0.28 g, 74%. H NMR (400 MHz,
5 W. A. Herrmann, M. Elison, J. Fischer, C. Kocher and G. R. J. Artus,
DMSO-d
6
): d 8.22 (d, 2H, J = 7.2 Hz, C
m, 1H, C N(COOH)
), 7.65 (d, 1H, J = 8.4 Hz, Ar-H),
.21 (t, 1H, J = 7.6 Hz, Ar-H), 7.08 (s, 1H, CH H(CH ),
.02 (t, 1H, J = 7.8 Hz, Ar-H), 6.46 (d, 1 H, J = 6.8 Hz,
5
H
3
N(COOH)
2
), 8.15
Angew. Chem., Int. Ed. Engl., 1995, 34, 2371.
6
7
C. Fleckenstein, S. Roy, S. Leuth a¨ uber and H. Plenio, Chem. Commun.,
(
7
7
5
H
3
2
2
007, 2870–2872.
2
C
6
)
3 4
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W. A. Herrmann, Wiley-VCH, Weinheim, 2004.
This journal is © The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7039–7044 | 7043

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7
044 | Dalton Trans., 2009, 7039–7044
This journal is © The Royal Society of Chemistry 2009