Synthesis and characterization of amide-functionalized N-heterocyclic carbene-Pd complexes

Article abstract of DOI:10.1016/j.jorganchem.2011.02.009

Amide-functionalized N-heterocyclic carbene (NHC) precursors such as azolium compounds have been designed and synthesized. Reaction of PdCl ₂(CH₃CN)₂ with the NHC-Ag complex derived from the azolium salt gave [(NHC)PdCl

Full text of DOI:10.1016/j.jorganchem.2011.02.009

Journal of Organometallic Chemistry 696 (2011) 1910e1915
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and characterization of amide-functionalized N-heterocyclic
carbeneePd complexes
*
Ryo Kamisue, Satoshi Sakaguchi
Department of Chemistry and Materials Engineering, Faculty of Chemistry, Materials and Bioengineering, Kansai University, 3-3-35 Yamate-cho, Suita, Osaka 564-8680, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Amide-functionalized N-heterocyclic carbene (NHC) precursors such as azolium compounds have been
designed and synthesized. Reaction of PdCl2(CH3CN)2 with the NHCeAg complex derived from the
azolium salt gave [(NHC)PdCl2]2 or (NHC)2PdCl2, whereas PdCl2(PPh3)2 reacted with the Ag complex to
afford a mixed carbene/phosphine complex such as (NHC)(PPh3)PdCl2 together with a cationic [(NHC)
(PPh3)2PdCl]þClꢀ whose structure was characterized by X-ray crystallographic studies. Thus, the library
of NHCePd complexes with a tethered amide group has been successfully expanded.
Ó 2011 Elsevier B.V. All rights reserved.
Received 9 December 2010
Received in revised form
3 February 2011
Accepted 8 February 2011
Keywords:
N-Heterocyclic carbene
Ligand design
Monodentate ligand
NHCePd complex
Functionalized NHC
1. Introduction
dianionic alkoxy/amidate/NHCePd(II) complexes have been
developed. Importantly, the Pd(II) complex catalyzes an asym-
In recent years, tremendous efforts have been made toward the
synthesis of transition metal complexes bearing N-heterocyclic
carbene (NHC) ligands [1]. Of particular interest is introduction of
a pendent functional group to an NHC, since the functionalized NHC
can anchor free carbene to a metal site, serve as a chelate ligand,
control the stability of metal center, or introduce chirality [2]. In
2007, Lee and co-workers designed amide-functionalized NHC
ligands and synthesized palladium(II) and nickel(II) complexes
with chelating anionic amidate/NHC ligands [3]. Structurally
similar anionic-tethered gold(I), silver(I) and nickel(II) complexes
were introduced by Ghosh and co-workers [4]. More recently,
Bouwman and co-workers subsequently reported on nickel(II)
complexes bearing bidentate NHC ligands functionalized with
anionic amidate moieties for the Kumada coupling reaction [5].
Gornitzka and Hemmert and co-workers introduced tetradentate
NHC ligands and their palladium(II) and nickel(II) complexes [6].
Thus, anionic amidate/NHC ligands have received considerable
attention.
metric oxidative Heck-type reaction with excellent enantiose-
lectivity [8]. The above-mentioned anionic amidate/NHCePd(II)
complexes by Lee and Ghosh were synthesized from amide-func-
tionalized azolium compounds in the presence of an appropriate
base such as K2CO3 [3,4]. In contrast, synthesis of the Pd(II) complex
from the hydroxyamide-functionalized azolium salt does not require
such a base [7]. These facts prompted us to examine the preparation
of NHCePd(II) complexes from amide-functionalized azolium
compounds in the absence of a base. During the course of this
study, we found that various palladium complexes were synthe-
sized by using PdCl2(CH3CN)2 or PdCl2(PPh3)2 as a palladium
precursor. Herein, a systematic study on the synthesis of the
NHCePd(II) complexes with amide functionalities is described.
2. Results and discussion
2.1. Synthesis of [(NHC)PdCl2]2 complexes
In 2008, we synthesized a novel hydroxyamide-functionalized
azolium salt derived from chiral b-amino alcohol [7]. By using the
azolium salt, new tridentate anionic amidate/NHCePd(II) and
The preparation of amide-functionalized NHC precursors such
as 1-methyl-3-N-(propylacetoamido)benzimidazolium chloride
(1a) and 1,3-N,N0-bis(propylacetoamido)benzimidazolium chloride
(2a) is shown in Eq. (1). 1a was prepared by reaction of 1-methyl-
benzimidazole with 2-chloro-N-propylacetamide in 1,4-dioxane
under reflux. Similarly, 2a was obtained in 73% yield.
* Corresponding author. Tel.: þ81 6 6368 0867; fax: þ81 6 6339 4026.
E-mail address: satoshi@ipcku.kansai-u.ac.jp (S. Sakaguchi).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.02.009

R. Kamisue, S. Sakaguchi / Journal of Organometallic Chemistry 696 (2011) 1910e1915
1911
O
O
H
N
Cl
R1
R1
N
N
HN
Cl
HN
dmso
N
N
O
N
N
DMSO
1,4-dioxane, rf.
N
N
Pd
Pd
Cl
(1)
R2
Cl
NH
Cl
NH
2
Cl
R1 = -CH3
O
O
71% yield
73% yield
1a
2a
R2 = -CH2C(O)NHC3H7
R1 = R2 = -CH2C(O)NHC3H7
2c
2c'
Scheme 1. Tentative structure of (NHC)(dmso)PdCl2 2c’ in DMSO.
NHC complexes were successfully synthesized according to the
Ag2O method that was introduced by Lin et al. [9]. Ag2O particularly
serves as a mild base, reacting predominantly at the C2 position of
the azolium salt without deprotonation of other acidic protons.
Treatment of 1a with Ag2O in CH2Cl2 at room temperature gave
a white solid. The 1H NMR spectrum of the solid without further
purification suggests that NHCeAg complex 1b was obtained in
almost pure form. The 13C NMR spectrum of 1b contains the char-
2.2. Synthesis of (NHC)2PdCl2 and (NHC)(PPh3)PdCl2 complexes
Because the chloride-bridged dimeric monodentate NHCePd
complex 2c was found to vary in the presence of a strongly coor-
dinating donor such as (CH3)2SO, we speculated that it might be
possible to synthesize (NHC)2PdCl2 or (NHC)(PPh3)PdCl2, which is
an analog of 2c’, from [(NHC)PdCl2]2 2c in the presence of an
additional NHC or PPh3 ligand, respectively (Scheme 2).
acteristic carbene signal at
d 191.4 ppm. Since the silver complexes
1b and 2b have light-sensitive character, synthesis of NHCePd
complexes 1c and 2c was carried out by a one-pot procedure
without purification of the NHCeAg intermediates from 1a and 2a,
respectively (Eq. (2)). After treatment of 1a with Ag2O, the resulting
silver complex 1b was allowed to react with PdCl2(CH3CN)2 at room
temperature to give the corresponding neutral amide-functional-
ized NHCePd complex 1c in good yield. NHCePd complex 2c was
obtained in 82% yield from the NHC precursor 2a. Synthesis of
a similar iodo-bridged dimeric monodentate NHCePd complex by
reaction of Pd(OAc)2 with an imidazolium salt in the presence of
NaI and NaOEt has been reported [10]. It should be noted that no
anionic amidate/NHCePd type complex was formed from the
reaction with amide-functionalized azolium salts 1a and 2a. These
facts would strongly indicate that the hydroxyl group on a hydrox-
yamide-functionalized azolium salt is crucial for the formation of an
anionic palladium amidate complex [7].
R
N
Cl
N
R
Pd
R
N
R
Cl
N
N
N
R
R
R
N
(NHC)2PdCl2
Cl
N
Pd
R
Cl
2
R
N
PPh3
[(NHC)PdCl2]2
PPh3
N
Pd
R
Cl
(NHC)(PPh3)PdCl2
Cl
Scheme 2. Working hypothesis for conversion of dimeric NHCePd complex into
(NHC)2PdCl2 or (NHC)(PPh3)PdCl2.
R1
1a
N
1) Ag2O, CH2Cl2, r.t.
Cl
2) PdCl2(CH3CN)2,
CH2Cl2, r.t.
N
2a
Pd
R2
R1
N
Cl
2
(2)
1a or 2a : Ag2O : PdCl2(CH3CN)2
1a
Cl
1) Ag2O, CH2Cl2, r.t.
R1
(or R2)
N
= 1.1 : 0.6 : 1
Pd
R2
R1 = -CH3
Cl
R2
(or R1)
N
2) PdCl2(CH3CN)2,
CH2Cl2, r.t.
2a
1c
89% yield
R2 = -CH2C(O)NHC3H7
N
(3)
R1 = R2 = -CH2C(O)NHC3H7
2c
82% yield
1a or 2a : Ag2O : PdCl2(CH3CN)2
= 2.1 : 1.05 : 1
R1 = -CH3
86% yield
1d
R2 = -CH2C(O)NHC3H7
Interestingly, the 1H NMR spectrum of 2c in (CD3)2SO indicates
R1 = R2 = -CH2C(O)NHC3H7
82% yield
2d
that it exists as a mixture of two NHCePd compounds, whereas the
spectrum in CD3OD indicates that it exists only a single compound
(Fig. 1). Attention should be paid to the signal of the methylene
proton adjacent to the carbonyl group. In CD3OD, it appears as
a singlet at
signals: an A2 system (
d
5.65 ppm. In (CD3)2SO, it appears as two kinds of
5.60 ppm) and an AX system [ 5.62 and
O
d
d
1) Ag2O, CH3OH, rf.
2) PdCl2(PPh3)2,
CH3CN, rf.
N
HN
PPh3
5.33 ppm (J ¼ 16.4 Hz)], in the ratio 17:83, as determined by inte-
gration. This might indicate that in (CD3)2SO the major component
(83%) is a new NHCePd complex 2c’ (Scheme 1). Indeed, it was
reported that the donor numbers of (CH3)2SO, CH3OH, H2O, and
CH3CN are 30, 19, 18, and 14, respectively [11], indicating that
(CH3)2SO can strongly coordinate with a metal.
1a
N
Me
(4)
Pd
Cl
Cl
1a : Ag2O : PdCl2(PPh3)2
86% yield
1e
= 1.1 : 0.55 : 1

1912
R. Kamisue, S. Sakaguchi / Journal of Organometallic Chemistry 696 (2011) 1910e1915
Fig. 1. 1H NMR spectra of 2c in CD3OD (upper) and (CD3)2SO (lower); signals for 2c and 2c’ are represented by
and C, respectively.
;
The desired bis(NHC)ePd(II) complexes 1d and 2d were
successfully obtained by the same one-pot procedure as described for
synthesis of 1c and 2c by simply changing the amount of NHC
precursor used (Eq. (3)). During the course of this study, Ghosh and
co-workers reported the synthesis of trans-[1-(iso-propyl)-3-{N-
(benzylacetoamido)}imidazol-2-ylidene]2PdCl2, which is structurally
similar to our complex 1d [12]. Their asymmetrical amide-function-
alized NHCePd complex, which was characterized by X-ray diffrac-
tion studies, was obtained as a single isomer in the solid state.
However, the 1H NMR spectrum of their complex indicates the exis-
tence of two isomers in solution, probably trans-syn and trans-anti.
Although we did not succeed in the X-ray analysis of 1d, the 1H NMR
spectrum of 1d in CDCl3 shows the existence of a 2:1 mixture prob-
ably due to the presence of two rotamers. In contrast, it should be
noted that the symmetrical bis(NHC)ePd complex 2d exists in solu-
tion as a single form (See Supplementary data).
of several unidentified products. After several trials, we eventually
developed an efficient synthetic route to the desired (NHC)(PPh3)
PdCl2 (1e) by using PdCl2(PPh3)2 as a palladium precursor (Eq. (4)).
Colorless crystals of 1e were successfully grown from a saturated
Attempts to obtain a mixed NHC/phosphine complex by the
reaction of1awithPPh3 were unsuccessful, giving a complex mixture
1) Ag2O, CH3OH, rf.
2a
2) PdCl2(PPh3)2,
CH3CN, rf.
2a : Ag2O : PdCl2(PPh3)2 = 1.1 : 0.55 : 1
O
O
Cl
N
N
HN
(5)
HN
PPh3
PPh3
N
N
+
Pd
Pd
Cl
NH
Cl
Ph3P
NH
Cl
O
O
Fig. 2. Molecular structure of cis-(NHC)(PPh3)PdCl2 complex 1e with the crystallo-
graphic numbering scheme; hydrogen atoms and CHCl3 are omitted for clarity and
selected lengths [Ǻ] and angles [deg] are as follows: Pd1eC1 1.967(7), Pd1eP1 2.2535
(19), Pd1eCl1 2.3562(17), Pd1eCl2 2.365(2), C1ePd1eP1 92.2(2), C1ePd1eCl1 83.6(2),
P1ePd1eCl2 91.46(7), Cl1ePd1eCl2 92.74(6).
2e 79% yield
11% yield
2f

R. Kamisue, S. Sakaguchi / Journal of Organometallic Chemistry 696 (2011) 1910e1915
1913
solution in chloroform by slow evaporation of the solvent at ambient
temperature. The X-ray single-crystal diffraction study of 1e revealed
that the carbene and phosphine ligands are in a cis conformation
(Fig. 2) [13]. The distance between the Pd and the Cl2 trans to carbene
(d(PdeCl2) ¼ 2.365(2) Ǻ) is similar to the distance between the Pd
and the Cl1 trans to the phosphine (d(PdeCl1) ¼ 2.3562(17) Ǻ). In 1H
NMR spectrum of cis-1e in CDCl3, the signal of the methylene proton
4H), 5.69 (s, 2H), 4.20 (s, 3H), 3.18 (q, J ¼ 6.4 Hz, 2H), 1.61e1.55 (m,
2H), 0.90 (t, J ¼ 7.2 Hz, 3H); 13C NMR (CDCl3):
d 164.2, 143.3, 131.8,
131.5, 127.5, 127.2, 114.5, 112.1, 49.8, 41.6, 33.6, 22.4, 11.5. Anal. Calc.
for C13H18ClN3O: C, 58.31; H, 6.78; N,15.69. Found: C, 57.71; H, 6.82;
N, 15.62%.
4.3. Synthesis of azolium salt 2a
adjacent to the carbonyl group appears as an AX system [d 5.63 and
4.07 ppm(J ¼ 15.2 Hz)]. Thismightsuggest thattheNHCePdcomplex
2c’ derived from 2c and DMSO involves cis-coordination of DMSO
and NHC on a palladium(II) center (Scheme 1).
To 1,4-dioxane (45 mL) were added N-propyl-1H-benzimid-
azole-1-acetamide (5.5 mmol, 1.19 g) and 2-chloro-N-propylaceta-
mide (5.5 mmol, 0.74 g). The reaction mixture was stirred at 110 ꢁC
for 2 days. The isolation procedure described above was performed
to give the desired product 2a as a white solid (1.42 g, 73% yield). 1H
The mixed NHC/phosphineePd(II) (2e) was also synthesized
from 2a (Eq. (5)). Interestingly, a small amount of new mixed
complex [(NHC)(PPh3)2PdCl]þClꢀ 2f was isolated together with 2e.
The yields of 2e and 2f were 79% and 11%, respectively, based on the
palladium precursor used. X-ray single-crystal diffraction study of 2f
shows that these two phosphine ligands are in a trans conformation
(Fig. 3). The torsion angles for P1ePd1eC1eN2 and P2ePd1eC1eN1
are 99.3(2) and 96.6(2) degrees, respectively. The 1H NMR spectrum
of 2f clearly indicates that it exists in solution as a C2 symmetric
form. Formation of the rare cationic complex 2f is probably because
of the strong donating capability of both NHC and PPh3, which can
stabilize the cationic metal center effectively. Quite receꢀntly, Hahn
et al. reported that the similar [(NHC)(PPh3)2PdCl]þBF4 complex
was synthesized by the oxidative addition of 2-chloro-N-methyl-
benzimidazole to Pd(PPh3)4 followed by protonation with NH4BF4
[14]. The bond lengths for the PdeCcarbene bond (2.000(3) Å) and the
PdeP bonds (PdeP1 2.3587(9) Å, PdeP2 2.3454(9) Å) of 2f fall into
the range reported for the [(NHC)(PPh3)2PdCl]þBF4ꢀ complex.
NMR (DMSO-d6):
d 9.86 (s, 1H), 8.96 (br, 1H), 7.98e7.65 (m, 4H),
5.42 (s, 4H), 3.08 (q, J ¼ 6.8 Hz, 4H), 1.50e1.41 (m, 4H), 0.86 (t,
J ¼ 7.2 Hz, 6H); 13C NMR (DMSO-d6):
d 164.4, 144.3, 131.3, 126.7,
113.7, 48.5, 40.8, 22.2, 11.5. Anal. Calc. for C17H25ClN4O2ꢂ1.5H2O: C,
53.75; H, 7.43; N, 14.74. Found: C, 53.71; H, 6.92; N, 14.71%.
4.4. One-pot synthesis of NHCePd complex 1c via NHCeAg
complex 1b from 1a
A suspension of 1a (0.11 mmol, 29 mg) and silver(I) oxide
(0.06 mmol,14 mg) in CH2Cl2 (10 mL) was stirred in the dark at room
temperature. After 4 h, PdCl2(CH3CN)2 (0.1 mmol, 26 mg) was added
in the dark at room temperature. The resulting suspension was
stirred for 16 h, filtered through a membrane filter (pore size:
0.2 mm), and evaporated to dryness in vacuo. The desired Pd complex
was purified by column chromatography (SiO2, CH2Cl2/CH3OH, 9/1)
to give 1c as a yellow solid (36 mg, 89% yield). 1b: 1H NMR (CDCl3):
3. Conclusion
d
8.40 (s, 1H), 7.70e7.38 (m, 4H), 5.34 (s, 2H), 4.05 (s, 3H), 3.19 (q,
J ¼ 6.8 Hz, 2H), 1.59e1.49 (m, 2H), 0.85 (t, J ¼ 8.0 Hz, 3H); 13C NMR
We have successfully expanded the collection of NHCePd(II)
complexes bearing an amide functional group. Several distinct types
of amide-functionalized NHCePd complexes such as [(NHC)PdCl2]2,
(NHC)2PdCl2, (NHC)(PPh3)PdCl2, and [(NHC)(PPh3)2PdCl]þClꢀ were
synthesized. Further studies focusing on design and synthesis of
functionalized NHC precursors for development of efficient cata-
lytic transformations are the subject of ongoing research in our
laboratory.
(CDCl3):
d 191.4, 166.7, 134.4, 134.0, 124.3, 124.1, 112.5, 110.8, 52.1,
41.4, 35.9, 22.5, 11.5. 1c: 1H NMR (CD3OD):
d 7.57e7.32 (m, 4H), 5.59
(s, 2H), 4.32 (s, 3H), 3.15 (t, J ¼ 6.8 Hz, 2H),1.53e1.44 (m, 2H), 0.83 (t,
J ¼ 7.2 Hz, 3H); 13C NMR (CD3OD):
d 168.3, 136.1, 135.7, 124.9, 124.9,
111.9,111.5, 52.1, 42.4, 35.3, 23.3,11.7, the carbene 13C NMR resonance
was not observed. Anal. Calc. for C26H34Cl4N6O2Pd2ꢂ2H2O: C, 36.60;
H, 4.49; N, 9.85. Found: C, 36.51; H, 4.46; N, 9.65%.
4.5. One-pot synthesis of NHCePd complex 2c via NHCeAg
complex 2b from 2a
4. Experimental
4.1. General procedures
The reaction was performed as described above using 2a
(0.11 mmol, 39 mg) instead of 1a. The desired Pd complex was
purified by column chromatography (SiO2, CH2Cl2/CH3OH, 9/1) to
give 2c as a yellow solid (40 mg, 82% yield). 2b: 1H NMR (DMSO-d6):
All chemicals were obtained from commercial sources and were
used as received. 1H and 13C NMR spectra were recorded on spec-
trometers at 400 and 100 MHz, respectively. CD3OD, (CD3)2SO or
CDCl3 was used as the NMR solvent. Flash column chromatography
was performed on silica gel 60 (Merck; mesh: 230e400; particle
size: 0.040e0.063 nm). Elemental analyses were performed at
Osaka University.
d
8.40 (t, J ¼ 5.6 Hz, 2H), 7.65e7.40 (m, 4H), 5.13 (s, 4H), 3.07 (q,
J ¼ 6.8 Hz, 4H), 1.49e1.40 (m, 4H), 0.85 (t, J ¼ 7.2 Hz, 6H); 13C NMR
(DMSO-d6):
d 165.9, 133.8, 123.9, 112.1, 51.0, 40.6, 22.3, 11.5, the
carbene 13C NMR resonance was not observed. 2c: 1H NMR
(CD3OD):
d
7.54e7.35 (m, 4H), 5.65 (s, 4H), 3.18 (t, J ¼ 7.2 Hz, 4H),
1.57e1.48 (m, 4H), 0.88 (t, J ¼ 7.6 Hz, 6H); 13C NMR (CD3OD):
4.2. Synthesis of azolium salt 1a
d 168.4, 160.8, 136.1, 125.2, 112.1, 52.2, 42.5, 23.4, 11.8.
To 1,4-dioxane (20 mL) were added N-methylbenzimidazole
(5.2 mmol, 687 mg) and 2-chloro-N-propylacetamide (5.0 mmol,
678 mg) derived from chloroacetyl chloride and propylamine. The
reaction mixture was stirred at 110 ꢁC for 2 days. The solvent was
removed under reduced pressure, and the residue was dissolved in
methanol. Activated carbon was added, and removed by filtration
after 16 h. The filtrate was concentrated under reduced pressure to
give a solid, which was purified by reprecipitation from ethyl
acetate and methanol to give 1a as a white solid (951 mg, 71%
4.6. One-pot synthesis of (NHC)2PdCl2 complex 1d from 1a
A suspension of 1a (0.21 mmol, 56 mg) and silver(I) oxide
(0.105 mmol, 24 mg) in CH2Cl2 (10 mL) was stirred in the dark at
room temperature. After 4 h, PdCl2(CH3CN)2 (0.1 mmol, 26 mg) was
added in the dark at room temperature. The resulting suspension
was stirred for 16 h, filtered through a membrane filter (pore size:
0.2
mm), and evaporated to dryness in vacuo. The desired Pd
complex was purified by column chromatography (SiO2, CHCl3/
CH3OH, 10/1) to give 1d as a white solid (55 mg, 86% yield). 1d
yield). 1H NMR (CDCl3):
d 10.70 (s, 1H), 9.35 (br, 1H), 8.03e7.64 (m,

1914
R. Kamisue, S. Sakaguchi / Journal of Organometallic Chemistry 696 (2011) 1910e1915
Fig. 3. Molecular structure of [(NHC)(PPh3)2PdCl]þClꢀ complex 2f with the crystallographic numbering scheme; hydrogen atoms are omitted for clarity and selected lengths [Ǻ] and
angles [deg] are as follows: Pd1eC1 2.000(3), Pd1eP1 2.3587(9), Pd1eP2 2.3454(9), Pd1eCl1 2.3344(7), C1ePd1eP1 91.99(9), C1ePd1eP2 90.09(9), P1ePd1eCl1 90.21(2),
P2ePd1eCl1 87.74(3).
(major): 1H NMR (CDCl3):
5.59 (s, 4H), 4.37 (s, 6H), 3.21e3.14 (m, 4H), 1.48e1.38 (m, 4H),
0.78e0.73 (m, 6H); 13C NMR (CDCl3):
180.5, 166.5, 133.9, 133.8,
124.1, 124.0, 110.8, 110.4, 52.3, 41.5, 34.5, 22.3, 11.2. 1d (minor): 1H
NMR (CDCl3): 7.59e7.35 (m, 8H), 7.06e7.01 (m, 2H), 5.51 (s, 4H),
4.44 (s, 6H), 3.21e3.14 (m, 4H), 1.48e1.38 (m, 4H), 0.78e0.73 (m,
6H); 13C NMR (CDCl3) :
180.2,166.2,134.8,133.8,124.1,124.0,111.2,
d
7.59e7.35 (m, 8H), 7.06e7.01 (m, 2H),
(0.2 mmol, 140 mg) in CH3CN (10 mL). The mixture was stirred at
reflux temperature in the dark for 24 h, filtered through a membrane
filter (pore size: 0.2 mm), evaporated to dryness in vacuo. The desired
d
Pd complex was purified by column chromatography (SiO2, CH2Cl2/
d
CH3OH, 9/1) to give 1e as a white solid (115 mg, 86% yield). 1e: 1H
NMR (CDCl3):
d
7.70e7.17 (m, 19H), 5.63 (d, J ¼ 15.2 Hz, 1H), 4.07 (d,
d
J ¼ 15.2 Hz,1H), 3.93 (s, 3H), 3.06 (q, J ¼ 6.4 Hz, 2H),1.41e1.33 (m, 2H),
110.3, 52.4, 41.5, 34.6, 22.3, 11.2. Anal. Calc. for C26H34Cl2N6O2Pd: C,
48.80; H, 5.36; N, 13.13. Found: C, 48.69; H, 5.30; N, 13.00%.
0.66 (t, J ¼ 7.6 Hz, 3H); 13C NMR (CDCl3):
d 207.0, 165.3, 133.9, 133.8,
133.3, 132.1, 131.5, 129.3, 128.7, 128.5, 124.1, 124.1, 110.9, 110.0, 41.6,
34.5, 30.9, 22.0,11.1. Anal. Calc. for C31H32Cl2N3OPPdꢂCHCl3ꢂ0.5H2O:
C, 48.09; H, 4.29; N, 5.26. Found: C, 47.78; H, 4.09; N, 5.17%. Crystal-
lization of 1e by slow evaporation from chloroform solution gave
colorless crystals suitable for study by X-ray diffraction. Crystal data:
C31H32Cl2N3OPPdꢂ2CHCl3, M ¼ 909.60, monoclinic, a ¼ 13.6410(12),
4.7. One-pot synthesis of (NHC)2PdCl2 complex 2d from 2a
The reaction was performed as described above using 2a
(0.21 mmol, 74 mg)instead of 1a. ThedesiredPdcomplexwaspurified
by column chromatography (SiO2, CHCl3/CH3OH, 9/1) to give 2d as
b ¼ 14.0267(14), c ¼ 20.0749(18) Å,
b
¼ 93.534(3)ꢁ, U ¼ 3833.8(6) Å3,
T ¼ 123(2) K, space group P21/c (no. 14), Z ¼ 4,
m (Mo-
a white solid (68 mg, 82% yield). 2d: 1H NMR (CDCl3):
d 7.63e7.42 (m,
Ka
) ¼ 10.321 cmꢀ1. The final Rw was 0.1382 (I > 1
s(I)).
8H), 6.90 (br, 4H), 5.51 (s, 8H), 3.21 (q, J ¼ 6.0 Hz, 8H), 1.50e1.41 (m,
8H), 0.78 (t, J ¼ 7.2 Hz, 12H); 13C NMR (CDCl3):
d 165.9, 154.6, 124.9,
111.4, 104.4, 64.9, 41.6, 22.4, 11.2. Anal. Calc. for C34H48Cl2N8O4Pd: C,
50.41; H, 5.97; N, 13.83. Found: C, 50.48; H, 5.73; N, 13.94%.
4.9. One-pot synthesis of (NHC)(PPh3)PdCl2 complex 2e and [(NHC)
(PPh3)2PdCl]þClꢀ complex 2f from 1a
4.8. One-pot synthesis of (NHC)(PPh3)PdCl2 complex 1e from 1a
The reaction was performed as described above using 2a
(0.22 mmol, 77 mg) instead of 1a. The desired Pd complexes were
purified by column chromatography (SiO2, CH2Cl2/CH3OH, 9/1) to
give 2e (119 mg, 79% yield) and 2f (22 mg, 11% yield) as white solids.
A mixture of1a (0.22 mmol, 55 mg) andsilver(I)oxide (0.11 mmol,
26 mg) in CH3OH (10 mL) was stirred in the dark at reflux tempera-
ture for 24 h, then concentrated under reduced pressure. To the
resulting white solid, silver complex was added PdCl2(PPh3)2
2e: 1H NMR (CD3OD):
d
7.66e7.26 (m, 19H), 5.30 (d, J ¼ 16.8 Hz, 2H),
4.77 (d, J ¼ 16.8 Hz, 2H), 3.06e3.01 (m, 2H), 2.93e2.87 (m, 2H),

R. Kamisue, S. Sakaguchi / Journal of Organometallic Chemistry 696 (2011) 1910e1915
1915
1.47e1.38 (m, 4H), 0.81 (t, J ¼ 7.2 Hz, 6H); 13C NMR (CD3OD):
d 167.4,
(d) M.C. Perry, K. Burgess, Tetrahedron: Asymmetry 14 (2003) 951e961;
(e) W. Kirmse, Angew. Chem. Int. 43 (2004) 1767e1769;
(f) V. César, S. Bellemin-Laponnaz, L.H. Gade, Chem. Soc. Rev. 33 (2004) 619e636;
(g) E.A.B. Kantchev, C.J. O’Brien, M.G. Organ, Angew. Chem. Int. 46 (2007)
2768e2813;
153.9,135.5,135.4,133.1,133.0,132.7, 130.0,129.9,129.8,129.7,125.3,
112.6, 52.2, 42.5, 23.3, 11.7. Anal. Calc. for C35H39Cl2N4O2PPdꢂH2O: C,
54.31; H, 5.34; N, 7.24. Found: C, 54.29; H, 5.16; N, 7.19%. 2f: 1H NMR
(h) F.E. Hahn, M.C. Jahnke, Angew. Chem. Int. 47 (2008) 3122e3172;
(i) S. Díez-González, N. Marion, S.P. Nolan, Chem. Rev. 109 (2009) 3612e3676.
[2] (a) O. Kühl, Funtionalised N-heterocyclic Carbene Complexes. Wiley-VCH,
Weinheim, 2010;
(CDCl3):
d
7.64e7.26 (m, 36H), 5.59 (d, J ¼ 15.1 Hz, 2H), 4.36 (d,
J ¼ 15.1 Hz, 2H), 3.16e3.11 (m, 2H), 3.01e2.98 (m, 2H), 1.41e1.33 (m,
4H), 0.66 (t, J ¼ 7.8 Hz, 6H); 13C NMR (CDCl3):
d 165.1, 137.1, 137.0,
(b) O. Kühl, Chem. Soc. Rev. 36 (2007) 592e607;
134.0, 133.9, 133.8, 133.6, 133.6, 131.6, 131.6, 128.8, 128.7, 128.5,
128.4, 124.7, 111.2, 52.8, 41.5, 22.1, 11.2. Anal. Calc. for
C53H54Cl2N4O2P2PdꢂH2O:C, 61.43;H, 5.45;N, 5.41. Found:C, 61.85; H,
5.26; N, 5.51%. Crystallization of 2f by slow evaporation from chlo-
roform solution gave colorless crystals suitable for study by X-ray
diffraction. Crystal data: C53H54Cl2N4O2P2Pd, M ¼ 1018.29, mono-
(c) D. Pugh, A.A. Danopoulos, Coord. Chem. Rev. 251 (2007) 610e641;
(d) A.T. Normand, K.J. Cavell, Eur. J. Inorg. Chem. (2008) 2781e2800;
(e) R. Corberán, E. Mas-Marzá, E. Peris, Eur. J. Inorg. Chem. (2009) 1700e1716.
[3] (a) C.-Y. Liao, K.-T. Chan, J.-Y. Zeng, C.-H. Hu, C.-Y. Tu, H.M. Lee, Organome-
tallics 26 (2007) 1692e1702;
(b) C.-Y. Liao, K.-T. Chan, Y.-C. Chang, C.-Y. Chen, C.-Y. Tu, C.-H. Hu, H.M. Lee,
Organometallics 26 (2007) 5826e5833;
(c) J.-Y. Lee, P.-Y. Cheng, Y.-H. Tsai, G.-R. Lin, M.-H. Sie, H.M. Lee, Organome-
tallics 29 (2010) 3901e3911;
(d) M.-H. Sie, Y.-H. Hsieh, Y.-H. Tsai, J.-R. Wu, S.-J. Chen, P.V. Kumar, J.-H. Lii,
H.M. Lee, Organometallics 29 (2010) 6473e6481.
clinic, a ¼ 12.4319(5), b ¼ 21.1834(9), c ¼ 18.5787(6) Å,
b
¼ 95.0686
(13)ꢁ, U ¼ 4873.6(3) Å3, T ¼ 123(2) K, space group P21/c (no.14), Z ¼ 4,
m
(Mo-K
a
) ¼ 3.005 cmꢀ1. The final wR2 was 0.1247 (all data).
[4] (a) M.K. Samantaray, K. Pang, M.M. Shaikh, P. Ghosh, Inorg. Chem. 47 (2008)
4153e4165;
Acknowledgments
(b) S. Ray, M.M. Shaikh, P. Ghosh, Eur. J. Inorg. Chem. (2009) 1932e1941;
(c) S. Ray, J. Asthana, J.M. Tanski, M.M. Shaikh, D. Panda, P. Ghosh, J. Organomet.
Chem. 694 (2009) 2328e2335.
This work was financially supported by a Grant-in-Aid for
Scientific Research (C) (20550103) from Japan Society for the
Promotion of Science (JSPS) and the Kansai University Grant-in-Aid
for progress of research in graduate course, 2010. We thank Dr. P.
Ghosh at Indian Institute of Technology for helpful suggestions.
[5] J. Berding, T.F. van Dijkman, M. Lutz, A.L. Spek, E. Bouwman, Dalton Trans.
(2009) 6948e6955.
[6] F.J.-B. dit Dominique, H. Gornitzka, C. Hemmert, Organometallics 29 (2010)
2868e2873.
[7] (a) S. Sakaguchi, K.S. Yoo, J. O’Neill, J.H. Lee, T. Stewart, K.W. Jung, Angew.
Chem. Int. 47 (2008) 9326e9329;
(b) K.S. Yoo, J. O’Neill, S. Sakaguchi, R. Giles, J.H. Lee, K.W. Jung, J. Org. Chem. 75
(2010) 95e101;
(c) S. Sakaguchi, M. Kawakami, J. O’Neill, K.S. Yoo, K.W. Jung, J. Organomet.
Chem. 695 (2010) 195e200.
Appendix A. Supplementary data
CCDC 799806 and 799807 contain the supplementary crystal-
lographic data for 1e and 2f. These data can be obtained free of
charge from The Cambridge Crystallographic Data Center via http://
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at doi:10.
1016/j.jorganchem.2011.02.009.
[8] (Asymmetric Cu-catalyzed conjugate addition reaction with the same ligand
was also successfully achieved, see): (a) M. Okamoto, Y. Yamamoto,
S. Sakaguchi, Chem. Commun. (2009) 7363e7365;
(b) N. Shibata, M. Okamoto, Y. Yamamoto, S. Sakaguchi, J. Org. Chem. 75
(2010) 5707e5715;
(c) A. Harano, S. Sakaguchi, J. Organomet. Chem. 696 (2011) 61e67.
[9] I.J.B. Lin, C.S. Vasam, Coord. Chem. Rev. 251 (2007) 642e670.
[10] W.A. Hermann, V.P.W. Böhm, C.W.K. Gstöttmayr, M. Grosche, C.-P. Reisinger,
T. Weskamp, J. Organomet. Chem. 617e618 (2001) 616e628.
[11] W. Linert, Y. Fukuda, A. Camard, Coord. Chem. Rew 218 (2001) 113e152.
[12] S. Kumar, M.M. Shaikh, P. Ghosh, J. Organomet. Chem. 694 (2009)
4162e4169.
[13] (A similar palladium complex such as cis-(NHC)(PPh3)PdBr2 has been repor-
ted, see): H.V. Huynh, C.H. Yeo, G.K. Tan Chem. Commun. (2006) 3833e3855.
[14] T. Kösterke, T. Pape, F.E. Hahn, J. Am. Chem. Soc. 133 (2011) 2112e2115.
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