N-heterocyclic carbene-acetylamide palladium complexes and their catalytic activities in Heck-Mizoroki reactions

Article abstract of DOI:10.1055/s-2008-1067199

A novel N-heterocyclic carbene-acetylamide ligand derived from binaphthyl-2,2′-diamine (BINAM) and its dinuclear NHC-Pd(II) complex as well as its corresponding complex bearing weakly coordinating acetate counterions, have been successfully synthesized in good yields. The dinuclear NHC-Pd(II) complex has been characterized by X-ray diffraction. Moreover, we found that these complexes are quite effective in Heck-Mizoroki reactions and give the corresponding products in good to excellent yields. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2008-1067199

SPECIAL TOPIC
2819
N-Heterocyclic Carbene–Acetylamide Palladium Complexes and Their
Catalytic Activities in Heck–Mizoroki Reactions
N
-Heterocyclic
a
C
arbene–A
o
cetylamide Palladi
Z
um Complexes
h
inHeck–Mi
a
n
tions g,a Sijia Liu,a Min Shi,*a,b Meixin Zhaoa
a
Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology,
130 Meilong Road, Shanghai 200237, P. R. of China
Fax +86(21)64166128; E-mail: mshi@mail.sioc.ac.cn
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
354 Fenglin Road, Shanghai 200032, P. R. of China
b
Received 7 March 2008
responding complexes bearing weakly coordinating ace-
tate counterions in Suzuki coupling reactions9
(Figure 1b). In this paper, we wish to report the synthesis
and characterization of a novel NHC-acetylamide ligand
Abstract: A novel N-heterocyclic carbene-acetylamide ligand de-
rived from binaphthyl-2,2¢-diamine (BINAM) and its dinuclear
NHC–Pd(II) complex as well as its corresponding complex bearing
weakly coordinating acetate counterions, have been successfully
synthesized in good yields. The dinuclear NHC–Pd(II) complex has D, derived from BINAM and its dinuclear palladium(II)
been characterized by X-ray diffraction. Moreover, we found that
complex, and the corresponding dinuclear NHC–Pd(II)
these complexes are quite effective in Heck–Mizoroki reactions and
give the corresponding products in good to excellent yields.
complex bearing weakly coordinating acetate counter-
ions. We also report on their catalytic abilities in the
Heck–Mizoroki reaction (Figure 1).
Key words: N-heterocyclic carbene-acetylamide, dinuclear NHC–
Pd(II) complex, binaphthyl-2,2¢-diamine, Heck–Mizoroki reaction
The synthesis of benzimidazolium salt 5 is shown in
Scheme 1. Using compound 19 as the starting material to
react with acetic anhydride in the presence of acetic acid
produced the corresponding product 2 in 89% yield at
room temperature (20 °C) in dichloromethane. Reduction
N-Heterocyclic carbenes (NHCs)1 represent a growing
class of ligand. Due to their stability to air and moisture
and their strong s-donor and poor p-acceptor properties,
they can replace phosphine ligands in transition-metal ca-
(a)
talysis to provide more effective metal complexes.2 Sig-
Me
Me
nificantly, NHC–Pd complexes have emerged as effective
NHAc
I
N
I
catalysts for a variety of coupling reactions,3 such as the
coupling of aryl halides with amines and amides (Buch-
wald–Hartwig amination),4a–4c alkenes (Heck–Mizoroki
reaction),4d alkynes (Sonogashira reaction),4e organomag-
nesium (Kumada reaction),4f organosilicon (Stille reac-
tion),4g organoboron (Suzuki reaction),4h,i and
organostannane reagents.4j Furthermore, recent studies
have revealed that NHC–Pd(II) complexes bearing weak-
ly coordinating counterions such as acetates, are highly
efficient catalysts for C–H activation,5a aerobic oxidation
of alcohols,5b,c hydroarylation of alkynes,5d Suzuki
coupling5e–g and Michael addition reactions.6 Previously,
we reported the synthesis of a novel bis(NHC) ligand
based on binaphthyl-2,2¢-diamine (BINAM) and its cis-
chelated bis(NHC)–palladium complex.7 In addition, we
also synthesized a NHC-acetylamide ligand A from trans-
cyclohexane-1,2-diamine and its NHC–palladium
complex8 (Figure 1a). Interestingly, the NHC-acetyl-
amide ligand only coordinates to the metal center through
NHC to form a dimeric mono-coordinated NHC–Pd(II)
complex. More recently, we also reported two NHC-sul-
fonamide ligands B and C, derived from BINAM and
their tridentate NHC–Pd(II) complexes as well as the cor-
N
N
I
I
N
O
Pd
AcHN
N
N
N
Me
ligand A
Me
O
O
R
R
(b)
S
S
O
O
N
N
N
N
Pd
N
X
N
Me
Me
R = Me, 4-MeC6H4; X = I, OAc
R = Me, ligand B
R = 4-MeC6H4, ligand C
Me
O
N
N
N
Me
SYNTHESIS 2008, No. 17, pp 2819–2824
x
x.
x
x
.
2
0
0
8
ligand D
Advanced online publication: 24.07.2008
DOI: 10.1055/s-2008-1067199; Art ID: C02908SS
© Georg Thieme Verlag Stuttgart · New York
Figure 1 Structure of NHC–Pd(II) complexes and NHC-acetyl-
amide ligand derived from BINAM

2820
T. Zhang et al.
SPECIAL TOPIC
O
Me
NH2
NH
NH
H2, Pd/C
Ac2O, AcOH
NO2
EtOAc, 60 °C, 4 h, 99%
CH2Cl2, r.t., 12 h, 89%
NO2
NH
2
1
O
O
O
Me
NH
Me
N
Me
NH
N
NH
MeI
MeCN, reflux, 6 h, 91%
HC(OEt)3, TsOH
100 °C, 10 h, 90%
Me
N
NH2
N
I
NH
5
4
3
Scheme 1 Synthesis of benzimidazolium salt 5
of 2 by means of Pd/C–H2 gave compound 3 in 99% yield
within four hours. Subsequent cyclization with triethyl
orthoformate catalyzed by p-toluenesulfonic acid at
100 °C, afforded product 4 in 90% yield after ten hours.
The alkylation of the benzimidazole ring of 4 by methyl
iodide under reflux for six hours then gave the corre-
sponding benzimidazolium salt 5 in 91% yield.
During the initial examination, we found that when benz-
imidazolium salt 5 was treated with Pd(OAc)2 at 90 °C in
dimethylsulfoxide for two hours in the presence of sodium
iodide,8 guanidine 6 was produced in 36% isolated yield
rather than the corresponding NHC–palladium complex
(Scheme 2). The structure of guanidine 6 was determined
by X-ray diffraction (Figure 2).10 Attempts to prepare the
corresponding NHC–Pd(II) complex by treating benzimi-
dazolium salt 5 with palladium(II) acetate in tetrahydrofu-
ran under reflux7 were also unsuccessful and 6 was only
isolated in very low yield (<10%) in these transforma-
tions.
Figure 2 X-ray crystal structure of compound 6
plex 7 with silver acetate in acetonitrile–dichloromethane
(1:2) at room temperature for three hours, the correspond-
ing dinuclear NHC–Pd(II) complex 8 bearing weakly co-
ordinating acetate counterions was obtained in 82% yield
(Scheme 3). These NHC–Pd(II) complexes were air- and
moisture-stable in the solid state and even in the solution
state. Their structures were determined by microanalysis,
IR and NMR spectroscopic data as well as ESI-MS spec-
troscopy.
Although the exact mechanism for the formation of guani-
dine 6 is not known, we assumed that during the formation
of the corresponding NHC–palladium(II) complex upon
heating, acetic acid was released, which may react with
the NHC–palladium(II) complex to form compound 6.
After several examinations, it was found that in the pres-
ence of cesium carbonate, the corresponding dinuclear
NHC–Pd(II) complex 7 was smoothly produced in 77%
yield by treatment of benzimidazolium salt 5 with palladi-
um(II) acetate at room temperature in tetrahydrofuran for
20 hours. Upon treatment of dinuclear NHC–Pd(II) com-
The crystal structure of 7 was also unambiguously deter-
mined by X-ray diffraction.11 Single crystals of this dinu-
clear palladium complex suitable for X-ray crystal
structure analysis were grown from a petroleum ether–
dichloromethane (2:3) mixture. Figure 3 depicts the X-ray
crystal structure of dinuclear NHC–Pd(II) complex 7,
which reveals a distorted square-planar geometry around
O
Me
NH
N
Pd(OAc)2, NaI
DMSO, 90 °C, 6 h, 36%
Me
Me
N
N
N
N
I
6
5
Scheme 2 Synthesis of compound 6
Synthesis 2008, No. 17, 2819–2824 © Thieme Stuttgart · New York

SPECIAL TOPIC
N-Heterocyclic Carbene–Acetylamide Palladium Complexes in Heck–Mizoroki Reactions
2821
Me
O
Me
O
N
Me
N
N
O
I
N
N
N
NH
Pd(OAc)2, Cs2CO3
THF, r.t., 20 h, 77%
Me
I
Pd
I
Pd
N
N
Me
Me
5
7
Me
Me
O
N
N
OAc
N
AgOAc
N
N
7
Pd
OAc
Me
Pd
MeCN–CH2Cl2, 40 °C, 3 h,
82%
N
O
Me
8
Scheme 3 Synthesis of Pd–NHC complexes 7 and 8
the two metal centers. One of the NHC-acetylamide anion longer than that of typical C=O double bond lengths, sug-
ligands chelates with one palladium center through the gesting partial π-conjugation between O(1), C(29) and
NHC and a nitrogen atom in the acetylamide; this palladi- N(3) [N(3)–C(29) bond length: 1.39(3) Å]. Partial π-con-
um was also coordinated by the oxygen atom of a second jugation also exists between O(2), C(59) and N(6).
acetylamide anion ligand and an iodide anion, stabilizing
a 16-electron configuration around the metal center. Com-
The application of NHC–Pd(II) complexes 7 and 8 (1.0
mol%) as catalysts for the Heck–Mizoroki coupling reac-
pared to the Pd–Pd distance [3.126(3) Å] in the NHC–
tion was examined. Sodium acetate was used as a base and
Pd(II) complex 7 as well as to the rather underestimated
N,N-dimethylformamide (DMF) was used as solvent in
sum of van der Waals radii (3.26 Å), we believe that met-
the reaction of arylbromides with tert-butyl acrylate at
allophilic interaction may exist in the NHC–Pd(II) com-
140 °C under an argon atmosphere. The results of these
plex because the Pd–Pd distance seen here is closer to the
experiments are summarized in Table 1. As can be seen,
the corresponding coupling products 9 were obtained in
80–99% yields within 20 hours, indicating that these
upper van der Waals limit.12 The bond lengths of Pd(1)–
C(1) and Pd(2)–C(31) are 1.879(17) and 1.91(2) Å, re-
spectively. The C(29)–O(1) bond length [1.19(2) Å] is
NHC–Pd(II) complexes are quite effective catalysts in the
Heck–Mizoroki coupling reaction (Table 1, entries 1–8).
NHC–Pd(II) complex 8, bearing a weakly coordinating
acetate counterion, was slightly more effective and gave
the coupled products 9a–d in higher yields than those of
NHC–Pd(II) complex 7 under the standard conditions.
Furthermore, using NHC–Pd(II) complex 8 as the catalyst
in the reaction of iodobenzene with tert-butyl acrylate, 9a
was obtained in 99% yield after 20 hours under identical
conditions (Table 1, entry 9). However, 9a was formed in
very low yield after 20 hours under identical conditions
using NHC–Pd(II) complex 8 as the catalyst in the reac-
tion of chlorobenzene with tert-butyl acrylate (Table 1,
entry 10), suggesting that these NHC–Pd(II) complexes
are not very effective in the Heck–Mizoroki coupling re-
action using arylchlorides as the substrates.
Figure 3 ORTEP drawing of NHC–Pd(II) complex 7 with thermal
ellipsoids shown at the 30% probability level; selected bond distances
(Å) and angles (°): Pd1–Pd2, 3.126(3); Pd1–C1, 1.879(17); Pd1–N3,
2.062(16); Pd1–O2, 2.095(14); Pd1–I1, 2.588(3); O1–C29, 1.19(2);
N3–C29, 1.39(3); N3–C28, 1.39(2); Pd2–C31, 1.91(2); Pd2–N6,
2.029(15); Pd2–O1, 2.131(13); Pd2–I2, 2.588(3); O2–C59, 1.24(2);
N6–C59, 1.35(3); N6–C58, 1.41(2); O2–Pd1–N3, 94.4(6); C1–Pd1–
N3, 88.8(7); C1–Pd1–I1, 87.7(6); I1–Pd1–O2, 89.4(4); O2–Pd1–C1,
165.4(7); I1–Pd1–N3, 176.2(4); O1–Pd2–N6, 93.5(6); C31–Pd2–N6,
96.54(12); C31–Pd2–I2, 85.7(6); I2–Pd2–O1, 89.2(4); O1–Pd2–C31,
163.5(7); I2–Pd2–N6, 176.7(4)
In conclusion, we have developed a novel NHC-acetyl-
amide ligand from BINAM and have successfully synthe-
sized its dinuclear palladium complexes 7 and 8. These
complexes have been isolated and characterized by IR,
NMR and ESI-MS spectroscopy. Moreover, complex 7
has been characterized by X-ray crystal structure analysis.
These interesting NHC-acetylamide complexes have
proven to be quite effective catalysts in the Heck–Mizoro-
Synthesis 2008, No. 17, 2819–2824 © Thieme Stuttgart · New York

2822
T. Zhang et al.
SPECIAL TOPIC
Table 1 Heck–Mizoroki Reaction Catalyzed by NHC–Pd(II) Complexes 7 and 8a
O
O
Pd source (1 mol%)
O
Br
+
DMF, NaOAc, 20 h,
140 °C
R
O
R
9
Entry
Aryl halide
Pd source
Product
Yield (%)b
1
2
7
8
9a
9a
80
82
Br
3
4
7
8
9b
9b
85
86
Me
Br
Br
Br
5
6
7
8
9c
9c
86
99
OHC
MeOC
I
7
8
7
8
9d
9d
99
99
9
8
8
9a
9a
99
<5
10
Cl
a Reaction conditions: aryl halide (1 mmol), tert-butyl acrylate (1.5 mmol), NaOAc (1.1 mmol), NHC–Pd(II) complex (0.01 mmol), DMF
(2 mL).
b Isolated yield.
7.76–7.82 (m, 3 H, ArH), 7.92–8.03 (m, 3 H, ArH), 9.27 (s, 1 H,
NH).
products in good to high yields. Efforts are underway to 13C NMR (75 MHz, CDCl3): d = 112.1, 116.2, 117.8, 118.1, 121.8,
ki coupling reaction of arylbromides and aryliodide with
tert-butyl acrylate to give the corresponding coupled
122.4, 123.3, 125.4, 125.5, 125.7, 126.4, 126.8, 127.1, 128.1, 128.2,
128.2, 129.1, 129.9, 131.4, 133.5, 133.6, 133.9, 135.2, 135.9, 141.5,
142.2.
elucidate the use of complexes 7 and 8 to catalyze other
C–C bond-forming transformations.
MS (EI): m/z = 405 [M+], 388, 370, 341, 267.
1H and 13C NMR spectra were recorded on a Varian Mercury VX-
Anal. Calcd for C26H19N3O2: C, 77.02; H, 4.72; N, 10.36. Found: C,
76.99; H, 4.72; N, 10.45.
300 spectrometer as solutions in CDCl3 with TMS as an internal
standard. Infrared spectra were measured on a Perkin–Elmer 983
spectrometer. Mass spectra and HRMS were recorded with an HP-
5989 instrument, a Finnigan MA+ mass spectrometer and a Micro-
mass GCT mass spectrometer. CHN microanalyses were obtained
with a Carlo–Erba 1106 analyzer. Organic solvents were dried by
standard methods when necessary. Melting points are uncorrected.
All reactions were monitored by TLC with Huanghai GF254 silica
gel coated plates. Flash column chromatography was carried out us-
ing 300–400 mesh silica gel at increased pressure.
Compound 2
A mixture of 1 (81 mg, 0.20 mmol), Ac2O (15 mL, 0.22 mmol) and
AcOH (0.12 mL, 2.1 mmol) in CH2Cl2 (4.0 mL) was stirred at r.t.
for 12 h. The solvent was removed under reduced pressure and the
residue was purified by flash column chromatography on silica gel
(hexane–EtOAc, 4:1) to give the product 2.
Yield: 79.6 mg (89%); red solid; mp 196.2–198.4 °C (dec.).
IR (CH2Cl2): 3470, 3351, 3058, 2248, 1919, 1695, 1614, 1520,
1426, 1282, 741 cm–1.
1H NMR (300 MHz, CDCl3): d = 1.65 (s, 3 H, CH3), 6.60–6.66 (m,
1 H, ArH), 7.07–7.26 (m, 5 H, ArH), 7.28–7.42 (m, 4 H, ArH), 7.70
(d, J = 9.0 Hz, 1 H, ArH), 7.83–7.86 (m, 3 H, ArH), 7.94 (t, J = 9.0
Hz, 2 H, ArH), 8.47 (d, J = 8.4 Hz, 1 H, NH), 8.97 (s, 1 H, NH).
13C NMR (75 MHz, CDCl3): d = 24.0, 115.5, 118.1, 120.53. 120.54,
121.11, 121.12, 121.6, 123.7, 124.5, 124.9, 125.5, 126.4, 126.8,
127.3, 128.1, 129.3, 129.8, 130.8, 131.0, 132.1, 133.1, 133.6, 134.5,
135.2, 135.9, 140.9, 168.3.
Compound 1
Under an argon atmosphere, a mixture of 1,1¢-binaphthalenyl-2,2¢-
diamine (568 mg, 2.0 mmol), 2-bromonitrobenzene (404 mg, 2.0
mmol), Pd2(dba)3 (48 mg, 0.05 mmol), bis(2-diphenylphosphi-
nophenyl)ether (80 mg, 0.15 mmol) and Cs2CO3 (2.080 g, 6.4
mmol) was stirred in anhydrous toluene (16 mL) at 80 °C for 48 h.
After the reaction mixture was cooled to r.t., the reaction was
quenched by the addition of H2O (40 mL) and the organic com-
pound was extracted with EtOAc (2 × 80 mL) and dried over anhy-
drous Na2SO4. The solvent was removed under reduced pressure
and the residue was purified by flash chromatography on silica gel
(hexane–EtOAc, 30:1) to give 1.
MS (ESI): m/z = 470 [M+ + Na], 447 [M+].
Anal. Calcd for C28H21N3O3: C, 75.15; H, 4.73; N, 9.39. Found: C,
74.82; H, 4.91; N, 9.35.
Yield: 680 mg (84%); red solid; mp 179–181 °C (dec.).
IR (CH2Cl2): 3300, 3262, 3058, 1611, 1499, 1254, 738 cm–1.
1H NMR (300 MHz, CDCl3): d = 3.66 (s, 2 H, NH2), 6.67–6.74 (m,
1 H, ArH), 6.96–6.99 (m, 1 H, ArH), 7.12–7.47 (m, 8 H, ArH),
Compound 3
A mixture of 2 (447 mg, 1.0 mmol) and 10% Pd/C (60 mg) in
EtOAc (60 mL) was stirred under an H2 atmosphere (1.0 atm) at
Synthesis 2008, No. 17, 2819–2824 © Thieme Stuttgart · New York

SPECIAL TOPIC
N-Heterocyclic Carbene–Acetylamide Palladium Complexes in Heck–Mizoroki Reactions
2823
60 °C for 4 h. After cooling to r.t., Pd/C was removed by filtration,
the solvent was evaporated under reduced pressure and the residue
was purified by flash column chromatography on silica gel (hex-
ane–EtOAc, 2:1 → 1:1) to give 3.
Anal. Calcd for C30H24IN3O: C, 63.28; H, 4.25; N, 7.38. Found: C,
63.18; H, 4.38; N, 7.20.
Compound 6
Compound 5 (114 mg, 0.20 mmol), NaI (30 mg, 0.20 mmol) and
Pd(OAc)2 (44 mg, 0.20 mmol) were stirred at 90 °C in DMSO (5
mL) for 3 h. The solvent was removed under reduced pressure and
the residue was purified by flash chromatography on silica gel (hex-
ane–EtOAc, 4:1) to give compound 6. The single crystals for X-ray
diffraction were obtained by recrystallization from CH2Cl2–petro-
leum ether.
Yield: 416 mg (99%); white solid; mp 199–201 °C (dec.).
IR (CH2Cl2): 3458, 3390, 3054, 2245, 1908, 1676, 1618, 1507,
1500, 1275, 909, 818, 745 cm–1.
1H NMR (300 MHz, CDCl3): d = 1.81 (s, 3 H, CH3), 3.59 (s, 2 H,
NH), 4.89 (s, 1 H, NH), 6.55–6.64 (m, 2 H, ArH), 6.86–6.96 (m,
3 H, ArH), 7.13–7.27 (m, 6 H, Ar), 7.34–7.43 (m, 1 H, ArH), 7.78
(d, J = 6.3 Hz, 1 H, ArH), 7.81 (d, J = 8.4 Hz, 1 H, Ar), 7.89 (d,
J = 8.4 Hz, 1 H, Ar), 7.99 (d, J = 9.0 Hz, 1 H, Ar), 8.51 (d, J = 9.0
Hz, 1 H, NH).
13C NMR (75 MHz, CDCl3): d = 24.3, 111.9, 115.8, 116.1, 118.6,
121.14, 121.15, 121.5, 122.8, 123.5, 125.1, 125.3, 126.1, 126.4,
126.96, 127.01, 127.2, 128.2, 128.3, 129.4, 130.0, 131.4, 132.5,
133.4, 135.1, 142.4, 142.7, 168.9.
Yield: 29 mg (36%); yellow solid; mp 248.4–249.5 °C (CH2Cl2–pe-
troleum ether).
IR (CH2Cl2): 3044, 2919, 1638, 1607, 1578, 1564, 1492, 1428,
1366, 1212, 1093, 742 cm–1.
1H NMR (300 MHz, CDCl3): d = 3.47 (s, 3 H, CH3), 6.97 (d, J = 7.5
Hz, 1 H, ArH), 7.06–7.26 (m, 6 H, ArH), 7.32–7.46 (m, 4 H, ArH),
7.62 (d, J = 9 Hz, 1 H, ArH), 7.77–7.84 (m, 4 H, ArH).
MS (EI): m/z = 397 [M+].
HRMS (ESI): m/z [M]+ calcd for C28H19N3: 397.1579; found:
MS (EI): m/z = 417 [M+], 375, 358, 267, 207.
Anal. Calcd for C28H23N3O: C, 80.55; H, 5.55; N, 10.06. Found: C,
80.18; H, 5.54; N, 9.97.
397.1579.
Compound 4
NHC–Pd(II) Complex 7
Compound 3 (208 mg, 0.50 mmol) and triethyl orthoformate
[HC(OEt)3] (5.0 mL) containing a catalytic amount of TsOH were
heated at 100 °C for 24 h. After the excess triethyl orthoformate was
removed under reduced pressure, the residue was purified by flash
chromatography on silica gel (hexane–EtOAc, 2:3) to give 4.
Compound 5 (114 mg, 0.20 mmol), Cs2CO3 (62 mg, 0.20 mmol)
and Pd(OAc)2 (44 mg, 0.20 mmol) were stirred at r.t. in THF (10
mL) for 20 h. The solvent was removed under reduced pressure and
the residue was purified by flash chromatography on silica gel (hex-
ane–EtOAc, 4:1) to give the Pd(II)–NHC complex 7. The single
crystals for X-ray diffraction were obtained by recrystallization
from CH2Cl2–petroleum ether.
Yield: 192 mg (90%); white solid; mp 223–224 °C.
IR (KBr): 3422, 3274, 3054, 2926, 1690, 1597, 1491, 1284, 1236,
820, 743 cm–1.
1H NMR (300 MHz, CDCl3): d = 1.65 (s, 3 H, CH3), 6.06 (s, 1 H,
NCHN), 7.10 (d, J = 8.1 Hz, 1 H, ArH), 7.24–7.44 (m, 8 H, ArH),
7.62–7.70 (m, 2 H, ArH), 7.80–7.90 (m, 3 H, Ar), 8.10 (d, J = 8.4
Hz, 1 H, ArH), 8.27–8.30 (m, 2 H, ArH + NH).
13C NMR (75 MHz, CDCl3): d = 24.2, 109.2, 120.2, 120.6, 121.2,
122.8, 123.6, 124.2, 124.9, 125.2, 126.6, 127.1, 127.5, 128.1, 128.4,
128.5, 129.0, 129.7, 130.8, 133.17, 133.19, 134.0, 134.6, 142.4,
142.9, 168.0.
Yield: 104 mg (77%); yellow solid; mp >250 °C (CH2Cl2–petro-
leum ether).
IR (KBr): 3067, 2963, 1701, 1526, 1401, 1134, 742 cm–1.
1H NMR (300 MHz, acetone-d6): d = 1.58 (s, 6 H, CH3), 4.01 (s,
6 H, CH3), 6.83 (d, J = 8.1 Hz, 2 H, ArH), 6.91–7.77 (m, 24 H,
ArH), 7.99 (d, J = 8.4 Hz, 2 H, ArH), 8.32 (d, J = 8.4 Hz, 2 H, ArH),
8.51 (d, J = 8.7 Hz, 2 H, ArH).
MS (ESI): m/z = 1221.0 [M+ – I].
Anal. Calcd for C60H44I2N6O2Pd2·H2O: C, 52.77; H, 3.39; N, 6.15.
Found: C, 52.19; H, 3.77; N, 5.89.
MS (EI): m/z = 427 [M+], 384, 369.
Anal. Calcd for C29H21N3O: C, 81.48; H, 4.95; N, 9.83. Found: C,
81.09; H, 5.05; N, 9.76.
NHC–Pd(II) Complex 8
Complex 7 (135 mg, 0.10 mmol) was dissolved in MeCN–CH2Cl2
(3:1, 10 mL), then AgOAc (35 mg, 0.21 mmol) was added and the
mixture was stirred at r.t. for 3 h. The resulting suspension was fil-
tered through Celite to remove AgI, then the solvent was removed
under reduced pressure to give the Pd(II)–NHC complex 8.
Benzimidazolium Salt 5
Compound 4 (86 mg, 0.20 mmol) and MeI (0.24 mL, 4 mmol) in
MeCN (4.0 mL) were stirred under reflux for 5 h. After cooling to
r.t., volatiles were removed under reduced pressure and the solid
compound 5 obtained was used in the next reaction without further
purification.
Yield: 100 mg (82%); white solid; mp >250 °C.
IR (KBr): 3252, 2848, 2230, 1685, 1457, 1264, 693–818 cm–1.
1H NMR (300 MHz, CDCl3): d = 1.59 (s, 6 H, CH3), 1.85 (s, 6 H,
CH3), 4.08 (s, 6 H, CH3), 6.89–7.36 (m, 20 H, ArH), 7.59–7.64 (m,
4 H, ArH), 7.69 (d, J = 8.7 Hz, 2 H, ArH), 7.92 (d, J = 8.1 Hz, 2 H,
ArH), 8.12 (d, J = 8.4 Hz, 2 H, ArH), 8.30 (d, J = 8.7 Hz, 2 H, ArH).
Mp 230–233 °C.
IR (CH2Cl2): 3152, 2958, 1676, 1597, 1564, 1499, 1427, 1367,
1270, 1013, 733 cm–1.
1H NMR (300 MHz, CDCl3): d = 1.90 (s, 3 H, CH3), 3.91 (s, 3 H,
CH3), 6.96 (s, 2 H, ArH), 7.21 (t, J = 7.2 Hz, 1 H, ArH), 7.45–7.72
(m, 8 H, ArH), 7.85–8.00 (m, 3 H, ArH), 8.04 (d, J = 8.1 Hz, 1 H,
ArH), 8.30 (d, J = 8.4 Hz, 1 H, ArH), 8.51 (br, 1 H, NH), 10.16 (br,
1 H, NCHN).
MS (ESI): m/z = 1153.1 [M+ + Na + K – 2 × OAc].
Anal. Calcd for C64H50N6O6Pd2: C, 63.43; H, 4.16; N, 6.93. Found:
C, 64.02; H, 4.16; N, 6.62.
13C NMR (75 MHz, CDCl3): d = 24.0, 34.0, 112.91, 112.95, 122.97,
123.03, 124.2, 125.7, 126.4, 126.8, 127.26, 127.31, 127.4, 127.9,
128.3, 128.4, 129.3, 129.6, 130.4, 130.9, 131.0, 131.1, 131.30,
131.33, 132.0, 133.8, 135.47, 135.50, 141.9, 170.3.
Heck–Mizoroki Reaction; General Procedure
Under an argon atmosphere, tert-butyl acrylate (1.5 mmol), aryl ha-
lide (1.0 mmol), NaOAc (1.1 mmol) and DMF (2.0 mL) were added
successively into a flash-dried Schlenk tube. The reaction mixture
was stirred at 140 °C and monitored by TLC (the reaction was usu-
MS (EI): m/z = 442 [M+ – I], 427, 369, 267.
Synthesis 2008, No. 17, 2819–2824 © Thieme Stuttgart · New York

2824
T. Zhang et al.
SPECIAL TOPIC
ally complete within 20 h). The reaction was quenched with H2O
(15 mL) and extracted with CH2Cl2 (3 × 15 mL). The combined or-
ganic layers were dried over anhydrous MgSO4 and the solution was
concentrated under reduced pressure. Pure products were obtained
by flash column chromatography (EtOAc–petroleum ether, 1:5).
1998, 17, 1608. (c) Zhang, C.; Trudell, M. L. Tetrahedron
Lett. 2000, 41, 595. (d) Perry, M. C.; Cui, X.-H.; Burgess,
K. Tetrahedron: Asymmetry 2002, 13, 1969. (e)Lee,H.-M.;
Lu, C.-Y.; Chen, C.-Y.; Chen, W.-L.; Lin, H.-C.; Chiu,
P.-L.; Cheng, P.-Y. Tetrahedron 2004, 60, 5807.
(f) Marshall, C.; Ward, M.-F.; Harrison, W. T. A.
9a13
Tetrahedron Lett. 2004, 45, 5703. (g) Clyne, D. S.; Jin, J.;
Genest, E.; Gallucci, J. C.; RajanBabu, T. V. Org. Lett. 2000,
2, 1125. (h) Kantchev, E. A. B.; O’Brien, C. J.; Organ, M. G.
Angew. Chem. Int. Ed. 2007, 46, 2768.
1H NMR (300 MHz, CDCl3): d = 1.51 (s, 9 H), 6.36 (d, J = 16.2 Hz,
1 H), 7.32–7.36 (m, 3 H), 7.46–7.52 (m, 2 H), 7.59 (d, J = 16.2 Hz,
1 H).
(4) (a) Huang, J.; Grasa, G.; Nolan, S. P. Org. Lett. 1999, 1,
1307. (b) Stauffer, S. R.; Lee, S.; Stambuli, J. P.; Hauck, S.
I.; Hartwig, J. F. Org. Lett. 2000, 2, 1423. (c) Lee, S.;
Hartwig, J. F. J. Org. Chem. 2001, 66, 3402. (d) Yang, C.;
Lee, H. M.; Nolan, S. P. Org. Lett. 2001, 3, 1511.
(e) Batey, R. A.; Shen, M.; Lough, A. J. Org. Lett. 2002, 4,
1411. (f) Huang, J.; Nolan, S. P. J. Am. Chem. Soc. 1999,
121, 9889. (g) Lee, H. M.; Nolan, S. P. Org. Lett. 2000, 2,
2053. (h) Zhang, C.; Huang, J.; Trudell, M. L.; Nolan, S. P.
J. Org. Chem. 1999, 64, 3804. (i) Zhang, C.; Trudell, M. L.
Tetrahedron Lett. 2000, 41, 595. (j) Grasa, G. A.; Nolan, S.
P. Org. Lett. 2001, 3, 119.
(5) (a) Huynh, H. V.; Le Van, D.; Hahn, F. E.; Hor, T. S. A.
J. Organomet. Chem. 2004, 689, 1766. (b) Jensen, D. R.;
Schultz, M. J.; Mueller, J. A.; Sigman, M. S. Angew. Chem.
Int. Ed. 2003, 42, 3810. (c) Mueller, J. A.; Goller, C. P.;
Sigman, M. S. J. Am. Chem. Soc. 2004, 126, 9724.
(d) Viciu, M. S.; Stevens, E. D.; Petersen, J. L.; Nolan, S. P.
Organometallics 2004, 23, 3752. (e) Singh, R.; Viciu, M.
S.; Kramareva, N.; Navarro, O.; Nolan, S. P. Org. Lett. 2005,
7, 1829. (f) Voges, M. H.; Romming, C.; Tilset, M.
Organometallics 1999, 18, 529. (g) Herrmann, W. A.;
Kocher, C. Angew. Chem. Int. Ed. 1997, 36, 2163.
(6) (a) Zhang, T.; Shi, M.; Zhao, M.-X. Tetrahedron 2008, 64,
2412. (b) Zhang, T.; Shi, M. Chem. Eur. J. 2008, 14, 3759.
(7) (a) Duan, W.-L.; Shi, M.; Rong, G.-B. Chem. Commun.
2003, 2916. (b) Xu, Q.; Duan, W. L.; Lei, Z. Y.; Zhu, Z. B.;
Shi, M. Tetrahedron 2005, 61, 11225. (c) Chen, T.; Jiang,
J.-J.; Xu, Q.; Shi, M. Org. Lett. 2007, 9, 865; and references
cited therein.
13C NMR (75 MHz, CDCl3): d = 28.1, 80.3, 120.1, 127.9, 128.7,
129.9, 134.6, 143.4, 166.2.
9b13
1H NMR (300 MHz, CDCl3): d = 1.50 (s, 9 H), 2.35 (s, 3 H), 6.31
(d, J = 16.2 Hz, 1 H), 7.58–7.63 (m, 4 H), 7.56 (d, J = 16.2 Hz,
2 H).
13C NMR (75 MHz, CDCl3): d = 21.3, 28.1, 80.2, 119.1, 127.9,
129.5, 131.9, 140.1, 143.4, 166.4.
9c13
1H NMR (300 MHz, CDCl3): d = 1.53 (s, 9 H), 6.48 (d, J = 16 Hz,
1 H), 7.58–7.67 (m, 3 H), 7.89 (d, J = 8.1 Hz, 2 H), 10.02 (s, 1 H).
13C NMR (75 MHz, CDCl3): d = 28.0, 80.9, 123.3, 128.3, 130.0,
136.8, 140.3, 141.7, 165.5, 191.4.
9d13
1H NMR (300 MHz, CDCl3): d = 1.54 (s, 9 H), 2.62 (s, 3 H), 6.46
(d, J = 16.2 Hz, 1 H), 7.58–7.63 (m, 3 H), 7.96 (d, J = 8.4 Hz, 2 H).
13C NMR (75 MHz, CDCl3): d = 26.2, 28.1, 80.9, 122.7, 128.0,
128.8, 137.7, 139.0, 141.9, 165.7, 197.3.
Acknowledgment
We thank the Shanghai Municipal Committee of Science and Tech-
nology (04JC14083, 06XD14005), the National Natural Science
Foundation of China (20472096, 20672127, 20772030 and
20732008), and the Cheung Kong Scholar Program for financial
support.
(8) (a) Shi, M.; Qian, H.-X. Appl. Organomet. Chem. 2005, 19,
1083. (b) Shi, M.; Qian, H.-X. Tetrahedron 2005, 61, 4949.
(9) Zhang, T.; Wang, W.-F.; Gu, X.-X.; Shi, M.
Organometallics 2008, 27, 753; and references cited therein.
(10) The X-ray crystal data for compound 6 have been deposited
in the CCDC with number 281153. Empirical formula:
C28H19N3; Formula weight: 397.46; Crystal color, habit:
colorless, prismatic; Crystal dimensions:
References
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0.480 × 0.378 × 0.216 mm; Crystal system: monoclinic;
Lattice type: primitive; Lattice parameters: a = 8.7871(8) Å,
b = 25.373(3) Å, c = 9.3514(9) Å, b = 101.837(2)°;
V = 2040.6(3) Å3; Space group: P21/c; Z = 4; Dcalc = 1.294
g/cm3; F000 = 832; Diffractometer: Rigaku AFC7R;
Residuals: R1, wR2: 0.0548, 0.1023.
(11) The X-ray crystal data of NHC–Pd(II) complex 7 have been
deposited in the CCDC with number 601088. Empirical
formula: C60H48I2N6O2Pd2; Formula weight: 1383.64;
Crystal color, habit: colorless, prismatic; Crystal
dimensions: 0.138 × 0.115 × 0.040 mm; Crystal system:
monoclinic; Lattice type: primitive; Lattice parameters:
a = 14.496(12) Å, b = 20.803(16) Å, c = 23.523(19) Å,
b = 101.179(15)°; V = 6959(10) Å3; Space group: P21/c;
Z = 4; Dcalc = 1.321 g/cm3; F000 = 2720; Diffractometer:
Rigaku AFC7R; Residuals: R1, wR2: 0.1167, 0.2771.
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Synthesis 2008, No. 17, 2819–2824 © Thieme Stuttgart · New York