A novel tridentate NHC-Pd(II) complex and its application in the Suzuki and Heck-type cross-coupling reactions

Article abstract of DOI:10.1016/j.tet.2006.04.034

A novel tridentate NHC-Pd(II) complex derived from binaphthyl-2,2′-diamine (BINAM) has been synthesized and its structure has been characterized by single crystal X-ray diffraction. This NHC-Pd(II) complex was fairly effective in Suzuki and Heck-type cross-coupling reactions to give the products in good to excellent yields in most cases.

Full text of DOI:10.1016/j.tet.2006.04.034

Tetrahedron 62 (2006) 6289–6294
A novel tridentate NHC–Pd(II) complex and its application
in the Suzuki and Heck-type cross-coupling reactions
Tao Chen,a Jun Gaob and Min Shia,
*
aSchool of Chemistry & Molecular Engineering, East China University of Science and Technology,
130 MeiLong Road, Shanghai 200237, China
bState Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, China
Received 2 March 2006; revised 17 April 2006; accepted 18 April 2006
Available online 3 May 2006
Abstract—A novel tridentate NHC–Pd(II) complex derived from binaphthyl-2,20-diamine (BINAM) has been synthesized and its structure
has been characterized by single crystal X-ray diffraction. This NHC–Pd(II) complex was fairly effective in Suzuki and Heck-type cross-
coupling reactions to give the products in good to excellent yields in most cases.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
presence of pyridine as the base for 5 h. The reaction of 1
with each 2.5 equiv of glyoxal, paraformaldehyde, and
ammonium chloride under these conditions reported by
Crabtree5 afforded 2-(tosylamino)-20-(imidazol-1-yl)-1,10-
binaphthyl 2 in 72% yield. The corresponding imidazolium
iodide 3 was obtained in 98% yield by stirring compound 2
with excess of iodomethane in acetonitrile at 80 ꢀC for 5 h.
Reaction of the NHC precursor 3 with Pd(OAc)2 under reflux
in THF for 6 h afforded the desired NHC–Pd(II) complex 4 in
56% yield. The metal complex was confirmed by elemental
analysis, 1H NMR spectroscopy and EIMS. Its crystal struc-
ture was also determined by X-ray diffraction (Fig. 1).6 The
complex is air and moisture stable in the solid state and it is
also stable for several days in solution.
Since the isolation and characterization of the stable free
N-heterocyclic carbene (NHC) by Arduengo and co-workers
in 1991,1 much attention had been paid toward their proper-
ties and applications. During the past decade, numerous
publications related to their metal complexes and catalytic
reactions have been reported in a broad range of reactions.2
Significantly, anumber of Pd–NHC complexes have emerged
as effective catalysts for a variety of coupling reactions.3
Previously, we reported the synthesis of a novel cis-chelated
Pd(II)–NHC complex derived from binaphthyl-2,20-diamine
(BINAM) and a new dimeric bidentated NHC–Pd(II) com-
plex from trans-cyclohexane-1,2-diamine and their applica-
tions in the Suzuki reaction and Heck reaction.4 In this paper,
we wish to report the synthesis of a novel tridentate NHC–
Pd(II) complex derived from BINAM and its application in
the Suzuki and Heck-type cross-coupling reactions.
Structural features of NHC–Pd(II) complex 4: The single
crystals of this complex suitable for X-ray crystal structure
analysis were grown from a saturated solution of PE/
EtOAc¼3/1. The structure of the compound, C31H24IN3O2
PdS, is refined in space group P-1. The bite angle of C–Pd–
N is slightly larger than 90ꢀ (95.2ꢀ). The bond lengths of
2. Results and discussion
˚
Pd–C and Pd–N are 1.939(4) and 2.017(3) A, respectively.
The crystal structure shows that the O atom of sulfonyl group
participates in chelating with Pd center. This is a tridentate
NHC–Pd(II) complex. The bond distance of Pd–O iꢀs
The synthesis of tridentate NHC–Pd(II) complex 4 is shown
in Scheme 1. Using BINAM (1.0 equiv) as starting materials
to react with p-toluenesulfonyl chloride (1.1 equiv) in di-
chloromethane, 2-(tosylamino)-20-amino-1,10-binaphthyl 1
was obtained in 76% yield at room temperature in the
˚
2.219(3) A. The angle of N–Pd–I is slightly less than 180
(170.6ꢀ), indicating that these three atoms extending as far
as possible, which are almost on the same line. While the
coordinated atoms of C (carbene), N, O, and I with Pd are
effectively planar, with the maximum deviation form the
Keywords: Tridentate NHC–Pd(II) complex; Binaphthyl-2,20-diamine;
Cross-coupling reactions; Suzuki–Miyaura cross-coupling reaction; Heck
reaction.
˚
best-squares plane of 0.0200 A for atom Pd, and the mean
˚
deviation is 0.0080 A.
* Correspondingauthor. Fax: +862164166128; e-mail:mshi@pub.sioc.ac.cn
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.04.034

6290
T. Chen et al. / Tetrahedron 62 (2006) 6289–6294
Me
O
S
NH
OHCCHO, (CH O)
O
2
n
NH
NH
2
p-MeC H SO Cl, Py
NH Cl, H PO
4 3 4
6
4
2
CH Cl , r.t., 5 h, 76%
H O, dioxane, reflux, 6 h, 72%
2
NH
2
2
2
2
1
Me
Me
O
O
S
S
O
NH
O
N
Pd(OAc) , THF
2
NH
MeI, CH CN
3
reflux, 15 h, 56%
Me
80 °C, 5 h, 98%
+
N
N
N
-
I
3
2
Me
O
N
S
O
Pd
I
N
N Me
NHC-Pd(II) complex 4
Scheme 1. Synthesis of the NHC–Pd(II) complex 4.
Table 1. Screening for bases in the NHC–Pd(II) complex 4 catalyzed Suzuki
cross-coupling reaction of bromobenzene (1.0 mmol) with phenylboronic
acid (1.2 mmol) in THF (2.0 mL)
NHC-Pd(II) complex 4 (1.0 mol%)
+
B(OH)
Br
2
80 °C, THF, Base (2.0 equiv)
5a
Entry
Base
Time (h)
Yield (%)a
5a
1
2
3
4
5
6
7
8
Na2CO3
K2CO3
Cs2CO3
KF$2H2O
K3PO4$3H2O
KOtBu
12
12
12
12
12
12
12
12
6
24
98
N.Rb
53
13
NaOAc
DMAP
N.Rb
N.Rb
a
Isolated yields.
No reaction occurred.
b
entry 3). The other inorganic bases such as Na2CO3,
K2CO3, K3PO4$3H2O, and KOtBu were not as effective as
Cs2CO3, only afforded moderate to low yields of coupling
products (Table 1, entries 1, 2, 5, and 6). When KF$2H2O,
NaOAc, and DMAP were employed as the bases, no reaction
occurred (Table 1, entries 4, 7, and 8). Then, we examined
a variety of solvents at 80 ꢀC with Cs2CO3 as the base.
We found that using THF as the solvent gave the highest
yield in 98% (Table 2, entries 1–8). Thus, Cs2CO3 was the
base of choice and THF was the preferred solvent for this
reaction.
Figure 1. ORTEP drawing of NHC–Pd(II) complex 4.
The application of NHC–Pd(II) complex 4 as a catalyst for
the Suzuki–Miyaura cross-coupling reaction was examined
where both base and solvent effects were carefully examined
in the reaction of phenylboronic acid with bromobenzene
under argon atmosphere. The results are summarized in
Tables 1 and 2, respectively. We found that using Cs2CO3
as the base in tetrahydrofuran (THF) at 80 ꢀC gave the cou-
pled product biphenyl 5a in 98% yield after 12 h (Table 1,
Using these optimized reaction conditions, the Suzuki–
Miyaura reaction of a variety of aryl halides, including
aryl bromides and phenyl iodide, with phenylboronic acid

T. Chen et al. / Tetrahedron 62 (2006) 6289–6294
6291
Table 2. Screening for solvents in the NHC–Pd(II) complex 4 catalyzed
Suzuki cross-coupling reaction of bromobenzene (1.0 mmol) with phenyl-
boronic acid (1.2 mmol) in various solvents (2.0 mL)
Table 4. NHC–Pd(II) complex 4 (1.0 mol %) catalyzed Heck coupling
reaction of bromobenzene (1.0 equiv) with butyl acrylate (1.5 equiv)
O
OBun
NHC-Pd(II) complex 4 (1.0 mol%)
160 °C, Base, DMA
O
OBun
NHC-Pd(II) complex 4 (1.0 mol%)
+
Br
Br
B(OH)
+
2
80 °C, Cs CO (2.0 equiv), solvent
6a
2
3
5a
Entry
Base
Time (h)
Yield (%)a
Entry
Solvent
Time (h)
Yield (%)a
6a
5a
1
2
3
4
5
6
7
8
Na2CO3
K2CO3
Cs2CO3
KF$2H2O
K3PO4$3H2O
NaOAc
18
18
18
18
18
18
18
18
62
26
36
21
33
24
84
97
1
2
3
4
5
6
7
8
THF
DMSO
DMF
DMA
Dioxane
ClCH2CH2Cl
CH3CN
PhCH3
12
12
12
12
12
12
12
12
98
24
55
67
96
21
19
54
b
Na2CO3c
Na2CO3
a
Isolated yields.
Bn4NBr (1.0 mol %) was added.
Bn4NBr (20 mol %) was added.
a
Isolated yields.
b
c
was examined. The results are summarized in Table 3. As
can be seen, aryl bromides and phenyl iodide afforded cou-
pling products 5 in 71–90% yields within 12 h (Table 3,
entries 1–6).
the yields of 6a were improved to 84 and 97%, respectively
(Table 4, entries 7 and 8).
Using these reaction conditions, we next examined the Heck
cross-coupling reaction of a variety of aryl halides with butyl
and methyl acrylate. The results are summarized in Table 5.
We found that the Heck reaction products 6 were obtained in
good to high yields in most cases under argon atmosphere
(Table 5, entries 1–3, 6, and 7). For electron-rich 4-bromo-
anisole, the reaction was sluggish and product 6e was
obtained in only 19% yield under the same conditions
Heck reaction was examined in N,N-dimethylacetamide
(DMA) by the reaction of bromobenzene with butyl acrylate
in the presence of various bases (Table 4, entries 1–6). We
found that Na2CO3 afforded the best results for this reaction
and allowed the coupling product 6a to be obtained in 62%
under argon atmosphere at 160 ꢀC after 18 h (Table 4, entry
1). In other organic solvents, the reactions were sluggish.
Adding 1.0 and 20 mol % Bu4NBr to the reaction system,
Table 5. NHC–Pd(II) complex 4 (1.0 mol %) catalyzed Heck coupling
reaction of aryl halides (1.0 equiv) with butyl acrylate (1.5 equiv)
Table 3. NHC–Pd(II) complex 4 catalyzed Suzuki cross-coupling reaction
between aryl halides (1.0 mmol) and phenylboronic acid (1.2 mmol) under
optimized conditions
NHC-Pd(II) complex 4 (1.0 mol%)
X +
OR'
Na2CO3 (2.0 equiv), Bn4NBr
(20 mol%) DMA, 160 °C
OR'
R
R
6
NHC-Pd(II) complex 4
(1.0 mol%)
80 °C, Cs2CO3 (2.0 equiv), THF
X
B(OH)2
+
Entry
Ar-X
R0
Time (h)
Yield (%)a
R
R
5
6
Entry
Ar-X
Time (h)
Yield (%)a
Me
Br
1
2
Bun
Bun
18
18
6b, 81
6c, 91
5
Me
Br
1
2
12
12
5b, 74
Br
Me
Br
5c, 71
3
4
5
Bun
Bun
Me
18
18
18
6d, 87
6e, 19
6f, 48
Cl
Br
Me
Cl
Br
3
4
12
12
5d, 90
5e, 81
Br
MeO
Br
MeO
Me
Br
Me
Me
Bun
Bun
18
18
6g, 86
6a, 99
5
Br
12
12
5f, 72
5a, 88
Br
6
Me
6
7
I
I
a
a
Isolated yields.
Isolated yields.

6292
T. Chen et al. / Tetrahedron 62 (2006) 6289–6294
(Table 5, entry 4). For methyl acrylate, the coupled product
6f was obtained in moderate yield of 48% (Table 5, entry 5).
Product conformations were determined by H NMR spec-
troscopy (see Supplementary data).
Anal. Calcd for C27H22N2O2S requires: C, 73.95, H, 5.06,
N, 6.39%. Found: C, 73.84, H, 5.00, N, 6.25%.
1
3.1.2. Synthesis of 2-(tosylamino)-20-(imidazol-1-yl)-1,10-
binaphthyl 2. Compound 1 (876 mg, 2.0 mmol) and one
drop of concentrated H3PO4 was added to 10 mL of
de-ionized water. Then 40% aqueous glyoxal (726 mg,
5 mmol) and paraformaldehyde (150 mg, 5 mmol) as well as
10 mL of dioxane were added. The mixture was heated with
stirring to 80 ꢀC, ammonium chloride (267 mg, 5 mmol) was
added and then the temperature of oil bath was elevated to
100 ꢀC. After 6 h, the reaction mixture was cooled and a
saturated aqueous solution of K2CO3 (20 mL) was added,
and the mixture was extracted with CH2Cl2 (3ꢂ20 mL).
The combined organic layers were dried over anhydrous
MgSO4, filtered, and concentrated in vacuo. The residue
was purified by a silica gel flash column chromatography
(eluent: PE/EtOAc¼1/1–0/1) to give compound 2 as a white
solid (704 mg, 72%). Mp 244–245 ꢀC; IR (CH2Cl2): n 3259,
In conclusion, we disclosed a novel tridentate NHC–Pd(II)
complex 4 as an effective catalyst for Suzuki–Miyaura reac-
tion and Heck cross-coupling reaction. The corresponding
coupled products were obtained in good to high yields in
most cases by this novel Pd(II)-catalyst under normal con-
ditions. Efforts are underway to elucidate the mechanistic
details of this C–C bond forming reaction catalyzed by
Pd(II)–NHC complex and the use of 4 to catalyze other
C–C bond forming transformations.
3. Experimental
3.1. General
3059, 2733, 1911, 1621, 1510, 1158, 1092, 981, 869, 523 cmꢁ1
;
The synthesis of ligands was performed in untreated solvents
under ambient atmosphere. The preparation of Pd complex
was performed under argon atmosphere. THF and toluene
were distilled from sodium (Na) under argon (Ar) atmo-
sphere; CH3CN and 1,2-dichloroethane were distilled from
CaH2 under argon (Ar) atmosphere. 1H and 13C NMR spectra
were recorded on a Bruker AM-300 spectrometer for solution
in CDCl3 with tetramethylsilane (TMS) as internal standard;
J-values are in hertz. Mass spectra were recorded by EI, and
HRMS was measured on a Finnigan MA+ mass spectrometer.
All of the solid compounds reported in this paper gave satis-
factory carbon, hydrogen, and nitrogen microanalyses
with a Carlo-Erba 1106 analyzer [3 was characterized by
high-resolution mass spectrometry (HRMS)]. Commercially
obtained reagents were used without further purification. All
reactions were monitored by thin layer chromatography
with silica gel coated plates. Flash column chromatography
was carried out using 300–400 mesh silica gel at increased
pressure.
1H NMR (300 MHz, CDCl3, TMS): d 2.35 (3H, s, CH3), 6.35
(1H, br, CH), 6.70 (1H, s, NH), 6.75–6.76 (2H, m, CH), 6.88
(1H, d, J¼8.7 Hz, ArH), 7.11–7.27 (5H, m, ArH), 7.33–7.40
(3H, m, ArH), 7.53–7.62 (2H, m, ArH), 7.80 (1H, d, J¼
7.5 Hz, ArH), 7.85–7.93 (2H, m, ArH), 8.00 (1H, d, J¼
8.4 Hz, ArH), 8.15 (1H, d, J¼9.0 Hz, ArH); 13C NMR
(75 MHz, CDCl3, TMS): d 21.5, 117.6, 119.5, 119.7, 124.0,
124.6, 125.2, 125.7, 125.8, 127.0, 127.1, 127.5, 128.0,
128.3, 128.4, 128.0, 127.7, 130.3, 130.4, 131.3, 132.5,
132.9, 133.0, 133.3, 135.0, 136.0, 136.9, 144.0; EIMS m/z
(%): 489 (30.77) [M+], 421 (13.21), 334 (100), 266 (36.91),
91 (11.86); Anal. Calcd for C30H23N3O2S requires: C,
73.60, H, 4.74, N, 8.58%. Found: C, 73.41, H, 4.60, N, 8.56%.
3.1.3. Synthesis of 2-(tosylamino)-20-(3-methylimidazo-
lium-1-yl)-1,10-binaphthyl iodide 3. A mixture of 2
(98 mg, 0.2 mmol) and iodomethane (0.2 mL) were stirred
in acetonitrile (5.0 mL) at 80 ꢀC for 5 h. The volatiles were
removed to give the crude product 3 as a yellow solid
(124 mg, 98%). Mp 151–153 ꢀC; IR (CH2Cl2): n 3045,
2956, 2855, 1655, 1595, 1508, 1321, 1161, 1092, 816, 733,
550 cmꢁ1; 1H NMR (300 MHz, CDCl3, TMS): d 2.38 (3H,
s, CH3), 3.97 (3H, s, CH3), 6.47 (1H, s, NH), 6.93 (1H, d, J¼
8.4 Hz, ArH), 7.01–7.06 (2H, m, CH), 7.15 (2H, d, J¼8.1 Hz,
ArH), 7.27–7.32 (2H, m, ArH), 7.38–7.45 (3H, m, ArH), 7.52
(2H, d, J¼8.1 Hz, ArH), 7.59 (1H, t, J¼7.8 Hz, ArH), 7.80–
7.84 (2H, m, ArH), 7.97 (1H, d, J¼8.4 Hz, ArH), 8.09 (2H, q,
J¼8.7 Hz, ArH), 9.48 (1H, s, CH); 13C NMR (75 MHz,
CDCl3, TMS): d 21.3, 37.5, 121.3, 121.8, 122.7, 122.9, 123.2,
124.5, 125.9, 126.6, 126.7, 127.7, 127.8, 127.9, 128.2, 128.3,
128.4, 129.4, 130.5, 130.6, 131.3, 131.4, 132.3, 132.4, 133.3,
133.4, 136.1, 136.6, 143.6; HRMS (ESI) Calcd for
C31H26N3O2S (M+ꢁI) requires: 504.1746, Found: 504.1746.
3.1.1. Synthesis of 2-(tosylamino)-20-amino-1,10-bi-
naphthyl1. To a mixture of 2,20-diamino-1,10-binaphthalene
(a racemic compound, 569 mg, 2.0 mmol) and pyridine
(2.0 mL, 24 mmol) in CH2Cl2 (15 mL) was added dropwise
p-toluenesulfonyl chloride solution (420 mg, 2.2 mmol in
5.0 mL of CH2Cl2). The mixture was stirred at room tem-
perature for 5 h. The reaction mixture was washed with
5% HCl and dried over anhydrous MgSO4. The solvent was
removed under reduced pressure and the residue was purified
by a silica gel flash column chromatography (eluent: PE/
EtOAc¼6/1) to give compound 1 as a white solid (667 mg,
76%). Mp 169–170 ꢀC; IR (CH2Cl2): n 3365, 3051, 1621,
1
1595, 1403, 1316, 1164, 1091, 977, 814, 666 cmꢁ1; H
NMR (300 MHz, CDCl3, TMS): d 2.31 (3H, s, CH3), 3.30
(2H, br, NH2), 6.41 (1H, d, J¼8.1 Hz, ArH), 6.70 (1H, s,
NH), 6.93–7.10 (5H, m, ArH), 7.19–7.24 (2H, m, ArH),
7.36–7.42 (3H, m, ArH), 7.77 (1H, d, J¼8.1 Hz, ArH),
7.85 (2H, t, J¼9.0 Hz, ArH), 8.03 (2H, dd, J1¼9.0 Hz,
J2¼49.2 Hz, ArH); 13C NMR (75 MHz, CDCl3, TMS):
d 21.4, 117.9, 119.4, 121.5, 122.4, 123.2, 125.3, 125.6,
127.0, 127.1, 128.0, 128.1, 129.4, 129.7, 130.1, 131.2,
132.6, 136.0, 133.4, 133.5, 142.5, 143.6; EIMS m/z (%):
438 (75.20) [M+], 283 (100), 267 (96.03), 91 (16.90);
3.1.4. Synthesis of NHC–Pd(II) complex 4. The compound
3 (126 mg, 0.2 mmol) and Pd(OAc)2 (44.8 mg, 0.2 mmol)
was refluxed in THF (10 mL) for 12 h. The volatiles were
then removed under reduced pressure and the residue
was purified by a silica gel flash column chromatography
(eluent: PE/EtOAc¼2/1) to give 4 as a red solid (82 mg,
56%). A single crystal suitable for X-ray crystal analysis
was obtained by recrystallization from a saturated solution
of PE/EtOAc¼3/1. Mp >250 ꢀC; IR (CH2Cl2): n 3057,

T. Chen et al. / Tetrahedron 62 (2006) 6289–6294
6293
2923, 1592, 1460, 1381, 1109, 1030, 878, 680, 553 cmꢁ1; 1H
NMR (300 MHz, CDCl3, TMS): d 2.12 (3H, s, Me), 3.94 (3H,
s, Me), 6.21 (1H, d, J¼8.7 Hz, ArH), 6.46 (2H, d, J¼8.4 Hz,
CH), 6.68–6.76 (3H, m, ArH), 6.84 (1H, d, J¼
2.1 Hz, ArH), 7.07–7.09 (1H, m, ArH), 7.16 (2H, d, J¼
8.1 Hz, ArH), 7.30 (1H, d, J¼7.2 Hz), 7.43 (1H, t,
J¼7.8 Hz, ArH), 7.68 (1H, d, J¼8.4 Hz, ArH), 7.75 (2H, d,
J¼8.7 Hz, ArH), 7.86 (1H, d, J¼8.7 Hz, ArH), 7.96 (1H,
d, J¼8.1 Hz, ArH), 8.19 (1H, d, J¼8.7 Hz, ArH); EIMS
m/z (%): 735 (1.66) [M+], 579 (6.51), 502 (8.28), 438
(15.37), 422 (17.26), 347 (41.10), 332 (100), 278 (58.45),
91 (22.04); Anal. Calcd for C31H24IN3O2PdS requires: C,
50.59, H, 3.29, N, 5.71%. Found:C, 50.76, H, 3.10, N, 5.52%.
evacuated and filled with argon (3 cycles), then charged with
aryl halide (1.0 mmol), butyl acrylate (1.5 mmol), sodium
carbonate (212 mg, 2.0 mmol), cetyltrimethylammonium
bromide (64.4 mg, 0.2 mmol), N,N-dimethylacetamide
(DMA, 2.0 mL), and NHC–Pd(II) complex 4 (7.3 mg,
0.01 mmol). The reaction mixture was stirred at 160 ꢀC for
18 h. The reaction mixture was diluted with H2O (15 mL)
and Et2O (15 mL), followed by extraction twice with Et2O.
The combined organic layers were dried over anhydrous
Na2SO4, filtered, and evaporated under reduced pressure to
give crude product. A pure product (198 mg, 97%) was iso-
lated by column chromatography (eluent: PE/EtOAc¼30/1)
on silica gel. The purified product was analyzed by 1H
NMR spectroscopy.
3.2. General procedure for the Suzuki cross-coupling
reaction of aryl halides with boronic acids
3.3.1. Compound 6a. A yellow liquid; 1H NMR (300 MHz,
CDCl3, TMS): d 0.97 (3H, t, J¼7.2 Hz, CH3), 1.40–1.48
(2H, m, CH2), 1.65–1.72 (2H, m, CH2), 4.21 (2H, t,
J¼6.6 Hz, OCH2), 6.45 (1H, d, J¼15.9 Hz, ]CH), 7.37–
7.40 (3H, m, ArH), 7.51–7.54 (2H, m, ArH), 7.69 (1H, d,
J¼15.9 Hz, ]CH).
3.3.2. Compound 6b. A yellow liquid; 1H NMR (300 MHz,
CDCl3, TMS): d 0.96 (3H, t, J¼7.2 Hz, CH3), 1.40–1.47 (2H,
m, CH2), 1.63–1.71 (2H, m, CH2), 2.37 (3H, s, CH3), 4.20
(2H, t, J¼6.9 Hz, OCH2), 6.40 (1H, d, J¼16.2 Hz, ]CH),
7.18–7.44 (4H, m, ArH), 7.66 (1H, d, J¼16.2 Hz, ]CH).
3.3.3. Compound 6c. A yellow liquid; 1H NMR (300 MHz,
CDCl3, TMS): d 0.93 (3H, t, J¼7.2 Hz, CH3), 1.37–1.44
(2H, m, CH2), 1.61–1.68 (2H, m, CH2), 2.33 (3H, s, CH3),
4.17 (2H, t, J¼6.9 Hz, OCH2), 6.40 (1H, d, J¼16.2 Hz,
]CH), 7.14–7.17 (1H, m, ArH), 7.21–7.24 (1H, m, ArH),
7.28–7.30 (2H, m, ArH), 7.62 (1H, d, J¼16.2 Hz, ]CH).
A typical procedure is given below for the reaction expressed
in entry 3 of Table 1. An oven-dried Schlenk flask was
evacuated and filled with argon (3 cycles), then charged
with NHC–Pd(II) complex 4 (7.3 mg, 0.01 mmol), cesium
carbonate (650 mg, 2.0 mmol), benzene bromide (105 mL,
1.0 mmol), phenylboronic acid (146 mg, 1.2 mmol), and THF
(2.0 mL). The mixture was stirred at 80 ꢀC for 12 h. The
reaction mixture was diluted with H2O (10 mL) and CH2Cl2
(10 mL), followed by extraction twice with CH2Cl2.
The combined organic layers were dried over anhydrous
Na2SO4, filtered, and evaporated under reduced pressure to
give crude product. The pure product was isolated by column
chromatography on silica gel (eluent: petroleum ether) to
give biphenyl (151 mg, 98%) as a white solid, which was
analyzed by 1H NMR spectroscopy.
1
3.2.1. Compound 5a. A white solid; H NMR (300 MHz,
CDCl3, TMS): d 7.37 (2H, m, ArH), 7.48 (4H, m, ArH),
7.65 (4H, m, ArH).
1
3.3.4. Compound 6d. A white solid; H NMR (300 MHz,
CDCl3, TMS): d 0.96 (3H, t, J¼7.5 Hz, CH3), 1.35–1.51
(2H, m, CH2), 1.63–1.73 (2H, m, CH2), 4.20 (2H, t,
J¼6.3 Hz, OCH2), 6.41 (1H, d, J¼15.9 Hz, ]CH), 7.33–
7.46 (4H, m, ArH), 7.62 (1H, d, J¼15.9 Hz, ]CH).
3.3.5. Compound 6e. A yellow liquid; 1H NMR (300 MHz,
CDCl3, TMS): d 0.96 (3H, t, J¼7.2 Hz, CH3), 1.37–1.49
(2H, m, CH2), 1.63–1.73 (2H, m, CH2), 3.83 (3H, s,
OCH3), 4.19 (2H, t, J¼6.6 Hz, OCH2), 6.31 (1H, d,
J¼15.9 Hz, ]CH), 6.89–7.47 (4H, m, ArH), 7.64 (1H, d,
J¼15.9 Hz, ]CH).
3.3.6. Compound 6f. A yellow liquid; 1H NMR (300 MHz,
CDCl3, TMS): d 3.81 (3H, s, OCH3), 6.45 (1H, d,
J¼16.2 Hz, ]CH), 7.37–7.40 (3H, m, ArH), 7.51–7.54
(2H, m, ArH), 7.70 (1H, d, J¼16.2 Hz, ]CH).
3.3.7. Compound 6g. A yellow liquid; 1H NMR (300 MHz,
CDCl3, TMS): d 0.96 (3H, t, J¼7.5 Hz, CH3), 1.38–1.50
(2H, m, CH2), 1.64–1.73 (2H, m, CH2), 2.33 (6H, s, CH3),
4.20 (2H, t, J¼6.9 Hz, OCH2), 6.41 (1H, d, J¼15.9 Hz,
]CH), 7.02 (1H, s, ArH), 7.15 (2H, s, ArH), 7.62 (1H, d,
J¼15.9 Hz, ]CH).
1
3.2.2. Compound 5b. A white solid; H NMR (300 MHz,
CDCl3, TMS): d 2.46 (3H, s, CH3), 7.31–7.63 (2H, m,
ArH), 7.36–7.41 (1H, m, ArH), 7.47–7.52 (2H, m, ArH),
7.56–7.58 (2H, m, ArH), 7.64–7.67 (2H, m, ArH).
3.2.3. Compound 5c. A colorlessliquid;1H NMR(300 MHz,
CDCl3, TMS): d 2.44 (3H, s, CH3), 7.17–7.69 (1H, m, ArH),
7.32–7.47 (6H, m, ArH), 7.59–7.62 (2H, m, ArH).
1
3.2.4. Compound 5d. A white solid; H NMR (300 MHz,
CDCl3, TMS): d 7.37–7.60 (9H, m, ArH).
1
3.2.5. Compound 5e. A white solid; H NMR (300 MHz,
CDCl3, TMS): d 3.86 (3H, s, OCH3), 6.98–7.01 (2H, m,
ArH), 7.32–7.35 (1H, m, ArH), 7.41–7.46 (2H, m, ArH),
7.53–7.59 (4H, m, ArH).
1
3.2.6. Compound 5f. A white solid; H NMR (300 MHz,
CDCl3, TMS): d 2.39 (6H, s, CH3), 7.01 (1H, s, ArH),
7.22 (2H, s, ArH), 7.30–7.36 (1H, m, ArH), 7.40–7.45
(2H, m, ArH), 7.57–7.60 (2H, m, ArH).
3.3. Typical reaction procedure for Heck reaction
Acknowledgements
A typical procedure is given below for the reaction expressed
in entry 8 of Table 4. An oven-dried Schlenk flask was
We thank the State Key Project of Basic Research (Project
973) (No. G2000048007), Shanghai Municipal Committee

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T. Chen et al. / Tetrahedron 62 (2006) 6289–6294
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G. R. J. Angew. Chem., Int. Ed. Engl. 1995, 34, 2371–2374; (b)
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2000, 41, 595–598; (d) Perry, M. C.; Cui, X.-H.; Burgess, K.
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of Science and Technology (04JC14083), and the National
Natural Science Foundation of China (203900502,
20472096 and 20272069) for financial support.
Supplementary data
Supplementary data associated with this article can be found
in the online version, at doi:10.1016/j.tet.2006.04.034.
References and notes
4. (a) Xu, Q.; Duan, W. L.; Lei, Z. Y.; Zhu, Z. B.; Shi, M.
Tetrahedron 2005, 61, 11225–11229 and references cited
therein; (b) Shi, M.; Qian, H. X. Tetrahedron 2005, 61, 4949–
4955.
5. Chianese, A. R.; Crabtree, R. H. Organometallics 2005, 24,
4432–4436.
1. Arduengo, A. J., III; Harlow, R. L.; Kline, M. J. Am. Chem. Soc.
1991, 113, 361–363.
2. (a) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290–
¨
1309; (b) Bourissou, D.; Guerret, O.; GabbaI, F. P.; Bertrand,
G. Chem. Rev. 2000, 100, 39–91; (c) Herrmann, W. A.; Bohm,
V. P. W.; Gstottmayr, C. W. K.; Grosche, M.; Reisinger, C.;
¨
Weskamp, T. J. Organomet. Chem. 2001, 617–618, 616–628;
(d) Enders, D.; Gielen, H. J. Organomet. Chem. 2001, 617–618,
70–80; (e) Tulloch, A. A. D.; Danopoulos, A. A.; Winston, S.;
Kleinhenz, S.; Eastham, G. J. Chem. Soc., Dalton Trans. 2000,
4499–4506; (f) Douthwaite, R. E.; Houghton, J.; Kariuki, B. M.
Chem. Commun. 2004, 698–699; (g) Lee, H. M.; Zeng, J. Y.;
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6. The crystal data of complex 4 has been deposited in CCDC with
number 290551. Empirical formula: C31H24IN3O2PdS; formula
weight: 735.89; crystal color, Habit: colorless, prismatic; crystal
dimensions: 0.506ꢂ0.345ꢂ0.133 mm; crystal system: triclinic;
¨
˚
lattice type: primitive; lattice parameters: a¼9.9182(6) A,
b¼12.4974(8) A, c¼13.4366(9) A, a¼114.8630(10)ꢀ, b¼
˚
˚
3
ꢀ
ꢀ
˚
105.8190(10) , g¼90.1450(10) , V¼1440.74(16) A ; space
group: P-1; Z¼2; Dcalcd¼1.696 g/cm3; F000¼724; diffracto-
meter: Rigaku AFC7R; residuals: R; Rw: 0.0461, 0.1268.