Ferrocenylimidazoline palladacycles: efficient phosphine-free catalysts for Suzuki-Miyaura cross-coupling reaction

Article abstract of DOI:10.1016/j.tet.2007.04.022

A series of new ferrocenylimidazoline ligands 5 with different substituents in the imidazoline ring and their corresponding cyclopalladated complexes 6 were synthesized. Chloride-bridged palladacycle dimers 6, which are thermally stable and insensitive to air?and moisture, have been evaluated as effective phosphine-free catalysts for the Suzuki reaction of aryl bromides with arylboronic acid. The catalyst 6b presents the highest efficiency in the coupling processes for less reactive 2-bromothiophene. Moreover, the reactions can be carried out at room temperature under aerobic conditions to give the corresponding biaryls in high yields. Additionally, the triphenylphosphine adduct of cyclopalladated ferrocenylimidazoline 7a was structurally characterized by single-crystal X-ray diffraction.

Full text of DOI:10.1016/j.tet.2007.04.022

Tetrahedron 63 (2007) 5529–5538
Ferrocenylimidazoline palladacycles: efficient phosphine-free
catalysts for Suzuki–Miyaura cross-coupling reaction
*
Ji Ma, Xiuling Cui, Bi Zhang, Maoping Song and Yangjie Wu
*
Chemistry Department, Henan Key Laboratory of Chemical Biology and Organic Chemistry, Key Laboratory of Applied
Chemistry of Henan Universities, Zhengzhou University, Zhengzhou 450052, PR China
Received 13 January 2007; revised 5 April 2007; accepted 10 April 2007
Available online 14 April 2007
Abstract—A series of new ferrocenylimidazoline ligands 5 with different substituents in the imidazoline ring and their corresponding
cyclopalladated complexes 6 were synthesized. Chloride-bridged palladacycle dimers 6, which are thermally stable and insensitive to
air and moisture, have been evaluated as effective phosphine-free catalysts for the Suzuki reaction of aryl bromides with arylboronic acid.
The catalyst 6b presents the highest efficiency in the coupling processes for less reactive 2-bromothiophene. Moreover, the reactions can
be carried out at room temperature under aerobic conditions to give the corresponding biaryls in high yields. Additionally, the triphenyl-
phosphine adduct of cyclopalladated ferrocenylimidazoline 7a was structurally characterized by single-crystal X-ray diffraction.
Ó 2007 Published by Elsevier Ltd.
1. Introduction
carbon monoxide and styrene,34–36 hydrogenation of
aromatic ketones,37 Heck reaction,38 as well as aza-Claisen
rearrangement reaction.39 To further search more efficient
catalysts and mild reaction condition for C–C bond
formation, we screened a series of cyclopalladated ferro-
cenylimidazoline (shown in Fig. 1) as catalysts for the
Suzuki–Miyaura cross-coupling reaction of aryl bromides
with arylboronic acid under mild reaction conditions. To
the best of our knowledge, this is the first time that ferro-
cenylimidazoline palladacycles as phosphine-free catalysts
have been used in the Suzuki reaction.
Palladium-catalyzed Suzuki–Miyaura reaction is one of the
most efficient methods for the syntheses of biaryls and
heterobiaryls,1,2 which are widely used in pharmaceuticals,
herbicides, and light-emitting materials. Considerable
efforts have been dedicated to develop new and effective
palladium complexes for this coupling reaction.3–5 The
utilization of palladium–phosphine complexes as catalysts
has been prevalent in the past decade, and many successful
examples are known.6–14 However, most of these catalysts
containing phosphines are generally sensitive to moisture
and air, and required air free handling to minimize oxidation
of ligand or stabilize oxidative addition products. Moreover,
its large-scale application is limited in industry due to the
expensive cost and toxic property.15 Hence, the exploring
of phosphine-free and more efficient catalysts is of current
interest. Recently, many significant advances have been
made in this area, including hydrazone–Pd complexes,16,17
N-heterocyclic carbenes (NHC)–Pd complexes,18–21 oxime
palladacycles,22–26 and sulfur-containing palladacycles.27
R2
6a: R1=H
R2=Ph
R2=H
R2=H
R2=H
R2=H
R2=Ph
R2=H
R1
N
6b: R1=Benzyl
6c: R1=n-C5H11
6d: R1=n-C8H17
6e: R1=n-C14H29
6f : R1=Acetyl
6g: R1=Acetyl
R2
N
Fe
Pd
Cl
2
6a-g
Figure 1. Ferrocenylimidazoline palladacycles.
2. Results and discussion
In our lab, we have developed some cyclopalladated ferro-
cenylimines as efficient catalysts for Suzuki–Miyaura
coupling reactions.28–31 In addition, the development of
imidazoline systems has emerged as an attractive research
area owing to their application in a range of transition
metal (Cu, Ir, Pd, or Ru) catalyzed reactions, such as
epoxidation,32 1,4-addition reaction,33 copolymerization of
2.1. Synthesis and characterization
Ferrocenylimidazolines 5 were synthesized in three steps
starting from ferrocenylcarboxyaldehyde 1, as shown in
Scheme 1, which is different from Peters’ method.39a Con-
densation reaction of ferrocenylcarboxyaldehyde with
hydroxylamine hydrochloride in NMP produced ferrocenyl-
cyanide 2 in 76% yield. Methyl ferrocenylimidoate hydro-
chloride 3 was obtained in nearly quantitative yield
by treatment of ferrocenylcyanide 2 with HCl (gas) and
Keywords: Palladacycles; Ferrocenylimidazoline; Suzuki–Miyaura
reaction; Phosphine-free catalysts; Crystal structure.
* Corresponding authors. Tel.: +86 0371 67767993; fax: +86 0371
67979408; e-mail addresses: cuixl@zzu.edu.cn; wyj@zzu.edu.cn
0040–4020/$ - see front matter Ó 2007 Published by Elsevier Ltd.
doi:10.1016/j.tet.2007.04.022

5530
J. Ma et al. / Tetrahedron 63 (2007) 5529–5538
R2
R2
NH2Cl
OCH3
HN
CHO
CN
iii
i
ii
N
Fe
Fe
Fe
Fe
R2
NH2
R2
4a,h
H2N
2
3
1
5a: R2 = phenyl
5h: R2 = H
R1
H2N
iii
N
H
iv
4b-e
R1
N
O
N
R2
R2
N
N
Fe
Fe
5b: R1= benzyl
5c: R1= n-C5H11
5d: R1= n-C8H17
5e: R1= n-C14H29
5f: R2 = phenyl
5g: R2 = H
Scheme 1. Reagents: (i) NH2OH$HCl, NMP; (ii) CH3OH, HCl, Et2O; (iii) CH3OH; (iv) CH3COCl, NEt3, CH2Cl2.
methanol in ethyl ether at 0 ꢀC. The target ligands 5a–e
were prepared by condensation of compound 3 with the
corresponding 4a–e. Compounds 5f and 5g were obtained
conveniently via 5a and 5h with acetyl chloride in dry
dichloromethane, respectively. It should be noted that com-
pounds 5c–e were not stable in the air. They were used imme-
diately for next reaction after purification without being
characterized by NMR spectra. However, 5a, 5f, and 5g with
acetyl group at the N-1 position or phenyl group at C-4 and
C-5 in the imidazoline ring are more stable and able to keep
under air. It is proposed that the alkyl group at the N-1 posi-
tion of imidazoline ring may increase the electric density of
imidazoline ring, which results in the less stability of 5c–e.
with free ligands 5. The similar shifts were also observed
for the cyclopalladated ferrocenylimines reported.41
Complexes 6b–e bearing alkyl groups at N-1 position of imi-
dazoline ring are soluble in common organic solvents such
as dichloromethane and acetone, while 6a, 6f, and 6g with
acetyl group at the N-1 position or with phenyl group
in the imidazoline ring have poor solubility. Namely, the
cyclopalladated ferrocenylimidazolines bearing electron-
donating substituents exhibit better solubility than those with
electron-withdrawing substituents in the imidazoline ring.
Furthermore, the reaction of chloride-bridged palladacycle
dimer 6a (Scheme 2) with 2 equiv of triphenylphosphine
(PPh3) in methanol at room temperature produced the corre-
sponding triphenylphosphine (PPh3) adduct 7a, which was
structurally characterized by single-crystal X-ray diffrac-
tion. It is air stable both in the solid state and in solution.
Complexes 6 were obtained successfully by cyclopallada-
tion of compounds 5 with Li2PdCl4 in methanol in the pres-
ence of NaOAc$3H2O at room temperature (Scheme 2), and
1
characterized by elemental analysis, IR, H, and 13C NMR
spectra. The IR spectra showed strong absorption peak at
ca. 1540–1560 cmꢁ1 assigned to the C]N stretching of
the imidazoline ring, which was shifted to lower wave num-
ber at about ca. 55 cmꢁ1 by comparison with free ligands 5
due to N/Pd coordination.40 The 1H and 13C NMR spectra
are completely consistent with the expected homoannularly
1,2-disubstituted structures. The proton and carbon signals
in complexes 6 were shifted to downfield in comparison
2.2. Crystal structure determination of the monomer
complex 7a
Well-shaped crystal suitable for single-crystal X-ray analy-
sis was obtained from methanol/dichloromethane. ORTEP
drawing is shown in Figure 2. The palladium atom is located
in a slightly distorted square-planar coordination geometry
R2
6a: R1=H
6b: R1=Benzyl
6c: R1=n-C5H11 R2=H
6d: R1=n-C8H17 R2=H
6e: R1=n-C14H29 R2=H
6f : R1=Acetyl
6g: R1=Acetyl
R2=Ph
R2=H
R1
R1
R2
R2
N
Pd
6
N
R2
2
N
Li2PdCl4
N
Fe
Fe
Cl
.
NaOAc 3H2O
R2=Ph
R2=H
CH3OH
5
Ph
Ph
HN
HN
Ph
Ph
N
N
PPh3
CH3OH
Fe
Pd
Fe
Cl
Pd
Cl
2
PPh3
6a
7a
Scheme 2.

J. Ma et al. / Tetrahedron 63 (2007) 5529–5538
5531
Table 1. Screening of bases for Suzuki–Miyaura cross-coupling reaction of
4-bromotoluene with phenylboronic acid using 6b as catalysta
B(OH)2
0.1mol% 6b
Base (2 equiv)
Toluene 110 °C, 3h
Br
H3C
Ph
H3C
+
8a
9a
10a
Entry
Base
Yieldb (%)
1
2
3
4
5
6
7
K2CO3
K3PO4$7H2O
NaOH
t-BuONa
KF$2H2O
K3PO4
80
98
82
19
84
57
48
KF
Figure 2. The molecular structure of 7a, showing 30% probability displace-
ment ellipsoids. H atoms have been omitted for clarity.
a
Reaction conditions: 1 equiv of ArBr, 1.5 equiv of PhB(OH)2, 2 equiv of
base, 0.1 mol % of catalyst 6b, toluene, 110 ꢀC, 3 h, under air.
Isolated yields, based on 4-bromotoluene, average of two runs.
b
with one N-donor atom (N1) from the imidazoline ring, one
carbon atom (C6) from the Cp, one phosphorus atom from
PPh3, and one chlorine atom (the mean deviation from plane
the best isolated yield of 98% (Table 1, entry 2). It can be
seen obviously from the results that the aqueous bases
showed higher efficiency than the anhydrous bases, indicat-
ing that a small amount of water was essential for this cata-
lytic system.42 It was presumed that water prevented boronic
acid dimerizations and cyclic trimerizations from forming
boronic acid anhydrides and boroxines, respectively.
˚
of 0.0238 A). The bond angles around Pd atom vary from
80.9(2) to 173.46(16)ꢀ, and the bond lengths of C–Pd and
˚
N–Pd are 2.017(6) and 2.088(5)A, respectively. Owing to
the steric hindrance of substituents on the imidazoline back-
bone, the imidazoline ring is twisted with the dihedral angle
of 20.7ꢀ between N(1)–C(19)–C(18) and N(1)–C(11)–N(2)–
C(18). In addition, there are two kinds of hydrogen bond in-
teractions (N2–H2E/O1 and O1–H1E/Cl1) between the
methanol molecule and hydrogen atom of the imidazoline
ring or chlorine atom from two neighboring molecules
to stabilize the corresponding crystal lattice, as shown in
Figure 3 and Table 3s (see Supplementary data).
Aryl bromides are cheaper, but more difficult to undergo the
Suzuki reaction in comparison with the corresponding
iodides. Therefore, it is significant to evaluate the catalytic
activity of the cyclopalladed ferrocenylimidazolines in
the Suzuki coupling reaction of aryl bromides with aryl
boronic acids. The experimental results carried out with
K3PO4$7H2O as base are listed in Table 2. Palladacycles
6a–g with a loading of 0.1 mol %, exhibited advantageous
catalytic activity and gave excellent yields in the reactions
of phenylboronic acid coupled with 4-bromotoluene (8a) or
1-bromonaphthalene (8b) (Table 2, entries 1–14). That is to
say, catalysts 6b–ewith the electron-donating groups showed
similar reactivity to 6a, 6f, and 6g with electron-withdrawing
group. It seemed that the substituents in the imidazoline
moiety did not remarkably affect the catalytic activity of
the corresponding palladacycles in Suzuki reaction.
2.3. Catalytic properties
2.3.1. Palladacycles catalyzed Suzuki–Miyaura reaction
under air. Initial studies were performed for 4-bromo-
toluene (8a) and phenylboronic acid (9a) as a model reaction
in toluene at 110 ꢀC with various bases under aerobic atmo-
sphere using compound 6b as the catalyst. As shown in Table
1, K3PO4$7H2O was found to be the best base and provided
In order to screen the best catalyst, 2-bromothiophene (8c),
which is with rich p-electron and less reactive, was selected
as substrate. Surprisingly, 6b gave an excellent yield of 96%
(Table 2, entry 16), while the lower yields (Table 2, entries
15, 17–21) were obtained for others. Palladacycle 6b is
the most efficient phosphine-free palladium catalyst for the
Suzuki coupling of 2-bromothiophene with phenylboronic
acid reported to date.43–46
To expand the scope of this reaction, various aryl bromides
were subjected to this coupling reaction in the presence of
6b as catalyst with a loading of 0.1 mol %, and the results
are summarized in Table 3. We were pleased to find that
both electron-rich aryl bromides such as 4-bromoanisole
(8d) and electron-deficient aryl bromides such as 40-bromo-
acetophenone (8e), 4-bromobenzonitrile (8f), and 1-bromo-
4-nitrobenzene (8g) could be efficiently coupled to give the
corresponding biaryls in excellent isolated yields (>94%),
which suggested that the catalytic system was applicable
Figure 3. The intermolecular interactions of 7a, showing 30% probability
displacement ellipsoids. Thin dashed lines indicated hydrogen bonds. H
atoms not involved in hydrogen bonding have been omitted.

5532
J. Ma et al. / Tetrahedron 63 (2007) 5529–5538
Table 2. Screening of catalysts for Suzuki–Miyaura cross-coupling reaction
So we studied the Suzuki–Miyaura coupling reaction of the
relatively less reactive 4-bromotoluene and phenylboronic
acid in mild conditions in the presence of 0.5 mol % 6b
(Table 4). TBAB as additives was added into the catalytic
system in the subsequent experiments since the ammonium
salts may accelerate the coupling reaction in virtue of
activating the arylboronic acid to react by the formation of
[ArB(OH)3]ꢁ[R4N]+.47 The results showed that K2CO3
was the best base (Table 4, entries 1–6). In light of the afore-
mentioned finding that the presence of a small amount
of water is necessary to accelerate this reaction, a series
of water-mixed solvents (v/v¼1:2), including THF/H2O,
1,4-dioxane/H2O, methanol/H2O, DMF/H2O, and toluene/
H2O, were investigated in the presence of K2CO3 as base
at room temperature (Table 4, entries 7–11). The highest
isolated yield (98%) was obtained for methanol/H2O system.
of aryl bromides with phenylboronic acida
B(OH)2
0.1mol% 6b
Base (2 equiv)
Toluene 110 °C, 3h
Ar
Ar Br
+
8
9a
10
CH3
S
Ar:
8a
8b
8c
Entry Ar–Br (8) Catalysts 6 Products (10) T (h) Yieldsb (%)
1
2
3
4
5
6
7
8
8a
8a
8a
8a
8a
8a
8a
8b
8b
8b
8b
8b
8b
8b
8c
8c
8c
8c
8c
8c
8c
6a
6b
6c
6d
6e
6f
6g
6a
6b
6c
6d
6e
6f
6g
6a
6b
6c
6d
6e
6f
10a
10a
10a
10a
10a
10a
10a
10b
10b
10b
10b
10b
10b
10b
10c
10c
10c
10c
10c
10c
10c
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
96
98
99
95
94
89
95
97
97
99
92
93
94
96
54
96
56
49
51
53
48
The scope of the reaction was probed under the optimized
conditions. The results are illuminated in Table 5. The vari-
ous aryl bromides containing electron-rich groups (methyl,
methoxyl) or electron-deficient group (acetyl) and steric
bulk, such as 2-bromo-m-xylene (8h), 2-bromotoluene (8i),
and 1-bromo-2-methyl-naphthalene (8j), can be coupled
with phenylboronic acid in good to excellent isolated yields
with a loading of 0.5 mol % of 6b at room temperature.
Moreover, the 2-, 3-, and 4-substituted pyridyl bromides
gave the desired products in high yields (Table 5, entries
8–10). The reactions of the 4-substituted arylboronic acids
(9b and 9c) with 8d also resulted in the corresponding
coupling products in excellent yields (Table 5, entries 11
and 12).
9
10
11
12
13
14
15
16
17
18
19
20
21
6g
a
Reaction conditions: 1 equiv of ArBr, 1.5 equiv of PhB(OH)2, 2 equiv of
K3PO4$7H2O, 0.1 mol % of catalyst, toluene, 110 ꢀC, under air.
Isolated yields, average of two runs.
3. Conclusion
b
In summary, a series of new ferrocenylimidazolines 5a–g
with various substituents on the imidazoline backbone and
their related chloride-bridged palladacycle dimers 6a–g
were prepared. These air- and moisture-stable ferrocenyl-
imidazoline palladacycles are found to act as potent catalysts
for a wide range of aryl bromides in Suzuki reactions at room
temperature under aerobic conditions. It is well believed that
they are sufficiently encouraging further investigations into
the applicability of these ferrocenylimidazoline pallada-
cycles in other catalytic reactions.
to various aryl bromides and tolerant of a broad range of
functional groups (Table 3, entries 1–8). Encouraged by
these results, we went ahead to determine the effect of steric
bulk in the aryl bromides. It was interesting to observe from
Table 3 that the nature of substituents in aryl group had min-
imal influence on the reaction. Using sterically hindered aryl
bromides, such as 2-bromo-m-xylene (8h), 2-bromotoluene
(8i), and 1-bromo-2-methyl-naphthalene (8j) as substrates,
the desired products were obtained in high yield of 90%,
98%, and 97%, respectively (Table 3, entries 9–11). When
the heterocyclic bromides such as 2-, 3-, 4-bromopyridine
(8k, 8l, 8m) and 3-bromothiophene (8n) were employed,
the desired products were also obtained in good to excellent
yields (Table 3, entries 12–15). In addition, the catalyst 6b
could maintain its high catalytic activity for the cross-
coupling of 4-bromoanisole (8d) with phenylboronic acid
at low loading of 0.01 mol % (Table 3, entry 5). The effect
of varying arylboronic acids was also investigated by using
4-bromoanisole (8d) as substrates. Using 4-substituted aryl-
boronic acids, such as 4-methylphenylboronic acid (9b) and
4-chlorophenylboronic acid (9c), the corresponding cou-
pling products were obtained in excellent yields (Table 3,
entries 16 and 17).
4. Experimental
4.1. General methods
Methanol was distilled from magnesium under nitrogen.
Ethyl ether was distilled from sodium and benzophenone
under nitrogen. Dichloromethane was distilled from calcium
hydride under nitrogen. Melting points were measured on
1
a WC-1 microscopic apparatus and uncorrected. H and
13C NMR spectra were recorded on a Bruker DPX 400
instrument using CDCl3 or DMSO-d6 as the solvent and
tetramethylsilane as the internal standard. Elemental analy-
ses were determined with a PE-2400 II apparatus. IR spectra
were collected on a Bruker VECTOR22 spectrophotometer
in KBr pellets. meso-1,2-Diphenylethylenediamine 4a,48
N-benzylethylenediamine 4b,49 N-pentylethylenediamine
2.3.2. Palladacycle 6b catalyzed Suzuki–Miyaura reac-
tion at room temperature under air. It is attractive that
the organic synthesis can be carried out at room temperature.

J. Ma et al. / Tetrahedron 63 (2007) 5529–5538
5533
Table 3. Palladacycle 6b catalyzed Suzuki coupling reaction of aryl bromides with arylboronic acid:a scope of substrates
Entry
Ar–Br
Arylboronic acid
Product
T (h)
Yieldsb (%)
98
B(OH)2
H3C
Ph
H3C
Br
1
3
(8a)
(9a)
(10a)
Ph
Br
B(OH)2
2
3
97
(9a)
(8b)
(10b)
S
S
Ph
Br
B(OH)2
3
4
5
6
7
8
3
2
8
2
2
2
96
94
85c
99
99
99
(9a)
(10c)
(10d)
(10d)
(8c)
H3CO
H3CO
Br
B(OH)2
H3CO
H3CO
Ph
(9a)
(8d)
(8d)
(8e)
Br
B(OH)2
(9a)
Ph
B(OH)2
H3COC
Ph
H3COC
Br
(10e)
(9a)
B(OH)2
(9a)
NC
Br
NC
Ph
(10f)
(8f)
O2N
Br
B(OH)2
O2N
Ph
(9a)
(10g)
(8g)
Ph
Ph
Br
B(OH)2
9
4
4
6
90
98
97
(9a)
(8h)
(10h)
B(OH)2
Br
10
11
(9a)
(8i)
(10i)
Ph
Br
CH3
CH3
B(OH)2
(9a)
(8j)
(10j)
B(OH)2
Br
Ph
N
(8k)
12
13
14
3
3
3
83
92
88
N
(10k)
(9a)
B(OH)2
Br
Br
Ph
Ph
N
N
N
(10l)
(8l)
(9a)
B(OH)2
N
(8m)
(10m)
(9a)
(continued)

5534
J. Ma et al. / Tetrahedron 63 (2007) 5529–5538
Table 3. (continued)
Entry
Ar–Br
Br
Arylboronic acid
B(OH)2
(9a)
Product
Ph
T (h)
Yieldsb (%)
S
S
15
6
81
(8n)
(10n)
H3C
Cl
OCH3
OCH3
H3C
Cl
B(OH)2
B(OH)2
H3CO
H3CO
Br
Br
16
3
95
(8d)
(9b)
(10o)
17
3
96
(8d)
(10p)
(9c)
a
Reaction conditions: 1 equiv of ArBr, 1.5 equiv of arylboronic acid, 2 equiv of K3PO4$7H2O, 0.1 mol % of 6b, toluene, 110 ꢀC, under air.
Isolated yields, average of two runs.
Using 0.01 mol % of 6b as catalyst.
b
c
4c,50 N-octylethylenediamine 4d,51 and N-tetradecylethyl-
(gas) was bubbled through till the solution was saturated.
Then the resulting solution was stirred for 2 h at 0 ꢀC and
kept overnight at room temperature. After evaporating the
solvent in vacuo, the crude product was washed with dry
ethyl ether (2ꢂ3 mL) under nitrogen, then the red solid 3
(1.37 g, 98%) was obtained. Mp 155–157 ꢀC (lit.53 155–
156 ꢀC). IR (KBr): 3079, 2921, 1625, 1502, 1389, 1227,
enediamine 4e51 were prepared according to the literature
procedure. All other chemicals were used as purchased.
4.1.1. Ferrocenylcyanide (2). A solution of ferrocene-
carboxyaldehyde 1 (2.14 g, 10 mmol) in NMP (25 mL)
and hydroxylamine hydrochloride (0.966 g 12 mmol) was
stirred at 110 ꢀC under nitrogen. Progress of the reaction
was monitored by TLC. After the reaction was completed,
the mixture was poured into water (50 mL) and extracted
with AcOEt (2ꢂ10 mL). The combined organic phase was
washed with brine (2ꢂ10 mL), dried (Na2SO4), and the
solvent was evaporated in vacuo. The crude product was
purified by column chromatography on silica gel (eluant:
petroleum ether (60–90 ꢀC)/dichloromethane¼1:1) to give
compound 2 (1.60 g, 76%) as golden-yellow solid. Mp
105–106 ꢀC (lit.52 107–108 ꢀC). IR (KBr): 3092, 2232,
1072, 1006 cmꢁ1
.
4.1.3. [cis-4,5-Diphenyl-4,5-dihydro-1H-2-imidazolyl]-
ferrocene (5a). Compound 4a (212 mg, 1 mmol) was added
into the solution of compound 3 (280 mg, 1 mmol) in dry
methanol (20 mL) under nitrogen. The solution was stirred
at room temperature for 1 h, and then refluxed for 6 h. After
the reaction was completed, methanol was removed invacuo.
The residue was dissolved into 20 mL of dichloromethane,
washed with a saturated aqueous solution of Na2CO3
(2ꢂ10 mL) and NaCl (2ꢂ10 mL), and dried over anhydrous
Na2SO4. Evaporation of the solventinvacuo gave acrude res-
idue, which was further purified by column chromatography
on silica gel (eluant: methanol/dichloromethane¼1:10) to
give 5a (332 mg, 82%) as orange solid. Mp 146–147 ꢀC
(dec). IR (KBr): 3273, 3083, 3027, 2921, 1602, 1494,
1451, 1105, 1001, 760, 699 cmꢁ1. 1H NMR (CDCl3, ppm):
d¼7.05–6.99 (m, 6H, ArH), 6.71–6.75 (m, 4H, ArH), 5.58
(s, 2H, CHPh), 5.08 (s, 2H, C5H4), 4.53 (s, 2H, C5H4),
4.32 (s, 5H, C5H5). 13C NMR (CDCl3, ppm): d¼169.9,
134.9, 128.3, 127.9, 127.7, 127.6, 127.3, 72.9, 70.9, 70.7,
69.6, 69.3, 65.7, 64.1, 62.7. Anal. Calcd for C25H22FeN2:
C, 73.90; H, 5.46; N, 6.89. Found: C, 73.76; H, 5.63; N,
6.97%.
1450, 870 cmꢁ1
.
4.1.2. Ferrocenylimidic acid methyl ester hydrochloride
(3). To an ice-cooled solution of ferrocenylcyanide 2
(1.055 g, 5 mmol) in the mixture of absolute anhydrous
Et2O (15 mL) and methanol (3 mL), dry hydrogen chloride
Table 4. Suzuki–Miyaura coupling of PhB(OH)2 and 4-BrC6H4CH3 at room
temperature: study on reaction conditions for base and solventa
B(OH)2
0.5mol% 6b
Br
H3C
Ph
H3C
+
Base (2 equiv)
TBAB(1 equiv)
rt, 14h
8a
Entry Baseb
9a
10a
Yieldd (%) Entry Solventc
Yieldd (%)
83
4.1.4. [1-Benzyl-4,5-dihydro-1H-2-imidazolyl]-ferrocene
(5b). Red solid. Yield: 65%. Mp 179–180 ꢀC (dec). IR
(KBr): 3066, 2997, 2923, 2864, 1592, 1495, 1449, 1416,
1
2
3
4
5
6
Na2CO3 53
7
8
9
10
11
THF/H2O
1,4-Dioxane/H2O 37
DMF/H2O
Methanol/H2O
Toluene/H2O
K2CO3
NaOH
KOH
K3PO4
KF
83
22
27
61
44
1
90
98
32
1385, 1359, 1289, 1105, 1002, 738, 699 cmꢁ1. H NMR
(CDCl3, ppm): d¼7.49–7.43 (m, 3H, ArH), 7.27–7.26
(m, 2H, ArH), 5.18 (s, 2H, CH2Ph), 4.85 (s, 2H, C5H4),
4.64 (s, 2H, C5H4), 4.42 (s, 5H, C5H5), 4.06 (s, 2H,
C]NCH2), 3.85 (s, 2H, NCH2). 13C NMR (CDCl3, ppm):
d¼169.3, 133.4, 129.6, 128.8, 126.4, 74.6, 73.3, 72.4,
71.2, 69.4, 62.8, 52.3, 51.5, 50.8. Anal. Calcd for
C20H20FeN2: C, 69.78; H, 5.86; N, 8.14. Found: C, 69.43;
H, 5.59; N, 7.89%.
a
Reaction conditions: 4-bromotoluene (0.5 mmol), PhB(OH)2 (0.75 mmol),
base (1 mmol), solvent (3 mL) (v/v¼2:1, 3 mL), NBu4Br (0.5 mmol),
0.5 mol % catalyst 6b, at room temperature under air for 14 h.
THF/H2O (v/v¼2:1, 3 mL) as solvent.
b
c
d
v/v¼2:1; K2CO3 as base.
Isolated yields, average of two runs.

J. Ma et al. / Tetrahedron 63 (2007) 5529–5538
5535
Table 5. Palladacycle 6b catalyzed coupling of aryl bromides with arylboronic acid at room temperature:a scope of substrates
Entry
Ar–Br
Catalyst
B(OH)2
(9a)
Products
T (h)
Yieldb (%)
H3C
Br
H3C
Ph
1
14
98
(8a)
(10a)
Br
Ph
B(OH)2
(9a)
2
3
4
14
14
14
99
97
84
(10b)
(8b)
H3CO
Ph
B(OH)2
(9a)
H3CO
Br
(8d)
(10d)
B(OH)2
(9a)
H3COC
Ph
H3COC
Br
(8e)
(10e)
B(OH)2
(9a)
Ph
Ph
Br
Br
5
20
82
(8h)
(10h)
B(OH)2
(9a)
6
7
14
14
92
95
(8i)
(10i)
Br
Ph
CH3
CH3
B(OH)2
(9a)
(10j)
(8j)
Ph
Br
B(OH)2
N
N
8
20
20
20
20
93
90
89
96
(9a)
(8k)
(10k)
B(OH)2
Ph
Ph
Br
Br
N
N
N
N
9
(8l)
(10l)
(9a)
B(OH)2
(9a)
10
11
(8m)
(10m)
H3C
Cl
B(OH)2
B(OH)2
H3C
Cl
OCH3
OCH3
H3CO
H3CO
Br
Br
(8d)
(10o)
(9b)
12
20
95
(8d)
(10p)
(9c)
a
Reaction conditions: aryl bromide (0.5 mmol), arylboronic acid (0.75 mmol), K2CO3 (1 mmol), methanol/H2O (v/v¼2:1, 3 mL), NBu4Br (0.5 mmol),
0.5 mol % 6b, under air.
Isolated yields, average of two runs.
b
4.1.5. [4,5-Dihydro-1H-2-imidazolyl]-ferrocene (5h).
Orange solid. Yield: 81%. Mp 161–162 ꢀC (dec). IR
(KBr): 3137, 3100, 3025, 2923, 2873, 2740, 1601, 1511,
C5H4), 4.19 (s, 5H, C5H5), 3.69 (s, 4H, C]NCH2CH2NH).
13C NMR (CDCl3, ppm): d¼166.1, 72.9, 70.6, 69.9,
69.7, 69.5, 67.9, 50.1. Anal. Calcd for C13H14FeN2: C,
61.45; H, 5.55; N, 11.02. Found: C, 61.63; H, 5.35; N,
11.25%.
1
1447, 1412, 1380, 1267, 1150, 1107, 1001 cmꢁ1. H NMR
(CDCl3, ppm): d¼4.71 (s, 2H, C5H4), 4.34 (s, 2H,

5536
J. Ma et al. / Tetrahedron 63 (2007) 5529–5538
4.1.6. [cis-1-Acetyl-4,5-diphenyl-4,5-dihydro-1H-2-imid-
azolyl]-ferrocene (5f). Acetyl chloride (1.2 mmol) was
added into the solution of 5a (406 mg, 1 mmol) and
2.5 mmol of Et3N in dry dichloromethane and kept at 0 ꢀC
under nitrogen for 1 h. Then the reaction mixture was stirred
for 20 h at room temperature. Evaporation of the solvent in
vacuo gave a crude product, which was purified by column
chromatography on silica gel (eluant: methanol/dichloro-
methane¼1:15) to give 5f (389 mg, 87%) as a red solid.
Mp 135–136 ꢀC. IR (KBr): 3328, 3067, 3032, 2934, 1682,
4.1.10. Bis-m-chloro-{2-[1-(n-pentyl)-4,5-dihydro-1H-
imidazolyl]-ferrocenyl} dipalladium (6c). Yellow solid.
Yield: 77%. Mp 220–221 ꢀC (dec). IR (KBr): 3089, 2955,
2929, 2866, 1558, 1460, 1373, 1279, 1182, 1105, 1051,
1000 cmꢁ1
.
1H NMR (CDCl3, ppm): d¼4.62 (s, 2H,
C5H3), 4.38 (s, 5H, C5H5), 4.37 (s, 5H, C5H5), 4.35 (s, 2H,
C5H3), 4.20 (s, 2H, C5H3), 3.73–3.56 (m, 8H, C]NCH2
and NCH2C4H9), 3.32–3.28 (m, 4H, CH2N), 1.65–1.62 (m,
4H, CH2C3H7), 1.45–1.38 (m, 8H, CH2CH2), 0.96–0.93
(m, 6H, CH3). 13C NMR (CDCl3, ppm): d¼175.1, 97.8,
72.5, 70.5, 67.1, 64.0, 51.3, 47.5, 29.0, 28.2, 22.5, 14.1.
Anal. Calcd for C36H46Cl2Fe2N4Pd2: C, 46.48; H, 4.98; N,
6.02. Found: C, 46.25; H, 4.71; N, 5.87%.
1
1622, 1378, 1260, 1034, 721, 698 cmꢁ1. H NMR (CDCl3,
ppm): d¼7.20–7.13 (m, 6H, ArH), 7.09–7.08 (m, 2H,
ArH), 7.02–7.01 (m, 2H, ArH), 5.61 (s, 1H, C]NCHPh),
5.50 (s, 1H, NCHPh), 5.11 (s, 1H, C5H4), 4.82 (s, 1H,
C5H4), 4.55 (s, 1H, C5H4), 4.43 (s, 1H, C5H4), 4.38 (s, 5H,
C5H5), 2.0 (s, 3H, CH3). 13C NMR (CDCl3, ppm):
d¼168.0, 162.0, 137.2, 136.5, 128.0, 127.8, 127.5, 127.1,
126.6, 75.5, 73.6, 72.8, 70.5, 69.7, 69.4, 69.2, 68.5, 25.0.
Anal. Calcd for C27H24FeN2O: C, 72.33; H, 5.40; N, 6.25.
Found: C, 72.02; H, 5.67; N, 6.16%.
4.1.11. Bis-m-chloro-{2-[1-(n-octyl)-4,5-dihydro-1H-imid-
azolyl]-ferrocenyl} dipalladium (6d). Yellow solid. Yield:
75%. Mp 186–187 ꢀC (dec). IR (KBr): 3090, 2925, 2853,
1
1561, 1461, 1372, 1281, 1177, 1104, 1046, 1000 cmꢁ1. H
NMR (CDCl3, ppm): d¼4.62 (s, 2H, C5H3), 4.39 (s, 5H,
C5H5), 4.35 (s, 5H, C5H5), 4.30 (s, 2H, C5H3), 4.20 (s, 2H,
C5H3), 3.68–3.57 (m, 8H, C]NCH2 and NCH2C7H15),
3.31–3.28 (m, 4H, CH2N), 1.64–1.63 (m, 4H, CH2C6H13),
1.36–1.25 (m, 20H, C5H10), 0.91–0.87 (m, 6H, CH3).
13C NMR (CDCl3, ppm): d¼175.6, 94.7, 75.2, 72.9, 72.6,
70.9, 67.5, 64.4, 51.8, 50.2, 47.9, 32.2, 29.8, 29.6,
28.9, 23.0, 14.5. Anal. Calcd for C42H58Cl2Fe2N4Pd2:
C, 49.73; H, 5.76; N, 5.52. Found: C, 49.58; H, 5.61; N,
5.74%.
4.1.7. [1-Acetyl-4,5-dihydro-1H-2-imidazolyl]-ferrocene
(5g). A procedure similar to the preparation of 5f was fol-
lowed to synthesize 5g. Red solid. Yield: 83%. Mp 101–
102 ꢀC. IR (KBr): 3094, 2926, 1670, 1628, 1553, 1381,
1
1290, 1101, 1021 cmꢁ1. H NMR (CDCl3, ppm): d¼4.72
(s, 2H, C5H4), 4.39 (s, 2H, C5H4), 4.24 (s, 5H, C5H5),
3.99–3.97 (m, 2H, C]NCH2), 3.84–3.82 (m, 2H, NCH2),
1.92 (s, 3H, CH3). 13C NMR (CDCl3, ppm): d¼168.5,
159.2, 71.3, 71.0, 70.6, 70.1, 68.9, 68.3, 52.8, 48.5, 25.1.
Anal. Calcd for C15H16FeN2O: C, 60.84; H, 5.45; N, 9.46.
Found: C, 60.69; H, 5.37; N, 9.27%.
4.1.12. Bis-m-chloro-{2-[1-(n-tetradecyl)-4,5-dihydro-
1H-imidazolyl]-ferrocenyl} dipalladium (6e). Yellow
solid. Yield: 64%. Mp 140–141 ꢀC. IR (KBr): 3091, 2923,
1
2852, 1560, 1464, 1372, 1282, 1104, 1051, 1000 cmꢁ1. H
4.1.8. Bis-m-chloro-{2-[cis-4,5-diphenyl-4,5-dihydro-1H-
imidazolyl]-ferrocenyl} dipalladium (6a). A mixture of
5a (203 mg, 0.5 mmol), LiPdCl4 (0.5 mmol), and NaOAc$
3H2O (68 mg, 0.5 mmol) in 10 mL of methanol was stirred
for 24 h at room temperature. The precipitate obtained was
filtered, washed with methanol, and dried in vacuo. The
red solid 6a (185 mg, 68% yield) was obtained. Mp 250–
251 ꢀC (dec). IR (KBr): 3380, 3084, 2925, 1540, 1455,
NMR (CDCl3, ppm): d¼4.62 (s, 2H, C5H3), 4.38 (s, 5H,
C5H5), 4.35 (s, 5H, C5H5), 4.30 (s, 2H, C5H3), 4.20 (s, 2H,
C5H3), 3.71–3.58 (m, 8H, C]NCH2 and NCH2C13H27),
3.31–3.28 (m, 4H, CH2N), 1.66–1.63 (m, 4H, CH2C12H25),
1.36–1.26 (m, 44H, C11H22), 0.89–0.82 (m, 6H, CH3). 13C
NMR (CDCl3, ppm): d¼175.1, 94.2, 74.9, 72.4, 70.5, 67.0,
64.0, 51.3, 50.5, 49.8, 47.5, 31.9, 29.7, 29.6, 29.4, 29.3,
28.4, 26.9, 22.6, 14.1. Anal. Calcd for C54H82Cl2Fe2N4Pd2:
C, 54.84; H, 6.99; N, 4.74. Found: C, 54.68; H, 6.84; N,
4.52%.
1104, 1003 cmꢁ1
.
1H NMR (DMSO-d6, ppm): d¼8.78
(s, 2H, NH), 7.20–7.03 (m, 20H, ArH), 5.58 (s, 2H,
C]NCHPh), 5.24 (s, 2H, NCHPh), 4.89 (s, 2H, C5H3),
4.70 (s, 2H, C5H3), 4.41 (s, 10H, C5H5), 4.13 (s, 2H,
C5H3). 13C NMR (DMSO-d6, ppm): d¼176.9, 139.0,
136.8, 127.4, 127.2, 126.7, 125.9, 99.4, 76.5, 72.5,
69.9, 69.7, 69.3, 67.4, 67.2, 64.6. Anal. Calcd for
C50H42Cl2Fe2N4Pd2: C, 54.88; H, 3.87; N, 5.12. Found: C,
54.67; H, 3.96; N, 4.93%.
4.1.13. Bis-m-chloro-{2-[cis-1-acetyl-4,5-diphenyl-4,5-
dihydro-1H-imidazolyl]-ferrocenyl} dipalladium (6f).
Red solid. Yield: 71%. Mp 273–275 ꢀC (dec). IR (KBr):
1
3067, 3032, 2925, 1715, 1628, 1551, 1376, 1003 cmꢁ1. H
NMR (DMSO-d6, ppm): d¼7.03–6.92 (m, 12H, ArH),
6.82–6.73 (m, 8H, ArH), 6.28 (s, 2H, C]NCHPh), 5.65
(s, 2H, NCHPh), 5.29 (s, 2H, C5H3), 5.22 (s, 2H, C5H3),
4.54 (s, 2H, C5H3), 4.39 (s, 10H, C5H5), 1.92 (s, 6H, CH3).
13C NMR (DMSO-d6, ppm): d¼173.7, 168.9, 137.8, 136.8,
128.2, 127.6, 127.2, 126.5, 104.2, 75.2, 74.8, 72.1, 70.5,
70.3, 69.4, 68.7, 24.6. Anal. Calcd for C54H46Cl2Fe2-
N4O2Pd2: C, 55.04; H, 3.93; N, 4.75. Found: C, 55.23; H,
3.71; N, 4.67%.
4.1.9. Bis-m-chloro-{2-[1-benzyl-4,5-dihydro-1H-imid-
azolyl]-ferrocenyl} dipalladium (6b). Dark red solid.
Yield: 57%. Mp 202–203 ꢀC (dec). IR (KBr): 3086, 2933,
2878, 1555, 1476, 1454, 1401, 1357, 1281, 1180, 1156,
1105, 1000 cmꢁ1
.
1H NMR (DMSO-d6, ppm): d¼7.40–
7.30 (m, 10H, ArH), 4.87 (s, 2H, C5H3), 4.68–4.53 (m,
4H, NCH2Ph), 4.61 (s, 2H, C5H3), 4.37 (s, 2H, C5H3), 4.19
(s, 10H, C5H5), 3.71–3.49 (m, 8H, C]NCH2CH2N). 13C
NMR (DMSO-d6, ppm): d¼174.9, 128.9, 127.8, 127.5,
99.4, 74.9, 73.0, 70.8, 70.2, 68.1, 66.1, 51.6, 50.3. Anal.
Calcd for C40H38Cl2Fe2N4Pd2: C, 49.52; H, 3.95; N, 5.77.
Found: C, 49.29; H, 4.19 N, 5.63%.
4.1.14. Bis-m-chloro-{2-[1-acetyl-4,5-dihydro-1H-imid-
azolyl]-ferrocenyl} dipalladium (6g). Red solid. Yield:
67%. Mp 233–235 ꢀC (dec). IR (KBr): 3090, 2943, 2887,
1708, 1563, 1470, 1391, 1359, 1306, 1185, 1104, 1073,
1030, 1000 cmꢁ1
.
1H NMR (DMSO-d6, ppm): d¼5.20

J. Ma et al. / Tetrahedron 63 (2007) 5529–5538
5537
(s, 2H, C5H3), 5.06 (s, 2H, C5H3), 4.40–4.26 (m, 6H,
Supplementary data
C]NCH2 and C5H3), 4.26 (s, 10H, C5H5), 3.71–3.73 (m,
4H, CH2N), 1.81 (s, 6H, CH3). 13C NMR (DMSO-d6,
ppm): d¼171.7, 168.0, 101.8, 75.7, 74.3, 71.4, 70.3, 68.9,
50.9, 49.0, 24.5. Anal. Calcd for C30H30Cl2Fe2N4O2Pd2:
C, 41.23; H, 3.46; N, 6.41. Found: C, 41.47; H, 3.68; N,
6.29%.
Supplementary data associated with this article can be found
in the online version, at doi:10.1016/j.tet.2007.04.022.
References and notes
4.1.15. Triphenylphosphine-{2-[cis-4,5-diphenyl-1H-imid-
azolyl]-ferrocenyl-C,N} palladium(II) chloride (7a). The
complex 6a (150 mg, 0.137 mmol) was treated with PPh3
(71 mg, 0.27 mmol) in methanol (15 mL) at room tempera-
ture for 1 h and the mixture was concentrated in vacuo. The
residue was purified by column chromatography on silica gel
(eluant: dichloromethane) to give the monomer orange-
yellow solid 7a (192 mg, 88%). Mp 208–209 ꢀC (dec). IR
(KBr): 3254, 3056, 2923, 1581, 1438, 1435, 1285, 1097,
1. Suzuki, A. Pure Appl. Chem. 1991, 63, 419–422.
2. Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457–2483.
3. Beller, M.; Fischer, H.; Herrmann, W. A.; Oefele, K.;
Brossmer, C. Angew. Chem., Int. Ed. Engl. 1995, 34, 1848–
1849.
4. Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290–1309.
5. Herrmann, W. A.; Bohm, V. P. W.; Gstottmayr, C. W. K.;
Grosche, M.; Reisinger, C. P.; Weskamp, T. J. Organomet.
Chem. 2001, 617–618, 616–628.
6. Kwong, F. Y.; Lam, W. H.; Yeung, C. H.; Chan, K. S.; Chan,
A. S. C. Chem. Commun. 2004, 1922–1923.
7. Pickett, T. E.; Roca, F. X.; Richards, C. J. J. Org. Chem. 2003,
68, 2592–2599.
8. Littke, A. F.; Fu, G. C. Angew. Chem., Int. Ed. 1999, 37, 3387–
3388.
9. DeVasher, R. B.; Spruell, J. M.; Dixon, D. A.; Broker, G. A.;
Griffin, S. T.; Rogers, R. D.; Shaughnessy, K. H.
Organometallics 2005, 24, 962–971.
10. Bedford, R. B.; Cazin, C. S. J.; Hursthouse, M. B.; Light, M. E.;
Scordia, V. J. M. Dalton Trans. 2004, 3864–3868.
11. DeVasher, R. B.; Moore, L. R.; Shaughnessy, K. H. J. Org.
Chem. 2004, 69, 7919–7927.
1
1029, 1001 cmꢁ1. H NMR (CDCl3, ppm): d¼7.71–7.67
(m, 9H, ArH), 7.39–7.33 (m, 12H, ArH), 7.08–7.06 (m,
4H, ArH), 5.60 (s, 1H, C]NCHPh), 5.51 (s, 1H, NCHPh),
5.39 (s, 1H, C5H3), 4.48 (s, 1H, C5H3), 4.12 (s, 5H, C5H5),
3.25 (s, 1H, C5H3). 13C NMR (CDCl3, ppm): d¼176.8,
138.6, 137.7, 136.8, 136.6, 135.2, 135.0, 134.9, 134.8,
128.1, 127.9, 127.8, 127.4, 127.3, 127.2, 126.4, 97.4, 76.3,
75.7, 70.6, 70.2, 69.2, 68.5, 63.6. Anal. Calcd for
C43H36ClFeN2PPd: C, 63.80; H, 4.48; N, 3.46. Found: C,
63.53; H, 4.63; N, 3.17%.
4.2. General procedure for the coupling reactions
4.2.1. General procedure A. A mixture of aryl bromide
(1 mmol), palladacycle dimer (0.1 mol %), arylboronic
acids (1.5 mmol), K3PO4$7H2O (2 mmol), and toluene
(3 mL) was stirred and refluxed under air. Then, the reaction
mixture was cooled and evaporated under reduced pressure
to dryness. CH2Cl2 (15 mL) and water (5 mL) were added.
The organic layer was separated and the aqueous layer was
extracted with dichloromethane, then the combined organic
phases were washed with water, dried over MgSO4, filtered,
and the solvent was evaporated under reduced pressure to
dryness. The residue was purified by flash column chromato-
graphy on silica gel.
12. Tewari, A.; Hein, M.; Zapf, A.; Beller, M. Synthesis 2004, 935–
941.
13. Bedford, R. B.; Cazin, C. S. J.; Coles, S. J.; Gelbrich,
T.; Horton, P. N.; Hursthouse, M. B.; Light, M. E.
Organometallics 2003, 22, 987–999.
14. Shaughnessy, K. H.; Booth, R. S. Org. Lett. 2001, 3, 2757–
2759.
15. Beletskaya, I. P.; Cheprakov, A. V. Chem. Rev. 2000, 100,
3009–3066.
16. Mino, T.; Shirae, Y.; Sakamoto, M.; Fujita, T. J. Org. Chem.
2005, 70, 2191–2194.
17. Mino, T.; Shirae, Y.; Sakamoto, M.; Fujita, T. Synlett 2003,
882–884.
4.2.2. General procedure B. A mixture of aryl bromide
(0.5 mmol), catalyst 6b (0.5 mol %), arylboronic acids
(0.75 mmol), K2CO3 (1 mmol), TBAB (0.5 mmol), and
methanol/H2O (2 mL/1 mL) was stirred at room temperature
under air. The mixture was diluted with ethyl ether and
water. The aqueous layer was extracted with ethyl ether,
then the combined organic phase was washed with water,
dried over MgSO4, filtered, and the solvent was evaporated
under reduced pressure to dryness. The residue was purified
by flash column chromatography on silica gel.
18. Navarro, O.; Marion, N.; Oonishi, Y.; Kelly, R. A., III; Nolan,
S. P. J. Org. Chem. 2006, 71, 685–692.
19. Marion, N.; Navarro, O.; Mei, J.; Stevens Edwin, D.; Scott
Natalie, M.; Nolan Steven, P. J. Am. Chem. Soc. 2006, 128,
4101–4111.
20. Kang, T.; Feng, Q.; Luo, M. Synlett 2005, 2305–2308.
21. Altenhoff, G.; Goddard, R.; Lehmann, C. W.; Glorius, F.
Angew. Chem., Int. Ed. 2003, 42, 3690–3693.
22. Alacid, E.; Alonso, D. A.; Botella, L.; Najera, C.; Pacheco,
M. C. Chem. Rec. 2006, 6, 117–132.
23. Solodenko, W.; Mennecke, K.; Vogt, C.; Gruhl, S.; Kirschning,
A. Synthesis 2006, 1873–1881.
Acknowledgements
24. Vicente, J.; Abad, J.-A.; Lopez-Serrano, J.; Jones, P. G.; Najera,
C.; Botella-Segura, L. Organometallics 2005, 24, 5044–5057.
25. Alonso, D. A.; Najera, C.; Pacheco, M. C. J. Org. Chem. 2002,
67, 5588–5594.
26. Alonso, D. A.; Najera, C.; Pacheco, M. C. Org. Lett. 2000, 2,
1823–1826.
We are grateful to the National Natural Science Foundation
of China (Project 20472074), the Innovation Fund for
Outstanding Scholar of Henan Province (Project
0621001100), Chinese Education Ministry and Personnel
Ministry Science Foundation for Chinese Oversea Scholar
for the financial support to this research.
27. Zim, D.; Gruber, A. S.; Ebeling, G.; Dupont, J.; Monteiro, A. L.
Org. Lett. 2000, 2, 2881–2884.

5538
J. Ma et al. / Tetrahedron 63 (2007) 5529–5538
28. Wu, Y.; Yang, L.; Zhang, J.; Wang, M.; Zhao, L.; Song, M.;
Gong, J. Arkivoc 2004, ix, 111–121.
Jautze, S.; Schweizer, W. B.; Peters, R. Angew. Chem., Int.
Ed. 2006, 45, 5694–5698.
29. Gong, J.; Liu, G.; Du, C.; Zhu, Y.; Wu, Y. J. Organomet. Chem.
2005, 690, 3963–3969.
30. Xu, C.; Gong, J.-F.; Yue, S.-F.; Zhu, Y.; Wu, Y.-J. Dalton Trans.
2006, 4730–4739.
31. Zhang, J.; Zhao, L.; Song, M.; Mak, T. C. W.; Wu, Y.
J. Organomet. Chem. 2006, 691, 1301–1306.
40. Moyano, A.; Rosol, M.; Moreno Rosa, M.; Lopez, C.; Maestro
Miguel, A. Angew. Chem., Int. Ed. 2005, 44, 1865–1869.
41. Huo, S. Q.; Wu, Y. J.; Du, C. X.; Zhu, Y.; Yuan, H. Z.; Mao,
X. A. J. Organomet. Chem. 1994, 483, 139–146.
42. Netherton, M. R.; Dai, C.; Neuschuetz, K.; Fu, G. C. J. Am.
Chem. Soc. 2001, 123, 10099–10100.
32. Arai, T.; Mizukami, T.; Yokoyama, N.; Nakazato, D.;
Yanagisawa, A. Synlett 2005, 2670–2672.
33. Halland, N.; Hazell, R. G.; Jorgensen, K. A. J. Org. Chem.
2002, 67, 8331–8338.
43. Bussolari, J. C.; Rehborn, D. C. Org. Lett. 1999, 1, 965–967.
44. Leadbeater, N. E.; Marco, M. Org. Lett. 2002, 4, 2973–2976.
45. Thiot, C.; Schmutz, M.; Wagner, A.; Mioskowski, C. Angew.
Chem., Int. Ed. 2006, 45, 2868–2871.
34. Bastero, A.; Claver, C.; Ruiz, A.; Castillon, S.; Daura, E.; Bo,
C.; Zangrando, E. Chem.—Eur. J. 2004, 10, 3747–3760.
35. Bastero, A.; Ruiz, A.; Claver, C.; Milani, B.; Zangrando, E.
Organometallics 2002, 21, 5820–5829.
46. Xiong, Z.; Wang, N.; Dai, M.; Li, A.; Chen, J.; Yang, Z. Org.
Lett. 2004, 6, 3337–3340.
47. Badone, D.; Baroni, M.; Cardamone, R.; Ielmini, A.; Guzzi, U.
J. Org. Chem. 1997, 62, 7170–7173.
36. Bastero, A.; Ruiz, A.; Claver, C.; Castillon, S. Eur. J. Inorg.
Chem. 2001, 12, 3009–3011.
48. Proskurnina, M. V.; Lozinskaya, N. A.; Tkachenko, S. E.;
Zefirov, N. S. Russ. J. Org. Chem. 2002, 38, 1149–1153.
49. Bruno, A. J.; Chaberek, S.; Martell, A. E. J. Am. Chem. Soc.
1956, 78, 2723–2728.
50. Yung, D. K.; Chatten, L. G.; MacLeod, D. P. J. Pharm. Sci.
1968, 57, 2073–2080.
51. Linsker, F.; Evans, R. L. J. Am. Chem. Soc. 1945, 67, 1581–
1582.
52. Broadhead, G. D.; Osgerby, J. M.; Pauson, P. L. J. Chem. Soc.
1958, 650–656.
37. (a) Menges, F.; Neuburger, M.; Pfaltz, A. Org. Lett. 2002, 4,
4713–4716; (b) Guiu, E.; Claver, C.; Benet-Buchholz, J.;
Castillon, S. Tetrahedron: Asymmetry 2004, 15, 3365–3373.
38. Busacca, C. A.; Grossbach, D.; So, R. C.; O’Brien, E. M.;
Spinelli, E. M. Org. Lett. 2003, 5, 595–598.
39. For preparation of ferrocenylimidazoline derivatives, see: (a)
Peters, R.; Fischer, D. F. Org. Lett. 2005, 7, 4137–4140; For
ferrocenylimidazoline palladacycles catalyzed aza-Clasien
rearrangement reaction, see: (b) Peters, R.; Xin, Z.-q.;
Fischer, D. F.; Schweizer, W. B. Organometallics 2006, 25,
2917–2920; (c) Weiss, M. E.; Fischer, D. F.; Xin, Z.-q.;
53. Nametkin, N. S.; Shvekhgeimer, G. A.; Tyurin, V. D.;
Tutubalina, A. I.; Kosheleva, T. N. Izv. Akad. Nauk SSSR,
Ser. Khim. 1971, 1567–1569.