N-heterocyclic carbene adducts of cyclopalladated ferrocenylchloropyrimidine: Synthesis, structural characterization and application in the Sonogashira reaction

Article abstract of DOI:10.1007/s11243-012-9617-0

Three N-heterocyclic carbene (NHC) adducts of cyclopalladated ferrocenylchloropyrimidine, 2-4 [PdCl{[(n⁵-C₅H ₅)]Fe[(n⁵-C₅H₃)-N₂C ₄H₂-Cl]}(NHCs)] have been prepared by reaction of the chloride-bridged palladacyclic dimer 1 [PdCl{[(n⁵-C₅H ₅)]Fe[(n⁵-C₅H₃)-N₂C ₄H₂-Cl]}]₂ with the corresponding imidazolium salts. These complexes were characterized by elemental analysis, IR, ESI-MS and NMR. The use of these complexes as catalysts for the Sonogashira reaction was examined. Complex 4 proved to be an efficient catalyst for the Sonogashira reaction of aryl bromides and some activated aryl chlorides under copperand amine-free conditions. Typically, using 0.1-2 mol % of catalyst in the presence of 1.5 equivalents of CsOAc as base in dimethylacetamide at 120 °C provided coupling products in good yields. Springer Science+Business Media B.V. 2012.

Full text of DOI:10.1007/s11243-012-9617-0

Transition Met Chem
DOI 10.1007/s11243-012-9617-0
N-heterocyclic carbene adducts of cyclopalladated
ferrocenylchloropyrimidine: synthesis, structural characterization
and application in the Sonogashira reaction
Chen Xu
Wei-Jun Fu
•
Xin-Hua Lou
•
Zhi-Qiang Wang
•
Received: 13 April 2012 / Accepted: 4 May 2012
Ó Springer Science+Business Media B.V. 2012
Abstract Three N-heterocyclic carbene (NHC) adducts
of cyclopalladated ferrocenylchloropyrimidine, 2–4
moisture, and their cost and toxicity limit large-scale
applications. Moreover, use of copper reagents can result in
contamination of the coupling products with metal resi-
dues. Thus, a lot of effort is being made toward developing
alternatives for phosphine, copper- and amine-free condi-
tions for the Sonogashira reaction [6–9]. As an alternative,
N-heterocyclic carbenes (NHCs) and their transition metal
complexes have been the focus of intense research in orga-
nometallic chemistry and homogeneous catalysis [10, 11].
Most significantly, NHC palladium(II) complexes have been
successfully developed as highly active catalysts for cou-
pling reactions including the Sonogashira reaction [12–16].
In these cases, NHCs not only exhibit strong r-donor ability,
which could enhance the oxidative addition of aryl halides,
but also promote the reductive elimination of the coupling
products.
5
5
[
PdCl{[(g -C H )]Fe[(g -C H )-N C H -Cl]}(NHCs)] have
5
5
5
3
2 4 2
been prepared by reaction of the chloride-bridged palladacy-
5
5
clic dimer 1 [PdCl{[(g -C H )]Fe[(g -C H )-N C H -Cl]}]
5
5
5
3
2
4
2
2
with the corresponding imidazolium salts. These complexes
were characterized by elemental analysis, IR, ESI–MS and
NMR. The use of these complexes as catalysts for the So-
nogashira reaction was examined. Complex 4 proved to be
an efficient catalyst for the Sonogashira reaction of aryl
bromides and some activated aryl chlorides under copper-
and amine-free conditions. Typically, using 0.1–2 mol % of
catalyst in the presence of 1.5 equivalents of CsOAc as base
in dimethylacetamide at 120 °C provided coupling products
in good yields.
In recent years, a wide variety of palladacycles
have been reported and used in the Sonogashira reaction
Introduction
[
17–22]. However, among these, only a few phosphine
The palladium-catalyzed Sonogashira reaction of aryl or
vinyl halides with terminal acetylenes has become an
extremely powerful tool for carbon–carbon bond forma-
tion, widely applied in natural product synthesis and
material science [1, 2]. Usually, the Sonogashira reaction is
mediated by a phosphine–palladium complex with copper
cocatalyst and amine base [3–5]. However, many phos-
phine–palladium complexes are sensitive to both air and
adducts of palladacycles have proved to be efficient for the
Sonogashira reaction [23, 24]. To the best of our knowl-
edge, there have been no reports concerning the NHC
adducts of palladacycles as catalysts for the Sonogashira
reaction. We have found that NHC adducts of pallada-
cycles are very efficient catalysts for coupling reactions
[25, 26]. These precatalysts combine the stability induced
by the presence of a palladacycle framework with the high
activity commonly associated with NHC ligands and are
far more active than the corresponding dimeric pallada-
cycles. In view of these findings and our continuous
interest in the synthesis and application of NHC palla-
dium(II) complexes [27–29], we have prepared three NHC
adducts of palladacycles, 2–4 (Scheme 1) and examined
their catalytic activity in the Sonogashira reaction. The
results of our studies are reported in this paper.
C. Xu (&) Á X.-H. Lou Á Z.-Q. Wang Á W.-J. Fu
College of Chemistry and Chemical Engineering, Luoyang
Normal University, Luoyang 471022, Henan, China
e-mail: xubohan@163.com
123

Transition Met Chem
Scheme 1 Synthesis of N-
heterocyclic carbene adducts of
cyclopalladated complexes 2–4.
Cl
Cl
Ar
N
N
2
(R
1
= H; R
= H; R = OCH
= CH(CH ; R
2
2
= CH
3
), 3
),
= H)
Cl
N
N
N
Fe
(
R
1
2
3
tBuOK, THF
Fe
Pd
Pd Cl
4
(R
1
3
)
2
Cl
R1
N
2
Ar
N
Ar
-4
Ar =
R2
Ar
N
1
2
R1
5
5
Experimental
[PdCl{[(g -C H )]Fe[(g -C H )-N C H -Cl]}(C N H )-
5
5
5
3
2
4
2
3 2 2
1
C H -OCH ) ] (3): Red solid, yield 93 %. H NMR
(
6 4 3 2
Solvents were dried and freshly distilled prior to use. All
other chemicals were commercially available expect for the
imidazolium salts and the chloride-bridged palladacyclic
dimer 1, which were prepared according to the published
procedures [30, 31]. Elemental analyses were determined
with a Carlo Erba 1160 Elemental Analyzer. IR spectra
were collected on a Bruker VECTOR22 spectrophotometer
using KBr pellets. NMR spectra were recorded on a Bruker
(400 MHz, CDCl ): d 9.32 (s, 1H, py), 8.34 (d, J = 8.8 Hz,
3
2H, Ar), 7.77 (d, J = 8.8 Hz, 2H, Ar), 7.42 (s, 1H,
NCHCHN), 7.36 (s, 1H, NCHCHN), 7.14 (d, J = 8.8 Hz,
2H, Ar), 6.95 (s, 1H, py), 6.85 (d, J = 8.8 Hz, 2H, Ar), 4.49
(s, 1H, C H ), 4.31 (s, 1H, C H ), 3.82 (s, 3H, OCH ), 3.74
5
3
5
3
3
13
C
(s, 3H, OCH ), 3.51 (s, 5H, C H ), 3.49 (s, 1H, C H ).
5
3
5
5 3
NMR (100 MHz, CDCl ): 173.5 (NCN), 165.2, 150.5,
3
147.1, 140.1, 138.7, 136.3, 134.2, 132.8, 127.7, 125.6, 123.1,
117.6, 116.1, 114.8, 94.3, 87.1, 73.2, 70.0 (CH, Fc-unsubst.),
DPX-400 spectrometer in CDCl with TMS as internal
3
?
68.6, 63.0, 55.9 (OCH ), 55.7 (OCH ). MS–ESI : m/z
standard. Mass spectra were measured on a LC-MSD-Trap-
XCT instrument.
3
3
?
-1
683.0 [M –Cl]. IR (KBr, cm ): 3064(w), 2956(w),
605(m), 1579(s), 1518(w), 1486(m), 1442(m), 1418(m),
1303(w), 1246(s), 1174(m), 1128(m), 1028(m), 973(w),
44(w), 898(w), 833(s), 783(m), 744(m), 697(m), 674(m).
Anal. Calcd for C H Cl FeN O Pd: C, 51.7; H, 3.6;
1
Synthesis of complexes 2–4
9
A Schlenk tube was charged with the palladacyclic dimer 1
(0.1 mmol), the corresponding imidazolium salt (0.25 mmol)
t
and BuOK (0.3 mmol) under nitrogen. Dry THF was added via
31
26
2
4 2
N, 7.8. Found: C, 52.0; H, 3.3; N, 8.1.
5
5
[PdCl{[(g -C H )]Fe[(g -C H )-N C H -Cl]}(C N H )-
5
5
5
3
2
4
2
3 2 2
1
a cannula, and the mixture was stirred at room temperature for
(C H -2C H ) ] (4): Red solid, yield 88 %. H NMR
6 3 3 7 2
3
h. The product was separated by passing through a short silica
(400 MHz, CDCl ): d 9.37 (s, 1H, py), 7.40–7.77 (m, 4H,
3
gel column with CH Cl as eluent, and the second band was
2
NCHCHN ? Ar), 7.21 (d, J = 8.8 Hz, 2H, Ar), 7.07 (d,
J = 8.8 Hz, 2H, Ar), 6.91 (s, 1H, py), 4.58 (m, 1H, CH),
4.44 (s, 1H, C H ), 4.12 (m, 1H, CH), 4.02 (s, 1H, C H ),
2
collected and afforded the corresponding carbene adducts of
cyclopalladated ferrocenylpyrimidine 2–4.
5
5
3
5 3
5
[
PdCl{[(g -C H )]Fe[(g -C H )-N C H -Cl]}(C N H )-
3.74 (s, 1H, C H ), 3.42 (s, 5H, C H ), 3.11 (m, 1H, CH),
5 3 5 5
5
5
5
3
2
4
2
3
2
2
1
C H -CH ) ] (2): Red solid, yield 86 %. H NMR
(
2.90 (m, 1H, CH), 1.54–1.58 (m, 6H, CH ), 1.52 (d,
3
6
4
3 2
(
400 MHz, CDCl ): d 9.33 (s, 1H, py), 8.31 (d, J =
J = 6.0 Hz, 3H, CH ), 1.42 (d, J = 6.0 Hz, 3H, CH ),
3
3
3
8
.8 Hz, 2H, Ar), 7.76 (d, J = 8.8 Hz, 2H, Ar), 7.46 (s, 1H,
NCHCHN), 7.42 (d, J = 8.8 Hz, 2H, Ar), 7.37 (s, 1H,
NCHCHN), 7.12 (d, J = 8.8 Hz, 2H, Ar), 6.94 (s, 1H, py),
1.27 (d, J = 6.0 Hz, 3H, CH ), 1.09 (d, J = 6.0 Hz, 3H,
3
CH3), 0.99 (d, J = 6.0 Hz, 3H, CH3), 0.57 (d,
1
3
J = 6.0 Hz, 3H, CH3). C NMR (100 MHz, CDCl3):
175.3 (NCN), 164.9, 150.6, 148.4, 147.3, 145.9, 145.1,
140.5, 137.2, 136.6, 130.7, 125.5, 125.2, 124.7, 123.6,
117.5, 114.0, 95.9, 86.7, 72.1, 70.2 (CH, Fc-unsubst.),
69.3, 62.6, 29.3, 29.1, 28.7, 28.3, 27.8 (CH ), 27.1 (CH ),
4
.49 (s, 1H, C H ), 4.31 (s, 1H, C H ), 3.50 (s, 1H, C H ),
5 3 5 3 5 3
3
.48 (s, 5H, C H ), 2.37 (s, 3H, CH ), 2.26 (s, 3H, CH ).
3
5
5
3
1
3
C NMR (100 MHz, CDCl ): 171.2 (NCN), 164.0, 150.3,
3
1
1
44.7, 140.6, 139.3, 137.0, 134.9, 132.4, 127.2, 124.6,
23.0, 117.2, 115.7, 114.6, 94.1, 87.3, 72.8, 70.4 (CH,
3
3
25.2 (CH ), 25.0 (CH ), 23.8 (CH ), 23.7 (CH ), 23.2
3
3
3
3
?
?
Fc-unsubst.), 68.2, 62.7, 22.7 (CH3), 21.5 (CH3).
?
MS–ESI : m/z 651.0 [M –Cl]. IR (KBr, cm ): 3086(w),
(CH ), 21.4 (CH ). MS–ESI : m/z 791.2 [M –Cl]. IR
3 3
?
-1
-1
(KBr, cm ): 3072(w), 2964(m), 1577(s), 1519(m),
1491(m), 1462(m), 1419(m), 1398(m), 1328(w), 1266(m),
1203(m), 1129(m), 1005(w), 924(m), 910(s), 817(m),
805(m), 784(m), 759(m), 724(s), 699(m). Anal. Calcd
for C H Cl FeN Pd: C, 59.5; H, 5.6; N, 6.8. Found:
2
1
9
923(w), 1574(s), 1515(s), 1408(s), 1357(s), 1344(m),
276(m), 1184(m), 1129(w), 1106(m), 1080(w), 1015(w),
82(w), 860(m), 819(s), 781(s), 732(s), 708(s), 689(m).
Anal. Calcd for C H Cl FeN Pd: C, 54.1; H, 3.8; N, 8.2.
3
1
26
2
4
41 46
2
4
Found: C, 54.4; H, 3.6; N, 8.4.
C, 59.8; H, 5.3; N, 7.0.
1
23

Transition Met Chem
General procedure for the Sonogashira reaction
Application in the Sonogashira reaction
In a Schlenk tube, a mixture of the prescribed amount of
catalyst, plus aryl halide (1.0 mmol), alkyne (1.2 mmol)
and the selected base (1.5 mmol) in solvent (3 mL) was
purged with nitrogen. The reaction mixture was then heated
at 120 °C for 12–24 h. After this, water was added, and the
mixture was extracted with ethyl acetate. The solvent was
removed under reduced pressure. The residue was isolated
by flash chromatography on silica gel to afford the desired
coupled products, which were identified by comparing
To evaluate the catalytic activity of these complexes, the
Sonogashira reactions of terminal alkynes with aryl bro-
mides were studied under copper- and amine-free condi-
tions (Scheme 1). Our initial exploration of the reaction
conditions focused on the coupling of bromobenzene with
phenylacetylene in the presence of 1 mol % of complex 4
at 120 °C for 12 h (Table 1). After screening a variety of
bases (entries 1–8), CsOAc was found to give the best
results (86 % yield), while KOAc and Cs CO displayed
2
3
1
melting points or H NMR spectra with those found in the
moderate efficiency (69–73 % yields). Next, a quick survey
of solvents indicated that DMA (at 120 °C) was much better
than other solvents such as acetonitrile, toluene, dioxane,
DMSO and DM (entries 9–13). The activities of complexes
1–3 in the same model reaction were then investigated
literature [6, 7, 22, 32].
Results and discussion
(entries 14–16). The dimeric complex 1 generated the
Synthesis and characterization
product in low yield, but complexes 2–3 displayed moderate
efficiency (entries 14–16). The triphenylphosphine adduct of
cyclopalladated ferrocenylimine is known to be an effective
precatalyst for the Sonogashira reaction of bromobenzene
with phenylacetylene in the presence of KOAc in DMA,
giving 60 % yield [24]. For comparison, using 1 mol % of
complex 4 for the above coupling reaction under the same
conditions provided the coupled product in 87 % yield (entry
17).
Three new NHC adducts of palladacycles, complexes 2–4,
have been easily prepared by reaction of the chloride-
bridged palladacyclic dimer 1 with the corresponding
t
imidazolium salts in the presence of BuOK in THF at room
temperature under N (Scheme 1). This one-pot synthesis
2
avoids multistep reactions employing free carbenes [33]. All
the new palladacycles are air- and moisture-stable, both in
the solid state and in solution. They are very soluble in
chloroform, dichloromethane and acetone, but insoluble in
petroleum ether and n-hexane.
Under the optimized reaction conditions (complex 4,
CsOAc, DMA), Sonogashira reactions of arylacetylenes
with a variety of electronically and structurally diverse aryl
bromides were carried out to explore the scope of this
system (Table 2). The catalyst system was very effective
for the coupling of 1-bromonaphthalene with phenylacet-
ylene, giving the product in 96 % yield (entry 1). Other
products were isolated in good yields for deactivated aryl
bromide substrates with this system (entries 2–3). Ortho-
substituents were tolerated, giving the products in 87–90 %
isolated yields (entries 4–5). For the activated aryl com-
pounds such as 4-bromonitrobenzene, 4-bromoacetophe-
none and 4-bromobenzonitrile, it was not surprising that
excellent yields were obtained with a catalytic loading as
low as 0.1 mol % by prolonging the reaction time from 12
to 24 h (entries 6–10). In addition, heterocyclic bromides
were found to be efficient coupling partners in this system
(entries 11–13). Similar to the results for phenylacetylene,
good yields (84–93 %) were also obtained for the reactions
of p-tolyacetylene with aryl bromides (entries 14–18).
Complexes 2–4 were characterized by elemental anal-
ysis, IR and ESI–MS, which were consistent with the
proposed structures. In the mass spectra of 2–4, the most
?
1
intense peak was attributed to [M-Cl] . The H NMR
spectra of these complexes exhibit peaks for the Cp ring
with the proton ratio of 1:1:1:5, clearly showing that they
are ortho-cyclopalladated products. The pyrimidine signals
are observed as singlets at d 9.33, 6.94; d 9.32, 6.95; and
9
1
.37, 6.91, for complexes 2, 3 and 4, respectively. The
H NMR spectra showed only one set of signals in a
symmetrical environment indicating the exclusive forma-
tion of one isomer. The backbone protons (–NCHCHN–) of
the NHCs are observed at d 7.46, 7.37; 7.42, 7.36; and
7
.48, 7.40 for the complexes 2, 3 and 4, respectively. The
benzene ring protons of the NHCs for complexes 2 and 3
appear as doublets at d 8.31, 7.76, 7.42, 7.12 and 8.34,
7
.77, 7.14, 6.85, respectively. Those in complex 4 appear at
d 7.74, 7.21, 7.07. Complexes 2 and 3 both exhibit two
singlets for the methyl groups of the NHCs at d 2.26, 2.37
and 3.74, 3.82, respectively, while 4 exhibits corresponding
doublet peaks at d 0.56–1.58. Additional evidence for the
Cat
Base, Solvent
+
Ar
X
Ar
R
R
1
3
R = H, CH3
X = Br, Cl
proposed structures was obtained from the C NMR
spectra, with carbon signals (NCN) of the NHCs at d 171.2,
Scheme 2 The Sonogashira reaction of terminal alkynes with aryl
halides
1
73.5 and 175.3 for complexes 2, 3 and 4, respectively.
123

Transition Met Chem
Table 1 Optimization of reaction conditions for the Sonogashira
reaction of bromobenzene with phenylacetylene
Table 2 The Sonogashira reaction of aryl bromides with arylacety-
lene catalyzed by complex 4
o
Solvent/T ( C)
a
a
Entry
Catalyst
mol%)
Base
Yield
(%)
Entry
R
Ar
Catalyst
(mol%)
Yield
(%)
(
1
2
3
4
5
6
7
8
9
4 (1)
4 (1)
4 (1)
4 (1)
4 (1)
4 (1)
4 (1)
4 (1)
4 (1)
4 (1)
4 (1)
4 (1)
4 (1)
1 (0.5)
2 (1)
3 (1)
4 (1)
Na
CO
CO
NaOH
PO
2
CO
3
DMF/120
DMF/120
DMF/120
DMF/120
DMF/120
DMF/120
DMF/120
DMF/120
38
46
69
27
32
35
73
86
54
43
67
81
95
40
61
68
87
1
2
3
4
5
6
7
H
H
H
H
H
H
Naphthalen-1-yl
1
1
1
96
94
92
90
87
98
95
93
94
91
89
86
80
93
90
85
88
84
K
2
3
p-MeC
p-MeOC
o-MeC
o-MeOC
p-NO
6
H
4
Cs
2
3
6
H
4
H
6 4
K
3
4
6
H
4
1
t
BuOK
2
6
C H
4
1
KOAc
0.5
0.1
0.5
0.1
0.5
0.5
1
b
8
CsOAc
CsOAc
CsOAc
CsOAc
CsOAc
CsOAc
CsOAc
CsOAc
CsOAc
KOAc
CH
3
CN/80
9
H
p-MeOCC
H
6 4
b
10
11
12
13
14
15
16
17
Toluene/100
Dioxane/100
DMSO/120
DMA/120
DMA/120
DMA/120
DMA/120
DMA/80
10
H
p-CNC H
6 4
11
12
H
pyridin-2-yl
pyridin-3-yl
H
b
13
H
Thiophen-2-yl
Ph
b
c
14
15
16
p-Me
p-Me
p-Me
p-Me
p-Me
1
p-MeC
o-MeC
6
H
4
1
H
6 4
1
b
17
p-NO
2 6
C H
4
0.1
0.5
1
8
pyridin-2-yl
Reaction conditions: bromobenzene (1.0 mmol), phenylacetylene
1.2 mmol), base (1.5 mmol), solvent (3 mL), 12 h
(
a
Reaction conditions: aryl bromides (1.0 mmol), arylacetylene
(1.2 mmol), CsOAc (1.5 mmol), DMA (3 mL), 120 °C, 12 h
Isolated yields (average of two experiments)
b
c
a
0
.5 mol % of the dimer
Isolated yields (average of two experiments)
b
n-Bu NBr (1.5 mmol)
4
24 h
Finally, Sonogashira couplings of phenylacetylene with
reaction of aryl bromides and some activated aryl chlorides
under copper- and amine-free conditions. Further efforts to
extend the applications involving this type of palladacycle
in other palladium-catalyzed reactions are under way in our
laboratory.
aryl chlorides were also studied in this system (Table 3).
For activated chlorides such as 4-chloronitrobenzene,
4
-chloro benzonitrile and 4-chloroacetophenone, the cou-
pled products were obtained in moderate yields by using
mol % of complex 4 (entries 1–3). However, for chlo-
1
robenzene, complex 4 showed low activity under the same
conditions (entry 4). Increasing the catalyst loading to
Table 3 The Sonogashira reaction of aryl chlorides with phenyl-
acetylene catalyzed by 4
2
mol % gave only moderate yield (60 %, entry 5) upon the
a
Entry
Ar
Catalyst
(mol%)
Yield
(%)
addition of CuI as a cocatalyst. Reactions of electron-rich
aryl chlorides such as 4-chlorotoluene, 4-chloroanisoles also
gave moderate yields (entries 6–7). Furthermore, couplings
of heteroaryl chlorides with phenylacetylene were exam-
ined. In the case of 2-chloropyridine, using 1 mol % of
complex4 affordedthe product in a 63 % yield, and the result
was slightly better than that obtained for 3-chloropyridine
1
2
3
4
p-NO
2
C
6
H
4
1
1
1
1
2
2
2
1
1
76
71
67
25
60
58
54
63
51
6 4
p-CNC H
6 4
p-MeOCC H
Ph
b
5
b
6
p-MeC
6 4
H
(
entries 8–9).
b
7
p-MeOC H
6 4
8
pyridin-2-yl
pyridin-3-yl
b
9
Conclusion
Reaction conditions: aryl chlorides (1.0 mmol), phenylacetylene
(1.2 mmol), CsOAc (1.5 mmol), DMA (3 mL), 120 °C, 24 h
In summary, we have prepared and characterized three new
a
N-heterocyclic carbene adducts of palladacycles. Complex
4
Isolated yields (average of two experiments)
b
was found to be an efficient catalyst for the Sonogashira
3 mol% CuI
1
23

Transition Met Chem
Acknowledgments We are grateful to the National Natural Science
Foundation of China (No. 20902043) and the Natural Science
Foundation of Henan Province and Henan Education Department,
China (No. 102300410220 and 2009B150019) for financial support of
this work.
17. Dupont J, Pfeffer
Weinheim
18. Eberhard MR, Wang ZH, Jensen CM (2002) Chem Commun 818
19. Alonso DA, Botella L, N a´ jera C, Pacheco MC (2004) Synthesis
1713
M (2008) Palladacycles. Wiley-VCH,
2
0. In e´ s B, SanMartin R, Churruca F, Dom ´ı nguez E, Urtiaga MK,
Arriortua MI (2008) Organometallics 27:2833
1. Zhang BS, Wang C, Gong JF, Song MP (2009) J Organomet
Chem 694:2555
2
References
2
2
2. Alonso DA, N a´ jera C (2010) Chem Soc Rev 39:2891
3. Consorti CS, Fabricio RF, Rominger F, Dupont J (2006) Adv
Synth Catal 348:133
1
2
3
. Chinchilla R, N a´ jera C (2007) Chem Rev 107:874
. Chinchilla R, N a´ jera C (2011) Chem Soc Rev 40:5084
. Kanda K, Koike T, Endo K, Shibata T (2009) Chem Commun
2
2
2
2
2
2
3
3
4. Yang F, Cui XL, Li YN, Zhang JL, Ren GR, Wu YJ (2007)
Tetrahedron 63:1963
5. Xu C, Li HM, Liu H, Zhang ZQ, Wang ZQ, Fu WJ, Zhang YQ
1
870
. Merkul E, Boersch C, Frank W, M u¨ ller TJJ (2009) Org Lett
1:2269
4
1
(
2012) Inorg Chim Acta 386:22
5
6
. Severin R, Reimer J, Doye S (2010) J Org Chem 75:3518
. Gholap AR, Venkatesan K, Pasricha R, Daniel T, Lahoti RJ,
Srinivasan KV (2005) J Org Chem 70:4869
. Yi CY, Hua RM (2006) J Org Chem 71:2535
. Gu SJ, Chen WZ (2009) Organometallics 28:909
. Samantaray MK, Shaikh MM, Ghosh P (2009) J Organomet
Chem 694:3477
0. Enders D, Niemeier O, Henseler A (2007) Chem Rev 107:5606
1. Hahn FE, Jahnke MC (2008) Angew Chem Int Ed 47:3122
2. Ma YD, Song SC, Jiang W, Wu QS, Wang Y, Liu XY, Andrus
MB (2003) Org Lett 5:3317
6. Xu C, Li HM, Wang ZQ, Fu WJ, Zhang YQ, Ji BM (2012) Aust J
Chem. doi:10.1071/CH12035
7. Xu C, Wang ZQ, Li Z, Wang WZ, Hao XQ, Fu WJ, Gong JF,
Ji BM, Song MP (2012) Organometallics 31:798
8. Xu C, Hao XQ, Li Z, Dong XM, Duan LM, Wang ZQ, Ji BM,
Song MP (2012) Inorg Chem Commun 17:34
9. Xu C, Li Z, Duan LM, Wang ZQ, Fu WJ, Hao XQ, Song MP
7
8
9
1
1
1
(
2012) Transition Met Chem. doi:10.1007/s11243-012-9598-z
0. Delaude L, Szypa M, Demonceau A, Noels AF (2002) Adv Synth
Catal 344:749
1. Xu C, Zhang YP, Wang ZQ, Fu WJ, Hao XQ, Xu Y, Ji BM
1
1
3. Viciu MS, Nolan SP (2005) Top Organomet Chem 14:241
4. Kantchev EAB, O’Brien CJ, Organ MG (2007) Angew Chem Int
Ed 46:2768
5. John A, Ghosh P (2010) Dalton Trans 39:7183
6. Fortman GC, Nolan SP (2011) Chem Soc Rev 40:5151
(
2. Li PH, Wang L, Li H (2005) Tetrahedron 61:8633
2010) Chem Commun 6852
3
3
3. Frey GD, Sch u¨ tz J, Herrmann WA (2006) J Organomet Chem
6
1
1
91:2403
123