Ferrocenyl bisoxazoline as an efficient non-phosphorus ligand for palladium-catalyzed copper-free Sonogashira reaction in aqueous solution

Article abstract of DOI:10.1002/aoc.4156

Pd(OAc)₂-catalyzed Sonogashira coupling reactions of alkynes and a variety of aryl halides with 1,3-bis(5-ferrocenylisoxazoline-3-yl)benzene as an efficient non-phosphorus ligand under copper-free conditions are presented. The main advantages over previous methodologies include low catalyst loading (0.2 mol% Pd(OAc)₂ and 0.4 mol% ferrocenyl bisoxazoline ligand are sufficient for these coupling reactions), less problematic reaction medium (water–dimethylformamide) and more convenient operation (no requirement for nitrogen protection).

Full text of DOI:10.1002/aoc.4156

Received: 9 July 2017
DOI: 10.1002/aoc.4156
Revised: 27 September 2017
Accepted: 29 September 2017
F U L L P A P E R
Ferrocenyl bisoxazoline as an efficient non‐phosphorus
ligand for palladium‐catalyzed copper‐free Sonogashira
reaction in aqueous solution
Shuyan Yu1
| Jingxin Wu1 | Xinwei He2
| Yongjia Shang2
1 Material and Chemical Engineering
College, Zhengzhou University of Light
Industry, Zhengzhou 450001, Henan
Province, People's Republic of China
2 College of Chemistry and Materials
Science, Anhui Normal University, Wuhu
241000, Anhui Province, People's Republic
of China
Pd(OAc)2‐catalyzed Sonogashira coupling reactions of alkynes and a variety of
aryl halides with 1,3‐bis(5‐ferrocenylisoxazoline‐3‐yl)benzene as an efficient
non‐phosphorus ligand under copper‐free conditions are presented. The main
advantages over previous methodologies include low catalyst loading (0.2 mol%
Pd(OAc)2 and 0.4 mol% ferrocenyl bisoxazoline ligand are sufficient for these cou-
pling reactions), less problematic reaction medium (water–dimethylformamide)
and more convenient operation (no requirement for nitrogen protection).
Correspondence
Shuyan Yu, Material and Chemical
Engineering College, Zhengzhou
University of Light Industry, Zhengzhou
450001, China.
KEYWORDS
copper‐free conditions, non‐phosphorus ligand, Sonogashira reaction
Email: yushuyan86@163.com
Yongjia Shang, College of Chemistry
and Materials Science, Anhui Normal
University, Wuhu 241000, China.
Email: shyj@mail.ahnu.edu.cn
Funding information
Doctoral Research Fund of Zhengzhou
University of Light Industry, Grant/Award
Number: 2014BSJJ009; Foundation of
Henan Educational Committee, Grant/
Award Number: 17A150022; National
Natural Science Foundation of China,
Grant/Award Number: 21372008 and
21602207
1 | INTRODUCTION
include phosphine‐ligated palladium catalysts together
with CuI as a co‐catalyst under degassed conditions.[7]
The coupling of aryl or vinyl halides (or triflate) with
terminal alkynes catalyzed by palladium, commonly
termed Sonogashira cross‐coupling reactions, has been
recognized as one of the most important sp2–sp carbon–
carbon bond formation reactions in organic synthesis.[1]
The resulting internal alkynes or enynes are important
intermediates for pharmaceuticals,[2] natural products,[3]
biologically active molecules,[4] conducting polymers[5]
and optical and liquid‐crystal materials.[6] The most com-
monly utilized catalytic systems for these reactions
However, phosphine ligands suffer some drawbacks, such
as sensitivity to air and moisture, requirement for an inert
environment and large amounts of palladium source for
carrying out the reaction.[8] Also, the presence of
copper(I) could result in the formation of some Cu(I)
acetylides in situ that can readily induce oxidative
homocoupling reactions of alkynes.[9] Hence, the develop-
ment of new non‐phosphorus ligands with adequate activ-
ity to avoid the use of copper has become an important
topic of research in organic synthesis.[10] Among them,
Appl Organometal Chem. 2017;e4156.
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Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4156

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YU ET AL.
N‐donor ligands have attracted widespread interest owing
to their easy availability, non‐toxicity and high stabil-
conditions, and the effects of various parameters such as
solvent, base, temperature and amount of catalyst were
investigated. The obtained results were summarized in
Table 1. The coupling reaction was firstly conducted with
different bases and water was chosen as solvent consider-
ing its safety, non‐toxicity and economical availability. To
our delight, the desired internal arylalkynes could be
obtained with good yields and piperidine turned out to
be the most efficient base. An aqueous solution of
dimethylformamide (DMF) and water (1:1 v/v) was better
than neat water (Table 1, entries 1–6). It was also found
that the reaction temperature had a great influence on
this reaction. An improvement in the yield could be
achieved at 60°C. Higher and lower reaction temperature
proved to be unsuitable (Table 1, entries 5, 7 and 8).
Tetrabutylammonium bromide (TBAB) was necessary
which could serve as a phase‐transfer catalyst for this het-
erogeneous transformation (Table 1, entry 7 versus 9).
The influence of catalyst loading and ratio of catalysts
was also investigated, with the result that 0.2 mol%
Pd(OAc)2 was determined as the optimal amount with
0.4 mol% 1,3‐bis(5‐ferrocenylisoxazoline‐3‐yl)benzene as
the ideal ligand (Table 1, entries 7 and 10–13). A control
experiment was conducted to explore the role of this
ferrocenyl bisoxazoline ligand, and the obtained result
indicated that this ligand indeed provides significant coor-
dinated property to the metal center. Without the non‐
phosphorus ligand, the desired coupling product was
ity.[11] Prompted by these advantages,
a program
concerning to the synthesis and application of novel nitro-
gen‐based ligands was undertaken in our laboratory.[12]
The ferrocenyl group was expected to be introduced
into these novel ligands considering that it could provide
a special and unique geometry and potential control
of the reactivity of the coordinated metal center via its
redox activity.[13]
In 2014, 1,3‐bis(5‐ferrocenylisoxazoline‐3‐yl)benzene
was conveniently synthesized through 1,3‐dipolar cyclo-
addition of vinylferrocene and nitrile oxide of 1,3‐
benzenedialdehyde in high yield and with excellent
diastereoselectivity in our laboratory (Scheme 1a).[14]
.
Further investigation showed that it could serve as an effi-
cient non‐phosphorus ligand in palladium‐catalyzed Heck
coupling reactions with neat water as solvent (Scheme 1b).
Prompted by these findings, in the work reported herein
we further explored its performance in palladium‐cata-
lyzed Sonogashira coupling reactions under copper‐free
conditions (Scheme 1c).
2 | RESULTS AND DISCUSSION
The reaction of iodobenzene with phenylacetylene was
chosen as a model reaction to optimize the reaction
(a) Synthesis of 1, 3-bis-(5-ferrocenylisoxazoline-3-yl) benzene
NH OH
(1) NCS
HCl
2
N
N
OHC
CHO
(2) Et N
3
HO
OH
Fe
N
N
O
Fe
O
N
O
N
Fe
O
(b) Palladium/1,3-bis-(5-ferrocenylisoxazoline-3-yl) benzene catalyzed Heck reaction (previuos work)
Pd(OAc) (0.2 mol%),
2
bisoxazoline Ligand (0.4 mol%)
2
3
R
R
2
R
X
3
+
R
1
R
NaOAc, TBAB,H O
2
80-100oC, 3-6h
1
R
2
3
R
R
= H or Ph
= EWG group
X = I, Br, Cl
Low catalys t loading!
Water as s olvent!
No N protection!
2
(c) Palladium/1,3-bis-(5-ferrocenylisoxazoline-3-yl) benzene catalyzed Sonogashira reaction (this work)
Pd(OAc)
2
SCHEME 1 Synthesis of 1,3‐bis(5‐
ferrocenylisoxazoline‐3‐yl)benzene and its
application in palladium‐catalyzed
coupling reactions
bisoxazoline Ligand
2
2
+
X
R
R
1
1
R
copper-free condition
??
R
2
R
= aryl or alkyl
X = I, Br, Cl

YU ET AL.
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TABLE 1 Optimization of coupling reaction conditions
Entry
Solvent
Base
Additive
Temperature (°C)
Time (h)
Yield (%)
1a
H2O
NaOAc
TBAB
80
4
77
2a
H2O
K2CO3
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
—
80
80
80
80
80
60
40
60
60
60
60
60
60
5
4
4
3
3
4
7
6
3
6
6
4
6
75
83
80
91
88
95
84
71
94
81
83
94
22
3a
H2O
Piperidine
NEt3
4a
H2O
5a
DMF–H2O
DMF
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
6a
7a
8a
DMF–H2O
DMF–H2O
DMF–H2O
DMF–H2O
DMF–H2O
DMF–H2O
DMF–H2O
DMF–H2O
9a
10b
11c
12d
13e
14f
TBAB
TBAB
TBAB
TBAB
TBAB
aReaction performed under the following conditions: iodobenzene(1 mmol), phenylacetylene (1.2 mmol), Pd(OAc)2 (0.2 mol%), 1,3‐bis(5‐ferrocenylisoxazoline‐3‐
yl)benzene (0.4 mol%), base (2 mmol) and TBAB (0.25 mmol) in 5 mL of solvent under air.
bAmount of Pd(OAc)2 catalyst increased to 0.5 mol% and 1,3‐bis(5‐ferrocenylisoxazoline‐3‐yl)benzene to 1.0 mol%.
cAmount of Pd(OAc)2 catalyst decreased to 0.1 mol% and 1,3‐bis(5‐ferrocenylisoxazoline‐3‐yl)benzene to 0.2 mol%. Uncompleted conversion was observed.
d0.2 mol% Pd(OAc)2 and 0.2 mol% ligand were used. The reaction could not fully transform and Pd black was observed in the flask.
e0.2 mol% Pd(OAc)2 and 0.6 mol% ligand were used.
fReaction was catalyzed using only 0.2 mol% Pd(OAc)2 and no ligand was added.
obtained in only 22% yield and marked homocoupling of
phenylacetylene was observed (Table 1, entry 14). Nota-
bly, all these reactions were conducted in air atmosphere,
indicating high thermal stability of the developed catalytic
system.
delight, aryl bromides were also ideal coupling substrates
and all the reactions could be accomplished in 3–6 h with
good to excellent yields (Table 2, entries 15–22). As for
inactive aryl chlorides, the coupling product could be
obtained in moderate yield at higher temperature. And
inspiringly, the efficiency could be improved by slightly
increasing the loading of catalyst (Table 2, entries 22
and 23). It is worth noting that little homocoupling prod-
ucts of alkynes was observed in these coupling reactions.
Based on these results, the optimal conditions were
determined (Table 1, entry 7). The scope of the terminal
alkynes was then examined. As evident from Table 2,
various terminal alkynes performed well in this catalytic
system. The corresponding products could be collected
in satisfactory yields (Table 2, entries 1–9). The electronic
effect of substituents of the arylalkynes seemed to have
little effect on these coupling reactions (Table 2,
entries 1–6). Also, alkylalkynes were equally applicable
(Table 2, entries 7–9). The generality of the reaction with
respect to aryl halide coupling partners was also investi-
gated. Compared to the weak steric effect of substituents
on the aryl halides (Table 2, entries 12–14), the electron
effect seemed to be more sensitive. The reactions of aryl
halides with nitro group could be accomplished in shorter
time and higher yields than those with electron‐releasing
groups (Table 2, entry 12 versus entries 10 and 11). To our
3 | CONCLUSIONS
1,3‐Bis(5‐ferrocenylisoxazoline‐3‐yl)benzene was found
to be an excellent non‐phosphorus ligand in palladium‐
catalyzed coupling reactions under copper‐free condi-
tions. The developed catalytic system is applicable for a
broad spectrum of substrates, affording the desired
coupling products in good to excellent yield with low
catalyst loading. Notably, further investigation of the real
catalytic species and its asymmetric version is underway
in our laboratory.

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YU ET AL.
TABLE 2 Examination of reaction scopea
Entry
Temperature (°C)
Time (h)
Product
Yield (%)b
1
60
4
95
2
60
60
60
60
60
40
60
60
60
4
4
3
3
3
6
4
4
4
92
94
94
95
92
87
85
90
89
3
4
5
6
7
8
9
10
11
12
13
14
60
40
40
40
4
3
5
3
87
94
92
94
15
16
70
60
4
5
90
93
(Continues)

YU ET AL.
5 of 7
TABLE 2 (Continued)
Entry
Temperature (°C)
Time (h)
Product
Yield (%)b
17
60
3
92
18
19
60
60
4
3
90
95
20c
21c
70
70
6
6
88
86
22
90
90
6
6
53
87
23d
aUnless mentioned, the reaction was performed with the following conditions: aryl halide(1 mmol), terminal alkyne (1.2 mmol), Pd(OAc)2 (0.2 mol%), 1,3‐bis(5‐
ferrocenylisoxazoline‐3‐yl)benzene (0.4 mol%), piperidine (2 mmol) and TBAB (0.25 mmol) in 5mL of DMF–H2O (1:1) under air.
bIsolated yield after flash chromatography.
cAryl halide (1 mmol) and terminal alkyne (2.4 mmol) were used and the double‐coupling product was obtained.
dReaction was conducted with 0.5 mol% Pd(OAc)2 and 1 mol% 1,3‐bis(5‐ferrocenylisoxazoline‐3‐yl)benzene.
dehydration of 1‐ferrocenylethanol following a previously
reported method.[14]
4 | EXPERIMENTAL
4.1 | General
Aldoxime (1 mmol) and chlorosuccinimide (2 mmol)
were stirred in 3 mL of dry dichloromethane (DCM) and
1.5 mL of DMF at 30°C for about 3 h. After the complete
conversion of aldoxime, vinylferrocene (2 mmol) was
added followed by dropwise addition of 0.28 mL of
triethylamine in 3 mL of DCM over 1.5 h and the mixture
was stirred overnight at room temperature. The formed
solid was filtered and washed with DCM to afford gold
crystals of the desired ferrocenyl isoxazoline ligand.
Yield: 90%; m.p. 237–238°C. 1H NMR (300 MHz,
CDCl3, δ, ppm): 8.03 (s, 1H), 7.78 (d, J = 7.8 Hz, 2H),
7.48 (t, J = 7.8 Hz, 1H), 5.58 (t, J = 9.0 Hz, 2H), 4.20–
4.48 (m, 18H), 3.68 (dd, J = 9.0 Hz, 10.8 Hz, 2H), 3.42
(dd, J = 9.0 Hz, 10.8 Hz). 13CNMR (75 MHz, CDCl3, δ,
ppm): 155.6, 130.4, 129.2, 128.0, 124.7, 86.6, 80.2, 68.8,
68.7, 67.5, 66.1, 41.2. IR (cm−1): 3001, 2380, 1643, 1250,
All chemicals were obtained from commercial suppliers
and used without further purification. Melting points
were measured using a WC‐1 microscopic apparatus.
Infrared (IR) spectra were recorded with a PerkinElmer
983 FT‐IR spectrometer. 1H NMR and 13C NMR
spectra were recorded with a Bruker 300M or 600M
instrument. Chemical shifts were measured relative to
tetramethylsilane (0.00 ppm) as internal standard.
4.2 | Synthetic Procedure for 1,3‐Bis(5‐
ferrocenylisoxazoline‐3‐yl)benzene
Aldoxime was prepared according to a previously
described procedure. Vinylferrocene was synthesized by

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YU ET AL.
1048, 803, 680. EI‐MS: m/z = 607 [M + Na]+. Anal. Calcd
for C32H28Fe2N2O2 (%): C, 65.78; H, 4.83; N, 4.79. Found
(%): C, 65.69; H, 4.64; N, 4.72.
[4] a) F. Liu, D. Ma, J. Org. Chem. 2007, 72, 4844. b) C.‐H. Lin, Y.‐J.
Wang, C.‐F. Lee, Eur. J. Org. Chem. 2010, 23, 4368.
c) I. Paterson, R. D. M. Davies, R. Marquez, Angew. Chem. Int.
Ed. 2001, 40, 603.
[5] a) B.‐L. Huang, P. Zhao, Y. Dai, S. Deng, A.‐G. Hu, J. Polym. Sci.
Polym. Chem. 2016, 54, 2285. b) T. Sekine, Y. Takashima, H.
Yamaguchi, A. Harada, Chem. Lett. 2016, 45, 1250.
4.3 | General Procedure for Sonogashira
Coupling Reactions
[6] a) M. Jeong, H. Nam, O.‐J. Sohn, J. Rhee, H.‐J. Kim, C.‐W. Cho,
S. Lee, Inorg. Chem. Commun. 2008, 11, 97. b) Z.‐A. Huang,
L. Ji, R.‐L. Tang, L.‐J. Huang, C. Ye, J.‐G. Qin, Z. Li, Polym.
Adv. Technol. 2011, 22, 675. c) H.‐H. Chen, H.‐H. Hung, Y.‐H.
Cheng, J.‐W. Yu, J.‐J. Lee, Liq. Cryst. 2015, 42, 1773.
TBAB (0.25 mmol) was added into a solution of palladium
acetate (0.2 mol%) and 1,3‐bis(5‐ferrocenylisoxazoline‐3‐
yl)benzene (0.4 mol%) in 5 mL of DMF–H2O (1:1) and
the resulting mixture was stirred for 10 min. Then aryl
halide (1 mmol), alkyne (1.2 mmol or 2.4 mmol) and
piperidine (2 mmol) were sequentially added into the
mixture. The resulting solution was heated to a suitable
temperature and monitored using TLC. After completion,
10 mL of ethyl acetate was added and the organic phase
was washed with water three times. The residue was dried
with anhydrous Na2SO4. The desired coupling product
was obtained using column chromatography with petro-
leum ether and ethyl acetate as eluent.
[7] a) K. Sonogashira, J. Organometal. Chem. 2002, 653, 46.
b) K. Sonogashira, Y. Tohda, N. Hagihara, Tetrahedron Lett.
1975, 16, 4467.
[8] a) X. Wang, Z.‐H. Wang, Y. Wu, Y.‐L. Luo, G.‐F. Zhang, Y.‐J.
Jian, H.‐M. Sun, W.‐Q. Zhang, Z.‐W. Gao, Appl. Organometal.
Chem. 2016, 30, 831. b) K. Srinivas, P. Srinivas, P. S. Prathima,
K. Balaswamy, B. Sridhar, M. M. Rao, Catal. Sci. Technol.
2012, 2, 1180.
[9] P. Siemsen, R. C. Livingston, F. Diederich, Angew. Chem. Int.
Ed. 2000, 39, 2632. b J. Cheng, Y. Sun, Z. Zhang, J. Org. Chem.
2004, 69, 5428.
ACKNOWLEDGMENTS
[10] For a selection of papers on the palladium/phosphine‐free
ligand system, see:a)M. Masrollahzadeh, M. Atarod, M.
Alizadeh, A. Hatamifard, S. M. Sajadi, Curr. Org. Chem. 2017,
21, 708. b) S. Sara, Z. Zohre, Z. Farzaneh. New J. Chem. 2015,
39, 7076. c) M. Takashi, S. Yoshiaki, S. Takeshi, S. Masami, F.
Tsutomu, J. Org. Chem. 2006, 71, 9499. d) M. Fsmaeilpour,
J. Javidi, F. N. Dedeji, M. M. Abarghoui, Transit. Met. Chem.
2014, 39, 797. e) M. Eckhardt, G.‐C. Fu, J. Am. Chem. Soc.
2003, 125, 13642. f) R. A. Batey, M. Shen, A. J. Lough, Org. Lett.
2002, 4, 1411. g) C. R. Eisnor, R. A. Gossage, P. N. Yadav,
Tetrahedron 2006, 62, 3395. h) F. Yang, X.‐L. Cui, Y.‐N. Li,
J.‐L. Zhang, G.‐R. Ren, Y.‐J. Wu, Tetrahedron 2007, 63, 1963.
i) C. Najera, J. GilMolto, L. R. Falvello, Org. Lett. 2003, 5,
1451. j) J. A. Loch, M. Albrecht, R. H. Crabtree, Organometallics
2002, 21, 700.
This work was supported financially by the National Nat-
ural Science Foundation of China (nos. 21602207 and
21372008), the Foundation of Henan Educational Com-
mittee (17A150022) and the Doctoral Research Fund of
Zhengzhou University of Light Industry (2014BSJJ009).
ORCID
Shuyan Yu http://orcid.org/0000-0001-9117-1195
Xinwei He http://orcid.org/0000-0002-1974-2464
REFERENCES
[1] a) K. Sonogashira, Y. Tohda, N. Hagihara, Tetrahedron Lett.
1975, 16, 4467. b) K. Sonogashira, Metal‐Catalyzed Cross‐
Coupling Reactions, Wiley‐VCH, Weinheim 2004 319. c) K. C.
Nicolaou, P. G. Bulger, D. Sarlah, Angew. Chem. Int. Ed. 2005,
44, 4442. d) R. Chinchilla, C. Najera, Chem. Rev. 2007, 107, 874.
e) H. Doucet, J. C. Hierso, Angew. Chem. Int. Ed. 2007, 46, 834.
[11] a) S. Lee, J. Organometal. Chem. 2006, 691, 1347. b) L. Botella,
C. Najera, J. Organometal. Chem. 2002, 663, 46. c) K.‐M. Wu,
C.‐A. Huang, K.‐F. Peng, C.‐T. Chen, Tetrahedron 2005, 61,
9679. d) D. F. Brayton, T. M. Larkin, D. A. Vici, O. Navarro, J.
Organometal. Chem. 2009, 694, 3008. e) S. Li, Y. Lin, J. Cao,
S. Zhang, J. Org. Chem. 2007, 72, 4067. f D. Mingji, B. Liang,
C. Wang, Z. You, J. Xiang, G. Dong, J. Chen, Z. Yang, Adv.
Synth. Catal. 2004, 346, 1669. g C. Najera, J. G. Molto, S.
Karlstrom, L. R. Falvello, Org. Lett. 2003, 5, 1451. g) S. Haneda,
C. Ueba, K. Eda, M. Hayashi, Adv. Synth. Catal. 2007, 349, 833. i
F. Li, T. S. A. Hor, Adv. Synth. Catal. 2008, 350, 2391. j T. Mino,
Y. Shirae, M. Sakamoto, Y. Sasai, T. Fujita, J. Org. Chem. 2006,
71, 6834.
[2] a) C. G. Bates, P. Saejueng, J. M. Murphy, D. Venkataraman,
Org. Lett. 2002, 4, 4727. b) L. Yu, X. Jiang, L. Wang, Z. Li, D.
Wu, X. Zhou, Eur. J. Org. Chem. 2010, 29, 5560. c) S. Dhara,
R. Singha, Y. Nuree, J. K. Ray, Tetrahedron Lett. 2014, 55, 795.
d) J. Petrignet, M. Abarbri, J. Thibonnet, Tetrahedron Lett.
2014, 55, 982.
[3] a) S. Erber, R. Ringshandl, E. Angerer, Anticancer Drug Des.
1991, 6, 417. b) G. D. McAllister, R. C. Hartley, M. J. Dawson,
A. R. Knaggs, J. Chem. Soc. Perkin Trans. 1 1998, 3453. c) R.
Nakajima, T. Ogino, S. Yokoshima, T. Fukuyama, J. Am. Chem.
Soc. 2010, 132, 1236. d) K. C. Nicolaou, P. G. Bulger, D. Sarlah,
Angew. Chem. 2005, 117, 4516.
[12] a) Y.‐J. Shang, J.‐W. Wu, C.‐L. Fan, J.‐S. Hu, B.‐Y. Lu, J.
Organometal. Chem. 2008, 693, 2963. b) Y.‐J. Shang, C.‐L. Fan,
M.‐G. Li, C.‐Y. Zheng, Appl. Organometal. Chem. 2006, 20,
626. c) Z.‐J. Feng, S.‐Y. Yu, Y.‐J. Shang, Appl. Organometal.
Chem. 2008, 22, 577.

YU ET AL.
7 of 7
[13] N. J. Long, Metallocenes: An Introduction to Sandwich Com-
plexes, Blackwell Science, Oxford 1998.
How to cite this article: Yu S, Wu J, He X,
Shang Y. Ferrocenyl bisoxazoline as an efficient
non‐phosphorus ligand for palladium‐catalyzed
copper‐free Sonogashira reaction in aqueous
solution. Appl Organometal Chem. 2017;e4156.
https://doi.org/10.1002/aoc.4156
[14] S.‐Y. Yu, Z.‐Q. Zhang, Z.‐Y. Yu, Y.‐J. Shang, Appl. Organometal.
Chem. 2014, 28, 657.
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