NHC-Pd(II)-Im (NHC = N-heterocyclic carbene; Im = 1-methylimidazole) complex catalyzed Hiyama reaction of aryl chlorides with aryltrimethoxysilanes

Article abstract of DOI:10.1016/j.jorganchem.2011.11.030

A well-defined NHC-Pd(II)-Im complex was proved to be an efficient catalyst for the Hiyama reaction of a variety of aryl chlorides with aryltrimethoxysilanes. Under the optimal conditions, all reactions took place smoothly to give the corresponding coupling products in moderate to high yields.

Full text of DOI:10.1016/j.jorganchem.2011.11.030

Journal of Organometallic Chemistry 700 (2012) 132e134
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NHCePd(II)eIm (NHC ¼ N-heterocyclic carbene; Im ¼ 1-methylimidazole)
complex catalyzed Hiyama reaction of aryl chlorides with aryltrimethoxysilanes
*
Zheng-Song Gu, Li-Xiong Shao, Jian-Mei Lu
College of Chemistry and Materials Engineering, Wenzhou University, Chashan University Town, Zhejiang Province 325035, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
A well-defined NHCePd(II)eIm complex was proved to be an efficient catalyst for the Hiyama reaction of
a variety of aryl chlorides with aryltrimethoxysilanes. Under the optimal conditions, all reactions took
place smoothly to give the corresponding coupling products in moderate to high yields.
Ó 2011 Elsevier B.V. All rights reserved.
Received 22 October 2011
Received in revised form
19 November 2011
Accepted 25 November 2011
Keywords:
N-Heterocyclic carbene
Palladium complex
Hiyama reaction
Aryl chloride
Synthetic method
1. Introduction
[24e27]. Recently, we have synthesized
a
well-defined
from
NHCePd(II)eIm (Im 1-methylimidazole) complex
¼
1
Palladium-catalyzed cross-coupling reactions between organo-
electrophiles and organonucleophiles are the most important
methods in modern organic synthesis for the formation of car-
bonecarbon and carboneheteroatom bonds [1e3]. Among them,
the reaction involving organosilanes, the Hiyama reaction, is
attractive because organosilanes are easily handled with low
toxicity and high stability, and in addition, the reaction usually
generates nontoxic by-products [4e7]. Generally, aryl iodides and
bromides were used as the reaction partners catalyzed by the
combination of palladium salts and air-sensitive phosphine ligands
[8e17]. On the other hand, despite the lower reactivity of aryl
chlorides comparing to the corresponding iodides and bromides,
aryl chlorides are the most desirable substrates because of their
lower cost and readily availability [18,19]. However, aryl chlorides
are not easy to activate in the Hiyama reaction. Therefore, there are
only a few examples of the Hiyama reaction using aryl chlorides as
the electrophiles [12,20e23].
IPr.HCl, PdCl2 and 1-methylimidazole in a one-step procedure
(Fig. 1) and found it to be an efficient catalyst in the amination and
SuzukieMiyaura coupling reactions of aryl chlorides [28e30].
These results prompted us to further expand the application of this
complex to the Hiyama reaction of aryl chlorides with aryl-
trimethoxysilanes [31e34]. Herein, we wish to report these results
in detail.
2. Experimental
2.1. General remarks
1H and 13C NMR spectra were recorded on a Bruker Avance-
300 MHz or Bruker Avance-500 MHz spectrometer for solution in
CDCl3 with tetramethylsilane (TMS) as an internal standard; J-
values are in Hz. Commercially obtained reagents were used
without further purification. Flash column chromatography was
carried out using Huanghai 300e400 mesh silica gel at increased
pressure.
During the past decades, N-heterocyclic carbene (NHC) and their
metal complexes, usually with higher air- and thermal-stability,
have attracted much attention as an alternative for phosphine
ligands in the palladium-catalyzed cross-coupling reactions
2.2. General procedure for the NHCePd(II)eIm complex 1 catalyzed
Hiyama reaction of aryl chlorides with aryltrimethoxysilanes
Under N2 atmosphere, NHCePd(II)eIm 1 (1.0 mol%), dry toluene
(2.0 mL), aryl chlorides 2 (0.81 mmol), aryltrimethoxysilanes 3
* Corresponding author. Tel./fax: þ86 577 86689300.
E-mail addresses: ljm@wzu.edu.cn, 47215101@qq.com (J.-M. Lu).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.11.030

Z.-S. Gu et al. / Journal of Organometallic Chemistry 700 (2012) 132e134
133
Table 2
Complex 1 catalyzed Hiyama reaction of 2 with 3a.
Pri
Cl
Si(OMe)3
Pri
Pri
Cl
NHC-Pd(II)-Im 1
N
N
(1.0 mol%)
Pd
Cl
N
+
.
N
toluene,TBAF 3H2O
R1
120 oC, 3 h
R1
4
2
3a
Pri
Entrya
2 (R1)
Yield (%)b
Fig. 1. NHCePd(II)eIm complex 1.
1
2
3
4
5
6
7
8
2b (4-NO2)
2c (2-NO2)
2d (4-CN)
2e (3-CO2Me)
2f (4-CO2Me)
2g (3-NO2)
2h (3-COMe)
2i (3-Me)
4b, 88
4c, 48
4d, 89
4e, 70
4f, 83
4g, 84
4h, 64
4i, 50
4j, 68
4k, 59
(2.0 equiv) and TBAF$3H2O (2.0 equiv) were successively added into
a Schlenk reaction tube. Then the tube was placed in a 120 ꢀC oil
bath and stirred for 3 h. The mixture was then allowed to cool to
room temperature, diluted with ethyl acetate and washed with
brine, dried over anhydrous Na2SO4, concentrated in vacuo and
then purified by flash chromatography to give the pure products 4.
9c
10c,d
2j (3-OMe)
2k (H)
(H)
3. Results and discussion
11c
4I, 90
2l
Initial examinations were carried out using 4-chloroacetophenone
2a (0.77 mmol) and phenyltrimethoxysilane 3a (2.0 equiv) as the
substrates in the presence of TBAF$3H2O (2.0 equiv) and NHCePd(II)e
Im complex 1 (1.0 mol%) at 120 ꢀC for 3 h to find out the most suitable
solvent. Toluene and xylene were found to be the best sovlents
(Table 1, entries 1 and 7). In other solvents suchas CH3CN, DMF, DMSO,
dioxane and tBuOH, reasonable to good yields were obtained (Table 1,
entries 2e6). Elevating the temperature to 130 and 140 ꢀC cannot
increase the yields of the reactions performed in toluene and xylene.
We also found that the addition of TBAF$3H2O was necessary and no
reaction occurred in the absence of TBAF$3H2O (Table 1, entry 8).
Finally, owing to its lower molecular mass and lower cost, toluene was
chosen as the solvent for this Hiyama reaction (Table 1, entry 1).
Under the optimized reaction conditions, we first examined the
Hiyama reaction of a variety of aryl chlorides 2 with phenyl-
trimethoxysilane 3a (Table 2). In most cases, the reactions took
palce smoothly to give the corresponding coupling products 4 in
moderate to high yields within 3 h. Substituents on the aryl
N
Cl
Cl
12c
4m, 59
2m
N
a
Otherwise specified, all reactions were carried out using 2 (0.81 mmol), 3a (2.0
equiv), TBAF$3H2O (2.0 equiv), 1 (1.0 mol%) in toluene (2.0 mL) at 120 ꢀC for 3 h.
b
Isolated yields.
c
1.5 g TBAF$3H2O was used without toluene.
d
The temeperature is 130 ꢀC.
chlorides 2 have some effects on the reactions. For example, steri-
cally hindered 2-nitrophenyl chloride 2c only gave product 4c in
48% yield (Table 2, entry 2). 2-Chloropyridine 2l was found to be
a good reaction partner to give the corresponding product 4l in 90%
yield (Table 2, entry 11). However, its analogue, 3-chloropyridine
2m, was not a suitable substrate and only gave product 4m in
moderate yield (Table 2, entry 12). Moderate yield can also be
achieved using deactivated 3-methoxyphenyl chloride 2j as the
substrate (Table 2, entry 9). The solvents used also have some effect
Table 1
Optimization for complex 1 catalyzed Hiyama reaction of 2a with 3a.
Cl
Si(OMe)3
Table 3
NHC-Pd(II)-Im 1
Complex 1 catalyzed Hiyama reaction of 2 with 3.
(1.0 mol%)
+
Ac
.
Cl
solvent, TBAF 3H2O
Si(OMe)3
NHC-Pd(II)-Im 1
120 oC, 3 h
4a
(1.0 mol%)
3a
Ac
+
.
toluene,TBAF 3H2O
2a
R1
R2
120 oC, 3 h
R2
R1
4
2
3
Entrya
Solvent
Yield (%)b
1
2
3
4
5
6
7
8c
Toluene
CH3CN
DMF
DMSO
Dioxane
tBuOH
Xylene
Toluene
85
75
71
48
56
32
87
e
Entrya
2 (R1)
3 (R2)
Yield (%)b
1
2
3
4
5
6
7
8
2a (4-Ac)
2b (4-NO2)
2d (4-CN)
2f (4-CO2Me)
2a
2b
2d
2f
3b (4-Me)
3b
3b
3b
4n, 73
4o, 84
4p, 81
4q, 79
4r, 64
4s, 74
4t, 67
4u, 54
3c (4-OMe)
3c
3c
3c
a
All reactions were carried out using 2a (0.77 mmol), 3a (2.0 equiv), TBAF$3H2O
(2.0 equiv), NHCePd(II)eIm 1 (1.0 mol%) in the listed solvent (2.0 mL) at 120 ꢀC for
a
3 h.
All reactions were carried out using 2 (0.81 mmol), 3 (2.0 equiv), TBAF$3H2O
(2.0 equiv), complex 1 (1.0 mol%) in toluene (2.0 mL) at 120ꢀ C for 3 h.
b
Isolated yields.
No TBAF$3H2O was added.
c
b
Isolated yields.

134
Z.-S. Gu et al. / Journal of Organometallic Chemistry 700 (2012) 132e134
on the reactions. For instance, for the reactions involving 3-
methoxyphenyl chloride 2j, chlorobenzene 2k, 2-chloropyridine
2l and 3-chloropyridine 2m, better results can be obtained when
the reactions were carried out in TBAF$3H2O without toluene
(Table 2, entries 9e12).
and InChiKeys of the most important compounds described in this
article.
References
[1] J. Tsuji, Palladium Reagents and Catalysis: Innovations in Organic Synthesis,
Wiley, New York, 1995.
Using 4-methylphenyltrimethoxysilane 3b and 4-methoxyph-
enyltrimethoxysilane 3c as the substrates, we also examined their
reactions with a variety of aryl chlorides 2 under the identical
conditions. The results are shown in Table 3. All reactions proceeded
well to give the corresponding Hiyama coupling products in moderate
to good yields. The substituents on the silanes slightly affect the
reactions. For instance, it seems that moderate electron-rich 4-
[2] E. Negishi, A. de Meijere (Eds.), Handbook of Organopalladium Chemistry for
Organic Synthesis, John Wiley & Sons, New York, 2002.
[3] A. de Meijere, F. Diederich (Eds.), Metal-Catalyzed Cross-Coupling Reactions,
vols. 1 and 2, Wiley-VCH, Weinheim, Germany, 2004.
[4] T. Hiyama, in: F. Diederich, P.J. Stang (Eds.), Metal-Catalyzed Cross-Coupling
Reactions, Wiley-VCH, New York, 1998 (Chapter 10).
[5] T. Hiyama, J. Organomet. Chem. 653 (2002) 58e61.
[6] S.E. Denmark, J.D. Baird, Chem. Eur. J. 12 (2006) 4954e4963.
[7] Y. Nakao, T. Hiyama, Chem. Soc. Rev. 40 (2011) 4893e4901.
[8] A. Komáromi, F. Szabó, Z. Novák, Tetrahedron Lett. 51 (2010)
5411e5414.
methylphenyltrimethoxysilane 3b was
a better substrate than
strong electron-rich 4-methoxyphenyltrimethoxysilane 3c in this
Hiyama reaction (Table 3).
[9] A. Pal, R. Ghosh, N.N. Adarsh, A. Sarkar, Tetrahedron 66 (2010)
5451e5458.
4. Conclusion
[10] L.-P.B. Beaulieu, L.B. Delvos, A.B. Charette, Org. Lett. 12 (2010)
1348e1351.
[11] J.-H. Li, C.-L. Deng, Y.-X. Xie, Synthesis (2006) 969e974.
[12] J. Ju, H. Nam, H.M. Jung, S. Lee, Tetrahedron Lett. 47 (2006) 8673e8678.
In conclusion, NHCePd(II)eIm complex 1 was found to be an
efficient catalyst in the Hiyama reaction of aryl chlorides with
aryltrimethoxysilanes. Under the optimal conditions, all reactions
can give the corresponding products in moderate to good yields.
Furthermore, the reactions can tolerate various electron-rich,
-neutral and -poor substituents on the aryl chlorides. It is worthy
of noting here that the NHCePd(II)eIm complex reported in this
paper is the most easily available and efficient one among the
NHCePd complexes for the Hiyama reaction of aryl chlorides
[31e33].
[13] A. Gordillo, E. de Jesús, C. López-Mardomingo, Org. Lett.
3517e3520.
8 (2006)
[14] P. Pierrat, P. Gros, Y. Fort, Org. Lett. 7 (2005) 697e700.
[15] J.-Y. Lee, G.C. Fu, J. Am. Chem. Soc. 125 (2003) 5616e5617.
[16] L. Zhang, J. Wu, J. Am. Chem. Soc. 130 (2008) 12250e12251.
[17] L. Zhang, J. Qing, P.-Y. Yang, J. Wu, Org. Lett. 10 (2008) 4971e4974.
[18] V.V. Grushin, H. Alper, in: S. Murai (Ed.), Activation of Unreactive Bonds and
Organic Synthesis, Springer, Berlin, 1999, pp. 193e226.
[19] V.V. Grushin, H. Alper, Chem. Rev. 94 (1994) 1047e1062.
[20] D.-H. Lee, J.-Y. Jung, M.-J. Jin, Chem. Commun. 46 (2010) 9046e9048.
[21] S.M. Raders, J.V. Kingston, J.G. Verkade, J. Org. Chem. 75 (2010) 1744e1747.
[22] L. Ackermann, C.J. Gschrei, A. Althammer, M. Riederer, Chem. Commun. (2006)
1419e1421.
[23] E. Alacid, C. Nájera, Adv. Synth. Catal. 348 (2006) 945e952.
[24] A.C. Hillier, G.A. Grasa, M.S. Viciu, H.M. Lee, C.-L. Yang, S.P. Nolan,
J. Organomet. Chem. 653 (2002) 69e82.
Acknowledgements
[25] E.A.B. Kantchev, C.J. O’Brien, M.G. Organ, Angew. Chem. Int. Ed. 46 (2007)
2768e2813.
[26] N. Marion, S.P. Nolan, Acc. Chem. Res. 41 (2008) 1440e1449.
[27] G.C. Fortman, S.P. Nolan, Chem. Soc. Rev. 40 (2011) 5151e5169.
[28] L. Zhu, T.-T. Gao, L.-X. Shao, Tetrahedron 67 (2011) 5150e5155.
[29] X.-X. Zhou, L.-X. Shao, Synthesis (2011) 3138e3142.
Financial support from the National Natural Science Foundation
of China (No. 21002072) and the Opening Foundation of Zhejiang
Provincial Top Key Discipline (No. 100061200123) is greatly
acknowledged.
[30] Y.-Q. Tang, J.-M. Lu, L.-X. Shao, J. Organomet. Chem. 696 (2011) 3741e3744.
[31] X.-M. Zhang, Q.-Q. Xia, W.-Z. Chen, Dalton Trans. (2009) 7045e7054.
[32] C. Dash, M.M. Shaikh, P. Ghosh, Eur. J. Inorg. Chem. (2009) 1608e1618.
[33] H.M. Lee, S.P. Nolan, Org. Lett. 2 (2000) 2053e2055.
[34] I. Peñafiel, I.M. Pastor, M. Yus, M.A. Esteruelas, M. Oliván, E. Oñate, Eur. J. Org.
Chem. (2011). doi:10.1002/ejoc.201101110.
Appendix. Supplementary material
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2011.11.030. These data include MOL files