Palladium-catalyzed coupling of aryl halides with arylhalosilanes in air and water

Article abstract of DOI:10.1016/S0040-4039(01)02193-1

In the presence of a palladium catalyst, various aryl halides reacted with arylhalosilanes in aqueous media and under an air atmosphere to give the corresponding unsymmetrical aryl-aryl coupling products conveniently.

Full text of DOI:10.1016/S0040-4039(01)02193-1

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 403–405
Palladium-catalyzed coupling of aryl halides with arylhalosilanes
in air and water
Taisheng Huang and Chao-Jun Li*
Department of Chemistry, Tulane University, New Orleans, LA 70118, USA
Received 30 October 2001; revised 16 November 2001; accepted 19 November 2001
Abstract—In the presence of a palladium catalyst, various aryl halides reacted with arylhalosilanes in aqueous media and under
an air atmosphere to give the corresponding unsymmetrical aryl–aryl coupling products conveniently. © 2002 Elsevier Science
Ltd. All rights reserved.
Palladium-catalyzed reductive couplings are among the
most important carbonꢀcarbon bond forming reactions
in modern synthetic organic chemistry.1 The Stille2 and
the Suzuki reactions3 have been widely used to generate
aryl–aryl coupling products. Although both reactions
are highly successful, a drawback of the Stille coupling
is the involvement and generation of relatively toxic tin
reagents and by-products and the limitations with
regard to synthesis and stability of boron reagents were
also noted.4 The use of hypervalent silicon reagents for
palladium-catalyzed cross couplings has been estab-
lished recently by Hiyama,5 DeShong6 and others. On
the other hand, Denmark and co-workers have devel-
oped highly activated silicon reagents for palladium-
catalyzed couplings with aryl halides.7 More recently,
Hiyama and co-workers reported the coupling of
silanols, silanediols and silanetriols with aryl iodides in
THF.8 In an effort to develop air9 and water-stable10
catalytic reactions, previously we reported a palladium-
catalyzed Ullmann-type reductive coupling of aryl
halides in aqueous conditions and under an air atmo-
sphere.11 Although the reaction offers synthetic conve-
nience, it is limited to the generation of symmetrical
biaryls. Recently, we found that arylhalosilanes under-
went conjugated additions catalyzed by rhodium in air
and water effectively.12 In this paper, we report that in
the presence of a palladium catalyst, arylhalosilanes
reacted with various aryl halides in air and water in the
presence of base or NaF to give the corresponding
unsymmetrical biaryl products conveniently (Eq. (1)).
Pd cat.
ArX+PhRSiCl2KꢀꢀOꢀHꢀ(ꢀoꢀr ꢀNꢀaꢀF)ꢀ/HꢀꢀOꢁArꢀPh
(1)
2
To begin the study, 4-iodoanisole was reacted with
various arylhalosilanes under a variety of conditions
(Table 1). Initially, Pd(OAc)2 was used as the catalyst.
The reaction of phenyltrichlorosilane with 4-iodoan-
isole under refluxing conditions overnight generated the
desired product in 20% isolated yield together with a
large amount of unreacted 4-iodoanisole. The use of
diphenyldichlorosilane in combination with sodium
fluoride slightly improved the yield. The yield was
further improved by using phenylmethyldichlorosilane
as the silicon reagent. The use of KOH instead of NaF
provided higher yields for both diphenyldichlorosilane
and phenylmethyldichlorosilane reactions. Very similar
but slightly better results were observed with Pd/C as
the catalyst. In this case, no reaction was observed in
the absence of KOH.
Table 1. Coupling of 4-iodoanisole with arylhalosilanes
under various conditions
Entry
Silicon
reagent
Catalyst
Additive
(equiv.)a
Yield (%)b
1
2
3
4
5
6
7
8
9
PhSiCl3
PhSiCl2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd/C
Pd/C
Pd/C
Pd/C
None
NaF
NaF
KOH
KOH
KOH
KOH
KOH
None
20
40
47
70
71
36
74
80
0
PhMeSiCl2
Ph2SiCl2
PhMeSiCl2
PhSiCl3
Ph2SiCl2
PhMeSiCl2
PhMeSiCl2
a 6–8 equiv. of additives were added.
b Isolated yields.
Subsequently, a variety of aryl halides were examined
* Corresponding author.
under the Pd/C-catalyzed conditions (Table 2).13 Nearly
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)02193-1

404
T. Huang, C.-J. Li / Tetrahedron Letters 43 (2002) 403–405
Table 2. Coupling of various aryl halides with methylphenylhalosilane
the same results were obtained with either iodo or
bromo derivatives. Iodo- and bromo-naphthalenes
(entries 1, 2, and 8) reacted similarly. A slightly better
yield was obtained with an electron-deficient aryl iodide
than electron-rich aryl halides. It is noteworthy to
mention that 4-bromophenol reacted smoothly to gen-
erate the desired product (entry 6). The use of simple
iodobenzene provided the corresponding product quan-
titatively (entry 7) (part of the product may be due to
homocoupling of the silicon reagent).
Pd/C (5 mol%) in 10 mL of water was stirred at 100°C
for 12 h under an air atmosphere. The reaction mixture
was cooled and extracted with ethyl acetate. After the
combined organic phase was dried and concentrated in
vacuo, the residue was separated by silica gel chro-
matography eluting with hexane to give the desired
biaryl product (140 mg, 80%).
A tentative mechanism for the reaction involves the
oxidative addition of the palladium catalyst to the aryl
halides to generate a palladium intermediate (Scheme
1). The intermediate then reacts with the silicate gener-
ated from the arylhalosilane derivative and KOH or
NaF to afford the cross-coupling product and regener-
ate the active palladium catalyst.
The following procedure is representative: A mixture of
4-iodoanisole (234 mg, 1 mmol), dichloromethylphenyl-
silane (382 mg, 2 mmol), KOH (448 mg, 8 mmol), and
Scheme 1. Tentative mechanism for the palladium-catalyzed
coupling of arylhalosilanes with aryl halides in air and water.

T. Huang, C.-J. Li / Tetrahedron Letters 43 (2002) 403–405
405
Acknowledgements
5. (a) Hiyama, T.; Hatanaka, Y. Pure Appl. Chem. 1994, 66,
1417; (b) Hagiwara, E.; Gouda, K.; Hatanaka, Y.;
Hiyama, T. Tetrahedron Lett. 1997, 38, 439; (c) Horn, K.
A. Chem. Rev. 1995, 95, 1317.
6. Mowery, M. E.; DeShong, P. J. Org. Chem. 1999, 64,
1684.
We are grateful to NSF (CAREER Award), the NSF–
EPA joint program for a sustainable environment for
partial support of our research.
7. (a) Denmark, S. E.; Sweis, R. F. J. Am. Chem. Soc. 2001,
123, 6439; (b) Denmark, S. E.; Wu, Z. Org. Lett. 1999, 1,
1495.
8. Hirabayashi, K.; Mori, A.; Kawashima, J.; Suguro, M.;
Nishihara, Y.; Hiyama, T. J. Org. Chem. 2000, 65, 5342.
9. For an air-stable and polymer-supported palladium-cata-
lyzed Suzuki reaction, see: Zhang, T. Y.; Allen, M. J.
Tetrahedron Lett. 1999, 40, 5813.
10. (a) Li, C. J.; Chan, T. H. Organic Reaction in Aqueous
Media; John Wiley & Sons: New York, 1997; (b) Li, C. J.
Chem. Rev. 1993, 93, 2023; (c) See also: Organic Synthesis
in Water; Grieco, P. A., Ed.; Thomson Science: Glasgow,
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11. (a) Ventrakaman, S.; Li, C. J. Tetrahedron Lett. 2000, 41,
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12. (a) Huang, T. S.; Li, C. J. Chem. Commun. 2001, 2348;
(b) For other works, see: Li, C. J.; Huang, T. S.; Venka-
traman, S.; Meng, Y.; Kort, D.; Ding, R.; Wang, D. Pure
Appl. Chem. 2001, 73, 1315.
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13. All products were known compounds.