An ionic liquid-coordinated palladium complex: A highly efficient and recyclable catalyst for the Heck reaction

Article abstract of DOI:10.1021/ol048327i

The monoquaternary product of 2,2′-biimidazole with iodobutane is an ionic liquid that acts as both the solvent and ligand for catalytic reactions. A new palladium complex was prepared by adding PdCl₂ to this ionic liquid to form a catalytic solution that is effective for Heck reactions with good recyclability.

Full text of DOI:10.1021/ol048327i

ORGANIC
LETTERS
2
004
Vol. 6, No. 21
845-3847
An Ionic Liquid-Coordinated Palladium
Complex: A Highly Efficient and
Recyclable Catalyst for the Heck
Reaction
3
Ji-Chang Xiao, Brendan Twamley, and Jean’ne M. Shreeve*
Department of Chemistry, UniVersity of Idaho, Moscow, Idaho 83844-2343
jshreeVe@uidaho.edu
Received August 21, 2004
ABSTRACT
The monoquaternary product of 2,2′-biimidazole with iodobutane is an ionic liquid that acts as both the solvent and ligand for catalytic
reactions. A new palladium complex was prepared by adding PdCl
reactions with good recyclability.
2
to this ionic liquid to form a catalytic solution that is effective for Heck
The design of ionic liquids for use as solvents that can serve
for both immobilization and as coordinating ligands for the
catalyst in processes involving homogeneous catalysis is a
worthwhile objective. Such a system would be useful in
avoiding catalyst leaching from the ionic layer. However,
the coordinating abilities of ordinary ionic liquids are often
transition-metal catalysts are often removed from the ionic
liquid catalyst solution by polar products. When this occurs
it is necessary to use specially designed polar ligands to avoid
3
c,7
catalyst leaching. To date, some efforts have been made
to address this by introducing functional groups into the ionic
2
,8
liquid which can complex the metal centers. Such func-
1
,2
very poor. One of the predominant applications of ionic
3
(3) For recent reviews, see, for example: (a) Wasserscheid, P.; Keim,
W. Angew. Chem., Int. Ed. 2000, 39, 3772-3789. (b) Welton, T. Chem.
ReV. 1999, 99, 2071-2083. (c) Dupont, J.; de Souza, R. F.; Suarez, P. A.
Z. Chem. ReV. 2002, 102, 3667-3692. (d) Rogers, S. Chem. Commun. 2001,
2399-2407. (e) Forsyth, S. A.; Pringle, J. M.; MacFarlane, D. R. Aust. J.
Chem. 2004, 57, 113-119. (f) Ionic Liquids as Green SolVents; Rogers, R.
D., Seddon, K. R., Eds.; ACS Symposium Series 856; American Chemical
Society: Washington, DC, 2003. (g) Ionic Liquids in Synthesis; Wasser-
scheid, P., Welton, T., Eds.; Wiley-VCH: Weinheim, 2003.
(4) For example, see: (a) Suarez, P. A. Z.; Dullius, J. E. L.; Einloft, S.;
de Souza, R. F.; Dupont, J. Polyhedron 1996, 15, 1217-1219. (b) Dyson,
P. J.; Ellis, D. J.; Parker, D. G.; Welton, T. Chem. Commun. 1999, 25-26.
(c) M u¨ ller, L. A.; Dupont, J.; de Souza, R. F. Macromol. Rapid Commun.
1998, 19, 409-411. (d) Dyson, P. J.; Ellis, D. J.; Welton, T. Can. J. Chem.
2001, 79, 705-708.
liquids as solvents focuses on homogeneous catalysis since
ionic liquids have been demonstrated to be ideal immobiliz-
ing agents for various classical transition-metal catalyst
4
5
precursors in hydrogenation, hydroformylation, and carbon-
6
carbon coupling reactions. However, in certain cases, the
(
1) Kottsieper, K. W.; Stelzer, O.; Wasserscheid, P. J. Mol. Catal. A:
Chem. 2001, 175, 285-288.
2) (a) Zhao, D.; Fei, Z.; Scopelliti, R.; Dyson, P. J. Inorg. Chem. 2004,
3, 2197-2205. (b) Audic, N.; Clav e´ ier, H.; Mauduit, M.; Guillemin,
(
4
J.-C. J. Am. Chem. Soc. 2003, 125, 9248-9249. (c) Brauer, D. J.; Kottsieper,
K.; Liek, C.; Stelzer, O.; Waffenschmidt, H.; Wasserscheid, P. J. Organomet.
Chem. 2001, 630, 177-184. (d) Brasse, C. C.; Englert, U.; Salzer, A.;
Waffenschmidt, H.; Wasserscheid, P. Organometallics 2000, 19, 3818-
(5) For example, see: (a) Favre, F.; Olivier-Bourbigou, H.; Commereuc,
D.; Saussine, L. Chem. Commun. 2001, 1360-1361. (b) Sellin, M. F.; Webb,
P. B.; Cole-Hamilton, D. J. Chem. Commun. 2001, 781-782. (c) Stenzel,
O.; Raubenheimer, H. G.; Esterhuysen, C. J. Chem. Soc., Dalton Trans.
2002, 1132-1138.
3
823. (e) Wasserscheid, P.; Waffenschmidt, H.; Machnitzki, P.; Kottsieper,
K. W.; Stelzer, O. Chem. Commun. 2001, 451-452. (f) Favre, F.; Olivier-
Bourbigou, H.; Commereuc, D.; Saussine, L. Chem. Commun. 2001, 1360-
1
361.
1
0.1021/ol048327i CCC: $27.50
© 2004 American Chemical Society
Published on Web 09/18/2004

tional groups include thiourea, thioether, and urea which were
employed for the extraction of metal ions from aqueous
9
9a,10
11
2c
2a
solutions, amines,
amides, phosphines, nitriles, and
8
,12
alkynes. Recently, metal complexes with pending imida-
2b,13
zolium tags have also been reported.
These incorporated
functional groups are sometimes play a role in the reaction.
Herein, we report a new type of ionic liquid-coordinated
palladium complex for the Heck reaction. This catalytic ionic
liquid solution can be recovered and recycled without
significant loss in activity.
In some molecules with multiple centers available for
quaternization, such as 4,4′-bipyridine, a coordination center
remains after monoquaternization. In our earlier work, it was
shown that the monoquaternary products of 4,4′-bipyridine
are not room temperature ionic liquids although they are
relatively low melting salts, 52-109 °C.14 We now have
Figure 1. Single-crystal X-ray structure of 4. Compound 4
crystallizes in the triclinic space group P-1 with the Pd atom on
the inversion center. The other half of the molecule and the extra
anion for charge balance are symmetry generated. The bi-imidazole
ligands are oriented trans to each other, and they are tilted out of
the PdCl
2
plane by 53.4°. There is also a twist between the two
imidazole rings of 68°. Both tilting and twisting are seen in other
17
18
2
imidazole-PdCl complexes and bi-imidazole systems. In this
case, the tilt is relatively large, probably due to the steric influence
of the Bu arms. These pendant Bu arms wrap around the Cl atoms
extended our research to 2,2′-biimidazole, 1, which was
prepared from glyoxal and ammonium acetate.15 Treatment
2
and encapsulate the PdCl group in a hydrocarbon shell. This may
have some bearing on the catalyst recovery rate seen for 4 in the
of 1 with 1-iodobutane in the presence of base leads readily
to 1,1′-dibutyl-2,2′-biimidazole, 2.16 Reaction with 1 equiv
of 1-iodobutane at 100 °C quaternizes one of the two basic
nitrogens of 2 to give the monoquaternary salt. Subsequent
metathetical reaction with potassium hexafluorophosphate
resulted in the formation of 3 (95% yield), which can be
classified as a room-temperature ionic liquid with a glass
transition temperature of -42.76 °C (Scheme 1).
Heck reaction (vide infra).
and is completely soluble in the coordinating ligandsionic
liquid 3. We believe that this is the first example of a
complex formed between an ionic liquid with more than one
center available for quaternization and a transition metal.
The palladium-catalyzed coupling of olefins with aryl or
vinyl halides, known as the Heck reaction, is one of the most
important, reliable, and general reactions for carbon-carbon
19
bond formation in organic synthesis. Various strategies are
Scheme 1. Synthesis of Complex 4
(
6) (a) Mathews, C. J.; Smith, P. J.; Welton, T. Chem. Commun. 2000,
1
1
249-1250. (b) Xu, L.; Chen, W.; Xiao, J. Organometallics 2000, 19,
123-1127. (c) Mathews, C. J.; Smith, P. J.; Welton, T.; White, A. J. P.;
Williams, D. J. Organometallics 2001, 20, 3848-3850. (d) Carmichael,
A. J.; Earle, M. J.; Holbrey, J. D.; McCormac, P. B.; Seddon, K. R. Org.
Lett. 1999, 1, 997-1000. (e) Handy, S. T.; Zhang, X. Org. Lett. 2001, 3,
2
33-236.
(7) (a) Dupont, J.; Silva, S. M.; de Souza, R. F. Catal. Lett. 2001, 77,
1
31-133. (b) Wasserscheid, P.; Waffenschmidt, H.; Machnitzki, P.;
Kottsieper, K. W.; Stelzer, O. Chem. Commun. 2001, 451-452.
(
8) Fei, Z.; Zhao, D.; Scopelliti, R.; Dyson, P. J. Organometallics 2004,
3, 1622-1628.
9) (a) Visser, A. E.; Swatloski, R. P.; Reichert, W. M.; Davis, J. H.,
Jr.; Rogers, R. D.; Mayton, R.; Sheff, S.; Wierzbicki, A. Chem. Commun.
2
(
2
001, 135-136. (b) Visser, A. E.; Swatloski, R. P.; Reichert, W. M.;
Mayton, R.; Sheff, S.; Wierzbicki, A.; Davis, J. H., Jr.; Rogers, R. D.
EnViron. Sci. Technol. 2002, 36, 2523-2529.
(10) Bates, E. D.; Mayton, R. D.; Ntai, I.; Davis, J. H., Jr. J. Am. Chem.
Soc. 2002, 124, 926-927.
11) Lee, K.-M.; Lee, Y.-T.; Lin, I. J. B. J. Mater. Chem. 2003, 13,
079-1084.
12) Schottenberger, H.; Wurst, K.; Horvath, U. E. I.; Cronje, S.;
Lukasser, J.; Polin, J.; McKenzie, J. M.; Raubenheimer, H. G. Dalton Trans.
(
1
(
2
003, 4275-4281.
(
13) (a) Geldbach, T. J.; Dyson, P. J. J. Am. Chem. Soc. 2004, 126, 8114-
8
115. (b) Yao, Q.; Zhang, Y. Angew. Chem., Int. Ed. Engl. 2003, 42, 3395-
3
398.
(
14) (a) Singh, R. P.; Shreeve, J. M. Inorg. Chem. 2003, 42, 7416-
7
3
421. (b) Singh, R. P.; Shreeve, J. M. Chem. Commun. 2003, 1366-1367.
(15) Cho, J. R.; Cho, S. G.; Goh, E. M.; Kim, J. K. FR2838440.
(
16) Thummel, R. P.; Goulle, V.; Chen, B. J. Org. Chem. 1989, 54,
057-3061.
The coordination ability of 3 was then tested. Dissolution
of PdCl in 2 equiv of 3 in methanol for 6 h at room
2
temperature afforded a yellow palladium complex, 4, in 90%
yield. A crystal suitable for X-ray single-crystal diffraction
(17) See, e.g.: (a) Ianellai, S.; Pelizzi, G.; Vitali, F.; Devoto, G.;
Massacesi, M.; Ponticelli, G. J. Crystallogr. Spectrosc. Res. 1985, 15, 351-
3
58. (b) Navarro-Ranninger, M. C.; Martinez-Carrera, S.; Garcia-Blanco,
S. Acta Crystallogr. 1983, C39, 186-188. (c) Lee, C. K.; Ling, M. J.; Lin,
I. J. B, Dalton Trans. 2003, 4731-4737.
(18) See, e.g.: (a) Ono, K.; Saito, K.; Uchiumi, H.; Tomurra, M. Chem.
3 2 5 2
analysis was obtained from a 1:3 CH OH/(C H ) O mixture
Lett. 2002, 622-623. (b) Lemke, M.; Knoch, F.; Kisch, H.; Salbeck, J.
Chem. Ber. 1995, 128, 131-136.
(
Figure 1). This complex is insensitive to oxygen or moisture
3846
Org. Lett., Vol. 6, No. 21, 2004

employed to recover and reuse the palladium catalyst for
the Heck reaction. Many studies on the Heck reaction by
immobilizing the palladium-bulky phosphine complexes in
ionic liquids have been reported, and only a few phosphine-
free Heck reactions are known.21
of starting materials were added to the recovered ionic liquid
solution again. A similarly high conversion was obtained
after 4 runs (cycle 5), showing that this catalytic ionic liquid
system remained active. Further, this recovered catalyst-ionic
liquid solution was used for a second substrate, the nonactive
chlorobenzene, leading to the same product in 75% yield
after two runs (cycle 8). Then, the recycled catalytic system
was employed in the reaction of chlorobenzene with styrene.
Two runs later, it was possible to obtain the product in 83%
yield (cycle 11). These observations show that this catalyst-
ionic liquid solution could be recycled at least 10 times
without significant decrease in catalytic performance. The
most important feature of the catalytic system is that this
catalyst is part of the ionic liquid and therefore not easily
lost during extraction of the product.
In conclusion, we present a new type of ionic liquid-
coordinated palladium complex as catalyst for the Heck
reaction. This catalytic ionic liquid solution can be recovered
and recycled without significant loss in activity. From these
results, it seems likely that many other transition-metal-
catalyzed reactions could be performed equally well in this
catalytic ionic liquid solution.
20
Since the ionic liquid 3 could coordinate well with PdCl
2
to form a stable phosphine-free complex, 4, it was interesting
to investigate its catalytic activity. Moreover, as mentioned
above, it was envisaged that 3 might be used both as the
solvent and as the ligand. Therefore, we tried the Heck
coupling reaction of iodobenzene with methyl acrylate (Table
1). Sodium carbonate, iodobenzene and methyl acrylate were
Table 1. Recyclable Heck Coupling Reaction of Aryl Halide
with Vinyl Compoundsa
X
R
cycle
yielda (%)
cycle
yielda (%)
Acknowledgment. This work was supported by the
National Science Foundation (Grant No. CHE0315275 and
AFOSR (Grant No. F49620-03-1-0209). We are grateful to
Dr. Alex Blumenfeld for NMR assistance.
I
CO2Me
1
2
3
6
7
9
92
90
94
70
78
86
81
4
5
91
91
Cl
Cl
CO2Me
Ph
8
75
83
Supporting Information Available: Experimental pro-
cedures and analytical data for the work described. X-ray
crystallographic data for 4 (CIF). This material is available
free of charge via the Internet at http://pubs.acs.org.
11
1
0
a
All reactions were carried out using 2 mmol of aryl halide, 1.25 equiv
of the vinyl compound, 1.5 equiv of Na2CO3, 2 mol % 4, and 2 g of 3, at
00 °C, 4 h. Isolated yield.
b
1
OL048327I
(19) (a) Negishi, E., Ed. Handbook of Organopalladium Chemistry for
Organic Synthesis; John Wiley & Sons: New York, 2002. (b) Tsuji, J.
Palladium Reagents and Catalysts. InnoVations in Organic Synthesis;
Wiley: Chichester, UK, 1995. (c) Beletskaya, I. P.; Cheprakov, A. V. Chem.
ReV. 2000, 100, 3009-3066. (d) Littke, A. F.; Fu, G. C. Angew. Chem.,
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Commun. 2004, 1559-1563.
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Lett. 2001, 3, 295-297. (e) Selvakumar, K.; Zapf, A.; Beller, M. Org. Lett.
added directly to a preformed solution of 2 mol % PdCl
. Complete formation of the coupled product was obtained
after heating at 100 °C for 4 h under ambient laboratory
conditions. The product, (E)-methyl cinnamate, was easily
separated from the reaction mixture by simple extraction and
decantation with ethyl ether. The desired product was isolated
in 92% yield by column chromatography on silica gel using
hexanes-ethyl acetate (40:1) as eluent.
These results prompted us to examine the reuse of this
catalytic system. The catalyst-ionic liquid solution was
recovered by washing with water to remove the sodium salt
and drying under vacuum before using. The same amounts
2
in
3
22
2
002, 4, 3031-3033. (f) Vallin, K. S. A.; Emilsson, P.; Larhed, M.;
Hallberg, A. J. Org. Chem. 2002, 67, 6243-6246.
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X.; Chen, B.; Lu, J.; Han, J.; She, X.; Pan, X. Tetrahedron Lett. 2004, 45,
6
235-6237.
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Org. Lett., Vol. 6, No. 21, 2004
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