3
804
J . Org. Chem. 1999, 64, 3804-3805
P a lla d iu m -Im id a zol-2-ylid en e Com p lexes a s
Ca ta lysts for F a cile a n d Efficien t Su zu k i
Cr oss-Cou p lin g Rea ction s of Ar yl Ch lor id es
w ith Ar ylbor on ic Acid s
Sch em e 1
Chunming Zhang, J inkun Huang,
Mark L. Trudell,*,† and Steven P. Nolan*,†
Department of Chemistry, University of New Orleans,
New Orleans, Louisiana 70148
rhodium carbene complexes in hydrosilylation,1 and ruthe-
4
nium carbene catalysts in olefin metathesis1
new opportunities in catalysis.
5,16a
has opened
Received March 30, 1999
Recently we examined the solution calorimetry of transi-
tion metal-centered ligand substitution involving nucleo-
philic N-heterocyclic carbenes.16 This class of ligands exhib-
The palladium-catalyzed Suzuki cross-coupling reaction
of aryl bromides, aryl iodides, and pseudohalides (e.g.
triflates) is a general method employed for the formation of
ited a considerable stabilizing effect in organometallic
systems.8
,17
An understanding of ligand stereoelectronic
1
C-C bonds. The use of aryl chlorides as chemical feedstock
effects provided by the thermochemical investigations led
to the use of this ligand class in a ring-opening/closing
metathesis system. Herrmann and co-workers have reported
Suzuki cross-coupling activity of carbene ancillary ligands
involving aryl bromides and activated aryl chlorides. In
view of the stereoelectronic phosphine factors required in
in coupling chemistry has proven difficult but would eco-
nomically benefit a number of industrial processes.2,3 The
use of phosphine ligands in organometallic chemistry and
4
5
6
catalysis is widespead. Recently, Buchwald and Fu have
reported phosphine-modified palladium-mediated Suzuki
coupling reactions which employ inexpensive aryl chlorides
1
8
6
t
the report of Fu and Littke and results from the thermo-
as substrates. The use of bulky phosphine (P Bu3) or phos-
chemical studies which more clearly defined the electron-
donating ability (better donating than PCy3) and steric
demand (larger than PCy3) of the carbene ligands, 1,3-bis-
2,4,6-trimethylphenyl)imidazol-2-ylidene (1, IMes) was
examined as a potential ancillary ligand in Suzuki cross-
coupling reactions of aryl chlorides and arylboronic acids.
phine-containing moiety (PCy2) in ancillary ligation was
shown to be fundamental in triggering the observed catalytic
behavior.
Nucleophilic N-heterocyclic carbenes, the imidazol-2-
ylidenes or so-called “phosphine mimics”, have attracted
considerable attention as possible alternatives for the widely
1
9
(
7
,8
used phosphine ligands in homogeneous catalysis. The
primary advantage of these ligands appears to be that they
do not dissociate from the metal center, as a result an excess
of the ligand is not required in order to prevent aggregation
8
of the catalyst to yield the bulk metal. The application of
these ligands in palladium-catalyzed Heck reactions,9
-13
In our initial experiments we observed that the coupling
of 4-chlorotoluene and phenylboronic acid (1.5 equiv) in the
presence of 1.5 mol % of Pd2(dba)3, 3.0 mol % of the carbene
†
M.L.T.: email mtrudell@uno.edu; tel (504) 280-733; fax (504) 280-6860.
S.P.N.: email snolan@uno.edu; tel. (504) 280-6445; fax (504) 280-6860.
(
1) (a) For a review, see: Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95,
457-2483. (b) For more recent palladium-based catalyzed couplings of aryl
chlorides, see: Hamann, B. C.; Hartwig, J . F. J . Am. Chem. Soc. 1998, 120,
369-7370. (c) Reetz, M. T.; Lohmer, G.; Schwickardi, R. Angew. Chem.,
Int. Ed. Engl. 1998, 37, 481-483. (d) Littke, A. F.; Fu, G. C. J . Org. Chem.
999, 64, 10-11.
2) Cornils, B.; Herrmann, W. A.,Eds. Applied Homogeneous Catalysis
with Organometallic Compounds; VCH: Weinheim, 1996.
3) (a) Chem. Eng. News 1998; J une 1, 24. (b) Chem. Eng. News 1998;
J uly 13, 71.
1
9
2
1, and Cs2CO3 in dioxane at 80 °C proceeded to give
-phenyltoluene in 59% isolated yield (Scheme 1). The
4
7
reaction proceeded rapidily with complete consumption of
the aryl chloride as observed by TLC within 1.5 h.
Since imidazol-2-ylidene carbenes are considerably less
stable to air and moisture than the corresponding imidazo-
lium salts, to avoid the preparation and isolation of the
carbene 1 we sought to develop a protocol in which the
carbene ligand 1 would be generated in situ from salt 2.
When the coupling reaction of 4-chlorotoluene with phenyl-
boronic acid was performed with 2 under the same general
conditions, the product 4-phenyltoluene was isolated in 96%
yield (Table 1, entry 5). This result represents a significant
improvement over the procedure employing the nucleophilic
carbene 1 in terms of both isolated yield and ease of
execution.
1
(
(
(4) (a) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G. Principles
and Applications of Organotransition Metal Chemistry; University Science
Books: Mill Valley, CA, 1987. (b) Parshall, G. W.; Ittel, S. Homogeneous
Catalysis; J . Wiley and Sons: New York, 1992. (c) Pignolet, L. H., Ed.
Homogeneous Catalysis with Metal Phosphine Complexes; Plenum: New
York, 1983.
(
5) Old, D. W.; Wolfe, J . P.; Buchwald, S. L. J . Am. Chem. Soc. 1998,
20, 9722-9723.
6) Littke, A. F.; Fu, G. C. Angew. Chem., Int. Ed. Engl. 1998, 37, 3387-
388.
7) (a) Regitz, M. Angew. Chem., Int. Ed. Engl. 1996, 35, 725-728. (b)
Arduengo, A. J ., III; Krafczyk, R. Chem. Zeit. 1998,32, 6-14.
8) Herrmann, W. A.; K o¨ cher, C. Angew. Chem., Int. Ed. Engl. 1997, 36,
163-2187.
9) Herrmann, W. A.; Elison, M.; Fisher, J .; K o¨ cher, C.; Autus, G. R. J .
Angew. Chem., Int. Ed. Engl. 1995, 34, 2371-2373.
10) Herrmann, W. A.; Brossmer, C.; Beller, M.; Fischer, H. DE 4,421,-
30 (Hoechst, AG), 1994; DE 4,421,753 (Hoechst, AG), 1994.
11) (a) Herrmann, W. A.; Fischer, J .; Elison, M.; K o¨ cher, C. DE 4,447,-
66 (Hoechst, AG), 1994; DE 4,447,067 (Hoechst, AG), 1994; DE 4,447,068
1
(
3
(
(
2
(
(14) Herrmann, W. A.; Goossen, L. T.; K o¨ cher, C.; Autus, G. R. J . Angew.
Chem., Int. Ed. Engl. 1996, 35, 2805-2807.
(
(15) Weskamp, T.; Schattenmann, W. C.; Spiegler, M.; Herrmann, W.
A. Angew. Chem., Int. Ed. Engl. 1998, 37, 2490-2493.
(16) (a) Huang, J .; Stevens, E. D.; Nolan, S. P.; Petersen, J . L. J . Am.
Chem. Soc. 1999, 121, 2674-2678. (b) Huang, J .; Schanz, H.-J .; Stevens,
E. D.; Nolan, S. P. Organometallics 1999, 18, in press.
(17) Voges, M. H.; Rømming, C.; Tilset, M. Organometallics 1999, 18,
529-533.
7
0
(
(
Hoechst, AG), 1994. (b) Herrmann, W. A.; Fischer, J .; Elison, M.; K o¨ cher,
C. EP 0,719,753 (Hoechst, AG), 1996; EP 0,719,758 (Hoechst, AG), 1996;
EP 0,719,953 (Hoechst, AG), 1996.
(
12) Herrmann, W. A.; Fischer, J .; Elison, M.; K o¨ cher, C.; Autus, G. R.
J . Chem. Eur. J . 1996, 2, 772-780.
13) McGuinness, D. S.; Green, M. J .; Cavell, K. J .; Skelton, B. W.; White,
A. H. J . Organomet. Chem. 1998, 565, 165-178.
(18) Herrmann, W. A.; Reisinger, C.-P.; Spiegler, M. J . Organomet. Chem.
1998, 557, 93-96.
(19) Arduengo, A. J ., III; Dias, H. V. R. Harlow, R. L.; Kline, M. J . Am.
Chem. Soc. 1992, 114, 5530-5534.
(
1
0.1021/jo990554o CCC: $18.00 © 1999 American Chemical Society
Published on Web 05/06/1999