11504
J. Am. Chem. Soc. 2001, 123, 11504-11505
and 2a are efficient catalyst precursors in the Heck reaction with
C6F5Br (eq 1). They work in the absence of stabilizing ligands
other than halide, the solvent and the reagents.12
Catalytic System for Heck Reactions Involving
Insertion into Pd-(Perfluoro-organyl) Bonds
Ana C. Albe´niz,† Pablo Espinet,*,† Blanca Mart´ın-Ruiz,† and
David Milstein*,‡
Departamento de Qu´ımica Inorga´nica
Facultad de Ciencias, UniVersidad de Valladolid
47005 Valladolid, Spain
Complexes 1 and 2a catalyze the reaction of C6F5Br and styrene
to give trans-PhCHdCHPf regioselectively. Since solutions of 1
in the presence of bromide give immediately 2a, after the first
catalytic cycle (where bromide is generated as byproduct) both
catalysts are essentially equivalent, and the experiments are
discussed for 2a. A summary of results is given in Table 1.13
Among the bases examined, CaCO3, KF, and Na2CO3 gave the
Department of Organic Chemistry
The Weizmann Institute of Science
76100 RehoVot, Israel
ReceiVed May 30, 2001
ReVised Manuscript ReceiVed October 11, 2001
t
highest yields. Na3PO4, BuOK, Na2CO3/NEt3, and Na2CO3/
collidine slowed the reaction rate or led to the reduction product
C6F5H. NaOAc or NaOH gave fast reactions, but products of
nucleophilic substitution of the para fluorine by acetate or OH
were formed. NMP was the best solvent, whereas iPrCN, dioxane,
or xylene gave poor results.
σ-Bonds between transition metals and perfluorinated groups
(M-Rf) are among the strongest M-C bonds. Very few sto-
ichiometric and, as far as we know, no catalytic reactions based
on insertion of unsaturated molecules into M-Rf bonds have been
reported. Alkene insertion into M-C bonds plays a key role in
important catalytic processes such as alkene oligomerization,1
polymerization,1a,2 and the Heck reaction.3 Such catalysis involv-
ing M-Rf bonds is desirable for the functionalization of perflu-
orinated compounds, important for the fine chemical and phar-
maceutical industries.4
In recent years the Heck reaction has been improved by the
discovery of very active catalysts based on palladacycles, or the
use of new reaction conditions,5-8 but despite the major effort in
this field, perfluoro-aryl or -alkyl halides have not been reported
as substrates.9 Here we report the first catalytic Heck reaction,
involving olefin insertion into an Rf-M bond.
Almost complete conversion of C6F5Br and styrene into
pentafluorostilbene was observed with 2a at 130 °C (entries 1
and 2, Table 1). Decreasing the amount of catalyst lowered yields,
but higher TON were obtained (entry 3). Using C6F5I lower
conversions and higher reaction times were observed (entry 4).
C6F5Cl failed to react with styrene under the same conditions
(entry 5). An activated alkene, such as methyl acrylate, gave a
faster reaction with catalyst 2a at 100 °C; in this case, the use of
KF as base led to higher conversions (entries 6 and 7). [Pd(PPh3)4]
failed to catalyze the reaction of styrene and C6F5Br under the
same conditions reported in entry 1. The reaction with styrene
was not affected by oxygen or by the addition of galvinoxyl (Pd:
galvinoxyl ) 1:10). No radical addition products of PfBr to the
alkene were obtained.
Some of us had studied the insertion of dienes into the Pd-Pf
bond of [Pd(Pf)Br(NCMe)2] (1) and (NBu4)2[Pd2(µ-Br)2(Pf)2Br2]
(2a) (Pf ) C6F5) and isolated intermediates relevant in the Heck
reaction.10,11 The stoichiometric reaction of 2a and styrene in the
presence of a silver salt gave trans-PhCHdCHPf,11 which
encouraged us to look for catalytic conditions for it. Indeed 1
Table 1. Selected Results for the Heck Reaction in Eq 1a
ArX
olefin
base
Pd (mol %) time yield %
‡ The Weizmann Institute of Science. E-mail: david.milstein@weizmann.
ac.il.
(1) (a) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis, 2nd ed.;
Wiley: New York, 1992; Chapter 4. (b) Skupinska, J. Chem. ReV. 1991, 91,
613-648.
(2) Ittlel, S. D.; Johnson, L. K.; Brookhart, M. Chem. ReV. 2000, 100,
1169-1203.
(3) (a) Heck, R. F. Palladium Reagents in Organic Synthesis; Academic
Press: London, 1985. (b) de Meije`re, A.; Meyer, F. E. Angew. Chem., Int.
Ed. Engl. 1994, 33, 2379-2411. (c) Cabri, W.; Candiani, I. Acc. Chem. Res.
1995, 28, 2-7. (d) Beletskaya, I.-P.; Cheprakov, A. V. Chem. ReV. 2000,
100, 3009-3066.
(4) Organofluorine Chemistry. Principles and Commercial Applications;
Banks, R. E., Smart, B. E., Tatlow, J. C., Eds; Plenum Press: New York,
1994.
1
2
3
4
5
6
7
C6F5Br styrene
C6F5Br styrene
C6F5Br styrene
CaCO3
CaCO3
CaCO3
CaCO3
CaCO3
KF
1
1 d
6 d
15 d
1 d
1 d
7 h
10 h
5 d
1 d
98
97
47
8
0.1
0.01
1
1
1
1
2
1
C6F5I
styrene
C6F5Cl styrene
2
C6F5Br Me-acrylate
C6F5Br Me-acrylate
80
36
79c
37c,d
CaCO3
8b C6F5Br R-Me-styrene CaCO3
9
C6F5Br 1-hexene
CaCO3
a The reactions were carried out with 2.29 mmol ArX, 2.52 mmol
(3.44 mmol for entries 2 and 3) of alkene, 2.52 mmol base, H2O (0.1
mL) in 4 mL of NMP at 130 °C. b C6F5Br:olefin ) 1:1.4, NBu4Br (8%)
was added. c Nonoptimized conditions. d Mixture of isomers.
(5) (a) Ohff, M.; Ohff, A.; Van der Boom, M. E.; Milstein, D. J. Am. Chem.
Soc. 1997, 119, 11687-11688. (b) Ohff, M.; Ohff, A.; Milstein, D. Chem.
Commun. 1999, 357-358. (c) Ben-David, Y.; Portnoy, M.; Gozin, M.;
Milstein, D. Organometallics 1992, 11, 1995-1996.
The proposed mechanism for the reaction is represented in
Scheme 1. Complex 2a in CDCl3 gives immediately a 1:1.6
mixture of two isomers corresponding to the cis and trans
arrangements of the two C6F5 groups in the dimer. When NMP
(6) (a) Herrmann, W. A.; Brossmer, C.; Reisinger, C.-P.; Riermeier, T.
H.; O¨ fele, K.; Beller, M. Chem. Eur. J. 1997, 3, 1357-1364. (b) Herrmann,
W. A.; Brossmer, C.; O¨ fele, K.; Reisinger, C.-P.; Riermeier, T. H.; Beller,
M.; Fischer, H. Angew. Chem., Int. Ed. Engl. 1995, 34, 1844-1848. (c)
Herrmann, W. A.; Bo¨hm, V. P. W.; Reisinger, C.-P. J. Organomet. Chem.
1999, 576, 23-41.
(10) (a) Albe´niz, A. C.; Espinet, P.; Jeannin, Y.; Philoche-Levisalles, M.;
Mann, B. M. J. Am. Chem. Soc. 1990, 112, 6594-6600. (b) Albe´niz, A. C.;
Espinet, P. J. Organomet. Chem. 1993, 452, 229-234. (c) Albe´niz, A. C.;
Espinet, P.; Lin, Y.-S. Organometallics 1995, 14, 2977-2986.
(11) Albe´niz, A. C.; Espinet, P.; Foces-Foces, C.; Cano, F. H. Organo-
metallics 1990, 9, 1079-1085.
(7) (a) Morales-Morales, D.; Redo´n, R.; Yung, C.; Jensen, C. M. Chem.
Commun. 2000, 1619-1620. (b) Brunel, J. M.; Hirlemann, M.-H.; Heumann,
A.; Buono, G. Chem. Commun. 2000, 1869-1870.
(8) (a) Shaw, B. L.; Pereda, S. D. Chem. Commun. 1998, 1863-1864. (b)
Shaw, B. L.; Pereda, S. D.; Staley, E. A. Chem. Commun. 1998, 1361-1362.
(c) Van Strijdonck, G. P. F.; Boele, M. D. K.; Kamer, P. C. J.; de Vries, J.
G.; Van Leeuwen, P. W. N. M. Eur. J. Inorg. Chem. 1999, 1073-1076.
(9) Radical addition of fluoroalkyl iodides to alkenes to yield the saturated
alkyl iodides, initiated by metals and other reagents, has been reported. Heck-
type products are not obtained: Chien, Q.-Y. Isr. J. Chem. 1999, 39, 179-
192.
(12) For other examples of Heck catalysis in the absence of good stabilizing
ligands, see: (a) Reetz, M. T.; Westermann, E. Angew. Chem., Int. Ed. 2000,
39, 165-168. (b) Reetz, M. T.; Westermann, E.; Lohmer, R.; Lohmer, G.
Tetrahedron Lett. 1998, 39, 8449-8452. (c) Stephan, M. S.; Teunissen, A. J.
J. M.; Verzijl, G. K. M.; de Vries, J. G. Angew. Chem., Int. Ed. 1998, 37,
662-664. (d) Jeffery, T.; David, M. Tetrahedron Lett. 1998, 39, 5751-5754.
(e) Zhao, F.; Bhanage, B. M.; Shirai, M.; Arai, M. Chem. Eur. J. 2000, 6,
843-848. (f) Beller, M.; Ku¨hlein, K. Synlett 1995, 441-442.
10.1021/ja016315b CCC: $20.00 © 2001 American Chemical Society
Published on Web 10/30/2001