First Heck reaction with arenediazonium cations with recovery of Pd-triolefinic macrocyclic catalyst

Article abstract of DOI:10.1021/ol034340b

(Matrix presented) The air- and moisture-stable phosphine-free palladium(0) complex 1 is a highly active and recoverable catalyst for Heck olefination of aryl diazonium tetrafluoroborates. The reactions were performed under aerobic conditions at room temperature to give the coupling products in excellent yields.

Full text of DOI:10.1021/ol034340b

ORGANIC
LETTERS
2003
Vol. 5, No. 9
1559-1561
First Heck Reaction with
Arenediazonium Cations with Recovery
of Pd-Triolefinic Macrocyclic Catalyst
Judit Masllorens,† Marcial Moreno-Man˜as,‡ Anna Pla-Quintana,† and
,†
Anna Roglans*
Department of Chemistry, UniVersitat de Girona, Girona, 17071-Girona, Spain, and
Department of Chemistry, UniVersitat Auto`noma de Barcelona, Cerdanyola,
08193-Barcelona, Spain
anna.roglans@udg.es
Received February 26, 2003
ABSTRACT
The air- and moisture-stable phosphine-free palladium(0) complex 1 is a highly active and recoverable catalyst for Heck olefination of aryl
diazonium tetrafluoroborates. The reactions were performed under aerobic conditions at room temperature to give the coupling products in
excellent yields.
The palladium(0)-catalyzed reaction of aryl and alkenyl
halides with alkenes (the Heck reaction) represents one of
the most versatile tools in modern synthetic chemistry and
has great potential for industrial applications.1 In view of
the economy of the reaction, the recovery as well as recycling
of the expensive palladium catalyst is essential. In general,
palladium(0) requires stabilization by phosphines, which are
readily oxidized and consequently cause the loss of the
catalyst. Therefore, the development of phosphine-free
palladium catalysts is a topic of enormous importance.
Recently, we published synthetic procedures for a novel
type of palladium(0) complexes of 15-membered macrocyclic
triolefins containing different aryl units, for example, the
structure 1 represented in Figure 1.2 These phosphine-free
Figure 1. Structure of Pd(0) catalyst, 1.
† Universitat de Girona.
‡ Universitat Auto`noma de Barcelona.
(1) (a) Heck, R. F. Acc. Chem. Res. 1979, 12, 146. (b) Heck, R. F. Org.
React. N.Y. 1982, 27, 345. (c) Heck, R. F. In ComprehensiVe Organic
Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, New
York, 1991; Vol. 4, pp 833-863. (d) De Meijere, A.; Meyer, F. E. Angew.
Chem., Int. Ed. Engl. 1994, 33, 2379. (e) Cabri, W.; Candiani, I. Acc. Chem.
Res. 1995, 28, 2. (f) Negishi, E.; Cope´ret, C.; Ma, S.; Liou, S.; Liu, F.
Chem. ReV. 1996, 96, 365. (g) Crisp, G. T. Chem. Soc. ReV. 1998, 27, 427.
(h) Beletskaya, I. P.; Cheprakov, A. V. Chem. ReV. 2000, 100, 3009. (i)
Whitcombe, N. J.; Kuok Hii, K.; Gibson, S. E. Tetrahedron 2001, 57, 7449.
(j) Beller, M.; Zapf, A. In Handbook of Organopalladium Chemistry for
Organic Synthesis; Negishi, E., Ed.; Wiley-Interscience: New York, 2002;
Vol. 1, pp 1209-1222.
palladium(0) complexes are air- and moisture-stable and
recoverable catalysts in Suzuki cross-couplings,2b in the
telomerization of butadiene,3 and in the hydroarylation of
alkynes in ionic liquids.4
(2) (a) Cerezo, S.; Corte´s, J.; Lago, E.; Molins, E.; Moreno-Man˜as, M.;
Parella, T.; Pleixats, R.; Torrejo´n, J.; Vallribera, A. Eur. J. Inorg. Chem.
2001, 1999. (b) Corte´s, J.; Moreno-Man˜as, M.; Pleixats, R. Eur. J. Org.
Chem. 2000, 239. (c) Llobet, A.; Masllorens, E.; Moreno-Man˜as, M.; Pla-
Quintana, A.; Rodr´ıguez, M.; Roglans, A. Tetrahedron Lett. 2002, 43, 1425.
10.1021/ol034340b CCC: $25.00 © 2003 American Chemical Society
Published on Web 04/02/2003

Table 1. Heck Reaction of Arenediazonium Salts 2 Using Pd(0) Complex 1a
entry
diazonium salt, 2
olefin
time (h)
product
yieldb (%)
recovery of 1b (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15c
16d
17c
18c
2a
2b
2c
2d
2e
2f
2g
2a
2b
2c
2d
2e
2f
3
3
3
3
3
3
3
4
4
4
4
4
4
4
5
5
5
5
1.25
0.75
1
1.50
1.25
0.75
0.75
3
2.75
4
3.75
6.5
3
6a
6b
6c
6d
6e
6f
6g
7a
7b
7c
7d
7e
7f
95
95
100
100
78
97
78
88
100
100
71
69
99
94
97
100
96
38
97
100
97
95
94
100
100
99
99
97
95
88
95
98
98
95
95
93
2g
2a
2b
2c
2d
2.5
4.25
3.5
4
7g
8a
8b
8c
8d
4
a Reactions were carried out under aerobic conditions. Molar ratio 2/olefin ca. 1:1.6, [2] ca. 0.023 M. b Isolated by column chromatography on silica gel.
c 10% of catalyst 1 was required. d 15% of catalyst 1 was required.
Another drawback in the Heck reaction is the need for
high-cost aryl iodides or bromides as the most used aryl
electrophile components (ArX). An interesting alternative to
aryl halides for Heck reactions has been the use of arene-
diazonium salts.5 Diazonium salts offer several advantages
over the aryl halides: economic advantage of anilines
compared to aryl bromides and iodides, short reaction times,
mild and aqueous reaction conditions without added base,
and superior reactivity of the diazonium nucleofuge (N2) over
the bromides and iodides.
recovered catalyst described to date. Thus, we want to present
here the efficiency and recovery of palladium(0) complex 1
as catalyst in several Heck reactions summarized in Table
1.
Initial screening of the reaction conditions with the
diazonium salt 2a and ethyl acrylate 3 revealed that the
arylation was achieved using 5 mol % of Pd(0) catalyst 1 in
ethanolic solution at room temperature. It has to be pointed
out that the reaction was practical and very fast under aerobic
conditions using commercial and not degassed solvent. Pd-
(0) complex 1 was almost quantitatively recovered (97%)
by column chromatography on silica gel. The synthetic
efficacy of this reaction was studied with a number of
arenediazonium salts 2a-g and the olefins ethyl acrylate, 3,
tert-butyl acrylate, 4, and styrene, 5. Table 1 shows that the
nature of the substituents did not exert significant effect on
the yields and recovery of the catalyst. Formation of nitro-
substituted derivatives 6b (entry 2), 7b (entry 9), and 8b
(entry 16), from the 4-nitro salt 2b, are also quite significant
since this salt failed in several Heck reactions with acrylates.5b,e
Surprisingly, 4-methoxydiazonium salt failed to participate
in this reaction. Steric effects of ortho or meta substituents
do not seem to affect the reactivity of arenediazonium salts
(entries 5 and 6 in the case of olefin 3; entries 12 and 13 in
the case of olefin 4). Only in the case of styrene 5 did steric
effects come into play causing lowering of yields (entry 18).
In addition, m-methylbenzenediazonium tetrafluoroborate 2e
To the best of our knowledge, there has been no general
study of Heck reactions of aryl diazonium salts with
(3) (a) Estrine, B.; Blanco, B.; Bouquillon, S.; He´nin, F.; Moreno-Man˜as,
M.; Muzart, J.; Pena, C.; Pleixats, R. Tetrahedron Lett. 2001, 42, 7055. (b)
Moreno-Man˜as, M.; Pleixats, R.; Spengler, J.; Chevrin, C.; Estrine, B.;
Bouquillon, S.; He´nin, F.; Muzart, J.; Pla-Quintana, A.; Roglans, A. Eur.
J. Org. Chem. 2003, 274.
(4) Cacchi, S.; Fabrizi, G.; Goggiamani, A.; Moreno-Man˜as, M.; Vall-
ribera, A. Tetrahedron Lett. 2002, 43, 5537.
(5) (a) Kikukawa, K.; Matsuda, T. Chem. Lett. 1977, 159. (b) Kikukawa,
K.; Nagira, K.; Wada, F.; Matsuda, T. Tetrahedron 1981, 37, 31. (c) Ikenaga,
K.; Matsumoto, S.; Kikukawa, K.; Matsuda, T. Chem. Lett. 1988, 873. (d)
Yong, W.; Yi, P.; Zhuangyu, Z.; Hongwen, H. Synthesis 1991, 967. (e)
Sengupta, S.; Bhattacharya, S. J. Chem. Soc., Perkin Trans. 1 1993, 1943.
(f) Beller, M.; Fischer, H.; Ku¨hlein, K. Tetrahedron Lett. 1994, 35, 8773.
(g) Beller, M.; Ku¨hlein, K. Synlett 1995, 441. (h) Sengupta, S.; Sadhukhan,
S. K. Tetrahedron Lett. 1998, 39, 715. (i) Brunner, H.; Le Cousturier de
Courcy, N.; Geneˆt, J. P. Tetrahedron Lett. 1999, 40, 4815. (j) Priego, J.;
Carretero, J. C. Synlett 1999, 1603. (k) Darses, S.; Pucheault, M.; Geneˆt, J.
P. Eur. J. Org. Chem. 2001, 1121. (l) Carpes, M. J. S.; Correia, C. R. D.
Tetrahedron Lett. 2002, 43, 741. (m) Andrus, M. B.; Song, C.; Zhang, J.
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Org. Lett., Vol. 5, No. 9, 2003

is much more sensitive to decomposition than the other
isomers, giving lower yields (entries 5 and 12), or failing in
the case of styrene. In general, longer reaction times were
needed using tert-butyl acrylate 4 and styrene 5. In the case
of styrene, using 5% of catalyst, 1, products were obtained
in excellent yields, but longer reaction times were required
and the catalyst was recovered only in 85% yield. To improve
the recovery of complex 1, 10% of catalyst was needed
(entries 15, 17, and 18).
In the case of diazonium salts in Heck reactions, it has
been postulated that oxidative addition of the palladium
catalyst to the diazonium intermediate is not the rate-
determining step, in contrast to the generally accepted
mechanism of aryl bromides and aryl chlorides.1b To go
further in the mechanistic aspects with our catalytic system,
we conducted an electrospray ionization mass spectrometry
(ESI-MS) study to detect oxidative addition species directly
under reaction conditions. Since ESI-MS is a soft ionization
mass spectrometry,6 its ability to detect ionic species in
solution provides a convenient technique for direct observa-
tion of reaction intermediates.7 ESI-MS has been applied to
intermediate detection in several Heck reactions using aryl
triflates and aryl iodides.7c-e An equimolar amount of
arenediazonium tetrafluoroborate 2a was added to Pd(0)
complex 1 in methanol. Nitrogen was evolved immediately,
and the mixture was injected to the mass spectrometer for
analysis. Although our ESI-MS study does not provide
quantitative or detailed structural information about the
intermediates, we have been able to observe one peak at m/z
) 946 corresponding to the [macrocycle-Pd+ + Ar] ion with
the predicted isotope pattern. After the addition of the olefin,
samples of the reaction taken at 10 min intervals were
injected for analysis until completion of the reaction. We
did not observe any intermediate involving the olefin, but
when the intermediate resulting from oxidative addition
started to disappear, a peak corresponding to catalyst 1 (m/z
) 870) emerged. Experiments were repeated for diazonium
salts 2b, 2f, and 2g, and we observed the corresponding
oxidative addition species for all cases (2b, m/z ) 991; 2f,
m/z ) 960; 2g, m/z ) 964).
In conclusion, Pd(0) complex 1 is a recoverable phosphine-
free catalyst with high activity for the Heck reaction of
diazonium salts with acrylates and styrene to form the
corresponding (E)-cinnamates and (E)-stilbenes respectively,
affording excellent yields. ESI-MS studies provide mecha-
nistic evidence for oxidative addition species formed in the
catalytic cycle. Current studies are directed toward the
characterization of the intermediates by NMR techniques.
Acknowledgment. Financial support from MEC of Spain
(Project Nos. PB98-0902 and BQU2002-04002-C02 and
predoctoral grant to J.M.) and “Generalitat de Catalunya”
(Project No. SGR2001-00291) is gratefully acknowledged.
(6) Electrospray Ionization Mass Spectrometry. Fundammentals, Instru-
mentation and Applications; Cole, R. B., Ed.; John Wiley & Sons: New
York, 1997.
Supporting Information Available: Details of synthesis
and characterization data for Pd(0) complex 1, diazonium
salts 2a-g, and compounds 6a-g, 7a-g, and 8a-d.
Observed electrospray mass spectra and calculated isotopic
distributions for ESI-MS studies. This material is available
free of charge via the Internet at http://pubs.acs.org.
(7) (a) Wilson, S. R.; Pe´rez, J.; Pasternak, A. J. Am. Chem. Soc. 1993,
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Brown, J. M.; Hii, K. K. Angew. Chem., Int. Ed. Engl. 1996, 35, 657. (e)
Hii, K. K.; Claridge, T. D. W.; Brown, J. M. Angew. Chem., Int. Ed. Engl.
1997, 36, 984. (f) Aramend´ıa, M. A.; Lafont, F.; Moreno-Man˜as, M.;
Pleixats, R.; Roglans, A. J. Org. Chem. 1999, 64, 3592. (g) Griep-Raming,
J.; Meyer, S.; Bruhn, T.; Metzger, J. O. Angew. Chem., Int. Ed. 2002, 41,
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