Heck reaction catalyzed by Pd-modified zeolites

Article abstract of DOI:10.1021/ja001087r

[Pd]-exchanged NaY zeolites have been prepared, characterized, and applied for the first time for catalytic carbon-carbon coupling reactions. The catalysts exhibit a high activity and selectivity toward the Heck reaction of aryl bromides with olefins for small palladium concentrations (≥0.1 mol % of Pd). The catalysts can easily be separated from the reaction mixture and reused after washing without loss in activity. No limitation to the diffusion of adducts in the zeolite cages was observed (for linear alkenes). The electronic nature of the aryl bromides and the olefins has a dominating effect on the reaction yield and selectivity. The heterogeneous catalysts quantitatively convert all types of all aryl bromide (complete conversion of bromobenzene within 30 min) and activated aryl chlorides under standard reaction conditions. Product form selectivity is observed in the Heck reaction with cyclic olefins.

Full text of DOI:10.1021/ja001087r

5990
J. Am. Chem. Soc. 2001, 123, 5990-5999
Heck Reaction Catalyzed by Pd-Modified Zeolites
Laurent Djakovitch*,† and Klaus Koehler
Contribution from the Technische UniVersita¨t Mu¨nchen, Anorganisch-Chemisches Institut,
Lichtenbergstrasse 4, D-85747 Garching b. Mu¨nchen, Germany
ReceiVed March 28, 2000
Abstract: [Pd]-exchanged NaY zeolites have been prepared, characterized, and applied for the first time for
catalytic carbon-carbon coupling reactions. The catalysts exhibit a high activity and selectivity toward the
Heck reaction of aryl bromides with olefins for small palladium concentrations (e0.1 mol % of Pd). The
catalysts can easily be separated from the reaction mixture and reused after washing without loss in activity.
No limitation to the diffusion of adducts in the zeolite cages was observed (for linear alkenes). The electronic
nature of the aryl bromides and the olefins has a dominating effect on the reaction yield and selectivity. The
heterogeneous catalysts quantitatively convert all types of all aryl bromide (complete conversion of
bromobenzene within 30 min) and activated aryl chlorides under standard reaction conditions. Product form
selectivity is observed in the Heck reaction with cyclic olefins.
Introduction
is due to homogeneous (resolved Pd species) or heterogeneous
processes.
The Heck reaction, a palladium-catalyzed carbon-carbon
bond formation between aryl halides and olefins, became an
excellent tool for the synthesis of elaborated styrene derivatives
due to its tolerance for a wide variety of functional groups on
both reactants1 and the broad availability of aryl bromides and
chlorides.
Very recently, we reported the first heterogeneous Pd-
catalyzed Heck reaction using zeolites as catalyst supports.10
(1) (a) Heck, R. F.; Nolley, J. P., Jr. J. Org. Chem. 1972, 37, 2320-
2322. (b) Heck, R. F. In Palladium Reagents in Organic Synthesis;
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ComprehensiVe Organic Synthesis; Vol. 4, p 585ff and 833ff and references
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Reactions; Diederich, F., Stang, P. J., Eds.; Wiley-VCH: Weinheim, 1998;
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metallics 1995, 14, 5605-5614. (f) Diminnie, J.; Metts, S.; Parsons, E. J.
Organometallics 1995, 14, 4023-4025. (g) Herrmann, W. A.; Brossmer,
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In the past few years, the development of new highly active
soluble Pd complexes allowed the activation and conversion of
aryl chlorides,1,2 which are less reactive than bromides and
iodides. Regarding industrial applications, however, these cata-
lysts are expensive (Pd, phosphanes, or special ligand systems).
Few experiments address the separation of the catalyst from
the reaction mixture and their reuse. In addition to the separation
problems, deactivation of the homogeneous catalysts by forma-
tion of less active or inactive colloidal Pd species is often
encountered at the comparatively high reaction temperature.3
Attempts were made to overcome the problems concerning
thermal stability (high reaction temperatures), separation, and
recovery of the Pd complexes by the use of heterogeneous
palladium systems.4 Polymer-supported Pd complexes were used
for the activation of aryl iodides (and bromides) by several
groups.5 Pd on carbon and Pd on different metal oxides were
found to be suitable catalysts for the conversion of aryl iodides
and bromides.6 More recently, Pd particles supported on
mesoporous silica were successfully applied for the activation
of aryl bromides.7 Activation of chlorobenzenes has been
reported, but only under drastic reaction conditions (high
temperature, no solvent or reacting solvent such as MeOH).7,8
Few investigations correlated the Pd dispersion and activity
(conversion, reaction yield).6 Stabilized Pd colloids can catalyze
the Heck reaction of aryl iodides (and partially bromides).9 Very
recent studies demonstrate that, for phosphane or ligand free
Pd catalyst systems based on simple Pd salts, in situ formed
nanometer scale palladium colloids act as catalyst in the Heck
reaction.9 In general, however, it seems to be not yet clear
whether the Heck reaction catalyzed by supported Pd catalysts
(3) (a) Herrmann, W. A.; Brossmer, C.; O¨ fele, K.; Beller, M.; Fischer,
H. J. Mol. Catal. A: Chem. 1995, 103, 133-146. (b) Beller, M.; Fischer,
H.; Ku¨hlein, K.; Reisinger, C. P.; Herrmann, W. A. J. Organomet. Chem.
1996, 520, 257-259.
† Current address: Institut de Recherches sur la Catalyse, UPR CNRS
5401, 2 avenue Albert Einstein, 69626 Villeurbanne, France.
10.1021/ja001087r CCC: $20.00 © 2001 American Chemical Society
Published on Web 06/05/2001

Heck Reaction Catalyzed by Pd-Modified Zeolites
J. Am. Chem. Soc., Vol. 123, No. 25, 2001 5991
The choice of a zeolite as support was motivated by observations
that complexes immobilized in zeolite supercages have almost
the same activity as the free complexes in solution11 and because
in this manner a very high palladium dispersion can be achieved.
It has been reported that molecules or small metal particles
immobilized in zeolite cavities are stable.11,12 In addition, the
zeolite microstructure could help to overcome the problems of
leaching present with heterogeneous catalysts in solution.
Zeolites are capable of stabilizing intermediate active species
in their cavities and of controlling the reaction pathway via
shape-selectivity.12 Corresponding effects could be expected
from the similar size of the zeolite pores and the molecules
involved (catalyst precursors, adducts and products). For practi-
cal applications, the separation of Pd/zeolites by filtration is
expected to be easier and faster than, for example, high surface
area metal oxides due to the larger zeolite grain size.
The present paper demonstrates that this new approach
allowed us to prepare the most active heterogeneous palladium
catalysts for the Heck reaction of aryl bromides with olefins.
The best catalysts also induced reaction with activated aryl
chlorides with significant yields. The paper also addresses a
number of important and interesting aspects of the catalytic
reaction such as the influence of preparation and treatment of
the catalysts, activity and selectivity for a variety of substituents
at the aryl halide and alkene, kinetic studies, leaching of Pd
species, and recovery and reuse of the catalysts.
Results and Discussions
Catalysts Preparation. To obtain highly active heteroge-
neous Heck catalysts, in particular of different Pd dispersion,
we prepared several “Pd”-exchanged zeolites by immobilization
of different Pd species: Pd particles ([Pd(0)]), ionic species
([Pd(II)] and [Pd(NH3)4]2+), and neutral complexes ([Pd(OAc)2]
and [Pd(C3H5)Cl]2). The catalysts loaded with [Pd(0)], [Pd(II)],
and [Pd(NH3)4]2+ were prepared according to the literature13
by ion exchange of NaY zeolite, using a 0.1 M aqueous solution
(4) (a) Hertley, F. R. Supported Metal Complexes: A New Generation
of Catalysts; Riedel: Dordrecht, 1985. (b) Ermakov, Y. I.; Aezamaskova,
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Catalysis of Organic Reactions; Herkes, F. E., Ed.; Marcel Dekker: Basel;
1988; pp 415-427.
of [Pd(NH3)4]2+and 2Cl-. After a period of 24 h, [Pd(NH3)4]2+
-
(5) (a) Andersson, C.-M.; Karabelas, K.; Hallberg, A. J. Org. Chem.
1985, 50, 3891-3895. (b) Andersson, C.-M.; Hallberg, A. J. Org. Chem.
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1988, 53, 235-239. (d) Yi, P.; Zhuangyu, Z.; Hongwen, H. J. Mol Catal.
1990, 62, 297-306. (e) Wang, P. W.; Fox, M. A. J. Org. Chem. 1994, 59,
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A: Chem. 1995, 101, 25-31. (g) Villemin, D.; Jaffres, P. A.; Nechab, B.;
Courivaud, F. Tetrahedron Lett. 1997, 38, 6581-6584. (h) Bhanage, B.
M.; Shirai, M.; Arai, M. J. Mol. Catal. A: Chem. 1999, 145, 69-74. (i)
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Herrmann, W. A.; Hieringer, W.; Raudaschl-Sieber, G. Chem. Eur. J. 2000,
6, 1773-1780.
NaY was obtained. Calcination at 500 °C under pure O2 (180
mL/min) of the exchanged [Pd(NH3)4]2+ zeolites gave the
[Pd(II)]-NaY zeolite, and subsequent treatment at 350 °C with
pure H2 (70 mL/min) gave [Pd(0)]-NaY. The absolute pal-
ladium content for these catalysts was determined by AAS to
be 1 ( 0.2 wt % of Pd. As known from the literature, calcination
and reduction of the Pd species at such high temperatures leads
to agglomeration and the formation of palladium (oxide)
particles. These correspondingly pretreated catalysts can be
regarded as the models of lower Pd dispersion.
(6) (a) Choudary, B. M.; Sarma, R. M.; Rao, K. K. Tetrahedron 1992,
48, 719-726. (b) Augustine, R. L.; O’Leary, S. T. J. Mol. Catal. 1992, 72,
229-242. (c) Augustine, R. L.; O’Leary, S. T. J. Mol. Catal. A: Chem.
1995, 95, 277-285. (d) Beller, M.; Ku¨hlein, K. Synlett 1995, 441-442.
(e) Hiroshige, M.; Hauske, J. R.; Zhou, P. Tetrahedron Lett. 1995, 36, 4567-
4570. (f) Wali, A.; Pillai, S. M.; Kaushik, V. K.; Satish, S. Appl. Catal. A:
Gen. 1996, 135, 83-93. (g) Reetz, M. T.; Breinbauer, R.; Wanninger, K.
Tetrahedron Lett. 1996, 37, 4499-4502. (h) Shmidt, A. F.; Mametova, L.
V.; TKach, V. S. Kinet. Katal. 1991, 32, 760-761. (i) Shmidt, A. F.;
Mametova, L. V.; Dmitrieva, T. V.; Shmidt, E. Y.; Tkach, V. S. IzV. Akad.
Nauk. SSSR 1991, 40, 190. (j) Shmidt, A. F.; Mametova, L. V.; Tumas’ev,
R. V. Kinet. Katal. 1994, 35, 363-365. (k) Shmidt, A. F.; Mametova, L.
V. Kinet. Katal. 1996, 37, 406-408. (l) Shmidt, A. F.; Vladimirova, T. A.;
Shmidt, E. Y. Kinet. Katal. 1997, 38, 245-250. (m) Shmidt, A. F.; Khalaika,
A.; Nindakova, L. O.; Shmidt, E. Y. Kinet. Katal. 1998, 39, 200-206. (n)
Eisenstadt, A. In Utilization of the heterogeneous Palladium-on-carbon
catalyzed Heck Reaction in Applied Synthesis; Herkes, F. E., Ed.; Marcel
Dekker: Basel, 1998; Vol. 1, pp 415-427. (o) Zhao, F.; Bhanage, B. M.;
Shirai, M.; Arai, M. Chem. Eur. J. 2000, 6, 843-848. (p) Wagner, M.;
Ko¨hler, K.; Djakovitch, L.; Weinkauf, S.; Hagen, V.; Muhler, M. Top. Catal.
2000, 13, 319-326.
Analogous to the ion-exchange process used for the above
preparations, we prepared the following Pd complexes im-
mobilized in zeolites: [Pd(OAc)2] and [Pd(C3H5)Cl]2 in the
zeolite supercage.
Because the diameter of the zeolite channels is limited (for
the Y zeolite: φ ) 7.4 Å),14 we performed molecular modeling
calculations in order to check whether the complexes can pass
through the zeolite window. The results obtained for [Pd-
(NH3)4]2+-NaY, [Pd(OAc)2]-NaY, and [Pd(C3H5)Cl]2-NaY
using the MM2 augmented parameters15 provided with the
CAChe software from Oxford Molecular LTD16 are reported
in Figure 1.
Concerning [Pd(NH3)4]2+, we did not find any limitation due
to its small size and its pseudo-spherical geometry which allows
it to pass through the zeolite pore in all directions and for all
orientations.
Limitations are expected for the[Pd(OAc)2] and [Pd(C3H5)-
Cl]2 complexes. We found that a perpendicular orientation or
an orientation with a minimum angle of 56° for the [Pd(OAc)2]
complex and 42° for the [Pd(C3H5)Cl]2 complex, versus the
plane defined by the pore, is required for the complex to pass
through the pore.
(7) (a) Mehnert, C. P.; Ying, J. Y. Chem. Commun. 1997, 2215-2216.
(b) Mehnert, C. P.; Weaver, D. W.; Ying, J. Y. J. Am. Chem. Soc. 1998,
120, 12289-12296.
(8) (a) Julia, M.; Duteil, M. Bull. Soc. Chim. Fr. 1973, 2790. (b) Julia,
M.; Duteil, M.; Grard, C.; Kuntz, E. Bull. Soc. Chim. Fr. 1973, 2791-
2794. (c) Bozell, J. J.; Vogt, C. E. J. Am. Chem. Soc. 1988, 110, 2655-
2657. (d) Scott, W. J. J. Chem. Soc., Chem. Commun. 1987, 1755-1756.
(e) Kaneda, K.; Higuchi, M.; Imanaka, T. J. Mol. Catal. 1990, 63, L33-
L36.
(9) (a) Beller, M,; Fischer, H.; Ku¨hlein, K.; Reisinger, C.-P.; Herrmann,
W. A. J. Organomet. Chem. 1996, 520, 257-259. (b) Reetz, M. T.; Lohmer,
G. Chem. Commun. 1996, 1921-1922. (c) LeBars, J.; Specht, U.; Bradley,
J. S.; Blackmond, D. G. Langmuir 1999, 15, 7621. (d) Reetz, M. T.;
Westermann, E. Angew. Chem., Int. Ed. 2000, 112, 170.
These calculations were supported by the time necessary for
sufficient ion exchange. To obtain reasonable amounts of
palladium in the zeolite when using the [Pd(OAc)2] and
(13) (a) Michalik, J.; Narayana, M.; Kevan, L. J. Phys. Chem. 1985, 89,
4553-4560. (b) Sachtler, W. M. H.; Cacalcanti, F. A. P. Catal. Lett. 1991,
9, 261-272.
(14) Structures of the zeolites Y were obtained from: Meier, W. M.,
Olson, D. H., Baechlocher, Ch.,Eds. Atlas of Zeolites Structures Type;
Elsevier: New York; 1996; p 104.
(15) Allinger, N. L. J. Am. Chem. Soc. 1977, 99, 8177.
(16) CAChe version 4.1.1 for PowerMacintosh from Oxford Molecular
Ltd. was used for the molecular modeling using the parameters provided
by Dr. E. Chamot to calculate the zeolite structure.
(10) (a) Djakovitch, L.; Koehler, K. J. Mol. Catal. A: Chem. 1999, 142,
275-284. (b) Djakovitch, L.; Heise, H.; Ko¨hler, K. J. Organomet. Chem.
1999, 584, 16-26.
(11) (a) Schmid, G. Chem. ReV. 1992, 92, 1709-1727. (b) Sachtler, W.
M. H. Acc. Chem. Res. 1993, 26, 383-387. (c) Sachtler, W. M. H.; Zhang,
Z. AdV. Catal. 1993, 39, 129-220. (d) Corma, A. Chem. ReV. 1997, 97,
2373-2419.
(12) Gates, B. C. In Catalytic Chemistry; Wiley: New York, 1992; p
259ff.

5992 J. Am. Chem. Soc., Vol. 123, No. 25, 2001
DjakoVitch and Koehler
Figure 1. Molecular modeling of the Pd complexes ([Pd(NH3)4]2+, [Pd(OAc)2], [Pd(C3H5)Cl]2) in Na-Y zeolite using the CAChe software with
extended MM2 molecular force field and molecular mechanics methods.
Scheme 1a
a Reaction conditions: 10 mmol of 4-bromofluorobenzene 1, 15 mmol of styrene 2, 15 mmol of NaOAc, 0.1 mol % of [Pd]-NaY, 8 mL of
DMAc, 140 or 100 °C, 20 h.
Table 1. Activity and Selectivity for the Heck Reaction of 4-Bromofluorobenzene with Styrene (Scheme 1) Catalyzed by [Pd]-NaY or,
When Available, by the Corresponding Homogeneous Complexes (0.1 mol %)
product yield [%]a
heterogeneous catalyst
homogeneous catalyst
catalyst
T [°C]
3
4
5
3
4
5
TOFb
[Pd(0)]-NaY
140
100
140
100
140
100
140
100
140
100
89.4 [88.2]
85.1 [78.9]
90.2 [87.6]
89.3 [76.2]
93.0 [89.1]
94.5 [89.5]
79.2 [68.7]
57.6 [39.9]
86.3 [78.2]
74.2
0.9
1.0
1.0
0.9
1.0
0.7
0.9
0.4
1.0
0.5
8.2
7.9
8.4
8.1
8.8
6.7
7.2
3.9
8.3
5.2
20
16
80
[Pd(II)]-NaY
75
[Pd(NH3)4]2+-NaY
[Pd(OAc)2]-NaY
[Pd(C3H5)Cl2-NaY
{94.0}
{92.2}
{83.8}
{47.6}
{87.1}
{30.9}
{1.0}
{1.0}
{0.9}
{0.3}
{0.9}
{0.2}
{8.8}
{8.4}
{7.6}
{3.9}
{8.4}
{2.1}
6000
2660
2000
1140
2700
1210
a GLC yields and [isolated yields] are given and compared to {GLC yields for homogeneous catalysts} (∆rel ) (10%). Reaction time 20 h.
b Turn-over-frequency calculated at the completion of the reaction (mol of aryl bromide transformed/mol of heterogeneous catalyst)/h using 0.05
mol % of catalyst. Although TOF changes during the reaction, it allows better comparison to other catalysts concerning the activity.
[Pd(C3H5)Cl]2 complexes, 3 days were required (giving 0.7%
and 0.5% Pd catalyst, respectively). MAS NMR of the Pd
complexes in the zeolites have been recorded and confirmed
that the immobilized complexes are intact within the zeolite
cages. The spectra (1H, 13C) were comparable to the solution
NMR spectra obtained for the corresponding free complexes
(see Experimental Section).
Catalytic Activity. As a first model reaction, we chose the
reaction of 4-bromofluorobenzene with styrene (Scheme 1). This
reaction is known to give high yields of the Heck product with
homogeneous catalysts, thereby allowing the observation of
small changes in activity of the catalysts, particularly when
applied to heterogeneous systems.10
The conversion and selectivity obtained at two temperatures
for the Pd-loaded zeolites (0.1 mol % of Pd/aryl bromide 1)
are reported in Table 1. For the Pd complexes immobilized in
NaY zeolite, the results are compared to results obtained with
the corresponding Pd complexes in bulk solution (i.e., homo-
geneous catalysis).
species gave higher activities. Variations are also observed for
the Pd complexes ([Pd(NH3)4]2+, [Pd(OAc)2], and [Pd(C3H5)Cl]2).
The results indicate that the catalytic activity of the Pd-loaded
zeolites depends on the nature of the complex. The activity
of [Pd(NH3)4]2+ was higher than that of [Pd(OAc)2] and
[Pd(C3H5)Cl]2. This dependence of the activity is probably
due to a higher stability of the active Pd species generated
from the [Pd(NH3)4]2+ complex than from the [Pd(OAc)2] or
[Pd(C3H5)Cl]2 complexes (ligand effect, see also recovery of
the catalysts). These interpretations are supported by the
comparison of these results with those of the free Pd complexes
in solution (homogeneous catalysts without zeolite). Table 1
illustrates that the Pd complexes immobilized in zeolites have
almost the same activity as the free Pd complex. A comparison
of the activity of free and immobilized [Pd(OAc)2] and
[Pd(C3H5)Cl]2 at 100 °C shows that higher activity for the
immobilized complexes is obtained. This is probably due to
better stabilization of the active Pd species by the zeolite
framework.12
For all types of heterogeneous catalysts, Table 1 shows that
the activity is less strongly dependent on the temperature of
the reaction than expected. Slightly lower yields based on Pd
complexes were observed at 100 °C for the catalysts. The small
Considering the Pd(0) particles or the ionic Pd species
([Pd(II)] or [Pd(NH3)4]2+), the results did not show a strong in-
fluence of the palladium oxidation state on product yields or
product selectivity. Generally the zeolites modified by ionic Pd

Heck Reaction Catalyzed by Pd-Modified Zeolites
J. Am. Chem. Soc., Vol. 123, No. 25, 2001 5993
differences could indicate that different active species are formed
at the two temperatures, the species generated at 100 °C being
probably more active but less stable (see recovery of the
catalysts).
Kinetic Studies. While we did not observe strong variations
for the heterogeneous Heck reaction using standard reaction
conditions (Scheme 1: 100 °C or 140 °C, 20 h), clear differences
were observed in kinetic experiments. We compared the activity
of the [Pd(0)]-, [Pd(II)]-, and [Pd(NH3)4]2+-NaY catalysts
during the reaction between p-BrFC6H4 (1) and the styrene (2)
under standard reaction conditions (Scheme 1: T ) 140 °C,
0.05 mol % of [Pd]).
ing of active species from heterogeneous catalysts in solution
must be evaluated to identify whether the active centers are solid
surfaces or dissolved palladium complexes. As a method, we
investigated the residual activity of the supernatant solution after
separation of the catalyst. The leaching was studied as fol-
lowed: the organic phase of a first run was separated from the
solid (Pd-modified zeolite). New reagents (p-BrFC6H4, styrene,
and NaOAc) were added to the clear filtrate, and the composition
of the reaction mixture was determined by GC. The amount of
p-BrFC6H4 was set to 100%. This homogeneous reaction mix-
ture was treated as a standard catalytic experiment (100 or 140
°C, 20 h). After 20 h, the composition was determined by GC
again. The differences observed between the two GC determina-
tions gave qualitative information about the “leaching” (Table
2). While this method did not allow the absolute quantifica-
tion of the palladium species (active and/or inactive) dissolved,
it gave information about the presence or absence of actiVe
species in bulk solution and the activity of leached species in
the heterogeneous Heck reaction. Palladium species dissolved
but retained in the zeolite cages cannot be detected by this
procedure.
In all cases, the leaching observed cannot explain the overall
activity of the catalysts (see also recovery of catalyst). In
addition, we never detected Pd in the isolated organic com-
pounds (AAS analysis).
However, small amounts of leaching of palladium were
detected. The amount of leaching depended on the tempera-
ture of the reaction and on the nature of the Pd species
immobilized in the zeolite cages (Table 2). Thus, no leaching
was observed for [Pd(0)]-NaY at both temperatures, and a
slight leaching (0.6%) was found for [Pd(II)]-NaY at 140 °C.
A better stabilization of the [Pd(0)] particles by the zeolite
framework at the beginning of the reaction could be an ex-
planation.12
For [Pd(II)]-NaY (Figure 2b) an induction period of ca. 8
min was required before the reaction started. This induction
period was not observed for the [Pd(0)]-NaY (Figure 2a).
When using [Pd(0)]-NaY the products of the reaction could
be detected by GC after 30 s. This result is similar to the
observations made with [Pd(NH3)4]2+-NaY (Figure 2c). With
this catalyst, an induction period of ca. 2 min was observed.
The curves obtained with [Pd(II)]-NaY or [Pd(NH3)4]2+-NaY
are similar to the ones observed for homogeneous catalysis.1
The induction period corresponds to the delay required for the
reduction of the [Pd(II)] species (catalyst precursor) to the active
[Pd(0)]. This reduction is probably caused both by the styrene17
and by the OH groups present in the zeolite cages.18 In other
experiments,10a we observed that the use of HY zeolites instead
of NaY as support reduce the induction period from 8 min for
the Na form to 4 min for the H form. This corroborates a partial
reduction of the [Pd(II)] species by OH groups.
As can be seen from the time axis (in Figure 2), the [Pd-
(NH3)4]2+-NaY catalyst was found to be the most active for
the reaction. Thus, the Heck reaction of p-BrFC6H4 with styrene
is completed after ca. 20 min using [Pd(NH3)4]2+-NaY, whereas
it required ca. 1450 min when using Pd(II)-NaY and ca. 7200
min when using the Pd(0)-NaY. The selectivity and the activity
observed are comparable to those obtained with standard
homogeneous catalysts but lower than those obtained with the
most recent, most active catalysts.1,2 The differences in activity
of the three catalysts can be rationalized by the different
treatment of the catalysts at higher temperature. As reported,
such treatments decrease the dispersion of the Pd species
entrapped into the zeolite cages.19 Thus, [Pd(NH3)4]2+-NaY
would present the highest dispersion, since it was not sub-
jected to any thermal treatment after the ion-exchange, in
contrast to the [Pd(II)]-NaY or the [Pd(0)]-NaY catalysts.
The calcination at 500 °C of [Pd(NH3)4]2+-NaY to give
[Pd(II)]-NaY tends to form aggregated [Pd(II)] species in the
zeolite cages. In addition, the reduction temperature influences
strongly the size of the [Pd(0)] particles formed in the zeo-
lites. The [Pd(II)] catalyst reduced in situ leads to [Pd(0)] spe-
cies with higher dispersion, since it is obtained by relatively
low-temperature treatment (140 °C). In contrast, the reduced
[Pd(0)] catalyst obtained by treatment under an H2 atmosphere
at 350 °C leads to larger palladium particles in the zeolite.19
These results suggest that there is a relation between the
dispersion of the [Pd(0)] species in the zeolite and the activity
of the catalysts.
For [Pd(NH3)4]2+, a higher degree of leaching is observed at
140 °C (0.5%) than at 100 °C, at which temperature it was not
detected. We did not observe leaching from the immobilized
[Pd(OAc)2] catalyst at either reaction temperature, but we
observed a relatively high leaching (9%) from the immobilized
[Pd(C3H5)Cl]2 catalyst at 140 °C. The leaching was strongly
reduced by the use of a lower reaction temperature (i.e., 100
°C). Actually, this observation can be correlated with the relative
stability of the complexes under the reaction conditions. Thus,
the [Pd(C3H5)Cl]2 decomposes quickly at 140 °C (Tdec ) 120
°C),20 whereas [Pd(OAc)2] decomposes more slowly (Tdec
)
205 °C)20 at this temperature. The [Pd(NH3)4]2+ complex
decomposes in two steps: Tdec1 ) 158 °C, and Tdec2 ) 285
°C,21 which can explain the slightly better stability of the catalyst
obtained at 100 °C.
Recovery of the Catalysts. An important point concerning
the use of heterogeneous catalysts is its lifetime, particularly
for industrial and pharmaceutical applications of the Heck
reaction.
After separation and washing, the heterogeneous catalysts
were used several times for the same or similar reactions under
the same conditions as for the initial run of the catalyst without
any regeneration. The conversion and selectivity are reported
in Table 3.
Examination of the Presence of Catalytically Active
Species in Homogeneous Bulk Solution (“Leaching”). Leach-
The results depend on the nature of the Pd species entrapped
in the zeolite at the beginning of the reaction. Thus, recycled
(17) Zina, M.; Olivier, D.; Ghorbel, A. ReV. Chim. Mine´r. 1985, 22, 321-
330.
(18) (a) Naccache, C.; Primet, M.; Mathieu, M. V. AdV. Chem. Ser. 1973,
121, 266-280. (b) Naccache, C.; Dutel, J. F.; Che, M. J. Catal. 1973, 29,
179-181. (c) Mo¨ller, K.; Bein, T. J. Phys. 1986, 47, C8 231-237.
(19) Gallezot, P. Stud. Surf. Sci. Catal. 1980, 5, 227.
(20) Lide, D. R., Ed. CRC Handbook of Chemistry and Physics, 76th
ed.; CRC Press: Boca Raton, FL; 1995-1996.
(21) The temperatures of decomposition of the [Pd(NH3)4]2+, 2Cl- was
measured by thermogravimetry coupled to a mass spectrometer.

5994 J. Am. Chem. Soc., Vol. 123, No. 25, 2001
DjakoVitch and Koehler
Figure 2. Kinetic investigations: conversion of 4-bromofluorobenzene 1 and product percentage (3, 4, and 5) obtained with the [Pd(0)]-NaY,
[Pd(II)]-NaY, and [Pd(NH3)4]2+-NaY catalysts, respectively, for the Heck reaction (Scheme 1).

Heck Reaction Catalyzed by Pd-Modified Zeolites
J. Am. Chem. Soc., Vol. 123, No. 25, 2001 5995
Table 2. Activity and AAS Analysis of the Clear Supernatant
Table 4. Recovery and Reuse (Catalyst Recycling): Heck Reaction
of 4-Bromofluorobenzene with Styrene (Scheme 1) Catalyzed by
Recovered [Pd complex]-NaY Used in a First Run at 100 °C (0.1
mol %) Before and After the Regeneration
activity of
the clear
AAS analysis
T [°C] of the
first run
of the clear
catalysts
supernatanta
supernatantb
yield of product 3 [%]a
[Pd(0)]-NaY
140
100
140
100
140
100
140
100
140
100
<1%
<1%
5%
<1%
3%
<1%
<1%
<1%
26%c)
<1%
<0.5 ppm
<0.5 ppm
8 ppm
<0.5 ppm
6 ppm
<0.5 ppm
<0.5 ppm
<0.5 ppm
112 ppm
<0.5 ppm
catalyst
[Pd(NH3)4]2+-NaY
reactivationb
first run
94.5
recycled
[Pd(II)]-NaY
no
yes
no
yes
no
yes
1.0
75.2
17.8
79.8
1.4
[Pd(NH3)4]2+-NaY
[Pd(OAc)2]-NaY
[Pd(C3H5)Cl2]-NaY
[Pd(OAc)2]-NaY
57.6
74.2
[Pd(C3H5)Cl2-NaY
75.3
a GLC yields are given (∆rel ) (10%). b After separation, the solid
catalyst was washed with CH2Cl2 and dried at room temperature; no
additional reactivation or reactivation was made by treating the recycled
catalyst for 1 h at 140 °C under the reaction conditions.
a The activity of the clear supernatant was measured for the Heck
reaction of 4-bromofluorobenzene with styrene (Scheme 1). GLC yields
for product 3 [%] resulting from a conversion of the 4-bromofluo-
robenzene are given (∆rel ) (10%). Values < 1% are considered to
be under the error limit of the analytical method. b The AAS analysis
was performed on the clear filtrate directly from the organic solution.
The detection limit was given to be 0.5 ppm. Values under this limit
are regarded as the absence of leaching concerning the analytical method
used here. c The relatively high activity observed in this case could be
due to the leaching of the Pd complex [Pd(C3H5)Cl2] that shows a high
activity at that reaction temperature.
Table 5. Yield of 3 [%] in the Heck Reaction of
4-Bromofluorobenzene with Styrene (Scheme 1) Catalyzed by
Recovered [Pd(0)]-NaY Used in a First Run at 140 °C (0.1 mol %)
with Dependence on the Drying Temperature (24 h) Applied Before
Reuse of the Catalyst. In Addition, the Corresponding Weight Loss
(Water) Determined by Thermogravimetric Investigation of the
Catalyst Is Given
T [°C]
3 [%]a
weight loss [%]
25
60
80
120
Table 3. Heck Reaction of 4-Bromofluorobenzene with Styrene
(Scheme 1) Catalyzed by Recovered [Pd]-NaY (0.1 mol %)
86.0
<1
50.1
<1
12.9
6
2.0
14
yield of product 3 [%]a
a GLC yields are given (∆rel ) (10%).
catalyst
T [°C]
first run
recycled
[Pd(0)]-NaY
140
100
140
100
140
100
140
100
140
100
89.4
85.1
90.2
89.3
93.0
94.5
79.2
57.6
86.3
74.2
86.0
80.1
89.2
88.7
80.9
1.0
81.2
17.8
72.0
1.4
situations (100 or 140 °C). We postulate that the active species
generated for all catalysts based on Pd complexes in these
systems have the same structure at 140 °C. This structure is
probably based on [Pd(0)] particles bound into the zeolite cage
(the different selectivity of homogeneous catalysts and the Pd/
zeolite system to polyaromatic compounds of large molecule
diameters are an additional indication for such a reaction inside
the zeolite pores, see below).
[Pd(II)]-NaY
[Pd(NH3)4]2+-NaY
[Pd(OAc)2]-NaY
[Pd(C3H5)Cl2-NaY
In other experiments, we evaluated the effect of the catalyst
posttreatments after separation from the reaction medium
(particularly the drying temperature). After filtration and wash-
ing, the catalysts were dried at different temperatures before
they were used without any other treatments. The drying
temperature played an important role. The results reported in
Table 5 for the recycled [Pd(0)]-NaY catalysts showed that
the activity decreased dramatically with the drying temperature
(the other catalysts gave similar results).
To explain these observations, we measured the loss of
volatile compounds (mainly water) by thermogravimetry. The
activity of the catalyst decreased as a function of the drying
temperature, i.e., the loss of water molecules (Table 5). We
postulate that the water molecules present in the zeolite
framework act as a “carrier-regulator” for the elimination of
the salt from the pores to the bulk solution. The partial
elimination of the water molecules from the support probably
tends to occlude the pores.
A clearer description of the loss in activity of the catalysts
by recycling can be obtained by the reaction of nonactivated
aryl bromides and using shorter reaction times. The results of
such recovery-reuse experiments are shown in Table 6 for the
reaction of bromobenzene with styrene (Scheme 2). With
repeated recycling, the mass of the solid (catalyst + residual
base + sodium bromide) increased significantly, making
handling difficult. Washing the solid with water, in addition to
the use of organic solvent, was necessary to remove the base
and sodium bromide. The results show that catalyst recycling
and reuse is possible, but with clearly decreased activity.
a GLC yields are given (∆rel ) (10%).
[Pd(0)]- and recycled [Pd(II)]-NaY show activities comparable
to those of the fresh catalysts. The catalysts were used up to
five times, and the yields were reduced only slightly (<5% for
each reuse).
For the catalysts based on Pd complexes, the situation was
different. Table 3 shows that all the complexes used in a first
run at 140 °C showed activity that was comparable to the activity
observed for the first run. In contrast, the catalysts used in a
first run at 100 °C showed a lower activity in these experiments
(at 100 °C).
To explain these results, we tried to regenerate the catalysts
used in a first run at 100 °C. This was accomplished by treating
the recovered catalysts at 140 °C for 1 h under the reaction
conditions.
The results reported in Table 4 show that the regenerated
catalysts showed an activity that was comparable to the high
activity observed for the recovered catalysts used in a first run
at 140 °C.
These observations can be rationalized by the generation of
different active species at the two temperatures, with the species
generated at 100 °C being irreversibly destroyed during the
extraction in air while the species generated at 140 °C is stable
in air.
These results can be compared to results obtained with
[Pd(0)]- or [Pd(II)]-NaY, for which we propose that the active
species are [Pd(0)] particles entrapped into a zeolite in all

5996 J. Am. Chem. Soc., Vol. 123, No. 25, 2001
DjakoVitch and Koehler
Table 6. Recovery and Reuse (Catalyst Recycling): Yields of
trans-Stilbene 8 [%] in the Reaction of Bromobenzene and Styrene
(Scheme 2, R1 ) H, R3 ) Br and R2 ) Ph) Catalyzed by
[Pd(NH3)4]2+-NaY. The Influence of the Washing Solvent
(Dichloromethane or Dichloromethane and Then Water) Is
Illustrated
chlorides more favorable. As already mentioned in the literature,
an interesting salt effect was observed with n-Bu4NBr.23
Addition of this salt gave increased activity for this reaction,
but this increased activity was accompanied by a dehalogenation
reaction leading to the formation of acetophenone in 8.3% yield.
(3) Selectivity of the Heterogeneously Catalyzed Heck
Reaction. In addition to the experiments described, we were
interested in studies concerning the selectivity of the Heck
reaction using cyclic olefins (Scheme 3).
While this area was extensively studied using homogeneous
catalysts,24 the isomerization of the product and the formation
of polyaryl compounds by successive Heck coupling reactions
remains an important problem.
yields of product 8 [%]a,b
washing procedure
1st runb
2nd run
3rd run
dichloromethane
dichloromethane + water
87
87
25
16
11
15
a Reaction conditions: 6 h reaction time, 0.1 mol % of Pd, 140 °C,
base (sodium acetate) in DMAc. b GLC yields are given (∆rel ) (10%).
c Without washing.
As a model reaction, we chose the coupling of 4-bromo-
acetophenone with cyclohexene (Scheme 3). This reaction is
known to be difficult. Low reactivity of this olefin is generally
observed in the Heck reaction, but this olefin provides the
advantage of limiting the number of possible product isomers.
We compared reactions containing the [Pd(NH3)4]2+-NaY
heterogeneous catalyst with those containing a standard homo-
geneous catalyst [Pd(OAc)2/PPh3].
Complete conversion can be achieved, however, using longer
reaction times (20 h).
Variation of the Educts. (1) Reaction between Aryl
Bromides and Olefins. To generalize the results obtained for
the heterogeneously catalyzed Heck reaction with the model
reaction (Scheme 1), experiments have been conducted using
other aryl halides and olefins as substrates and the [Pd-
(NH3)4]2+-NaY catalyst (Scheme 2).
The results reported in Table 10 show that we obtained almost
the same selectivity (respectively 13:14:15 ≈ 1:15:84 in DMAc)
using a heterogeneous catalyst as with homogeneous systems
and that the product 15 is formed as the major isomer. As found
by molecular modeling calculations,25 such a distribution would
correspond to the formation of the thermodynamically most
stable isomer. In addition, we found that replacing DMAc by
DMF as solvent would disfavor the formation of acetophenone
16, one of the main side products of the reaction. While
conversion of the aryl bromides is low compared to that of
homogeneous systems (possibly due to the diffusion control),
the heterogeneous catalysts are never formed polyaromatic
compounds, which represent 10-12% of the products formed
with homogeneous systems. This observation can be rationalized
by the similar sizes of zeolite pores, and the polyaromatic
compounds and can be interpreted as an interesting example of
product form selectivity of zeolite-based catalysts.
The results reported in Table 7 show that the heterogeneous
catalyst has a high activity toward the activation of aryl
bromides, even for the nonactivated bromoanisole (R1 ) CH3O,
R3 ) Br). Concerning the variation of the olefins, the electron-
n
poor olefins (R2 ) Ph, BuO-CO) gave better yields than the
electron-rich olefins (R2 ) nBuO) as expected. The activity trend
observed for aryl bromides was similar to that observed with
homogeneous catalysis and depended on the para-substituent
and the π-electron density of the olefins.1,2 In addition to these
experiments, kinetic studies have been performed for the reaction
of aryl bromides (R1 ) F, H, and OCH3, R3 ) Br) with styrene
(R2 ) Ph) using 0.05 mol % of Pd catalyst. The results showed
that [Pd(NH3)4]2+-NaY is a highly active heterogeneous
catalyst for the Heck reaction, including the nonactivated
bromobenzene and the “deactivated” 4-bromoanisole. After an
initiation period of ca. 2-5 min, complete conversion of the
aryl bromides was achieved in 20, 35, and 51 min, respectively,
for R1 ) F, H, OCH3.
Conclusions
For a fair comparison of the activity of the Pd/zeolite catalysts
to the best heterogeneous catalysts reported in the literature very
recently, the Heck reaction of bromobenzene with styrene or
methyl acrylate is the most suitable and important. It can be
[Pd]-NaY zeolites exhibit a high activity toward the Heck
reaction of aryl bromides with olefins, under standard reaction
conditions. Small amounts of palladium (0.1 mol %) are required
to perform the reaction. As for the homogeneous Heck reaction,
the electronic nature of the aryl bromides and the olefins has a
dominating effect on the reaction yield and selectivity. The
activated aryl bromides and the electron-poor olefins (R2 ) Ph,
nBuO-CO) react nearly quantitatively. The catalysts can be
easily separated from the reaction mixture (filtration) and reused
after washing. Depending on the reaction temperature, some
catalysts were deactivated during the extraction. However, active
species could be regenerated by a simple procedure. Except for
concluded from Table 8 that the activity of the [Pd(NH3)4]2+
-
NaY-zeolite system reported here exceeds that of the other
catalysts by at least 1 order of magnitude (TOF, reaction rate).
In addition, the necessary reaction temperature is lower.
(2) Activation of Aryl Chlorides. Another important issue
concerning the heterogeneous Heck reaction is the possibility
to activate the economically more interesting aryl chlorides. To
examine this possibility, we studied the reaction between
4-chloroacetophenone (R1 ) CH3CO, R3 ) Cl, Scheme 2) and
styrene (R2 ) Ph) using [Pd(NH3)4]2+-NaY as heterogeneous
catalyst.
(23) (a) Jeffery, T. Tetrahedron Lett. 1994, 35, 3051-3054. (b) Jeffery,
T. Tetrahedron Lett. 1994, 35, 4103-4106. (c) Jeffery, T. Tetrahedron 1996,
52, 10113-10130.
As expected, the results reported in Table 9 show that the
activation of aryl chlorides required a higher temperature than
did activation of the bromo derivatives. This result parallels the
halogen-carbon bond energy, which was calculated for bro-
moacetophenone (ca. 80.5 kcal/mol)22 and chloroacetophenone
(ca. 96 kcal/mol).22 However, one should also consider that the
Pd-Cl bond is stronger in the resulting Pd complex, and this
stronger bond makes the thermodynamics for activation of aryl
(24) (a) Kikukawa, K.; Nagira, K.; Wada, F.; Matsuda, T. Tetrahedron
1981, 37, 31-44. (b) Larock, R. C.; Baker, B. E. U.S. Patent 4,879,426,
1988. (c) Larock, R. C.; Baker, B. E. Tetrahedron Lett. 1988, 29, 905-
908. (d) Larock, R. C.; Gong, W. H. J. Org. Chem. 1989, 54, 2047-2050.
(e) Larock, R. C.; Gong, W. H.; Baker, B. E. Tetrahedron Lett. 1989, 30,
2603-2606. (f) Larock, R. C. Pure Appl. Chem. 1990, 62, 653ff. (g)
Loiseleur, O.; Meier, P.; Pfaltz, A. Angew. Chem. 1996, 108, 218-220.
(h) Loiseleur, O.; Hayashi, M.; Schmees, N.; Pfaltz, A. Synthesis 1997,
1338-1345.
(22) Streitwieser, A.; Heathcock, C. H.; Kosower, E. M. Introduction to
Organic Chemistry, 4th ed.; MacMillan Press: London, 1992.
(25) CAChe version 4.1.1 for PowerMacintosh from Oxford Molecular
Ltd. was used for the molecular modeling.

Heck Reaction Catalyzed by Pd-Modified Zeolites
J. Am. Chem. Soc., Vol. 123, No. 25, 2001 5997
Scheme 2a
a Reaction conditions: 10 mmol of aryl halide 6, 15 mmol of olefin 7, 15 mmol of NaOAc, 0.1 mol % of [Pd]-NaY, 8 mL of DMAc, 140 °C,
20 h.
Table 7. Heck Reaction of Various Aryl Bromides with Different
Alkenes (Scheme 2, R3 ) Br) Catalyzed by [Pd(NH3)4]2+-NaY at
140°C (0.1mol % Pd)
Pd complexes entrapped in zeolites. The active palladium species
could be complexes formed in situ by decomposition of the
entrapped Pd complexes. These complexes may coexist with
adsorbed entities by a dissolution-adsorption equilibrium of
Pd(0/II) species but are retained in the zeolite cages. Current
investigations focus on kinetic and mechanistic aspects.
product yield [%]a
R1
R2
8
9
10
CH3O
H
F
NO2
Ph
Ph
Ph
Ph
Ph
81.2 [75.8]
84.9 [77.8]
93.0 [89.1]
94.8 [89.8]
93.7 [79.6]
25.7
9.5
0.7
1.0
1.1
1.1
20.4
0.5
0.7
6.5
8.8
4.1
4.9
12.4
0.4
Experimental Section
All preparations, manipulations, and reactions were carried out under
argon, including the transfer of the catalyst to the reaction vessel. All
glassware was base- and acid-washed and oven dried. THF was freshly
distilled under argon over sodium from purple benzophenone ketyl
before use. The zeolite NaY was purchased from Sigma-Aldrich
Chemical (LZ-Z-52) and dried under 5 × 10-2 mmHg at 120 °C for
48 h before use. All other chemicals (organic reagents and solvent)
were deaerated by an argon flow before they were used. The Pd-loaded
zeolites were stored after drying under an Ar atmosphere.
CH3CO
H
H
F
n-BuO
CH3O(CO)
CH3O(CO)
91.0 [69.4]
93.2 [72.6]
0.6
a GLC yields and [isolated yields] are given (∆rel ) (10%).
one catalyst ([Pd(C3H5)Cl]2-NaY used at 140 °C), no substan-
tial leaching was observed.
The kinetics performed with [Pd(NH3)4]2+-NaY showed that
the heterogeneous catalysts have an activity comparable to that
of the homogeneous catalysts. Complete conversion of nonac-
tivated aryl bromides was achieved after ca. 30 min. This
represents the most active heterogeneous catalyst for the
activation of aryl bromides reported up to now. We also report
a direct activation of aryl chlorides using a heterogeneous
catalyst under standard reaction conditions. No undesired
reactions (i.e., strong dehalogenation of the aryl chlorides,
biphenyl derivatives, or reacting solvent) were observed. In the
Heck reaction with cyclic olefins, the zeolite obviously controls
the selectivity of the reaction by the well established “product
form selectivity”. No polyaromatic side products were formed.
On the other hand the turnover numbers are one or several
orders of magnitude lower than those of the best homogeneous
catalytic systems (reviewed in ref 1g). Nevertheless, the catalysts
reported here can be regarded as an important step toward simple
systems with the potential for commercial application of
heterogeneous catalysts in CC coupling reactions. The possibility
of carrying out the reactions without exclusion of air and
moisture and using nondried solvents are of particular interest
for practical applications. In addition, separation of the catalyst
by filtration is easy and possible within a short time for the
zeolites (large grain size) in comparison to various silicas.
Whereas the reaction mechanism of the homogeneously
catalyzed Heck reaction is today generally accepted,1 the
mechanism of the heterogeneously catalyzed Heck reaction
remains unclear. Our experiments indicate that Pd(0) species
are the active species as they are for the homogeneous systems.
The results observed are consistent with an oxidative addition
of the aryl bromide to the Pd(0) center. In addition, the identical
product distributions in the homogeneous and heterogeneous
reactions suggest a similar reaction mechanism for both. At this
stage, we propose that a homogeneous mechanism takes place
in the zeolite cage for the heterogeneous Heck reaction using
Solution NMR spectra of the organic products were recorded with
a Bruker AM 400 spectrometer (1H NMR were referenced to the
residual protio solvent: CDCl3, d ) 7.25 ppm. 13C NMR were
referenced to the C-signal of the deutero solvent: CDCl3, d ) 77 ppm).
Solid-state 1H and 13C MAS NMR spectra of the exchanged zeolites
were recorded on a Bruker MSL 300 spectrometer operating at a field
strength of 7.05 T. For the 1H and 13C MAS NMR spectra, ap-
proximately 300 mg of the sample was packed into 4 mm ZrO2 Bruker
1
rotors with Kel-F caps. H and 13C NMR shifts are referenced to an
external sample of adamantane; the proton signal is set to 2 ppm and
the low-frequency signal of the 13C spectrum to 29.472 ppm relative
1
to TMS. H MAS NMR spectra were recorded at a sample spinning
speed of 15 kHz. The 13C CP-MAS NMR spectrum was recorded at a
spinning speed of 8 kHz, using high-power proton decoupling, with a
recycle time of 8 s and a contact time of 5 ms.
Gas chromatography was performed on a HP 6890 series chromato-
graph equipped with a FID detector and a HP-1 column (cross-linked
methylsiloxane, 30 m × 0.25 mm × 0.25 mm film thickness).
The absolute palladium content of the catalysts was determined by
AAS for the Pd complex loaded zeolites after drying and calcination
(in order to remove all organic material) from a solution obtained by
treatment with a mixture of HBF4, HNO3, and HCl in a Teflon reactor
at 180 °C.
Preparation of the Catalysts. (1) Procedure for the Preparation
of [Pd(NH3)4]-NaY. A 0.1 M ammonia solution of [Pd(NH3)4]Cl2s
prepared from PdCl2 and a commercial ammoniac solutions(0.95 mL/g
zeolite, corresponding approximately to 1% Pd in the final catalyst)
was added dropwise to a suspension of the zeolite Na-Y in bi-distilled
water (100 mL/g of zeolite). The mixture was stirred for 24 h at room
temperature and the exchanged zeolite was filtered off and washed
until no trace of chloride was detected in the filtrate (AgNO3 test).
Then the zeolite was allowed to dry at room temperature to give the
entrapped [Pd(NH3)4]2+ zeolite as a slightly yellow material. The AAS
gave 1.0 ( 0.2 wt % of Pd.
(2) Procedure for the Preparation of [Pd(II)]-NaY. The Pd(II)-
NaY was obtained by calcination of the entrapped [Pd(NH3)4]-NaY
in a U-reactor under a pure oxygen flow (180 mL/min) using a heating
rate of 2 K/min from room temperature to 500 °C. The temperature

5998 J. Am. Chem. Soc., Vol. 123, No. 25, 2001
DjakoVitch and Koehler
Table 8. Comparison of the Activity and Reaction Conditions of Heterogeneous Catalysts in the Heck Reaction of Bromobenzene with
Styrene (Scheme 2, R1 ) H, R3 ) Br and R2 ) Ph) and Methyl Acrylate (Scheme 2, R2 ) CH3O-CO) Published in the Literature Very
Recently
catalyst concentration reaction reaction
yield 8-10 [%]
catalyst
[mol %]a)
temp [°C] time [h] (all coupling products) TONb TOFc [h-1
]
reference
Pd/Cd
Pd/mesoporous silica
>1
160
170
150
140/100
12
48
60
<20
39
75
e20
390
3750
1920
2
8
63
Zhao et al. 6o
Mehnert et al.7b
Schwartz et al.5j
this paper
0.1
polymer- supported Pd carbenes
0.02
0.05
[Pd(NH3)4]2+/Na-Y
0.5
96
3840
a mol of Pd/mol of bromobenzene. b [mol of coupling product (all isomers)]/(mol of Pd). c TON/reaction time in hours. d Reaction of bromobenzene
and methyl acrylate. High selectivity (up to 80%) to undesired benzene (dehalogeneation).
Scheme 3a
a Reaction conditions: 10 mmol of 4-bromoacetophenone 11, 15 mmol of cyclohexene 12, 15 mmol of NaOAc, 0.1 mol % of [Pd]-NaY, 8 mL
of DMAc or DMF, 140 °C, 20 h.
Table 9. Heck Reaction of an Aryl Chloride with Styrene (Scheme
2, R1 ) CH′3CO, R2 ) Ph, R3 ) Cl) Catalyzed by
[Pd(OAc)2] zeolite as a slightly brown material. The AAS gave a 0.7
( 0.2 wt % of Pd.
[Pd(NH3)4]2+-NaY at 140 or 170 °C (0.1 mol % of Pd)
MAS NMR: 1H NMR, ppm 2.10 (CH3CO).
MAS NMR: 13C NMR, ppm 186,84 (CH3CO); 23.04 (CH3CO).
(5) Procedure for the Preparation of [Pd(C3H5)Cl]2-NaY. A
solution of [Pd(C3H5)Cl]2 (88.4 mg, 0.47 mmol, corresponding ap-
proximately to 1% Pd in the final catalyst) in THF was added dropwise
to a suspension of the zeolite Na-Y (4.95 g) in THF (20 mL/g of
zeolite). The mixture was stirred for 3 days at room temperature, and
the [Pd(C3H5)Cl]2 loaded zeolite was filtered off and washed with THF
until no trace of non-immobilized complex was detected in the filtrate.
Then the zeolite was allowed to dry at room temperature to give the
entrapped [Pd(C3H5)Cl]2 zeolite as a yellow material. The AAS gave
a 0.5 ( 0.1 wt % of Pd.
product yield [%]a
T [°C]
cocatalysta
8
9
10
140
170
170
no
no
yes
0.3
nd
1.2
1.0
0.3
3.3
2.0
44.1 [31.2]
59.2 [38.1]
a t-Bu4NBr. b GLC yields and [isolated yields] are given (∆rel
(10%).
)
Table 10. Heck Reaction of Aryl Bromides with Cyclic Alkenes
(Scheme 3) Catalyzed by [Pd(NH3)4]-NaY at 140 °C (0.1 mol % of
Pd)
MAS NMR: 1H NMR, ppm 2.14 (CH1H2CHCH1H2); 4.03
(CH1H2CHCH1H2); 7.15 (CH1H2CHCH1H2).
product yield [%]a
conversion
MAS NMR: 13C NMR, ppm 107.15 (CH2CHCH2); 69.07
(CH2CHCH2).
solvent
DMAc 0.1 (0.7)
3.1 (4.6) 13.1 (18.9) 54.1 (78.2)
0.1 (0.2) 8.6 (19.0) 36.5 (80.7)
2.8 (3.5) 10.0 (12.4) 68.1 (84.1)
13
14
15
16c
of 11 [%]b
2.1 (15.1) 11.7 (84.2) 15.0
29.1
86
46.4
94
Test of the Catalytic Activity. The catalytic reactions were carried
out in pressure tubes under argon. The qualitative and quantitative
analysis of the reactants and the products was made by gas liquid
chromatography. Conversion and selectivity are represented by product
distribution () relative area of GC signals), and GC yields are in
parentheses () relative area of GC signals referred to an internal
standard calibrated to the corresponding pure compound, ∆rel ) (10%).
Where available, yields in isolated products are given in brackets. The
catalysts were transferred under Ar.
7.0
0.8
1.1
DMF
a For heterogeneous (plain text) and homogeneous (bold text)
catalysts, GLC yields and (relative selectivity for Heck products) are
given (∆rel ) (10%). b Determined by GLC (∆rel ) (10%). c Aceto-
phenone is the major side product in the reaction.
was maintained at 500 °C for 30 min, and the reactor was cooled to
room temperature under a flow of argon to give the modified Pd(II)-
NaY as a tobacco-colored powder. The Pd(II)-loaded zeolite was then
stored under an Ar atmosphere to prevent hydration. The AAS gave a
1.0 ( 0.2 wt % of Pd.
(3) Procedure for the Preparation of [Pd(0)]-NaY. The Pd(0)-
NaY was obtained by reduction of Pd(II)-NaY in a U-reactor under a
pure hydrogen flow (70 mL/min) using a heating rate of 8 K/min from
room temperature to 350 °C. The temperature was maintained at 350
°C for 15 min, and the reactor was cooled to room temperature under
a flow of argon to give Pd(0)-NaY as a black powder. The Pd(0)-
loaded zeolite was then stored under an Ar atmosphere to prevent
reoxidation. The AAS gave a 1.0 ( 0.2 wt % of Pd.
(1) General Procedure for the First Run and the Recycling of
the Catalysts. A total of 10 mmol of aryl halide, 15 mmol of olefin,
15 mmol of NaOAc, and 0.1 mol % of Pd (as heterogeneous catalysts,
the mass of catalysts depending of the palladium concentration) was
introduced in a pressure tube under argon. Then 8 mL of solvent (DMAc
p.a. previously deaerated) was added and the mixture was deaerated
by an argon flow for 5 min. The reactor was then placed in a preheated
oil bath at 100 or 140 °C for 20 h with vigorous stirring and then cooled
to room temperature before the reaction mixture was analyzed by GC.
For the recycling studies, a catalyst issue from a first run was used.
After separation of the reaction mixture, it was washed with CH2Cl2
in order to remove adsorbed organic substrates and dried at room
temperature.
(4) Procedure for the Preparation of [Pd(OAc)2]-NaY. A solution
of the Pd(OAc)2 (110.2 mg, 0.47 mmol, corresponding approximately
to 1% Pd in the final catalyst) in THF was added dropwise to a
suspension of the zeolite Na-Y (4.95 g) in THF (20 mL/g of zeolite).
The mixture was stirred for 3 days at room temperature, and the [Pd-
(OAc)2]-loaded zeolite was filtered off and washed with THF until no
trace of non-immobilized complex was detected in the filtrate. Then
the zeolite was allowed to dry at room temperature to give the entrapped
(2) General Procedure for the Examination of the Presence of
Catalytically Active Species in Homogeneous/Bulk Solution (“Leach-
ing”). A clear filtrate of the first run of the catalyst (obtained by
filtration using a microglass Whatman filter in order to remove the
fine particles) was used as solvent basis for these experiments. The
filtrate (free of catalyst) was placed in a pressure tube and deaerated
by an Ar flow for 5 min. Then new organic reactants were added under
argon atmosphere (10 mmol of aryl halide, 15 mmol of olefin, 15 mmol

Heck Reaction Catalyzed by Pd-Modified Zeolites
J. Am. Chem. Soc., Vol. 123, No. 25, 2001 5999
of NaOAc) and well homogenized. A GC analysis of the composition
of the mixture was made before the reactor was placed in a preheated
oil bath at 100 or 140 °C for 20 h with vigorous stirring. After the
reaction, the reactor was cooled to room temperature and a second GC
analysis was performed. The comparison between the two GC analyses
gave a qualitative measure for the presence of active species in
homogeneous/bulk solution.
L.D. and the Technische Universita¨t Mu¨nchen and the Fonds
der Chemischen Industrie (Germany) for support. We acknowl-
edge Degussa AG (Germany) for the donation of PdCl2 and
zeolites.
Supporting Information Available: Additional experimen-
tal details. This material is available free of charge via the
Internet at http://pubs.acs.org.
Acknowledgment. We are grateful to the European Com-
munity (Marie-Curie, TMR program) for a research grant to
JA001087R