N4-tetradentate dicarboxyamidate/dipyridyl palladium complexes as robust catalysts for the Heck reaction of deactivated aryl chlorides

Article abstract of DOI:10.1002/chem.200802144

The utility of palladium(II) complexes of tetradentate dicarboxyamide/ dipyridyl ligands as catalysts for the Heck reaction of deactivated aryl chlorides and olefins was studied. The square-planar palladium complexes were prepared by treatment of the ligands with Pd(OAc)₂ in THF at room temperature. Thermogravimetric analysis show that both the palladium complexes have high thermal stability up to 350°C. LiOH·H₂O has a pronounced effect on the product yield, while a yield of 74% is obtained by using DMA as a solvent at 160°C in 44 h. The reactions of less reactive aryl chlorides such as 4-chloroanisole, 4-chlorotoluene, and chlorobenzene with styrene and 4-methylstyrene, proceed smoothly and provide good yields. Both palladium complexes are found to be efficient and active for the Heck reaction of deactivated aryl chlorides and olefins.

Full text of DOI:10.1002/chem.200802144

DOI: 10.1002/chem.200802144
N4-Tetradentate Dicarboxyamidate/Dipyridyl Palladium Complexes as
Robust Catalysts for the Heck Reaction of Deactivated Aryl Chlorides
Pottabathula Srinivas,[a] Pravin R. Likhar,[a] Hariharasarma Maheswaran,[a]
Balasubramanian Sridhar,[b] Krishnan Ravikumar,[b] and Mannepalli Lakshmi Kantam*[a]
The palladium-catalyzed Heck reaction is one of the
“power tools of contemporary organic synthesis”.[1] It is
used for the olefination of aryl halides, and has found appli-
cation in natural products synthesis, materials science, and
bioorganic chemistry.[2] The olefination of chloroarenes is of
bond. In recent years, transition-metal complexes containing
N-donor ligands with amide functionality have received
much attention and have shown that the anionic amide (de-
protonated amide) ligands strongly donate electrons to the
metal center thus stabilizing various oxidation states of
metals.[6]
À
immense importance, since C Cl bond activation contrib-
utes to the fundamental understanding of the reactivity of
such very stable bonds and they are cheaper and more
widely available than their bromide or iodide counterparts.[3]
In particular, the activation of deactivated aryl chlorides has
become a challenging task. In the past, phosphine complexes
and P-donor palladacycles have been used for the activation
of deactivated aryl chlorides.[4] However, phosphorus-con-
taining ligands are expensive, toxic, and sensitive to air and
temperature. Consequently phosphine-free Pd-catalyzed ole-
fination of deactivated aryl chlorides has become highly de-
sirable.
We believe that such ionic-type amidate bonding in palla-
dium complexes could impart larger thermodynamic stabili-
zation to active metal species thus rendering a metal elec-
tron-rich and therefore facilitate oxidative addition of aryl
[7–14]
À
chlorides in the C C cross coupling reactions.
In addi-
tion, the amide ligands have advantages over P-donor li-
gands due to their facile synthesis and their stability in air.
Despite having these appealing characteristics, the amidate
complexes are relatively unexplored in the field of catalysis.
This is particularly the case for the Heck reaction. Herein,
we present our studies on the utility of palladium(II) com-
plexes of tetradentate dicarboxyamide/dipyridyl ligands as
catalysts for the Heck reaction of deactivated aryl chlorides
and olefins.
Among the phosphine-free catalysts, N-based palladacy-
cles, N-heterocyclic carbenes (NHCs), and carbocyclic car-
benes containing catalysts have performed well in the olefi-
nation of aryl chlorides.[5] The activity of catalysts is howev-
er essentially limited to activated and non-activated sub-
strates. A key feature of several homogeneous catalytic sys-
tems is the stabilization of the active catalysts, which
depends on the ligand stability, chelation or steric shielding
of the metal center, and the strength of the metal–ligand
As depicted in Scheme 1, the new chelating tetradentate
ligands 5a and 5b are readily accessible in four steps start-
ing with the amino acid precursors l-phenyl alanine and l-
valine, 1a and 1b, respectively. The square-planar palladium
complexes 6a and 6b were readily prepared by treatment of
the ligands with Pd
ACHTUNGERTN(NUNG OAc)2 in THF at room temperature.
The bis(amide) ligand (5a) and its amidate palladium com-
AHCTUNGTRENNUNG
plex (6a) were structurally characterized by X-ray crystal-
lography (see Figure 1 for complex 6a and Supporting Infor-
mation for the ligand 5a). The ligand contains amide hydro-
gen atoms and in contrast, the amidate palladium complex
displays tetradentate N4 coordination via N atoms of two
different functions, namely amidate (deprotonated amide)
(N1 and N2) and pyridine (N3 and N4). The coordination
geometry around the palladium center is slightly distorted
from ideal square-planar, as elucidated by bond angles and
inter-planar angles around the metal atom (Figure 1). The
solution structure of the palladium complexes was studied
[a] P. Srinivas, Dr. P. R. Likhar, Dr. D. H. Maheswaran,
Dr. M. L. Kantam
Inorganic and Physical Chemistry Division
Indian Institute of Chemical Technology
Tarnaka, Hyderabad 500607 (India)
Fax : (+91)40-27160921
E-mail: mlakshmi@iict.res.in
[b] Dr. B. Sridhar, Dr. K. Ravikumar
X-Ray Crystallography Division
Indian Institute of Chemical Technology
Tarnaka, Hyderabad 500607 (India)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200802144.
1
by H NMR and 13C NMR spectroscopy, and these studies
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Chem. Eur. J. 2009, 15, 1578 – 1581

COMMUNICATION
thermogravimetric analysis (see
the Supporting Information).
The thermal robustness of the
amidate palladium complexes is
further confirmed by the ab-
sence of inactive palladium
black in solution on heating in
N,N-dimethylacetamide (DMA)
at 1608C for several days.
Owing to such high thermal
stability of these complexes, we
initially studied the Heck reac-
tion of 4-chlorotoluene and 4-
methylstyrene using 1 mol% of
6a (relative to aryl chloride).
To optimize the efficiency of
our catalytic system, various re-
action conditions were used,
and the product mixture was
Scheme 1. Synthesis of dicarboxyamide/dipyridyl ligands 5a and 5b and their respective palladium complexes
6a and 6b.
analyzed by gas chromatogra-
phy (Table 1). Among the dif-
Table 1. Optimization of the Heck reaction of 4-chlorotoluene and 4-
methylstyrene catalyzed by complex 6a.[a]
Entry
Base (mmol)
Solvent
Conv. [%]
Yield [%][b]
1
2
3
4
5
6
7
8
9
K2CO3 (2)
K3PO4 (2)
NaOAc (2)
NaHCO3 (2)
KOH (2)
LiOH·H2O (2)
LiOH·H2O (1.2)
LiOH·H2O (1.2)
LiOH.H2O (1.2)
LiOH·H2O (1.2)
DMA
DMA
DMA
DMA
DMA
DMA
DMA
DMSO
DMF
NMP
22
12
3
2
5
82
80
3
8
73
15
5
–
–
–
75
74
–
–
64
10
[a] Reaction conditions: 4-chlorotoluene (1 mmol), 4-methylstyrene
(2 mmol), and 6a (1 mol%) in solvent (3 mL) at 1608C for 44 h.
[b] Yield of isolated product.
ferent bases screened, LiOH·H2O has a pronounced effect
on the product yield and we obtained 74% yield using
DMA as a solvent at 1608C in 44 h (entry 7, Table 1).
Under our optimized reaction conditions, the maximum
number of turnovers (TON ca. 620) was achieved with a cat-
alyst loading of 0.1 mol% of 6a (entry 2, Table 2). The activ-
ity of the catalyst 6b was also tested for the Heck reaction,
and the corresponding cross-coupled products were obtained
in good yields (entries 3 and 4, Table 2). As can be seen, the
reactions of less reactive aryl chlorides such as 4-chloroani-
sole, 4-chlorotoluene, and chlorobenzene with styrene and
4-methylstyrene, proceeded smoothly, and good yields were
obtained under our experimental conditions (entries 5–8,
Table 2). Unlike most previously reported systems for the
Heck coupling of aryl chlorides, additional co-catalysts such
as [NBu4]Br[5a,b,11a,b] or [PPh4]Cl[16] are not required in our
catalytic system to achieve high catalytic activity. It is very
clear from these results that both palladium complexes 6a
Figure 1. X-ray structure of the PdII complex 6a with one molecule of
water in the crystal (hydrogen atoms are included to highlight amidate
anion bonding to palladium atom; ORTEP plot created at 50% probabil-
À
ity). Selected bond lengths [ꢁ] and bond angles [8]: Pd N1 1.9276(17),
À
À
À
À
Pd N2 1.9426(16), Pd N3 2.0744(16), Pd N4 2.0650(16), C12 O1
À
1.244(2), C14 O2 1.240(3); N1-Pd-N2 83.12(6), N3-Pd-N4 114.08(6), N1-
Pd-N3 163.90(6), N2-Pd-N4 165.02(6), N1-Pd-N4 81.90(6), N2-Pd-N3
80.90(6); dihedral angle [8] between the least-square planes (N1-Pd-N2)
and (N3-Pd-N4) is 2.090(1)8, which is a measure of the deviation from
square-planarity.
show presence of amidate bonding to palladium similar to
that observed in the solid state (see the Supporting Informa-
tion). Remarkably, both the palladium complexes 6a and 6b
show high thermal stability up to 3508C, as analyzed by
Chem. Eur. J. 2009, 15, 1578 – 1581
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www.chemeurj.org
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M. L. Kantam et al.
Table 2. The Heck reaction of aryl chlorides catalyzed by PdII complexes
Experimental Section
6a and 6b.[a]
Typical procedure for the synthesis of compounds (5a and 5b): N-(Pyri-
dine-2-carbonyl)amino acid (20 mmol) and N,N’-dicyclohexylcarbodii-
mide (DCC) (20 mmol) were dissolved in dry dichloromethane (50 mL)
and cooled down to 08C. The solution was stirred for 30 min and then a
solution of 2-(aminomethyl)pyridine (25 mmol) in dichloromethane
(20 mL) was added dropwise over 15 min. After the addition, the mixture
was warmed to room temperature and stirred for another 12 h. After fil-
tration, the solvent was removed under reduced pressure. The residue
was purified by column chromatography on silica gel (eluent: hexane/
ethyl acetate) to afford the compound as a white solid (83–84% yield).
Entry
R1
R2
Conv. [%]
Yield [%][b]
TON
1
2[c]
3[d]
4[d]
5
CH3
CH3
CH3
OCH3
OCH3
OCH3
CH3
H
CH3
CH3
CH3
CH3
CH3
CH3
H
H
H
CH3
CH3
80
73
81
69
82
74
72
80
89
85
74
62
73
62
70
62
60
71
80
75
74
620
73
62
70
62
60
71
80
Synthesis of dicarboxyamidate/dipyridyl palladium complexes (6a and
6b): The N4-donor ligand (5a or 5b, 1 mmol) was added in one portion
at room temperature to a stirred orange solution of palladium acetate
(1 mmol) in THF (10 mL). Upon stirring the solution for 30 min, a pale
yellow precipitate was obtained. This mixture was stirred for another 5 h
at room temperature then filtered, and with washed THF (ca. 20 mL) to
afford pure 6a or 6b. The complex (6a) was dissolved in methanol, and
on slow evaporation of methanol at room temperature gave single crys-
tals suitable for X-ray diffraction studies.
6
7
8[e]
9[f]
10[f]
OCH3
75
[a] Unless otherwise noted, the reaction was carried out with aryl chlo-
ride (1 mmol), alkene (2 mmol), catalyst (1 mol%), LiOH·H2O
(1.2 mmol) and DMA (3 mL) at 1608C for 44 h. [b] Yield of isolated
product. [c] 0.1 mol% of the catalyst was used. [d] Catalyst 6b was used.
[e] Chlorobenzene (2 mmol) and styrene (1 mmol) under N2 balloon
pressure. [f] Reaction carried out using [nBu4N]Br additive (20 mol%
relative to aryl chlorides).
General procedure for the Heck reaction: The catalyst 6a (4.6 mg, 1
mol%) was added to a solution of lithium hydroxide monohydrate
(1.2 mmol), aryl chloride (1 mmol), and alkene (2 mmol) in N,N-dimethy-
lacetamide (3 mL). The reaction mixture was heated to 1608C and the
progress of reaction was monitored by GC. At the end of the reaction,
the reaction solution was cooled to room temperature, treated with 1n
aq. HCl (1.5 mL), and extracted with ethyl acetate (3ꢂ10 mL). The com-
bined organic phase was dried over Na2SO4. After removal of the sol-
vent, the residue was subjected to column chromatography on silica gel
using ethyl acetate and hexane mixtures to afford the Heck product in
high purity.
and 6b are efficient and active for the Heck reaction of de-
activated aryl chlorides and olefins.
With regard to the stability and catalytic activity, the ami-
date palladium complexes are comparable to palladacycles.
The unprecedented activity of 6a and 6b may be attributed
to an amidate metal coordination achieved with high ther-
mal stability such that the metal amidate unit is retained in
the catalytic cycle. Above all it is expected that the strength
of Pd–amidate bond and ligand chelation or steric shielding
of the metal center have a far greater effect on the stabiliza-
tion of the active catalysts. It is very likely that one of the
main functions of the unsymmetrical dicarboxyamide/dipyr-
idyl ligands during the reaction is to stabilize the palladium
center and deliver an electron-rich and well-defined active
lower valent palladium species at such a rate and in such
manner that prevents decomposition to inactive bulk metal.
To the best of our knowledge, this is the first report on the
use of purely N-donor ligands that shows significant catalyt-
ic activity with deactivated aryl chlorides in the Heck reac-
tion.
In conclusion, we have shown that highly active amidate/
pyridyl palladium complexes for the Heck reaction of deac-
tivated aryl chlorides can be constructed from readily avail-
able ligand precursors. The concept of using an anionic car-
boxyamide as an ancillary ligand for palladium demonstrat-
ed here provides a new opportunity for the development of
phosphine-free transition metal catalysis. Kinetic and quan-
tum-mechanical studies to determine the effect of the
metal–amidate bond on the catalytic properties are in prog-
ress.
Acknowledgements
P. S. thanks the UGC, India, for a fellowship.
À
Keywords: aryl chlorides · C C coupling · Heck reaction ·
N ligands · oxidative addition · palladium
[1] a) K. C. Nicolaou, E. J. Sorensen, Classics in Total Synthesis, VCH,
Weinheim, 1996; b) R. F. Heck, Comprehensive Organic Synthesis,
Vol. 4 (Eds.: B. M. Trost, I. Flemming), Pergamon Press, Oxford,
1991, ch. 3.4, p. 833; c) A. de Meijere, F. E. Meyer, Angew. Chem.
1994, 106, 2473–2506; Angew. Chem. Int. Ed. Engl. 1994, 33, 2379–
2411; d) W. Cabri, I. Caudiani, Acc. Chem. Res. 1995, 28, 2–7; e) T.
Jeffery, Adv. Met. Org. Chem. 1996, 5, 153–260; f) S. Brꢃse, A. de
Meijere in Metal Catalyzed Cross-Coupling Reactions (Eds.: P. J.
Stang, F. Diederich), Wiley-VCH, New York, 1998, ch. 3.
[2] a) J. T. Link, L. E. Overman in Metal-Catalyzed Cross-Coupling Re-
actions (Eds.: F. Diederich, P. J. Stang), Wiley-VCH, Weinheim,
1998, ch. 6; b) Step-Growth Polymers for High-Performance Materi-
als (Eds.: J. L. Hedrick, J. W. Labadie), ACS Symposium Series, 624,
American Chemical Society, Washington, DC, 1996, ch. 1, 2, and 4;
c) A. Hꢃberli, C. J. Leumann, Org. Lett. 2001, 3, 489–492.
[3] a) V. V. Grushin, H. Alper, Chem. Rev. 1994, 94, 1047–1062; b) V. V.
Grushin, H. Alper in Activation of Unreactive Bonds and Organic
Synthesis (Ed.: S. Murai), Springer, Berlin, 1999, p. 193.
[4] a) D. Morales-Morales, R. Redon, C. Yung, C. M. Jensen, Chem.
Commun. 2000, 1619–1620; b) Y. Ben-David, M. Portnoy, M.
Gozin, D. Milstein, Organometallics 1992, 11, 1995–1996; c) M.
Portnoy, Y. Ben-David, D. Milstein, Organometallics 1993, 12, 4734–
4735; d) A. F. Littke, G. C. Fu, J. Org. Chem. 1999, 64, 10–11;
e) A. F. Littke, G. C. Fu, J. Am. Chem. Soc. 2001, 123, 6989–7000.
1580
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Palladium-Catalyzed Heck Reaction of Deactivated Aryl Chlorides
COMMUNICATION
[5] a) R. B. Bedford, C. S. J. Cazin, D. Holder, Coord. Chem. Rev. 2004,
248, 2283–2321; b) W. A. Herrmann, K. Ofele, S. K. Schneider, E.
Herdtweck, S. D. Hoffmann, Angew. Chem. 2006, 118, 3943–3947;
Angew. Chem. Int. Ed. 2006, 45, 3859–3862; c) Q. Yao, M. Zabawa,
J. Woo, C. Zheng, J. Am. Chem. Soc. 2007, 129, 3088–3089; d) D. F.
Wass, M. F. Haddow, T. W. Hey, A. G. Orpen, C. A. Russell, R. L.
Wingad, M. Green, Chem. Commun. 2007, 2704–2706.
[6] a) A. K. Patra, M. Ray, R. Mukherjee, Inorg. Chem. 2000, 39, 652–
657; b) M. Ray, D. Ghosh, Z. Shirin, R. Mukherjee, Inorg. Chem.
1997, 36, 3568–3572; c) M. Ray, R. Mukherjee, J. F. Richardson,
R. M. Buchanan, J. Chem. Soc. Dalton Trans. 1993, 2451–2457;
d) A. K. Patra, R. Mukherjee, Polyhedron 1999, 18, 1317–1322;
e) J. C. Noveron, M. M. Olmstead, P. K. Mascharak, Inorg. Chem.
1998, 37, 1138–1139; f) D. S. Marlin, M. M. Olmstead, P. K. Ma-
scharak, Inorg. Chem. 1999, 38, 3258–3260; g) M. J. Bartos, C. Kid-
well, K. E. Kauffmann, S. W. Gordon-Wylie, T. J. Collins, G. C.
Clark, E. Mꢄnck, S. T. Weintraub, Angew. Chem. 1995, 107, 1345–
1348; Angew. Chem. Int. Ed. Engl. 1995, 34, 1216–1219; h) K.
Bowman-James, Acc. Chem. Res. 2005, 38, 671–678; i) S. O. Kang,
R. A. Begum, K. Bowman-James, Angew. Chem. 2006, 118, 8048–
8061; Angew. Chem. Int. Ed. 2006, 45,7882–7894; j) S. O. Kang,
M. A. Hossain, K. Bowman-James, Coord. Chem. Rev. 2006, 250,
3038–3052.
[7] For recent reviews on the Heck reaction, see ref. [5a] and: a) N. J.
Whitcombe, K. K. Mimi Hii, S. E. Gibson, Tetrahedron 2001, 57,
7449–7476; b) M. T. Reetz, J. G. de Vries, Chem. Commun. 2004,
1559–1563; c) I. P. Beletskaya, A. V. Cheprakov, Chem. Rev. 2000,
100, 3009–3066; d) G. T. Crisp, Chem. Soc. Rev. 1998, 27, 427–436;
e) V. Farina, Adv. Synth. Catal. 2004, 346, 1553–1582.
[8] For recent work on Heck–Mizoroki reactions: a) D. D. Pathak, H.
Maheswaran, K. L. Prasanth, M. L. Kantam, Synlett 2007, 5, 757–
760; b) B.-L. Lin, L. Liu, Y. Fu, S.-W. Luo, Q. Chen, Q.-X. Guo, Or-
ganometallics 2004, 23, 2114–2123; c) H. Hagiwara, Y. Sugawara, T.
Hoshi, T. Suzuki, Chem. Commun. 2005, 2942–2944; d) V. Calꢅ, A.
Nacci, A. Monopoli, E. Leva, N. Cioffi, Org. lett. 2005, 7, 617–620;
e) S. Mukhopadhyay, G. Rothenberg, A. Joshi, M. Baidossi, Y.
Sasson, Adv. Synth. Catal. 2002, 344, 348–354; f) S. S. Prçckl, W.
Kleist, M. A. Gruber, K. Kçhler, Angew. Chem. 2004, 116, 1917–
1918; Angew. Chem. Int. Ed. 2004, 43, 1881–1882; g) R. K. Arvela,
N. E. Leadbeater, J. Org. Chem. 2005, 70, 1786–1790; h) Q. Yao,
E. P. Kinney, C. Zheng, Org. Lett. 2004, 6, 2997–2999.
singer, T. Priermeier, M. Beller, H. Fischer, Angew. Chem. 1995, 17,
1989; Angew. Chem. Int. Ed. Engl. 1995, 34,1844–1848; b) W. A.
Herrmann, C. Brossmer, C.-P. Reisinger, T. H. Riermeier, K. ꢆfele,
M. Beller, Chem. Eur. J. 1997, 3, 1357–1364; c) R. B. Bedford,
Chem. Commun. 2003, 1787–1796; d) M. Albrecht, G. van Koten,
Angew. Chem. 2001, 113, 3866–3898; Angew. Chem. Int. Ed. 2001,
40, 3750–3781; e) J. Dupont, M. Pfeffer, J. Spencer, Eur. J. Inorg.
Chem. 2001, 1917–1927; f) W. A. Herrmann, V. P. W. Bçhm, C.-P.
Reisinger, J. Organomet. Chem. 1999, 576, 23–41; g) D. A. Albisson,
R. B. Bedford, P. N. Scully, Tetrahedron Lett. 1998, 39, 9793–9796;
h) S. Iyer, C. Ramesh, Tetrahedron Lett. 2000, 41, 8981–8984; i) S.
Iyer, A. Jayanthi, Tetrahedron Lett. 2001, 42, 7877–7878; j) Y. Wu, J.
Hou, H. Yun, X. Cui, R. Yuan, J. Organomet. Chem. 2001, 637–639,
793–795; k) C. S. Consorti, M. L. Zanini, S. Leal, G. Ebeling, J.
Dupont, Org. Lett. 2003, 5, 983–986.
[12] For N-heterocyclic carbenes (NHCs) in the Heck reaction with aryl
chloride substrates, see: a) A. C. Hillier, G. A. Grasa, M. S. Viciu,
H. M. Lee, C. Yang, S. P. Nolan, J. Organomet. Chem. 2002, 653, 69–
82; b) W. A. Herrmann, M. Elison, J. Fischer, C. Kçcher, G. R. J.
Artus, Angew. Chem. 1995, 107, 2602–2605; Angew. Chem. Int. Ed.
Engl. 1995, 34, 2371–2374; c) J. Schwarz, V. P. W. Bçhm, M. G.
Gardiner, M. Grosche, W. A. Herrmann, W. Hieringer, G. Rau-
daschl-Sieber, Chem. Eur. J. 2000, 6, 1773–1780; d) W. A. Herr-
mann, C. P. Reisinger, M. Spiegler, J. Organomet. Chem. 1998, 557,
93–96; e) D. S. McGuiness, K. J. Cavell, Organometallics 2000, 19,
741–748; f) V. Cꢇsar, S. Bellemin-Laponnaz, L. H. Gade, Organo-
metallics 2002, 21, 5204–5208; g) E. Peris, J. A. Loch, J. Mata, R. H.
Crabtree, Chem. Commun. 2001, 201–202; h) K. Selvakumar, A.
Zapf, M. Beller, Org. Lett. 2002, 4, 3031–3033; i) S. Caddick, W.
Kofie, Tetrahedron Lett. 2002, 43, 9347–9450; j) J. Liu, Y. Zhao, Y.
Zhou, L. Li, T. Y. Zhang, H. Zhang, Org. Biomol. Chem. 2003, 1,
3227–3231.
[13] For carbocyclic carbenes in the Heck reaction with aryl chloride
substrates, see refs. [5b–d] and: B. Dhudshia, A. N. Thadani, Chem.
Commun. 2006, 668–670.
[14] For the recent applications of N-donor ligands in palladium cata-
lyzed cross-coupling reactions; see: a) S. Haneda, C. Ueba, K. Eda,
M. Hayashi, Adv. Synth. Catal. 2007, 349, 833–835; b) C. Nꢈjera, J.
Gil-Moltꢉ, S. Karlstrçm, L. R. Falvello, Org. Lett. 2003, 5, 1451–
1454; c) T. Schultz, N. Schmees, A. Pfaltz, Appl. Organomet. Chem.
2004, 18, 595–601; d) H. Weissman, D. Milstein, Chem. Commun.
1999, 1901–1902; e) B. Tao, D. W. Boykin, Tetrahedron Lett. 2002,
43, 4955–4957; f) C. J. Mathews, P. J. Smith, T. Welton, J. Mol. Catal.
A: Chemical 2003, 206, 77–82; g) V. Montoya, J. Pons, V. Brancha-
dell, J. Garcia-Anton, X. Solans, M. Font-Bardia, J. Ros, Organome-
tallics 2008, 27, 1084–1091.
[9] For ligand-free palladium, palladium colloids, and nanoparticulate
palladium in Heck reactions, see: a) J. G. de Vries, Dalton Trans.
2006, 421–429; b) I. P. Beletskaya, A. V. Cheprakov, J. Organomet.
Chem. 2004, 689, 4055–4082; c) R. B. Bedford, M. E. Blake, C. P.
Butts, D. Holder, Chem. Commun. 2003, 466–467.
[10] For electron-rich sterically congested phosphine ligands in Heck re-
action with aryl chloride substrates, see refs. [4b–e] and: a) M. Port-
noy, Y. Ben-David, I. Rousso, D. Milstein, Organometallics 1994, 13,
3465–3479; b) M. R. Netherton, G. C. Fu, Org. Lett. 2001, 3, 4295–
4298; c) K. H. Shaughnessy, P. Kim, J. F. Hartwig, J. Am. Chem. Soc.
1999, 121, 2123–2132; d) A. Ehrentraut, A. Zapf, M. Beller, Synlett
2000, 1589–1592.
[15] CCDC-689837 and CCDC-689838 contain the supplementary crys-
tallographic data for this paper. These data can be obtained free of
charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
[16] M. T. Reetz, G. Lohmer, R. Schwickardi, Angew. Chem. 1998, 110,
492–495; Angew. Chem. Int. Ed. 1998, 37, 481–483.
[11] For palladacycles in Heck reaction with aryl chloride substrates, see
ref. [4a] and: a) W. A. Herrmann, C. Brossmer, K. ꢆfele, C.-P. Rei-
Received: October 16, 2008
Published online: January 2, 2009
Chem. Eur. J. 2009, 15, 1578 – 1581
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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