Copper-free monomeric and dendritic palladium catalysts for the sonogashira reaction: Substituent effects, synthetic applications, and the recovery and re-use of the catalysts

Article abstract of DOI:10.1002/chem.200400150

A series of bis(tert-butyl-phosphine)- and bis(cyclohexylphosphine)- functionalized Pd^II monomers and polyamino (DAB) dendritic catalysts were synthesized and investigated for Sonogashira carbon-carbon coupling reactions in a copper-free proced

Full text of DOI:10.1002/chem.200400150

FULL PAPER
Copper-Free Monomeric and Dendritic Palladium Catalysts for the
Sonogashira Reaction: Substituent Effects, Synthetic Applications, and the
Recovery and Re-Use of the Catalysts
Karine Heuzÿ,*[a] Denise Mÿry,[a] Dominique Gauss,[a] Jean-Claude Blais,[b] and
Didier Astruc*[a]
Abstract:
A
series of bis(tert-butyl-
stituents (tBu versus Cy) on the reac-
tion kinetics was investigated by a
GPC technique to monitor the reac-
tions. The dendritic catalysts containing
the cyclohexylphosphine ligands could
be recovered and reused without loss
of efficiency until the fifth cycle. The
dendritic PdII catalysts show a negative
dendritic effect, that is, the catalyst ef-
ficiency decreases as the dendrimer
generation increases.
phosphine)- and bis(cyclohexylphos-
phine)-functionalized Pdii monomers
and polyamino (DAB) dendritic cata-
lysts were synthesized and investigated
for Sonogashira carbon carbon cou-
pling reactions in a copper-free proce-
dure. The influence of phosphine sub-
Keywords: catalysis
¥ C C cou-
pling ¥ dendrimers ¥ P ligands ¥ pal-
ladium ¥ star-shaped molecules
Introduction
that were dependent on the phosphine substituents (tBu
versus Cy).
One of the most promising applications of dendrimers[1] is
their use as recoverable and reusable homogeneous cata-
lysts.[2] Indeed, they combine the potential kinetic informa-
tion available for monomeric homogeneous catalysts and
the possibility of insolubilization as for heterogeneous cata-
lysts. The considerable richness and perfection of their mo-
lecular definition makes them superior to supported cata-
lysts. The use of metallodendrimers in catalysis has been
known for a decade, and reusable dendritic catalysts have
started to appear more recently.[3,4]
The Sonogashira cross-coupling reaction has become a
standard method for the synthesis of functionalized acety-
lides (Scheme 1). Its popularity is based on its wide toler-
Scheme 1. Sonogashira coupling of aryl or vinyl halides with alkynes.
A large body of work along this line has been achieved by
the van Leeuwen and van Koten groups with particular em-
phasis on membrane filtration for catalyst recovery. Recent-
ly, we published a preliminary report on a family of recover-
able pallado-dendritic catalysts for the Sonogashira coupling
in a copper-free procedure.[4] These catalysts exhibited tre-
mendous differences in their reactivities and recoverabilities
ance to functional groups, the availability of common aryl
halides and access to pharmacologically important com-
pounds.[5] The Sonogashira cross-coupling reaction usually
0
proceeds with Pd /Cui catalysts and a base as the solvent,[6] if
necessary starting from the more convenient Pdii/Cui system.
0
Active 14-electron Pd species are generated in situ by a bis-
alkynylation of the Pd complex followed by reductive elimi-
nation of diacetylene. Nevertheless, only a few examples of
efficient copper-free procedures have been described with
aryl bromides or aryl chlorides.[7] Recently, we reported a
Pdii complex based on a bulky, electron-rich chelating bis-
(tert-butylphosphine) ligand coordinated to a Pdii center that
allowed very high turnover numbers (TONs).[8] The absence
of Cui in the reaction medium allowed avoidance of the oxi-
dative Glaser homo-coupling of the acetylenic reagent.[9]
Herein, we report an advanced study of the reactivity, ki-
netics and recoverability of monomeric and dendritic bis-
[a] Dr. K. Heuzÿ, D. Mÿry, D. Gauss, Prof. Dr. D. Astruc
Nanosciences and Catalysis Group, LCOO, UMR CNRS No. 5802
University Bordeaux I
351 cours de la Libÿration, 33405 Talence Cedex (France)
Fax : (+33)5-4000-6646.
E-mail: k.heuze@lcoo.u-bordeaux1.fr
d.astruc@lcoo.u-bordeaux1.fr
[b] Dr. J.-C. Blais
LCSOB, UMR CNRS No. 7613, University Paris VI
4 place Jussieu, 75252 Paris (France)
3936
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/chem.200400150
Chem. Eur. J. 2004, 10, 3936 3944

3936 3944
(tert-butylphosphine) and bis(cyclohexylphosphine)palladi-
um(ii) complexes and an example of their application to the
synthesis of star-shaped organoiron-centered and organic
molecules.
Results and Discussion
Synthesis and characterization of monomeric and dendritic
bis{alkylaminomethylphosphine}palladium(ii)
complexes:
We have synthesized monomeric and dendritic Pdii-based
catalysts in which bulky and electron-rich chelating bisphos-
phine ligands (bis(tert-butylphosphines) and bis(cyclohexyl-
phosphines)) are coordinated to a Pdii center. The six den-
dritic complexes are derived from the commercial polyami-
no dendrimers DAB-dendr-(NH2)x (x = 4, 8, or 16 for gen-
eration 1, 2, or 3, respectively).
The bis(tert-butyl)aminomethylphosphine (1a) and bis(cy-
clohexyl)aminomethylphosphine (1b) were obtained from
the corresponding phosphines by addition of benzylamine to
the bis(tert-butyl)- or bis(cyclohexyl)hydroxymethylphos-
phonium salts according to
a
known procedure
(Scheme 2).[10] The Pdii complexes 1c and 1d (Scheme 2)
Scheme 2. Synthesis of 1a d. Reagents and conditions: i) HCHO, HCl;
ii) Et3N, MeOH/H2O, PhCH2NH2; iii) [Pd(OAc)2], CH2Cl2.
were then readily obtained by treatment of 1a and 1b, re-
spectively, with [Pd(OAc)2].
The monomers, the PdII dendrimers of the first, second,
and third generation, 2c,d, 3c,d, and 4c,d, respectively,
were readily prepared by treatment of the corresponding
aminophosphines 2a,b, 3a,b, 4a,b with [Pd(OAc)2]
(Schemes 3 and 4). All the compounds were characterized
by 1H, 13C, and 31P NMR spectroscopy and by elemental
analysis of the PdII complexes. Chemical shifts of the inner
CH2 of the dendrimers were determined in accordance with
the literature.[11]
Complete metallation was established by 31P NMR spec-
troscopy. Thus, the 31P NMR spectra clearly demonstrate the
absence of unreacted phosphine units after complete conver-
sion, which occurs within a few hours at most. The corre-
sponding Pdii complexes 1c 4c (with tert-butylphosphine
substituents) were very soluble in various solvents (including
even pentane) and were stable towards moisture. However,
they were stored under nitrogen because since some degra-
dation occurred after a few days in air. Conversely, the Pdii
complexes 1d 4d (with cyclohexylphophine substituents)
were stable towards air and moisture for at least one year.
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D. Astruc, K. Heuzÿ et al.
FULL PAPER
drimers of the third generation (4c and 4d) for which a
lower reactivity was observed (Figure 1).[4]
In all the experiments, triethylamine was chosen both as a
base and as a solvent. The functional group tolerance inher-
ent to the Sonogashira reaction, however, means that any
co-solvent may be used when required to help solubilize the
reagents or to improve the reactivity by increasing the reac-
tion temperature. Thus, solvents other than triethylamine
were tested (Table 4). No significant improvement in reac-
tivity with these solvents was observed, however, because a
degradation of the catalyst occurred rapidly at such high
À
temperatures as a result of the P C bond degradation in the
phosphine ligands.[12]
Application to the construction of organoiron and organic
stars: Recently, we were able to extend the CpFe+-induced
hexabenzylation of hexamethylbenzene[5d] to p-BrCH2-
C6H4Br in excellent yields under mild conditions.[13] The
hexabenzylated stars bearing bromo substituents in the para
position of the arene rings are excellent candidates for the
Sonogashira reaction.
The cross-coupling of phenylacetylene with the iron com-
plex [FeCp{C6(CH2CH2C6H4Br6)6}][PF6][13] was investigated
(Scheme 5). The good activity (one-step six C C coupling)
and the good tolerance toward functional groups of the Pd
catalyst 1c was demonstrated because the hoped-for iron
complex product was obtained. In addition, cross-coupling
of
phenylacetylene
with
the
iron-free
star
C6(CH2CH2C6H4Br)6 allowed the isolation of the product re-
sulting from cross-coupling (Scheme 5). This original one-
step multiple C C cross-coupling reaction provides a valua-
ble strategy for the synthesis of stars and dendrimers.
Scheme 3. Synthesis of 4b and 4d.Reagents and conditions: i) HCHO,
HCl, HPCy2; ii) [Pd(OAc)2], CH2Cl2.
Kinetics of the reactions with tBu and Cy ligand-based cata-
lysts: We carried out kinetic investigations in order to
obtain a better quantification of the differences in reactivity
between the tert-butylphosphine- and cyclohexylphosphine-
functionalized catalysts. Mechanistic and kinetic studies of
Pdii catalytic systems have often been reported in detail and
have highlighted the intermediacy of catalytic species in the
cross-coupling reactions.[14] Different techniques may be
used, such as NMR spectroscopy,[15] analytical techniques
(conductivity measurements)[16] or electrochemical techni-
ques (cyclic voltammetry).[17] This study was based on the
overall reaction, that is, only the final product was isolated.
The tert-butyl and cyclohexylpalladium(ii) catalysts 1c
(1 mol%) and 1d (1 mol%) were used in a typical Sonoga-
shira reaction procedure involving iodobenzene (4 mmol)
and phenylacetylene (6 mmol) in Et3N (10 mL). A GPC
technique was used to monitor the appearance of diphenyl-
acetylene and the disappearance of iodobenzene from which
the rate constants were determined. To study the kinetics
with 1c, the GPC samples were frozen in liquid nitrogen as
soon as they were taken from the reaction because the ki-
netics were too fast compared to the retention times for
each GPC experiment. The variation of lnx versus time
(x = c/c0) was linear for both plots (Figure 2a and b). This
establishes an overall reaction order of +1. The observed ap-
parent rate constants kobs for the overall reactions were then
Scheme 4.
Catalytic C C cross-coupling between acetylenes and aryl
halides: In previous work,[8] the reactivity of 1c towards aryl
iodides, bromides and chlorides was investigated in a Sono-
gashira copper-free procedure (Table 1). Excellent activity
was observed towards aryl iodides with TONs as high as
71000. Good activity was also obtained for aryl bromides
and a substantial reactivity was found with aryl chlorides,
thus demonstrating the efficiency of bis(tert-butylphosphine)
ligands in such C C cross-coupling. Nevertheless, 1d showed
a lower, albeit good, activity towards aryl iodides and bro-
mides in copper-free Sonogashira procedures (Table 2). The
conversion observed for aryl iodides and bromides with the
dendritic series of catalysts 2c,d, 3c,d, 4c,d revealed the
same distinction in the reactivity between the phosphine
substituents (tert-butyl versus cyclohexyl)(Table 3). Also, a
negative dendritic effect was demonstrated for metalloden-
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Palladium Catalysts for the Sonogashira Reaction
3936 3944
Table 1. Sonogashira coupling of aryl halide substrates with phenylacetylene and the monomeric catalyst 1c.[a]
Entry
X
R
R’
T[8C]
Catalyst[mol%]
Reaction time
Conversion[%][b]
TON
1
2
3
4
5
6
7
8
I
I
I
I
I
I
I
I
I
Br
Br
Br
Br
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
80
25
À20
À40
25
80
80
80
80
80
25
80
25
80
25
25
80
1
1
1
1
1
0.5
0.1
0.01
15 min
30 min
1 day
2 days
8 h
15 min
2 h
1 day
7 days
20 min
1 h
3 h
15 h
50 min
3 h
2 days
5 days
5 days
3 days
3 days
3 days
100
100
70
51
76
100
100
87
71
100
100
96
54
4
100
100
70
51
76
200
1000
8700
71000
100
100
96
Si(CH3)3
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
9
0.001
10
11
12
13
14
15
16
17
18
19
20
21
C6H5
C6H5
1
1
1
1
1
1
1
1
1
1
2
1
(p-Me)C6H5
C6H5
Si(CH3)3
C6H5
C6H5
Si(CH3)3
C6H5
54
4
9
5
13
14
15
30
C6H5
C6H5
C6H5
9
5
(p-CN)C6H5
(p-F)C6H5
(p-COOCH3)C6H5
(p-COOCH3)C6H5
(p-COOCH3)C6H5
13
14
15
30
22
C6H5
C6H5
C6H5
C6H5
80
25
80
40
22
[a] Reaction conditions: aryl halide (2 mmol), acetylene (3 mmol), Et3N (6 mL). [b] Yield of isolated product.
Table 2. Sonogashira coupling of aryl halide substrates with phenylacetylene and the monomeric catalyst 1d.[a]
lyst was recovered by precipita-
tion from the product solution
once the reaction was comple-
te.[3b,18]
We have processed a set of
recycling experiments based on
the precipitation of the metallo-
dendritic catalyst. In a typical
Entry
X
R
R’
T[8C]
Reaction time
Conversion[%][b]
TON
1
2
3
4
I
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
80
45
80
80
5 h
3 days
4 h
76
100
71
76
100
71
I
Br
Cl
5 h
traces
[a] Reaction conditions: aryl halide (2 mmol), phenylacetylene (3 mmol), catalyst 1d (1 mol%), Et3N (6 mL).
[b] Yield of isolated product.
procedure,
iodobenzene
Table 3. Sonogashira coupling of aryl halide substrates with phenylacetylene and dendrimeric catalysts 2c,d,
3c,d and 4c,d.[a]
(2 mmol) in Et3N (8 mL) with
catalyst 2d, 3d or 4d (2 mol%
based on the catalytic sites) was
treated with phenylacetylene
(3 mmol) at 808C for 48 h. The
reaction time was chosen in
order to complete all the reac-
tions, even with the dendritic
catalyst of third generation
whose reactivity is lower than
that of the first and second
ones (see above). Subsequently,
pentane (30 mL) was added to
the reaction mixture to precipi-
tate the catalyst and extract the
product. The pentane extraction
was carried out five times to
optimize product recovery. The
Entry
Aryl halide
Solvent
Catalyst[1 mol%]
T[8C]
Reaction time [h][b]
Conversion[%][c]
1
2
3
4
5
6
7
8
iodobenzene
iodobenzene
iodobenzene
iodobenzene
iodobenzene
iodobenzene
bromobenzene
bromobenzene
bromobenzene
bromobenzene
bromobenzene
bromobenzene
bromobenzene
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Bu2NH
Et3N
Et3N
Et3N
Et3N
2d
3d
4d
2c
3c
4c
2d
3d
3d
4d
2c
3c
4c
80
80
80
25
25
25
80
80
120
80
25
25
25
24
24
24
15
40
48
48
48
20
48
17
48
48
79
72
46
97
100
100
17
15
20
6
100
93
9
10
11
12
13
96
[a] Reaction conditions: aryl halide (2 mmol), phenylacetylene (3 mmol), Et3N (6 mL). [b] The reaction was
monitored by TLC. [c] Yield of isolated product.
determined from the slopes of the regression for each plot.
The calculated rate constants were 0.925 molLÀ1 hÀ1 at 258C
for 1c and 0.028 molLÀ1 hÀ1 278C for 1d. This gives a k(1c)/
k(1d) ratio of ꢀ33.
reactants and solvents were then re-added to the dried cata-
lyst under nitrogen to proceed to the next cycles. The results
are summarized in Table 5 and Figure 3. The catalytic activi-
ty for all the generations of dendrimers remained the same
up to the fifth cycle. However, a significant drop in the ac-
tivity was observed from the fifth cycle for all the genera-
tions of dendrimers. This behavior mostly resulted from a
decomposition of the dendritic ligand because no leaching
was observed. The subsequent decomposition was confirmed
Recovery of metallodendritic catalysts: Various techniques
can be used to recycle the metallodendritic catalysts.[3a] The
most recent one required CFMR devices based on nanofil-
tration through membranes. Very often, however, the cata-
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D. Astruc, K. Heuzÿ et al.
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ever, the signal for the active catalytic species was still ob-
served at d = 25 ppm (with a slight shift of 2 ppm in com-
parison with the initial signal of the Pdii catalyst). This de-
composition has also been reported with a variety of other
dendritic systems that employ either precipitation or other
recovery techniques. Interestingly, the fifth cycle often
seems to be of crucial importance in the reactivity
drop.[18a,19]
Conclusion
New copper-free Sonogashira Pd catalysts were synthesized.
that exhibit very good reactivity under mild conditions with
aryl iodides, bromides, and even some reactivity with acti-
vated aryl chlorides. The catalytic activity was much higher
with tBu substituents on the phosphines than with Cy sub-
stituents. The monomeric Pd catalyst bearing tBu substitu-
ents on the phosphines was applied to the synthesis of orga-
noiron and organic stars whereby six Sonogashira C C cou-
pling reactions occur. Dendritic versions of these copper-
free catalysts were designed, synthesised and used with a re-
activity that showed a negative dendritic effect, the largest
dendritic catalysts being the less active ones. This negative
dendritic effect is attributed to the increasing steric bulk
around the active metal centres as the dendrimer generation
increases, and this finding confirms similar observations
made previously.[20] The kinetics of the reaction, monitored
by GPC, are much faster with tBu substituents on the phos-
phine ligands than with Cy substituents. The dendritic cata-
Figure 1. Conversion of aryl halides with phenylacetylene catalyzed by
2d, 3d, and 4d at 808C.
Table 4. Solvent effect in the Sonogashira coupling between iodobenzene
and phenylacetylene with the dendritic catalyst 3d.[a]
Entry
Solvent
T[8C]
Reaction time [h]
Conversion[%][b]
1
2
3
4
Et3N
Et3N/DMF
Bu3N
80
140
140
120
5
3
8
8
72
34
16
31
Bu2NH
[a] Reaction conditions: iodobenzene (2 mmol), phenylacetylene
(3 mmol), solvent (6 mL). [b] Yield of isolated product.
by 31P NMR analysis of the catalyst after the cycles. Indeed,
the appearance of several peaks at dꢀ50 ppm confirmed
the presence of oxidation and decomposition species. How-
Scheme 5. Reagents and conditions: i) p-Br-C6H5CH2Br, KOH, DME, 408C, 6 days; ii) PPh3, MeCN, 24 h, (Xe lamp); iii) phenylacetylene, Et3N, catalyst
1c.
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Palladium Catalysts for the Sonogashira Reaction
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Figure 3. Reaction conditions: iodobenzene (4 mmol), phenylacetylene
(6 mmol), catalyst (1 mol%), Et3N (10 mL), 808C, 48 h. The product was
extracted and purified by silica gel column chromatography.
lysts with R = Cy are recoverable by precipitation with
pentane and can be reused up to five times with a good ac-
tivity level. However, the dendritic catalysts with R = tBu
could not be easily recovered by this method on account of
their high solubility in pentane. Ongoing studies are under-
way in our laboratory in order to investigate catalysts for
Pd-catalyzed C C coupling that are both extremely reactive
and recoverable.
Experimental Section
Figure 2. Kinetics of the disappearance of iodobenzene in a Sonogashira
reaction with a) 1c at 258C, and b) 1d at 278C. Variation of ln(c/c0)
versus time (c: concentration of iodobenzene at t, c0: initial concentration
of iodobenzene).
All reactions were performed under a nitrogen atmosphere in standard
(Schlenk) glassware. The solvents were dried according to standard pro-
cedures and saturated with nitrogen. The 1H, 13C and 31P NMR spectra
were recorded with the following spectrometers: Brucker DPX200 FT
NMR spectrometer (1H: 200.16, 13C: 50.33, 31P: 81.02 MHz), Brucker
AC250 FTNMR spectrometer ( 1H: 250.13, 13C: 62.90 MHz) and Avance
300FTNMR spectrometer ( 1H: 300.13, 13C: 75.46, 31P: 121.49 MHz).
Mass spectroscopic measurements (MALDI-TOF) were performed at the
LCSOB, University of Paris6. The elemental analyses were carried out in
the analysis laboratory of the elemental analysis department at CNRS-
Vernaison. The starting materials were obtained commercially and were
used without further purification.
Table 5. Coupling of iodobenzene with phenylacetylene and the dendritic
catalysts 2d, 3d and 4d.[a]
Catalyst
Cycle
Conversion[%][b]
2d
first
second
third
fourth
fifth
sixth
first
second
third
fourth
fifth
sixth
seventh
first
second
third
fourth
fifth
92
74
61
56
26
26
83
66
66
71
21
26
16
78
70
78
76
51
46
39
General procedure for the syntheses of aminophosphine 1a and 1b mo-
nomers:
3d
4d
Bis(tert-butylaminophosphine) (1a): Triethylamine (0.29 mL, 2.1 mmol)
was added to a stirred solution of the phosphonium salt (0.5 g, 2.1 mmol)
in water/methanol (2:1, 3 mL). On addition of benzylamine (0.11 mL,
1 mmol) the mixture became viscous, thus toluene (3 mL) was added.
The solution was refluxed for 1 h. On cooling, two layers separated, and
the organic layer was extracted and dried over sodium sulfate. Methanol
was added to precipitate a white gummy solid. The solvents were re-
moved, and the solid was dried under a high vacuum to yield the product
as a white solid (385 mg, 91%). 1H NMR (200.16 MHz, CDCl3, 300 K): d
= 7.24 (m, 5H, CHarom), 3.79 (s, 2H, CH2N), 2.73 (s, 4H, PCH2N), 1.09
(s, 18H, tBu), 1.04 ppm (s, 18H, tBu); {1H}13C NMR (62.90 MHz, CDCl3,
300 K): d = 130.14 (Carom), 129.1 (Carom), 128.2 (Carom), 127.6 (Carom), 61.0
(CH2N), 60.7 (PCH2N), 33.4 (tBu), 27.3 (tBu), 26.9 ppm (tBu);
{1H}31P NMR (81.02 MHz, CDCl3, 300 K): d = 12.9 ppm.
sixth
seventh
[a] Reaction conditions: iodobenzene (2 mmol), phenylacetylene
(3 mmol), Et3N (8 mL), catalyst (2 mol%), N2. [b] Yield of isolated prod-
uct.
Bis(cyclohexylaminophosphine) (1b): The same procedure as for 1a was
used. Phosphonium salt (1.466 g, 5 mmol), triethylamine (0.68 mL,
5 mmol), benzylamine (0.27 mL, 2.5 mmol). Yield: 1.07 g (82%) of a
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D. Astruc, K. Heuzÿ et al.
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white solid. 1H NMR (200.16 MHz, CDCl3, 300 K): d = 7.25 (m, 5H,
CHarom), 3.77 (s, 2H, CH2N), 2.82 (s, 4H, PCH2N), 2.45 (s, 4H, PCHCy),
2.37 (s, 4H, CHCy), 1.73 1.21 ppm (m, 40H, CH2,Cy); {1H}13C NMR
(NH2)16 (720 mg, 42.7 mmol). Yield: 2.5 g (70%) of a white solid. 1H
NMR (200.16 MHz, CDCl3, 300 K): d = 2.69 (m, 64H, PCH2N), 2.58 (m,
64H, PCHCy), 2.33 (m, 116H, CH2N), 1.70 (m, 320H, CH2,Cy), 1.50 (m,
60H, CH2CH2,dendr), 1.17 ppm (m, 320H, CH2,Cy); {1H}13C NMR
(62.90 MHz, CDCl3, 300 K):
d = 129.7 (Carom), 129.1 (Carom), 128.2
(Carom), 127.8 (Carom), 61.4 (CH2N), 60.7 (PCH2N), 32.9 (Cy), 29.7 (Cy),
27.3 (Cy), 26.6 ppm (Cy); {1H}31P NMR (81.02 MHz, CDCl3, 300 K): d =
À17.4 ppm; elemental analysis calcd (%) for C33H55P2N (527.75): C 75.10,
H 10.50; found: C 73.87, H 10.37.
(75.47 MHz, CDCl3, 300 K): d = 53.86 (CH2Ncentral), 51.72 (CH2N +
PCH2N + PCH), 31.9 (d,Cy), 29.05 (dd,Cy), 28.75 (CH2-CH2,dendr) 26.4
(d,Cy), 25.7 (Cy), 22.66 ppm (CH2,dendr); {1H}31P NMR (81.02 MHz, CDCl3,
300 K): d = À18.1 ppm.
General procedure for the syntheses of (tert-butylaminophosphine)palla-
dium(ii) monomer 1c and dendrimers 2c, 3c, 4c:
General procedure for the syntheses of aminophosphine dendrimers 2a,
3a, 4a and monomers 2b, 3b, 4b:
G1-DAB-dendr-[bis(tert-butylaminophosphine)]4 (2a): Di-tert-butylphos-
phine (1.05 mL, 6 mmol) and paraformaldehyde (0.17 g, 6 mmol) in
methanol (5 mL) were heated at 658C for 10 min. Upon cooling, DAB-
dendr-(NH2)4 (0.2 g, 0.7 mmol) in methanol (3 mL) was added, and the
mixture was stirred at room temperature for 30 min. Toluene (15 mL)
was added, and the mixture was heated at 658C for 30 min. The reaction
medium was stirred at room temperature for another 12 h. The solvent
was removed under vacuum, and the solid was recrystallised (cold pen-
tane) and dried to yield the aminophosphine dendrimer as a white solid
(830 mg, 75%). 1H NMR (250.13 MHz, CDCl3, 300 K): d = 2.74 (m,
16H, NCH2P), 2.39 (m, 20H, NCH2), 1.24 (m, 12H, CH2-CH2), 1.16 (s,
72H, tBu), 1.11 ppm (s, 72H, tBu); {1H}13C NMR (62.90 MHz, CDCl3,
300 K): d = 54.8 (NCH2), 53.2 (NCH2), 52.4 (NCH2), 29.6 (tBu), 29.5
(tBu), 24.7 (CH2,dendr), 23.4 ppm (CH2,dendr); {1H}31P NMR (81.03 MHz,
Bis(tert-butylaminophosphine)palladium(ii) complex 1c: [Pd(OAc)2]
(70 mg, 0.32 mmol) was added to a solution of aminophosphine 1a
(132 mg, 0.32 mmol) in CH2Cl2 (5 mL). The solution was stirred for 2 h at
room temperature. The solvent was removed under vacuum to give a
solid that was washed with cold pentane and dried under vacuum to yield
complex 1c as a yellowish solid (190 mg, 94%). 1H NMR (300.13 MHz,
CDCl3, 300 K): d = 7.25 (m, 5H, CHarom), 3.58 (s, 2H, CH2N), 2.66 (s,
4H, PCH2N), 1.89 (s, 6H, CH3), 1.39 (s, 18H, tBu), 1.32 ppm (s, 18H,
tBu); {1H}13C NMR (62.90 MHz, CDCl3, 300 K): d = 176.0 (CO), 135.1
128.6 (Carom), 67.5 (CH2N), 54.6 (PCH2N), 36.3 (CH3), 33.2 (Bu),
31.8 ppm (tBu); {1H}31P NMR (81.02 MHz, CDCl3, 300 K):
d =
35.9 ppm. elemental analysis calcd (%) for C29H53P2NO4Pd (648.10): C
53.74, H 8.24, P 9.56; found: C 53.23, H 8.02, P 9.44.
G1-DAB-dendr-[bis(tert-butylaminophosphine)]4pallaium(ii) complex 2c:
The same procedure as for 1c was used with [Pd(OAc)2] (100 mg,
0.44 mmol) and aminophosphine 2a (170 mg, 0.11 mmol). Yield: 204 mg
(75%) of a yellow solid; 1H NMR (250.13 MHz, CDCl3, 300 K): d = 2.75
(m, 16H, NCH2P), 2.40 (m, 20H, NCH2), 1.89, (s, 24H, CH3), 1.46 (s,
72H, tBu), 1.39 (s, 72H, tBu), 1.26 ppm (m, 12H, CH2-CH2); {1H}13C
NMR (62.90 MHz, CDCl3, 300 K): d = 176.2 (CO), 54.4(NCH2), 53.5
(NCH2), 52.9 (NCH2), 30.1 (CH3,OAc), 29.7 (tBu), 29.5 (tBu), 24.9
(CH2,dendr), 23.5 ppm (CH2,dendr); {1H}31P NMR (81.03 MHz, CDCl3,
CDCl3, 300 K):
d = 12.2 ppm; elemental analysis calcd (%) for
C88H192P8N6 (1579.792): C 66.80, H 12.23; found: C 66.76, H 12.17.
G2-DAB-dendr-[bis(tert-butylaminophosphine)]8 (3a): The same proce-
dure as for 2a was used with di-tert-butylphosphine (0.86 mL, 4.6 mmol),
paraformaldehyde (0.14 g, 4.6 mmol) and DAB-dendr-(NH2)8 (0.2 g,
0.26 mmol). Yield: 1.05 g (91%) of a white solid. 1H NMR (250.13 MHz,
CDCl3, 300 K): d = 2.73 (m, 32H, NCH2P), 2.39 (m, 52H, NCH2), 1.24
(m, 28H, CH2-CH2), 1.16 (s, 144H, tBu), 1.11 (s, 144H, tBu); {1H}13C
NMR (62.90 MHz, CDCl3, 300 K): d = 54.7(NCH2), 53.6 (NCH2), 52.4
(NCH2), 29.7 (tBu), 29.6 (tBu), 24.9 (CH2,dendr), 23.6 (CH2,dendr); {1H}31P
NMR (81.03 MHz, CDCl3, 300 K): d = 12.2; elemental analysis calcd
(%) for C184H400P16N14 (4434.974): C 66.87, H 12.20; found: C 66.45, H
11.98.
300 K):
d
=
35.20 ppm; elemental analysis calcd (%) for
C104H216P8N6O16Pd4 (2480.360): C 50.36, H 8.78; found: C 50.11, H 8.53.
G2-DAB-dendr-[bis(tert-butylaminophosphine)]8pallaium(ii) complex 3c:
The same procedure as for 1c was used with [Pd(OAc)2] (100 mg,
0.44 mmol) and aminophosphine 3a (184 mg, 0.056 mmol). Yield: 182 mg
(64%) of a yellow solid; 1H NMR (200.16 MHz, CDCl3, 300 K): d = 2.71
(m, 32H, NCH2P), 2.34 (m, 52H, NCH2), 1.89, (s, 48H, CH3), 1.47 (s,
144H, tBu), 1.40 (s, 144H, tBu), 1.28 ppm (m, 28H, CH2-CH2); {1H}13C
NMR (62.90 MHz, CDCl3, 300 K): d = 177.0 (CO), 54.8(NCH2), 53.6
(NCH2), 52.5 (NCH2), 30.5 (CH3,OAc), 30.0 (tBu), 29.9 (tBu), 24.6
(CH2,dendr), 23.3 ppm (CH2,dendr); {1H}31P NMR (81.03 MHz, CDCl3,
G3-DAB-dendr-[bis(tert-butylaminophosphine)]16 (4a): The same proce-
dure as for 2a was used with di-tert-butylphosphine (0.79 mL, 4.2 mmol),
paraformaldehyde (126 mg, 4.2 mmol), and DAB-dendr-(NH2)16 (0.2 g,
0.12 mmol). Yield: 0.727 g (90%) of
(250.13 MHz, CDCl3, 300 K): d 2.73 (m, 64H, NCH2P), 2.39 (m,
a
white solid. 1H NMR
=
116H, NCH2), 1.28 (m, 60H, CH2-CH2), 1.16 (s, 288H, tBu), 1.11 ppm (s,
288H, tBu); {1H}13C NMR (62.90 MHz, CDCl3, 300 K): d = 54.7(NCH2),
53.3 (NCH2), 52.2 (NCH2), 30.0 (tBu), 29.7 (tBu), 24.6 (CH2,dendr),
300 K):
d
=
35.22 ppm; elemental analysis calcd (%) for
C
216H448P16N14O32Pd8 (5094.944): C 50.86, H 8.85; found: C 50.53, H 8.45.
23.5 ppm (CH2,dendr); {1H}31P NMR (81.03 MHz, CDCl3, 300 K): d
=
G3-DAB-dendr-[bis(tert-butylaminophosphine)]16palladium(ii) complex
4c: The same procedure as for 1c was used with [Pd(OAc)2] (100 mg,
0.44 mmol) and aminophosphine 4a (188 mg, 0.028 mmol). Yield: 199 mg
12.2 ppm; elemental analysis calcd (%) for C376H816P32N30 (6739.168): C
66.91, H 12.18; found: C 66.22, H 11.53.
1
G1-DAB-dendr-[bis(cyclohexylaminophosphine)]4 (2b): The same proce-
dure as for 2a was used with dicyclohexylphosphine (2.82 mL,
13.98 mmol), paraformaldehyde (0.46 g, 13.98 mmol), and DAB-dendr-
(NH2)4 (500 mg, 1.58 mmol). Yield: 2.29 g (73%) of a white solid. 1H
NMR (200.16 MHz, CDCl3, 300 K): d = 2.72 (m, 16H, PCH2N), 2.65 (m,
16H, PCHCy), 2.37 (m, 20H, CH2N), 1.72 (m, 80H, CH2,Cy), 1.53 (m,
12H, CH2CH2,dendr), 1.20 ppm (m, 80H, CH2,Cy); {1H}13C NMR
(69%) of a yellow solid; H NMR (200.16 MHz, CDCl3, 300 K): d = 2.73
(m, 64H, NCH2P), 2.39 (m, 116H, NCH2), 1.90, (s, 96H, CH3), 1.47 (s,
288H, tBu), 1.40 (s, 288H, tBu), 1.26 ppm (m, 60H, CH2-CH2); {1H}13C
NMR (62.9 MHz, CDCl3, 300 K): d
= 176.9 (CO), 54.7(NCH2), 53.7
(NCH2), 52.6 (NCH2), 30.8 (CH3,OAc), 30.5 (tBu), 30.2 (tBu), 24.6
(CH2,dendr), 23.6 ppm (CH2,dendr); {1H}31P NMR (81.03 MHz, CDCl3,
300 K):
d
=
35.30 ppm; elemental analysis calcd (%) for
(50.33 MHz, CDCl3, 300 K): d
=
55.35 (CH2Ncentral), 52.48 (CH2N
+
C440H912P32N30O64Pd16 (10329.888): C 51.10, H 8.89; found: C 50.79, H
8.61.
PCH2N), 32.7 (d,Cy), 29.7 (t,Cy), 28.89 (CH2-CH2,dendr) 27.16 (d, Cy), 27.35
(s, Cy), 25.24 ppm (CH2,dendr); {1H}31P NMR (81.02 MHz, CDCl3, 300 K):
d = À17.8 ppm.
General procedure for the syntheses of (cyclohexylaminophosphine)pal-
ladium(ii) monomer 1d and dendrimers 2d, 3d, 4d:
G2-DAB-dendr-[bis(cyclohexylaminophosphine)]8 (3b): The same proce-
dure as for 2a was used with dicyclohexylphosphine (2.54 mL,
12.56 mmol), paraformaldehyde (342 mg, 11.44 mmol), and DAB-dendr-
Bis(cyclohexylaminophosphine)palladium(ii) complex 1d: [Pd(OAc)2]
(326 mg, 1.45 mmol) was added to a solution of aminophosphine 1b
(765 mg, 1.45 mmol) in CH2Cl2 (50 mL). The solution was stirred for 2 h
at room temperature. The volume was reduced to 10 mL, and pentane
was added to precipitate complex 1d that was dried under vacuum to
yield a yellow solid (803 mg, 87%). 1H NMR (200.16 MHz, CDCl3,
300 K): d = 7.37 7.25 (m, 5H, CHarom), 3.58 (s, 2H, CH2N), 2.58 (s, 4H,
PCH2N), 2.26 (s, 4H, PCHCy), 1.95 (s, 6H, CH3), 1.65 1.19 ppm (m, 40H,
(NH2)8 (500 mg, 0.64 mmol). Yield: 1.64 g (64%) of
a white solid.
1H NMR (200.16 MHz, CDCl3, 300 K): d = 2.73 (m, 32H, PCH2N), 2.63
(m, 32H, PCHCy), 2.34 (m, 52H, CH2N), 1.74 (m, 160H, CH2,Cy), 1.54 (m,
28H, CH2CH2,dendr), 1.21 ppm (m, 160H, CH2,Cy); {1H}31P NMR
(81.02 MHz, CDCl3, 300 K): d = À17.8 ppm.
G3-DAB-dendr-[bis(cyclohexylaminophosphine)]16 (4b): The same pro-
cedure as for 2a was used with dicyclohexylphosphine (3.35 mL,
16.5 mmol), paraformaldehyde (454 mg, 15.1 mmol), and DAB-dendr-
CH2,Cy); {1H}13C NMR (75.47 MHz, CDCl3, 300 K): d
135.74 (CHarom),130.23 (CHarom), 128.81 (CHarom), 128.40 (CHarom), 67.5
(PCHCyclo), 47.73 (CH2N PCH2N), 35.3 (dt, CH2,Cy), 28.7 (CH2,Cy),
= 177.1 (CO),
+
3942
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 3936 3944

Palladium Catalysts for the Sonogashira Reaction
3936 3944
27.24 (dt, CH2,Cy), 25.78 (CH3), 24.19 ppm (CH2,Cy); {1H}31P NMR
(81.02 MHz, CDCl3, 300 K): d = 26.5 ppm; elemental analysis calcd (%)
for C37H61P2NO4Pd (752.263): C 59.08, H 8.17, N 1.86; found: C 58.34, H
8.24 N 1.96.
[1] a) Dendrimers and Nanosciences (Ed.: D. Astruc) C. R. Chimie,
Elsevier, 2003, Vol. 8 10; b) G. R. Newkome, C. N. Moorefield, F.
Vˆgtle, Dendrimers and Dendrons, Concepts, Syntheses and Applica-
tions, Wiley-VCH, Weinheim, 2002; c) Dendrimers and other den-
dritic polymers (Eds.: J. M. J. Frÿchet, D. A. Tomalia), Wiley, Chi-
chester, 2001.
[2] D. Astruc, F. Chardac, Chem. Rev. 2001, 101, 2991; G. E. Oosterom,
J. N. H. Reek, P. C. J. Kamer, P. W. N. M. van Leeuwen, Angew.
Chem. 2001, 113, 1878; Angew. Chem. Int. Ed. 2001, 40, 1828; R.
Kreiter, A. W. Kleij, R. J. M. Klein Gebbink, G. van Koten, Top.
Curr. Chem. 2001, 217, 163.
G1-DAB-dendr-[bis(cyclohexylaminophosphine)]4palladium(ii) complex
2d: The same procedure as for 1d was used with [Pd(OAc)2] (900 mg,
4 mmol) and aminophosphine 2b (2 g, 1 mmol). Yield: 2.175 g (75%) of
1
a yellow solid; H NMR (300.13 MHz, CDCl3, 300 K): d = 2.55 (m, 32H,
PCH2N + PCHCy), 2.33 (m, 20H, CH2N), 1.89 (s, 24H, CH3), 1.70 (m,
80H, CH2,Cy), 1.59 (m, 12H, CH2CH2,dendr), 1.16 ppm (m, 80H, CH2,Cy);
{1H}13C NMR (62.90 MHz, CDCl3, 300 K): d = 175.9 (CO), 61.0 (CHP),
52.0 (CH2Ncentral), 48.94 (CH2N
(CH2,Cy), 23.52 ppm (CH2,dendr); {1H}31P NMR (121.49 MHz, CDCl3,
300 K): 27 ppm; elemental analysis calcd (%) for
+ PCH2N), 30.5 (CH3), 29.79 26.25
[3] a) R. van Heerbeek, P. C. J. Kamer, P. W. N. M. van Leeuwen,
J. N. H. Reek, Chem. Rev. 2002, 102, 3717; b) M. T. Reetz, G.
Lohmer, R. Schwickardi, Angew. Chem. 1998, 110, 492; Angew.
Chem. Int. Ed. Engl. 1997, 36, 1526.
d
=
C136H248P8N6O16Pd4 (2896.966): C 56.39, H 8.63; found: C 55.65, H 8.71.
G2-DAB-dendr-[bis(cyclohexylaminophosphine)]8palladium(ii) complex
3d: The same procedure as for 1d was used with [Pd(OAc)2] (736 mg,
3.3 mmol) and aminophosphine 3b (1.64 g, 0.41 mmol). Yield: 2.3 g
(96%) of a yellow solid; 1H NMR (300.13 MHz, CDCl3, 300 K): d = 2.61
(m, 64H, PCH2N + PCHCy), 2.42 (m, 52H, CH2N), 1.96 (s, 48H, CH3),
1.79 (m, 160H, CH2,Cy), 1.66 (m, 12H, CH2CH2), 1.24 ppm (m, 160H,
CH2,Cy); {1H}31P NMR (121.49 MHz, CDCl3, 300 K): d = 27.2 ppm; ele-
mental analysis calcd (%) for C280H512P16N14O32Pd8 (5934.161): C 56.67, H
8.63; found: C 54.98, H 8.79.
[4] K. Heuzÿ, D. Mÿry, D. Gauss, D. Astruc, Chem. Commun. 2003,
2274.
[5] a) J. S. Moore, Acc.Chem. Res. 1997, 30, 402; b) T. Hiyama in Metal-
Catalyzed Cross-Coupling Reactions (Eds.: F. Diederich, P. J. Stang),
Wiley-VCH, Weinheim, 1998, Chapt. 10; c) E.-J. Negishi, L. Anasta-
sia, Chem. Rev. 2003, 103, 1979; d) Modern Arene Chemistry (Ed.:
D. Astruc), Wiley-VCH, Weinheim, 2002; e) L. Brandsma, S. F. Vali-
levsky, H. D. Verkruijsse, Application of Transition Metal Catalysts
in Organic Synthesis, Springer, Berlin, 1988, Chapt. 10; f) K. C. Nico-
laou, E. J. Sorensen, Classics in Total Synthesis, Wiley-VCH, Wein-
heim, 1966, p. 582.
[6] a) K. Sonogashira, Y. Tohoda, N. Hagihara, Tetrahedron Lett. 1975,
16, 4467; b) I. B. Campbell in Organocopper Reagents: A Practical
Approach (Ed.: R. J. K. Taylor), OUP, New York, 1994, Chapt. 10,
p. 218; c) K. Sonogashira, Comprehensive Organic Synthesis (Ed.:
B. M. Trost, I. Fleming) Pergamon Press, Oxford, 1991, Vol. 3,
p. 521; d) R. Rossi, A. Carpita, F. Bellina, Org. Prep. Proced. 1995,
27, 129.
G3-DAB-dendr-[bis(cyclohexylaminophosphine)]16palladium(ii) complex
4d: The same procedure as for 1d was used with [Pd(OAc)2] (592 mg,
2.64 mmol) and aminophosphine 4b (1.39 g, 0.17 mmol). Yield: 1.6 g
(81%) of a yellow solid; 1H NMR (300.13 MHz, CDCl3, 300 K): d = 2.57
(m, 128H, PCH2N
CH3), 1.77 (m, 320H, CH2,Cy), 1.63 (m, 12H, CH2CH2,dendr) 1.23 ppm (m,
320H, CH2,Cy); {1H}13C NMR (75.47 MHz, CDCl3, 300 K): d
175.1
PCH2N), 32.4
+ PCHCy), 2.29 (m, 104H, CH2N), 1.91 (s, 96H,
=
(CO), 59.35 (CHP), 50.2 (CH2Ncentral), 47.1 (CH2N
+
(CH3), 27.1 24.29 (CH2,Cy), 22.32 ppm (CH2,dendr); {1H}31P NMR
(121.49 MHz, CDCl3, 300 K): d = 27.3 ppm.
[7] J.-P. GenÜt, E. Blart, M. Savignac, Synlett 1992, 715; V. P. Bˆhm,
W. A. Hermann, Eur. J. Org. Chem. 2000, 3679; M. Alami, F. Ferri,
G. Linstrumelle, Tetrahedron Lett. 1993, 34, 6403; D. A. Alonso, C.
Nµjera, M. C. Pacheco, Tetrahedron Lett. 2002, 43, 9365; X. Fu, S.
Zhang, J. Yin, D. Schumacher, Tetrahedron Lett. 2002, 43, 6673; M.
Pal, K. Parasuraman, S. Gupta, K. R. Yeleswarapu, Synlett Synlett.
2002, 12, 1976; T. Fukayama, M. Shinmen, S. Nishitani, M. Sato, I.
Ryu, Org. Lett. 2002, 4, 1691; D. A. Alonso, C. Najera, M. C. Pa-
checco, Adv. Synth. Catal. 2003, 345, 1146; D. Gelman, S. L. Buch-
wald, Angew. Chem. 2003, 115, 6175; Angew. Chem. Int. Ed. 2003,
42, 5993; ; L. Djakovitch, P. Rollet, Tetrahedron Lett. 2004, 45, 1367.
[8] D. Mÿry, K. Heuzÿ, D. Astruc, Chem. Commun. 2003, 1934.
[9] C. Glaser, Ber. Dtsch. Chem. Ges. 1869, 2, 422; P. Siemsen, R. C.
Livingston, F. Diederich, Angew. Chem. 2000, 112, 2740; Angew.
Chem. Int. Ed. 2000, 39, 2632.
[10] J. Fawcett, P. A. T. Hoye, R. D. W. Kemmit, D. J. Law, D. R. Russell,
J. Chem. Soc. Dalton Trans. 1993, 2563.
[11] M. Chai, Y. Niu, W. J. Youngs, P. L. Rinaldi, J. Am. Chem. Soc.
2001, 123, 4670.
[12] P. W. N. M. van Leeuwen, Appl. Catal. A 2001, 212, 61; P. E. Garrou,
Chem. Rev. 1985, 85, 171.
[13] B. Alonso, J.-C. Blais, D. Astruc, Organometallics 2002, 21, 1001.
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[15] L. J. Ackerman, J. P. Sadighi, D. M. Kurtz, J. A. Labinger, J. B.
Bercaw, Organometallics 2003, 22, 3884.
Synthesis of [FeCp{C6(CH2CH2C6H4CCC6H5)6}][PF6]: To a solution of
[FeCp{C6(CH2CH2C6H4Br)6}][PF6] (1 g, 0.7 mmol) and catalyst 1c
(27 mg, 6 mol%) in dry Et3N (3 mL) was added dropwise a solution of
phenylacetylene (0.7 mL, 6 mmol) in dry Et3N (3 mL).The mixture was
heated to 808C for three days. Et3N was then removed, and the product
was extracted with ether (5î20 mL). The organic layer was dried over
Na2SO4, and flash silica gel chromatography with petroleum ether yielded
a light brown solid (291 mg, 27%); 1H NMR (300.13 MHz, CDCl3,
300 K): d = 7.02 7.59 (m, 54H, Har), 5.35 (s, 5H, Cp), 2.78 and 2.88 ppm
(m, 12H, CH2); {1H}13C NMR (62.90 MHz, CDCl3, 300 K): d = 120.82
140.93 (Car), 80.11 (Cp), 37.12 (CH2), 33.05 ppm (CH2); MS (MALDI-
TOF, m/z): calcd: 1424.68; found: 1425.38 [MÀPF6]+.
Synthesis
of
C6(CH2CH2C6H4CCC6H5)6:
To
a
solution
of
C6(CH2CH2C6H4Br)6 (0.2 g, 0.17 mmol) and catalyst 1c (7 mg, 6 mol%)
in dry Et3N (3 mL) was added dropwise a solution of phenylacetylene
(0.16 mL, 1.5 mmol) in dry Et3N (3 mL). The mixture was heated at 808C
for 8 h. Et3N then was removed, and the product was extracted with
ether (3î20 mL). The organic layer was dried over Na2SO4, and flash
silica gel chromatography with petroleum ether yielded a light brown
solid (141 mg, 59%). 1H NMR (300.13 MHz, CDCl3, 300 K): d = 7.03
7.45 (m, 54H, Har), 2.79 and 2.89 ppm (m, 12H, CH2); {1H}13C NMR
(62.90 MHz, CDCl3, 300 K):
d = 122.24 139.59 (Car), 37.02 (CH2),
33.15 ppm (CH2); elemental analysis calcd (%) for C102H78 (1403.741): C
93.97,
H 6.03; found: C 93.28, H 5.59; MS (MALDI-TOF): m/z
(%):calcd: 1411.61; found: 1411.54 (100) [M+Ag]+.
[16] A. Jutand, Eur. J. Inorg. Chem. 2003, 2017; C. Amatore, A. A. Bah-
soun, A. Jutand, G. Meyer, A. N. Ntepe, L. Ricard, J. Am. Chem.
Soc. 2003, 125, 4212.
[17] C. Amatore, A. Bucaille, A. Fuxa, A. Jutand, G. Meyer, A. N.
Ntepe, Chem. Eur. J. 2001, 7, 2134.
[18] a) Y.-C. Chen, T.-F. Wu, J.-G. Dend, H. Liu, Y.-Z. Jiang, M. C. K.
Choi, A. S. C. Chan, Chem. Commun. 2001, 1488; b) Q.-H. Fan, Y.-
M. Chen, X.-M. Chen, D.-Z. Jiang, F. Xi, A. S. C. Chan, Chem.
Commun. 2000, 789; c) V. Maraval, R. Laurent, A.-M. Caminade, J.-
P. Majoral, Organometallics 2000, 19, 4025; d) H. Zeng, G. R. New-
kome, C. L. Hill, Angew. Chem. Int. Ed. 2000, 39, 1771; Angew.
Chem. 2000, 112, 1841; e) Q.-S. Hu, V. Pugh, M. Sabat, L. Pu, J.
Org. Chem. 1999, 64, 7528; f) M. Petrucci-Samija, V. Guillemette,
Acknowledgment
The Institut Universitaire de France (IUF, D.A.), the Centre National de
la Recherche Scientifique (CNRS), the Universities Bordeaux I and Par-
is VI, and the Ministõre de la Recherche et de la Technologie (MRT,
PhD grant to D.M.) are acknowledged for financial support.
Chem. Eur. J. 2004, 10, 3936 3944
www.chemeurj.org
¹ 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3943

D. Astruc, K. Heuzÿ et al.
FULL PAPER
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Received: February 13, 2004
Published online: June 24, 2004
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