Synthesis of 9- and 27-armed tetrakis(diperoxotungsto)phosphate-cored dendrimers and their use as recoverable and reusable catalysts in the oxidation of alkenes, sulfides, and alcohols with hydrogen peroxide

Article abstract of DOI:10.1002/chem.200500556

A series of 3- and 9-armed dendrons. functionalized at the focal position to quaternary ammonium salts, were synthesized and characterized. The reaction of these ammonium dendrons with the heteropolyacid H₃PW ₁₂O₄₀ in the

Full text of DOI:10.1002/chem.200500556

FULL PAPER
DOI: 10.1002/chem.200500556
Synthesis of 9- and 27-Armed Tetrakis(diperoxotungsto)phosphate-Cored
Dendrimers and Their Use as Recoverable and Reusable Catalysts in the
Oxidation of Alkenes, Sulfides, and Alcohols with Hydrogen Peroxide
Sylvain Nlate,* Lauriane Plault, and Didier Astruc[a]
Abstract: A series of 3- and 9-armed
dendrons, functionalized at the focal
position to quaternary ammonium
salts, were synthesized and character-
ized. The reaction of these ammonium
dendrons with the heteropolyacid
H3PW12O40 in the presence of hydrogen
peroxide led to a family of 9- and 27-
fects showed that the dendritic struc-
ture increased the stability of the POM
species and facilitated the recovery of
the catalyst up to the eighth cycle,
whereas the increased bulkiness
around the POM center led to a nega-
tive kinetic dendritic effect. Within the
9-armed POM-cored dendrimer series,
the reaction kinetics were susceptible
to the nature of the peripheral
endgroups. Indeed, the 9-armed n-
propyl-terminated POM-cored den-
drimer was identified as the most
active catalyst. In addition, the results
obtained with POM-cored dendrimers
versus tetraalkylammonium POMs
({[n-(C8H17)3NCH3]+}3[PO4{WO(O2)2}4]3À
and [{nC18H37(75%) + nC16H33(25%)]2N-
(CH3)2}+]3[PO4{WO(O2)2}4]3À) clearly
reveal that the dendritic structures are
more stable than their nondendritic
counterparts. After the reactions were
complete, the dendrimer catalysts were
easily recovered and recycled without a
discernable lost of activity, whereas at-
tempts to recover tetraalkylammonium
POMs gave unsatisfactory results. A
significant advantage of the dendritic
structures is that they enable the recov-
ery and recyclability of the POM cata-
lyst, in contrast to the other tetraalky-
lammonium POMs.
armed
air-stable
polyoxometalate
(POM)-cored dendrimers containing a
catalytically active trianionic POM spe-
cies [PO4{WO(O2)2}4]3À in the core.
These POM-cored dendrimers are air-
stable, efficient, recoverable, and reusa-
ble catalysts for the selective oxidation
of alkenes to epoxides, sulfides to sul-
fones, and alcohols to ketones, in an
aqueous/CDCl3 biphasic system with
hydrogen peroxide as the primary oxi-
dant. A study of the countercation ef-
Keywords: catalysis · dendrimers ·
oxidation
tungsten
·
polyoxometalate
·
Introduction
endgroups have been assembled and used in different do-
mains, such as supramolecular chemistry,[3] nanosciences,[1c]
drug delivery,[4] and catalysis.[2,5] However, dendritic cata-
lysts for oxidation reactions are relatively under represent-
ed.[6] Of those reported thus far, only a few are based on
polyoxometalates (POMs). POMs are distinctive inorganic
transition metal–oxygen clusters that are the source of fasci-
Dendrimers and metallodendrimers are generating much at-
tention for their potential applications in various areas.[1]
The increasing use of these macromolecules in catalysis is
an emerging field because they may allow the facile recov-
ery of the catalysts after use, an essential feature for reac-
tion efficiency, economy, and environmental concern.[2] In
this context, a variety of dendrimers, cores, branches, and
[8]
nating architectures[7] and very rich redoxchemistry, upon
with their catalytic activity in oxidation reactions is based.[9]
Recently, a few heterogeneous[10] and homogeneous[11] den-
dritic polyoxometalate catalysts were reported and shown to
be effective in oxidation reactions. For example, Bruceꢀs
group prepared heterogeneous dendrimer-templated meso-
porous titanosilicate and vanadosilicate oxidation catalysts
by means of sol–gel techniques, and have used them in the
epoxidation of cyclohexene with tert-butyl hydroperoxide.[10]
In homogeneous catalysis, only four reports concerning the
[a] Dr. S. Nlate, L. Plault, Prof. Dr. D. Astruc
Nanosciences and Catalysis Group, LCOO
UMR CNRS No 5802, University BordeauxI
351 Cours de la LibØration, 33405 Talence Cedex(France)
Fax: ( +33)540006994
E-mail: s.nlate@lcoo.u-bordeaux1.fr
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903

use of dendritic polyoxometalate catalysts in oxidation reac-
tions are known. Three of them involve dendrimers with
POM units at the peripheral positions. In the first, the
groups of Newkome and Hill prepared two dendritic tetra-
POM molecules with [HP2V3W15O59]5À units covalently
bonded to a 4-armed core, and used them as a recoverable
catalyst in the oxidation of tetrahydrothiophene to its sulf-
oxide by tBuOOH and H2O2.[11a] The second report de-
scribes the synthesis of recoverable dendritic POM catalysts
based on electrostatic bonding[11b] by using the Venturello
trianionic species [PO4{WO(O2)2}4]3À,[12] and their applica-
tion in the oxidation of cyclooctene and sulfides.[11b] Recent-
ly, Neumann and co-workers synthesized two generations of
dendritic catalysts based on the in situ assembly of dendritic
phosphonates with diperoxotungstates, yielding peroxophos-
phonatotungstate mixtures that are efficient in the epoxida-
tion of alkenes with hydrogen peroxide.[11c] To the best of
our knowledge, only one report involved the synthesis of
POM-cored dendrimers and their application to catalytic ox-
idation reactions. In a preliminary communication, we re-
cently reported a one-pot synthesis of epoxy-terminated 9-
and 27-armed dendrimers that have a tetrakis(diperoxotung-
sto)phosphate species at the core. Their stability, solubility,
catalytic efficiency in the oxidation reaction, and recyclabili-
ty have been studied.[11d] We discovered that the stability of
the anionic polyoxometalate unit in the oxidation reactions
was dependent on the dendritic structure. Indeed, within the
dendrimer series, the bulk increased the stability of the
POM species, but decreased the reaction kinetics. The pur-
pose of the current investigation is to point out the influence
of dendritic countercations on the POM properties. It is well
known from phase-transfer experiments that the organic
structure of the cation not only influences its ability to trans-
fer an anion from the aqueous to the organic phase, but it
also strongly affects the rate of the reaction in the organic
phase. Therefore, various tetraalkylammonium dendrons
with various sizes and endgroups were used as counterca-
tions of the trianionic POM species. We investigated the
dendritic effects on the solubility, stability, and catalytic
properties. Herein, we describe the synthesis[13] (by ionic
bonding between cationic ammonium dendrons and the tria-
nionic POM species [PO4{WO(O2)2}4]3À) and characteriza-
tion of a family of 9- and 27-armed POM-cored dendrimers,
respectively, terminated with epoxy, n-propyl, and aryl sul-
fide groups. We describe the synthesis, isolation, and charac-
terization of POM-cored dendrimers as well as their use, re-
covery, and re-utilization in the catalytic oxidation of al-
kenes, sulfides, and alcohols with hydrogen peroxide.
Indeed, it is essential to isolate and characterize the POM
salts before their reactivity behavior is investigated. The ef-
fects of dendritic structure on the POM properties will be
emphasized with respect to the tetraalkylammonium POM
derivatives.
Results and Discussion
Synthesis and spectroscopic characterization of tetrakis(di-
peroxotungsto)phosphate-cored dendrimers
Formation of epoxy-terminated 9- and 27-armed POM-
cored dendrimers: The synthetic strategy used to prepare
these compounds is summarized in Scheme 1.
The selective reaction of p-dibromoxylene (in excess)
with the phenol triallyl dendron 1a and the phenol nonaallyl
dendron 1b[14] leads to the corresponding bromobenzyl den-
drons 2a and 2b.[15] The triallyl and nonaallyl dendrons 2a
and 2b were reacted with tri-n-hexylamine to give quaterna-
ry ammonium dendrons 3a and 3b in yields of 70 and 68%,
respectively. The ammonium cations 3a and 3b were then
used as countercations for the trianionic POM complex
[PO4{WO(O2)2}4]3À that is known for its catalytic efficiency
in alkene epoxidation and alcohol oxidation with hydrogen
peroxide.[11b,d,16,17] [PO4{WO(O2)2}4]3À was attached to the
ammonium dendrons 3a and 3b by electrostatic bonding.
We used the synthetic procedure involving peroxide-mediat-
ed decomposition of H3PW12O40 that gives high yields and a
good reproducibility.[11b,d,16,17] According to this procedure,
the heteropolyacid H3PW12O40 was decomposed in the pres-
ence of excess H2O2 to form the dinuclear peroxotungstate
[{WO(O2)2(H2O)}2O]2À and the trianionic peroxophospho-
tungstate [PO4{WO(O2)2}4]3À. The latter reacts selectively
with the ammonium dendrons 3a and 3b (phase-transfer
agents) in a biphasic mixture of water and methylene chlo-
ride to give the epoxy-terminated 9- and 27-armed dendrim-
ers 4a and 4b, which contain the [PO4{WO(O2)2}4]3À core, in
yields of 90 and 95%, respectively. The dinuclear peroxo-
tungstate decomposition product [{WO(O2)2(H2O)}2O]2À re-
mained in the aqueous phase of the reaction mixture and
was isolated as a potassium salt in the presence of potassium
chloride. According to previous studies,[11b,d,16,17] it has clear-
ly been established that [PO4{WO(O2)2}4]3À is selectively
transferred into the organic phase with the phase-transfer
agents, whereas [{WO(O2)2(H2O)}2O]2À remains in the aque-
ous phase. The appropriate choice of countercations allowed
the selective isolation of the two peroxo salts. Interestingly,
the trianionic species [PO4{WO(O2)2}4]3À catalyzed the epox-
idation of the olefinic termini in a one-pot reaction and
became the anionic core of 4a and 4b. 1H NMR spectra
showed the complete disappearance of the signals at d =
5.54, 5.03 and 2.42 attributed to CH2CH=CH2 and the ap-
pearance of a broad multiplet at d = 2.91–2.43 assigned to
the terminal epoxide groups. These two POM-cored den-
drimers were isolated from the organic layer and fully char-
acterized by NMR spectroscopy (1H, 13C, and 31P), elemental
analysis, and IR spectroscopy. The results summarized in
Table 1 for significant data are consistent with the proposed
structures. Only one signal was obtained in the 31P NMR for
4a (d = 2.96) and 4b (d = 2.74). These values are compa-
rable to those obtained for the Arquad salt of the [PO4-
{WO(O2)2}4]3À species (d = 3.12); (Arquad = [nC18H37 -
904
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Multi-Armed Dendrimers
FULL PAPER
Scheme 1. Syntheses of the epoxy-terminated 9- and 27-armed POM-cored dendrimers 4a and 4b.
conditions used to prepare 4a
and 4b, no destruction of the
oxirane ring was observed; this
is attributed to the protective
effect of the biphasic system.
Table 1. Representative analytical data for 9- and 27-armed POM-cored dendrimers 4a,b, 8a,b, and 13a,b.
POM-Cored
dendrimers
31P NMR
[d]
Elemental analysis[%]
C
IR n˜
H
[cmÀ1
]
4a
2.96
2.74
3.02
3.54
2.87
2.08
calcd
found
calcd
found
calcd
found
calcd
found
calcd
found
calcd
found
48.86
47.93
59.44
58.84
50.53
49.59
64.06
64.75
54.80
53.90
65.00
64.46
6.44
6.30
6.98
6.76
7.39
6.56
8.60
8.47
6.44
5.93
6.82
6.58
1084, 1052, 963, 845
580, 521
1080, 1056, 959, 830
580, 521
1083, 1052, 969, 840
580, 522
1083, 1057, 974, 845
590, 517
1076, 1052, 963, 830
580, 521
1083, 1052, 963, 830
580, 521
4b
Formation of the n-propyl-ter-
minated 9- and 27-armed
POM-cored dendrimers: Cata-
lytic hydrogenation of triallyl
and nonaallyl dendrons 1a and
1b in the presence of Pd/C cat-
alyst (10% Pd) led to quantita-
tive yields of tri-n-propyl and
nona-n-propyl dendrons 5a and
5b, respectively. The reaction
8a
8b
13a
13b
1
(75%) + nC16H33 (25%)]2N(CH3)2]), and n-tetrahexylam-
monium salts (d = 0.37).
was easily monitored in the H NMR spectrum by the disap-
pearance of the allyl signals at d = 5.54, 5.03, and 2.42, and
the appearance of a multiplet at d = 1.64–1.54 and 1.09,
which is assigned to the terminal n-propyl groups. We were
also able to prepare 5b by a convergent route, starting from
5a and protected p-EtO2CC6H4(CH2CH2I)3 1c.[13] The n-
propyl-terminated 9- and 27-armed POM-cored dendrimers
Polyoxometalate-centered dendrimers 4a and 4b are air-
stable compounds. They can be stored and handled without
any special precautions, in contrast to dendritic compounds
with POMs located at their periphery. The latter are air sen-
sitive over periods of several days.[11b] In spite of the acidic
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905

S. Nlate et al.
Scheme 2. Syntheses of the n-propyl-terminated 9- and 27-armed POM-cored dendrimers 8a and 8b.
8a and 8b were easily prepared from 5a and 5b (Scheme 2),
following the procedure already described for 4a and 4b.
The reaction of p-dibromoxylene with tri-n-propyl and
nona-n-propyl phenol dendrons 5a and 5b gives the mono-
substituted bromobenzyl derivatives 6a and 6b in very good
yields (91 and 92%). The corresponding quaternary ammo-
nium salts 7a and 7b were obtained by treatment of 6a and
6b with tri-n-hexylamine. The ammonium dendrons 7a and
7b react by electrostatic bonding with trianionic [PO4-
{WO(O2)2}4]3À, to give 9- and 27-armed n-propyl POM-
cored dendrimers 8a and 8b, as a light yellow solids, in 85
and 91% yields, respectively. Representative characteriza-
tion data of 8a and 8b are summarized in Table 1. These
data are consistent with the proposed structures. One
31P NMR signal was observed for 8a and 8b (d = 3.02 and
3.54, respectively). These values are similar to those ob-
tained for epoxy-terminated POM-cored dendrimers 4a and
4b (see Table 1).
The triaryl sulfide phenol dendron 10a was synthesized in
85% yield by reaction of the known triiodo phenol dendron
9[13] with the sodium thiophenolate salt without protection
of the phenol function. The reaction was easily monitored in
the 1H NMR spectrum by the complete disappearance of
the triplet at d = 3.23, assigned to the CH2I groups, and the
appearance of a new triplet at d = 2.95, attributed to the
CH2S groups. The convergent synthesis of the nonaaryl sul-
fide phenol dendrons 10b was achieved by reacting the pro-
[13]
tected triiodo dendron p-EtO2CC6H4(CH2CH2I)3
1c and
10a in DMF in the presence of K2CO3. Compound 10b was
obtained in 73% yield after chromatography. The coupling
reaction of 10a and 10b with a large excess of p-dibromoxy-
lene led to the monobrominated compounds 11a and 11b in
80 and 70% yields, respectively. The corresponding quater-
nary ammonium salts 12a and 12b were obtained in 89 and
82% yields from 11a and 11b with tri-n-hexylamine. The
commercially available heteropolyacid H3PW12O40 reacts
with 12a and 12b in the presence of H2O2 to give the aryl
sulfide-terminated 9- and 27-armed POM cored dendrimers
13a and 13b as light yellow solids, in 85 and 95% yields, re-
spectively. Surprisingly, aryl sulfide termini are not sensitive
to oxidation under these conditions. No trace of aryl sulfox-
ide or aryl sulfone was observed (see the Experimental Sec-
Formation of aryl sulfide-terminated 9- and 27-armed
POM-cored dendrimers: Aryl sulfide-terminated 9- and 27-
armed POM-cored dendrimers 13a and 13b were prepared
from triaryl and nonaaryl sulfide phenol dendrons 10a and
10b, respectively (Scheme 3).
906
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Multi-Armed Dendrimers
FULL PAPER
Scheme 3. Syntheses of the aryl sulfide-terminated 9- and 27-armed POM-cored dendrimers 13a and 13b.
tion). An argument in support of this approach is that the
signal attributed to the CH2S group in the H NMR spec-
nals of the substrate versus TMS and the new peaks of the
product.
1
trum was not shifted and remained similar to that obtained
for the ammonium salts 12a and 12b (d = 2.95). In addi-
tion, correct (C,H) elemental analyses were obtained for
13a and 13b. As in the case of 4a,b and 8a,b, the 31P NMR
spectra of 13a and 13b show a signal at d = 2.87 and 2.08,
respectively.
The effects of the dendritic countercation on the POM
stability, catalytic efficiency, and selectivity in the oxidation
of various alkenes, sulfides, and alcohols were investigated.
The results listed in Table 2 clearly show that the 9- and 27-
armed POM-cored dendrimers 4a,b, 8a,b, and 13a,b quan-
titatively oxidized alkenes to the corresponding epoxides,
sulfides to sulfones, and secondary alcohol to ketones.
The oxidation of cyclooctene 14a was monitored over
time by plotting the ratio between the intensity of the disap-
Catalytic oxidation reactions by using 9- and 27-armed
POM-cored dendrimers 4a,b, 8a,b, and 13a,b: Among vari-
ous substrates (alkenes,[16a,b,18] alkynes,[19] alcohols,[16a,b]
diols,[16a,b] sulfides,[18] and amines[20]) already reported as
good candidates in oxidation processes with heteropolyacids
or their salts and hydrogen peroxide, we have selected some
of them, included in Tables 2 and 3, as well as in Scheme 4,
for catalytic oxidation tests. The reaction was accomplished
by vigorous stirring at 358C of an aqueous/CDCl3 biphasic
mixture containing 250 equiv of the appropriate substrate,
800 equiv of hydrogen peroxide, and 0.4 mol% of the re-
spective POM-cored dendrimers 4a,b, 8a,b, and 13a,b. The
reaction kinetics were monitored over time by plotting the
1
pearance of the H NMR signal at d = 5.6 attributed to cy-
clooctene and the new peak of the epoxide 15a at d = 2.9.
As shown by entries 1–6, the POM-cored dendrimers 4a,b,
8a,b, and 13a,b oxidized cyclooctene with 100% conversion
1
within the limits of H NMR detection, with reaction times
between 30 min and 5 h. The reaction complete after 30 min
in the case of the 9-armed n-propyl terminated POM-cored
dendrimer 8a, 2 h for 9-armed epoxy dendrimer 4a, and 5 h
for 9-armed aryl sulfide 13a. Five hours were generally re-
quired for the 27-armed catalysts 4b, 8b, and 13b (entries 2,
4, and 6). The results included in Table 2 indicate that the 9-
armed n-propyl-terminated POM-cored dendritic 8a was the
1
ratio between the intensity of the disappearing H NMR sig-
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907

S. Nlate et al.
Table 2. Oxidation of representative alkene, sulfide, and alcohols by H2O2, catalyzed by 4a,b, 8a,b, and 13a,b at T = 358C.[a]
Entry
Substrate
Catalyst
t[b]
Product
Conversion[%][c]
1
2
3
4
5
6
7
8
4a
4b
8a
8b
13a
13b
4a
4b
8a
2 h
5 h
30 min
5 h
5 h
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
11
5 h
10 min
60 min
5 min
90 min
20 min
120 min
10 min
33 min
5 min
20 min
15 min
20 min
22 h
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
8b
13a
13b
4a
4b
8a
8b
13a
13b
4a
4b
8a
24 h
23 h
24 h
20 h
5
95
12
11
8b
13a
13b
4a
4b
8a
24 h
19
10 min
30 min
5 min
90 min
90 min
180 min
22 h
23 h
20 h
22 h
21 h
100
100
100
100
100
100
91
78
95
99
85
8b
13a
13b
4a
4b
8a
8b
13a
13b
25 h
95
1
[a] Reaction conditions: catalyst (0.4 mol%), substrate (250 equiv), H2O2 (800 equiv), CDCl3 (3 mL). [b] Reactions were monitored by H NMR. [c] Con-
1
version determined from the relative intensities of the H NMR signals of the substrate and the product.
Table 3. Catalytic oxidation of 1-octen-3-ol (14 f) with 4a,b, 8a,b, and 13a,b, by H2O2.[a]
phenyl methyl sulfone 15b, tri-
allyl phenyl methyl sulfone 15c,
and diallyl sulfone 15d with re-
action times of up to 2 h
(Table 2, entries 7–18 and 25–
30). Neither the sulfoxide inter-
mediate nor the epoxidation of
allyl groups was observed in the
cases of 14c and 14d. However,
for reaction times of up to
one day, the triallyl phenyl
methyl sulfone 15c provided
the epoxy sulfone compound 16
(with probably the mono-and
Catalyst
Reaction
Conversion
[%][c]
Chemoselectivity
Epoxide/Ketone
Diastereoselectivity
t [h][b]
(threo/erythro)
(15 f)
(17)
4a
4b
8a
8b
13a
13b
24
30
3
24
55
24
85
85
93
99
84
94
75
62
85
61
52
70
10
23
8
38
32
23
70
55
44
40
53
47
30
45
56
60
47
53
[a] Reaction conditions: catalyst (0.4 mol%), substrate (250 equiv), H2O2 (800 equiv), CDCl3 (3 mL). [b] Reac-
1
1
tions were monitored by H NMR. [c] Conversion determined from the relative intensities of the H NMR sig-
nals of the substrate and the product.
most reactive catalyst. The oxidation of cyclooctene with the
27-armed POM-cored dendrimers did not show any signifi-
cant difference within this series (Figure 1b), in contrast to
the 9-armed POM-cored dendrimer series (Figure 1a).
The oxidation of phenyl methyl sulfide 14b, triallyl
phenyl methyl sulfide 14c, and diallyl sulfide 14d with
POM-cored dendrimers selectively gave the corresponding
the diallyl phenyl methyl sulfone) in 5 to 95% conversion
(Table 2, entries 19–24). Interestingly, the kinetics of sulfide
oxidation decreased with 27-armed POM-cored dendrimers,
and the sulfoxide intermediate could be observed. However,
the reaction selectively led to the corresponding sulfone
after total conversion of the sulfoxide. It was possible to ob-
serve the sulfoxide intermediate in reaction times up to
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Multi-Armed Dendrimers
FULL PAPER
attributed to the epoxy group
appear as a multiplet between
d = 3.01 and 2.75. The a,b-un-
saturated 1-octen-3-one 17 was
identified by a new triplet at d
= 2.57, assigned to the CH2CO
group. The chemoselectivity of
olefin epoxidation predomi-
nates over alcohol ketonization.
More interestingly, 8a was the
most efficient catalyst for the
oxidation of 1-octen-3-ol 14 f, as
obtained previously with cyclo-
octene and sulfide. The reaction
time was only 3 h for 8a,
whereas 24 h were required in
all the other cases. The threo:er-
ythro diastereoselectivity given
in Table 3 is comparable to that
obtained with alkylammonium
POM [{n-(C8H17)3NCH3}+]3[PO4
{WO(O2)2}4]3À (18, a ratio of
55:45 has already been report-
ed),[22] and no significant dia-
stereoselectivity difference was
Scheme 4. Catalytic oxidation reactions with 0.4 mol% of 9- and 27-armed POM-cored dendrimers 4a,b, 8a,b,
and 13a,b, substrate (250 equiv), H2O2 (800 equiv), and CDCl3 (3 mL).
3 min, even if 9-armed POM-cored catalysts were used. A
comparison between the 9-armed dendritic catalysts and the
27-armed dendrimers shows a negative dendritic effect on
the reaction kinetics. This negative dendritic effect is proba-
bly caused by the increased bulk around the catalytic center.
It has been reported that the increased bulkiness of the
cation reduces the electrophilicity of the peroxopolyoxo spe-
cies.[18] When the ions are bulky, the interionic distance in-
creases, thus decreasing the interionic interaction. In the
case of the 27-armed POM-cored dendrimers, the bulkiness
of the dendritic ammonium cation might be responsible for
the large distance between the ammonium site of the den-
dron and the anionic POM.
observed within the POM-cored dendrimer series. The in-
creased bulk around the catalytic center does not appear to
affect the stereocontrol of oxygen transfer to the allylic alco-
hols.
Recovery and reutilization of the POM-cored dendritic cata-
lysts: Two reaction cycles were performed in order to test
the stability of the POM-cored dendrimers 4a,b, 8a,b, and
13a,b under catalytic reaction conditions. Cyclooctene 14a,
thioanisole 14b, and cyclohexanol 14e were used as model
substrates (Table 4).
The catalyst was recovered by precipitation after each cat-
1
alytic cycle and checked by H and 31P NMR before a new
In addition, within the 9-armed POM-cored dendrimer
series, the lower electrophilicity of the aryl sulfide and
epoxy endgroups in 4a and 13a, respectively, compared with
the n-propyl groups of 8a, might be responsible for the
lower reactivity of 13a and 4a (Figure 1a).
The oxidation of cyclohexanol 14e to cyclohexanone 15e
was also successful, with conversions between 75 and 100%
and a reaction time of nearly one day (Table 2, entries 31–
36). In the case of 1-octen-3-ol 14 f, the catalytic oxidation
reaction gave a diastereoisomeric mixture of threo:erythro-
1,2-epoxy-3-octanol 15 f as the major product, together with
1-octen-3-one 17 (Scheme 4 and Table 3) with excellent con-
version rates. The reaction was easily monitored in the
1H NMR spectrum by the disappearance of the three mul-
catalytic experiment was performed.
1H and 31P NMR characterization of the recovered cata-
lyst showed the absence of any structural change. In addi-
tion, no discernable loss of activity was observed over the
two catalytic cycles. Substrates 14a and 14b were quantita-
tively oxidized to the corresponding epoxide and sulfone, re-
spectively, over the two cycles. An excellent conversion was
also obtained in the oxidation of 14e, despite longer reac-
tion times (20–25 h) than those required for the alkene and
the sulfide. The results obtained in these experiments reveal
that all the POM-cored dendrimers studied are air-stable
and easy to recover and handle. Interestingly, oxidation of
14a and 14b with the alkylammonium POMs [{n-
(C8H17)3NCH3}+]3[PO4{WO(O2)2}4]3À 18 and [{Arquad}+]3
[PO4{WO(O2)2}4]3À 19 quantitatively led to epoxide 15a in
150 and 120 min, respectively, and sulfone 15b in 30 min
under the same reaction conditions. These results are com-
parable with those obtained in the dendrimer series. Howev-
er, an important difference was found in the recovery of the
tiplets at d
= 5.84, 5.15 and 4.10, attributed to the
CHOHCH=CH2 group, and the appearance of two multip-
lets at d = 3.80 and 3.40, respectively assigned to the
CHOH group of (2S,3R)-1,2-epoxy-3-octanol (15 f, threo)
and (2S,3S)-1,2-epoxy-3-octanol (15 f, erythro). The signals
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909

S. Nlate et al.
catalyst. Indeed, the POM-cored dendrimers were easily re-
covered by precipitation without decomposition over two
cycles, whereas precipitation of 19 after the first run was
very difficult, and gave a small amount of a solid identified
by two signals at d = 0.5 and À0.99 in the 31P NMR spec-
trum. These 31P NMR signals differed from those obtained
for 19 at d = 3.12, indicating that the structure of these
POM species had changed. Attempts to precipitate 18 after
the first run were unsuccessful. These results indicate that
the dendritic structures increase the stability of the anionic
POM species, a key feature for the recovery and recycling
of the POM catalysts in oxidation reactions. Interestingly, in
the catalytic oxidation of thioanisole with the 9-epoxy-termi-
nated POM-cored dendrimer 4a, we were able to recover
and reutilize the catalyst up to the eighth cycle without loss
of activity. No decomposition of the catalyst was observed
after the eighth cycle; the 31P NMR signal remained similar
to that obtained for 4a.
Conclusion
A series of 9- and 27-armed polyoxometalate-centered den-
drimers that bear epoxy, n-propyl, and aryl sulfide
endgroups has been synthesized and characterized. These
compounds are efficient catalysts in the epoxidation of cy-
clooctene, the selective oxidation of sulfides to sulfones, and
the oxidation of cyclohexanol to cyclohexanone with hydro-
gen peroxide. Study of countercation effects reveals that the
dendritic structures increase the stability of the POM unit,
allowing the facile recovery and reutilization of the catalyst
without loss of activity up to the eighth cycle, as for exam-
ple, in the case of 9-epoxy-terminated POM-cored dendrim-
er 4a. However, the dendritic structure of the cation de-
creases the reaction kinetics. It was observed that, within
the 9-armed POM-cored dendrimer series, the reaction ki-
netics were sensitive to the nature of the peripheral
endgroups. In contrast with aryl sulfide- and epoxy-terminat-
ed dendrimers, the n-propyl-terminated POM-cored den-
drimer 8a was the most active catalyst. In addition, it was
also observed that increasing the dendritic structure of the
cation decreased the reaction kinetics, probably on account
of the lower electrophilic character of the POM unit. This
series of 9- and 27-armed dendrimer catalysts are air-stable,
easy to handle, and can be stored at room temperature with-
out degradation.
Figure 1. Kinetics of cyclooctene epoxidation. a) With 9-armed POM-
~
&
*
cored dendrimers 4a ( ), 8a ( ), and 13a ( ); b) with the 27-armed
~
&
*
POM-cored dendrimers 4b ( ), 8b ( ), and 13b ( ).
Table 4. Isolated yields of POM-cored dendrimers catalysts 4a,b, 8a,b,
and 13a,b, in the oxidation of cyclooctene (14a), thioanisole (14b), and
cyclohexanol (14e) respectively, with H2O2, after the first and second
runs.
Substrate
Catalyst
First cycle
yield[%]
Second cycle
yield[%]
cyclooctene (14a)
4a
4b
8a
75
96
80
70
75
80
95
75
95
90
95
85
95
85
90
80
91
95
67
85
50
60
70
70
80
75
96
80
80
90
75
75
70
76
85
85
8b
13a
13b
4a
4b
8a
thioanisole (14b)
Experimental Section
8b
13a
13b
4a
4b
8a
8b
13a
13b
Reagent-grade tetrahydrofuran (THF), diethyl ether, and pentane were
predried over Na foil and distilled from sodium/benzophenone under
argon immediately prior to use. Acetonitrile (CH3CN) was stirred over-
night over phosphorus pentoxide and under argon, distilled from sodium
carbonate, and stored under argon. Methylene chloride (CH2Cl2) was dis-
tilled from calcium hydride just before use. All other chemicals were
used as received. The 1H, 13C, and 31P NMR spectra were recorded at
258C with the following spectrometers: Bruker AC250FT (1H: 250.13,
cyclohexanol (14e)
910
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Chem. Eur. J. 2006, 12, 903 – 914

Multi-Armed Dendrimers
FULL PAPER
13C: 62.91 MHz), Bruker AC200FT (1H: 200.16, 13C: 50.33, 31P:
81.02 MHz). All chemical shifts are reported referenced to Me4Si (TMS).
Elemental analyses were performed by the Center of Microanalyses of
the CNRS at Lyon-Villeurbanne (France).
(CH, Ar), 126.71 (CH, Ar), 114.10 (CH, Ar), 69.02 (CH2O), 58.79
(CH2N), 42.72 (Cq-CH2), 41.88 (CH2), 31.05 (CH2), 25.80 (CH2), 23.40
(CH2), 22.70 (CH2), 22.47 (CH2), 13.90 (CH3); elemental analysis calcd
(%) for C42H72OBrN: C 73.44, H 10.56; found: C 72.75, H 11.05.
Synthesis of 3-armed ammonium dendrons
3-Aryl sulfide phenol dendron (10a): A mixture of triiodophenol den-
dron 9 (0.500 g, 0.820 mmol) and NaSC6H5 (0.647 g, 4.900 mmol) in DMF
(20 mL) was stirred at 708C for 24 h. The mixture was then extracted
with CH2Cl2 (3”20 mL), and the resulting solution washed with water
and dried over sodium sulfate. After removal of the solvent under
vacuum, the residue was washed with Et2O (3”20 mL) and chromato-
graphed (silica gel, diethyl ether/acetone 8:2) to afford 10a as a beige
solid (0.390 g, 0.694 mmol, 85%). 1H NMR (CDCl3, 250.13 MHz): d =
7.82–7.53 (m, 15H, Ar), 6.95 (d, 2H, Ar), 6.71 (d, 2H, Ar), 2.95 (t, 6H,
SCH2), 1.64 (brm, 6H, CH2), 1.44 (brm, 6H, CH2); 13C NMR (CDCl3,
62.91 MHz): d = 154.50 (Cq, ArO), 139.22 (Cq, Ar), 135.95 (Cq, Ar),
134.20 (CH, Ar), 129.78 (CH, Ar), 128.22 (CH, Ar), 127.55 (CH, Ar),
115.83 (CH, Ar), 56.61 (SCH2), 42.98 (Cq-CH2), 35.76 (CH2), 17.34
(CH2); elemental analysis calcd (%) for C34H38OS3: C 73.07, H 6.85;
found: C 72. 75, H 6.30.
Bromobenzyl 3-allyl dendron (2a): A mixture of triallyl dendron 1a
(2.000 g, 8.77 mmol), K2CO3 (3.696 g, 26.40 mmol), and p-dibromoxylene
(9.263 g, 35.09 mmol) in CH3CN, was stirred for 4 d at room temperature.
After removal of the solvent under vacuum, the product was extracted
with pentane (3”30 mL), washed with water, and dried over sodium sul-
fate. The solvent was removed under vacuum and the product was puri-
fied by chromatography (silica gel, pentane/diethyl ether 9:1) to afford
1
2a as a colorless oil (3.180 g, 91%); H NMR (CDCl3, 250.13 MHz): d =
7.42 (s, 4H, Ar), 7.23 (d, 2H, Ar), 6.92 (d, 2H, Ar), 5.54 (m, 3H, CH=
CH2), 5.03 (m, 8H, CH=CH2, CH2O), 4.51 (s, 2H, BrCH2), 2.43 (d, 6H,
CH2=CH-CH2); 13C NMR (CDCl3, 62.91 MHz): d = 156.44 (Cq, ArO),
138.05 (Cq, Ar), 137.43 (Cq, Ar), 137.32 (Cq, Ar), 134.50 (CH=CH2),
127.17 (CH, Ar), 127.79 (CH, Ar), 127.67 (CH, Ar), 117.54 (CH=CH2),
114.06 (CH, Ar), 69.56 (CH2O), 42.60 (Cq-CH2), 41.82 (CH2), 33.10
(BrCH2); MALDI TOF MS: m/z: calcd for 434.37; found 433.42
[M+Na]+; elemental analysis calcd (%) for C24H27OBr: C 70.07, H 6.62;
found: C 70.58, H 6.80.
Bromobenzyl 3-aryl sulfide dendron (11a): This compound was obtained
according to the procedure described above for 2a, but from 10a instead
of 1a. After removal of the solvent under vacuum, the product was ex-
tracted with CH2Cl2, (3”20 mL), and the solvent was evaporated under
vacuum. The excess p-dibromoxylene was removed by washing the resi-
due with Et2O. Further purification by chromatography (silica gel, diethyl
ether/acetone 8:2) afforded 11a as a beige solid (0.531 g, 0.715 mmol,
3-Allyl ammonium salt dendron (3a):
A mixture of 2a (0.390 g,
0.950 mmol) and tri-n-hexylamine (1.9 mL, 5.7 mmol) in CH3CN was stir-
red for 16 h at 808C. After removal of the solvent under vacuum, the res-
idue was washed with pentane (3”50 mL) and dried under vacuum, to
afford ammonium salt 3a (0.424 g, 0.666 mmol, 70%). 1H NMR (CDCl3,
200.16 MHz): d = 7.53 (s, 4H, Ar), 7.23 (d, 2H, Ar), 6.91 (d, 2H, Ar),
5.54 (m, 3H, CH=CH2), 5.03 (m, 8H, CH=CH2, CH2O), 3.22 (m, 8H,
NCH2), 2.42 (d, 6H, CH2CH=CH2), 1.80 (m, 6H, CH2), 1.34 (m, 18H,
CH2), 0.90 (m, 9H, CH3); 13C NMR (CDCl3, 62.91 MHz): d = 156.20
(Cq, ArO), 140.29 (Cq, Ar), 138.50 (Cq, Ar), 134.49 (Cq, Ar), 132.70 (CH=
CH2), 128.19 (CH, Ar), 127.81 (CH, Ar), 126.71 (CH, Ar), 117.59 (CH=
CH2), 114.10 (CH, Ar), 69.02 (CH2O), 62.80 (CH2O), 58.79 (CH2N),
42.72 (Cq-CH2), 41.88 (CH2), 31.17 (CH2), 26.05 (CH2), 23.61 (CH2),
22.47 (CH2), 22.43 (CH2), 13.83 (CH3) cmÀ1; elemental analysis calcd (%)
for C42H66OBrN: C 74.09, H 9.77; found: C 74.19, H 9.34.
1
80%). H NMR (CDCl3, 250.13 MHz): d = 7.82–7.53 (m, 15H, Ar), 7.44
(s, 4H, Ar), 7.02 (d, 2H, Ar), 6.84 (d, 2H, Ar), 5.02 (s, 2H, CH2O), 4.52
(s, 2H, CH2Br), 2.95 (t, 6H, SCH2), 1.68 (brm, 6H, CH2); 1.43 (brm, 6H,
CH2); 13C NMR (CDCl3, 62.91 MHz): d = 157.38 (Cq, ArO), 139.47 (Cq,
Ar), 137.67 (Cq, Ar), 136.97 (Cq, Ar), 134.11 (Cq, Ar), 132.59 (CH, Ar),
129.72 (CH, Ar), 128.27 (CH, Ar), 127.46 (CH, Ar), 125.61 (CH, Ar),
115.15 (CH, Ar), 115.03 (CH, Ar), 69.95 (CH2O), 56.67 (SCH2), 43.07
(Cq-CH2), 35.88 (CH2), 33.59 (CH2Br), 17.31 (CH2); elemental analysis
calcd (%) for C42H45OBrS3: C 67.99, H 6.11; found: C 67.30, H 6.50.
3-Aryl sulfide ammonium salt dendron (12a): This compound was ob-
tained as a beige solid according to the procedure described above for
3a, but from 11a instead of 2a. Yield: 0.573 g, 0.556 mmol, 84%;
3-n-Propyl phenol dendron (5a): 10% Pd/C catalyst (5 mg, 0.046 mmol)
was added to a THF solution (30 mL) of triallyl phenol dendron 1a
(0.500 g, 2.2 mmol) in a thick-walled tube capped with a Youngꢀs stop-
cock. The tube was flushed, pressurized with hydrogen, sealed, and stir-
red at room temperature for 3 h. The solvent was removed under
vacuum, and the residue was extracted with pentane (3”20 mL) and fil-
tered through celite. After evaporation of pentane, 5a was obtained as a
colorless oil (0.490 g, 2.090 mmol, 95%). 1H NMR (CDCl3, 250.13 MHz):
d = 7.21 (d, 2H, Ar), 6.80 (d, 2H, Ar), 4.75 (s, 1H, OH), 1.61 (m, 6H,
CH2), 1.06 (m, 6H, CH2), 0.88 (t, 9H, CH3); 13C NMR (CDCl3,
50.33 MHz): d = 156.20 (Cq, ArO), 140.55 (Cq, Ar), 127.41 (CH, Ar),
114.06 (CH, Ar), 42.59 (Cq-CH2), 41.21 (CH2), 17.26 (CH2), 14.80 (CH3);
elemental analysis calcd (%) for C16H26O: C 81.99, H 11.18; found: C
81.85, H 11.26.
1H NMR (CDCl3, 250.13 MHz): d
= 7.80–7.34 (brm, 19H, Ar), 7.01
(brd, 2H, Ar), 6.84 (brd„ 2H, Ar), 5.05 (brs, 2H, CH2O), 3.26 (brs„ 8H,
CH2N), 2.94 (brt, 6H, SCH2), 1.78 (br, CH2), 1.64 (br, CH2), 1.42 (br,
6H, CH2), 0.86 (br, 9H, CH3); 13C NMR (CDCl3, 62.91 MHz): d
=
156.40 (Cq, ArO), 142.09 (Cq, Ar), 139.09 (Cq, Ar), 136.78 (Cq, Ar),
133.71 (Cq, Ar), 132.94 (CH, Ar), 129.32 (CH, Ar), 129.28 (CH, Ar),
127.81 (CH, Ar), 125.11 (CH, Ar), 114.72 (CH, Ar), 114.52 (CH, Ar),
69.40 (CH2O), 58.85 (NCH2), 56.24 (SCH2), 42.69 (Cq-CH2), 41.72 (CH2),
35.46 (CH2), 31.16 (CH2), 26.08 (CH2), 22.55 (CH2), 22.40 (CH2), 22.47
(CH2), 16.77 (CH2), 13.85 (CH3); elemental analysis calcd (%) for
C60H84OBrNS3: C 71.25, H 8.37; found: C 70.58, H 7.68.
Synthesis of 9-armed ammonium dendrons
Bromobenzyl 9-allyl dendron (2b): A mixture of phenol-9-allyl dendron
1b (0.500 g, 0.547 mmol), K2CO3 (0.230 g 1.645 mmol), and p-dibromoxy-
lene (0.722 g, 2.735 mmol) in CH3CN was stirred for 7 d at room temper-
ature. After removal of the solvent under vacuum, the residue was ex-
tracted with pentane (3”30 mL). The solvent was removed under
vacuum and the product was purified by chromatography (silica gel, pen-
Bromobenzyl 3-n-propyl dendron (6a): This compound was obtained as
a colorless oil according to the procedure described above for 2a, but
from 5a instead of 1a. Yield: 90%; 1H NMR (CDCl3, 250.13 MHz): d =
7.43 (m, 4H, Ar), 7.23 (d, 2H, Ar), 6.93 (d, 2H, Ar), 5.05 (s, 2H, CH2O),
4.62 (s, 2H, BrCH2), 1.62 (m, 6H, CH2), 1.08 (m, 6H, CH2), 0.89 (t, 9H,
CH3); 13C NMR (CDCl3, 62.91 MHz): d = 156.19 (Cq, ArO), 140.50 (Cq,
Ar), 138.21 (Cq, Ar), 136.71 (Cq, Ar), 128.54 (CH, Ar), 128.23 (CH, Ar),
113.87 (CH, Ar), 113.51 (CH, Ar), 42.66 (Cq-CH2), 40.21 (CH2), 16.70
(CH2), 14.87 (CH3); elemental analysis calcd (%) for C24H35OBr: C
68.73, H 8.41; found: C 68.32, H 8.64.
tane/diethyl ether 9:1) to provide 2b as
a colorless oil (0.570 g,
1
0.519 mmol, 95%). H NMR (CDCl3, 200.16 MHz): d = 7.42 (s, 4H, Ar),
7.28 (d, 2H, Ar), 7.19 (d, 6H, Ar), 6.93 (d, 2H, Ar), 6.81 (d, 6H, Ar),
5.54 (m, 9H, CH=CH2), 5.00 (m, 20H, CH=CH2, CH2O), 4.51 (s, 2H,
BrCH2), 3.88 (t, 6H, CH2O), 2.41 (d, 18H, CH2CH=CH2), 1.86 (m, 6H,
CH2), 1.63 (m, 6H, CH2); 13C NMR (CDCl3, 62.91 MHz): d = 156.74
(Cq, ArO), 156.52 (Cq, ArO), 138.82 (Cq, Ar), 138.73 (Cq, Ar), 137. 45
(Cq, Ar), 136. 82 (Cq, Ar), 134.58 (CH=CH2), 129.19 (CH, Ar), 127.78
(CH, Ar), 127.70 (CH, Ar), 127.50 (CH, Ar), 117.38 (CH=CH2), 114.27
(CH, Ar), 113.72 (CH, Ar), 69.63 (CH2O), 68.07 (CH2O), 42.56 (Cq-
CH2), 41.99 (Cq-CH2), 41.84 (CH2), 33.68 (CH2), 33.11 (BrCH2), 23.66
(CH2); MALDI TOF MS: m/z: calcd for 1119.45; found 1119.37
3-n-Propyl ammonium salt dendron (7a): This compound was obtained
as a colorless solid according to the procedure described above for 3a,
but from 6a instead of 2a. Yield: 98%; 1H NMR (CDCl3, 200.16 MHz):
d = 7.38 (s, 4H, Ar), 7.18 (d, 2H, Ar), 6.93 (d, 2H, Ar), 5.01 (CH2O),
3.42 (brs, 8H, NCH2), 1.75 (brm, 12H, CH2), 1.33 (brm, 30H, CH2), 0.84
(brt, 18H, CH3); 13C NMR (CDCl3, 62.91 MHz): d = 157.06 (Cq, ArO),
138.84 (Cq, Ar), 134.20 (Cq, Ar), 133.49 (Cq, Ar), 128.04 (CH, Ar), 127.81
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911

S. Nlate et al.
[M+Na]+; elemental analysis calcd (%) for C72H87O4Br (1096.38): C
78.88, H 8.00; found: C 78.80, H 8.06.
tography (silica gel, diethyl ether/acetone 8:2) to afford 10b as a beige
solid (0.415 g, 0.218 mmol, 73%). 1H NMR (CDCl3, 250.13 MHz): d =
7.82–7.52 (m, 45H, Ar), 7.00 (br, 8H, Ar), 6.72 (br, 8H, Ar), 3.86 (br,
6H, CH2O), 2.95 (brt, 18H, SCH2), 1.63 (br, 24H, CH2), 1.48 (br, 24H,
CH2); 13C NMR (CDCl3, 62.91 MHz): d = 157.26 (Cq, ArO), 157.13 (Cq,
ArO), 139.00 (Cq, Ar), 135.84 (Cq, Ar), 133.66 (CH, Ar), 129.07 (CH,
Ar), 127.81 (CH, Ar), 127.05 (CH, Ar), 125.17 (CH, Ar), 114.36 (CH,
Ar), 68.19 (CH2O), 56.25 (SCH2), 42.58 (Cq-CH2), 42.26 (Cq-CH2), 41.96
(CH2), 35.68 (CH2), 23.78 (CH2), 16.87 (CH2); elemental analysis calcd
(%) for C118H134O4S9: C 74.40, H 7.09; found: C 73.12, H 6.98.
9-Allyl ammonium salt dendron (3b): This compound was obtained as a
colorless solid according to the procedure described above for 3a, but
from 2b instead of 2a. Yield: 0.886 g, 0.648 mmol, 68%; 1H NMR
(CDCl3, 200.16 MHz): d = 7.56 (s, 4H, Ar), 7.28 (d, 2H, Ar), 7.19 (d,
6H; Ar), 6.97 (d, 2H, Ar), 6.82 (d, 6H, Ar), 5.53 (m, 9H, CH=CH2), 5.00
(m, 20H CH=CH2, and CH2O), 3.88 (t, 6H, CH2O), 3.30 (m, 8H, NCH2),
2.42 (d, CH2CH=CH2), 1.83 (m, CH2), 1.60 (m, CH2), 1.40 (m, CH2), 0.90
(m, 9H, CH3); 13C NMR (CDCl3, 62.91 MHz): d = 156.76 (Cq, ArO),
156.52 (Cq, ArO), 140.18 (Cq, Ar), 137.53 (Cq, Ar), 134.58 (CH=CH2),
132.75 (Cq, Ar), 128.15 (Cq, Ar), 127.56 (CH, Ar), 126.86 (CH, Ar),
124.06 (CH, Ar), 117.41 (CH=CH2), 114.25 (CH, Ar), 113.74 (CH, Ar);
69.10 (CH2O), 68.10 (CH2O), 58.80 (CH2N), 42.60 (Cq-CH2), 42.09 (Cq-
CH2), 41.87 (CH2), 33.70 (CH2), 31.16 (CH2), 26.53 (CH2), 26.04 (CH2),
23.70 (CH2), 22.63 (CH2), 22.40 (CH2), 13.80 (CH2); elemental analysis
calcd (%) for C90H126O4BrN: C 79.14, H 9.30; found: C, 78.80, H 8.64.
Bromobenzyl 9-aryl sulfide dendron (11b): This compound was obtained
as a beige solid according to the procedure described above for 2a, but
from 10b instead of 1a. Yield: 0.310 g, 0.146 mmol, 70%; 1H NMR
(CDCl3, 200.16 MHz): d = 7.80–7.36 (br, Ar), 6.97 (br, Ar), 6.75 (br,
Ar), 5.15 (br, 2H, CH2O), 4.49 (br, 2H, BrCH2), 3.88 (br, 6H, CH2O),
2.93 (br, 18H, SCH2), 1.80 (br, CH2), 1.46 (br, CH2); 13C NMR (CDCl3,
62.91 MHz): d
= 139.15 (Cq, Ar), 134.10 (Cq, Ar), 129. 72 (Cq, Ar),
129.09 (CH, Ar), 128.90 (CH, Ar), 128.25 (CH, Ar), 127.62 (CH, Ar),
127.42 (CH, Ar), 114.79(CH, Ar), 69.71 (CH2O), 69.59 (CH2O), 56.68
(SCH2), 43.02 (Cq-CH2), 35.88 (CH2), 33.32 (CH2Br), 23.98 (CH2), 17.32
(CH2); elemental analysis calcd (%) for C126H141O4S9Br: C 72.79, H 6.73;
found: C 72.29, H 6.66.
9-n-Propyl phenol dendron (5b): This compound was obtained as a col-
orless solid according to the procedure described above for 5a, but from
1b instead of 1a. Yield: 0.489 g, 0.525 mmol, 96%; 1H NMR (CDCl3,
200.16 MHz): d
= 7.22 (d, 8H, Ar), 6.82 (d, 8H, Ar), 3.85 (t, 6H,
CH2O), 1.61 (m, 24H, CH2), 1.05 (m, 24H, CH2), 0.88 (t, 27H, CH3);
13C NMR (CDCl3, 62.91 MHz): d = 156.32 (Cq, ArO), 152.86 (Cq, ArO),
140. 51 (Cq, Ar), 140.31 (Cq, Ar), 127.56 (CH, Ar), 127.33 (CH, Ar),
114.56 (CH, Ar), 113.56 (CH, Ar), 68.18 (CH2O), 42.80 (Cq-CH2), 42.60
(Cq-CH2), 40.22 (CH2), 35.23 (CH2), 29.56 (CH2), 28.62 (CH2), 16.70
(CH2), 14.89 (CH3); elemental analysis calcd (%) for C64H98O4: C 82.53,
H 10.60; found: C 81.79, H 10. 24.
9-Aryl sulfide ammonium salts dendron (12b): This compound was ob-
tained as a beige solid according to the procedure described above for
3a, but from 11b instead of 2a. Yield: 0.298 g, 0.126 mmol, 89%;
1H NMR (CDCl3, 200.16 MHz): d = 7.80–7.35 (brm, Ar), 6.98 (br, Ar),
6.71 (br, Ar), 5.16 (br, 2H, CH2O), 3.88 (br, 6H, CH2O), 3.26 (br,
CH2N), 2.93 (br, 18H, SCH2), 1.77 (br, CH2), 1.65 (br, CH2), 1.42 (br,
CH2), 0.87 (br, CH3); 13C NMR (CDCl3, 62.91 MHz): d = 156.57 (Cq,
ArO), 139.07 (Cq, Ar), 133.72 (Cq, Ar), 132.84 (CH, Ar), 129.33 (CH,
Ar), 128.61 (CH, Ar), 127.80 (CH, Ar), 127.11 (CH, Ar), 114.30 (CH,
Ar), 68.18 (CH2O), 58.90 (CH2N), 56.29 (CH2S), 42.37 (Cq-CH2), 35.48
(CH2), 31.16 (CH2), 26.55 (CH2), 26.08 (CH2), 22.61 (CH2), 22.40 (CH2),
16.88 (CH2), 13.86 (CH3); elemental analysis calcd (%) for
Bromobenzyl 9-n-propyl dendron (6b): This compound was obtained as
a colorless solid according to the procedure described above for 2a, but
from 5b instead of 1a. Yield: 0.440 g, 0.395 mmol, 92%; 1H NMR
(CDCl3, 200.16 MHz): d = 7.42 (s, 4H, Ar), 7.28 (d, 2H, Ar), 7.19 (d,
6H; Ar), 6.93 (d, 2H, Ar), 6.78 (d, 6H, Ar), 5.54 (m, 9H, CH=CH2), 5.03
(s, 2H, CH2O), 4.51 (s, 2H, BrCH2), 3.88 (t, 6H, CH2O), 1.89 (m, 6H,
CH2), 1.61 (m, 24H, CH2), 1.05 (m, 24H, CH2), 0.88 (t, 27H, CH3);
13C NMR (CDCl3, 62.91 MHz): d = 156.63 (Cq, ArO), 156.36 (Cq, ArO),
140.02 (Cq, Ar), 139.20 (Cq, Ar), 138.90 (Cq, Ar), 129.21 (CH, Ar), 128.12
(CH, Ar), 127.81 (CH, Ar), 127.54 (CH, Ar), 127.30 (CH, Ar), 114.32
(CH, Ar), 113.53 (CH, Ar), 69.49 (CH2O), 68.15 (CH2O), 42.60 (Cq-
CH2), 42.07 (Cq-CH2), 40.64 (CH2), 40.21 (CH2), 33.70 (CH2), 33.13
(CH2Br), 23.75 (CH2), 17.25 (CH2), 14.84 (CH3); elemental analysis calcd
(%) for C72H105O4Br: C 77.59, H 9.50; found: C 76.80, H 9.10.
C
144H180O4S9BrN: C 73.36, H 7.70; found: C 72.89, H 7.39.
General procedure for the synthesis of POM-cored dendrimers: H2O2
(4.8 mL, 35% in water) was added to a solution of commercial heteropo-
lyacid H3PW12O40 (0.096 mmol) in water (0.160 mL). The mixture was
stirred at room temperature for 30 min. A solution of ammonium bro-
mide salt (0.250 mmol) in CH2CH2 (1.5 mL) was added, and the mixture
was stirred for an additional hour for the 9-armed dendrimer and 2 h for
the 27-armed dendrimer. The CH2Cl2 layer was washed with water
(0.5 mL) and dried over sodium sulfate. The product was obtained by re-
moving the solvent under vacuum.
9-n-Propyl ammonium salt dendron (7b): This compound was obtained
as a colorless solid according to the procedure described above for 3a,
but from 6b instead of 2a. Yield: 0.886 g, 0.640 mmol, 80%. After re-
moval of the solvent under vacuum, the residue was washed with cooled
pentane, and dried under vacuum. 1H NMR (CDCl3, 200.16 MHz): d =
7.53 (s, 4H, Ar), 7.16 (d, 2H, Ar), 6.92 (d, 2H, Ar), 6.77 (d, 6H, Ar),
5.05 (s, 2H, CH2O), 3.86 (br, 6H, CH2O), 3.22 (br, CH2N), 1.89 (br, 6H,
CH2), 1.61 (m, CH2), 1.32 (br, CH2), 1.05 (br, CH2), 0.88 (br, CH3);
13C NMR (CDCl3, 62.91 MHz): d = 157.19 (Cq, ArO), 156.36 (Cq, ArO),
140. 02 (Cq, Ar), 139. 24 (Cq, Ar), 138.90 (Cq, Ar), 129.21 (CH, Ar),
128.12 (CH, Ar), 127.75 (CH, Ar), 127.54 (CH, Ar), 127.30 (CH, Ar),
114.32 (CH, Ar), 113.53 (CH, Ar), 69.49 (CH2O), 68.15 (CH2O), 42.72
(Cq-CH2), 42.07 (Cq-CH2), 40.88 (CH2), 31.05 (CH2), 25.81 (CH2), 22.75
(CH2), 22.47 (CH2), 16.28 (CH2), 14.84 (CH3), 13.92 (CH3); elemental
analysis calcd (%) for C90H144O4BrN: C 78.10, H 10.49; found: C 77.06,
H 9.98.
9-Armed tetrakis(diperoxotungsto)phosphate-cored dendrimers
9-Epoxide tetrakis(diperoxotungsto)phosphate-cored dendrimer (4a):
Light yellow solid (0.075 mmol, 233 mg, 90%); 1H NMR (CDCl3,
200.16 MHz, broad signals): d = 7.58 (s, 12H, Ar), 7.30 (d, 6H, Ar), 7.00
(d, 6H, Ar), 5.07 (s, 6H, CH2O), 4.75 (m, 6H, NCH2), 3.13 (m, 18H,
NCH2), 2.91–2.00 (m, CH, CH2), 1.80 (m, 18H, CH2), 1.34 (m, 54H,
CH2), 0.90 (m, 18H, CH3); 13C NMR (CDCl3, 62.91 MHz): d = 157.03
(Cq, ArO), 138.95 (Cq, Ar), 137.15 (Cq, Ar), 132.97 (Cq, Ar), 127.85 (CH,
Ar), 127.73 (CH, Ar), 126.46 (CH, Ar), 114.63 (CH, Ar), 69.34 (CH2O),
58.46 (CH2N), 48.89 (CH), 46.76 (CH2), 42.70 (Cq-CH2), 31.14 (CH2),
25.85 (CH2), 22.39 (CH2), 22.11 (CH2), 13.95 (CH3); 31P NMR (CDCl3,
81.02 MHz): d = 2.96 (PO4); FT-IR (KBr plates): n˜ = 1084–1052 (P–O),
963 (W=O), 845 (O–O), 580 and 521 cmÀ1 (W(O2)s, as); elemental analysis
calcd (%) for C126H198O36N3PW4: C 48.86, H 6.44; found: C 47.93, H 6.30.
9-Aryl sulfide phenol dendron (10b): A mixture of 3-aryl sulfide phenol
dendron 10a (0.914 g, 1.340 mmol) and K2CO3 (0.348 g, 2.480 mmol) in
DMF (20 mL) was stirred at room temperature for 30 min. To this mix-
ture was added the protected triiodophenol dendron 10c (0.200 g,
0.299 mmol) dissolved in DMF (10 mL). The reaction mixture was stirred
for 2 d at room temperature. K2CO3 (0.188 g, 1.340 mmol) and water
(0.350 mL) were added, and the reaction mixture was stirred at 408C for
48 h. The mixture was extracted with CH2Cl2 (3”20 mL), and the result-
ing solution washed with water and dried over sodium sulfate. After re-
moval of the solvent under vacuum, the product was purified by chroma-
9-n-Propyl tetrakis(diperoxotungsto)phosphate-cored dendrimer (8a):
Light yellow solid (0.071 mmol, 210 mg, 85%); 1H NMR (CDCl3,
200.16 MHz, broad signals): d = 7.41 (m, 12H, Ar), 7.19 (d, 6H, Ar),
6.89 (d, 6H, Ar), 5.33 (s, 6H, CH2O), 3.30 (NCH2), 1.72 (CH2), 1.33
(CH2), 0.87 (CH3); 13C NMR (CDCl3, 62.91 MHz): d
= 157.03 (Cq,
ArO), 138.95 (Cq, Ar), 137.15 (Cq, Ar), 132.97 (Cq, Ar), 127.85 (CH, Ar),
127.73 (CH, Ar), 126.46 (CH, Ar), 114.63 (CH, Ar), 69.34 (CH2O), 58.06
(CH2N), 42.70 (Cq-CH2), 31.04 (CH2), 25.87 (CH2), 22.40 (CH2), 21.75
(CH2), 21.72 (CH2), 16.71 (CH3), 13.94 (CH3); 31P NMR (CDCl3,
81.02 MHz): d = 3.02 (PO4), FT-IR (KBr plates): n˜ = 1083–1052 (P–O),
912
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Chem. Eur. J. 2006, 12, 903 – 914

Multi-Armed Dendrimers
FULL PAPER
969 (W=O), 840 (O–O), 580 and 522 cmÀ1 (W(O2)s, as); elemental analysis
calcd (%) for C124H216O27N3PW4: C 50.53, H 7.39; found: C 49.59, H 6.56.
The catalyst was recovered following the typical procedure and condi-
tions described above for the first cycle, CDCl3 and reactants being ad-
justed to the amount of catalyst used. The reaction was performed with
cyclooctene 14a, thioanisole 14b, and cyclohexanol 14e using dried, re-
covered compound 4a,b, 8a,b, and 13a,b. The catalyst was completely
dissolved in CDCl3, and the reactants were added to the solution. After
completion, the kinetics remained unchanged because the data collected
were comparable to those summarized in Table 2 for the first cycle. The
9-Aryl sulfide tetrakis(diperoxotungsto)phosphate-cored dendrimer
(13a): Light yellow solid (0.070 mmol, 278 mg, 85%); 1H NMR (CDCl3,
200.16 MHz, broad signals): d = 7.82–7.36 (m, Ar), 6.99 (d, Ar), 6.86 (d,
Ar), 5.03 (s, 6H, CH2O), 2.95 (CH2N and SCH2), 1.77 (CH2), 1.64 (CH2),
1.41 (CH2), 1.30 (CH2), 0.86 (CH3); 13C NMR (CDCl3, 62.91 MHz): d =
156.79 (Cq, ArO), 139.07 (Cq, Ar), 133.74 (Cq, Ar), 133.66 (Cq, Ar),
129.32 (CH, Ar), 127.81 (CH, Ar), 127.79 (CH, Ar), 114.80 (CH, Ar),
69.34 (CH2O), 58.38 (CH2N), 56.24 (SCH2), 42.84 (Cq-CH2), 35.36 (CH2),
31.08 (CH2), 25.74 (CH2), 22.35 (CH2), 16.84 (CH3), 13.92 (CH3);
31P NMR (81 MHz, CDCl3): d = 2.87 (PO4); FT-IR (KBr plates): n˜ =
1076–1052 (P–O), 963 (W=O), 830 (O–O), 580 and 521 cmÀ1 (W(O2)s, as);
elemental analysis calcd (%) for C180H252O27N3PS9W4: C 54.80, H 6.44;
found: C 53.90, H 5.93.
1
catalyst was recovered and checked by H and 31P NMR, with a yield be-
tween 50 and 96% (Table 4).
Acknowledgements
27-Armed tetrakis(diperoxotungsto)phosphate-cored dendrimers
Financial support from the University BordeauxI, the CNRS, the IUF
(DA) and the MRT (LP) is gratefully acknowledged.
27-Epoxide tetrakis(diperoxotungsto)phosphate-cored dendrimer (4b):
Light yellow solid (0.079 mmol, 432 mg, 95%); 1H NMR (CDCl3,
200.16 MHz, broad signals): d = 7.52 (s, 12H, CH2), 7.31 (d, 24H, Ar),
6.90 (d, 6H; Ar), 6.86 (d, 18H, Ar), 5.05 (s, 6H, CH2O), 3.90 (br, 18H,
CH2O), 3.20 (br, 24H, NCH2), 2.91–2.00 (brm, CH and CH2), 1.80 (br,
CH2), 1.37 (br, CH2), 0.88 (br, CH3); 13C NMR (CDCl3, 62.91 MHz): d =
157.00 (Cq, ArO), 156.14 (Cq, ArO), 139.07 (Cq, Ar), 138.53 (Cq, Ar),
136.10 (Cq, Ar), 132.48 (Cq, Ar), 127.76 (CH, Ar), 127.57 (CH, Ar),
127.47 (CH, Ar), 127.40 (CH, Ar), 127.31 (CH, Ar), 114.50 (CH, Ar),
114.25 (CH, Ar), 69.28 (CH2O), 68.23 (CH2O), 58.47 (CH2N), 48.90
(CH), 46.62 (CH2), 33.70 (Cq-CH2), 31.14 (CH2), 29.63 (CH2), 25.89
(CH2), 23.67 (CH2), 22.41 (CH2), 22.13 (CH2), 13.91 (CH3); 31P NMR
(CDCl3, 81.02 MHz): d = 2.47 (PO4); FT-IR (KBr plates): n˜ = 1080–
1056 (P–O), 959 (W=O), 830 (O-O), 580 and 521 cmÀ1 (W(O2)s, as); ele-
mental analysis calcd (%) for C270H378N3O64PW4: C 59.44, H 6.98; found:
C 58.84, H 6.76.
[1] a) G. R. Newkome, C. N. Moorefield, F. Vçgtle, Dendrimers and
Dendrons, Concepts, Synthesis and Applications, VCH-Wiley, Wein-
heim, 2001; b) Dendrimers and other Dendritic Polymers (Eds.: D.
Tomalia, J. M. J. FrØchet), Wiley-VCH, New York, 2002; c) Den-
drimers and Nanoscience, Vol. 6 (Ed.: D. Astruc), C. R. Chimie,
Elsevier, Paris, 2003; d) F. Zeng, S. C. Zimmerman, Chem. Rev.
1997, 97, 1681.
[2] a) D. Astruc, F. Chardac, Chem. Rev. 2001, 101, 2991; b) R. Kreiter,
A. Kleij, R. J. M. Klein Gebbink, G. van Koten, Top. Curr. Chem.
2001, 217, 163; c) R. van Heerbeek, P. C. J. Kamer, P. W. N. M. van -
Leeuwen, J. N. H. Reek, Chem. Rev. 2002, 102, 3717; d) L. J.
Twyman, A. S. H. King, I. K. Martin, Chem. Soc. Rev. 2002, 31, 69.
[3] J.-M. Lehn, Supramolecular Chemistry: Concepts and perspectives,
VCH, Weinheim, 1995.
[4] a) G. R. Newkome, E. He, C. N. Moorefield, Chem. Rev. 1999, 99,
1689; b) A. W. Bosman, H. M. Janssen, E. W. Meijer, Chem. Rev.
1997, 97, 1665; c) I. Cuadrado, M. Moran, C. M. Casado, B. Alonzo,
J. Losada, Coord. Chem. Rev. 1999, 193–195, 395; d) M. A. Hear-
shaw, J. R. Moss, Chem. Commun. 1999, 1.
[5] G. E. Oosterom, J. N. H. Reek, P. C. J. Kamer, P. W. N. M. van Leeu-
wen, Angew. Chem. 2001, 113, 1878; Angew. Chem. Int. Ed. 2001,
40, 1828.
[6] a) P. Bhyrappa, J. K. Young, J. S. Moore, K. S. Suslick, J. Am. Chem.
Soc. 1996, 118, 5708; b) P. Bhyrappa, J. K. Young, J. S. Moore, K. S.
Suslick, J. Mol. Catal. A Chem. 1996, 113, 109; c) P. Weyermann, J.-
P. Gisselbrecht, C. Boudon, F. Diederich, M. Gross, Angew. Chem.
1999, 111, 3400; Angew. Chem. Int. Ed. 1999, 38, 3215; d) P. Weyer-
mann, F. Diederich, J. Chem. Soc. Perkin Trans. 1 2000, 4231; e) F.
Diederich, P. Weyermann, Polym. Mater. Sci. Eng. 2001, 84, 168;
f) P. Weyermann, F. Diederich, Helv. Chim. Acta 2002, 85, 599; g) P.
Weyermann, F. Diederich, J.-P. Gisselbrecht, C. Boudon, M. Gross,
Helv. Chim. Acta 2002, 85, 571; h) C. Francavilla, M. D. Drake, F. V.
Bright, M. R. Detty, J. Am. Chem. Soc. 2001, 123, 57; i) K. Ahsan,
M. D. Drake, D. E. Higgs, A. L. Wojciechowski, B. N. Tse, M. A. Ba-
teman, Y. You, M. R. Detty, Organometallics 2003, 22, 2883.
[7] a) M. T. Pope, A. Mꢂller, Angew. Chem. 1991, 103, 56; Angew.
Chem. Int. Ed. Engl. 1991, 30, 34; b) J. T. Rhule, C. L. Hill, D. A.
Rud, R. F. Schinazi, Chem. Rev. 1998, 98, 327; c) D. E. Katsoulis,
Chem. Rev. 1998, 98, 359; d) M. T. Pope, A. Mꢂller, Polyoxometa-
late Chemistry: From Topology via Self-Assembly to Applications,
Kluwer Academic, Dordrecht, 2001.
27-n-Propyl tetrakis(diperoxotungsto)phosphate-cored dendrimer (8b):
Light yellow oily solid (0.076 mmol, 384 mg, 91%); 1H NMR (CDCl3,
200.16 MHz, broad signals): d = 7.54 (s, 4H, Ar), 7.16 (d, 6H, Ar), 6.92
(d, 2H, Ar), 6.77 (d, 6H, Ar), 5.02 (s, 2H, CH2O), 3.86 (br, 6H, CH2O),
3.23 (br, CH2N), 1.75 (br, 6H, CH2), 1.54 (br, CH2), 1.32 (br, CH2) 1.03
(br, CH2) 0.88 (br, CH3); 13C NMR (CDCl3, 62.91 MHz): d = 157.19 (Cq,
ArO), 140.53 (Cq, Ar), 128.50 (CH, Ar), 127.75 (CH, Ar), 113.53 (CH,
Ar); 64.42 (CH2O), 57.75 (CH2N), 42.20 (Cq-CH2), 39.97 (CH2), 36.08
(CH2), 31.40 (CH2), 31.05 (CH2), 26.05 (CH2), 25.81 (CH2), 22.75 (CH2),
22.40 (CH2), 21.84 (CH2), 16.28 (CH2), 14.62 (CH3), 13.92 (CH3);
31P NMR (CDCl3, 81.02 MHz): d = 3.54 (PO4); FT-IR (KBr plates): n˜ =
1083 and 1057 (P–O), 974 (W=O), 845 (O–O), 590 and 517 cmÀ1
(W(O2)s, as); elemental analysis calcd (%) for C270H432N3O36PW4: C 64.06,
H 8.60; found: C 64.75, H 8.47.
27-Aryl sulfide tetrakis(diperoxotungsto)phosphate-cored dendrimer
(13b): Light yellow solid (0.079 mmol, 632 mg, 95%); 1H NMR (CDCl3,
200.16 MHz, broad signals): d = 7.86–7.39 (m, Ar), 7.01 (br, Ar), 6.80
(br, Ar) 5.16 (br, CH2O), 3.89 (br, CH2O), 3.08 (br, CH2N), 2.95 (SCH2),
1.71 (CH2), 1.36 (CH2), 1.30 (CH2), 0.86 (CH3); 13C NMR (CDCl3,
62.91 MHz): d = 139.07 (Cq, Ar), 139.04 (Cq, Ar), 133.66 (Cq, Ar), 133.62
(Cq, Ar), 129.29 (CH, Ar), 128.45 (CH, Ar), 127.80 (CH, Ar), 127.79
(CH, Ar), 114.35 (CH, Ar), 68.31 (CH2O), 58.80 (CH2N), 56.23 (SCH2),
42.58 (Cq-CH2), 35.47 (CH2), 31.18 (CH2), 25.90 (CH2), 22.39 (CH2),
16.88 (CH3), 13.81 (CH3); 31P NMR (CDCl3, 81.02 MHz): d
= 2.74
(PO4); FT-IR (KBr plates): n˜ = 1086 and 1057 (P–O), 974 (W=O), 845
(O–O), 590 and 522 cmÀ1 (W(O2)s, as); elemental analysis calcd (%) for
C432H540O36N3PS27W4: C 65.00, H 6.82; found: C 64.46, H 6.58.
General procedure for the catalytic oxidation reactions with the 9-and
27-armed POM-cored dendritic catalysts and for the catalyst recovery ex-
periments: The substrate (250 equiv) and 35% H2O2 (800 equiv) was
added to a CDCl3 solution (3 mL) of catalyst (0.004 mmol). The reaction
mixture was stirred at 358C and monitored by 1H NMR. Upon comple-
tion, the CDCl3 layer was separated and concentrated under a vacuum to
ꢀ1 mL. The catalyst was precipitated by addition of Et2O (10 mL). The
solid was filtered and washed with Et2O (3”10 mL) to afford the POM
catalyst in a good-to-excellent yield (70–96%, see Table 4, main text).
[8] For the multiple facets of POM chemistry, see refs. [7], [9]–[12] and
the special issue dedicated to POMs: Chem. Rev. 1998, 98, whole
Issue.
[9] a) I. V. Kozhevnikov, Catalysis by Polyoxometalates, Wiley, Chi-
chester, 2002; b) I. V. Kozhevnikov, Chem. Rev. 1998, 98, 171; c) N.
Mizuno, M. Misono, Chem. Rev. 1998, 98, 199; d) R. Neumann,
Prog. Inorg. Chem. 1998, 47, 317.
[10] M. C. Rogers, B. Adisa, D. Bruce, Catal. Lett. 2004, 98, 29–36.
Chem. Eur. J. 2006, 12, 903 – 914
ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
913

S. Nlate et al.
[11] a) H. Zeng, G. R. Newkome, C. L. Hill, Angew. Chem. 2000, 112,
1841; Angew. Chem. Int. Ed. 2000, 39, 1772; b) L. Plault, A. Hausel-
er, S. Nlate, D. Astruc, J. Ruiz, S. Gatard, R. Neumann, Angew.
Chem. 2004, 116, 2984; Angew. Chem. Int. Ed. 2004, 43, 2924;
c) M. V. Vasylyev, D. Astruc, R. Neumann, Adv. Synth. Catal. 2005,
347, 39; d) S. Nlate, D. Astruc, R. Neumann, Adv. Synth. Catal.
2004, 346, 5517.
R. Thouvenot, F. Chauveau, C. Huet, H. Ledon, Inorg. Chem. 1991,
30, 4409.
[17] a) L. Salles, C. Aubry, R. Thouvenot, F. Robert, C. DorØmieux-
Morin, G. Chottard, H. Ledon, Y. Jeannin, J.-M. BrØgault, Inorg.
Chem. 1994, 33, 871; b) A. J. Bailey, W. P. Griffith, B. C. Parkin, J.
Chem. Soc. Dalton Trans. 1995, 1833; c) D. C. Duncan, R. C. Cham-
bers, E. Hecht, C. L. Hill, J. Am. Chem. Soc. 1995, 117, 681.
[18] F. P. Ballistreri, A. Bazzo, G. A. Tomaselli, R. M. Toscano, J. Org.
Chem. 1992, 57, 7074.
[12] C. Venturello, R. DꢀAloisio, J. C. J. Bart, M. Ricci, J. Mol. Catal.
1985, 32, 107.
[13] For recent review on dendrons, see: S. M. Grayson, J. M. J. FrØchet,
Chem. Rev. 2001, 101, 3819.
[19] a) F. P. Ballistreri, S. Failla, G. A. Tomaselli, J. Org. Chem. 1988, 53,
830; b) Y. Ishii, Y. Sakata, J. Org. Chem. 1990, 55, 5545; c) F. P. Bal-
listreri, S. Failla, E. Spina, G. A. Tomaselli, J. Org. Chem. 1989, 54,
947.
[20] F. P. Ballistreri, U. Chiacchio, A. Rescifina, G. A. Tomaselli, Tetrahe-
dron 1992, 48, 8677.
[21] a) K. Mori, T. Otsuka, Tetrahedron 1985, 41, 553; b) K. Mori, T.
Otsuka, Tetrahedron 1985, 41, 3253.
[22] C. Venturello, M. Gambaro, J. Org. Chem. 1991, 56, 5924.
[14] a) V. Sartor, L. Djakovitch, J.-L. Fillaut, F. Moulines, F. Neveu, V.
Marvaud, J. Guittard, J.-C. Blais, D. Astruc, J. Am. Chem. Soc. 1999,
121, 2929; b) V. Sartor, S. Nlate, J.-L. Fillaut, L. Djakovitch, F. Mou-
lines, V. Marvaud, F. Neveu, J.-C. Blais, New J. Chem. 2000, 24, 351.
[15] S. Nlate, J.-C. Blais, D. Astruc, Inorg. Chim. Acta 2004, 357, 1670.
[16] a) C. Venturello, R. DꢀAloisio, J. Org. Chem. 1988, 53, 1553; b) Y.
Ishii, Y. Yamawaki, T. Ura, H. Yamada, T. Yoshida, M. Ogawa, J.
Org. Chem. 1988, 53, 3587; c) Y. Ishii, M. Ogawa, Reviews on Het-
eroatom Chemistry, Vol. 3 (Eds.: A. Ohno, N. Furukawa), MYU,
Tokyo, 1990, p. 121; d) R. Neumann, A. M. Khenkin, J. Org. Chem.
1994, 59, 7577; e) C. Aubry, G. Chottard, N. Platzer, J.-M. BrØgault,
Received: May 19, 2005
Published online: September 30, 2005
914
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ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 903 – 914