Peripheral functionalisation of dendrimers with polyoxotungstate complexes assembled by ionic bonding and their use as oxidation catalysts: Influence of the tether length

Article abstract of DOI:10.1039/b616288f

Two series of dendritic compounds functionalized at the periphery with polyoxometalate (POM) units were synthesized using two synthetic strategies. The first series involved the [CpFe]⁺-induced functionalization of polymethylarenes, leading to dendrimers in which the dendronic tripod is directly bonded to the arene core. In the second procedure, dendrimers with a spacer group of six atoms between the arene core and the tripod units were synthesized through a coupling reaction between the phenol dendron and bromobenzyl derivatives. These polyallyl dendrimers were functionalized at the periphery to give quaternary poly-ammonium salts. Reactions of the latter with H₃PW₁₂O₄₀ in the presence of hydrogen peroxide led to dendrimers containing {PO₄[WO(O₂)₂] ₄}^3- species at the periphery. These compounds are efficient catalysts for the selective oxidation of alkenes, sulfides and alcohols in an aqueous-CDCl₃ biphasic system, using hydrogen peroxide as the primary oxidant. The complexes with dendritic wedges directly bonded to the arene core were found to be efficient, epoxidation catalysts that are stable if they are stored under an inert atmosphere, but they do not efficiently catalyze oxidation of alcohols. The dendritic POMs containing spacers, on the other hand, are shown to be more stable in air, they could be recycled and were efficient for the catalytic oxidation of alcohols. Recycling was carried out for the epoxidation reaction using both series of POM catalysts and yielded 50% to 85% of epoxides using the recovered catalysts, the best yields after recycling being obtained with the tris-POM catalyst built from mesitylene and containing spacers (100% conversion; yields in epoxide: first run: 90%; recycled catalyst: 85%). In the case of alcohol oxidation, the tris-POM catalyst was recycled with moderate success (92% conversion; ketone yields: first run: 75%; recycled catalyst: 50%). Among these POM catalysts, dendritic effects on the oxidation yields were found concerning the number of POM units. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

Full text of DOI:10.1039/b616288f

View Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/njc | New Journal of Chemistry
Peripheral functionalisation of dendrimers with polyoxotungstate
complexes assembled by ionic bonding and their use as oxidation
catalysts: Influence of the tether lengthwz
Sylvain Nlate,* Lauriane Plault and Didier Astruc*
Received (in Montpellier, France) 7th November 2006, Accepted 12th December 2006
First published as an Advance Article on the web 31st January 2007
DOI: 10.1039/b616288f
Two series of dendritic compounds functionalized at the periphery with polyoxometalate (POM)
units were synthesized using two synthetic strategies. The first series involved the [CpFe]+-
induced functionalization of polymethylarenes, leading to dendrimers in which the dendronic
tripod is directly bonded to the arene core. In the second procedure, dendrimers with a spacer
group of six atoms between the arene core and the tripod units were synthesized through a
coupling reaction between the phenol dendron and bromobenzyl derivatives. These polyallyl
dendrimers were functionalized at the periphery to give quaternary poly-ammonium salts.
Reactions of the latter with H3PW12O40 in the presence of hydrogen peroxide led to dendrimers
containing {PO4[WO(O2)2]4}3ꢀ species at the periphery. These compounds are efficient catalysts
for the selective oxidation of alkenes, sulfides and alcohols in an aqueous–CDCl3 biphasic system,
using hydrogen peroxide as the primary oxidant. The complexes with dendritic wedges directly
bonded to the arene core were found to be efficient, epoxidation catalysts that are stable if they
are stored under an inert atmosphere, but they do not efficiently catalyze oxidation of alcohols.
The dendritic POMs containing spacers, on the other hand, are shown to be more stable in air,
they could be recycled and were efficient for the catalytic oxidation of alcohols. Recycling was
carried out for the epoxidation reaction using both series of POM catalysts and yielded 50% to
85% of epoxides using the recovered catalysts, the best yields after recycling being obtained with
the tris-POM catalyst built from mesitylene and containing spacers (100% conversion; yields in
epoxide: first run: 90%; recycled catalyst: 85%). In the case of alcohol oxidation, the tris-POM
catalyst was recycled with moderate success (92% conversion; ketone yields: first run: 75%;
recycled catalyst: 50%). Among these POM catalysts, dendritic effects on the oxidation yields
were found concerning the number of POM units.
polyoxometalates (POMs). These POMs are a large class of
Introduction
inorganic transition metal–oxygen clusters that are the source
of fascinating architectures6 and rich redox chemistry7 that is
the basis of their catalytic activity in oxidation reactions.8
Recently, a few heterogeneous9 and homogeneous10 dendritic
polyoxometalate catalysts were reported and shown to be
effective in oxidation reactions. In homogeneous catalysis,
few reports concerning the use of dendritic polyoxometalate
catalysts in oxidation reactions are known including POM-
cored dendrimers and their application in catalytic oxidation
reactions.10e,f The synthesis of dendritic tetra-POMs with
[HP2V3W15O59]5ꢀ units covalently bonded to a tetra-armed
core for their use as efficient and recoverable catalysts in the
oxidation of tetrahydrothiophene to its sulfoxide by tBuOOH
and H2O2 was described.11a Then, the structure and properties
of a heteropolytungstate cluster encapsulated in a shell of
dendritic branching surfactants was reported.10b Recently, the
synthesis of two generations of dendritic catalysts based on the
in situ assembly of dendritic phosphonates with diperoxotung-
states, yielding peroxophosphonatotungstate mixtures that are
efficient in the epoxidation of alkenes using hydrogen peroxide
has been reported.10d In a preliminary communication,10c we
Dendrimers and metallodendrimers are generating much at-
tention for their potential applications in various areas.1,2 The
increasing use of these macromolecules in catalysis, pioneered
by van Leeuwen,2b,d is an emerging field, as the size of these
macromolecules allows their easy recovery, an essential feature
for reaction efficiency, economy and environmental concern.2
In this context, a variety of dendrimers, cores, branches and
end groups were assembled and used in different domains such
as supramolecular chemistry,3 nanosciences,1c drug delivery4
and catalysis.2 However, dendritic oxidation catalysts are
relatively under-represented,5 a few of them being based on
Nanosciences and Catalysis Group, LCOO, UMR CNRS N1. 5802,
´
´
Universite Bordeaux I, 351 Cours de la Liberation, 33405 Talence
Cedex, France. E-mail: s.nlate@lcoo.u-bordeaux1.fr. E-mail:
d.astruc@lcoo.u-bordeaux1.fr; Fax: +33-540-00-69-94
w This paper was published as part of the special issue on Dendrimers
and Dendritic Polymers: Design, Properties and Applications.
z Electronic supplementary information (ESI) available: spectroscopic
characterization of intermediates compounds for the synthesis of
dendritic POM complexes. See DOI: 10.1039/b616288f
ꢁc
This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2007
1264 | New J. Chem., 2007, 31, 1264–1274

View Online
[PO4{WO(O2)2}4]3ꢀ was selectively transferred into the organ-
published a series of dendritic POMs based on ionic bonding
between dendritic ammonium wedges and the trianionic spe-
cies {PO4[WO(O2)2]4}3ꢀ, previously reported by Venturello.11
In the present article, we now compare the syntheses, catalytic
efficiencies and stabilities towards recycling of these POM
dendrimers in which each methyl group can be transformed
into three allyl groups using temporary complexation/activa-
tion by the CpFe+ fragment,12 with a new series of dendritic
POMs in which a spacer group of six atoms was introduced
between the dendritic wedges and the arene core. We were
seeking, in this way, to investigate the influence of the neigh-
bouring interactions of the POMs.
ic phase upon contact with the phase-transfer agent, whereas
[{WO(O2)2(H2O)}2O]2ꢀ remained in the aqueous phase. The
appropriate choice of counter-cations allowed the two peroxo
salts to be selectively isolated. The tri(POM) dendrimer 7 was
indeed isolated from the organic layer and fully characterized
1
by H, 13C and 31P NMR, elemental analysis and IR (see the
experimental section).
This procedure was also applied to the hexaallyl dendrimer
8 and the triallyl dendrimer 9, providing the bis(POM) deri-
vative 10 and the mono(POM) derivative 11 in 52 and 73%
1
yield, respectively. Standard characterizations by H, 13C, 31P
NMR and IR as well as elemental analysis were performed for
these dendrimers, and these results are reported in the experi-
mental section. The 31P NMR spectra of the tri(POM) 7, the
bis(POM) 10 and the mono(POM) 11 show one signal at 3.44,
3.54 and 3.37 ppm, respectively.
Results and discussion
Synthesis of dendrimers containing
tetrakis(diperoxotungsto)phosphate units at the periphery
Since the trifunctionalization of polymethylarenes used here
requires that each methyl be free of methyl neighbours in the
arene structure, it could not be extended to more than three
methyl groups on a single arene ring. In order to extend our
study to dendrimers with four POM units, we used the dodeca-
allyl derivative 12.15 This synthetic strategy was successful and
also provided the tetra(POM) derivative 17 according to
Scheme 2.
Dendritic POMs without a spacer between the dendritic
wedge and the arene core. Dendritic polyoxometalate com-
pounds with the tripod units directly bonded to the arene core
were synthesized following the procedure summarized in
Scheme 1 for the tris(POM) complex. In order to build the
supramolecular assembly of the dendritic oxidation catalysts
in which each POM trianion is connected to a trication unit,
we have designed tricationic tripods consisting of triammo-
nium groups. For this purpose, our synthetic strategy involved
poly-methylarenes, in which each methyl group can be func-
tionalized by three allyl groups, using temporary complexa-
tion/activation by the 12-electron fragment CpFe+ (see
Scheme 1 with the example of mesitylene).12 Regioselective
hydroboration of the nona-alkene 2, which was synthesized
from the mesitylene complex 1, and oxidation of the nona-
borane to give the nona-ol 3, followed by treatment with
SiMe3Cl–NaI, provided the nona-iodo compound 4.13 Alkyla-
tion of tri-hexylamine using 4 gave the nona-ammonium salt 5
as an iodide salt that cannot be used as such for oxidation
chemistry, because of the easy oxidation of the iodide anion.14a
Dendritic POMs 7, 10, 11 and 17 were slightly air sensitive;
it was noticed that if they were left in air for several days, they
became less soluble in CDCl3 or CH2Cl2, and their 31P NMR
spectrum changed (peak shift from 3.44 to 1.11 ppm for
tris(POM) 7). However, if the POM catalysts were kept under
an inert atmosphere, they did not decompose, as could be
checked by the observation of the 31P NMR peak at 3.44 ppm
that remained unchanged.
Dendritic POMs containing a spacer between the dendritic
wedges and the arene core. The tris(POM) complex 25 and
bis(POM) complex 32 were prepared from commercially avail-
able 2,4,6-tri(bromomethyl)mesitylene and p-dibromoxylene,
respectively, following the procedure14 described in Scheme 3
for compound 25. The nona-allyl derivative 19 and hexa-allyl
dendrimers 26 were synthesized in 80 and 90% yield, respec-
tively, after chromatography, by reaction of the phenol den-
dron p-HO-C6H4C(allyl)3 18 with the appropriate
bromobenzyl derivative in the presence of K2CO3. The tris-
(POM) complex 25 and bis(POM) complex 32 were obtained
as white solids in 90 and 85% yield by conversion of the allyl
dendrimers 19 and 26, respectively to the nona-ol dendrimer
20 and hexa-ol dendrimer 27. The nona-mesylate dendrimer 21
and hexa-mesylate dendrimer 28 were then prepared, respec-
tively by reaction of 20 and 27 with chloromethylsulfonate at
–5 1C. The reaction of 21 and 28 with sodium iodide gave the
nona-iodo dendrimer 22 and the hexa-iodo dendrimer 29 in 95
and 90% yield, respectively. The nona-ammonium iodide salt
23 and the hexa-ammonium iodide salt 30 were then prepared
by alkylation of tri-hexylamine, respectively with the nona-
iodo dendrimer 22 and the hexa-iodo dendrimer 29. Treatment
of 23 and 30 with AgBF4 in ethanol gaveꢀthe nona-ammonium
ꢀ
Treatment of 5 with AgBF4 in ethanol gave the BF4 ammo-
nium salt 6 in 98% yield. The ammonium cations of 6 were
then used as counter-cations for the tri-anionic POM complex
[PO4{WO(O2)2}4]3ꢀ, known for its catalytic efficiency in oxi-
dation reactions. The tri-anionic species [PO4{WO(O2)2}4]3ꢀ
was attached to the ammonium cation of 6 by electrostatic
bonding. We used the synthetic procedure involving peroxide
mediated decomposition of H3PW12O40 that gave high yields
and a good reproducibility.10b–e,15 Using this procedure, the
heteropolyacid H3PW12O40 was decomposed in the presence
of excess H2O2 to form the dinuclear peroxotungstate
[{WO(O2)2(H2O)}2O]2ꢀ and the tri-anionic peroxophospho-
tungstate [PO4{WO(O2)2}4]3ꢀ. The latter selectively reacted
with the nona-ammonium salt 6 in a biphasic mixture of water
and methylene chloride to give the dendritic POM 7 that
contains three [PO4{WO(O2)2}4]3ꢀ units at the periphery in
70% yield. As for the dinuclear peroxotungstate decomposi-
tion by-product [{WO(O2)2(H2O)}2O]2ꢀ, it remained in the
aqueous phase of the reaction mixture, and was isolated as a
potassium salt in the presence of potassium chloride. In
previous studies,10b–e,15 it was clearly established that
ꢀ
BF4 salt 24 and hexa-ammonium BF4 salt 31. The nona-
ammonium salt 24 and the hexa-ammonium salt 31 were then
ꢁc
This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2007
New J. Chem., 2007, 31, 1264–1274 | 1265

View Online
Scheme 1 Synthesis of the tris(POM) 7.
used to prepare the tris(POM) complex 25 and the bis(POM) This synthetic strategy was also attempted in the synthesis
complex 32 in a way similar to that described for the mono-
(POM) 11, bis(POM) 10, tris(POM) 7 and tetra(POM) 17.
Standard characterization techniques (1H and 13C NMR, and
elemental analysis) are consistent with the proposed struc-
tures. Only one 31P NMR signal was observed for 25 (3.12
ppm) and 32 (3.21 ppm). These values are similar to those
obtained for the mono(POM) complex 11, bis(POM) complex
10, tris(POM) complex 7 and tetra(POM) complex 17 (see
experimental section).
of the tetra(POM) derivative, starting from the dodeca-allyl
dendrimer 33, prepared in 75% yield by reaction of the phenol
dendron 18 with the commercially available 1,2,4,5-tetra(bro-
momethyl)benzene, in the presence of K2CO3 (See supplemen-
tary informationz). Regioselective hydroboration of the
dodeca-allyl dendrimer 33, followed by oxidation of the
dodeca-borane, led to the dodeca-ol dendrimer 34 in 85%
yield. Many attempts to prepare the dodeca-mesylate from the
dodeca-ol dendrimer 34 and chloromethylsulfonate at –5 1C
ꢁc
This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2007
1266 | New J. Chem., 2007, 31, 1264–1274

View Online
Scheme 2 Synthesis of the tetra(POM) 17.
were unsuccessful. Indeed, the reaction was not complete, and
conditions. The experimental results summarized in Scheme 4
the 1H NMR spectra showed the two triplets, respectively
attributed to SO3Me (4.15 ppm) and CH2OH (3.48 ppm)
groups. This unsatisfied result to the dodeca-mesylate 35 is
probably due to the increased bulk at the dendrimer periphery.
and Table 1 indicate that all these dendritic POMs are efficient
catalysts. In accord with our previous studies, the reaction was
accomplished with vigorous stirring of an aqueous–CDCl3
biphasic mixture containing 284 equivalents of the appropriate
substrate, 800 equivalents of hydrogen peroxide per POM unit
and 0.3 mol% of dendritic POM, at 30 1C. The reaction
kinetics were monitored over time by plotting the ratio
between the intensity of the disappearing 1H NMR signals
substrate vs. TMS and the rising peaks of the product.
Oxidation of sulfides, alkenes and alcohols with hydrogen
peroxide using dendritic POM catalysts 7, 10, 11, 17, 25 and 32
The catalytic performances in oxidation reactions of all the
POM dendrimers described herein were examined under mild
ꢁc
This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2007
New J. Chem., 2007, 31, 1264–1274 | 1267

View Online
Scheme 3 Synthesis of the tris(POM) 25.
All the polyoxometalate dendrimers oxidized alkenes quan-
tored over time by plotting the ratio between the intensity of
titatively to their corresponding epoxides, and sulfides to their
corresponding sulfones. The dendritic POMs that do not
contain a spacer were ineffective in catalyzing the oxidation
of secondary alcohols to ketones, whereas their homologues
bearing a spacer were efficient in the oxidation of cyclohexanol
to cylohexanone. The oxidation of cyclooctene 36 was moni-
the disappearance of the 1H NMR signal of cyclooctene at
5.6 ppm attributed to cyclooctene and the new peak of the
epoxide at 2.9 ppm. As shown in Table 2 (entries 1–6), the
POM dendrimers 7–32 oxidized cyclooctene with 100% con-
1
version within the limits of H NMR detection, with reaction
times between 3.5 to 6 hours. High conversion and good
ꢁc
This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2007
1268 | New J. Chem., 2007, 31, 1264–1274

View Online
Scheme 4 Catalytic oxidation reactions using 0.3 mol% of POM dendrimers, 284 equiv. of substrate, 800 equiv. H2O2 and 3 mL CDCl3.
Table 1 Oxidation of representative alkenes, sulfides and alcohols using H2O2, catalyzed by 7, 10, 11, 17, 25, and 32a
Entry
1
Substrate
Catalyst
T (1C)
Timeb (h)
4.8
Product
Conversion (%)c
100
36
7
30
37
2
3
4
5
6
10
11
17
25
32
30
30
30
30
30
5
4.6
6
4.0
3.5
100
100
100
100
100
7
38
7
30
1.4
39
100
8
9
25
32
30
30
0.2
0.2
100
100
100
100
10
40
42
25
30
1
41
43
11
12
32
7
30
30
1.1
36
100
2
13
15
25
32
30
30
36
36
92
79
15
44
25
30
34
45
95
7
45a
45b-threo
45c-erythro
53
35
a
b
Reaction conditions: catalyst (0.3 mol%), substrate (284 equiv.), H2O2 (800 equiv.), CDCl3 (3 mL). Reactions were monitored by 1H
c
NMR. Conversion determined from the relative intensities of the H NMR signals of the substrate and product.
1
ꢁc
This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2007
New J. Chem., 2007, 31, 1264–1274 | 1269

View Online
Table 2 Isolated yields of recovered POM dendrimer catalysts 7–32, after the first and second runs, in the oxidation of cyclooctene 36 and
cyclohexanol 42, using H2O2
Substrate
Catalyst
First cycle yield (%)
Second cycle yield (%)
Cyclooctene 36
7
81
87
74
98
90
95
75
70
68
50
20
55
85
80
50
40
10
11
17
25
32
25
32
Cyclohexanol 42
selectivity were observed in the oxidation of phenyl methyl
sulfide 38 and diallyl sulfide 40 to the corresponding sulfones
39 and 41, with dendritic POM catalysts 7, 25 and 32 (Table 2,
entries 7–9). The dendritic POM catalysts 25 and 32 contain-
ing spacer groups oxidized cyclohexanol 42 to cyclohexanone
43 with conversion up to 92% after a reaction time of 36 hours
(Table 2, entries 12–15), in contrast to compound 7 that does
not contain spacer groups, which gave only traces of cyclo-
hexanone 43 (Table 2, entry 12). In addition, the tris(POM) 25
oxidized 1-octen-3-ol 44 with excellent conversion rates after
34 hours (Table 2, entry 15), leading to a diastereoisomeric
mixture of threo:erythro-1,2-epoxy-3-octanol 45b and c as
major products, together with 1-octen-3-one 45a. On the other
hand, no trace of conversion was observed using the periph-
ery-congested tris(POM) 7. The reaction was easily monitored
in the 1H NMR spectrum using the disappearance of the three
multiplets at 5.84, 5.15 and 4.10 ppm attributed to the
CHOHCHQCH2 group, and the appearance of two multi-
plets at 3.80 and 3.40 ppm, respectively assigned to the CHOH
group of (2S,3R)-1,2-epoxy-3-octanol (45b threo) and (2S,3S)-
1,2-epoxy-3-octanol (45c erythro). The signals attributed to the
epoxy group appear as a multiplet between 3.01 and 2.75 ppm.
The a,b-unsaturated 1-octen-3-one 45a was identified by a new
triplet at 2.57 ppm assigned to the CH2CO group. The
chemoselectivity of the olefin epoxidation predominated over
the alcohol ketonization. Table 1, entries 7–9 and 12–15. This
clearly shows that the oxidation of phenyl methyl sulfide 38
and cyclohexanol 42 proceeded more rapidly with POM
dendrimers containing spacer groups between the arene core
and the POM units, than with their homologues that did not
contain spacer groups.
periphery with POM units studied in the present work, we
have recently found that POM-cored dendrimers (with only
one POM unit) are air stable and highly effective catalysts in
oxidation reactions.10f This indicates that the microenviron-
ment of the catalytic species in dendritic catalysts largely
determines their properties.
Recovery and reutilization of dendritic POMs 7–32
Two reaction cycles were performed in order to investigate the
stability of the dendritic POMs 7–32 under catalytic reaction
conditions. Cyclooctene 36 and cyclohexanol 42 were used as
model substrates for catalyst recycling experiments. The den-
dritic POM catalyst was recovered by precipitation from the
organic layer with pentane (isolated yields varied between 74
and 95% for the first cycle and between 20 and 85% for the
second cycle as shown in Table 2). The quality of the recovered
1
catalyst was checked by H and 31P NMR before the second
catalytic experiment.
Cyclooctene 36 and cyclohexanol 42 were oxidized with
conversion between 79 and 100%, over the two cycles. In the
case of tris(POM) complex 25 and bis(POM) complex 32, only
one signal, respectively at 3.12 and 3.21 ppm was obtained in
the 31P NMR spectrum of the recovered catalyst, indicating
the presence of the active species for reaction times of up to 24
hours. In addition, the reaction kinetics showed no discernable
loss of activity over the two catalytic cycles, contrary to
tris(POM) 7, bis(POM) 10, mono(POM) 11 and tetra(POM)
17, which slowly decomposed in solution (yields ranged from
20 to 68% after the second cycle). The results obtained in these
experiments reveal that all the POM dendrimers with a spacer
group are more stable and easier to recover and to handle than
their homologues without a spacer. However, compared to
non-dendritic POMs, both series of dendritic POMs with and
without spacers are more stable and reusable. Indeed, it has
been shown that precipitation of the alkyl ammonium POMs
>n-(C8H17)3NCH3]+3[PO4{WO(O2)2}4]3ꢀ 46 was very diffi-
cult after the first run, and gave a small amount of a solid,
identified using 31P NMR by two signals at 0.5 and ꢀ0.99
ppm. These 31P NMR signals differed from those obtained for
46 at 3.12 ppm, indicating that the structure of these POM
species had changed. In addition, attempts to recover the
POM compound, [Arquad]+3[PO4{WO(O2)2}4]3ꢀ 47 (Arquad
= didecyldimethylammonium) after the first run were unsuc-
cessful. These results indicate that dendritic structures stabi-
lized the POM species and facilitated the recovery and
recycling of the POM catalysts.
The relationship between the dendritic structure and the
catalyst properties is complex, and the question as to what is
responsible for this difference in activity and selectivity be-
tween the two series of dendrimers is not easy to answer.
However, the decreased steric constraints around the POM
units in the dendrimers containing spacers compared to the
ones that do not contain spacers may provide a possible
explanation for the dramatically increased catalytic efficiency
in the oxidation of alcohols by dendritic POMs containing
spacer groups. The POM units may also interact more easily
with one another in the series of compounds without spacer
groups, due to the proximity among the POM units. As a
result, the decomposition of the catalyst might occur more
rapidly for the series that does not contain spacers than in the
case of compounds 25 and 32, each of which contains spacer
groups. Unlike the dendritic compounds functionalized at the
ꢁc
This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2007
1270 | New J. Chem., 2007, 31, 1264–1274

View Online
CH2Cl2 layer was dried over sodium sulfate and evaporated
under reduced pressure, providing 7 (4.456 g, 70%) as a white
solid. 1H NMR (200 MHz, CDCl3) dppm: 3.6–3.3 (mbroad
N–CH2), 1.83 (mbroad, N–CH2–CH2), 1.35 (m, CH2), 0.88
(m, CH3). 13C NMR (63 MHz, CDCl3) dppm 58.5 (CH2–N),
31.1 (CH2–CH2–N), 29.6 (CH2), 26.2 (Cq–CH2), 25.8 (CH2),
23.2 (CH2), 22.3 (CH2), 21.6 (CH2), 13.8 CH3. 31P (81 MHz,
CDCl3) dppm 3.44 (PO4). FTIR (KBr plates) ncmꢀ1: 1088–1052
(P–O), 970 (WQO), 845 (O–O), 580 and 521 W(O2)s,as, other
bands at 649.8, 574.6, 549.0. Elemental analysis calcd for
Conclusion
In this paper, we are reporting the synthesis of two series of
dendrimers with POM units at the periphery. In the first series,
dendritic tripods were directly bonded to the arene core,
whereas in the second series, spacer groups were introduced
between the arene core and the dendritic wedges. These POM
compounds were found to be effective in the catalytic oxida-
tion of alkenes, sulfides and alcohols, with good to excellent
conversion and selectivity. Among these dendritic POM cata-
lysts, those with spacer groups were especially efficient in the
oxidation of alcohols, displaying possibilities of recycling up
to the second cycle. The dendritic structures dramatically
increase the stability of the POM unit, allowing the recovery
and eventually a re-use of the catalyst with variable success
depending on the catalyst structure. Given the recycle cap-
abilities, as well as the competitive efficiency in the oxidation
of alcohols, dendritic POMs with spacer groups between the
core and the peripheral POM units are more stable than their
homologues without a spacer group in the presence of air
(both series being stable in the absence of air). This stability
feature is a key one in the oxidation of more challenging
substrates as well as in catalyst recovery.
,
C198H408N9P3W12O72: C, 37.35; H, 6.46; P, 1.46. Found: C,
37.48; H, 6.08; P, 1.56%.
Bis(POM) dendrimer 10. Dendrimer 10 was obtained from
the hexa-allyl 8 as a colorless solid in 52% yield using the
procedure described above for 7. 1H NMR (200 MHz, CDCl3)
dppm: 3.18 (mbroad, N–CH2), 1.78 (m, N–CH2–CH2), 1.34 (m,
CH2), 0.91 (m, CH3). 13C NMR (63 MHz, CDCl3) dppm: 58.5
(CH2–N), 31.8 (CH2–CH2–N), 29.6 (CH2), 26.3 (Cq–CH2),
25.8 (CH2), 23.2 (CH2), 22.7 (CH2), 21.6 (CH2), 14.3 (CH3).
31P (81 MHz, CDCl3) dppm: 3.54 (PO4). FTIR (KBr plates)
ncmꢀ1: 1086 and 1057 (P–O), 974 (WQO), 845 (O–O), 590 and
522 W(O2)s,as, other bands at 651, 575, 548.8. Elemental
analysis calcd for C134H274N6P2W8O48: C, 38.67; H, 6.49.
Found: C, 39.01; H, 6.49%.
Experimental
Mono(POM)dendrimer 11. Dendrimer 11 was obtained as a
colorless solid in 73% yield from the tri-allyl 9 using the
procedure described above for 7. 1H NMR (CDCl3, 200
MHz) dppm: 7.4 (m, 4H, Harom), 3.3 (mbroad, CH2–N), 1.7
(m, CH2), 1.3 (m, CH2), 0.9 (s, 27H, CH3). 13C NMR (CDCl3,
63 MHz) dppm: 58.5 (CH2–N), 31.3 (CH2–CH2–N), 26.5
(CH2–Cq), 22.5 (CH2), 14.0 (CH3). 31P NMR (CDCl3, 81
MHz) dppm: 3.37 (PO4). FTIR (KBr plates) ncmꢀ1: 1083 and
General remarks
Reagent-grade tetrahydrofuran (THF), diethyl ether, and
pentane were pre-dried over Na foil and distilled from so-
dium-benzophenone anion under argon immediately prior to
use. Acetonitrile (CH3CN) was stirred under argon overnight
over phosphorus pentoxide, distilled from sodium carbonate,
and stored under argon. Methylene chloride (CH2Cl2) was
distilled from calcium hydride just before use. All other
chemicals were used as received. The 1H, 13C, 31P NMR
spectra were recorded at 25 1C with a Brucker AC 250 FT
spectrometer (1H: 250.13, 13C: 62.91 MHz) and a Brucker AC
200 FT spectrometer (1H: 200.16, 13C: 50.33, 31P: 81.02 MHz).
All chemical shifts are reported in parts per million (d, ppm)
with reference to Me4Si (TMS). Elemental analyses were
carried out at the Vernaison CNRS center. The infrared
spectra were recorded in KBr pellets on a FT-IR Paragon
1000 Perkin-Elmer spectrometer. The matrix-assisted laser-
desorption (MALDI) mass spectra were recorded using a
Perseptive Biosystems Voyager Elite (Framingham, MA)
time-of-flight (TOF) mass spectrometer. Organic oxidation
1057 (P–O), 974 (WQO), 845 (O–O), 590 and 517 W(O2)s,as
,
other bands at 652, 574, 548. Elemental analysis calcd for
C70H140N3P1W4O24: C, 37.69; H, 6.47. Found: C, 38.67; H,
6.49%.
Tetra(POM)dendrimer 17. Dendrimer 17 was obtained as a
colorless solid in 54% yield from the dodeca-allyl 12 using the
procedure described above for 7. 1H NMR (200 MHz, CDCl3)
dppm: 3.18 (mbroad, N–CH2), 1.74 (m, N–CH2–CH2), 1.35 (m,
CH2), 0.91 (m, CH3). 13C NMR (63 MHz, CDCl3) dppm: 58.5
(CH2–N), 31.1 (CH2–CH2–N), 29.6 (CH2), 26.2 (Cq–CH2),
25.8 (CH2), 23.2 (CH2), 22.3 (CH2), 21.6 (CH2), 13.8 (CH3).
31P (81 MHz, CDCl3) dppm: 3.15 (PO4). FTIR (KBr plates)
ncmꢀ1: 1087 and 1057 (P–O), 972 (WQO), 846 (O–O), 580 and
521 W(O2)s,as, other bands at 658, 575, 549. Elemental analysis
calcd for C268H546N12P4W16O96: C, 37.70; H, 6.45. Found: C,
38.00; H, 6.56%.
products were identified by H and 13C NMR using compar-
1
ison of these spectra with those of authentic samples.
Synthesis of dendritic polyoxometalate compounds 7, 10, 11 and
17 without spacer group between dendritic tripods and the arene
core: [CpFe]+ induced activation of polymethylarene procedure
Synthesis of dendritic polyoxometalate complexes containing
spacer groups between the arene core and dendritic tripod units:
dendrimers 25 and 32
Tris(POM) dendrimer 7. H2O2 (5.1 ml , 35% in water) was
added to a water solution (5 mL) of commercial hetero-
polyacid H3PW12O40 (8.941 g, 3.11 mmol). The mixture was
stirred at room ꢀtemperature for 30 minutes. Then, a CH2CH2
solution of BF4 ammonium salt 6 (0.896 mmol) was added,
and the mixture was stirred for an additional hour. The
Nona-allyl dendrimer 19. A mixture of phenol-tri-allyl den-
dron 18 (1.000 g, 4.386 mmol), K2CO3 (0.817 g 5.839 mmol),
and 2,4,6-tri(bromomethyl)mesitylene (0.387 g, 0.970 mmol)
in DMF, was stirred for 2 days at 60 1C. The product was
extracted with 3 ꢂ 30 ml of ether and the ether solution
ꢁc
This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2007
New J. Chem., 2007, 31, 1264–1274 | 1271

View Online
washed with 5 ꢂ 20 ml of water. The organic phase was dried
over sodium sulfate, then filtered and evaporated under va-
cuum. The product was purified by chromatography on a
silica-gel column with a pentane–diethyl ether mixture (8 : 2)
to provide 19 (2.767 g, 75%) as a colorless solid. 1H NMR
(CDCl3, 200.16 MHz) dppm: d 7.24 (d, 6H, Ar), 6.93 (d, 2H,
Ar), 6.98 (d, 6H, Ar), 5.57 (m, 9H, CHQCH2), 5.03 (m, 24H,
CHQCH2, and CH2O), 2.46 (s, 9H, CH3), 2.44 (d, 18H,
CH2CHQCH2). 13C NMR (CDCl3, 62.91 MHz) dppmu
157.07 (Cq, ArO), 139.35 (Cq, arom), 138.04 (Cq, arom), 134.72
(CHQCH2), 131.92 (Cq, arom), 127.73 (CHarom), 117.57
(CHQCH2), 114.08 (CHarom), 64.88 (CH2O), 42.71 (Cq–CH2),
42.03 (CH2), 16.01 (CH3). MALDI TOF mass spectrum, m/z:
863.43 [M + Na]+ (calcd 864.21). Elemental analysis calcd for
C60H72O3: C, 85.67; H, 8.63. Found: C, 85.31; H, 8.47%.
(CDCl3, 62.91 MHz): d = 157.27 (Cq, ArO), 139.25 (Cq, arom),
138.68 (Cq, arom), 134.91 (Cq, arom), 127.23 (CHarom), 114.48
(CHarom), 62.59 (CH2O), 59.45 (CH2–N), 31.48
(CH2–CH2–N), 26.93 (CH2–Cq), 25.95 (CH2), 22.53, (CH2),
22.21 (CH2), 13.93 (CH3). Elemental analysis calcd for
C164H305O3I9N9: C, 54.79; H, 8.55. Found: C, 55.04; H,
8.74%.
Nona-ammonium nona-tetrafluoroborate dendrimer 24. Den-
drimer 24 was obtained from the salt 23, in 90% yield using
1
the procedure described for 6. H NMR (200 MHz, CDCl3)
dppm: 7.26 (sbroad, 6H, Harom), 6.95 (sbroad, 6H, Harom), 5.05
(sbroad, 6H, CH2O), 3.34 (mbroad, N–CH2), 1.75–1.53 (mbroad
,
N–CH2–CH2), 1.27 (mbroad, CH2), 0.85 (mbroad, CH3). 13C
NMR (CDCl3, 62.91 MHz) dppm: 157.27 (Cq, ArO), 139.25
(Cq, arom), 138.68 (Cq, arom), 134.91 (Cq, arom), 127.23 (CHarom),
114.48 (CHarom), 62.59 (CH2O), 58.81 (CH2–N), 31.08
(CH2–CH2–N). Elemental analysis calcd for C164H305O3I9N9
B9F36: C, 60.94; H, 9.51. Found: C, 60.32, H, 9.15%.
Nona-ol dendrimer 20. Dendrimer 20 was obtained as a
colorless solid in 95% yield from the nona-allyl 19, using the
procedure described in ref. 14. 1H NMR (CD3OD, 200.16
MHz) dppm: 7.12 (d, 6H, Ar), 6.80 (d, 2H, Ar), 4.90 (s, 6H,
CH2O), 3.28 (t, 18H, CH2O), 1.55 (m, 18H, CH2), 1.12 (m,
18H, CH2). 13C NMR (CD3OD, 62.91 MHz) dppm: 156.79 (Cq,
ArO), 139.31 (Cq, arom), 138.68 (Cq, arom), 131.76 (Cq, arom),
127.23 (CHarom), 113.76 (CHarom), 62.14 (CH2O), 41.41
(Cq–CH2), 33.28 (CH2), 26.40 (CH2), 14.57 (CH3). MALDI
TOF mass spectrum, m/z: 1025.88 [M + Na]+ (calcd
1026.35). Elemental analysis calcd for C60H90O12: C, 71.81;
H, 9.04. Found: C, 71.09; H, 9.22%.
Tris(POM) dendrimer 25. This dendrimer was obtained as a
colorless solid in 75% yield from the nona-ammonium salt 24
using the procedure described above for 7. 1H NMR (CDCl3,
200.16 MHz) dppm: 7.2 (d, 6H, Ar), 7.01 (d, 6H, Ar), 5.13
(s, 6H, CH2O), 3.3 (mbroad, CH2–N), 1.85–1.66 (mbroad
,
N–CH2–CH2), 1.36 (mbroad, CH2), 0.91 (m, CH3). 13C NMR
(CDCl3, 62.91 MHz) dppm: 157.27 (Cq, ArO), 139.25 (Cq, arom),
138.68 (Cq, arom), 134.91 (Cq, arom), 127.23 (CHarom), 114.48
(CHarom),
62.59
(CH2O),
59.45
(CH2–N),
31.48
Nona-mesylate dendrimer 21. Dendrimer 21 was obtained as
a yellow oil in 98% yield from the nona-ol 20, using the
procedure described in ref. 14. 1H NMR (CDCl3, 200.16
MHz) dppm: 7.20 (d, 6H, Ar), 6.96 (d, 2H, Ar), 5.08
(s, 6H, CH2O), 4.15 (t, 18H, CH2O), 2.97 (s, 27H, CH3SO2),
1.75 (mbroad, 18H, CH2), 1.53 (mbroad, 18H, CH2). 13C NMR
(CDCl3, 62.91 MHz) dppm: 157.27 (Cq, ArO), 139.25 (Cq, arom),
138.68 (Cq, arom), 134.91 (Cq, arom), 127.23 (CHarom), 114.48
(CHarom), 70.47 (CH2OSO2), 62.59 (CH2O), 41.67 (Cq–CH2),
37.37 (SO2CH3), 23.59 (CH2), 15.98 (CH3). Elemental analysis
calcd for C69H108O30S9: C, 48.57; H, 6.38. Found: C, 48.78; H,
6.40%.
(CH2–CH2–N), 31.02 (CH3), 26.93 (CH2–Cq), 25.95 (CH2),
22.53, (CH2), 22.21 (CH2), 13.93 (CH3). 31P NMR (CDCl3, 81
MHz) dppm: 3.12 (PO4). FTIR (KBr plates) ncmꢀ1: 1076 and
1058 (P–O), 963 (WQO), 830 (O–O), 580 and 521 W(O2)s,as
Elemental analysis calcd for C219H436O75N9 P3W12: C, 39.29;
.
H, 6.56; P, 1.39. Found: C, 39.90; H, 6.58; P, 1.35%.
Hexa-allyl dendrimer 26. This dendrimer was obtained as a
white solid in 90% yield using the procedure described above
1
for the nona-allyl 19. H NMR (CDCl3, 200.16 MHz) dppm
7.47 (s, 4H, Ar), 7.23 (d, 4H, Ar), 6.94 (d, 4H, Ar), 5.57 (m,
:
6H, CHQCH2), 5.03 (m, 16H, CHQCH2, and CH2O), 2.43
(d, 9H, CH2CHQCH2). 13C NMR (CDCl3, 62.91 MHz) dppm
:
Nona-iodo dendrimer 22. This dendrimer was obtained as a
yellow oil in 95% yield from the nona-mesylate 21 using the
procedure described in ref. 14. 1H NMR (CDCl3, 200.16
MHz) dppm: 7.28 (d, 6H, Ar), 7.02 (d, 2H, Ar), 5.13 (s, 6H,
156.69 (Cq, ArO), 138.10 (Cq, arom), 136.95 (Cq, arom), 134.68
(CHQCH2), 127.81 (Cq, arom), 127.75 (CHarom), 117.57
(CHQCH2), 114.08 (CHarom), 69.72 (CH2O), 42.74 (Cq–CH2),
41.99 (CH2). MALDI TOF mass spectrum, m/z: 581.13 [M +
Na]+ (calcd 581.79). Elemental analysis calcd for C40H46O2:
C, 85.98; H, 8.30. Found: C, 85.86; H, 8.34%.
CH2O), 3.18 (t, 18H, CH2I), 2.51 (s, 9H, CH3), 1.78 (mbroad
,
18H, CH2), 1.65 (mbroad, 18H, CH2). 13C NMR (CDCl3,
62.91 MHz) dppm: 157.16 (Cq, ArO), 139.30 (Cq, arom),
137.94 (Cq, arom), 131.75 (Cq, arom), 127.15 (CHarom), 114.35
(CHarom), 64.86 (CH2O), 41.71 (Cq–CH2), 38.52 (CH2), 27.55
(CH2), 16.03 (CH3), 7.89 (CH2I). Elemental analysis calcd for
C60H81O3I9: C, 36.17; H, 4.10. Found: C, 36.75; H, 4.56%.
Hexa-ol dendrimer 27. The hexa-ol 27 was obtained as a
colorless solid in 90% yield from 26 using the procedure
1
described in ref. 14. H NMR (CD3OD, 200.16 MHz) dppm
:
7.43 (s, 4H, Ar), 7.20 (d, 4H, Ar), 7.95 (d, 4H, Ar), 5.03 (s, 4H,
CH2O), 3.46 (t, 12H, CH2O), 1.65 (m, 12H, CH2), 1.30 (m,
12H, CH2). 13C NMR (CD3OD, 62.91 MHz) dppm: 156.50 (Cq,
ArO), 139.19 (Cq, arom), 137.03 (Cq, arom), 127.13 (CHarom),
113.90 (CHarom), 69.17 (CH2O), 62.10 (CH2O), 41.34
(Cq–CH2), 33.25 (CH2), 26.37 (CH2). MALDI TOF mass
spectrum, m/z: 689.65 [M + Na]+ (calcd 689.88). Elemental
Nona-ammonium nona-iodide dendritic salt 23. This dendritic
salt was obtained from the nona-iodo derivative 22, in 93%
1
yield using the procedure described for 5. H NMR (CDCl3,
200.16 MHz) dppm: 7.28 (d, 6H, Ar), 7.01 (d, 6H, Ar), 5.13
(s, 6H, CH2O), 3.3 (mbroad, CH2–N), 1.85-1.66 (mbroad
,
N–CH2–CH2), 1.36 (mbroad, CH2), 0.91 (m, CH3). 13C NMR
ꢁc
This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2007
1272 | New J. Chem., 2007, 31, 1264–1274

View Online
analysis calcd for C60H90O12: C, 72.04; H, 8.77. Found: C,
71.34; H, 8.67%.
3.56–3.18 (mbroad, CH2–N), 1.90–1.57 (mbroad, N–CH2–CH2),
1.32 (mbroad, CH2), 0.91 (m, CH3). 13C NMR (CDCl3,
62.91 MHz) dppm: 157.50 (Cq, ArO), 138.88 (Cq, arom),
134.18 (Cq, arom), 133.03 (Cq, arom), 127.62 (CHarom), 114.62
Hexa-mesylate dendrimer 28. This dendrimer was obtained
as yellow oil in 95% yield from the hexa-ol dendrimer 27 using
1
the procedure described in ref. 14. H NMR (CDCl3, 200.16
(CHarom),
69.36
(CH2O),
58.43
(CH2–N),
31.18
(CH2–CH2–N), 25.85 (CH2), 22.41, (CH2), 22.13 (CH2),
13.98 (CH3); 31P NMR (CDCl3, 81 MHz) dppm: 3.21 (PO4).
FTIR (KBr plates) ncmꢀ1: 1083 and 1056 (P–O), 960 (WQO),
840 (O–O), 580 and 521 W(O2)s,as. Elemental analysis calcd for
MHz) dppm: 7.50 (s, 4H, Ar), 7.25 (d, 4H, Ar), 6.98 (d, 4H, Ar),
5.09 (s, 6H, CH2O), 4.19 (t, 18H, CH2O), 3.01 (s, 18H,
CH3SO2), 1.75 (mbroad, 12H, CH2), 1.53 (mbroad, 12H, CH2).
13C NMR (CDCl3, 62.91 MHz) dppm: 156.92 (Cq, ArO),
137.13 (Cq, arom), 136.74 (Cq, arom), 127.78 (Cq, arom), 127.20
(CHarom), 122.88 (CHarom), 114.69 (CHarom), 70.33 (CH2O-
SO2), 69.63 (CH2O), 41.67 (Cq–CH2), 37.34 (SO2CH3), 32.87
(CH2), 21.98 (CH2). Elemental analysis calcd for C46H70O20S6:
C, 48.66; H, 6.21. Found: C, 48.59; H, 6.75%.
C148H286O50N6 P2W8: C, 39.66; H, 6.43; P, 1.38. Found: C,
40.14; H, 7.06; P, 1.25%.
General procedure for catalytic reactions and recycling of the
dendritic POM catalyst
The POM catalyst 7–32 (0.003 mmol) and cyclooctene (284
equiv. per POM unit) were dissolved in 3 ml CDCl3 then H2O2
(35% in water, 800 equiv. per POM unit) was added. The
mixture was stirred at 30 1C, and the reaction was followed by
1H NMR. Upon completion, the CDCl3 layer was separated
and concentrated under a vacuum to about 1 ml. The catalyst
was precipitated by addition of pentane or diethyl ether
(10 ml). The solid was filtered and washed with diethyl ether
(3 ꢂ 5 ml) which gave the POM catalyst in a good to excellent
yield (see Table 2, main text). The catalyst was recovered
following the typical procedure and conditions described
above for the first cycle, CDCl3 and reactants were adjusted
to the amount of catalyst used. The reaction was performed
with cyclooctene 36, and cyclohexanol 42 using dried, recov-
ered catalyst. The catalyst was completely dissolved in CDCl3,
and the reactants were added to the solution. After comple-
tion, the catalyst was recovered and checked by 1H and
31P NMR, with a yield between 20 and 85% (Table 2).
Hexa-iodo dendrimer 29. Dendrimer 29 was obtained as a
yellow oil in 90% yield from the hexa-mesylate 28 using the
procedure described in ref. 14. 1H NMR (CDCl3, 200.16
MHz) dppm: 7.47 (s, 4H, Ar), 7.20 (d, 4H, Ar), 6.94 (d, 4H,
Ar), 5.06 (s, 4H, CH2O), 3.12 (t, 12H, CH2I), 2.51 (s, 9H,
CH3), 1.75 (mbroad, 12H, CH2), 1.65 (mbroad, 12H, CH2). 13C
NMR (CDCl3, 62.91 MHz) dppm
: 156.80 (Cq, ArO),
138.01 (Cq, arom), 136.78 (Cq, arom), 127.79 (Cq, arom), 127.16
(CHarom), 114.51 (CHarom), 69.67 (CH2O), 41.70 (Cq–CH2),
38.48 (CH2), 27.52 (CH2), 7.77 (CH2I). Elemental analysis
calcd for C40H52O2I6: C, 36.23; H, 3.95. Found: C, 36.75; H,
4.45%.
Hexa-ammonium hexa-iodide salt dendrimer 30. The hexa-
iodo salt 30 was obtained from 29 in 85% yield using the
procedure described for 5. 1H NMR (CDCl3, 200.16 MHz)
dppm: 7.46 (s, 4H, Ar), 7.22 (d, 4H, Ar), 6.97 (d, 4H, Ar), 5.09
(s, 4H, CH2O), 3.27 (mbroad, CH2–N), 1.90–1.53 (mbroad
,
N–CH2–CH2), 1.25 (mbroad, CH2), 0.84 (m, CH3). 13C NMR
(CDCl3, 62.91 MHz) dppm: 157.27 (Cq, ArO), (Cq, arom),
138.68 (Cq, arom), 134.91 (Cq, arom), 127.23 (CHarom), 114.56
Acknowledgements
We are grateful to Dr J.-C. Blais (University Paris 6) for mass-
spectrometric studies and to Dr J. Ruiz Aranzaes (University
Bordeaux I) for AFM studies. Financial support from the
University Bordeaux I, the CNRS, the MRT (LP) and the IUF
(DA) is also gratefully acknowledged.
(CHarom),
69.72
(CH2O),
59.45
(CH2–N),
31.48
(CH2–CH2–N), 26.91 (CH2–Cq), 25.04 (CH2), 22.52, (CH2),
22.39 (CH2), 13.94 (CH3). Elemental analysis calcd for
C
148H286O2I6N6: C, 60.37; H, 9.79. Found: C, 60.32; H,
9.15%.
Hexa-ammonium hexa-tetrafluoroborate dendrimer 31. The
References
hexa-tetrafluoroborate salt 31 was obtained from the corre-
sponding hexa-iodo salt 30 in 95% yield, using the procedure
described above for 6. 1H NMR (200 MHz, CDCl3) dppm: 7.42
(s, 4H, Ar), 7.22 (d, 4H, Ar), 6.92 (d, 4H, Ar), 5.06 (s, 4H,
1 (a) G. R. Newkome, C. N. Moorefield and F. Vogtle, Dendrimers
¨
and Dendrons: Concepts, Synthesis and Applications, VCH-Wiley,
New York, 2001; (b) Dendrimers and other Dendritic Polymers, ed.
D. A. Tomalia and J. M. J. Frechet, Wiley-VCH, New York, 2002;
´
(c) Dendrimers and Nanoscience, ed. D. Astruc, C. R. Chim.,
Elsevier, Paris, 2003, vol. 8–10; (d) F. Zeng and S. C. Zimmerman,
Chem. Rev., 1997, 97, 1681.
CH2O), 3.32–3.10 (mbroad
, CH2–N), 1.90–1.55 (mbroad,
N–CH2–CH2), 1.35 (mbroad, CH2), 0.85 (m, CH3). 13C NMR
(CDCl3, 62.91 MHz) dppm: 157.00 (Cq, ArO), 137.25 (Cq, arom),
138.68 (Cq, arom), 134.91 (Cq, arom), 127.38 (CHarom), 114.56
2 (a) D. Astruc and F. Chardac, Chem. Rev., 2001, 101, 2991–3023;
(b) G. E. Oosterom, J. N. H. Reek, P. C. J. Kramer and P. W. N.
M. van Leeuwen, Angew. Chem., Int. Ed., 2001, 40, 1828; (c) R.
Kreiter, A. Kleij, R. J. M. Klein Gebbink and G. van Koten, Top.
Curr. Chem., 2001, 217, 163; (d) R. van Heerbeek, P. C. J. Kamer,
P. W. N. M. van Leeuwen and J. N. H. Reek, Chem. Rev., 2002,
102, 3717; (e) L. J. Twyman, A. S. H. King and 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 and C. N. Moorefield, Chem. Rev.,
1999, 99, 1689; (b) A. W. Bosman, H. M. Janssen and E. W.
Meijer, Chem. Rev., 1997, 99, 1665; (c) I. Cuadrado, M. Moran,
(CHarom),
69.60
(CH2O),
59.72
(CH2–N),
31.02
(CH2–CH2–N), 26.11 (CH2–Cq), 25.84 (CH2), 22.32, (CH2),
22.04 (CH2), 13.82 (CH3).
Bis(POM) dendrimer 32. The Bis(POM) 32 was obtained as
a colorless solid in 70% yield from the hexa-ammonium hexa-
tetrafluoroborate dendrimer 31, using the procedure described
1
above for 7. H NMR (200 MHz, CDCl3) dppm: 7.44 (s, 4H,
Ar), 7.31 (d, 4H, Ar), 6.98 (d, 4H, Ar), 5.09 (s, 4H, CH2O),
ꢁc
This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2007
New J. Chem., 2007, 31, 1264–1274 | 1273

View Online
C. M. Casado, B. Alonzo and J. Losada, Coord. Chem. Rev., 1999,
193–195, 395; (d) M. A. Hearshaw and J. R. Moss, Chem. Com-
mun., 1999, 1.
10 (a) H. Zeng, G. R. Newkome and C. L. Hill, Angew. Chem., Int.
Ed., 2000, 39, 1772; (b) D. Volkmer, B. Bredenkotter, J. Tellen-
¨
broker, P. Kogerler, D. G. Kurth, P. Lehmann, H. Schnableggen,
¨
¨
5 (a) P. Bhyrappa, J. K. Young, J. S. Moore and K. S. Suslick, J.
Am. Chem. Soc., 1996, 118, 5708; (b) P. Bhyrappa, J. K. Young, J.
S. Moore and K. S. Suslick, J. Mol. Catal. A: Chem., 1996, 113,
109; (c) P. Weyermann, J.-P. Gissel-brecht, C. Boudon, F. Dieder-
ich and M. Gross, Angew. Chem., Int. Ed., 1999, 38, 3215; (d) P.
Weyermann and F. Diederich, J. Chem. Soc., Perkin Trans., 2000,
1, 4231; (e) F. Diederich and P. Weyermann, Polym. Mater. Sci.
Eng., 2001, 84, 168; (f) P. Weyermann and F. Diederich, Helv.
Chem. Acta, 2002, 85, 599; (g) P. Weyermann, F. Diederich, J.-P.
Gissel-brecht, C. Boudon and M. Gross, Helv. Chim. Acta, 2002,
85, 571; (h) C. Francavilla, M. D. Drake, F. V. Bright and 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.
Bateman, Y. You and M. R. Detty, Organometallics, 2003, 22, 2883.
D. Schwahn, M. Piepenbrink and B. Krebs, J. Am. Chem. Soc.,
2002, 124, 10489; (c) L. Plault, A. Hauseler, S. Nlate, D. Astruc, J.
Ruiz, S. Gatard and R. Neumann, Angew. Chem., Int. Ed., 2004,
43, 2924; (d) M. V. Vasylyev, D. Astruc and R. Neumann, Adv.
Synth. Catal., 2005, 347, 39; (e) S. Nlate, D. Astruc and R.
Neumann, Adv. Synth. Catal., 2004, 346, 1445; (f) S. Nlate, L.
Plault and D. Astruc, Chem.-Eur. J., 2006, 12, 903.
11 C. Venturello, R. D’aloisio, J. C. J. Bart and M. Ricci, J. Mol.
Catal., 1985, 32, 107.
12 D. Astruc, S. Nlate, R. Ruiz, in Modern Arene Chemistry, ed. D.
Astruc, Wiley-VCH, Weinheim, 2002, Chap. 12, p. 400.
13 (a) V. Sartor, J. L. Fillaut, L. Djakovitch, F. Moulines, V.
Marvaud, F. Neveu, J. C. Blais and D. Astruc, J. Am. Chem.
Soc., 1999, 21, 2929; (b) V. Sartor, S. Nlate, J. L. Fillaut, L.
Djakovitch, F. Moulines, V. Marvaud, F. Neveu, J. C. Blais, J. F.
6 (a) M. T. Pope and A. Muller, Angew. Chem., Int. Ed. Engl., 1991,
¨
30, 34; (b) J. T. Rhule, C. L. Hill, D. A. Rud and R. F. Schinazi,
Chem. Rev., 1998, 98, 327; (c) Dimitris E. Katsoulis, Chem. Rev.,
Letard and D. Astruc, New J. Chem., 2000, 24, 351.
´
14 (a) C. Venturello and R. D’aloisio, J. Org. Chem., 1988, 53, 1553;
(b) Y. Ishii, Y. Yamawaki, T. Ura, H. Yamada, T. Yoshida and M.
Ogawa, J. Org. Chem., 1988, 53, 3587; (c) C. Aubry, G. Chottard,
1998, 98, 359; (d) M. T. Pope and A. Muller, Polyoxometalate
¨
Chemistry: From Topology via Self-Assemblyto Applications,
Kluwer Academic, Dordrecht, 2001.
N. Platzer, J.-M. Bregeault, R. Thouvenot, F. Chauveau, C. Huet
´
7 For the multiple facets of POM chemistry, see refs. 7, 9–12 and the
special issue dedicated to POMs: Chem. Rev., 1998, 98, 1.
8 (a) I. V. Kozhevnikov, Catalysis by Polyoxometalates, John Wiley
& Sons, Chichester, 2002; (b) I. V. Kozhevnikov, Chem. Rev., 1998,
98, 171; (c) N. Mizuno and M. Misono, Chem. Rev., 1998, 98, 199;
(d) R. Neumann, Prog. Inorg. Chem., 1998, 47, 317.
and H. Ledon, Inorg. Chem., 1991, 30, 4409; (d) Y. Ishii and M.
Ogawa, Reviews on Heteroatom Chemistry, ed. A. Ohno and N.
Furukawa, MYU, Tokyo, 1990, vol. 3, p. 121; (e) R. Neumann and
A. M. Khenkin, J. Org. Chem., 1994, 59, 7577; (f) D. C. Duncan,
R. C. Chambers, E. Hecht and C. L. Hill, J. Am. Chem. Soc., 1995,
117, 681.
9 M. C. Rogers, B. Adisa and D. Bruce, Catal. Lett., 2004, 98, 29.
15 V. Martinez, J. C. Blais and D. Astruc, Org. Lett., 2002, 4, 651.
ꢁc
This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2007
1274 | New J. Chem., 2007, 31, 1264–1274