New polyalkynyl dendrons and dendrimers: "Click" chemistry with azidomethylferrocene and specific anion and cation electrochemical sensing properties of the 1,2,3-triazole-containing dendrimers

Article abstract of DOI:10.1002/chem.200801999

The synthesis and use of the new tris-alkynyl dendrons 2 to 5 are reported, including the Williamson reaction of 5 with 9-iodo (9), 27-iodo (11), and 81-iodo (12) dendritic cores to yield 27-alkynyl (13), 81-alkynyl (14), and 243-alkynyl (15) dendrimers.

Full text of DOI:10.1002/chem.200801999

DOI: 10.1002/chem.200801999
New Polyalkynyl Dendrons and Dendrimers: “Click” Chemistry with
Azidomethylferrocene and Specific Anion and Cation Electrochemical
Sensing Properties of the 1,2,3-Triazole-Containing Dendrimers
Jꢀrꢀmy Camponovo,[a] Jaime Ruiz,[a] Eric Cloutet,[b] and Didier Astruc*[a]
Abstract: The synthesis and use of the
new tris-alkynyl dendrons 2 to 5 are re-
ported, including the Williamson reac-
tion of 5 with 9-iodo (9), 27-iodo (11),
and 81-iodo (12) dendritic cores to
yield 27-alkynyl (13), 81-alkynyl (14),
and 243-alkynyl (15) dendrimers. So-
called “click” reactions of these three
dendrimers with azidomethylferrocene
(20) give 27-ferrocenyl (16), 81-ferro-
cenyl (17), and 243-ferrocenyl (18) den-
Derivatization of Pt electrodes with the
dendrimers for recognition becomes
more facile with increasing size of the
dendrimer. This first “click” dendrimer
bearing 243-ferrocenyl groups is the
best one in the series to obtain robust,
recyclable modified Pt electrodes,
whereas previous “click” ferrocenyl
dendrimers have not been suitable for
this purpose.
drimers. Electrochemical recognition of
oxo-anions (H2PO4 and ATP2ꢀ) and
ꢀ
Pd2+ cation has been compared using
the three polyferrocenyl dendrimers.
Keywords: alkynes
·
click
chemistry · dendrimers · ferrocenes ·
redox chemistry
Introduction
243 alkynyl termini. Indeed, polyiodomethyl dendrimers,
used here as dendritic cores, are known for up to nine gener-
ations (more than 105 branches).[10]
The good overall yield of the synthesis reported here and
the easily performed steps used to obtain this Percec-type
dendron[11] make it a good tool for obtaining dendronized
polyalkynyl molecules. The phenol function located at the
focal point of the dendron also allows its introduction onto
materials using the classical Williamson reaction.
The multifaceted supramolecular properties of dendrimers[1]
can be applied to various fields of nanoscience, such as vec-
tors,[2] sensors,[3] and green catalysts.[4] The terminal alkyne
function has high potential for chemical properties[5] (as ex-
emplified by the recently reported catalysis of 1,3-dipolar
cycloadditions by “click” reaction).[6] Alkynyl functions have
previously been used by Newkome et al.[7] and Moore
et al.[8] for dendritic construction. Various syntheses of den-
drimers with alkynyl termini have also been reported.[9] We
have now synthesized the new dendrons 2 to 5 containing
three propargyl groups, and have used 5 to open the way to
a set of larger polyalkynyl dendrimers containing 27, 81, and
The reactivity of the three alkynyl dendrimers 13, 14, and
15 has now been tested in the “click” reaction with azidome-
thylferrocene (20), a substrate that has not previously been
used for this reaction. Our previous “click” dendrimer syn-
thesis involved azido-terminated dendrimers and terminal
alkyne substrates. We now report “inverse click” reactions,
that is, click dendrimer synthesis in which the terminal
alkyne is located on the dendrimer branch termini.[9d,e] Final-
ꢀ
ly, electrochemical recognition of ATP2ꢀ, H2PO4 , and Pd2+
[a] J. Camponovo, Prof. Dr. J. Ruiz, Prof. Dr. D. Astruc
Institut des Sciences Molꢀculaires, UMR CNRS No 5255
Universitꢀ Bordeaux I
has been probed using the new ferrocenyl dendrimers 16,
17, and 18 (containing 27, 81, and 243 ferrocenyl groups, re-
spectively).[12] We recently reported[12d] syntheses of polyfer-
rocenyl dendrimers, along with their redox recognition abili-
ties. We now describe “inverse click” reactions using polyal-
kynyl cores. The resulting “inverse click” dendrimers display
electrochemical properties that differ from those of the pre-
viously reported “normal click” dendrimer series. The large
size of the dendrimers synthesized here has allowed the
preparation of modified Pt electrodes that could not be ob-
351 Cours de la libꢀration, 33405 Talence Cedex (France)
Fax : (+33)5-4000-6994
E-mail: d.astruc@ism.u-bordeaux1.fr
[b] Dr. E. Cloutet
Laboratoire de Chimie des Polymꢁres Organiques
UMR CNRS No 5629, Universitꢀ Bordeaux I—ENSCP, CNRS
16 Avenue Pey Berland, 33607 Pessac (France)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200801999.
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FULL PAPER
tained with the previously reported “normal click” dendrim-
ers. The resulting dendritic effects are discussed.
+ Na+ at m/z 385.1050, calcd for [M+Na]+ 385.1046; see
the Supporting Information).
The known nona-allylation of [FeCp(h6-mesitylene)]
ACHTUNGTRENNUNG[PF6]
6 (Cp=h5-C5H5) quantitatively furnished the 9-allyl dendrit-
ic core, 7, on a large scale after visible-light photolysis to
remove the metal moiety (Scheme 2).[10] Hydrosilylation of
the terminal olefinic bonds of 7, a reaction pioneered in
dendrimer synthesis by van Leeuwen et al.,[13] was carried
Results and Discussion
Dendrimer synthesis: The tris-alkynyl dendron 5 was synthe-
sized from commercially available methyl 3,4,5-trihydroxy-
benzoate 1 (Scheme 1). Four classical organic chemistry
steps were performed to obtain the desired dendron 5 in
45% overall yield. This synthesis only requires a purification
step at the end of the process. The three first steps could be
easily accomplished on a wide range of scales (from 100 mg
to 10 g). The last step proved to be very sensitive to the di-
lution and addition time, and it was important to remove
DMF prior to column chromatographic work-up. The den-
dron 5 was characterized by classical spectroscopic and ana-
lytical means, including mass spectrometry (molecular peak
out as previously reported, using HSiMe
Karsted catalyst, to regioselectively afford the known 9-
chloromethyl(dimethyl)silyl intermediate 8. Compound 8
2ACHTUNGTRENUN(NG CH2Cl) and the
AHCTUNGTRENNUNG
was then stirred for 5 h with sodium iodide in refluxing bu-
tanone, which quantitatively afforded the known 9-
iodomethylACTHNUTRGNEUG(N dimethyl)silyl dendritic core 9 (Scheme 2). Wil-
liamson reaction of 9 with the known triallyl-phenol den-
dron, 10, has previously been reported to give the polyallyl
dendritic core of the next higher generation. Repetition of
the hydrosilylation and halogen-exchange steps is known to
Scheme 1. Tris-alkynyl and tris-allyl dendrons.
yield the 27-iodo dendritic core, 11, and the last three steps
have previously been used on the latter to yield the 81-iodo
dendritic core 12.[10b]
Coupling between the phenol dendron 5 and the dendritic
core, using either of two methods, proceeded with similar
yields. The first method involved reaction between the 9-
Abstract in French: Nous reportons ici la synthꢀse et lꢁutilisa-
tion de nouveaux dendrons tris-alcynes (composꢂs 2 ꢃ 5). La
rꢂaction de Williamson entre 5 et les cœurs dendritiques poly-
iodꢂs comportant 9, 27 ou 81 branches (composꢂs 9, 11 et
12) conduit aux dendrimꢀres poly-alcynes ꢃ 27, 81 et 243
branches respectivement (composꢂs 13 ꢃ 15). La rꢂaction
“click” de ces dendrimꢀres avec lꢁazidomꢂthylferrocꢀne (20)
permet dꢁobtenir des dendrimꢀres polyferrocꢂniques ꢃ 27, 81
et 243 branches (composꢂs 16 ꢃ 18). La reconnaissance ꢂlec-
iodomethyl
dendron 5 in the presence of K2CO3 (Scheme 2). The second
involved the 9-chloromethyl(dimethyl)silyl dendritic core 8,
ACHTUNGTREN(NUNG dimethyl)silyl dendritic core 9 and the phenol
AHCTUNGTRENNUNG
together with a stoichiometric amount of NaI, the phenol
dendron 5, and K2CO3. Both methods gave the 27-propargyl
dendrimer 13 in 65–70% yield. The MALDI-TOF mass
spectrum showed the [M+Na]+ peak at m/z 4415.1 (calcd
for [M+Na]+ 4415.7; see the Supporting Information). The
first method was used with the 27-iodo dendritic core 11 to
yield the 81-alkynyl dendrimer 14 (Scheme 3), and with the
81-iodo dendritic core 12 to yield the 243-alkynyl dendrimer
15 (Scheme 4). The only difference was in the reaction time,
which was higher for each added generation. This set of
dendrimers was characterized by dynamic light scattering
(DLS) for the two larger dendrimers (6.2ꢁ0.2 nm for 14
trochimique dꢁoxo-anions (H2PO4 et ATP2ꢀ) et du cation
ꢀ
Pd2+ est comparꢂe avec trois dendrimꢀres polyferrocꢂniques,
et lꢁobtention dꢁꢂlectrodes de Pt modifiꢂes ꢃ lꢁaide de ces den-
drimꢀres pour cette reconnaissance est de plus en plus facile
lorsque la taille du dendrimꢀre augmente. Le premier dendri-
mꢀre “click” comportant 243 ferrocꢀnes est le meilleur de la
sꢂrie pour la modification dꢁꢂlectrodes de Pt. Ces ꢂlectrodes
sont robustes et recyclables avec ce dendrimꢀre, alors que les
dendrimꢀres “click” prꢂcꢂdemment publiꢂs nꢁꢂtaient pas utili-
sables pour cette fonction.
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D. Astruc et al.
Scheme 2. Synthesis of the 27-alkynyl dendrimer 13 and 27-ferrocenyl dendrimer 16. For the synthesis of 9, see ref. [10].
1
and 6.6ꢁ0.2 nm for 15), H, 13C, 29Si, and DOSY NMR, IR,
and elemental analysis (see the Experimental Section). Size-
exclusion chromatography (SEC) showed the size progres-
sion from 13 to 15 (retention times of 20.53, 18.70, and
17.67 min, respectively) and the low polydispersities (1.02
for each compound). The size progression was also shown
by the DOSY NMR data (4.1, 4.8, and 4.9 nm, respectively).
Huisgen 1,3-dipolar cycloaddition reactions of 13, 14, and
15 with azidomethylferrocene, 20, were “catalyzed” by CuI
(used in stoichiometric amount)[12d] in a homogeneous THF/
water medium yielding the 27-ferrocenyl dendrimer 16
(Scheme 2), the 81-ferrocenyl dendrimer 17 (Scheme 3), and
the 243-ferrocenyl dendrimer 18 (Scheme 4), under the
same reaction conditions (Scheme 5).[14] These functional-
ized dendrimers were characterized by DLS for the largest
1
(5.3ꢁ1.0 nm for 18), SEC, H, 13C, 29Si, and DOSY NMR,
IR, and cyclic voltammetry (see the Experimental Section
and the Supporting Information). SEC showed the size pro-
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New Alkynyl and Ferrocenyl Dendrimers
FULL PAPER
Scheme 3. Synthesis of the 81-alkynyl dendrimer 14 and 81-ferrocenyl dendrimer 17. For the synthesis of 11, see ref. [10].
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D. Astruc et al.
Scheme 4. Synthesis of the 243-alkynyl dendrimer 15 and 243-ferrocenyl dendrimer 18. For the synthesis of 12, see ref. [10].
gression from 16 to 18 (retention times of 20.18, 18.70, and
17.82 min, respectively) and the low polydispersities (1.01 to
1.03). The size progression was also shown by the DOSY
NMR data (3.2, 3.8, and 4.2 nm, respectively).
0.61 V versus the internal reference redox system [FeACHTUNGTRENNUNG
(h5-
C5Me5)2]+/0 (Table 1).[15] This wave corresponds to the
oxido-reduction of the ferrocenyl group and shows that all
of the ferrocenyl groups of the dendrimer are equivalent
and independent on the electrochemical time scale. The
number of ferrocenyl units was determined to be 30ꢁ3 for
the 27-ferrocenyl dendrimer 16, using the Bard–Anson
Cyclic voltammetry and electrochemical sensing: The cyclic
voltammogram of 16 shows a single reversible wave at
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New Alkynyl and Ferrocenyl Dendrimers
FULL PAPER
slow heterogeneous electron
transfer between the electrode
and the dendrimer redox sites
is due to the very substantial
structural transformation of the
ꢀ
H2PO4 /redox site ensemble in
the course of electron transfer
(in particular, tight ion pairs or
Scheme 5. “Click” reactions with azidomethylferrocene 20.
Table 1. Electrochemical properties of the ferrocenyl CV waves for the
three polyferrocenyl dendrimers 16, 17, and 18.
E1/2 vs Fc*[a]
Epa ꢀ Epc [mV]
Ipc/Ipa
27-Fc 16[b]
81-Fc 17[b]
243-Fc 18[b]
0.610
0.600
0.595
30
0
0
3.80
1.90
2.00
[a] E1/2 in V vs Fc*=[FeACTHNUTRGNEUNG
(h5-C5Me5)2]+/0 (average of the cathodic and
anodic CV peaks). [b] Degassed solutions of the metallodendrimers in
CH2Cl2; concentrations: 1.7ꢃ10ꢀ5 m for 16, 5.8ꢃ10ꢀ6 m for 17, and 1.9ꢃ
10ꢀ6 m for 18.
equation.[3b,16,17] This kind of calculation is precluded for
compounds 17 and 18 by the adsorption of the dendrimers
onto the electrode surface, because it yields excessively high
Figure 1. Titration of [nBu4N]ACHTNUTRGNE[NUG H2PO4] with the 81-alkynyl dendrimer 17
in CH2Cl2 at 208C by adding the salt of the ion to the dendrimer solution.
Decrease of the intensity of the initial CV wave and increase of the in-
tensity of the new CV wave vs. the number of equivalents of [nBu4N]-
AHCTUNGTREN[GUNN H2PO4] added per ferrocenyl branch. (See the supporting information
for other titration curves).
ꢀ
results. Electrochemical recognition of both H2PO4 and
ꢀ
ATP2ꢀ was investigated. The interaction with HSO4 is
ꢀ
much weaker than that with H2PO4 , but the titration of
ꢀ
HSO4 was nevertheless possible.1
Numerous studies by Beer et al. with endoreceptors[18]
bearing one or more ferrocenyl groups have paved the way
for the recognition of oxo-anions. Addition of [nBu4N]-
ACHTUNGTRENNUNG[H2PO4] to an electrochemical cell containing a solution of
polyferrocenyl dendrimer (16, 17, or 18) in CH2Cl2 led to
the appearance of a new wave at a potential less positive
than the initial wave, the intensity of which decreased while
that of the new wave increased (Figure 1). The equivalence
point was reached when the initial wave was completely re-
placed by the new wave, as has previously been established
for endoreceptors[18] and other ferrocenyl dendrimer struc-
tures.[12] Analysis of the CV waves using the square scheme
has been rationalized by Echegoyen and Kaifer in a seminal
article.[19]
We used this analysis to determine the ratio of apparent
equilibrium constants K(+) and K(0) related to the strong in-
teraction of the anion with the cationic ferrocenium form of
the redox system, as well as with the neutral ferrocenyl form
(K@1). Only a rough estimate of K(+)/K(0) and K(+) values
could be obtained, because of the irreversible behaviour of
the CVs of the dendrimers in the presence of [nBu4N]-
A
2ACHTUNGTNER[NUNG ATP].
(EpcꢀEpa) values of 0.140ꢁ0.010 V for compound 16, under
the conditions of Figure 2 at the end of the titration. This
Figure 2. Cyclic voltammograms for the titration of [nBu4N]2ACTHNUTRGNE[NUG ATP] with
1
A slightly positive dendritic effect (i.e., the variation in E1/2 is larger for
the 27-ferrocenyl dendrimer 16 in CH2Cl2 at 208C by adding the salt of
the ion to the dendrimer solution: a) before addition of [nBu4N]2A[ATP],
b) during titration of [nBu4N]2A[ATP], and c) after addition of excess
[nBu4N]2A[ATP]; * internal reference: [Fe
(h5-C5Me5)2].
the dendrimer than for the monomer) is observed for the electrochemi-
cal recognition of the three oxo-anions by the dendrimer as compared
to their recognition by the ferrocenyl monomer 19.
CHTUNGTRENNUNG
CTHUNGTRENNUNG
C
ACHTUNGTRENNUNG
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D. Astruc et al.
aggregates are formed at the redox sites upon anodic oxida-
tion in CH2Cl2; vide infra). The difference in E1/2 values be-
tween the initial and the new wave (determined after addi-
For [nBu4N]ACTHNGUTERN[NUG HSO4] in CH2Cl2, the interaction with the
27-ferrocenyl dendrimer 16 was indeed weak, but the titra-
tion and the recognition could nevertheless be carried out.
tion of 0.5 equiv of [nBu4N]
G
The addition of [nBu4N]ACTHNGUTERN[UNG HSO4] to an electrochemical cell
both waves at the same time) was found to be 0.210ꢁ
0.010 V. This corresponds to a ratio of apparent association
constants (K(+)/K(0)) of 4200ꢁ400 according to the Echegoy-
en–Kaifer model.[19]
containing a solution of the dendrimer 16 in CH2Cl2 did not,
however, lead to the appearance of a new wave, and only a
shift of the CV wave towards a less positive potential was
observed (Figures 4 and 5). The maximum shifts of 75 mV
logðKðþÞ=Kð0ÞÞ ¼ DE1=2=0:058 at 20 ꢂC
For ATP2ꢀ, electrochemical recognition was also studied in
CH2Cl2, and the observed trends closely followed those
ꢀ
found for H2PO4 . The addition of [nBu4N]
N
electrochemical cell containing a solution of the 27-ferrocen-
yl dendrimer 16 in CH2Cl2 caused, as in the case of [nBu4N]-
ACHTUNGTRENNUNG[H2PO4], the appearance of a new wave at a potential less
positive than the initial one. Indeed, the interaction of the
anions with redox groups releases electron density, render-
ing oxidation of the ferrocene group easier. The intensity of
the initial wave decreased, while that of the new wave in-
creased (Figures 2 and 3). Thus, this is a case of a strong-
Figure 4. Titration of [nBu4N]ACTHNUTRGNE[UGN HSO4] with the 27-ferrocenyl dendrimer
16 in CH2Cl2 at 208C by adding the salt of the ion to the dendrimer solu-
tion: shift of Epa toward less positive potentials recorded by CV as a func-
tion of the number of equivalents of [nBu4N]ACTHNUTRGNE[NUG HSO4] added per ferrocen-
yl branch.
Figure 3. Titration of [nBu4N]2ACTHUNRTGNEUNG[ATP] with the 81-ferrocenyl dendrimer 17
in CH2Cl2 at 208C by adding the salt of the ion to the dendrimer solution.
Decrease of the intensity of the initial CV wave and increase of the in-
tensity of the new CV wave vs. the number of equivalents of [nBu4N]2-
ACHTUNGTRENNUNG[ATP] added per ferrocenyl branch (see Supporting Information for
other titration curves).
type interaction that can be treated using the square
Figure 5. Cyclic voltammograms for the titration of [nBu4N]
the 27-ferrocenyl dendrimer 16 in CH2Cl2 at 208C by adding the salt of
the ion to the dendrimer solution: a) before addition of [nBu4N][HSO4],
[HSO4]; * internal reference: [Fe
(h5-
ACHTUNGRTENN[UNG HSO4] with
scheme,[19] as with [nBu4N]
ACTHNUTRGNEU[NG H2PO4]. The difference in ferro-
ACHTUNGTRENNUNG
cenyl redox potential between the initial wave and the new
wave is of the same order of magnitude as with [nBu4N]-
ACHTUNGTRENNUNG
b) after addition of excess [nBu4N]
G
ACHTUNGTRENNUNG
C5Me5)2].
AHCTUNGTRENNUNG
corresponding ratio of apparent association constants is
K(+)/K(0) =1300ꢁ150. The equivalence point is reached
for the anodic wave potential and 70 mV for the cathodic
one were reached around the equivalence point, which al-
when 0.5 equiv of [nBu4N]2ACTHNUTRGNE[UNG ATP] has been added, which is
in accord with the double negative charge of this anion.
These strong interactions seen with [nBu4N][H2PO4] and
[nBu4N]2A[ATP] are all the more remarkable as there is no
conjugation between the triazole ring and the ferrocenyl
group.
lowed the titration of [nBu4N]
feature was that a rather strong adsorption was observed
throughout the titration. With [nBu4N][H2PO4] and
[nBu4N]2A[ATP], the wave was clearly electrochemically irre-
versible during the titration. The absolute apparent associa-
ACHTUNGRTEN[NUNG HSO4]. A further noteworthy
AHCTUNGTRENNUNG
G
ACHTUNGTRENNUNG
CHTUNGTRENNUNG
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New Alkynyl and Ferrocenyl Dendrimers
FULL PAPER
ꢀ
ꢀ
tion constant K(+) between compound 16 and the anion
HSO4 could then be defined by:
of the interactions with H2PO4 and HSO4 , and this differ-
ence is larger in the presence of the nearby triazole ring
than in its absence.[3b]
ꢀ
logKðþÞc ¼ DE1=2=0:058 at 20 ꢂC
Fabrication of electrodes modified with the “click” den-
drimers: The accessibility of modified electrodes[20] has also
been explored. Each generation of polyferrocenyl dendrimer
allows the fabrication of Pt electrodes with adsorbed dendri-
mer, but the capacity for strong adsorption on a Pt electrode
increases with increasing generation (Tables 3 and 4). The
first-generation dendrimer with 27 ferrocenyl groups does
not adsorb well, whereas that with 243 ferrocenyl groups ad-
sorbs very strongly and is resist-
giving K(+) =(4ꢁ0.4)ꢃ104 Lmolꢀ1. The same analyses with
ꢀ
ATP2ꢀ and H2PO4 were performed for the 81-ferrocenyl
dendrimer 17 and for the 243-ferrocenyl dendrimer 18. A
slightly positive dendritic effect (i.e., an increase in the po-
tential difference with increasing dendritic generation) was
ꢀ
observed for H2PO4 . The results are summarized in
Table 2.
ant to washing the salt of
Table 2. Results of the electrochemical recognition of the oxo-anions using the three ferrocenyl dendrimers
16, 17, and 18 and the three modified Pt electrodes.
ATP2ꢀ or Pd2+ with CH2Cl2
(Table 4 and Figure 6).
ꢀ
H2PO4
ATP2ꢀ
K(+)/K(0)
[a]
[b]
[b]
E1/2 (EpaꢀEpc)
DE1/2
K(+)/K(0)
E1/2[a] (EpaꢀEpc)
DE1/2
The modified electrodes were
compared after 50 adsorption
cycles and after 200 adsorption
cycles (see the Experimental
Section for details of the exper-
imental procedure). The inten-
sity obtained, the stability at
various scan rates (Figure 6),
27-Fc 16 on Pt
27-Fc 16[c]
–
–
–
4200
–
20400
–
0.410 (100)
0.430 (215)
0.390 (135)
0.420 (115)
0.375 (170)
0.415 (120)
0.200
0.180
0.210
0.180
0.220
0.180
2800
1300
4200
1300
6200
1300
0.400 (140)
–
0.350 (75)
–
0.340 (85)
0.210
–
0.250
–
81-Fc 17 on Pt
81-Fc 17[c]
243-Fc 18 on Pt
243-Fc 18[c]
0.255
24900
[a] E1/2 in V vs [FeACHTUNGTRENNUNG
in V. [c] Degassed solutions of the metallodendrimers in CH2Cl2; concentrations: 1.7ꢃ10ꢀ5 m for 16, 5.8ꢃ10ꢀ6
for 17, and 1.9ꢃ10ꢀ6 m for 18.
m
and the recognition of [Pd-
2
G
N
It is important to notice that
Table 3. Results of the electrochemical recognition of Pd2+ using the three ferrocenyl dendrimers 16, 17, and
18 and the three modified Pt electrodes.
the recognition is as good here
when the ferrocenyl unit is not
conjugated with the triazolyl
ring as when there is conjuga-
tion.[12d] A possible explanation
is that the chelation of the posi-
tively charged iron atom in the
oxidized ferrocenium form by
E1/2 (EpaꢀEpc)[a]
E1/2 (EpaꢀEpc)[a]
DE1/2 [mV]
K(+)
Before addition of Pd2+
After addition of excess Pd2+
27-Fc 16 on Pt
27-Fc 16[b]
0.610 (0)
0.610 (30)
0.600 (0)
0.600 (0)
0.595 (0)
0.595 (0)
0.645 (30)
0.650 (35)
0.650 (30)
0.650 (20)
0.660 (40)
0.660 (0)
ꢀ35
ꢀ40[c]
ꢀ50
ꢀ50
ꢀ65
ꢀ65
–
10700
–
15500
–
81-Fc 17 on Pt
81-Fc 17[b]
243-Fc 18 on Pt
243-Fc 18[b]
28600
ꢀ1/2
ꢀ
the two P O
bonds of
[a] E1/2 in V vs [FeACHTUNGTRENNUNG
ꢀ
H2PO4 is stabilized by the che-
gassed solutions of the metallodendrimers in CH2Cl2; concentrations: 1.7ꢃ10ꢀ5 m for 16, 5.8ꢃ10ꢀ6 m for 17, and
1.9ꢃ10ꢀ6 m for 18. [c] Shift of 40 mV toward more positive potential, in contrast to what is observed for
lating double H-bonding of the
ꢀ
O
two dihydrogenphosphate
[nBu4N]ACHTNUTRGNENG[U HSO4] (shift toward less positive potential).
Hd+ bonds with two neighbor-
ing nitrogen atoms of the tria-
zole ring (see below). This discards the direct intramolecular
ferrocenyl–triazole electronic interaction as being the most
[nBu4N]2ACTHNGUTERNNU[G ATP] (Figure 8) were explored (Table 2 and
Table 3). The robustness of the various modified electrodes
was tested by measuring the intensity before and after oper-
ation for 30 min (about 200 cycles) with a fresh solution of
0.1m [nBu4N]ACHTNUGTRNEG[UN PF6] in CH2Cl2 (Table 4). The electrode modi-
fied with 18 proved to be an excellent, re-usable redox
sensor.
Finally, electrochemical recognition of [Pd
by the dendrimers (Figure 9) was also found to be possible
but, as with [nBu4N][HSO4], was weak with only a CV wave
ACHUTNGTREN(NUG MeCN)4]ACHTUNGTRENNUNG[BF4]2
AHCTUNGTRENNUNG
shift rather than the appearance of a new wave. Moreover,
the CV waves remained fully chemically and electrochemi-
important factor of the oxo-anion–ferrocenium interaction
in the case of the “normal click” ferrocenyl dendrimers.[12d]
This chelating double H-bonding does not exist in the case
2
The addition of [PdACHTNUTRGNEN(UG MeCN)4]AHCUTNGTREN(NUGN BF4)2 to both the dendrimer solution and
ꢀ
of HSO4 , which is responsible for the difference in strength
the modified Pt electrode provokes only a shift of the CV wave.
Chem. Eur. J. 2009, 15, 2990 – 3002
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
2997

D. Astruc et al.
Table 4. Robustness of the various modified Pt electrodes.
cores yielding a 27-alkynyl, an
81-alkynyl, and a 243-alkynyl
dendrimer.
The “click” reaction of these
dendrimers with azidomethyl-
ferrocene yields the new 27-fer-
rocenyl, 81-ferrocenyl, and 243-
ferrocenyl dendrimers, which
are capable of electrochemical-
I [mA] after
200 cycles
adsorption
I [mA] after
200 cycles
in CH2Cl2
I [mA] after
50 cycles
adsorption
I [mA] after
recycling[b]
[a]
27-Fc 16 on Pt
81-Fc 17 on Pt
243-Fc 18 on Pt
11.6
26.6
40.2
7.8
18.5
22.6
6.4
11.6
11.8
1.7
7.4
8.2
[a] On the modified Pt electrode obtained after 200 adsorption cycles (see Experimental Section). [b] Intensity
obtained for the electrode after 50 adsorption cycles (see the Experimental Section) after titrating ATP2ꢀ and
washing with CH2Cl2.
Figure 7. Cyclic voltammograms for the recognition of Pd2+ by the modi-
fied Pt electrode with adsorbed 243-ferrocenyl dendrimer 18 in CH2Cl2 at
208C: a) before addition of [PdACHUTNGTRENNUG(MeCN)4]ACHTUNGTRENNUNG
excess [Pd(MeCN)4](BF4)2; * internal reference: [FeACHTUNGTRENNUNG
A
U
the flattening of the CV of the internal reference (for discussion, see
ref. [15b]).
ꢀ
ꢀ
ly recognizing oxo-anions such as HSO4 , H2PO4 , and
ATP2ꢀ as well as the Pd2+ cation.
Recognition of the phosphorus-containing oxo-anions re-
sults from a strong interaction with the ferrocenyl redox
system that is accentuated by the presence of the triazole
ring, probably due to double H-bonding to the N atoms. On
Figure 6. Stability of the Pt electrode with adsorbed 243-ferrocenyl den-
drimer 18 for various scan rates (from smaller to larger at 100, 200, 300,
400, 500, and 600 mVsꢀ1) observed by cyclic voltammetry.
ꢀ
the other hand, the interactions with HSO4 and Pd2+ are
cally reversible without adsorption. This is most likely indi-
cative of a weak ionic interaction. Interestingly, this is in
sharp contrast with the previously reported “normal click”
ferrocenyl dendrimers, which provided a strong interaction.
This is obviously due to the fact that the previous click fer-
rocenyl dendrimers were conjugated whereas the present
ones are not.
weak, but nevertheless allow titrations.
These three dendrimers form modified Pt electrodes,
which are increasingly robust with increasing size of the
dendrimer and allow the sensing of ATP2ꢀ better than in so-
lution. A positive dendritic effect is obtained with the modi-
fied electrodes, whereas this is not the case in solution. The
described access to such large “click” dendrimers represents
a significant advance, since it allows the preparation of
modified electrodes that could not be prepared with the pre-
vious series of “click” ferrocenyl dendrimers.
Conclusion
Prospective uses include the possibility of applying this
Williamson reaction to our larger polyiodo dendrimers and
of using the 1,2,3-triazole dendritic rings as ligands for
supramolecular catalysis applications using dendrimer-stabi-
lized nanoparticles.
New, easily prepared tris-alkynyl dendrons have been syn-
thesized from commercial precursors. The use of these den-
drons in dendrimer synthesis has been exemplified by their
efficient Williamson reactions with three polyiodo dendritic
2998
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ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 2990 – 3002

New Alkynyl and Ferrocenyl Dendrimers
FULL PAPER
Experimental Section
General: All operations were performed under nitrogen atmosphere
using standard Schlenk techniques. Prior to use, THF was dried over
sodium benzophenone ketyl and freshly distilled under a nitrogen atmos-
phere. Whenever mentioned, CH2Cl2 was dried over calcium hydride and
freshly distilled under a nitrogen atmosphere. All other reagents were ob-
tained from commercial sources and were used without further purifica-
tion. All glassware was previously dried in an oven and cooled under a
nitrogen flow.
Physical measurements: 1H NMR spectra were recorded at 258C on a
Bruker AC 250 (250 MHz), a Bruker Advance 300 (300 MHz), or a
Bruker DPX 400 (400 MHz) spectrometer. 13C NMR spectra were re-
corded in pulse FT mode on
a Bruker AC 300 spectrometer at
75.50 MHz. 29Si NMR spectra were recorded on a Bruker AC 300 spec-
trometer at 59.6 MHz. All chemical shifts are reported in parts per mil-
lion (d, ppm) with reference to SiMe4 (TMS). Mass spectra were ob-
tained at the CESAMO, Universitꢀ Bordeaux I, on a PerSeptive Biosys-
tems Voyager Elite (Framingham, MA) time-of-flight mass spectrometer.
This instrument is equipped with a nitrogen laser (337 nm), a delayed ex-
traction, and a reflector. It was operated at an accelerating potential of
20 kV in both linear and reflection modes. The mass spectra shown repre-
sent an average over 256 consecutive laser shots (3 Hz repetition rate).
Peptides were used to calibrate the mass scale using the two-points cali-
bration software 3.07.1 from PerSeptive Biosystems. Elemental analyses
were performed at the Center of microanalysis of the CNRS, Lyon Vil-
leurbanne, France. All electrochemical measurements were performed in
degassed CH2Cl2 at 208C. Supporting electrolyte: 0.1m [nBu4N]
ACHTUNGTRENNUNG[PF6];
working and counter electrode: Pt; quasi-reference electrode: Ag; inter-
[15]
nal reference: [Fe
(h5-C5Me5)2]+/0
;
scan rate: 0.200 Vsꢀ1
.
Modification of Pt electrodes with polyferrocenyl dendrimers 16, 17, and
18: A platinum electrode (Sodimel, Pt 30) was immersed in 10% aque-
ous HNO3 for 3 h, then rinsed with distilled water, dried in air, and pol-
ished using cerium oxide powder (5 MU). The dendrimers 16, 17, and 18
were electrodeposited onto such platinum-disk electrodes (A=
Figure 8. Cyclic voltammograms for the titration of [nBu4N]2ACTHNUTRGNE[UNG ATP] by
the modified Pt electrode with adsorbed 243-ferrocenyl dendrimer 18 in
CH2Cl2 at 208C: a) before addition of [nBu4N]2A[ATP], b) during titration
of [nBu4N]2A[ATP], and c) after addition of excess [nBu4N]2A[ATP]; * inter-
nal reference: [Fe
(h5-C5Me5)2].
CTHUNGTRENNUNG
C
CHTUNGTRENNUNG
ACHTUNGTRENNUNG
0.0078 cm2) from degassed solutions of metallodendrimer (1.7ꢃ10ꢀ5
(16), 5.8ꢃ10ꢀ6 m (17), and 1.9ꢃ10ꢀ6 m (18), in order to obtain the same
concentration in ferrocenyl groups) and [nBu4N][PF6] (0.1m) in CH2Cl2
by continuous scanning (0.20 Vsꢀ1) up to 50 cycles or up to 200 cycles be-
tween 0.0 and 0.9 V versus [Fe
(h5-C5Me5)2]+/0. The coated electrodes
m
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
were washed with CH2Cl2 in order to remove the solution of material
and dried in air. The modified electrodes were characterized by CV in
freshly distilled CH2Cl2 containing only the supporting electrolyte. They
showed a single symmetrical CV wave, and the linear relationship be-
tween the peak current and the potential sweep rate was verified. The
surface coverage G (molcmꢀ2) by the ferrocenyl dendrimers 16, 17, and
18 was determined from the integrated charge of the CV wave, G=Q/
nFA, where Q is the charge, n is the number of electrons transferred, F is
the Faraday constant, and A is the area. For example, the surface cover-
age for the electrode modified with 16 was 3.62ꢃ10ꢀ9 molcmꢀ2 (ferro-
cenyl sites), corresponding to 1.34ꢃ10ꢀ10 molcmꢀ2 of 16 after 50 adsorp-
tion cycles, and 6.23ꢃ10ꢀ9 molcmꢀ2 (ferrocenyl sites), corresponding to
2.31ꢃ10ꢀ10 molcmꢀ2 of 16 after 200 cycles (Table 5).
Synthesis of methyl 3,4,5-tris(prop-2-yn-1-yloxy)benzoate (2): A mixture
of methyl 3,4,5-trihydroxybenzoate 1 (10 g, 0.0543 mol) and propargyl
bromide (80% in toluene) (21 mL, 0.19 mol) was stirred for 10 min in de-
gassed acetone. K2CO3 (50 g, 0.362 mol) was then added, and the reaction
was carried out overnight under reflux. Thereafter, the solvent was re-
moved from the resulting brown solution by rotary evaporation. The
solid was redissolved in CH2Cl2 (200 mL), and this solution was dried
over anhydrous magnesium sulfate and filtered. The solvent was removed
by rotary evaporation. The product 2 was obtained as a slightly yellow oil
Figure 9. Cyclic voltammograms for the titration of [Pd
with the 81-ferrocenyl dendrimer 17 in CH2Cl2 at 208C by adding the salt
of the ion to the dendrimer solution: a) before addition of [Pd(MeCN)4]-
(BF4)2, b) after addition of excess [Pd(MeCN)4](BF4)2; * internal refer-
ence: [Fe
(h5-C5Me5)2].
ACHUTNGTREN(NUG MeCN)4]ACHTUNGTREN(NUNG BF4)2
AHCTUNGTRENNUNG
G
R
ACHTUNGTRENNUNG
that recrystallized (15.1 g, 93%). M.p. 89.48C; 1H NMR (300 MHz,
G
4
CDCl3, 258C, TMS): d=7.44 (s, 2H; HAr), 4.80 (d, J
N
p-O-CH2-C C), 4.78 (d, 4J
G
ꢃ
ꢃ
3H; CH3-O), 2.53 (t, 4J
G
(H,H)=2.3 Hz, 1H; C C-H); 13C NMR (75 MHz, CDCl3, 258C, TMS):
d=166.23, 151.27, 141.07, 125.74 (quat. CAr), 109.84 (CAr-H), 78.68, 77.94,
ꢃ
Chem. Eur. J. 2009, 15, 2990 – 3002
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
2999

D. Astruc et al.
Table 5. Electrode surface coverage (G in molcmꢀ2) for the various modified Pt electrodes.
151.67, 149.92, 136.63, 133.53 (quat.
CAr), 116.14, 116.08, 107.74 (CAr-H),
[a]
[a]
[b]
[b]
G [molcmꢀ2
]
G [molcmꢀ2
]
G [molcmꢀ2
]
G [molcmꢀ2
]
ꢃ
ꢃ
79.14, 78.37, 75.98, 75.34 (C C-H, C
C-H), 70.65 (CAr-CH2-O), 60.36,
(ferrocenyl sites)
(ferrocenyl sites)
27-Fc 16 on Pt
81-Fc 17 on Pt
243-Fc 18 on Pt
3.62ꢃ10ꢀ9
6.56ꢃ10ꢀ9
7.46ꢃ10ꢀ9
1.34ꢃ10ꢀ10
8.10ꢃ10ꢀ11
3.07ꢃ10ꢀ11
6.23ꢃ10ꢀ9
2.13ꢃ10ꢀ8
3.75ꢃ10ꢀ8
2.31ꢃ10ꢀ10
2.63ꢃ10ꢀ10
1.54ꢃ10ꢀ10
ꢃ
57.04 ppm (O-CH2-C C-H); IR: n˜ =
ꢀ1
ꢃ
ꢃ
2123 (C C), 3283 (C C-H), 3500 cm
(O-H); MS: m/z: 747 [2M+Na+], 385
[M+Na+]; elemental analysis calcd
(%) for C22H18O5: C 72.91, H 5.01, O
22.08; found: C 72.39, H 4.99, O 22.25.
[a] On the modified Pt electrode obtained after 50 adsorption cycles. [b] On the modified Pt electrode ob-
tained after 200 adsorption cycles.
General procedure for the synthesis of
the polyalkynyl dendrimers: A mix-
ture of poly-iodomethylACTHNUTRGENUG(N dimethyl)silyl dendritic core (1 equiv), phenol
ꢃ
ꢃ
ꢃ
76.22, 75.60 (C C-H, C C-H), 60.30, 57.05 (O-CH2-C C-H), 52.35 ppm
ꢀ1
ꢃ
ꢃ
(O-CH3); IR: n˜ =1724 (C=O), 2121 (C C), 3274 cm (C C-H); MS:
dendron 5 (2 equiv per branch), and K2CO3 (5 equiv per branch) was
stirred in dry DMF at room temperature (1 d for the 27-iodo, 2 d for the
81-iodo, and 4 d for the 243-iodo dendritic core) under nitrogen atmos-
phere. The mixture was then stirred for a further 48 h at 808C. There-
after, the solvent was removed in vacuo, and the residue was redissolved
in CH2Cl2. This solution was filtered through silica and concentrated by
rotary evaporation. The product was precipitated by treating the concen-
trated solution with excess MeOH three times to give the desired polyal-
kynyl dendrimer as an off-white gum in yields of 67, 61, and 59%, re-
spectively.
m/z: 619 [2M+Na+], 321 [M+Na+], 299 [M+H+].
Synthesis of [3,4,5-tris(prop-2-yn-1-yloxy)phenyl]methanol (3): LiAlH4
(19.3 g, 0.508 mol) was added to dry THF and this suspension was cooled
to 08C. A solution of methyl 3,4,5-tris(prop-2-yn-1-yloxy)benzoate 2
(15.1 g, 0.0507 mol) in dry THF was then added dropwise. The mixture
was stirred at 08C for 1 h, then at room temperature for a further 5 h.
Thereafter, excess LiAlH4 was quenched with water, and the solution
was concentrated by rotary evaporation. The concentrate was extracted
with CH2Cl2 (3ꢃ200 mL), and the combined organic layers were dried
over anhydrous magnesium sulfate and filtered. The solvent was removed
by rotary evaporation. The product 3 was obtained as a white powder
27-Alkynyl dendrimer 13: C261H282O45Si9; MW 4391.89 gmolꢀ1 1H NMR
;
(300 MHz, CDCl3, 258C, TMS): d=7.00–6.80 (m, 57H; HAr), 4.88 (s,
1
ꢃ
(9.6 g, 70%). M.p. 103.08C; H NMR (300 MHz, CDCl3, 258C, TMS): d=
18H; O-CH2-CAr), 4.74 (s, 54H; O-CH2-C C), 3.46 (s, 18H; Si-CH2-O),
4
ꢃ
ꢃ
ꢃ
6.78 (s, 2H; HAr), 4.76 (d, J
(H,H)=2.4 Hz, 4H; m-O-CH2-C C), 4.72 (d,
2.49 (s, 18H; C C-H), 2.47 (s, 27H; C C-H), 1.66 (s, 18H; CH2-CH2-
CH2-Si), 1.15 (s, 18H; CH2-CH2-CH2-Si), 0.60 (s, 18H; CH2-CH2-CH2-Si),
0.05 ppm (s, 54H, Si-CH3); 13C NMR (63 MHz, CDCl3, 258C, TMS): d=
156.46, 152.85, 152.03, 146.19, 136.98, 133.91 (quat. CAr), 116.45, 116.08,
4J
(H,H)=2.1 Hz, 2H; p-O-CH2-C C), 4.65 (s, 3J
(H,H)=6.1 Hz, 2H;
ꢃ
HO-CH2-CAr), 2.51 (t, 4J
(H,H)=2.4 Hz, 2H; C C-H), 2.46 (t, 4J
ACHTUNGTRNE(NUNG H,H)=
ꢃ
2.1 Hz, 1H; C C-H), 1.73 ppm (t, 3J
A
ꢃ
ꢃ
ꢃ
(75 MHz, CDCl3, 258C, TMS): d=151.59, 145.31, 137.38 (quat. CAr),
115.14, 108.04 (CAr-H), 79.55, 78.83, 76.34, 75.69 (C C-H, C C-H), 70.91
ꢃ
ꢃ
ꢃ
106.88 (CAr-H), 79.17, 78.51, 75.91, 75.29 (C C-H, C C-H), 64.93 (HO-
(CAr-CH2-O), 61.25 (Si-CH2-O), 60.72, 57.37 (O-CH2-C C-H), 44.29
ꢃ
ꢃ
ꢃ
CH2), 60.27, 56.94 ppm (O-CH2-C C-H); IR: n˜ =2121 (C C), 3294 (C
C-H), 3538 cmꢀ1 (O-H); MS: m/z: 563 [2M+Na+], 293 [M+Na+], 271
[M+H+].
(quat. C), 42.36 (CH2-CH2-CH2-Si), 18.24 (CH2-CH2-CH2-Si), 14.98 (CH2-
CH2-CH2-Si), ꢀ4.08 ppm (Si-CH3); 29Si NMR (60 MHz, CDCl3, 258C,
TMS): the spectrum showed only one peak at d=0.85 ppm (all the
branches had reacted); IR: n˜ =2122 (C C), 3291 cmꢀ1 (C C-H);
MALDI-TOF: m/z: calcd for 4415.7; found: 4415.1 [M+Na+]; elemental
analysis calcd (%) for C261H282O45Si9: C 71.38, H 6.47; found: C 70.41, H
6.30; DOSY NMR gave D=2.77ꢃ10ꢀ10 m2 sꢀ1 in chloroform at 258C,
which corresponds to a size of 4.1 nm; SEC showed the low polydispers-
ity (1.02) and the size progression for the three alkynyl dendrimers.
ꢃ
ꢃ
Synthesis of 5-(bromomethyl)-1,2,3-tris(prop-2-yn-1-yloxy)benzene (4):
Compound 3 (9.6 g, 0.0356 mol) and PBr3 (3.35 mL, 0.0356 mol) were
stirred together in CH2Cl2 (dried over calcium hydride and freshly dis-
tilled) for 12 h at room temperature. Water was then added to quench
the excess PBr3. The mixture was concentrated by rotary evaporation
and extracted with CH2Cl2 (3ꢃ200 mL). The combined organic layers
were then dried over anhydrous magnesium sulfate and filtered. The sol-
vent was removed by rotary evaporation to give compound 4 as a slightly
yellow oil that recrystallized (9.2 g, 77%). M.p. 63.78C; 1H NMR
81-Alkynyl dendrimer 14: C882H1002O144Si36
;
MW 14918.46 gmolꢀ1
;
1H NMR (300 MHz, CDCl3, 258C, TMS): d=7.20–6.80 (m, 201H; HAr),
ꢃ
4.90 (s, 54H; O-CH2-CAr), 4.74 (s, 162H; O-CH2-C C), 3.57 (s, 18H;
inner Si-CH2-O), 3.48 (s, 54H; outer Si-CH2-O), 2.50 (s, 81H; C C-H),
(300 MHz, CDCl3, 258C, TMS): d=6.75 (s, 2H; HAr), 4.71 (d, 4J
A
ꢃ
4
ꢃ
2.6 Hz, 4H; m-O-CH2-C C), 4.67 (d, J
(H,H)=2.2 Hz, 2H; p-O-CH2-C
1.65 (s, 72H; CH2-CH2-CH2-Si), 1.16 (s, 72H; CH2-CH2-CH2-Si), 0.59 (s,
72H; CH2-CH2-CH2-Si), 0.12 (s, 54H; inner Si-CH3), 0.05 ppm (s, 162H;
outer Si-CH3); 13C NMR (75 MHz, CDCl3, 258C, TMS): d=158.00,
155.04, 151.41, 150.60, 144.76, 138.26, 135.58, 132.53 (quat. CAr), 126.14,
117.01, 114.70, 113.76, 112.38, 106.68 (CAr-H), 78.17, 77.44, 74.98, 74.34
C), 4.41 (s, 2H; Br-CH2-CAr), 2.52 (t, 4J
(H,H)=2.6 Hz, 2H; C C-H),
2.45 ppm (t, 4J
(H,H)=2.2 Hz, 1H; C C-H); 13C NMR (75 MHz, CDCl3,
ꢃ
258C, TMS): d=150.54, 136.16, 132.75 (quat. CAr), 108.42 (CAr-H), 78.06,
ꢃ
ꢃ
ꢃ
77.26, 75.19, 74.45 (C C-H, C C-H), 59.31, 56.04 (O-CH2-C C-H),
ꢀ1
52.61 ppm (CH2-Br); IR: n˜ =2120 cmꢀ1 (C C), 3290.6 cm (C C-H);
(C C-H, C C-H), 69.50 (CAr-CH2-O), 59.89, 59.27, 59.07, 55.98 (O-CH2-
ꢃ
ꢃ
ꢃ
ꢃ
MS: m/z: 355, 357 [M+Na+], 333, 335 [M+H+].
C C-H, Si-CH2-O), 42.00 (Cquat), 40.98 (CH2-CH2-CH2-Si), 16.61 (CH2-
ꢃ
CH2-CH2-Si), 13.53 (CH2-CH2-CH2-Si), ꢀ5.44, ꢀ5.60 ppm (Si-CH3); 29Si
Synthesis of the “trialkyne-phenol” dendron 4-{[3,4,5-tris(prop-2-yn-1-
yloxy)benzyl]oxy}phenol (5): Hydroquinone (0.99 g, 9 mmol) and K2CO3
(0.89 g, 6.5 mmol) were stirred together at 808C in dry dimethylforma-
NMR (60 MHz, CDCl3, 258C, TMS): the spectrum showed only one
ꢃ
peak at d=0.793 ppm (all the branches had reacted); IR: n˜ =2122 (C
C), 3292 cmꢀ1 (C C-H); elemental analysis calcd (%) for
ꢃ
mide (DMF; 250 mL), and then
a solution of compound 4 (0.5 g,
C882H1002O144Si36: C 71.01, H 6.77; found: C 70.51, H 7.28; DOSY NMR
gave D=2.41ꢃ10ꢀ10 m2 sꢀ1 in chloroform at 258C, which corresponds to a
size of 4.8 nm; DLS was indicative of only one population at a size of
6.2ꢁ0.2 nm; SEC showed the low polydispersity (1.02) and the size pro-
gression for the three alkynyl dendrimers.
1.5 mmol) in DMF (100 mL) was added dropwise over a period of 1 h.
The reaction was carried out for 18 h at 808C. The DMF was then re-
moved in vacuo and the residue was partitioned between water and
CH2Cl2. The organic layer was concentrated in vacuo and chromato-
graphed on silica gel, eluting first with CH2Cl2 and then with CH2Cl2/
MeOH 9:1. The obtained oil was dissolved in the minimum volume of
CH2Cl2 and precipitated using excess pentane. The “trialkyne-phenol”
dendron 5 was obtained as an off-white powder (0.5 g, 92%). M.p.
76.58C; 1H NMR (300 MHz, CDCl3, 258C, TMS): d=6.87–6.74 (m, 6H;
243-Alkynyl dendrimer 15: C2745H3162O441Si117
;
MW 46498.43 gmolꢀ1
;
1H NMR (300 MHz, CDCl3, 258C, TMS): d=7.14–6.75 (m, 633H; HAr
)
ꢃ
4.84 (s, 162H; O-CH2-CAr), 4.69 (s, 486H; O-CH2-C C), 3.50 (s, 72H;
inner Si-CH2-O), 3.42 (s, 162H; outer Si-CH2-O), 2.47–2.43 (m, 243H;
C C-H), 1.61 (s, 234H; CH2-CH2-CH2-Si), 1.11 (s, 234H; CH2-CH2-CH2-
Si), 0.54 (s, 234H; CH2-CH2-CH2-Si), 0.06 (s, 216H; inner Si-CH3),
0.01 ppm (s, 486H; outer Si-CH3); 13C NMR (75.5 MHz, CDCl3, 258C,
HAr), 4.95 (s, 2H; O-CH2-CAr), 4.76 (d, 4J
N
ꢃ
C C), 4.73 (d, 4J
G
ꢃ
3H; C C-H); 13C NMR (75 MHz, CDCl3, 258C, TMS): d=152.67,
ꢃ
3000
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ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 2990 – 3002

New Alkynyl and Ferrocenyl Dendrimers
FULL PAPER
TMS): d=159.05, 156.10, 152.49, 151.69, 139.33, 136.69, 133.58 (quat.
CAr), 127.21, 115.57, 114.83, 113.46, 107.76 (CAr-H), 79.24, 78.51, 76.04,
159.07 (inner quat. CAr), 156.10, 152.46, 152.22 (outer quat. CAr), 144.33,
143.60 (quat. Ctriazole), 139.26 (inner quat. CAr), 136.84, 133.51 (outer quat.
CAr), 127.18 (inner CAr-H), 123.48, 123.00 (Ctriazole-H), 116.07, 115.56
(outer CAr-H), 114.87 (inner CAr-H), 107.00 (outer CAr-H), 81.49, 81.21
(quat. Cferrocene), 72.02, 70.41, 68.93, 68.75, 66.30, 65.94 (Cferrocene-H), 63.04
(Ctriazole-CH2-O), 60.97 (Si-CH2-O), 50.02, 49.88 (Cferrocene-CH2-N), 43.06
(Cquat), 42.00 (CH2-CH2-CH2-Si), 17.62 (CH2-CH2-CH2-Si), 14.57 (CH2-
CH2-CH2-Si), ꢀ4.49 ppm (Si-CH3); 29Si NMR: the spectrum showed only
one peak at d=ꢀ0.412 ppm; no azide or alkyne absorption was visible in
the IR spectrum; DOSY NMR gave D=3.02ꢃ10ꢀ10 m2 sꢀ1 in chloroform,
which corresponds to a size of 3.8 nm; SEC showed the low polydispers-
ity (1.01) and the size progression for the three ferrocenyl dendrimers.
ꢃ
ꢃ
75.37 (C C-H, C C-H), 70.55 (CAr-CH2-O), 60.92, 60.35, 60.15, 57.06 (O-
ꢃ
CH2-C C-H, Si-CH2-O), 43.06 (quat. C), 42.09 (CH2-CH2-CH2-Si), 17.71
(CH2-CH2-CH2-Si), 14.62 (CH2-CH2-CH2-Si), ꢀ4.51 ppm (Si-CH3); 29Si
NMR (59.6 MHz, CDCl3, 258C, TMS): the spectrum showed only one
ꢃ
peak at d=0.792 ppm (all the branches have reacted); IR: n˜ =2122 (C
C), 3293 cmꢀ1 (C C-H); DOSY NMR gave D=2.35ꢃ10ꢀ10 m2 sꢀ1 in
ꢃ
chloroform at 258C, which corresponds to a size of 4.9 nm; DLS was indi-
cative of only one population at a size of 6.6ꢁ0.2 nm; SEC showed the
low polydispersity (1.02) and the size progression for the three alkynyl
dendrimers.
243-Ferrocenyl
dendrimer
18:
C5418Fe243H5835N729O441Si117
;
MW
Second procedure for the synthesis of the 27-alkynyl dendrimer 13: The
105080.24 gmolꢀ1
;
1H NMR (300 MHz, CDCl3, 258C, TMS): d=7.61,
nona-chloromethyl
(dimethyl)silyl dendrimer
8
(0.1 g, 0.069 mmol),
7.59 (s, 243H; Htriazole), 7.16–6.64 (m, 633H; HAr), 5.15–5.01 (m, 972H;
Ctriazole-CH2-Cferrocene, Ctriazole-CH2-O), 4.70 (s, 162H; CAr-CH2-O), 4.22–
4.08 (m, 2187H; Cferrocene-H), 3.51 (s, 72H; inner Si-CH2-O), 3.43 (s,
162H; outer Si-CH2-O), 1.60 (s, 234H; CH2-CH2-CH2-Si), 1.10 (s, 234H;
CH2-CH2-CH2-Si), 0.55 (s, 234H; CH2-CH2-CH2-Si), 0.07 (s, 216H; inner
Si-CH3), 0.02 ppm (s, 486H; outer Si-CH3); 13C NMR (75.5 MHz, CDCl3,
258C, TMS): d=159.09 (inner quat. CAr), 156.08, 152.46, 152.22 (outer
quat. CAr), 144.33, 143.60 (quat. Ctriazole), 138.92 (inner quat. CAr), 136.81,
133.48 (outer quat. CAr), 128.85, 127.17 (inner CAr-H), 123.42, 122.97
(Ctriazole-H), 115.82, 115.55 (outer CAr-H), 114.87 (inner CAr-H), 106.99
(outer CAr-H), 81.56, 81.24 (quat. Cferrocene), 72.07, 70.41, 68.93, 68.61,
66.34, 65.94 (Cferrocene-H), 63.08 (Ctriazole-CH2-O), 60.95 (Si-CH2-O), 50.02,
49.87 (Cferrocene-CH2-N), 43.06 (Cquat), 42.54 (CH2-CH2-CH2-Si), 17.62
(CH2-CH2-CH2-Si), 14.66 (CH2-CH2-CH2-Si), ꢀ4.44 ppm (Si-CH3); 29Si
NMR: the spectrum showed only one peak at d=ꢀ0.425 ppm; no azide
or alkynyl absorption was visible in the IR spectrum. DOSY NMR gave
sodium iodide (0.1 g, 0.67 mmol), and the phenol dendron 5 (0.45 g,
1.24 mmol) were stirred in DMF at 808C for two days and then for a fur-
ther day at room temperature. The DMF was then removed in vacuo.
The residue was redissolved in CH2Cl2 and the product was precipitated
with excess MeOH to give the 27-propargyl dendrimer, 10, as an off-
white gum (0.21 g, 70%). The spectroscopic data were identical to those
obtained in the first synthesis (vide supra).
General procedure for the “click” coupling: The polyalkynyl dendrimer
(1 equiv) and azidomethylferrocene 20 (2 equiv per branch) were dis-
solved in THF (30 mL). Copper(II) sulfate pentahydrate (4 equiv per
branch) was then added with a small amount of water (20 mL), and the
mixture was stirred and heated until complete dissolution. Sodium ascor-
bate (8 equiv per branch) was dissolved in water (10 mL) and this solu-
tion was added dropwise to the mixture. The resulting mixture was
stirred overnight at room temperature under a nitrogen atmosphere. It
was then concentrated by rotary evaporation and the residue was parti-
tioned between CH2Cl2 and aqueous ammonia solution. The organic
layer was washed with water, dried over anhydrous magnesium sulfate,
filtered, and concentrated by rotary evaporation. The residue was puri-
fied by flash column chromatography, eluting first with CH2Cl2 and then
with CH2Cl2/MeOH 9:1, to yield the desired dendrimers as yellow pow-
ders in yields of 72, 70, and 69%, respectively.
D=2.74ꢃ10ꢀ10 m2 sꢀ1 in chloroform, which corresponds to
a size of
4.2 nm. DLS was indicative of only one population with a size of 5.3ꢁ
1.0 nm. SEC showed the low polydispersity (1.1) and the size progression
for the three ferrocenyl dendrimers.
Synthesis of the triazolylferrocenyl monomer 19: Propargyl alcohol
(50 mL, 0.86 mol) and azidomethylferrocene 20 (0.1 g, 0.42 mmol) were
dissolved in THF (20 mL). Copper(II) sulfate pentahydrate (0.42 g,
1.7 mmol) was then added with a small amount of water (15 mL), and
the mixture was stirred and heated until complete dissolution. Sodium as-
corbate (0.66 g, 3.3 mmol) was dissolved in water (5 mL) and this solution
was added dropwise to the mixture. The resulting mixture was stirred at
room temperature overnight. It was then concentrated by rotary evapora-
tion and the residue was partitioned between CH2Cl2 and aqueous am-
monia solution. The organic layer was washed with water, dried over an-
hydrous magnesium sulfate, filtered, and concentrated by rotary evapora-
tion. The desired click-ferrocenyl monomer was precipitated with excess
pentane. It was recovered in quantitative yield as a yellow powder
(0.12 g). M.p. 161.28C; 1H NMR (300 MHz, CDCl3, 258C, TMS): d=7.42
27-Ferrocenyl
dendrimer
16:
C
558Fe27H579N81O45Si9;
MW
10900.88 gmolꢀ1
;
1H NMR (300 MHz, CDCl3, 258C, TMS): d=7.62, 7.60
(s, 27H; Htriazole), 7.12–6.66 (m, 57H; HAr), 5.24–5.05 (m, 108H; Ctriazole
-
CH2-Cferrocene, Ctriazole-CH2-O), 4.72 (s, 18H; CAr-CH2-O), 4.27–4.13 (m,
243H; Cferrocene-H), 3.48 (s, 18H; Si-CH2-O), 1.68 (s, 18H; CH2-CH2-CH2-
Si), 1.15 (s, 18H; CH2-CH2-CH2-Si), 0.60 (s, 18H; CH2-CH2-CH2-Si),
0.05 ppm (s, 54H; Si-CH3); 13C NMR (63 MHz, CDCl3, 258C, TMS): d=
156.44, 152.82, 152.58 (quat. CAr), 146.62 (core quat. CAr), 144.72, 143.98
(quat. Ctriazole), 137.10, 133.84 (quat. CAr), 123.77, 123.28 (Ctriazole-H),
116.38, 115.88 (CAr-H), 115.19 (core CAr-H), 107.26 (CAr-H), 81.80, 81.48
(quat. Cferrocene), 72.58, 70.73, 69.30, 69.14, 66.67, 66.01 (Cferrocene-H), 63.41,
63.36 (Ctriazole-CH2-O), 61.27 (Si-CH2-O), 50.40, 50.24 (Cferrocene-CH2-N),
44.31 (Cquat), 42.35 (CH2-CH2-CH2-Si), 18.24 (CH2-CH2-CH2-Si), 14.95
(CH2-CH2-CH2-Si), ꢀ4.04 ppm (Si-CH3); 29Si NMR: the spectrum
showed only one peak at d=ꢀ0.388 ppm; no azide or alkyne absorption
was visible in the IR spectrum; MALDI-TOF MS: m/z: calcd for 10924
[M+Na+]; found: 10927, side peaks: 10686 [Mꢀferrocenyl+], 10444
[Mꢀ2 ferrocenyl+], 9866 [Mꢀdendron+], 9632 [Mꢀdendronꢀferrocenyl+
]; DOSY NMR gave D=3.65ꢃ10ꢀ10 m2 sꢀ1 in chloroform, which corre-
sponds to a size of 3.2 nm; SEC showed the low polydispersity (1.03) and
the size progression for the three ferrocenyl dendrimers. Some signals ap-
peared as doublets in the NMR spectra due to the difference between
meta and para substituents (such as for the 81-ferrocenyl and the 243-fer-
rocenyl dendrimers).
(s, 1H; Htriazole), 5.29 (s, 2H; N-CH2-Cferrocene), 4.74 (d, 3J
2H; Ctriazole-CH2-OH), 4.29–4.19 (m, 9H; Cferrocene-H), 2.31 ppm (t, 3J-
(H,H)=6.1 Hz, 1H; O-H); 13C NMR (75.5 MHz, CDCl3, 258C, TMS):
ACHTUNGTREN(NUNG H,H)=6.1 Hz,
AHCTUNGTRENNUNG
d=147.43 (quat. Ctriazole), 120.91 (Ctriazole-H), 80.65 (quat. Cferrocene), 69.12,
68.95, 68.91 (Cferrocene-H), 56.70 (Cferrocene-CH2-N), 50.09 ppm (CH2-OH);
IR: no alkyne or azide absorption was visible; MS: m/z: 617 [2M+Na+],
320.05 [M+Na+], 298 [M+H+]; elemental analysis calcd (%) for
C14H15ON3Fe: C 56.59, H 5.09; found: C 56.82, H 5.34.
81-Ferrocenyl
dendrimer
17:
C1773Fe81H1893N243O144Si36
;
MW
Acknowledgements
34445.72 gmolꢀ1
;
1H NMR (300 MHz, CDCl3, 258C, TMS): d=7.62, 7.59
(s, 81H; Htriazole), 7.16–6.66 (m, 201H; HAr), 5.20–5.02 (m, 324H; Ctriazole
-
Financial support from the Institut Universitaire de France (IUF, D.A.),
the University Bordeaux I, the Centre National de la Recherche Scienti-
fique (CNRS), the Agence Nationale pour la Recherche (ANR
PNANO–06-NANO-026 BATMOL), and the Ministꢁre de la Recherche
et de la Technologie (MRT, Ph.D. grant to J.C.) is gratefully acknowl-
edged. We are grateful to a referee for excellent remarks.
CH2-Cferrocene, Ctriazole-CH2-O), 4.71 (s, 54H; CAr-CH2-O), 4.25–4.11 (m,
729H; Cferrocene-H), 3.54 (s, 18H; inner Si-CH2-O), 3.44 (s, 54H; outer Si-
CH2-O), 1.63 (s, 72H; CH2-CH2-CH2-Si), 1.12 (s, 72H; CH2-CH2-CH2-Si),
0.56 (s, 72H; CH2-CH2-CH2-Si), 0.12 (s, 54H; inner Si-CH3), 0.02 ppm (s,
162H; outer Si-CH3); 13C NMR (75.5 MHz, CDCl3, 258C, TMS): d=
Chem. Eur. J. 2009, 15, 2990 – 3002
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3001

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Received: September 26, 2008
Published online: February 3, 2009
3002
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