'Click' synthesis and redox properties of triazolyl cobalticinium dendrimers

Article abstract of DOI:10.1021/ic400747y

The derivatization of macromolecules with redox-stable groups is a challenge for molecular electronics applications. The large majority of redox-derivatized macromolecules involve ferrocenes, and there are only a few reports with cobalticinium. We report here the first click derivatization of macromolecules with the cobalticinium redox group using ethynylcobalticinium hexafluorophosphate, 1. Cu^I catalysis was used for these selective click metallodendrimer syntheses starting from 1 and providing the tripodal dendron 3 that contains three 1,2,3-triazolylcobalticinium termini and a phenol focal point and the dendrimers of generations 0, 1, and 2 containing 9, 27, and 81 triazolylcobalticinium units for the dendrimers 4, 5, and 6, respectively. Atomic force microscopy (AFM) statistical studies provided the progression of height upon increase of dendrimer generation. Cyclic voltammetry studies in MeCN and dimethylformamide (DMF) show the solvent-dependent reversibility of the Co^III/II wave (18e/19e) and generation dependent reversibility of the Co^II/I (19e/20e) wave in DMF. The H₂PO₄ ^- anion is only recognized by the largest metallodendrimer 6 by a significant cathodic shift of the Co^III/II wave.

Full text of DOI:10.1021/ic400747y

Article
pubs.acs.org/IC
‘Click’ Synthesis and Redox Properties of Triazolyl Cobalticinium
Dendrimers
Amalia Rapakousiou, Yanlan Wang, Colette Belin, Noel Pinaud, Jaime Ruiz, and Didier Astruc*
̈
ISM, UMR CNRS N° 5255, Univ. Bordeaux 1, 33405 Talence Cedex, France
S
* Supporting Information
ABSTRACT: The derivatization of macromolecules with redox-
stable groups is a challenge for molecular electronics applications.
The large majority of redox-derivatized macromolecules involve
ferrocenes, and there are only a few reports with cobalticinium. We
report here the first click derivatization of macromolecules with the
cobalticinium redox group using ethynylcobalticinium hexafluor-
ophosphate, 1. CuI catalysis was used for these selective click
metallodendrimer syntheses starting from 1 and providing the
tripodal dendron 3 that contains three 1,2,3-triazolylcobalticinium
termini and a phenol focal point and the dendrimers of generations
0, 1, and 2 containing 9, 27, and 81 triazolylcobalticinium units for
the dendrimers 4, 5, and 6, respectively. Atomic force microscopy
(AFM) statistical studies provided the progression of height upon
increase of dendrimer generation. Cyclic voltammetry studies in MeCN and dimethylformamide (DMF) show the solvent-
dependent reversibility of the CoIII/II wave (18e/19e) and generation dependent reversibility of the CoII/I (19e/20e) wave in
DMF. The H2PO4− anion is only recognized by the largest metallodendrimer 6 by a significant cathodic shift of the CoIII/II wave.
have been synthesized in this way,18 and advantage of the
INTRODUCTION
■
introduction of trz ligands on the dendritic tethers has appeared as
Cobalticinium salts1 have been the subject of attention for their
a powerful means to stabilize palladium19 and gold20 nanoparticles
useful electrochemistry and electron-transfer chemistry. They
with remarkable catalytic19 and sensor properties.18
present a relative stability of three oxidation states, including the
Recently, complexes containing a single trz-cobalticinium unit
19-electron neutral cobaltocene1,2 and the very electron rich 20-
have been synthesized from ethynylcobalticinium, verifying the
electron cobaltocene anion.3 When redox-reversible transition-
possibility to link cobalticinium to other groups in this way by
metal complexes are linked to nanosystems, they undergo
CuAAC click chemistry.21 Herein we now report the use of the
chemically and electrochemically reversible transfer of a large
click CuAAC strategy using ethynyl cobalticinium to synthesize a
metallodendron with 1→3 connectivity22 and three generations
number of electrons, and these multiple redox processes are
useful for nanodevices behaving as nanobatteries,4 redox
(G0, G1, and G2) of cobalticinium dendrimers 4, 5, and 6 (Chart 1)
sensing,5 and biosensing,6 modified electrode surfaces7 and
with the same connectivity containing respectively 9, 27, and 81
redox catalysis.8 Poly cobalticinium receptors were extensively
cobalticinium termini. Cyclic voltammetry studies of these new
studied by Beer et al. for anion recognition,5 and various cobaltici-
redox-active metallodendrimers including redox recognition of the
nium polymers obtained either by ring-opening cobaltocenophane9
or from cobalticinium carboxylic acid as a side group10 have been
reported.
H2PO4− anion with positive dendritic effects23 are also reported
here.
Metallodendrimers have a rich chemistry that has been
extensively reviewed.11 The dendritic structures offer the
opportunity of introduction of many redox centers at the
periphery of the molecular frame, allowing multiple possibilities
of functionalization.12 This concept has been widely studied with
ferrocene dendrimers.13 However, cobalticinium dendrimers are
much less developed even though they have been already
reported by several groups.14 These metallodendritic syntheses
have systematically used cobalticinium carboxylic acid. Click
methodology,15 in particular the copper catalyzed azide−alkyne
cycloaddition (CuAAC) forming 1,2,3 triazoles (trz),16 however,
has recently appeared as one of the most powerful and practical
means to form such nanoassemblies.17 Ferrocenyl dendrimers
RESULTS AND DISCUSSION
■
1. Synthesis of the Dendrimers Series and Phenol-
triallyl Dendron. The construction for the G0, G1, and G2
chloromethyl(dimethyl)silyl dendrimers with 1→3 connectiv-
ity22 were synthesized as described previously upon CpFe+-
induced triallylation of mesitylene and p.methoxytoluene
followed, after decomplexation, by hydrosilylation of the
polyallyl dendritic cores and dendron using chloromethyldime-
thylsilane and iteration using a Williamson reaction with the
Received: March 26, 2013
© XXXX American Chemical Society
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Chart 1
Scheme 1. Click Synthesis of the tris-trz-Cobalticinium Phenoltriallyl Dendron 3
tribranched phenol dendron (phenol triallyl).24 The terminal
chloro groups were then substituted by azido groups by reaction
with sodium azide providing azido-terminated dendrimers and
dendron.18
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2. Click Synthesis of the Dendron and Dendrimers.
Ethynylcobalticinium 1 was synthesized as previously described
in 60% overall yield from cobalticinium hexafluorophosphate.25
The uncatalyzed Huisgen reaction26 between 1 and benzyl azide
conducted in the absence of copper catalyst in 1,2 dimethoxy-
ethane at 80 °C was completed in 2 days giving 92% of the 1−4
disubstituted triazole 2 (a) and only 8% of the 1−5 disubstituted
triazole 2 (b) (see Supporting Information). The selectivity for
the 1−4 isomer is remarkable under these conditions; it is likely
due to steric reasons favoring the 1−4 substitution.23 The
mixture of isomers was characterized by 1H, 13C, and 31P NMR,
IR, UV−vis, and ESI mass spectrometry. Comparing to the
CuAAC click reaction with the use of copper catalyst (CuSO4 +
ascorbic acid), however, the latter does not give isomerization at
all, but only the 1−4 disubstituted trz product, and the reaction is
much more rapid. Consequently, the catalyzed CuAAC reaction
of 1 with the azido-terminated dendron and dendrimers was
appropriate for the metallodendrimer assembly. Thus the
syntheses of the trz-cobalticinium dendron 3 and dendrimers
4, 5, 6 were carried out using CuSO4/sodium ascorbate between
the terminal alkyne 1 and the tris-azido phenoltriallyl dendron
(Scheme 1) and three generations G0, G1, and G2 of dendrimers
dend-N3 containing 3, 9, 27, 81 azido termini respectively
(Scheme 2). The solvents in each reaction were chosen to
acetone, acetonitrile, and DMF, whereas the dendrimer 6 can be
solubilized only in very polar solvents such as CH3CN, DMF,
and DMSO. The solubility of the products is summarized in
Table 1.
Table 1. Solubilities of the trz-Cobalticinium
Hexafluorophosphate Derivatives 2 (a), 3, 4, 5, and 6 as a
Function of the Number of trz-Cobalticinium Termini, at
a
25°C
product
CH2Cl2
THF
acetone
CH3CN/DMF
2 (a)
+
+
+
+
+
+
−
+
+
+
+
+
3
4
5
6
−
−
−
−
+
−
−
−
a
+: very soluble; −: insoluble.
The infrared spectra are a very useful tool to monitor the click
reactions, because the characteristic peak of the azido groups at
about 2094 cm−1 disappears at the end of the reactions
confirming that the azido groups are replaced by the 1,2,3-
triazole groups. The characteristic absorption of the PF6 anion of
these trz-cobalticinium products shows a strong band in the
range 836−838 cm−1. The absorptions due to the =C−H
stretching of the triazole and Cp groups of the trz-cobalticinium
unit are found in the range 3118−3127 cm−1 (Figure 1).
Scheme 2. Click Synthesis of the Dendrimers 4, 5, and 6 with
9, 27, and 81 trz-Cobalticinium Termini, Respectively
achieve the solubility of the final product, because the
polycationic cobalticinium dendrimers were soluble only in
high polarity solvents, the reaction of the dendron was carried
out in THF/H2O, that of 4 in CH3CN/H2O and those of 5 and 6
in a mixture of THF/CH3CN/H2O, because the azido-
terminated precursors were not soluble in CH3CN. The
temperature of the reaction was 60 °C, and the reactions were
left stirring during 16 h. The reactions needed stoichiometric
rather than catalytic amounts of CuI because of encapsulation of
CuI by coordinating to the resulting trz ligand, as previously
encountered with ferrocenyl analogues.18,27 The copper salt was
finally removed as [Cu(NH3)2(H2O)2] [SO4] by adding an
aqueous solution of NH3 that was left stirring for 15 min. The
resulting tris-trz-cobalticinium terminated dendron and trz-
cobalticinium dendrimers were purified, after workup, by precip-
itation in diethyl ether as orange powder. They were isolated as
orange-red products in high yields. They were characterized by 1H,
13C, and 29Si NMR, IR, UV−vis., DOSY NMR, MALDI-TOF mass
spectrometry, AFM measurements, cyclic voltammetry, and
elemental analysis.
Figure 1. IR spectra of the tris-azido phenoltriallyl precursor and
product 3 after the CuAAC click reaction.
NMR spectroscopy confirms the structure of the trz-cobalticinium
products. Particularly, in 1H NMR the formation of the trz ring is
clearly shown by the appearance of the peaks around 8.4 ppm (in
CD3COCD3) for the products 3, 4, and 5, and around 8.0 (in
CD3CN) for the product 6. In all the cases, the peak of SiCH2-N3 at
2.7−2.8 ppm has disappeared, whereas the appearance of the new
peak of SiCH2-trz takes place at about 4.1 ppm. The presence of the
trz group is also confirmed by the appearance of the characteristic
peaks of Cq and CH of trz as well as SiCH2-trz in the 13C NMR
spectra. The 29Si NMR spectra of the dendrimers are very simple,
showing one peak at 3.41 ppm (compounds 4 and 5) and 3.50 ppm
(compound 6) for SiCH2-trz and another smaller peak at 0.46 ppm
that corresponds to SiCH2O for compounds 5 and 6. Finally, the
3. Characterizations. The characterization of the dendritic
cobalticinium salts depends on their solubility that varies with the
number of cobalticinium moieties in the molecule. The trz-
cobalticinium group is very hydrophilic, and it is soluble only in
polar solvents. As the number of trz-cobalticinium groups
increases in a molecule, the polarity of the solvent in which it can
be solubilized also increases. Indeed the monomers 2 (a), 2 (b)
can be dissolved in dichloromethane, tetrahydrofuran (THF),
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Figure 2. AFM images and statistical height distribution of dendrimers 4, 5, and 6.
1
assignments of the number of protons in H NMR show the
expected ratio between the dendritic frame part and the
cobalticinium part, including for the large dendrimer 6.
at 354.8 nm, whereas a less intense absorption shoulder is
observed in the visible region peaking at about 427 nm. From the
Lambert−Beer’s law, we calculated the molar extinction coefficient
ε for the compounds 3, 4, 5, and 6. Its value increases upon increase
of dendrimer generation, which also confirms the progressivity of
the trz-cobalticinium generations (3, 4, 5, and 6). (For ε values: see
the Supporting Information)
DOSY (diffusion-ordered spectroscopy) experiments were
carried out for the dendrimers 4, 5, and 6. The main goal of these
experiments was to measure the diffusion coefficient D that was
Maldi-TOF mass spectrometry confirms the structure of the
positively monocharged trz-cobalticinium dendron 3 (showing
two PF6 anions) and trz-cobalticinium dendrimer 4 (see
Supporting Information). Elemental analysis also confirms the
structures of 3, 4, 5, and 6.
UV−visible Spectroscopy. A strong absorption band is
observed for all the dendrimers in the ultraviolet region peaking
D
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extracted from the DOSY 1H NMR spectra. The latter also reflect
the purity of the products. For compound 4, the average diffusion
coefficient value obtained is D = 2.85 ( 0.1) × 10−6 cm2/s. In the
case of the dendrimer 5 (27 branches), the calculated diffusion
coefficient is D = 2.58 ( 0.1) × 10−6 cm2/s, whereas in the case
of the dendrimer 6 (81 branches), the calculated diffusion
coefficient is D = 6.46 ( 0.1) × 10−7 cm2/s.
Table 2. Redox Potentials and Chemical (ia/ic) and
Electrochemical (Epa − Epc = ΔE) Reversibility Data for
a
Compounds 2(a)−6
CoIII/II [V]
CoII/I [V]
ΔE
solvent
E1/2
ΔE
ia/ic
E
ia/ic
2 (a)21
3
MeCN −0.75 0.060
MeCN −0.78 0.040
MeCN −0.78 0.060
1.0 Ep = −1.76
0.6 Ep = −1.72
1.0
0
0
0
0
In an effort to better characterize the three polycobalticinium
dendrimers and their interaction with surfaces, and obtain a
clearer evidence of the size progression, atomic force microscopy
(AFM) studies have been conducted. Freshly cleaved mica
surfaces (that have a negative surface charge density) have been
used as clean imaging substrates. A diluted acetonitrile solution
of each dendrimer was deposited on a mica surface by spin-
coating (800−1000 rpm for one minute, 0.1% w/w). In their
condensed phase, the dendrimers collapse onto the mica surface.
The height of the dendrimer layer usually represents a
monolayer, and the dendrimers agglomerate in large packages
of variable sizes on the surface.13 In our studies, the heights of the
dendrimers were quite uniform. Therefore, statistical study of the
height of each dendrimer by AFM analysis was obtained and
provided a clear evidence of the size progression upon increase of
dendrimer generation. (Figure 2).
b
3
3
4
DMF
−0.81 0.060
0.3 Ep = −1.81
0
0
MeCN −0.74 0.030
MeCN −0.74 0.065
DMF
0.5
1.1
0.7
0.3
2.0
0.9
2.7
0.9
1.0
E
1/2 = −1.65 0.050
0.2
b
4
4
5
−0.81 0.060
E
1/2 = −1.79 0.070
1/2 = −1.80 0.010
0.8
0.3
MeCN −0.75 0.015
MeCN −0.75 0.010
DMF
E
b
5
5
−0.82 0.060
E
1/2 = −1.77 0.060
1/2 = −1.78 0.050
1
b
6
MeCN −0.72 0.030
DMF
DMF
6
−0.82 0.040
−0.82 0.040
E
0.7
b
6
a
Supporting electrolyte: [n-Bu4N][PF6] 0.1M; working and counter
electrodes: Pt; reference electrode: Ag; internal reference: FeCp*2
b
(Cp* = η5-C5Me5); scan rate: 0.200 V s−1. Scanning until −1.0 V.
1
Although both the DOSY H NMR and AFM experiments
generations. This large adsorption phenomenon for the large
dendrimers is due to the low solubility of the reduced neutral
dendrimerinacetonitrile. The monomerand dendron compounds
2 (a) and 3 do not adsorb on the electrode. Adsorption begins
with the nona-cobalticinium dendrimer 4 (ia/ic =1.1) and
gradually increases as the generation number of dendrimer
increases. In particular, the ia/ic value for dendrimers 5 (Figure 3)
and 6 is 2.0 and 2.7 respectively (Table 2).
yield dendrimer sizes, the two methods are not comparable, because
the former provides a diameter that includes peripheral solvation or/
and even eventually dendritic agglomerates in solution, whereas the
latter gives the height (thicknesses) of a collapsed dendrimer in the
condensed phase. The reproducible DOSY measuments indicated
above leads to diameters of 4.8 nm for 4, 5.6 nm for 5, and 19.6 nm
for 6 that are much larger than the AFM thicknesses indicated in the
condensed phase for the reasons indicated above. In the present
case, it is highly probable that interdendrimer ion-pairing intervenes
for the formation of agglomerates in solution given the charged
branch termini of the dendrimers, which increases the observed
DOSY sizes in solution.
4. Cyclic Voltammetry Studies. The tris-triazolyl cobalti-
cinium dendron 3 and the three generations of triazolyl-
cobalticinium dendrimers (compounds 4, 5, and 6) were studied
by cyclic voltammetry using decamethylferrocene as the internal
reference.28 The cyclic voltammograms (CVs) were recorded in
acetonitrile and DMF, a good solubility being accessible with
both solvents, and the results are gathered in Table 2. The first
reduction wave of all the products corresponds to the reduction
of cobalticinium to the 19-electron complex cobaltocene
(CoIII/II), and the second wave corresponds to the reduction of
cobaltocene to the 20-electron cobaltocenyl anion (CoII/I). Both
waves are single in acetonitrile and DMF, which can be explained
by the weakness of the electrostatic factor between the redox sites
of the metallodendrimers, these redox centers being far from one
another and separated by long tethers.29
Figure 3. CV of 5 in CH3CN. The wave at 0.0 V corresponds to the
internal reference FeCp*2. Solvent: CH3CN; reference electrode: Ag;
working and counter electrodes: Pt; scan rate: 0.2 V/s; supporting
electrolyte: [n-Bu4N][PF6].
The first wave in both acetonitrile and DMF appears
chemically and electrochemically reversible, a result similar to
that obtained with the monomeric complex 2 (a).21 The
electrochemical reversibility involving equally all the redox
groups is due to very fast rotation within the electrochemical time
scale, where all the redox groups come close to the electrode
provoking fast electron transfer between all the redox groups and
the electrode,30 and/or the electron-hopping mechanism.31
Adsorption during the cyclic voltammetry recording of
dendrimer is common, and it is more marked with cationic
dendrimers than with neutral ones. It is observed for the first
wave only in acetonitrile, and it is marked for the high dendrimer
The second wave for compound 3 is completely irreversible
just like for the monomer 2 (a), whereas in dendrimers (4, 5, and 6)
the situation changes. In acetonitrile, this second wave is reversible at
the electrochemical time scale but chemically irreversible. This is
due to partial degradation of the dendritic products during reduction
(CoII/I), caused by population of antibonding e*1 orbitals, which
destabilizes the cobalt-ligand bonds in synergy with the solvent
interaction.32 This thermodynamic destabilization is indeed
combined with kinetic destabilization when the solvent is a ligand
that can easily displace the Cp ring, which is especially the case
with MeCN. This chemical irreversibility is responsible for the
appearance of a shoulder at the anode of the first wave during
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oxidation. Upon scanning until less negative potentials in the same
solvent, the first CoIII/II wave is completely reversible, and no
splitting is observed (Figure 4), showing that decomposition of the
sensing of anions are of importance in many fields, ranging from
environmental monitoring, biology, and industrial applications
to clinical diagnostics. To investigate this property, the
recognition of the H2PO4 anion as its n-Bu4N+ salt was probed.
Such redox recognition has been first studied by Beer’s group
with polycobalticinium endoreceptors,4 and extended by our
group to dendritic exoreceptors.23 Indeed, its addition to the
electrochemical cell containing compound 6 provokes a splitting
of the CoIII/II CV wave for which the new part resulting from the
addition of [n-Bu4N][H2PO4] is found at a potential 0.15 V more
negative than the original one (Figure 6). The electrostatic
Figure 4. CV of 4 in CH3CN. The wave at 0.0 V corresponds to the
internal reference FeCp*2. Solvent: CH3CN; reference electrode: Ag;
working and counter electrodes: Pt; scan rate: 0.2 V/s; supporting
electrolyte: [n-Bu4N][PF6].
Co complex does not occur at the 19-electron level, but only upon
scanning the 20-electron state. However, in DMF such degradation
does not take place as the second wave appears both chemically and
electrochemically reversible (Figure 5). Another observation is
Figure 6. CVs of compound 6: (a) In DMF, [n-Bu4N][PF6] 0.1M; see
Table 2 for data and conditions; (b) splitting of the reduction CV wave
upon addition of Bu4NH2PO4; (c) complete disappearance of the first
wave upon addition of Bu4NH2PO4.
binding of the anionic guest partly masks the positive charge,
rendering the positively charged cobalticinium moiety more
difficult to reduce to its neutral 19-electron form. Overall, the
reasons for redox recognition combine the electrostatic and
supramolecular interaction with dendritic (exoreceptor) effect.
The supramolecular interactions are those of the hydrogen
bonding between the OH groups of the H2PO4− anion and the
nitrogen atoms of the trz group and eventually the interaction of
oxygen atoms of the anion with the positively charged cobalt
center (or eventually a chelating interaction involving both the
trz and the Co center). The combined electrostatic and
supramolecular interactions are not sufficient, however, to
induce redox recognition in the present case (as in others
involving monomers and small dendrimers), as demonstrated by
the lack of redox recognition here with the trz-cobalticinium 2
(a), 3, 4, and 5. A significant topological effect is required in
synergy with the electrostatic and supramolecular effect to
recognize the oxo-anions. This strong dendritic effect (i.e., the
effect increases as the dendrimer generation increases) is only
obtained here with the second-generation metallodendrimer 6,
whereas interestingly it is insufficient with the zeroth and first-
generation dendrimers 4 and 5. This confirms the positive dendritic
effect in redox recognition, that is, the recognition improves as the
dendrimer generation increases (note that we believe that in
homogeneous catalysis, the dendritic effect with dendrimers
terminated with catalysts is negative for steric reasons33). These
trz-cobaticinium dendrimers are not adequate for H2PO4− anion
titration, however, because the exact number of equivalents of the
anion could not be calculated because of some precipitation
occurring during addition of [n-Bu4N][H2PO4].
Figure 5. (a) CV of 4 in DMF. (b) CV of 5 in DMF. The wave at 0.0 V
corresponds to the internal reference FeCp*2. Solvent: DMF; reference
electrode: Ag; working and counter electrodes: Pt; scan rate: 0.2 V/s;
supporting electrolyte: [n-Bu4N][PF6].
that the envelope of the first redox wave is broad, whereas in
the CoII/I wave that does not contain cationic species this
phenomenon does not appear. Thus the broad first wave could
be due to electrostatic interactions differentiating the various
single electron-transfer steps, that is, the electrostatic interaction
for the first electron transfer involves all the cationic charges,
whereas that for the last electron transfer involves only one
positive charge for the whole dendrimer. Interactions between
the cationic centers and the counteranions and the solvent
molecules are responsible for the variation of the energy engaged
in the heterogeneous electron transfers.
CONCLUDING REMARKS
■
Redox recognition of anions by cyclic voltammetry is possible
with the triazolylcobalticinium dendrimers. Recognition and
The paucity of cobalticinium chemistry has largely favored the
development of ferrocene-containing dendrimers and polymers.
F
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Dendrimer 4. The synthesis was carried out from ethynylcobalti-
cinium 1 (252 mg, 0.705 mmol) and G0−9N3 (79.1 mg, 0.052 mmol)
using the general procedure for click synthesis above. The reaction was
carried out into 20 mL of CH3CN−5 mL of H2O. Product 4 was
The great interest in polycationic dendrimers and polymers has
recently led to research on cobalticinium polymers especially
favored by the cobaltocenophane ring-opening polymerization
and the use of cobalticinium-carboxylic acid. Click chemistry
introduced a decade ago was ideal for the synthesis of
cobaltocenyl dendrimer and polymers, which has been achieved
for dendrimers in this article. The redox-active click
cobalticinium dendrimers also benefit from the location of a
1,2,3-triazolyl (trz) ring attached to the cobalticinium group.
Previous work has shown the interest of the trz ring as a ligand
that was very useful for the stabilization of catalytically active
nanoparticles19 in metallodendrimers and for sensing.17 Thus the
present click metallodendrimers that are the first cobalticinium
dendrimers benefit from both the trz unit attached to the
cobalticinium redox group allowing facile redox recognition of
substrates interacting with this heterocycle and the positive charge
on each dendrimer termini that should enable further supra-
molecular anion design and ion-pair interaction. These systems
will thus serve as a basis for further research in these directions as
well as the development of soft materials of interest. Reduction
studies of the trz-cobalticinium monomers involving 19-electron
species34 should also be extended to trz-cobalticinium dendrimers
and polymers to search for molecular battery materials. Such
studies are currently underway in our laboratory.
1
obtained as an orange-red powder (239 mg). Yield: 97% H NMR
(1D 1H), (CD3COCD3, 400 MHz): δppm: 8.39 (9H, CH of trz), 7.14
(3H, CH of arom.core), 6.39 (18H, CH of Cp sub.), 5.99 (18H, CH of
Cp sub.), 5.70 (45H, CH of Cp), 4.12 (18H, SiCH2-trz), 1.76 (18H,
CH2CH2CH2Si), 1.23 (18H, CH2CH2CH2Si), 0.71 (18H, 18H,
CH2CH2CH2Si), 0.10 (54H, Si(CH3)2). 13CNMR(1D1H), (CD3COCD3,
75 MHz): δppm: 146.72 (Cq of arom.core), 138.41 (Cq of trz), 125.92 (CHof
trz), 122.58 (CH of arom.core), 97.21 (Cq of Cp sub.), 86.78 (CH of Cp),
85.39, 81.59 (CH of Cp sub.), 44.84 (CqCH2CH2CH2Si), 42.63
(CqCH2CH2CH2Si), 41.87 (trz-CH2Si), 18.53 (CqCH2CH2CH2Si),
15.56 (CqCH2CH2CH2Si), −3.51 (Si(CH3)2). 29Si NMR (CD3COCD3,
79.5 MHz): δppm: 3.41 (9Si, SiCH2trz). MALDI-TOF-MS (m/z) of
C171H225Si9N27Co9(PF6)2: calc. 3729.0; found 3729.1. Anal. Calc. for
C171H219Si9N27Co9(PF6)9: C 43.32, H 4.66; found: C 43.59 H 4.82.
Dendrimer 5. The synthesis was carried out from ethynylcobalti-
cinium 1 (232 mg, 0.648 mmol) and G1-27N3 (100.0 mg, 0.016 mmol)
using the general procedure for click synthesis above. The reaction was
carried out into 15 mL of CH3CN−20 mL of THF and 5 mL of H2O.
Product 5 was obtained as an orange powder (202 mg). Yield: 80% 1H
NMR (1D 1H), (CD3COCD3, 400 MHz): δpmp: 8.37 (27H, CH of trz),
7.23, 6.91 (39H, CH of arom.core), 6.38 (54H, CH of Cp sub.), 5.97
(54H, CH of Cp sub.), 5.67 (135H, CH of Cp), 4.10 (54H, SiCH2-trz),
3.60 (18H, SiCH2O), 1.66 (72H, CH2CH2CH2Si), 1.20 (72H,
CH2CH2CH2Si), 0.66 (72H, 18H, CH2CH2CH2Si), 0.08 (216H,
Si(CH3)2). 13C NMR (1D 1H), (CD3COCD3, 75 MHz): δppm: 160.05
(arom. OCq), 139.76 (Cq of trz), 138.40 (Cq of arom.core), 128.02 and
114.34 (arom. CH), 125.92 (CH of trz), 97.35 (Cq of Cp sub.), 86.66 (CH
of Cp), 85.27, 81.44 (CH of Cp sub.), 60.81 (CH2OAr), 43.97
(CqCH2CH2CH2Si), 42.77 (CqCH2CH2CH2Si), 41.67 (trz-CH2Si),
18.26 (CqCH2CH2CH2Si), 15.33 (CqCH2CH2CH2Si), −3.78 (Si(CH3)2).
29Si NMR (CD3COCD3, 79.5 MHz): δppm: 0.46 (9 Si, SiCH2O), 3.41
(27Si, SiCH2trz). Anal. Calc. for C612H786Si36N81Co27O9(PF6)27: C 46.11,
H 4.97; found: C 45.98 H 5.12.
Dendrimer 6. The synthesis was carried out from ethynylcobalti-
cinium 1 (218 mg, 0.608 mmol) and G2-81N3 (100.0 mg, 0.005 mmol)
using the general procedure for click synthesis above. The reaction was
carried out into 15 mL of CH3CN−20 mL of THF and 5 mL of H2O.
Product 6 was obtained as an orange powder (175 mg). Yield: 73% 1H
NMR (1D 1H), (CD3CN, 400 MHz): δppm: 8.04 (81H, CH of trz), 7.15,
6.82 (147H, CH arom.), 6.16 (162H, CH of Cp sub.), 5.74 (162H, CH
of Cp sub.), 5.48 (405H, CH of Cp), 3.98 (162H, SiCH2-trz), 3.50 (72H,
SiCH2O), 1.57 (234H, CH2CH2CH2Si), 1.08 (234H, CH2CH2CH2Si),
0.56 (234H, 18H, CH2CH2CH2Si), 0.01 (702H, Si(CH3)2). 13C NMR
(1D 1H), (CD3CN, 75 MHz): δppm: 160.45 (arom. OCq), 140.60 (Cq of
arom.core), 138.77 (Cq of trz), 128.66 and 114.82 (arom. CH), 126.07
(CH of trz), 97.30 (Cq of Cp sub.), 87.10 (CH of Cp), 85.70, 81.89 (CH of
Cp sub.), 61.67 (CH2OAr), 44.31 (CqCH2CH2CH2Si), 42.92
(CqCH2CH2CH2Si), 42.31 (trz-CH2Si), 18.61 (CqCH2CH2CH2Si),
15.74 (CqCH2CH2CH2Si), −3.35 (Si(CH3)2). 29Si NMR (CD3CN, 79.5
MHz): δppm: 0.46 (36 Si, SiCH2O), 3.50 (81Si, SiCH2trz). Anal. Calc. for
C1935H2514Si117N243Co81O36(PF6)81(H2O)5: C 46.81, H 5.12; found: C
47.00 H 5.16.
EXPERIMENTAL SECTION
■
General Data. For general data including solvents, apparatuses,
compounds, reactions, spectroscopies, and CV, see the Supporting
Information. Gn indicates the generation number n. The mononuclear
compound 1 was synthesized according to ref 25.
General Procedure for the Click Synthesis of Polycobaltici-
nium Dendron and Dendrimers. The compound 1 (1.5 equiv per
branch) and the azido-terminated dendron or dendrimers (3, 4, 5, or 6)
were dissolved in degassed THF, CH3CN or both, then degassed water
was added and the reaction mixture was cooled to 0 °C. Then, an
aqueous solution of CuSO4 1 M (1.1 equiv per branch) was added
dropwise, followed by the dropwise addition of a freshly prepared
solution of sodium ascorbate (2.2 equiv per branch) The color of the
solution changed from orange to dark red upon addition of sodium
ascorbate. The reaction mixture was allowed to stir for 16 h at 60 °C
under nitrogen atmosphere. Then, the mixture of solvents was removed
under vacuum, and 100 mL of nitromethane was added followed by the
addition of an aqueous solution of ammonia. The mixture was allowed to
stir for 15 min to remove all the copper salt trapped inside the dendron
or dendrimer. The organic phase was washed twice with water, dried
over sodium sulfate, filtered, and the solvent was removed under
vacuum. Then the product was washed with THF to remove the excess
of alkyne and precipitated from an acetone or acetonitrile solution in
diethyl ether.
Tris-triazolylcobalticinium Dendron 3. The synthesis was carried
out from ethynylcobalticinium 1 (406 mg, 1.134 mmol) and tris-azido
phenoltriallyl dendron (144.6 mg, 0.252 mmol) using the above general
procedure for click synthesis. The reaction was carried out in 60 mL of
THF−40 mL of H2O. The product 3 was obtained as an orange-red
powder (400 mg). Yield: 96% 1H NMR (1D 1H), (CD3COCD3,
400 MHz): δppm: 8.39 (3H, CH of trz), 7.15 and 6.78 (4H, CH arom.),
6.42 (6H, CH of Cp sub.), 6.03 (6H, CH of Cp sub.), 5.73 (15H, CH
of Cp), 4.12 (6H, SiCH2-trz), 1.67 (6H, CH2CH2CH2Si), 1.18 (6H,
CH2CH2CH2Si), 0.67 (6H, 18H, CH2CH2CH2Si), 0.11 (18H, Si(CH3)2).
13C NMR (1D 1H), (CD3COCD3, 75 MHz): δppm: 155.74 (CqOH),
ASSOCIATED CONTENT
■
S
* Supporting Information
General data, detailed experimental procedures, spectroscopic
data for compounds, NMR, and MALDI-TOF mass spectra, and
CVs. This material is available free of charge via the Internet at
http://pubs.acs.org.
138.34 (Cq-trz), 128.14 and 115,63 (CH arom.), 125.77 (CH of trz), 97.02
(Cq of Cp sub.), 86.69 (CH of Cp), 85.29 (CH of Cp sub.), 81.52 (CH of
Cp sub.), 43.74 (CqCH2CH2CH2Si), 42.50 CqCH2CH2CH2Si), 41.67
(trz-CH2Si), 18.14 (CqCH2CH2CH2Si), 15.20 (CqCH2CH2CH2Si),
−3.82 (Si(CH3)2). MALDI-TOF-MS (m/z) of C61H77Si3N9Co3(PF6)2:
calc. 1503.29; found 1503.35. Anal. Calc. for C61H77Si3N9-
Co3(PF6)3(C4H8O): C 45.81, H 5.03; found: C 46.05 H 4.93.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: d.astruc@ism.u-bordeaux1.fr.
G
dx.doi.org/10.1021/ic400747y | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(g) Astruc, D., Ed.; Elsevier: Paris, C. R. Chim. 2003, 6, 709−1208.
(h) van Heerbeeck, R.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.; Reek,
J. N. H. Chem. Rev. 2002, 102, 3717−3756. (i) Astruc, D.; Heuze, K.;
Notes
The authors declare no competing financial interest.
Gatard, S.; Mer
(j) Liang, C.; Frec
(k) Scott, R.W. J.; Wilson, O. M.; Crooks, R. M. J. Phys.Chem. B 2005,
109, 692−704. (l) Mery, D.; Astruc, D. Coord. Chem. Rev. 2006, 250,
́
y, D.; Nlate, S. Adv. Syn. Catal. 2005, 347, 329−338.
ACKNOWLEDGMENTS
■
́
het, J. M. J. Prog. Polym. Sci. 2005, 30, 385−402.
Helpful assistance and discussion with Claire Mouche (mass
spectrometry), Jean-Michel Lanier (29Si NMR) from the
́
CESAMO, Universite
the Universite Bordeaux 1, the Centre National de la Recherche
Scientifique (CNRS) and the Agence Nationale de la Recherche
(ANR) are gratefully acknowledged.
́
Bordeaux 1, and financial support from
1965−1979. (m) de Jesus, E.; Flores, J. C. Ind. Eng. Chem. Res. 2008, 47,
7968−7981. (n) Astruc, D.; Boisselier, E.; Ornelas, C. Chem. Rev. 2010,
110, 1857−1959. (o) Caminade, A.-M.; Turin, C.-O.; Laurent, R.; Ouali,
A.; Delavaux-Nicot, B. Dendrimers. Towards Catalytic, Material and
Biomedical Uses; Wiley: Weinheim, Germany, 2011. (p) Campana, S.;
Ceroni, P.; Punteriero, F. Designing Dendrimers; Wiley: New York, 2012.
(12) (a) Newkome, G. R.; Moorefield, C. N.; Vogtle, F. Dendrimers and
Dendrons, Syntheses, Concepts, Applications; Wiley-VCH: Weinheim,
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