Giant cobalticinium dendrimers

Article abstract of DOI:10.1021/om900079y

Giant redox dendrimers were synthesized with pentamethylcobalticinium termini for the fifth, sixth, and seventh generations (in addition to the nine-arm generation 0) up to a theoretical number of 3⁹ tethers (seventh generation, G₇).

Full text of DOI:10.1021/om900079y

2716
Organometallics 2009, 28, 2716–2723
Giant Cobalticinium Dendrimers
Ca´tia Ornelas, Jaime Ruiz, and Didier Astruc*
Institut des Sciences Mole´culaires, UMR CNRS No. 5255, UniVersite´ Bordeaux 1,
351 Cours de la Libe´ration, 33405 Talence Cedex, France
ReceiVed January 31, 2009
Giant redox dendrimers were synthesized with pentamethylcobalticinium termini for the fifth, sixth,
and seventh generations (in addition to the nine-arm generation 0) up to a theoretical number of 39 tethers
(seventh generation, G7). Therefore, a functional pentamethyl cobalticinium derivative was synthesized
with a long arm. This tether-lengthening strategy was used as in the previously reported ferrocenyl and
pentamethylferrocenyl series to overcome the bulk constraint at the periphery of short-tethered dendrimers.
1
These polycationic cobalt-sandwich metallodendrimers were characterized by H, 13C, and 29Si NMR,
MALDI-TOF mass spectrometry (for generation 0), elemental analysis, UV-vis spectroscopy, dynamic
light scattering (DLS), atomic force microscopy (AFM), and cyclic voltammetry. UV-vis spectroscopy
and analytical data are consistent with a moderate amount of defects (G5 and G6) that largely increases
for G7 (which contains 14 000 ( 1000 pentamethylcobalticinium termini). Cyclic voltammetry reveals
full chemical and electrochemical reversibility for the cathodic reduction [dendr-C5H4CoIIICp*]+ f [dendr-
C5H4CoIIICp*] up to G7 as in the iron-sandwich series, showing that electron transfer is fast among the
flexible peripheral redox sites.
including very stable (although air -sensitive and reactive)
neutral cobaltocene,10 a so-called “19-electron” complex, and
a very electron-rich species, the 20-electron cobaltocene
anion.11 The cobalticinium moiety has been used inter alia
to design coordination polymers,12 organic-organometallic
crystals,13 and metal-containing polymers,14 for ion pairing
with metal-carbonyl anions,15 for anion recognition,16 to
induce radical polymerization,17 and as a starting point to
Introduction
Metallodendrimers1 belong to the rich family of metal-
containing macromolecules2 that have potential applications in
material science,3 biology,4 and catalysis.5 In particular, ferro-
cenyl dendrimers6 have attracted much attention because of their
properties in molecular electronics, sensing, redox catalysis, and
templates for the fabrication of precise nanoparticles of catalytic
interest.7
Since their first synthesis by Wilkinson in 1952,8 cobal-
ticinium salts (also named cobaltocenium) have been the
subject of attention,9 because their redox robustness provides
a useful electrochemistry and electron-transfer chemistry
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* Corresponding author. E-mail: d.astruc@ism.u-bordeaux1.fr.
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10.1021/om900079y CCC: $40.75
2009 American Chemical Society
Publication on Web 04/06/2009

Giant Cobalticinium Dendrimers
Organometallics, Vol. 28, No. 9, 2009 2717
build polyolefin and polybenzyl dendritic cores.18 Although
many ferrocenyl dendrimers are known,6,7 there are only few
reports on cobalticinium dendrimers,19,20 and the known
cobalticinium dendrimers are relatively small. Recently, we
constructed giant ferrocenyl dendrimers based on the tether-
lengthening strategy in order to provide more space around
the dendrimer periphery so that they can be functionalized
with redox groups at the end of the tethers of giant
dendrimers.7g Indeed, the de Gennes dense-packing limit,21
which applied to Tomalia’ seminal giant PAMAM dendrim-
ers,22 predicted a steric limit to the number of generations
due to periphery bulk.21 Although we have shown that back-
folding of small termini toward the dendrimer’s center thus
Scheme 1. Schematic Representation of the Tether-
Lengthening Strategy for the Introduction of Bulky
Functional Groups at the Periphery of Large Dendrimers
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partially circumvent the dense packing limit,23,24 back-folding
is all the less possible as the termini are larger.25 For instance,
with a former dendrimer series for which the tethers were
terminated by amidoferrocenyl groups, insolubility was
reached for a dendrimer containing 36 redox termini.7a Thus,
using the tether-lengthening construction, it was possible to
synthesize dendrimers with up to the seventh generation with
approximately 14 000 ferrocenyl units.9 We now report the
use of a related strategy (Scheme 1) to synthesize giant
dendrimers terminated by cobalticinium groups. The synthe-
ses, characterizations, and electrochemical properties of the
resulting giant pentamethylcobalticinium dendrimers are
detailed in this article.
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Results and Discussion
The strategy of lengthening the dendrimer tethers was applied
by introducing, in the cobalt-sandwich moiety, a presynthesized
functional cyclopentadienyl ligand bearing a long chain termi-
nated by an olefinic group. We choose the pentamethylcyclo-
pentadienyl ancillary ligand because of its ability to stabilize
the precursor cobalt(III) species, and the robustness and solubil-
ity properties that it brings to the cobalt system including its
dendritic series. Note the difference of approach compared to
the giant dendritic ferrocene series whereby the metallocene was
functionalized, due to its rich electrophilic chemistry, before
binding to the dendrimers.
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Maeda, K.; Miyazawa, M.; Unoura, K.; Kawaguchi, H. Inorg. Chem. 2004,
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1. Synthesis of the Organic Dendrimers. The dendritic
construction starts by the known nona-allylation of [FeCp(η6-
mesitylene)][PF6]26 giving the nona-allyl organic compound
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2718 Organometallics, Vol. 28, No. 9, 2009
Scheme 2. Synthesis of the G1-27-Allyl Dendrimer23
Ornelas et al.
1 after decomplexation, using visible light,27 of the dendritic
cores. It follows our previously reported procedure for the
iterative synthesis of giant polyolefin dendrimers that had
been constructed until generation 9 according to a catalytic
hydrosilylation/Williamson sequence of reactions (Schemes
2 and 3).23 In this 1f3 connectivity pioneered by Newko-
me,28 the number of terminal allyl branches is multiplied by
3 from a generation to the next one and is thus equal to 3n+2
,
the dendritic core of generation 0 containing 32 terminal allyl
groups.29
2. Functionalization of the Dendrimers with the
Pentamethylcobalticinium Termini. The pentamethylcyclo-
pentadienyl-cobalt chloride intermediate resulting from the
reaction between cobalt trichloride and pentamethylcyclopen-
(28) (a) Newkome, G. R.; Yao, Z.; Baker, G. R.; Gupta, V. K. J. Org.
Chem. 1985, 50, 2003. (b) Newkome, G. R.; Moorefield, C. N.; Baker,
G. R. Aldrichim. Acta 1992, 25 (2), 21.
(29) Sartor, V.; Djakovitch, L.; Fillaut, J.-L.; Moulines, F.; Neveu, F.;
Marvaud, V; Guittard, J.; Blais, J.-C.; Astruc, D. J. Am. Chem. Soc. 1999,
121, 2929–2930.

Giant Cobalticinium Dendrimers
Organometallics, Vol. 28, No. 9, 2009 2719
Scheme 3. Construction of the Organic Pentane-Soluble Dendrimer Precursors to the Metallocene-Terminated Dendrimers23
Scheme 4. Synthesis of the Pentamethylcobalticinium Salt 14 Containing a Long Alkyl Chain and a Phenol Termini
tadienyllithium is stable enough, in a dimeric form (unlike the
iron analogue), to withstand further substitution of the chloride
ligands by a functional cyclopentadienyl group.30 This property
allows the direct synthesis at -60 °C in THF of cationic mixed
cobalticinium derivatives containing both the pentamethylcy-
clopentadienyl and the functional cyclopentadienyl ligands.
Thus, the functionalized cyclopentadienyl 10 was used in the
synthesis of the pentamethylcobalticinium salt, yielding the
functionalized pentamethylcobalticinium salt 11. Hydrosilylation
of 11 with (dimethyl)chloromethylsilane in the presence of
Kartsted catalyst yielded compound 12. After substitution of
chloride by iodide yielding 13, Williamson reaction with
hydroquinone afforded the phenolic derivative 14 (Scheme 4).
The pentamethylcobalticinium dendrimers (Co*) were syn-
thesized using the Williamson reaction between the iodomethyl
dendrimers and 14. The reaction was carried out for G0, G5,
G6, and G7, and these metallodendrimers were characterized by
1H, 13C, and 29Si NMR, elemental analysis, UV/vis spectroscopy,
dynamic light scattering, and cyclic voltammetry (eqs 1-4).
The dendrimer 15 (G0-Co*) shows a broad peak near 6500 Da
(calcd for [C378H606O18Si18Co9]9+: 6 474.00 Da) in the MALDI-
TOF mass spectra. The elemental analyses of 16 (G5-Co*), 17
(G6-Co*), and 18 (G7-Co*) show a carbon deficiency that
becomes very important for G7-Co*, a general trend for giant
dendrimers of that generation, attributable to the enormous
encapsulation capacity (inorganic salts).
G5-2187-CH2I
8 G -21(817-6C)o*PF
(2)
(3)
(4)
14, K2CO3
5
6
(7)
DMF, 80 °C, 48h
G6-6561-CH2I
8 G -65(611-7C)o*PF
14, K2CO3
6
6
(8)
DMF, 80 °C, 48h
G7-19683-CH2I
(9)
8 G -196(8138-C)o*PF
14, K2CO3
7
6
DMF, 80 °C, 48h
3. Characterization of the Metallodendrimers 3.1. UV-
Vis Spectroscopy. In order to estimate the number of defects
in the dendritic structures due to the divergent synthesis, we
investigated the UV-vis spectroscopy of the metallodendrimers.
The Lambert-Beer law (A ) εlc) was used to determine the
actual total number of metallocene groups in the dendrimers.18
The UV-vis spectra of the metallocenes present an absorption
band at 399 nm in this pentamethylcobalticinium series. The
number of metallocene termini in each dendrimer can be
estimated by comparing the molar extinction coefficient ε of
the dendrimers with that of the corresponding monomer (ε0).
In the ferrocenyl series, the linearity of the absorption with the
number of redox groups in the low-generation metallodendrim-
ers confirmed that there is no interaction between the metallo-
cenyl groups that would perturb the validity of the Lambert-Beer

2720 Organometallics, Vol. 28, No. 9, 2009
Ornelas et al.
rate: 200 mV s-1, 20 °C, working and counter electrodes: Pt;
quasi-reference electrode: Ag). The adsorption phenomenon is
important specifically in acetonitrile, probably due to the low
solubility of the reduced neutral dendrimer in acetonitrile (Figure
1). DMF was used in order to observe the second reduction
wave CoII/CoI (Figure 2). In dichloromethane, the calculation
of the number of electrons using the Anson-Bard equation35
for G5-Co* gives a difference of only 20% (number of electrons
found is 2628 instead of 2187) attributable to adsorption.
Table 1. Number of Branches Calculated Using the Lambert-Beer
Law for Pentamethylcobalticinium Dendrimers
calculateda
theoretical number
of brances
number of
branches
dendrimer
λ (nm)
ε
monomer 14
G0-Co* (15)
G5-Co* (16)
G6-Co* (17)
G7-Co* (18)
399
399
399
399
399
1
9
ε0 ) 566
5319
1 105 973
3 603 810
9 ( 1
2000 ( 100
6400 ( 300
2187
6561
19 683
8 122 100 14000 ( 1000
a ε/ε0 represents the experimental branch number calculated from the
Lambert-Beer law.
The single wave can be explained by the weakness of the
electrostatic factor36 (influence of ion pairing36,37) among the
redox sites of the metallodendrimers, these redox centers being
very far from one another (large through-bond distances). The
electrochemical reversibility observed for all the generations
in dichloromethane shows that the electron-hopping mechanism
among the redox centers of the periphery is extremely efficient.4b,9
Thus, electron transfer is fast between all the redox groups of
the dendrimers and the electrode. The electron-hopping mech-
anism in metallodendrimers has been proposed by Amatore et
al.38a,b for dendrimers containing 64 peripheral branches ter-
minated by [Ru(terpy)2]2+. It is based on the measured electron-
hopping rate constant using ultramicroelectrodes and on a
Smoluchowski-type model developed to take into account
viscosity effects during the displacement of the RuIII/RuII(tpy)2
redox centers around their equilibrium positions.38c These studies
involved ultramicroelectrodes with very fast scan rates.39
Accordingly, the events have time to proceed within the time
scale of the present studies. Also note that the dendrimers rotate
fast within the electrochemical time scale, so that all the redox
groups come close to the electrode within this time scale.40 Fast
rotation alone can explain the fast heterogeneous electron
transfer with the small dendrimers. For the high generation,
however, the hopping mechanism between nearby centers
appears to be much easier than the fast-rotation mechanism. In
DMF, the second reduction wave CoII/CoI is observed at -2.19
V vs FeCp*2 and looks fairly normal,11 although not fully
chemically reversible. On the other hand, the first wave appears
considerably flattened, indicating that that all the CoIII centers
are not reduced at the same potential (same trend for the
oxidation of CoII) because of a very substantial electrostatic
factor.36 The solvent considerably influences ion pairing, whose
energy plays an important role in the redox potential.36 Thus
DMF strongly coordinates to the cationic CoIII species, unlike
the other solvents, which provokes the redox-potential distinction
among the redox sites of the dendrimer, and a broad envelope
of redox waves is observed. The CoII/CoI wave11 does not
involve cations, and this phenomenon does not appear, which
indicates that it is specific to cations.
law.23 Thus, we tentatively assume that this same law applies
to the cobalticinium dendrimers, although the dendrimers from
generations 1 to 4 were not synthesized. The number of termini
calculated using the Lambert-Beer law confirms the existence
of the defects in the dendritic structures that is marked for the
high generations (Table 1). More specifically, these defects are
not present in G0, they are relatively not numerous for
generations 5, but their number increases from G5 to G7 and
reached a high level for this last generation. The structural
defects are present in similar amounts independently of the
nature of the peripheral redox group. For example, G5-Fc (Fc:
ferrocenyl), G5-Fc* (Fc*: pentamethylferrocenyl), and G5-Co*
present an experimental number of termini of 2000 ( 100, and
G7-Fc, G7-Fc*, and G7-Co* all present an experimental number
of termini of 14 000 ( 1000. The similarity of these data for
the iron and cobalt series of dendrimers indicates that the defects
in the metallodendrimer structures are attributable to the
divergent construction rather than to metallocene branching.
3.2. Dynamic Light Scattering (DLS). DLS is a very useful
technique for the characterization of the metallodendrimers,
because it allows the determination of the size (hydrodynamic
diameter) of the dendrimers in solution and consequently their
diffusion coefficient (D) using the Stokes-Einstein equation D
) kT/6πηRh, where the Rh is the hydrodynamic radius, η is the
solvent viscosity, k is the Boltzmann constant, and T is the
temperature. It is known that dendrimers present globular shapes,
and usually they are considered as perfect spheres in order to
determine their physical properties. We also used this ap-
proximation to calculate the volume and the density of these
metallodendrimers (Table 2).
3.3. Cyclic Voltammetry. The four generations of pentam-
ethylcobalticinium dendrimers were studied by cyclic voltam-
metry. The cyclic voltammograms were recorded using dichlo-
romethane, acetonitrile, or dimethylformamide (DMF) as the
solvent. For the first reduction wave that corresponds to the
reduction of cobalticinium derivatives to cobaltocenes, in
dichloromethane, this wave is single and reversible and, in first
approximation (neglecting the electrostatic and statistic factors
that are very weak), at the same potential as that of monomeric
pentamethyl cobaltocene.10,11,18,31-34 The unicity of the first
reduction wave is observed in dichloromethane or acetonitrile
at -1.16 V vs FeCp2* (electrolyte: [n-Bu4N][PF6] 0.1 M, scan
(35) (a) Flanagan, J. B.; Margel, S.; Bard, A. J.; Anson, F. C. J. Am.
Chem. Soc. 1978, 100, 4248–4253. (b) Bard, A. J.; Faulkner, R. L.
Electrochemical Methods, 2nd ed.; Wiley: New York, 2001.
(36) (a) Barrie`re, F.; Camine, N.; Geiger, W. E. J. Am. Chem. Soc. 2002,
124, 7262–7263. (b) Barrie`re, F.; Geiger, W. E. J. Am. Chem. Soc. 2006,
128, 3980–3989.
(30) (a) Bunel, E. E.; Valle, L.; Manriquez, J. M. Organometallics 1985,
4, 1680–1682. (b) Ko¨lle, U.; Fuss, B.; Belting, M.; Raabe, E. Organome-
tallics 1986, 5, 980–987.
(37) Loupy, A.; Tchoubar, B.; Astruc, D. Chem. ReV. 1992, 92, 1141–
1165.
(31) Koelle, U.; Khouzami, F. Angew. Chem., Int. Ed. 1980, 19, 640–
641.
(32) (a) Ruiz, J.; Astruc, D. C. R. Acad. Sci. Paris, Se´r. II c 1998, 21–
27. (b) Ruiz, J.; Daniel, M.-C.; Astruc, D. Can. J. Chem. 2006, 84, 288–
299.
(33) Astruc, D. Electron Transfer and Radical Processes in Transition
Metal Chemistry; VCH: New York, 1995; Chapter 2.
(34) These references report electrochemical data for various cobal-
tocenes. For pentamethylcobaltocene itself, see ref 18.
(38) (a) Amatore, C.; Grun, F.; Maisonhaute, E. Angew. Chem., Int. Ed.
2003, 40, 4944–4947. (b) Amatore, C.; Bouret, Y.; Maisonhaute, E.;
Goldsmith, J. I.; Abrun˜a, H. D. Chem.-Eur. J. 2001, 7, 2206–2226. For
electrochemical redox recognition with ferrocene systems, see: (c) Beer,
P. D.; Gale, P. A. Angew. Chem., Int. Ed. 2001, 40, 486–506.
(39) See also Hauquier, F.; Ghilane, J.; Fabre, B.; Hapiot, P. J. Am.
Chem. Soc. 2008, 130, 2748.
(40) Gorman, C. B.; Smith, B. L.; Parkhurst, H.; Sierputowska-Gracz,
H.; Haney, C. A. J. Am. Chem. Soc. 1999, 121, 9958.

Giant Cobalticinium Dendrimers
Organometallics, Vol. 28, No. 9, 2009 2721
Table 2. Hydrodynamic Diameter of the Pentamethylcobalticinium Dendrimers Obtained by DLS and Calculated Diffusion Coefficient, Volume,
and Density of These Metallodendrimers
MW
hydrodynamic
diameterb (nm)
diffusion
density
(kg/m3)
dendrimera
(g mol-1
)
coefficientc (m2 s-1
)
volumed (m3)
G5-Co* (16)
G6-Co* (17)
G7-Co* (18)
2 101 351
6 305 795
18 919 128
28.5 ( 0.7
30.0 ( 0.8
32.1 ( 1.1
3.41 × 10-14
3.24 × 10-14
3.03 × 10-14
(1.21 ( 0.2) × 10-23
(1.41 ( 0.2) × 10-23
(1.73 ( 0.2) × 10-23
(2.9 ( 0.1) × 102
(7.4 ( 0.4) × 102
(1.8 ( 0.2) × 103
a It was not possible to obtain the hydrodynamic diameter of the dendrimer of G0 by DLS, because its size is below the limit for this technique.
b Measured at 25 °C in acetone; the hydrodynamic diameter value was obtained from statistical CONTIN analysis with 2% error. c Calculated using the
d
Stokes-Einstein equation. Considering the globular dendrimer shape a perfect sphere (V ) (4/3)πr3).
Figure 1. Cyclic voltammograms obtained for the G5-Co* (CoIII/CoII), in (a) dichloromethane and (b) acetonitrile (3 cycles).
Scheme 5.
Potential Function of G7 Pentame-
thylcobalticinium Dendrimers as Molecular Batteries Using
the Robustness of the Co(III)/Co(II) Redox System at -1.16
V vs Cp*2Fe+/Cp*2Fe
Figure 2. Cyclic voltammograms obtained for the G6-Co* in DMF.
E1/2(CoIII/CoII) ) -1.19 V vs FeCp*2 and E1/2(CoII/CoI)) ) -2.19
V vs FeCp*2.
strong DMF-CoII cation interaction differentiates the redox sites
by the electrostatic factor within a polycationic metalloden-
drimer. The analogy of results in the Co and Fe sandwich-
terminated dendrimers indicates that the tether-lengthening
strategy works in both series and that the defects are due to the
divergent dendritic organic core construction rather than to
functionalization with the redox groups. Finally, these metal-
lodendrimers provide fast electron-transfer connectors, and a
behavior of stable molecular batteries is anticipated and will
be the subject of further studies (Scheme 5).
Conclusion
Functional pentamethylcobalticinium hexafluorophosphate
salts have been synthesized by successive introduction of the
ancillary pentamethylcyclopentadienyl ligand followed by that
of the functional cyclopentadienyl ligand onto CoIII. The long
functional tether of the monosubstituted cyclopentadienyl ligand
allowed the synthesis of giant dendrimers containing a theoreti-
cal number of 3n+2 pentamethylcobalticinium termini, n being
the generation number. This robust redox group was connected
to organic dendrimers using a Williamson coupling reaction
between a phenol group located at the termini of the metallocene
substituent and the iodomethylsilyl group located at the den-
drimer branch termini. The metallodendrimers, synthesized for
the generation 0 and 5-7, were shown by UV-vis spectroscopy
to contain a number of redox groups that are relatively close to
the theoretical ones until G6 with numbers of defects increasing
as the generation number increases. The size increase of the
dendrimers from G5 to G7 is also clearly observed in the DLS
experiments. The last generation, G7, contained a large number
of defects, however, as the number of terminal branches, as in
the ferrocenyl and pentamethylferrocenyl dendrimer series, was
only 14 000 ( 1000 instead of the theoretical number of 19 683.
The full chemical and electrochemical reversibility was main-
tained in cyclic voltammetry, with CH2Cl2 as the solvent, until
G7, confirming a fast electron-hopping mechanism as in the
ferrocenyl series in this solvent. On the other hand, in DMF,
Experimental Section
General Data. Solvents, Compounds, and Reactions. Reagent-
grade diethyl ether and tetrahydrofuran (THF) were predried over
Na foil and distilled from sodium-benzophenone anion under argon
immediately prior to use. Dichloromethane and acetonitrile were
distilled from calcium hydride just before use. All other solvents
and chemicals were used as received. Kartsted catalyst and dry DMF
were purchased from Aldrich. The organic dendrimers23 used here
and the phenoltriallyl dendronic brick p-HOC4H4C(CH2CHd
41
CH2)3 were synthesized according to our previous reports.
(41) (a) Moulines, F.; Djakovitch, L.; Delville, M.-H.; Robert, F.;
Gouzerh, P.; Astruc, D. J. Chem. Soc., Chem. Commun. 1995, 463–464.
(b) Moulines, F.; Djakovitch, L.; Astruc, D. New J. Chem. 1996, 20, 1071–
1080.

2722 Organometallics, Vol. 28, No. 9, 2009
Ornelas et al.
1
NMR Spectroscopy. H NMR spectra were recorded at 25
under agitation, the solvent was removed under vacuum, the crude
product was dissolved in water and filtered under Celite, and the
aqueous solution was washed with ether. The product was then
precipitated from water upon addition of an aqueous HPF6 solution
(24 mmol), and it was recovered by filtration and washed with ether.
The product 11 was obtained as yellow oil in 25% yield (1.70 g).
1H NMR (CDCl3, 300 MHz): 5.77 (m, 1H, CHdCH2), 4.96 (m,
6H, CHdCH2 and CH of Cp), 2.17 (m, 2H, CH2Cp), 1.99 (s, 15H,
CH3 of Cp*), 1.69 (m, 2H, CH2CHdCH2), 1.29 (CH2)7. 13C NMR
(CDCl3, 75.47 MHz): 139.1 (CHdCH2), 114.1 (CHdCH2), 104.6
(Cq of Cp), 96.8 (Cq of Cp*), 86.3 and 84.6 (CH of Cp), 36.3
(CpCH2), 33.7 (CH2CHdCH2), 29.3 ((CH2)7), 9.9 (CH3 of Cp*).
MS (MALDI-TOF; m/z): calcd for C26H40Co+ 411.49, found 411.28.
Anal. Calcd for C26H40Co+PF6: C 56.12, H 7.24. Found: C 56.32,
H 7.07.
Synthesis of [Cp*CoCp(CH2)11Si(Me2)CH2Cl][PF6], 12. Com-
pound 12 was synthesized from 11 (1.09 g, 1.96 mmol) and
(dimethyl)chloromethylsilane (0.439, 3.92 mmol) using the general
procedure for hydrosilylation reactions (using THF as the solvent
instead of ether). The catalyst residue was removed by flash
chromatography on alumina using dichloromethane as the solvent.
After removing the solvent, 0.8635 g of yellow oil was obtained
(66% yield).
1H NMR (CDCl3, 300 MHz): 5.06 and 4.87 (d, 4H, CH of Cp),
2.71 (SiCH2Cl), 2.12 (m, 2H, CH2Cp), 1.94 (s, 15H, CH3 of Cp*),
1.40 (s, 2H, CH2CH2Si), 1.19 (m, 14H, (CH2)8), 0.56 (s, 2H,
CH2CH2Si), 0.032 (Si(CH3)2). 13C NMR (CDCl3, 75.47 MHz): 104.7
(Cq of Cp), 96.8 (Cq of Cp*), 86.2 and 84.6 (CH of Cp), 36.3
(CpCH2), 33.8 (CH2CH2CH2Si), 29.3 ((CH2)7), 25.9 (SiCH2Cl), 23.4
(CH2CH2CH2Si), 13.6 (CH2CH2CH2Si), 9.9 (CH3 of Cp*), -4.7
(Si(CH3)2). 29Si NMR (CDCl3, 59.62 MHz), δppm: 3.70 (Si(CH3)2).
MS (MALDI-TOF; m/z): calcd for C29H49ClSiCo+ 520.17, found
519.30. Anal. Calcd for C29H49ClCoF6PSi: C 52.37, H 7.43. Found:
C 53.49, H 7.43.
°C with a Bruker AC 300 (300 MHz) spectrometer. 13C NMR
spectra were obtained in the pulsed FT mode at 75.0 MHz with a
Bruker AC 300 spectrometer, and 29Si NMR spectra were obtained
at 59.6 MHz with a Bruker AC 300 spectrometer. All chemical
shifts are reported in parts per million (δ, ppm) with reference to
Me4Si (TMS).
MALDI-TOF Mass Spectrometry. The mass spectra reported
in this article are MALDI TOF mass spectra. MALDI mass spectra
were recorded with a PerSeptive Biosystems Voyager Elite
(Framingham, MA) time-of-flight mass spectrometer. This instru-
ment is equipped with a nitrogen laser (337 nm), a delayed
extraction, and a reflector. It was operated at an accelerating
potential of 20 kV in both linear and reflection modes. The mass
spectra shown represent an average over 256 consecutive laser shots
(3 Hz repetition rate). Peptides were used to calibrate the mass
scale using the two-point calibration software 3.07.1 from PerSep-
tive Biosystems. Mentioned m/z values correspond to monoisotopic
masses. The dendrimer solutions (10-3 M) were prepared in
tetrahydrofuran (THF). Matrix compounds were from Sigma
(France) and used without further purification. The matrixes, 2,5-
dihydroxybenzoic acid (2.5-DHB), 1,8-dihydroxy-9[10H]-anthra-
cenone (dithranol), 6-azathiothymine, 2,4,6-trihydroxyacetophenone,
7-hydroxycoumarin, or 2-anthramine, were also dissolved in THF
(10 g L-1). One microliter of dendrimer solution was mixed with
50 µL of matrix solution. Ten microliters of alkali iodide (LiI, NaI)
solution (5 g L-1 in THF) was added in some experiments to induce
cationization. One microliter of the final solution was deposited
onto the sample stage and allowed to dry in air.
Dynamic Light Scattering Measurements. The DLS measure-
ments were made using a Malvern Zetasizer 3000 HSA instrument
at 25 °C at an angle of 90°.
Cyclic Voltammetry Measurements. All electrochemical mea-
surements were recorded under nitrogen atmosphere. Conditions:
solvent, dry dichloromethane; temperature, 20 °C; supporting
electrolyte, [n-Bu4N][PF6] 0.1 M; working and counter electrodes,
Pt; reference electrode, Ag; internal reference, FeCp*2 (Cp* ) η5-
Synthesis of [Cp*CoCp(CH2)11Si(Me2)CH2I][PF6], 13. Com-
pound 13 (0.8635 g, 1.29 mmol), NaI (0.581 g, 3.87 mmol), and
butanone (50 mL) were introduced in a Schlenk flask. The reaction
mixture was stirred at 80 °C for 16 h. The solvent was removed
under vacuum, and the residue was dissolved in dichloromethane
(20 mL) and washed with a saturated aqueous solution of Na2S2O3.
This solution was dried with Na2SO4 and filtered, and the solvent
was removed under vacuum. The product 13 was obtained as a
yellow oil in 91% yield (0.891 g).
C5Me5); scan rate, 0.200 V s-1
.
Elemental Analyses. These were performed by the Center of
Microanalyses of the CNRS at Lyon Villeurbanne, France.
General Hydrosilylation Reactions. The olefin compound,
diethyl ether, the silane derivative (2 equiv per branch), and Kartsted
catalyst (0.1%) were successively introduced into a Schlenk flask
under a nitrogen atmosphere. The reaction solution was stirred at
25 °C for 16 h. The solvent was removed under vacuum, the catalyst
residue was removed by flash chromatography with ether, and the
solvent was removed.
General Synthesis of the Cobalticinium Dendrimers. The
iodomethylsilane dendrimer, 14 (2 equiv per branch), and K2CO3
(10 equiv per branch) were introduced into a Schlenk flask, then
dry DMF (30 mL) was added and the reaction mixture was heated
at 80 °C for 48 h under magnetic stirring. After removing the solvent
in Vacuo, dichloromethane (20 mL) was added and the mixture
was filtered on Celite to remove K2CO3. The product was dissolved
in methanol and after addition of KPF6 a brown solid precipitated.
The solution was filtrated on Celite, washed with methanol, and
dissolved in CH2Cl2. After removing the solvent in Vacuo a yellow
solid was obtained.
Synthesis of [Cp*CoCp(CH2)9HCdCH2][PF6], 11. To a THF
solution of pentamethylcyclopentadiene (1.88 mL, 12.0 mmol) was
added dropwise 7.68 mL of a n-butyllithium solution (2.5 M), -60
°C, under a nitrogen atmosphere at -60 °C. After agitation for 30
min, a THF solution of CoCl2 (1.548 g, 12.0 mmol) was added
slowly at -60 °C (dark blue solution). After 1 h, a THF solution
of 10 (2.633 g, 12.0 mmol), resulting from the deprotonation of
the corresponding diene with n-butyllithium, was added, and the
final brown solution was left under agitation for 16 h. After 5 h
1H NMR (CDCl3, 300 MHz): 5.01 and 4.83 (d, 4H, CH of Cp),
2.11 (m, 2H, CH2Cp), 1.88 (s, 15H, CH3 of Cp*), 1.82 (SiCH2I),
1.34 (s, 2H, CH2CH2Si), 1.12 (m, 14H, (CH2)7), 0.52 (s, 2H,
CH2CH2Si), -0.0004 (Si(CH3)2). 13C NMR (CDCl3, 75.47 MHz):
104.6 (Cq of Cp), 96.7 (Cq of Cp*), 86.2 and 84.6 (CH of Cp),
36.3 (CpCH2), 33.4 (CH2CH2CH2Si), 29.4 ((CH2)7), 23.5
(CH2CH2CH2Si), 14.7 (CH2CH2CH2Si), 9.9 (CH3 of Cp*), -3.06
(Si(CH3)2), -12.8 (SiCH2I). 29Si NMR (CDCl3, 59.62 MHz), δppm
4.82 (Si(CH3)2).
:
Synthesis of Cp*CoCp(CH2)11Si(Me2)CH2OC6H4OH, 14. Com-
pound 14 (0.891 g, 1.17 mmol), hydroquinone (0.644 g, 5.85 mmol),
and K2CO3 (0.819 g, 5.85 mmol) were introduced into a Schlenk
flask. Dry DMF (20 mL) was added, and the reaction mixture was
heated at 80 °C for 48 h under magnetic stirring. After removing
the solvent under vacuum, dichloromethane (20 mL) was added
and the mixture was filtered on Celite in order to remove K2CO3.
The solvent was removed under vacuum, and the product was
precipitated with CH2Cl2/ethyl ether (5:95). Product 14 was obtained
as a yellow waxy product in 74% yield (0.6436 g).
1H NMR (CDCl3, 300 MHz): 6.91 and 6.73 (d, 4H, CH arom.),
5.26 and 5.07 (d, 4H, CH of Cp), 3.49 (SiCH2O), 2.20 (m, 2H,
CH2Cp), 2.05 (s, 15H, CH3 of Cp*), 1.41 (s, 2H, CH2CH2Si), 1.19
(m, 14H, (CH2)8), 0.62 (s, 2H, CH2CH2Si), -0.0067 (Si(CH3)2).
13C NMR (CH3COCH3, 75.47 MHz): 155.7 (arom. Cq), 152.3 (arom.

Giant Cobalticinium Dendrimers
Organometallics, Vol. 28, No. 9, 2009 2723
COH), 116.7 and 115.5 (arom. CH), 99.30 (Cq of Cp), 98.4 (Cq of
Cp*), 87.3 and 86.5 (CH of Cp), 61.4 (SiCH2O), 37.2 (CpCH2),
34.3 (CH2CH2CH2Si), 28.2 ((CH2)7), 24.4 (CH2CH2CH2Si), 14.4
(CH2CH2CH2Si), 10.6 (CH3 of Cp*), -4.4 (Si(CH3)2). 29Si NMR
(CDCl3, 59.62 MHz), δppm: 0.35 (Si(CH3)2). MS (MALDI-TOF;
m/z): calcd for C35H54O2SiCo+ 593.78, found 593.31.
mmol), 14 (0.280 g, 0.379 mmol), and K2CO3 (0.348 g, 2.48 mmol)
using the general procedure for the synthesis of cobalticinium
dendrimers. The product 17 was obtained as a yellow waxy product
in 19% yield (0.040 g).
1H NMR (CH3COCH3, 300 MHz), δppm: 7.11 (d, CH arom), 6.74
(d, OCqCH arom.), 5.18 (d, Cp), 3.47 and 3.40 (d, SiCH2O), 2.28
(t, CH2Cp), 1.99 (s, CH3 of Cp*), 1.60 (s, CH2CH2CH2Si), 1.17
(m, (CH2)7 and CH2CH2CH2Si), 0.56 (s, CH2CH2CH2Si), 0.0005
Synthesis of G0-Co*, 15. The G0-Co* metallodendrimer 15 was
synthesized from 9-iodide dendrimer 2 (0.039 g, 0.0170 mmol),
14 (0.175 g, 0.237 mmol), and K2CO3 (0.274 g, 1.95 mmol) using
the general synthesis for cobalticinium dendrimers. The product
15 was obtained as a yellow waxy product in 41% yield (0.054 g).
1H NMR (CH3COCH3, 300 MHz), δppm: 7.04 (s, 3H, CH core),
6.75 (d, 36H, arom), 5.25 and 5.15 (d, 36H, Cp), 3.46 and 3.41 (d,
36H, SiCH2O), 2.30 (t, 18H, CH2Cp), 1.99 (s, 135H, CH3 of Cp*),
1.64 (s, 36H, CH2CH2CH2Si), 1.19 (m, 144H, (CH2)7 and
CH2CH2CH2Si), 0.56 (s, 36H, CH2CH2CH2Si), 0.00 and -0.044
(d, 108H, Si(CH3)2). 13C NMR (CH3COCH3, 62 MHz), δppm: 155.3
(arom. OCq), 114.2 (arom. CH), 104.70 (Cq of Cp), 97.3 (Cq of
Cp*), 89.2 and 84.6 (CH of Cp), 60.2 (OCH2Si), 44.0 (benzylic
Cq), 35.9 (CH2CH2CH2Si), 33.1 (CpCH2), 28.2 ((CH2)7), 23.2
(CH2CH2CH2Si), 13.2 (CH2CH2CH2Si), 8.8 (CH3 of Cp*), -5.7
(Si(CH3)2). 29Si NMR (CH3COCH3, 59.62 MHz), δppm: 0.30 and
0.19 (Si(CH3)2). MS (MALDI-TOF; m/z): calcd for
[C378H606O18Si18Co9]9+ 6 474.00, found 6 500. Anal. Calcd for
C378H606O18Si18Co9P9F54: C 58.36, H 7.85. Found: C 57.16, H 7.77.
Synthesis of G5-Co*, 16. The G5-Co* dendrimer 16 was
synthesized from 2187-iodide dendrimer 7 (0.060 g, 0.0000621
mmol), 14 (0.161 g, 0.217 mmol), and K2CO3 (0.190 g, 1.36 mmol)
using the general procedure for the synthesis of cobalticinium
dendrimers. The product 16 was obtained as a yellow waxy product
with 53% yield (0.069 g).
and -0.062 (d, Si(CH3)2). 13C NMR (CH3COCH3, 75 MHz), δppm
:
156.6 (arom. CqOCH2Si), 147.8 (arom. Cq of the dendron), 127.2
and 113.4 (arom. CH of the dendron), 115.5 (arom. CH), 97.7 (Cq
of Cp), 92.8 (Cq of Cp*), 87.3 and 85.8 (CH of Cp), 61.4 (OCH2Si),
42.8 (benzylic Cq), 34.4 (CpCH2), 31.6 (CH2CH2CH2Si), 29.6
((CH2)7), 25.5 (CH2CH2CH2Si), 14.4 (CH2CH2CH2Si), 10.1 (CH3
of Cp*), -4.2 (Si(CH3)2). 29Si NMR (CDCl3, 59.62 MHz), δppm
:
-
0.31 and 0.098 (Si(Me)2). Anal. Calcd for C311598H498558O16398
Si16398Co6561P6561F39366: C 59.35, H 7.97. Found: C 56.37, H 7.44.
Synthesis of G7-Co*, 18. The G7-Co* dendrimer 18 was
synthesized from 19683-iodide dendrimer 9 (0.050 g, 0.00000786
mmol), 14 (0.204 g, 0.314 mmol), and K2CO3 (0.220 g, 1.57 mmol)
using the general procedure for the synthesis of cobalticinium
dendrimers. The product 18 was obtained as a yellow waxy product
in 17% yield (0.025 g).
1H NMR (CH3COCH3, 300 MHz), δppm: 7.12 (m, arom.), 6.78
(m, arom), 5.28 (d, Cp), 3.53 and 3.44 (m, SiCH2O), 2.31 (m,
CH2Cp), 1.95 (s, CH3 of Cp*), 1.62 (s, CH2CH2CH2Si), 1.29 (m,
(CH2)7 and CH2CH2CH2Si), 0.68 (s, CH2CH2CH2Si), 0.012 (s,
Si(CH3)2). 13C NMR (CH3COCH3, 75 MHz), δppm: 156.5 (arom
CqOCH2Si), 147.8 (arom. Cq of the dendron), 127.2 and 113.2
(arom. CH of the dendron), 115.3 (arom. CH), 97.6 (Cq of Cp),
92.7 (Cq of Cp*), 87.3 and 85.9 (CH of Cp), 61.4 (OCH2Si), 42.7
(benzylic Cq), 34.4 (CpCH2), 31.5 (CH2CH2CH2Si), 29.6 ((CH2)7),
25.7 (CH2CH2CH2Si), 14.4 (CH2CH2CH2Si), 10.2 (CH3 of Cp*),
-4.3 (Si(CH3)2). 29Si NMR (CDCl3, 59.62 MHz), δppm: 0.31
1H NMR (CH3COCH3, 300 MHz), δppm: 7.11 (d, CH arom.),
6.74 (d, OCqCH arom.), 5.18 (d, Cp), 3.47 and 3.40 (d, SiCH2O),
2.28 (t, CH2Cp), 1.99 (s, CH3 of Cp*), 1.60 (s, CH2CH2CH2Si),
1.17 (m, (CH2)7 and CH2CH2CH2Si), 0.56 (s, CH2CH2CH2Si),
0.0005 and -0.062 (d, Si(CH3)2). 13C NMR (CH3COCH3, 75 MHz),
(Si(Me)2).
Anal.
Calcd
for
C934893H1495830O49203Si49203-
Co19683P19683F118098: C 59.35, H 7.97. Found: C 56.12, H 7.38.
δ
ppm: 156.6 (arom. CqOCH2Si), 147.8 (arom. Cq of the dendron),
127.2 and 113.4 (arom. CH of the dendron), 115.5 (arom. CH),
97.7 (Cq of Cp), 92.8 (Cq of Cp*), 87.3 and 85.8 (CH of Cp), 61.4
(OCH2Si), 42.8 (benzylic Cq), 34.4 (CpCH2), 31.6 (CH2CH2CH2Si),
29.6 ((CH2)7), 25.5 (CH2CH2CH2Si), 14.4 (CH2CH2CH2Si), 10.1
(CH3 of Cp*), -4.2 (Si(CH3)2). 29Si NMR (CDCl3, 59.62 MHz),
Acknowledgment. Financial support from the Fundac¸a˜o
para a Cieˆncia e a Tecnologia (FCT), Portugal (Ph.D. grant
to C.O.), the Institut Universitaire de France (IUF, D.A.),
the University Bordeaux 1, the Centre National de la
Recherche Scientifique (CNRS), and the Agence Nationale
de la Recherche (Project ANR-06-NANO-026) is gratefully
acknowledged.
δ
ppm: 0.31 and 0.098 (Si(Me)2). Anal. Calcd for C103833H166134-
O5463Si5463Co2187P2187F13122: C 59.35, H 7.97. Found: C 60.53, H
8.57.
Synthesis of G6-Co*, 17. The G6-Co* dendrimer 17 was
synthesized from 6561-iodide dendrimer 8 (0.060 g, 0.0000379
OM900079Y