Multiredox heterometallic carbosilane dendrimers

Article abstract of DOI:10.1021/om700559t

A convergent growth approach for the synthesis of novel heterometallic dendritic molecules derived from carbosilane frameworks and functionalized with silicon-bridged ferrocenyl and (η⁶-aryl)tricarbon-ylchromium moieties has been developed. The synthetic route involves the construction of the dendritic fragments (CH₂=CH)MePhSiFc (1) (Fc = (η⁵-C₅H₄)Fe(η⁵-C ₅H₅)) (CH₂=CHCH₂)PhSi[(CH ₂)₂MePhSiFc]₂ (3), (CH₂=CH) MeSi[{(η⁶-C₆H₅)Cr(CO)₃}Fc] (4), and (CH₂=CHCH₂){(η⁶-C₆H ₅)Cr(CO)₃}MeSi[(CH₂)₂- Me{(η⁶-C₆H₅)Cr(CO)₃}SiFc] ₂ (5), containing a single reactive C=C functionality, in addition to ferrocenyl (1 and 3) and linked ferrocenyl and (η⁶-C ₆H₅)Cr(CO)₃ moieties (4 and 5) and their subsequent attachment to the tetrafunctional core Si[(CH₂) ₃Si(Me)₂H]₄ (6), via platinum-catalyzed hydrosilylation reactions. The first- and second-generation dendrimers 8 and 9, containing four and eight ferrocenyl units on the dendritic surface, respectively, have been prepared by this procedure. Thermal treatment of 8 and 9 with Cr(CO)₆ afforded the targeted heterometallic dendrimers 7 and 10, carrying silicon-bridged (η⁵-C₅H ₄)Fe(η⁵-C₅H₅) and (η⁶-C₆H₅)Cr(CO)₃ moieties appended at the dendrimer periphery. The molecular structures of the vinyl-functionalized silanes 1 and 4 have been determined by single-crystal X-ray diffraction. The crystal structure of 4 showed that the Cr(CO)₃ group is disposed in a transoid configuration with respect to the ferrocenyl moiety. The heterobimetallic 4 also shows an interesting self-assembly of the metals (Fe and Cr) in the crystal. The electrochemical behavior of all new dendritic molecules has been investigated. For the heterometallic 4, 7, and 10 the oxidation of the iron centers becomes more anodic compared to the oxidation of the ferrocenyl units in the homometallic molecules 1, 8, and 9, due to the electron-withdrawing nature of the neighboring silicon-linked (η-C ₆H₅)Cr(CO)₃ moieties. In addition, stable electrode surfaces modified with dendrimers 8 and 9 have been prepared.

Full text of DOI:10.1021/om700559t

Organometallics 2007, 26, 5153-5164
5153
Multiredox Heterometallic Carbosilane Dendrimers
Magdalena Zamora, Beatriz Alonso, Ce´sar Pastor, and Isabel Cuadrado*
Departamento de Qu´ımica Inorga´nica, Facultad de Ciencias, UniVersidad Auto´noma de Madrid,
Cantoblanco, 28049, Madrid, Spain
ReceiVed June 8, 2007
A convergent growth approach for the synthesis of novel heterometallic dendritic molecules derived
from carbosilane frameworks and functionalized with silicon-bridged ferrocenyl and (η6-aryl)tricarbon-
ylchromium moieties has been developed. The synthetic route involves the construction of the dendritic
fragments (CH2dCH)MePhSiFc (1) (Fc ) (η5-C5H4)Fe(η5-C5H5)) (CH2dCHCH2)PhSi[(CH2)2MePhSiFc]2
(3), (CH2dCH)MeSi[{(η6-C6H5)Cr(CO)3}Fc] (4), and (CH2dCHCH2){(η6-C6H5)Cr(CO)3}MeSi[(CH2)2-
Me{(η6-C6H5)Cr(CO)3}SiFc]2 (5), containing a single reactive CdC functionality, in addition to ferrocenyl
(1 and 3) and linked ferrocenyl and (η6-C6H5)Cr(CO)3 moieties (4 and 5) and their subsequent attachment
to the tetrafunctional core Si[(CH2)3Si(Me)2H]4 (6), via platinum-catalyzed hydrosilylation reactions. The
first- and second-generation dendrimers 8 and 9, containing four and eight ferrocenyl units on the dendritic
surface, respectively, have been prepared by this procedure. Thermal treatment of 8 and 9 with Cr(CO)6
afforded the targeted heterometallic dendrimers 7 and 10, carrying silicon-bridged (η5-C5H4)Fe(η5-C5H5)
and (η6-C6H5)Cr(CO)3 moieties appended at the dendrimer periphery. The molecular structures of the
vinyl-functionalized silanes 1 and 4 have been determined by single-crystal X-ray diffraction. The crystal
structure of 4 showed that the Cr(CO)3 group is disposed in a transoid configuration with respect to the
ferrocenyl moiety. The heterobimetallic 4 also shows an interesting self-assembly of the metals (Fe and
Cr) in the crystal. The electrochemical behavior of all new dendritic molecules has been investigated.
For the heterometallic 4, 7, and 10 the oxidation of the iron centers becomes more anodic compared to
the oxidation of the ferrocenyl units in the homometallic molecules 1, 8, and 9, due to the electron-
withdrawing nature of the neighboring silicon-linked (η6-C6H5)Cr(CO)3 moieties. In addition, stable
electrode surfaces modified with dendrimers 8 and 9 have been prepared.
tion of the specific properties of their dissimilar constituent
organometallic moieties. This may result in the development
of a variety of novel and improved characteristics that do not
occur in homometallic dendritic molecules. Although synthetic
methods for homometallic dendrimers are well developed,2,3
synthetic efforts for the construction of dendritic molecules
containing two or more different organotransition metal moieties
are limited, and only a few attempts have been made in this
direction.4-9 In particular, metallodendrimers having two dif-
ferent redox-active organometallic units are systems of intrinsic
interest, as each of the chemically different organometallic units
introduces into the same dendritic structure its own ability to
Introduction
One of the most significant recent highlights in the field of
dendrimer chemistry1 lies in the incorporation of transition
metals into dendritic structures to create metallodendrimers,
which offers many additional possibilities for applications as
functional materials with interesting electrochemical, catalytic,
photo-optical, and magnetic properties.2,3 A challenging target
is the possibility to insert a controlled number of different
organometallic centers in predetermined sites of the dendritic
structure. The presence of two (or more) different metal centers
within the same dendritic molecule can profoundly affect both
the physical properties and the reactivity of the dendritic system.
It is thus possible to construct heterometallic dendrimers capable
of performing complex functionality resulting from the integra-
(3) For reviews on organometallic dendrimers, see for example: (a)
Cuadrado, I.; Mora´n, M.; Casado, C. M.; Alonso, B.; Losada, J. Coord.
Chem. ReV. 1999, 193-195, 395. (b) Hearshaw, M. A.; Moss, J. R. Chem.
Commun. 1999, 1. (c) Rossell, O.; Seco, M.; Angurell, I. C. R. Chim. 2003,
6, 805. (d) Chase, P. A.; van Koten, G. J. Organomet. Chem. 2004, 689,
4016. (e) Manners, I. In Synthetic Metal-Containing Polymers; Manners,
I., Ed.; Wiley-VCH: Weinheim, 2004; p 237. (f) Astruc, D. In Frontiers
in Transition Metal-Containing Polymers; Abd-El-Aziz, A. S. A., Manners,
I., Eds.; Wiley: Hoboken, NJ, 2007; Chapter 11.
* Corresponding author. E-mail: isabel.cuadrado@uam.es. Tel: (+34)
91 397 4834. Fax: (+34) 91 397 4833.
(1) See for example: (a) Newkome, G. R., Moorefield, C. N., Vo¨gtle,
T., Eds.; Dendrimers and Dendrons: Concept, Syntheses and Applications;
Wiley-VCH Verlag: Weinheim, Germany, 2001. (b) Freche´t, J. M. J.,
Tomalia, D. A., Eds.; Dendrimers and Other Dendritic Polymers; VCH:
Weinheim, Germany, 2002. (c) Vo¨gtle, F.; Gestermann, S.; Hesse, R.;
Schwierz, H.; Windisch, B. Prog. Polym. Sci. 2000, 25, 987. (d) Tomalia,
D. A. Prog. Polym. Sci. 2005, 30, 294.
(4) (a) Angurell, I.; Rossell, O.; Seco, M.; Ruiz, E. Organometallics 2005,
24, 6365. (b) Angurell, I.; Lima, J. C.; Rodriguez, L.-I.; Rossell, O.; Seco,
M. New J. Chem. 2006, 30, 1004.
(2) For metallodendrimers, see for example: (a) Newkome, G. R.;
Moorefield, C. N. Chem. ReV. 1999, 99 1689. (b) Gorman, C. AdV. Mater.
1998, 10, 295. (b) Majoral, J.-P.; Caminade, A.-M. Chem. ReV. 1999, 99,
845. (c) Metal-Containing and Metallosupramolecular Polymers and
Materials; Schubert, U. S., Newkome, G. R., Manners, I., Eds.; Oxford
University Press: London, 2006. (d) Mery, D.; Astruc, D. Coord. Chem.
ReV. 2006, 250, 1965. (e) Berger, A.; Gebbink, R. J. M.; van Koten, G.
Top. Organomet. Chem. 2006, 20, 1. (f) Newkome, G. R. In Frontiers in
Transition Metal-Containing Polymers; Abd-El-Aziz, A. S. A, Manners,
I., Eds.; Wiley: Hoboken, NJ, 2007; Chapter 10.
(5) Me´ry, D.; Plault, L.; Ornelas, C.; Ruiz, J.; Nlate, S.; Astruc, D.; Blais,
J.-C.; Rodrigues, J.; Ste´phane, C.; Kiracki, K.; Perrin, C. Inorg. Chem. 2006,
45, 1156.
(6) Casado, C. M.; Gonza´lez, B.; Cuadrado, I.; Alonso, B.; Mora´n, M.;
Losada, J. Angew. Chem., Int. Ed. 2000, 39, 2135.
(7) Achar, S.; Immoos, C. E.; Hill, M. G.; Catalano, V. J. Inorg. Chem.
1997, 36, 2314.
(8) Liu, G. X.; Puddephatt, R. J. Organometallics 1996, 15, 5257.
(9) Juris, A.; Balzani, V.; Campagna, S.; Denti, G.; Serroni, S.; Frei,
G.; Guedel, H. U. Inorg. Chem. 1994, 33, 1491.
10.1021/om700559t CCC: $37.00 © 2007 American Chemical Society
Publication on Web 09/15/2007

5154 Organometallics, Vol. 26, No. 21, 2007
Zamora et al.
undergo redox processes at a certain potential. Therefore, these
metallodendrimers can be used to perform valuable functions
such as reversible exchange (storage and release) of a controlled
number of electrons at a certain potential, an attractive
characteristic for the design of molecular electronic devices and
multi-electron-transfer catalysts.10 Furthermore, such hetero-
metallic dendrimers offer the unique opportunity to explore the
dependence of electronic cooperativity on redox asymmetry and
of chemical reactivity upon the presence of a second, different
redox center in the same metallodendritic molecule. In this
context, we have reported metallodendrimers containing neutral
ferrocene and cationic cobaltocenium units located simulta-
neously at the surface of a dendritic structure.6 These hetero-
metallic dendrimers are of significance because they exhibit a
double function. Thus, conducting films of electrodeposited
dendrimers containing both ferrocene and cobaltocenium units
have been used successfully in a double way for the aerobic
and anaerobic determination of glucose.11
On the other hand, in the last years we have been exploring
routes for the construction of new families of redox-active
organometallic dendritic structures, containing nitrogen- and
silicon-based frameworks.12-15 One of our synthetic approaches
to the synthesis of such organometallic macromolecules was
based on hydrosilylation reactions that exploit the reactivity of
Si-H polyfunctionalized carbosilanes and siloxanes toward
suitable ferrocenyl derivatives containing reactive vinyl or allyl
groups.13-15 In this way, we have reported the first examples
of organometallic dendritic molecules possessing peripheral
electronically communicated ferrocenyl moieties, which were
constructed using a convergent methodology by sequences of
hydrosilylation and alkenylation reactions.14,15 Our objective
now is to extend this synthetic strategy to new dendritic
molecules containing a controlled number of different electro-
active organometallic units, precisely located in the dendritic
structure. As a continuation of our efforts toward the develop-
ment of new families of redox-active organometallic dendrimers,
we have chosen now to combine in a dendritic molecule a
typical strong electron-donating fragment such as ferrocene
together with the electron-withdrawing moiety η6-aryltricarbo-
nylchromium.
Results and Discussion
Synthesis of the Homo- and Heterometallic Precursor
Dendritic Fragments 1-5. We are interested in developing
methods for the synthesis of new redox-active silicon-based
heterometallic dendritic molecules based on the convergent
methodology.16,17 In our designed convergent approach, suitable
organometallic dendritic wedges containing a CdC functionality
at the focal point are constructed first, and then these dendrons
are attached to a Si-H polyfunctionalized core molecule via
hydrosilylation chemistry in the final steps of the dendrimer
construction.14
There were several key requirements that had to be met by
the starting redox-active organometallic molecule in our con-
vergent methodology. These considerations are based on our
foreknowledge that organometallic dendrimer synthesis is
inherently labor intensive, which involves lengthy and difficult
synthetic steps and requires relatively large quantities of readily
accessible starting organometallic materials.18 Our prerequisites
therefore call for a polyfunctional organometallic molecule that
meets all the following criteria: (i) be easy to prepare; (ii) bear
a single reactive CdC functionality appropriate for dendritic
convergent growth; (iii) have tolerance to the conditions
necessary for carbosilane chemistry (in particular, hydrosilyla-
tion conditions and inertness to Grignard reagents); (iv) carry a
potential ligand binding site for attachment of a second different
organotransition metal fragment; (v) this second organometallic
moiety must to be incorporated without decomplexing the first
starting organotransition metal fragment. With this in mind, the
target redox-active precursor molecule was chosen to be the
novel derivative ferrocenylmethylphenylvinylsilane (1), shown
in Scheme 1.
The pivotal molecule 1 was easily accessible by the salt
elimination reaction of ferrocenyllithium with methylphenylvi-
nylchlorosilane in THF at -30 °C (Scheme 1). For this purpose
(tri-n-butylstannyl)ferrocene was selected as starting material,
since it has proved to be an excellent precursor of pure
monolithioferrocene19 (see Experimental Section). This is
crucial, in order to exclude the formation of the dimetalated
ferrocene, Fe(η5-C5H4Li)2, which could produce undesirable
additional disubstituted dendritic materials. After appropriate
workup, the target vinyl-terminated 1 was isolated in high purity
and reasonable yield (75%) as an orange, crystalline solid. This
simple organometallic molecule features several key components
that meet the requirements detailed above. First, the reactive
vinyl group attached to the silicon atom of 1 enables further
elaboration via hydrosilylation reaction with Si-H polyfunc-
tionalized building blocks in order to provide either a branched
second-generation dendron or a first-generation final dendrimer
in a typical convergent dendrimer growth. Second, the free aryl
ring can be readily coordinated to a second different organ-
otransition metal moiety via π-interaction. In addition, the redox-
active 1 is thermally and air stable and soluble in common
organic solvents. In fact, 1 can be stored for a long period
(several months) under an air atmosphere at room temperature
without noticeable decomposition (1H NMR spectroscopy).
The convergent growth of the ferrocenyl derivative 1 was
achieved by hydrosilylation reaction with phenylchlorosilane
We report herein full details on the synthesis, characterization,
and redox behavior of a series of novel redox-active multim-
etallic dendritic systems, derived from carbosilane frameworks,
containing ferrocenyl and (η6-C6H5)Cr(CO)3 moieties linked
together in close proximity by a bridging silicon atom.
(10) (a) Supramolecular Electrochemistry; Kaifer, A. E., Go´mez-Kaifer,
M., Eds.; Wiley-VCH: Weinheim: Germany, 1999; Chapter 16, p 207.
(b) Inorganic Electrochemistry. Theory, Practice and Application; Zanello,
P., Ed.; Royal Society of Chemistry: Cambridge, 2003; Chapter 5, p 185.
(c) Astruc, D.; Daniel, M. C.; Nlate, S.; Ruiz, J. In Trends in Molecular
Electrochemistry; Pombeiro, A. J. L., Amatore, C., Eds.; Marcel Dekker:
New York, 2004; Chapter 9, p 283.
(11) Alonso, B.; Garc´ıa-Armada, P.; Losada, J.; Cuadrado, I.; Gonza´lez,
B.; Casado, C. M. Biosens. Bioelectron. 2004, 19, 1617.
(12) (a) Cuadrado, I.; Mora´n, M.; Casado, C. M.; Alonso, B.; Lobete,
F.; Garc´ıa, B.; Ibisate, M.; Losada, J. Organometallics 1996, 15, 5278. (b)
Gonzalez, B.; Casado, C. M.; Alonso, B.; Cuadrado, I.; Mora´n, M.; Wang,
Y.; Kaifer, A. E. Chem. Commun. 1998, 2569. (c) Zamora, M.; Herrero,
S.; Losada, J.; Cuadrado, I.; Casado, C. M.; Alonso, B. Organometallics
2007, 26, 2688.
(13) (a) Alonso, B.; Cuadrado, I.; Mora´n, M.; Losada, J. J. Chem. Soc.,
Chem. Commun. 1994, 2575. (b) Alonso, B; Mora´n, M; Casado, C. M.;
Lobete, F.; Losada, J.; Cuadrado, I. Chem. Mater. 1995, 7, 1440. (c) Garc´ıa,
B.; Casado, C. M.; Cuadrado, I.; Alonso, B.; Mora´n, M.; Losada, J.
Organometallics 1999, 18, 2349.
(14) Cuadrado, I.; Casado, C. M.; Alonso, B.; Mora´n, M.; Losada, J.;
Belsky, V. J. Am. Chem. Soc. 1997, 119, 7613.
(16) (a) Hawker, C. J.; Fre´chet, J. M. J. J. Chem. Soc., Chem. Commun.
1990, 1010. (b) Hawker, C. J.; Frechet, J. M. J. J. Am. Chem. Soc. 1990,
112, 7638.
(17) For an excellent recent review on convergent construction of
dendrimers see: Grayson, S. K.; Fre´chet, J. M. J. Chem. ReV. 2001, 101,
3819.
(15) Alonso, B.; Gonza´lez, B.; Ram´ırez, E.; Zamora, M.; Casado, C.
M.; Cuadrado, I. J. Organomet. Chem. 2001, 637-639, 642.
(18) Zamora, M. Ph.D. Thesis, Universidad Auto´noma de Madrid, 2006.
(19) Guillaneux, D.; Kagan, H. B. J. Org. Chem. 1995, 60, 2502.

Multiredox Heterometallic Carbosilane Dendrimers
Organometallics, Vol. 26, No. 21, 2007 5155
Scheme 1. Synthesis of the Homo- and Heterometallic Dendritic Fragments 1-5a
a Reagents and conditions: (i) ClSiPhMe(CHdCH2), THF, -30 °C; (ii) ClSiPhH2, toluene, 40 °C, Karstedt’s cat.; (iii) (CH2CHdCH2)MgBr,
Et2O, reflux; (iv) Cr(CO)6, n-Bu2O/THF (9:1, v/v), reflux.
in toluene at 40 °C in the presence of Karstedt’s catalyst
(Scheme 1). H NMR and IR spectroscopies were utilized to
solutions. The novel heterobimetallic dendrons 4 and 5 were
isolated as yellow-orange crystals. The solids 4 and 5 may be
handled in air for short periods of time, but the solutions must
be handled under an inert atmosphere.
1
follow the progress of the reaction, and it was established that
complete reaction of the two Si-H functionalities of phenyl-
chlorosilane was easily achieved under these mild conditions.
The intermediate compound 2 was isolated as an orange,
The structural identities of the novel dendritic molecules 1-5
were straightforwardly established on the basis of elemental
analysis, IR, and multinuclear (1H, 13C, 29Si) NMR spectroscopy
1
moisture-sensitive, oily product. The H NMR spectrum of 2
1
evidences that only the â-isomer was formed under the described
reaction conditions and no Markownikow addition (which would
lead to R-isomer) took place,20 which assures a regular dendritic
convergent growth and the generation of molecules of maximum
symmetry. Subsequent treatment of the terminal Si-Cl func-
tionality in 2 with allylmagnesium bromide, followed by
hydrolytic workup and purification via column chromatography,
afforded an orange solid, which was isolated and characterized
as being the desired growth dendron fragment 3 shown in
Scheme 1, carrying two ferrocenyl units linked to phenyl rings
by a bridging silicon atom.
The π-coordinating ability of the free phenyl rings of 1 and
3 toward transition metals offered a good chance to gain an
easy synthetic access to the targeted first- and second-generation
heterometallic dendrons. Thus, thermal treatment of 1 and 3
with Cr(CO)6 in the donor solvent medium of n-dibutyl ether/
tetrahydrofuran (9:1, v/v) at 140 °C afforded the heterobimetallic
4 and the heteropentametallic 5, respectively (see Scheme 1).
1H NMR spectroscopy was used to follow the progress of these
reactions, by monitoring the considerable upfield shift of the
aryl proton resonances upon coordination to the Cr(CO)3 group.
After these reactions were finished, it is necessary to remove
some insoluble decomposition materials by filtration through a
short column of Celite, resulting in bright yellow-orange
and mass spectrometry. H NMR spectra of 1-5 show in all
cases the pattern of resonances centered at about δ 4.0 and 4.3
ppm, respectively, characteristic of the unsubstituted and
substituted cyclopentadienyl ligands in the ferrocenyl moieties.
1
The H NMR spectra of 1 and 4 show a set of resonances
characteristic of the reactive vinyl group at δ 5.9, 6.2, and 6.4
ppm in the expected integration ratios. Likewise, the three
signals of the allyl part in 3 and 5 include two multiplets for
each of dCH(trans) and dCH(cis) and a doublet at 1.9 ppm for
1
the methine proton. In addition, in the H NMR spectra of the
heterometallics 4 and 5 the complete η6-coordination of the Cr-
(CO)3 moieties to the phenyl rings in the homometallic 1 and
3 was confirmed by the total absence of resonances in the range
7.3-7.5 ppm, in which the aryl resonances of the noncoordi-
nated dendritic wedge are observed. As a consequence of the
withdrawal of the π-electrons from the aryl rings by the Cr-
(CO)3 moieties, the aromatic protons on the complexed den-
drimer resonate at significantly higher field, in the region from
5.1 to 5.5 ppm. For both heterometallic molecules 4 and 5
additional evidence for the η6-coordination of the Cr(CO)3 group
to the phenyl ring included the presence of the two typical ν-
(CtO) strong bands near 1970 and 1870 cm-1 in the IR spectra,
related to the A1 and E vibration modes of the Cr(CO)3 tripod.
The structures of 4 and 5 were also confirmed by the 13C NMR
spectra, which display exclusively the resonances expected for
the different carbon atoms, with the characteristic upfield shift
of ca. 37 ppm in the resonances of the coordinated aryl carbon
nuclei relative to the uncoordinated aromatics of the ferrocenyl
(20) (a) ComprehensiVe Handbook on Hydrosilylation; Marciniec, B.,
Ed.; Pergamon Press: Oxford, 1992. (b) Ojima, I. In The Chemistry of
Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.; John Wiley &
Sons: New York, 1989; Part 2, p 1479.

5156 Organometallics, Vol. 26, No. 21, 2007
Zamora et al.
Figure 1. Molecular structures of 1 (A) and of the heterometallic 4 (B). Hydrogen atoms have been omitted for clarity.
derivatives 1 and 3. In addition, resonances at ca. δ 233 ppm
due to the carbonyl carbon atoms were observed in the 13C NMR
spectra of 4 and 5. The 29Si NMR spectra of these dendritic
molecules are of interest, as they exhibit only the signals
expected for one (in 1 and 4) and two (for 3 and 5) different
types of silicon environments present in the molecules. Mass
spectral analysis of dendritic wedges 1, 3, 4, and 5 confirmed
the targeted dendritic structures. Specifically, in the fast atom
bombardment (FAB) mass spectra of the heterometallic 4 and
5, characteristic consecutive loss of M+ - 3CO and M+ - Cr-
(CO)3 units was detected, in addition to the peak corresponding
to the molecular ion M+ at m/z 468.1 (for 4) and m/z 1221.0
(for 5).
a solution of the corresponding compound in hexane. Figure 1
shows views of the molecular structures of 1 and 4. A summary
of crystallographic data and data collection parameters is
included in Table 1. Table 2 contains a comparison of selected
bond lengths and angles of compounds 1 and 4.
The two ferrocenyl-functionalized silanes 1 and 4 are chiral
about the silicon atom, and both form monoclinic crystals with
space group P21/c. In the monometallic 1 there are two different
molecules in the unit cell corresponding to the two enantiomers
(36.5% and 63.5%, respectively). The phenyl substituent is
arranged in an almost perpendicular position relative to the
ferrocenyl cyclopentadienyl rings. In the heterometallic 4 the
Cr(CO)3 tripod is coordinated in a transoid arrangement with
respect to the silicon-bridged ferrocenyl moiety. The silicon
atoms are nearly tetrahedral, with C-Si-C bond angles of
108.8° (for 1) and 106.1° (for 4). The cyclopentadienyl rings
X-ray Structures of 1 and 4. Single-crystal X-ray diffraction
studies of the two vinyl-substituted molecules 1 and 4 were
undertaken. Crystals of 1 and 4 were obtained at -40 °C from

Multiredox Heterometallic Carbosilane Dendrimers
Organometallics, Vol. 26, No. 21, 2007 5157
Table 1. Crystal Data and Structure Refinement Details for Compounds 1 and 4
1
4
empirical formula
fw
C19H18FeSi
330.27
C22H20CrFeO3Si
468.32
temp, K
100(2)
wavelength, Å
cryst syst
space group
a, Å
b, Å
c, Å
1.54178
monoclinic
P21/c
10.4463(2)
11.9294(2)
16.3013(3)
90
97.0010(10)
90
2016.29(6)
4
1.543
10.945
960
0.10 × 0.09 × 0.04
4.26 to 67.07
-12 e h e 10
-14 e k e 13
-17 e l e 18
13 231
7.3569(2)
12.9056(4)
17.5057(5)
90
100.907(2)
90
1632.06(8)
4
1.344
R, deg
â, deg
γ, deg
V, Å3
Z
density (calcd), mg m-3
abs coeff, mm-1
F(000)
8.012
688
cryst size, mm3
θ , deg
0.25 × 0.10 × 0.10
4.28 to 71.32
-8 e h e 7
-15 e k e 14
20 e l e 20
17 159
3083 [R(int) ) 0.0322]
97.6%
index ranges
no. of reflns collected
no. of indep reflns
completeness to θ ) 71.32°
absorp corr
3434 [R(int) ) 0.0482]
95.5%
semiempirical from equivalents
full-matrix least-squares on F2
3434/0/254
refinement method
no. of data/restraints/params
goodness-of-fit on F2
final R indices (I > 2σ(I))
R indices (all data)
3083/0/200
1.063
R1 ) 0.0290, wR2 ) 0.0781
R1 ) 0.0298, wR2 ) 0.0787
0.478 and -0.235
1.019
R1 ) 0.0412, wR2 ) 0.1027
R1 ) 0.0577, wR2 ) 0.1110
0.785 and -0.310
largest diff peak and hole, e Å-3
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Compounds 1 and 4
heterobimetallic 4 the Cr(CO)3 tripod adopts a nearly staggered
exo conformation with similar Cr-Carene and Cr-CO bond
distances that compare well with those found for related Cr-
(CO)3-containing compounds.22
1
4
Fe(1)-C(1)
2.0534(16)
1.8528(18)
1.8638(19)
1.8695(19)
1.8845(17)
1.298(4)
2.048(3)
1.853(4)
1.853(4)
1.870(4)
1.894(4)
1.320(6)
2.246(3)
1.851(4)
Si(1)-C(1)
The molecular arrangement of 4 in the crystal structure shown
in Figure 2 is of interest. An examination of the crystal packing
diagram along the c-axis shows that association of similar
organometallic moieties, a type of self-assembly, is apparently
driving the packing in the crystal. The intermolecular chromium
distances to the next neighboring molecules range between 6.206
and 8.487 Å and place the Cr(CO)3 tripods in a favorable
proximity for cluster-forming intermolecular solid-state reac-
tions. Thus, one can clearly observe repeating chromium-rich
and ferrocene-rich layers lying in the ab-plane; the distance
between one of these Fe pseudolayers to the Cr neighbor one
is 4.0318 Å.
Synthesis of the Homo- and Heterometallic Dendrimers
7-10. In the convergent approach, the previously synthesized
dendritic wedges are attached to a multifunctional core unit in
the final steps of the dendrimer construction.16,17 In this work,
the availability of free olefinic substituents at the focal point of
the dendritic wedges 1, 3, 4, and 5, potentially enables their
attachment to many different Si-H functionalized cores via
hydrosilylation chemistry. The four-directional carbosilane Si-
[(CH2)3Si(Me)2H]4 (6), in which the reactive Si-H are located
at the end of quite long silicon-containing chains, was selected
as a dendritic core, in order to prevent the possibility of steric
congestion and provide the final dendrimers with a fourth
branched core. Having obtained two different key starting vinyl-
functionalized molecules 1 and 4, the two synthetic pathways
Si(1)-C(11)
Si(1)-C(13)
Si(1)-C(14)
C(11)-C(12)a
Cr(1)-C(14)
Cr(1)-C(20)
Cr(1)-C(21)
1.840(4)
1.849(4)
Cr(1)-C(22)
Si(1)-C(1)-Fe(1)
C(1)-Si(1)-C(11)
C(1)-Si(1)-C(13)
C(1)-Si(1)-C(14)
C(11)-Si(1)-C(13)
C(12)-C(11)-Si(1)
C(13)-Si(1)-C(14)
C(21)-Cr(1)-C(20)
C(21)-Cr(1)-C(22)
C(22)-Cr(1)-C(20)
125.02(9)
109.29(8)
110.04(8)
108.80(7)
110.96(9)
124.21(19)
126.34(19)
111.08(17)
111.92(18)
105.91(16
110.99(19)
108.55(16)
108.17(17)
87.52(16)
88.18(17)
88.24(17)
a For 1 this distance is shorter than for 4 due to the contribution of the
disorder of the vinyl group.
of the ferrocenyl moiety in 1 are essentially planar and nearly
parallel and exhibit a fully eclipsed conformation. By contrast,
the two cyclopentadienyl groups of the heterometallic 4 are
arranged in a conformation between eclipsed and staggered,
which is presumably due to the sterically demanding Cr(CO)3
tripod coordinated to the phenyl ring. In η6-areneCr(CO)3
compounds, the orientation of the carbonyl ligands with respect
to the arene substituents has been shown to be dependent on
both the donor and steric properties of the substituent.21 In the
(22) See for example: (a) Santi, S.; Ceccon, A.; Bisello, A.; Durante,
C.; Ganis, P.; Orian, L. Organometallics 2005, 24, 4691. (b) Gomes, E. L.
S.; Ho¨rner, M.; Young, V. G., Jr.; Dupont, J.; Caliman, V.; Casagrande, O.
L., Jr. Organometallics 1999, 18, 3869. (c) Mu¨ller, T. J. J.; Blu¨mel, J. J.
Organomet. Chem. 2003, 683, 354.
(21) Davis, R.; Kane-Maguire, L.A. P. In ComprehensiVe Organometallic
Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon:
Oxford, England, 1982; Vol. 3, pp 1001-54.

5158 Organometallics, Vol. 26, No. 21, 2007
Zamora et al.
Figure 2. Crystal-packing diagram of 4 showing the iron-rich and chromium-rich pseudolayers.
depicted in Scheme 2 can be envisaged to obtain the targeted
first-generation heterooctametallic dendrimer 7, and both were
attempted.
involves two reaction steps and allowed the synthesis of both
the first-generation tetraferrocenyl dendrimer 8 and the targeted
heterooctametallic first-generation dendrimer 7. In contrast to
the above-described results, the hydrosilylation reaction of the
more electron-rich vinyl-substitued 1 with the Si-H tetrafunc-
tionalized dendrimer 6, in the presence of Karstedt’s catalyst,
in toluene solution at 40 °C, proceeded cleanly to completion,
affording the first-generation dendrimer 8 (Scheme 2). In the
same way, the second-generation octaferrocenyl dendrimer 9
(Chart 1) was synthesized by hydrosilylation reaction of the
growth dendritic wedge 3 and the carbosilane core 6. Again,
1H NMR and IR spectroscopies established that complete
reaction of the four Si-H functionalities in 6 was easily
achieved under mild conditions. After purification of the
hydrosilylated products by column chromatography, the tetra-
ferrocenyl and octaferrocenyl dendrimers 8 and 9 were isolated
as air-stable, orange, tacky oils. Subsequent thermal treatment
of dendrimers 8 and 9 with Cr(CO)6 in n-Bu2O/THF afforded
the desired first- and second-generation heterometallic den-
drimers 7 and 10 (see Scheme 2 and Chart 1, respectively).
Not surprisingly, thermal displacement of CO in Cr(CO)6 by
the phenyl rings of dendrimer 9 was not as facile as with 8,
and more forcing conditions than those used in the synthesis of
the octametallic dendrimer 7 were required. After appropriate
workup, the desired heterometallic dendrimers 7 and 10,
containing eight and 20 organometallic units, respectively, were
isolated as yellow-orange, tacky oils.
The two routes that were employed to prepare dendrimer 7
involve either (A) hydrosilylation reaction of the heterobimetallic
4 with the carbosilane core 6 or (B) synthesis of the first-
generation tetraferrocenyl dendrimer 8, by hydrosilylation
reaction of 1 and 6, followed by thermal treatment of 8 with
chromium hexacarbonyl. Route A has the advantage that the
desired heterometallic dendrimer 7 is produced directly, in a
single hydrosilylation reaction step after chromium complexation
of the phenyl ring to Cr(CO)3 units in 4. However, attempts to
graft by hydrosilylation reaction the Cr(CO)3-complexed den-
dritic wedge 4 to the core molecule 6 failed in large measure to
afford the expected heterooctametallic dendrimer 7. Reaction
of 4 with 6, in toluene at 70 °C, in the presence of Karstedt’s
catalyst led to significant amount of the starting 4, in addition
to a small amount of the desired 7 and other presumably
decomposition materials as inferred from 1H NMR and IR
spectra. This result indicates that the presence of the Cr(CO)3
moiety in 4 induces an electron-deficient character on the phenyl
ring bound to the Si-CHdCH2 group that clearly decreases
the effectiveness of the hydrosilylation reaction with the Si-H
functionalized core molecule 6.23-25 Furthermore, isolation of
the pure dendrimer 7 from this multicomponent mixture proved
to be a very difficult task. Consequently, for further synthetic
studies this path to the desired heterometallic dendrimers did
not seem very promising and was therefore abandoned.
In route B the hydrosilylation reaction of the Si-CHdCH2
group with the core 6 was done prior to the coordination of the
phenyl ligand to the tricarbonylchromium fragment. This route
The structural identities of the novel ferrocenyl dendrimers
8 and 9 and of the heterometallic dendrimers 7 and 10 were
confirmed by IR, 1H, 13C, and 29Si NMR spectroscopies, matrix-
assisted laser desorption, ionization time-of-flight mass spec-
trometry (MALDI-TOF-MS), and elemental analysis. In the 1H
NMR spectra of 8 and 9, confirming evidence for the complete
functionalization of the four reactive Si-H sites in the carbosi-
lane dendritic framework 6 with silicon-bridged phenyl and
ferrocenyl moieties is provided by the total absence of the Si-H
resonance near δ 3.8 ppm, as well as by the expected integration
ratio of the protons corresponding to the ferrocenyl groups, the
methylene units, and the methyl groups of the carbosilane
dendritic framework. The structures of dendrimers 7-10 were
corroborated by mass spectrometry (FAB or MALDI-TOF). The
(23) It is well-known that electron-withdrawing substituents on the vinyl
group decrease the rate of hydrosilylation processes compared to the more
electron-donating groups. On the other hand, steric factors due to substituents
in both silane and vinyl groups may also affect the rate and completeness
of hydrosilylation reactions. See, for example, refs 20, 24, and 25.
(24) (a) Stein, J.; Lewis, L. N.; Smith, K. A.; Lettko, K. X. J. Inorg.
Organomet. Polym. 1991, 1, 325. (b) Liu, H. Q.; Harrod, J. F. Can. J. Chem.
1990, 68, 1100.
(25) For a recent interesting work illustrating the effect of the substituents
of the Si-H and CdC groups on hydrosilylation reactions see: Hilf, S.;
Cyr, P. W.; Rieder, D. A.; Manners, I.; Ishida, T.; Chujo, Y. Macromol.
Rapid Commun. 2005, 26, 950.

Multiredox Heterometallic Carbosilane Dendrimers
Organometallics, Vol. 26, No. 21, 2007 5159
Scheme 2. Two Alternative Synthetic Routes for the Construction of the Heterometallic Dendrimer 7
Chart 1
main peaks in the spectra of the tetra- and octanuclear
dendrimers 8 and 9 are singly charged molecular ions at m/z
1761.7 (FAB) and 3684.3 (MALDI-TOF), respectively, which
in both cases correspond to the correct molecular mass. The
FAB mass spectrum of the heterometallic 7 shows the molecular
ion M+ at m/z 2304.5 as well as a clear characteristic pattern

5160 Organometallics, Vol. 26, No. 21, 2007
Zamora et al.
Table 3. Cyclic Voltammetric Data for the Homometallic
and Heterometallic Dendritic Compoundsa
and eight-electron redox systems has been successful, resulting
in detectable electroactive material persistently attached to the
electrode surfaces. The voltammetric response of an electrode-
posited film of the second-generation dendrimer 9 in CH2Cl2 is
shown in Figure 3, as an illustrative example. The electroactive
dendrimer film behaved almost ideally with rapid electron- and
charge-transfer kinetics.
Fe centered
1/2 (V)b
Cr centered
1/2 (V)b
compound
E
E
1
3
4
5
7
8
9
10
0.44 [0.79]
0.46 [0.83]
0.50 [0.96]
0.52 [1.00]
0.51 [0.97]
0.44 [0.80]
0.45 [0.50]
0.53 [1.05]
0.90 [0.55]
0.91 [1.10]
0.92 [0.60]
A well-defined, symmetrical oxidation-reduction wave is
observed, which is characteristic of a surface-confined redox
couple, with the expected linear relationship of peak current
with potential sweep rate V (see inset in Figure 3).28 The shape
of the features in the cyclic voltammograms is independent of
the scan rate from 5 to 1000 mV s-1, and repeated scanning
does not change the voltammograms, demonstrating that films
of the octaferrocenyl 9 are stable to electrochemical cycling. A
formal potential value of E1/2 ) +0.45 V vs SCE was found
for films of 9, which is nearly identical to the formal potential
of the octametallic dendrimer 9 in solution. For films examined
at scan rates lower than 100 mV s-1 no splitting between the
oxidation and reduction peaks was observed, and ∆Epk increases
only slightly with increasing sweep rate (∆Epk ) 15 mV at 150
mV s-1), suggesting that the rate of electron transfer is rapid
on the experimental time scale. Likewise, a value of the full
width at half-maximum, ∆Efwhm, of 58 mV was measured for
the surface wave (at a scan rate of 100 mV s-1), which is smaller
than the ideal peak width expected for surface-confined redox
species,29 indicating that attractive interactions take place
between the electroactive ferrocenyl sites attached to the
electrode surface.28 Noteworthy, Pt and glassy-carbon electrodes
modified with films of 9 are extremely durable and reproducible.
Extended cyclic voltammetric scans can be carried out in CH2-
Cl2 and CH3CN solutions with no detectable loss of electrode-
posited material. This is an important observation since many
of the potential applications of the modified electrodes as multi-
electron-transfer mediators will require extensive redox cycling.
Electrodeposited films of the tetraferrocenyl first-generation
dendrimer 8, obtained under the same conditions as for 9,
showed qualitatively similar voltammetric responses and a
comparable stability to the redox process.
Electrochemistry of the Heterometallic Dendritic Mol-
ecules 4, 5, 7, and 10. The electrochemical oxidation of 4, 5,
7, and 10 has been examined by cyclic voltammetry and
differential pulse voltammetry using CH2Cl2 as non-nucleophilic
solvent and n-Bu4NPF6 as supporting electrolyte. The electro-
chemical behavior of these dendritic molecules is in accordance
with their heterometallic nature. For the bimetallic 4 and the
octametallic 7 the voltammetric behavior of the two molecules
is quite analogous, and the CV for dendrimer 7 is illustrated in
Figure 4 as an example.
Scanning up to the potential of 1.20 V vs SCE, the cyclic
voltammogram of 7 reveals two diffusion-controlled, reversible
oxidation processes at about E1/2 ) 0.51 V and E1/2 ) 0.93 V
vs SCE, respectively (see data in Table 3). The first oxidation
process can be ascribed to the oxidation of the iron centers,
and the second one to the oxidation of the chromium centers.
For both heterometallic compounds 4 and 7, the E1/2 values of
the first oxidation process are slightly higher than the E1/2 found
for the oxidation of the iron centers of the related homometallic
0.95 [1.13]
a Measured in CH2Cl2 solution, V ) 0.1 V s-1
separation values, ∆E (V), are indicated in brackets.
.
b The peak potential
of peaks that arise from species formed by consecutive loss of
Cr(CO)3 moieties (see Supporting Information). In the MALDI-
TOF spectrum of dendrimer 10 the molecular ion peak at m/z
5317.0 is detectable but is much less intense than peaks that
arise from the dendrimer minus CO and Cr(CO)3 losses.
Electrochemical Behavior of the Ferrocenyl Dendritic
Molecules 1, 3, 8, and 9. An important aspect of this work is
to evaluate the redox properties of the new multimetallic
dendritic molecules, not only in homogeneous solution but also
confined onto electrode surfaces (i.e., where the molecules serve
as electrode modifiers). Electrochemical data for the homome-
tallic compounds 1, 3, 8, and 9 are shown in Table 3, together
with those of the related heterometallic dendritic molecules.
The cyclic voltammograms (CVs) of 1, 3, 8, and 9 show a
single reversible oxidation process. The voltammetric features
(ipc/ipa essentially equal to one unit, ∆Epk values about 50-85
mV, and Epk independent of the scan rate) clearly show that
the oxidation of 1 and 3 and of the dendrimers 8 and 9 is
chemically and electrochemically reversible, resulting in the
production of the ferricinium species [1]+ and the stable and
soluble polycations [3]2+, [8]4+, and [9]8+. Coulometry mea-
suments in CH2Cl2 solutions indicated the removal of one (for
1), two (for 3), four (for 8), and eight (for 9) electrons/molecule.
In addition, differential pulse voltammetry measurements (DPV)
gave only one wave (see Supporting Information), indicating
that the oxidation of all the ferrocenyl moieties in the dendritic
molecules occurs at the same potential. The electrochemical
results unequivocally demonstrate that in the polyferrocenyl
dendrimers 8 and 9 the observed reversible oxidation waves
represent a simultaneous multielectron transfer of four and eight
electrons, respectively, as expected for independent, reversible
one-electron process, at the same potential, of the four (in 8)
and eight (in 9) noninteracting ferrocenyl redox centers.26
On the other hand, the diffusion coefficients (Do) for the
polyferrocenyl dendrimers in CH2Cl2 solution have been
calculated from cyclic voltammetry using the Randles-Sevcik
equation.27 As expected, the diffusion coefficients of the
multimetallic dendritic molecules 8 and 9 (Do ) 4.13 × 10-6
and 6.57 × 10-7 cm2 s-1, respectively) are lower than that of
the monometallic 1 (Do ) 6.92 × 10-6 cm2 s-1) of small size.
Furthermore, the values of the diffusion coefficients increase
as the number of peripheral ferrocenyl moieties increases; that
is, Do increases with increasing dendrimer generation.
A key feature concerning the ferrocenyl dendrimers 8 and 9
is their ability to deposit onto electrode surfaces as they become
oxidized. Thus, modification of electrodes with films of
dendrimers 8 and 9 containing, respectively, reversible four-
(28) (a) Murray, R. W. In Molecular Design of Electrode Surfaces;
Murray, R. W., Ed.; Techniques of Chemistry XXII; Wiley: New York,
1992. (b) Abrun˜a, H. D. In ElectroresponsiVe Molecular and Polymeric
Systems; Skotheim, T. A., Ed.; Dekker: New York, 1988; Vol. 1.
(29) In surface-immobilized redox species, the peak width for an ideal
surface wave is EFWHM ) 90.6/n (n ) number of electrons transferred per
molecule). See ref 28.
(26) Flanagan, J. B.; Margel, S.; Bard, A. J.; Anson, F. C. J. Am. Chem.
Soc. 1978, 100, 4248.
(27) Analytical Electrochemistry, 2 ed.; Wang, J., Ed.; Wiley-VCH: New
York, 2000.

Multiredox Heterometallic Carbosilane Dendrimers
Organometallics, Vol. 26, No. 21, 2007 5161
Figure 3. Voltammetric response of a glassy-carbon disk electrode modified with a film of the octaferrocenyl dendrimer 9, measured in
CH2Cl2 with 0.1 M n-Bu4NPF6. Scan rates: 25, 50, 75, 100, and 150 mV s-1. Inset: Scan rate dependence of the anodic peak current. The
surface electroactive coverage of ferrocenyl sites in the film was Γ ) 2.11 × 10-10 mol of ferrocenyl sites cm-2
.
Figure 5. Differential pulse voltammogram of the pentametallic
5 in CH2Cl2/n-Bu4NPF6 solution.
The pentametallic dendritic wedge 5, which has two ferro-
cenyl moieties and three (η6-aryl) cromiumtricabonyl subunits,
shows a somewhat different electrochemical oxidation volta-
mmetric feature. The presence of an extra (η6-C6H5)Cr(CO)3
moiety, nonbonded to a ferrocenyl unit, is naturally reflected
by an additional chromium-centered oxidation process. The
cyclic voltammogram of the pentametallic 5 in CH2Cl2 solution
exhibits two separated oxidation waves, the second one being
broad and poorly resolved. Both electron transfers exhibit
directly associated responses in the reverse scan. For both waves,
the ratio of cathodic to anodic peak current (ipc/ipa) was close
to unity, and the plot of peak current vs V1/2 was linear, indicating
diffusion-controlled redox processes. On the other hand, the
differential pulse voltammogram of 5 in CH2Cl2 solution shown
in Figure 5 exhibits two separated peaks of different heights.
The second peak is broader than the first and displays a shoulder
(marked in Figure 5 with an asterisk), suggesting two overlapped
redox processes. Integration of the peak areas gives a first to
second wave ratio of 2:3. Formal potentials were calculated from
Figure 4. Cyclic voltammogram (A) and differential pulse
voltammogram (B) of 7 in CH2Cl2 solution.
ferrocenyl precursor molecules 1 and 8, and this is reasonably
due to the electron-withdrawing nature of the adjacent (η6-
C6H5)Cr(CO)3 moieties, bonded through a bridging silicon atom.
In addition, the chromium-centered oxidations of the hetero-
metallic 4 and 7 show a slight anodic shift with respect to the
E
1/2 for (η6-C6H5)Cr(CO)3 as a result of the positive charges in
[4]+ and [7]4+ generated after the first oxidation process.
the DPV peak potentials, and the results obtained were E1/2
0.51 V for the process corresponding to the first peak, E1/2
)
≈

5162 Organometallics, Vol. 26, No. 21, 2007
Zamora et al.
Silica gel (70-230 mesh) (Merck) was used for column chromato-
graphic purifications. (Tri-n-butylstannyl)ferrocene was synthesized
as described in the literature.19 Phenylchlorosilane was prepared
by reaction of phenylsilane (Fluka) with PCl5 according to the
literature.31 The carbosilane Si[(CH2)3SiMe2H]4 (6) was prepared
by treatment of Si[(CH2)3SiMe2Cl]4 with LiAlH4, as we have
described previously.14 Infrared spectra were recorded on a Bomem
MB-100 FT-IR spectrometer. NMR spectra were recorded on
Brucker-AMX-300 and Bruker DRX-500 spectrometers. Chemical
shifts are reported in parts per million (δ) with reference to residual
solvent resonances for 1H and 13C NMR (CDCl3, 1H, δ 7.27 ppm;
13C, δ 77.0 ppm). 29Si NMR spectra were recorded with inverse-
gated proton decoupling in order to minimize nuclear Overhauser
effects. In some cases the solutions contained 0.015 M Cr(acac)3
in order to reduce T1’s. FAB mass spectral analyses were conducted
on a VG Auto Spec mass spectrometer equipped with a cesium
ion gun. The MALDI-TOF mass spectra were obtained using a
Reflex III (Bruker) mass spectrometer equipped with a nitrogen
laser emitting at 337 nm. The matrix was ditranol. Elemental
analyses were performed by the Microanalytical Laboratory,
Universidad Auto´noma de Madrid, Madrid, Spain.
Electrochemical Measurements. Cyclic voltammetric experi-
ments were recorded on a BAS-CV-50W potentiostat. CH2Cl2
(spectrograde) for electrochemical measurements was freshly
distilled from calcium hydride under argon. The supporting
electrolyte was tetra-n-butylammonium hexafluorophosphate (Flu-
ka), which was purified by recrystallization from ethanol and was
typically used at a concentration of 0.1 M. A conventional three-
electrode cell connected to an atmosphere of prepurified nitrogen
was used. All cyclic voltammetric experiments were performed
using either a platinum-disk working electrode (A ) 0.020 cm2) or
a glassy carbon-disk working electrode (A ) 0.070 cm2). All
potentials are referenced to the saturated calomel electrode (SCE).
A coiled platinum wire was used as a counter electrode. Solutions
were typically 10-4 to 10-3 M in the redox-active species for cyclic
voltammetry. The solutions for the electrochemical experiments
were purged with nitrogen and kept under an inert atmosphere
throughout the measurements. Differential pulse voltammetry was
done with scan rates of 20 and 50 mV s-1, a pulse height of 50
mV, duration of 50 ms, and pulse intervals of 2 s. Formal potentials
0.80 V for the second peak (observed as a shoulder), and E1/2
) 0.91 V for the peak at higher potential.
Assignment of the formal potentials observed in the DPV of
5 to the corresponding electrochemical processes has been
carried out by comparison with the redox potentials observed
for the related dendritic homo- and heretometallic dendritic
molecules 3 and 4, respectively. On this basis, it looks
reasonable to suggest that the two ferrocenyl moieties of 5 are
the first metallic centers to be oxidized. Consequently, the first
oxidation peak is attributed to the simultaneous two-electron
transfer of two electrons removed from the two ferrocenyl
subunits in the molecule, resulting in the formation of the
dicationic species [5]2+. The central, almost unresolvable,
oxidation peak (at about E1/2 ) 0.80 V) presumably is centered
in the chromium center of the isolated (η6-C6H5)Cr(CO)3 unit
linked to the Si-allyl group. Finally, two electrons are removed
(at E1/2 ) 0.91 V) from the remaining chromium centers of the
(η6-C6H5)Cr(CO)3 moieties neighboring the ferrocenyl moieties
already oxidized. The heterometallic dendrimer 10 displayed a
qualitatively similar DPV response, although in this case the
second oxidation wave was considerably broadened and the
redox process displays electrochemical irreversibility, as shown
by the absence of the corresponding cathodic peak in the reverse
scan.
Concluding Remarks
We have designed and explored an efficient convergent
growth approach that permits the preparation of a new family
of redox-active heterometallic dendritic molecules, derived from
carbosilane frameworks and functionalized with silicon-linked
ferrocenyl and (η6-C6H5)Cr(CO)3 moieties. In this synthetic
strategy suitable organometallic dendritic wedges containing a
single olefinic functionality at the focal point are constructed
first. Subsequently, these dendrons are attached to a Si-H
tetrafunctionalized core molecule via hydrosilylation chemistry
in order to provide the final first- and second-generation
heterometallic dendrimers with a fourth branched core. The
convergent methodology described here is advantageous because
of its simplicity and offers ample opportunities for structural
variations; therefore, it will represent a versatile method for
accessing a potentially large number of dendritic molecules
containing organometallic moieties of different nature. Further
extension of this synthetic aproach is in progress in order to
prepare siloxane-based heterometallic dendritic polymeric as-
semblies (dendronized polymers).30
were calculated from the DPV peak potentials using E1/2 ) Epk
+
E
pulse/2, where Epulse is the pulse height. Coulometric measurements
were made with a PAR-379 digital coulometer, using Pt gauze as
a working electrode.
X-ray Crystal Structure Determination. Compounds 1 and 4
were structurally characterized by single-crystal X-ray diffraction.
A suitable orange crystal of 1 of needle shape and dimensions 0.25
× 0.10 × 0.10 mm and a suitable yellow crystal of 4 of star shape
and dimensions 0.10 × 0.09 × 0.04 mm were located and mounted
on a glass fiber with “magic oil”. The samples were transferred to
a Bruker SMART 6K CCD area-detector three-circle diffractometer
with a MacScience rotating anode (Cu KR radiation, λ ) 1.54178
Å) generator equipped with Goebel mirrors at settings of 50 kV
and 100 mA. For compound 1 a total of 3083 independent
reflections (Rint ) 0.0322) were colleted in the range 4.28° < θ <
71.32°. For 2 a total of 3434 independent reflections (Rint ) 0.0482)
were colleted in the range 4.26° < θ < 67.07°. X-ray data were
collected at 100 K, with a combination of six runs at different æ
and 2θ angles, 3600 frames. The data were collected using 0.3°
wide ω scans with a crystal-to-detector distance of 4.0 cm. The
substantial redundancy in data allows empirical absorption correc-
tions (SADABS)32 to be applied using multiple measurements of
symmetry-equivalent reflections. The raw intensity data frames were
integrated with the SAINT program,33 which also applied correc-
Experimental Section
Materials and Equipment. All reactions and compound ma-
nipulations were performed under an oxygen- and moisture-free
atmosphere (N2 or Ar) using standard Schlenk techniques. Solvents
were dried by standard procedures over the appropriate drying
agents and distilled immediately prior to use. Ferrocene and Cr-
(CO)6 (Fluka) were purified by sublimation prior to use. tert-
Butyllithium (1.7 M solution in pentane), n-butyllithium (2.5 M
solution in hexane), allylmagnesium bromide (1.0 M solution in
diethyl ether), and tetraallylsilane (Aldrich) were used as received.
(Tri-n-butylstannyl) chloride (Aldrich) and methylphenylvinylchlo-
rosilane (Fluka) were distilled prior to use. Platinum-divinyltet-
ramethyldisiloxane complex (3-3.5% in xylene) (Karstedt’s cata-
lyst), available from Petrarch Systems Inc., was used as received.
(30) Further studies of the use of 1 and 4 in the synthesis of siloxane-
based heterometallic dendritic and polymeric assemblies are in progress
and will be reported.
(31) Mawaziny, S. J. Chem. Soc. (A) 1970, 1641.
(32) Sheldrick, G. M. SADABS Version 2.03, Program for Empirical
Absorption Correction; University of Go¨ttingen: Germany, 1997-2001.

Multiredox Heterometallic Carbosilane Dendrimers
Organometallics, Vol. 26, No. 21, 2007 5163
tions for Lorentz and polarization effects. The software package
SHELXTL version 6.10 was used for space group determination,
structure solution, and refinement.34 The space group determination
was based on a check of the Laue symmetry and systematic
absences and was confirmed using the structure solution. The
structures were solved by direct methods (SHELXS-97), completed
with difference Fourier syntheses, and refined with full-matrix least-
squares using SHELXL-97, minimizing w(Fo2 - Fc2)2.35,36 Weighted
R factors (Rw) and all goodness of fit S are based on F2; conventional
R factors (R) are based on F. All non-hydrogen atoms were refined
with anisotropic displacement parameters. The hydrogen atom
positions were calculated geometrically and were allowed to ride
on their parent carbon atoms with fixed isotropic U. All scattering
factors and anomalous dispersions factors are contained in the
SHELXTL 6.10 program library. The crystal structures of 1 and 4
have been deposited at the Cambridge Crystallographic Data Centre
and allocated the deposition numbers CCDC648116 and CCDC
648117, respectively.
ether containing 2.0 mL (1.9 mmol) of allylmagnesium bromide
(1 M in diethyl ether). The resulting orange solution was refluxed
for 4 h, cooled to 0 °C, and then hydrolyzed with aqueous NH4Cl
(10%). The organic layer was separated, washed with water, and
dried over anhydrous MgSO4. The solvent was removed under
vacuum, and the residue was purified by column chromatography.
An orange band was colleted using hexane as eluent. Solvent
removal afforded the desired growth dendron 3, carrying two
ferrocenyl units. Yield: 0.70 g (57%). Anal. Calcd for C47H52Si3-
Fe2: C, 69.45; H, 6.45. Found: C, 69.38; H, 6.36. 1H NMR (CDCl3,
300 MHz): δ 0.51 (s, 6H, CH3), 0.83 (m, 8H, CH2CH2), 1.83 (d,
2H, CH2CHdCH2), 3.99 (s, 10H, C5H5), 4.05, 4.10, 4.33 (m, 8H,
C5H4), 4.82-4.90 (m, 2H, CHdCH2), 5.75-5.80 (m, 1H, CHd
CH2), 7.35, 7.50 (m, 15H, C6H5). 13C{1H} NMR (CDCl3, 75.43
MHz): δ -4.43 (CH3), 4.10, 7.78 (CH2), 19.69 (CH2CHdCH2),
68.39, 69.01, 70.91, 71.08, 73.65, 73.70 (C5H4/C5H5), 113.6, 134.10
(CHdCH2), 127.80, 127.91, 129.01, 129.16, 136.30 (C6H5). 29Si-
{1H} NMR (CDCl3, 59.3 MHz): δ -5.15 (SiFc), 0.30 (SiCH2-
CHdCH2).MS(FAB): m/z(%)812.0[M+](7),305.0[SiFcCH3C6H5]+,
(100).
Synthesis of (CH2dCH)MeSi[{(η6-C6H5)Cr(CO)3}Fc] (4). A
degassed solution of 0.40 g (1.8 mmol) of chromium hexacarbonyl
and 0.50 g (1.5 mmol) of 1 in a mixture of 90 mL of n-dibutyl
ether and 10 mL of THF was heated to reflux temperature (oil bath
140 °C). Over the course of the reaction, new IR carbonyl bands
at 1972 and 1873 cm-1 were observed to increase in intensity.
Likewise, in the 1H NMR (CDCl3) spectrum, the resonances in the
7.3-7.5 ppm region progressively disappeared while new reso-
nances in the range 5.9-6.5 ppm were detected. After 48 h, the
suspension was filtered through a pad of Celite to remove the small
amounts of insoluble decomposition products and some unreacted
Cr(CO)6. From the resulting light orange solution, the solvent was
removed under vacuum, affording a yellow solid, which was
purified by treatment with hexane solution at low temperature. After
standing at -30 °C, a yellow solid was formed, which was filtered
off to afford the desired molecule 4, which was isolated as an air-
unstable, crystalline, yellow solid. Yield: 0.40 g (63%). Anal. Calcd
for C22H20O3SiFeCr: C, 56.41; H, 4.31. Found C, 56.30; H, 4.22.
1H NMR (CDCl3, 300 MHz): δ 0.66 (s, 3H, CH3), 4.14 (s, 5H,
C5H5), 4.22, 4.23, 4.45 (m, 4H, C5H4), 5.09, 5.38, 5.48 (m, 5H,
C6H5), 5.93 (dd, 3J ) 20.5 Hz, 2J ) 3.6 Hz, 1H, CHdCHtrans Hcis),
Synthesis of (CH2dCH)MePhSiFc (1). Ferrocenyllithium was
generated in situ via the reaction of (tri-n-butylstannyl)ferrocene
(30.0 g, 63.2 mmol) with n-butyllithium (28.5 mL, 2.5 M solution
in hexane) in 50 mL of THF at -78 °C. After 90 min, the mixture
was warmed to -30 °C. To this stirred system was added dropwise
methylphenylvinylchlorosilane (11.30 g, 52.0 mmol) in 20 mL of
THF. The mixture was allowed to warm to room temperature and
was stirred for 14 h. The solution was concentrated, treated with
hexane, and then filtered to remove the lithium chloride byproduct.
Solvent removal yielded an orange, oily product, which was purified
by column chromatography on silica gel using hexane as eluent. A
first band containing ferrocene was eluted and, subsequently, a
second major orange band was collected. Solvent removal afforded
the desired product 1 as an air-stable, orange, crystalline solid.
Yield: 14.50 g (75%). Anal. Calcd for C19H20SiFe: C, 68.66; H,
1
6.07. Found: C, 68.58; H, 6.10. H NMR (CDCl3, 300 MHz): δ
0.61 (s, 3H, CH3), 4.10 (s, 5H, C5H5), 4.14, 4.17, 4.40 (m, 4H,
C5H4), 5.85 (dd, 3J ) 19.8 Hz, 2J ) 3.3 Hz, 1H, CHdCHtrans Hcis),
3
2
6.15 (dd, J ) 14.8 Hz, J ) 3.3 Hz, 1H, CHdCHtrans Hcis), 6.40
3
2
(dd, J ) 19.8 Hz, J ) 14.8 Hz, 1H, CHdCH2), 7.34 (m, 3H,
C6H5), 7.53 (m, 2H, C6H5). 13C{1H} NMR (CDCl3, 75.43 MHz):
δ -3.75 (CH3), 67.38, 68.32, 71.12, 73.66 (C5H5/C5H4), 127.61,
128.95, 134.26, 136.84 (C6H5), 133.53, 137.70 (CHdCH2). 29Si-
{1H} NMR (CDCl3, 59.3 MHz): δ -14.05 (Si(CH3)). MS (FAB):
m/z (%): 332.6 [M+], (100), 147.6 [SiMe(CHdCH2)]+, (35.2).
Synthesis of PhClSi[(CH2)2MePhSiFc]2 (2). To a solution of
1 (1.00 g, 3.0 mmol) in toluene (30 mL) was added 40 µL of a
solution of Karstedt’s catalyst. The mixture was stirred at room
temperature for 0.5 h. A solution of phenylchlorosilane (0.20 g,
1.5 mmol) in dry toluene (10 mL) was added dropwise. The mixture
was heated to 40 °C, and after a few minutes, a FTIR spectrum of
the reaction mixture showed complete loss of the ν(Si-H)
3
2
6.24 (dd, J ) 15.3 Hz, J ) 3.6 Hz, 1H, CHdCHtrans Hcis), 6.50
(dd, J ) 20.5 Hz, J ) 15.3 Hz, 1H, CHdCH2). 13C{1H} NMR
(CDCl3, 75.43 MHz): δ -4.11 (CH3), 64.42, 68.49, 71.66, 71.84,
73.57 (C5H4/C5H5), 90.31, 95.73, 97.90, 100.22 (C6H5), 134.82
(CHdCH2), 232.91 (CO). 29Si{1H} NMR (CDCl3, 59.3 MHz): δ
-10.88 (SiFc). IR (KBr): ν(CtO) 1972 and 1873 cm-1. MS
(FAB): m/z (%) 468.1 [M+] (65), 384.1 [M+ - 3CO] (100), 332.1
[M+ - Cr(CO)3], (80).
3
2
1
Synthesis of (CH2dCHCH2){(η6-C6H5)Cr(CO)3}Si[(CH2)2Me-
{(η6-C6H5)Cr(CO)3}SiFc]2 (5). Using the same method as detailed
for the preparation of 4, the pentametallic 5 was synthesized starting
from 0.57 g (0.7 mmol) of 3 and 0.58 g of Cr(CO)6 (2.6 mmol).
The reaction was completed after 72 h as it was established from
absorption at 2179 cm-1. Likewise, H NMR spectroscopy con-
firmed the complete disappearance of the Si-H proton resonances
of the starting phenylchlorosilane. The mixture was filtered, the
solvent was removed under vacuum, and the remaining orange oil
1
(1.10 g, 95%) was used immediately in the next reaction step. H
1
IR and H NMR spectroscopies. The reaction mixture treated as
NMR (300 MHz, CDCl3): δ 0.43 (s, 6H, CH3), 0.92, 1.20 (m, 8H,
CH2CH2), 4.10 (s, 10H, C5H5), 4.08-4.40 (br, 8H, C5H4), 7.35,
7.50 (m, 15H, C6H5).
Synthesis of (CH2dCHCH2)PhSi[(CH2)2MePhSiFc]2 (3). A
solution of 1.10 g (1.42 mmol) of recently prepared 2 in diethyl
ether was added dropwise with vigorous stirring to 50 mL of diethyl
above and the heterometallic dendron 5 was isolated as an air-
unstable yellow solid. Yield: (0.21 g, 43%). Anal. Calcd for
C56H52O9Si3Fe2Cr3: C, 55.08; H, 4.30. Found: C, 54.96; H, 4.21.
1H NMR (CDCl3, 300 MHz): δ 0.57 (s, 6H, CH3), 1.02 (br, 8H,
CH2), 1.94 (d, 2H, CH2CHdCH2), 4.10, 4.17, 4.45 (m, 18H, C5H5/
C5H4), 4.98, 5.81 (m, 3H, CHdCH2), 5.13, 5.43, 5.51 (m, 15H,
C6H5). 13C{1H} NMR (CDCl3, 125.8 MHz): δ -4.87 (SiCH3), 4.67,
7.75, (CH2CH2), 19.29 (CH2CHdCH2), 66.08, 68.42, 71.53, 71.72,
73.54 (C5H4/C5H5), 90.52, 90.77, 95.79, 98.45, 99.75, 100.10,
100.25 (C6H5), 115.32, 133.30 (CHdCH2), 233.10 (CO). 29Si{1H}
NMR (CDCl3, 99.4 MHz): δ -4.87 (SiFc), 1.03 (SiCH2CHdCH2).
IR (KBr): ν(CtO) 1972 and 1873 cm-1. MS (FAB): m/z (%)
(33) SAINT+NT Version 6.04; SAX Area-Detector Integration Program;
Bruker Analytical X-ray Instruments: Madison, WI, 1997-2001.
(34) Bruker AXS SHELXTL Version 6.10, Structure Determination
Package; Bruker Analytical X-ray Instruments: Madison, WI, 2000.
(35) Sheldrick, G. M. Acta Crystallogr. A 1990, 46, 467.
(36) Sheldrick, G. M. SHELXL97, Program for Crystal Structure Refine-
ment; Germany, 1997.

5164 Organometallics, Vol. 26, No. 21, 2007
Zamora et al.
1221.0 [M+] (1), 1084.0 [M+ - Cr(CO)3] (8), 948.13 [M+ - 2Cr-
(CO)3] (4), 812.2 [M+ - 3Cr(CO)3] (6), 305.0 [SiFcCH3C6H5]+
(100).
case, longer reaction periods (12 h) with a higher temperature
(65 °C) were required to achieve the complete incorporation of the
growth dendron 3 to the core molecule 6. After filtration and
purification by column chromatography using hexane as eluent, the
desired octaferrocenyl dendrimer 9 was isolated as an air-stable,
dark orange, tacky oil. Yield: 0.24 g (60%). Anal. Calcd for
C208H260Si17Fe8: C, 67.81; H, 7.12. Found: C, 67.65; H, 6.91. 1H
NMR (CDCl3, 300 MHz): δ 0.08 (s, 24H, Si(CH3)2), 0.52 (m, 24H,
CH3), 0.52 (m, 32H, CH2CH2CH2), 0.89 (m, 32H, SiCH2CH2), 1.28
(q, 16H, CH2CH2CH2), 4.00 (m, 40H, C5H5), 4.06, 4.10, 4.33 (m,
32H, C5H4), 7.35, 7.51 (m, 60 H, C6H5). 13C{1H} NMR (CDCl3,
125.75 MHz): δ -4.48 (CH3), -3.12 (Si(CH3)2), 7.69, 7.73
(CH2CH2), 18.45, 20.48 (CH2CH2CH2), 68.28, 69.03, 70.79, 70.95,
73.55, 73.60 (C5H5/C5H4), 127.70, 127.75, 128.81, 128.88, 134.11,
134.29, 138.31 (C6H5). 29Si{1H} NMR (CDCl3, 99.36 MHz): δ
-5.24 (SiFc), -0.90 (SiPh), 0.95 (SiCH2), 3.46 (SiCH3). MS
(MALDI-TOF): m/z 3684.3 [M+].
Synthesis of Dendrimer 7. This heterometallic derivative 7 was
obtained by the same thermal procedure as described for 4 and 5,
starting from 0.70 g (0.4 mmol) of 8 and Cr(CO)6 0.40 g (1.9
mmol). After 72 h the reaction was finished and the residue was
treated in a manner similar to 5. The desired heterometallic
dendrimer was isolated as an air-unstable, yellow-orange oil.
Yield: 0.32 g (37%). Anal. Calcd for C108H132Si9Fe4O12Cr4: C,
1
56.24; H, 5.77. Found: C, 56.17; H, 5.68. H NMR (CDCl3, 300
MHz): δ 0.01 (s, 24H, Si(CH3)2), 0.56 (m, 12H, CH3), 0.56 (br,
16H, CH2CH2CH2), 0.88 (m, 16H, CH2), 1.30 (br, 8H, CH2CH2-
CH2), 4.12 (s, 20H, C5H5), 4.21, 4.43 (m, 16H, C5H4), 5.08, 5.35,
5.47 (m, 20H, C6H5). 13C{1H} NMR (CDCl3, 75.43 MHz): δ -4.45
(CH3), -3.84 (Si(CH3)2), 8.02, 7.41 (CH2), 17.51, 18.60, 19.65
(CH2CH2CH2), 66.57, 68.34, 71.31, 71.46, 73.48 (C5H5/C5H4),
90.13, 95.55, 99.15, 100.33 (C6H5). 29Si{1H} NMR (CDCl3, 59.3
MHz): δ -1.68 (SiFc), 1.05 (SiCH2), 3.80 (SiCH3)). IR (KBr):
ν(CtO) 1961 and 1882 cm-1. MS (FAB): m/z (%) 2304.5 [M+]
(11.0), 2170.2 [M+ - Cr(CO)3] (8), 2035.1 [M+ - 2Cr(CO)3] (0.5),
1896.7 [M+ - 3Cr(CO)3] (0.3), 305.1 [SiFcCH3C6H5]+ (100).
Synthesis of Dendrimer 8. To a toluene solution (25 mL) of 1
(0.85 g, 2.5 mmol) was added 30 µL of Karstedt’s catalyst. The
mixture was stirred at room temperature for 0.5 h. A solution of
0.20 g (0.4 mmol) of the carbosilane 6 in toluene was added
dropwise, and then the mixture was warmed to 40 °C. The
attachment of 1 to the four Si-H active sites of the dendritic core
Synthesis of Dendrimer 10. In analogy with the synthesis of 7,
thermal treatment of 9 (0.32 g, 0.08 mmol) with an excess of Cr-
(CO)6 was carried out during 96 h. After appropriate workup, 10
was isolated as an air-unstable, yellow, tacky oil. Anal. Calcd for
C244H260Si17Fe8O32Cr8: C, 55.12; H, 4.93. Found: C, 54.92; H,
1
4.74. H NMR (CDCl3, 300 MHz): δ 0.06 (br, 24H, Si(CH3)2),
0.49 (br, 24H, CH3), 0.49 (br, 32H, CH2CH2CH2), 0.90 (m, 32H,
CH2CH2), 1.31 (br, 16H, CH2CH2CH2), 3.90 (s, 40H, C5H5), 4.09,
4.34 (br, 32H, C5H4), 5.10-5.44 (br, 60H, C6H5). 13C{1H} NMR
(CDCl3, 125. 75 MHz): δ -4.50 (CH3), -3.15 (Si(CH3)2), 7.41,
7.70 (CH2CH2), 18.45, 19.95 (CH2CH2CH2), 68.19, 69.00, 70.04,
70.90, 72.98, 73.40 (C5H5/C5H4), 90.50, 95.76, 99.30, 100.20
(C6H5). 29Si{1H} NMR (CDCl3, 99.36 MHz): δ -4.83 (SiFc),
-3.70 (SiPh), 0.98 (SiCH2), 3.20 (SiCH3)). MS (MALDI-TOF):
m/z 5317.0 [M+], 5181.0 [M+ - Cr(CO)3], 5045.0 [M+ - 2Cr-
(CO)3], 4909.0 [M+ - 3Cr(CO)3].
1
6 proceeded cleanly to completion in 4 h, as established from H
NMR and IR analysis of the reaction mixture. The solvent was
removed and the resulting oil was subjected to column chroma-
tography using hexane as eluent. A first band containing 1 was
separated, and with additional hexane, the desired 8 was eluted.
Solvent removal afforded the homometallic dendrimer 8 as an air-
stable, orange oil. Yield: 0.73 g (90%). Anal. Calcd for C96H132
-
Acknowledgment. The authors thank the Spanish Ministerio
de Educacio´n y Ciencia, Projects CTQ2005-02282/BQU and
CTQ2004-07381-C01-C02/BQU, for support of this research.
We are grateful to Prof. Jose´ Losada (Universidad Polite´cnica
de Madrid) for helpful discussions.
1
Si9Fe4: C, 65.43; H, 7.56. Found: C, 65.28; H, 7.45. H NMR
(CDCl3, 300 MHz): δ -0.08 (s, 24H, Si(CH3)2), 0.52 (m, 12H,
CH3), 0.52 (m, 16H, CH2CH2CH2), 0.86 (t, 16H, SiCH2CH2), 1.29
(q, 8H, CH2CH2CH2), 4.05 (m, 20H, C5H5), 4.10, 4.15, 4.35 (m,
16H, C5H4), 7.34 (m, 12H, C6H5), 7.53 (m, 8H, C6H5). 13C{1H}
NMR (CDCl3, 75.46 MHz): δ -4.38 (CH3), -3.75(Si(CH3)2), 7.78,
7.91 (CH2), 17.56, 18.66, 19.75 (CH2CH2CH2), 68.32, 69.32, 70.78,
70.94, 73.66 (C5H5/C5H4), 127.61, 128.945, 134.11, 138.54 (C6H5).
29Si{1H} NMR (CDCl3, 59.62 MHz): δ -5.15 (SiFc), 0.73 (SiCH2),
3.56 (SiCH3). MS (FAB): m/z (%) 1761.7 [M+] (5), 305.0
[SiFcCH3C6H5]+ (100).
Supporting Information Available: Complete crystallographic
data for compounds 1 and 4 (CIF files), representative mass spectra
for dendrimers 7 (FAB) and 8 (MALDI-TOF), representative CV
and DPV figures of ferrocenyl dendrimers, and detailed electro-
chemical procedure for the modification of electrode surfaces with
8 and 9. This material is available free of charge via the Internet at
http://pubs.acs.org.
Synthesis of Dendrimer 9. This dendrimer was prepared by the
same procedure as that described for the synthesis of 8, starting
from 0.42 g (0.5 mmol) of 3 and 0.05 g (0.1 mmol) of 6. In this
OM700559T