1,1′-Bis(dimethylvinylsilyl)ferrocene as a Two-Directional Core for the Construction of Homo- And Heterometallic Systems

Article abstract of DOI:10.1021/om990109j

The divinyl derivative Fe[(η⁵-C₅H₄)Me₂SiCH=CH ₂)]₂ (1), prepared by the low-temperature reaction of 1,1′-dilithioferrocene·TMEDA with ClSiMe₂(CH=CH₂), has been used as a readily functionalizable core unit for the synthesis of multimetallic systems. The hydrosilylation reaction of 1 with Cl₂MeSiH and Ph₂MeSiH provides the tetrafunctional ferrocenes Fe[(η⁵-C₅H₄)(SiMe₂(CH ₂)₂SiMeCl₂)]₂ (2) and Fe[(η⁵-C₅H₄)(SiMe₂(CH ₂)₂SiMePh₂)]₂ (5), which after reaction with Fe(η⁵-C₅H₄Li)(η⁵-C ₅H₅ and Cr(CO)₆, respectively, afforded the pentametallic molecules Fe[(η⁵-C₅H₄)(SiMe₂(CH ₂)₂SiMeFc₂)]₂(3) (Fc = (η⁵-C₅H₄)Fe(η⁵-C ₅H₅)) and Fe[(η⁵-C₅H₄)(SiMe₂(CH ₂)₂SiMe{(η⁶-C₆H ₅)Cr(CO)₃}₂]₂ (6). Characterization of the synthesized molecules by ¹H, ¹³C, and ²⁹Si NMR and IR spectroscopy, mass spectrometry, and elemental analysis supports their assigned structures. The electrochemical behavior has been studied. While 3 contains two pairs of outer silicon-bridged ferrocenyl units, in which the iron centers interact with one another, in the related 6 the chromium tricarbonyl groups complexed to arene rings, also joined by a single silicon, are essentially noninteracting.

Full text of DOI:10.1021/om990109j

Organometallics 1999, 18, 2349-2356
2349
1,1′-Bis(d im eth ylvin ylsilyl)fer r ocen e a s a
Tw o-Dir ection a l Cor e for th e Con str u ction of Hom o- a n d
Heter om eta llic System s
Bele´n Garc´ıa,† Carmen M. Casado,† Isabel Cuadrado,*,† Beatriz Alonso,†
Moise´s Mora´n,† and J ose´ Losada‡
Departamento de Quı´mica Inorga´nica, Facultad de Ciencias, Universidad Auto´noma
de Madrid, Cantoblanco 28049-Madrid, Spain, and Departamento de Ingenier´ıa
Quı´mica Industrial, Escuela Te´cnica Superior de Ingenieros Industriales,
Universidad Polite´cnica de Madrid, 28006-Madrid, Spain
Received February 18, 1999
The divinyl derivative Fe[(η5-C5H4)(Me2SiCHdCH2)]2 (1), prepared by the low-temperature
reaction of 1,1′-dilithioferrocene‚TMEDA with ClSiMe2(CHdCH2), has been used as a readily
functionalizable core unit for the synthesis of multimetallic systems. The hydrosilylation
reaction of 1 with Cl2MeSiH and Ph2MeSiH provides the tetrafunctional ferrocenes Fe[(η5-
C5H4)(SiMe2(CH2)2SiMeCl2)]2 (2) and Fe[(η5-C5H4)(SiMe2(CH2)2SiMePh2)]2 (5), which after
reaction with Fe(η5-C5H4Li)(η5-C5H5) and Cr(CO)6, respectively, afforded the pentametallic
molecules Fe[(η5-C5H4)(SiMe2(CH2)2SiMeFc2)]2 (3) (Fc ) (η5-C5H4)Fe(η5-C5H5)) and Fe[(η5-
C5H4)(SiMe2(CH2)2SiMe{(η6-C6H5)Cr(CO)3}2)]2 (6). Characterization of the synthesized mol-
1
ecules by H, 13C, and 29Si NMR and IR spectroscopy, mass spectrometry, and elemental
analysis supports their assigned structures. The electrochemical behavior has been studied.
While 3 contains two pairs of outer silicon-bridged ferrocenyl units, in which the iron centers
interact with one another, in the related 6 the chromium tricarbonyl groups complexed to
arene rings, also joined by a single silicon, are essentially noninteracting.
In tr od u ction
Very recently, functionalized ferrocenes have become
attractive units for the construction of novel organome-
tallic molecules, in the rapidly emerging area of den-
drimers.12 The combination of the unique and valuable
redox properties of ferrocene with the architectural
features of dendrimers provides access to new materials
with high overall symmetries, well-defined internal
cavities, and nanometer dimensions together with spe-
cific physical and chemical properties which would be
Much attention has been currently devoted to the
chemistry of ferrocenyl compounds because of their
importance in many fields such as organic synthesis,
catalysis, and materials science.1 The ferrocene unit has
proved to be a versatile building block with excellent
thermal and photochemical stability. Thus, the synthe-
sis of ferrocenes with tailor-made properties has been
a goal for many synthetic chemists. In particular, the
ferrocenyl unit has been successfully incorporated into
polymers as a pendant group and also as an integral
part of the polymer backbone.2-11
(5) (a) Pannell, K. H.; Sharma, H. K. Organometallics 1997, 16,
3077. (b) Kapoor, R. N.; Crawford, G. M.; Mahmoud, J .; Dement’ev, V.
V.; Nguyen, M. T.; Diaz, A. F.; Pannell, K. H. Organometallics 1995,
14, 4944. (c) Pannell, K. H.; Dement’ev, V. V.; Li, H.; Cervantes-Lee,
F.; Nguyen, M. T.; Diaz, A. F. Organometallics 1994, 13, 3644. (d)
Nguyen, M. T.; Diaz, A. F.; Dement’ev, V. V.; Pannell, K. H. Chem.
Mater. 1994, 6, 952.
(6) (a) Compton, D. L.; Rauchfuss, F. Organometallics 1994, 13,
4367. (b) Brandt, P. F.; Rauchfuss, T. B. J . Am. Chem. Soc. 1992, 114,
1926.
(7) Southard, G. E.; Curtis, M. D. Organometallics 1997, 16, 5618.
(8) Buretea, M. A.: Tilley, T. D. Organometallics 1997, 16, 1507.
(9) Hirao, T.; Kurashina, M.; Aramaki, K.; Nishihara, H. J . Chem.
Soc., Dalton Trans. 1996, 2929.
(10) Crumbliss, A. L.; Cooke, D.; Castillo, J .; Wisian-Neilson, P.
Inorg. Chem. 1993, 32, 6088.
* To whom correspondence should be addressed. Tel: 91-397-48-
34. Fax: 91-397-48-33. E-mail: isabel.cuadrado@uam.es.
† Universidad Auto´noma de Madrid.
‡ Universidad Polite´cnica de Madrid.
(1) Ferrocenes: Homogeneous Catalysis-Organic Synthesis-Materials
Science; Togni, A., Hayashi, T., Eds.; VCH: Weinheim, Germany, 1995.
(2) For excellent recent reviews on ferrocene-based polymers see:
(a) Peckham, T. J .; Go´mez-Elipe, P.; Manners, I. In Metallocenes; Togni,
A., Halterman, R. L., Eds.; Wiley-VCH: Weinheim, Germany, 1998;
Vol. 2, p 723. (b) Gonsalves, K. E.; Chen, X. Togni, A. In ref 1, p 497.
(3) For recent examples of ferrocenyl-based polymers, see refs
3-11: (a) Casado, C. M.; Cuadrado, I.; Mora´n, M.; Alonso, B.; Lobete,
F.; Losada, J . Organometallics 1995, 14, 2618. (b) Casado, C. M.;
Mora´n, M.; Losada, J .; Cuadrado, I. Inorg. Chem. 1995, 34, 1668. (c)
Mora´n, M.; Casado, C. M.; Cuadrado, I.; Losada, J . Organometallics
1993, 12, 4237. (d) Casado, C. M.; Cuadrado, I.; Mora´n, M.; Alonso,
B.; Garc´ıa, B.; Gonza´lez, B.; Losada, J . Coord. Chem. Rev., in press.
(4) (a) Go´mez-Elipe, P.; Resendes, R.; Macdonald, P. M.; Manners,
I. J . Am. Chem. Soc. 1998, 120, 8348. (b) J a¨kle, F.; Rulkens, R.; Zech,
G.; Foucher, D. A. Lough, A. J .; Manners, I. Chem. Eur. J . 1998, 4,
2117. (c) Ni, Y.; Rulkens, R.; Manners, I. J . Am. Chem. Soc. 1996, 118,
4102. (d) Manners, I. Adv. Organomet. Chem. 1995, 37, 131. (e)
Foucher, D. A.; Tang, B.-Z.; Manners, I. J . Am. Chem. Soc. 1992, 114,
6246.
(11) Albagly, D.; Bazan, G.; Wrighton, M. S.; Schrock, R. R. J . Am.
Chem. Soc. 1992, 114, 4150.
(12) For recent reviews on dendrimers, see, for example: (a)
Newkome, G. R.; Moorefield, C. N.; Vo¨gtle, F. Dendritic Molecules:
Concepts, Synthesis, Perspectives; VCH: Weinheim, Germany, 1996.
(b) Newkome, G. R. Advances in Dendritic Macromolecules; J AI
Press: Greenwich, CT, 1994-1995; Vols. 1-3. (c) Vo¨gtle, F., Ed. Topics
in Current Chemistry; Springer-Verlag: Berlin, 1998; Vol. 197. (d)
Ardoin, N.; Astruc, D. Bull. Soc. Chim. Fr. 1995, 132, 875. (e) Gorman,
C. Adv. Mater. 1998, 10, 295. (f) Frey, H.; Lach, C.; Lorenz, K. Adv.
Mater. 1998, 10, 279. (g) Hearshaw, M. A.; Moss, J . R. Chem. Commun.
1999, 1.
10.1021/om990109j CCC: $18.00 © 1999 American Chemical Society
Publication on Web 05/19/1999

2350 Organometallics, Vol. 18, No. 12, 1999
Garc´ıa et al.
expected to differ from those of the ferrocene-based
materials prepared to date.13
and 1,1′-divinyloctamethylferrocene,3a,c (ii) to grow dif-
ferent generations of dendrimers from tetraallylsil-
ane13,14a and tetramethylcyclotetrasiloxane14c as starting
cores, and (iii) to assemble ferrocenyl moieties to Si-
H-functionalized silicon-based dendrimers.13,19,27
This paper describes the successful use of 1,1′-bis-
(dimethylvinylsilyl)ferrocene as a two-directional start-
ing core, for the synthesis of novel redox-active homo-
and heterometallic pentanuclear molecules, which can
be considered as first generations and useful models for
dendrimers of higher nuclearity with regard to the
structural and electrochemical properties.
In this context, over the past few years, we and others
have prepared dendrimers of different chemical nature
and structure containing ferrocenyl moieties.13-25 In
some of these dendrimers the ferrocenyl moieties are
located at the periphery and behave as independent,
electronically isolated units, and they can act as molec-
ular multielectron reservoirs. Interesting applications
relying upon the use of some of these ferrocenyl den-
drimers as amperometric biosensors,15a in molecular
recognition of anions,13,15b,20a as materials to modify elec-
trode surfaces,13,16,17 and as multisite guests for com-
plexation by â-cyclodextrins18 have been already recog-
nized. In addition, we have also prepared dendrimers
possessing redox-active organometallic units linked
together in close proximity so that there is electronic
communication between the metal sites in the dendritic
structure.19
In our quest for new series of dendrimeric macromol-
ecules possessing redox-active organometallic moieties
at predetermined sites, our aim now is to use suitable
polyfunctional ferrocenyl derivatives as starting cores.
In particular, vinyl-functionalized molecules potentially
constitute valuable building blocks in the convergent or
divergent synthesis of dendrimers, as the reactive vinyl
groups would allow attachment of many different groups
through hydrosilylation reactions to afford the desired
multimetallic systems. Hydrosilylation is one of the
most versatile reactions in organosilicon chemistry.26
We have previously used the hydrosilylation strategy
with the following different goals: (i) to prepare novel
redox-active organometallic molecules and network
polymeric structures through the reactions of Si-H-
functionalized tetramethylcyclotetrasiloxane and a cubic
silsesquioxane with vinylferrocene, 1,1′-divinylferrocene,
Resu lts a n d Discu ssion
Syn th esis of th e P en ta fer r ocen yl 3. Our first at-
tempts to synthesize novel redox-active polymetallic
molecules from a vinyl-functionalized starting core
involved the reaction of 1,1′-divinylferrocene with Cl2-
MeSiH. Unfortunately, this reaction failed either com-
pletely or in large measure since it mainly afforded
oxidation products of the starting ferrocene derivative,
and other presumably polymeric materials, which have
not been characterized. These difficulties prompted us
to explore the use of a different divinyl-functionalized
ferrocene as the key reactive organometallic molecule,
such as 1,1′-bis(dimethylvinylsilyl)ferrocene (1) (Scheme
1), in which the reactive vinyl sites are separated from
the cyclopentadienyl ring and protected by the SiMe2
group. Thirty-five years ago, Greber and Hallensleben
briefly described the synthesis of compound 1, which
was prepared at that time by the hydrosilylation reac-
tion of 1,1′-bis(dimethylhydrosilyl)ferrocene with acet-
ylene in the presence of H2PtCl6 as catalyst.28 Only
minimal characterization data (IR) were reported. In our
laboratory, we have prepared and fully characterized
this divinyl-functionalized ferrocenyl derivative 1, which
has now been synthesized by reaction of Fe(η5-C5H4Li)2‚
TMEDA (TMEDA ) N,N,N′,N′-tetramethylethylenedi-
amine) with dimethylvinylchlorosilane in hexane at -78
°C. After appropriate workup, the crude product was
purified by column chromatography on silica to afford
1, which was isolated in a 65% overall yield as a reddish
orange liquid.
The availability of the vinyl groups in the difunctional
ferrocene 1 enables further functionalization with reac-
tive SiCl groups through a hydrosilylation reaction.
Thus, compound 1 was reacted with an excess of
dichloromethylsilane in toluene at 40 °C in the presence
of Karstedt’s catalyst (divinyltetramethyldisiloxane-
platinum complex) (Scheme 1). The reaction was com-
pleted in 15 min, affording in excellent yield the
intermediate 2, which was isolated as an orange oil. It
is known that a critical problem in carrying out hy-
drosilylation reactions is the possible occurrence of
Markovnikov addition, yielding the R-isomer. According
to the 1H NMR spectrum of the hydrosilylation product,
only the â-isomer was formed under the described
reaction conditions, which ensures a regular growth
and the generation of molecules of maximum sym-
metry.
(13) (a) Cuadrado, I.; Mora´n, M.; Losada, J .; Casado, C. M.; Pascual,
C.; Alonso, B.; Lobete, F. In Advances in Dendritic Macromolecules;
Newkome, G. R., Ed.; J AI Press: Greenwich, CT, 1996; Vol. 3, p 151.
(b) Cuadrado, I.; Mora´n, M.; Casado, C. M.; Alonso, B.; Losada, J .
Coord. Chem. Rev., in press.
(14) (a) Alonso, B.; Cuadrado, I.; Mora´n, M.; Losada, J . J . Chem.
Soc., Chem. Commun. 1994, 2575. (b) Cuadrado, I.; Mora´n, M.; Casado,
C. M.; Alonso, B.; Lobete, F.; Garc´ıa, B.; Ibisate, M.; Losada, J .
Organometallics 1996, 15, 5278. (c) Casado, C. M.; Cuadrado, I.; Mora´n,
M.; Alonso, B.; Barranco, M.; Losada, J . Appl. Organomet. Chem. 1999,
13, 245.
(15) (a) Losada, J .; Cuadrado, I.; Mora´n, M.; Casado, C. M.; Alonso,
B.; Barranco, M. Anal. Chim. Acta 1996, 251, 5. (b) Casado, C. M.;
Cuadrado, I.; Alonso, B.; Mora´n, M.; Losada, J . J . Electroanal. Chem.
1999, 463, 87.
(16) Alonso, B.; Mora´n, M.; Casado, C. M.; Lobete, F.; Losada, J .;
Cuadrado, I. Chem. Mater. 1995, 7, 1440.
(17) Takada, K.; D´ıaz, D. J .; Abrun˜a, H.; Cuadrado, I.; Casado, C.
M.; Alonso, B.; Mora´n, M.; Losada, J . J . Am. Chem. Soc. 1997, 119,
10763.
(18) Castro, R.; Cuadrado, I.; Alonso, B.; Casado, C. M.; Mora´n, M.;
Kaifer, A. J . Am. Chem. Soc. 1997, 119, 5760.
(19) Cuadrado, I.; Casado, C. M.; Alonso, B.; Mora´n, M.; Losada, J .;
Belsky, V. J . Am. Chem. Soc. 1997, 119, 7613.
(20) Vale´rio, C.; Fillaut, J .-L.; Ruiz, J .; Guittard, J .; Blais, J .-C.;
Astruc, D. J . Am. Chem. Soc. 1997, 119, 9, 2588.
(21) Cardona, C. M.; Kaifer, A. E. J . Am. Chem. Soc. 1998, 120, 4023.
(22) Ko¨llner, C.; Pugin, B.; Togni, A. J . Am. Chem. Soc. 1998, 120,
10274.
(23) Shu, C.-F.; Shen, H.-M. J . Mater. Chem. 1997. 7, 47.
(24) Achar, S.; Immoos, C. E.; Hill, M. G.; Catalano, V. J . Inorg.
Chem. 1997, 36, 2314.
(25) J utzi, P.; Batz, C.; Neumann, B.; Stammler, H.-G. Angew.
Chem., Int. Ed. Engl. 1996, 35, 2118.
(26) (a) Comprehensive Handbook on Hydrosilylation; Marciniec, B.,
Ed.; Pergamon Press: Oxford, U.K., 1992. (b) Ojima, I. In The
Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z.,
Eds.; Wiley: New York, 1989; Part 2, p 1479.
(27) Alonso, B. Ph.D. Thesis, Universidad Auto´noma de Madrid,
1997.
(28) Greber, V. G.; Hallensleben, M. L. Makromol. Chem. 1965, 83,
148.

1,1′-Bis(dimethylvinylsilyl)ferrocene
Organometallics, Vol. 18, No. 12, 1999 2351
Sch em e 1
The compositions and structures of both ferrocenyl
derivatives 1 and 2 were straightforwardly determined
by elemental analyses, mass spectrometry (FAB-MS),
whereas two resonances are detected in the spectrum
of 2; the interior silicon directly bonded to the ferrocenyl
unit appears at 0.21 ppm, and the signal for the
terminal MeSiCl2 is shifted downfield at 33.7 ppm
(Figure 1E).
1
and IR and H, 13C, and 29Si NMR spectra. For example,
1
the H NMR spectrum of 1 (see Figure 1A) shows the
set of resonances characteristic of the reactive vinyl
groups at δ 5.77, 6.02, and 6.31 ppm in the expected
integration ratio. The complete disappearance of the
vinyl resonances in the spectrum of 2 (Figure 1B) pro-
vides evidence of the completeness of the hydrosilyla-
tion reaction. In the 29Si NMR espectrum of 1 (Figure
1D) a single resonance at -10.05 ppm is observed,
The high reactivity of the tetrafunctional 2 was
exploited by subsequent conversion to the pentametallic
3 by the salt-elimination reaction illustrated in Scheme
1. For this purpose (tri-n-butylstannyl)ferrocene was
selected as the starting material, since it has proved to
be an excellent precursor of pure lithioferrocene.29 This
is crucial, in order to exclude the formation of the
F igu r e 1. 1H NMR (300 MHz, CDCl3) spectra of 1 (A), 2 (B), and 3 (C), and 29Si{1H} NMR (59.3 MHz, CDCl3) spectra of
1 (D), 2 (E), and 3 (F).

2352 Organometallics, Vol. 18, No. 12, 1999
Garc´ıa et al.
F igu r e 2. Structure of 3 from molecular modeling.
dimetalated ferrocene, Fe(η5-C5H4Li)2, which could pro-
duce undesirable polymerization products or intramo-
lecular side reactions. In this way, ferrocenyllithium
thus generated was allowed to react with 2 in THF at
-30 °C. After purification by column chromatography
the desired compound 3, possessing a central ferrocene
and four outer ferrocenyl units linked together in pairs
through a bridging silicon atom, was isolated as an air-
stable orange crystalline solid.
The pentametallic molecule 3 was fully characterized
by NMR (1H, 13C, and 29Si) and IR spectroscopy, mass
spectrometry, and elemental analysis. As expected, only
two different silicon resonances were observed in the
29Si NMR (Figure 1F). The signal at δ -4.48 ppm was
assigned to the outer silicon atom bridging two ferro-
cenyl units, and the resonance at δ -0.32 ppm was
attributed to the inner silicon atoms linked to the
disubstituted ferrocene core. In addition, in the 1H NMR
spectrum, for the five sets of different ferrocene protons,
five distinguishable signals were detected with an
integration ratio of 4:4:8:8:20. The singlet at δ 4.05 ppm
was assigned to the nonsubstituted cyclopentadienyl
ring, whereas the AA′BB′ systems at δ 4.09 and 4.32
ppm and at δ 4.11 and 4.26 ppm correspond to the outer
and inner disubstituted ferrocene cyclopentadienyl rings,
respectively (Figure 1C). Evidence of the pentametallic
structure was also provided by mass spectrometric (EI-
MS) analysis, which gave the molecular ion at 1182.3
amu as the dominant peak, as well as some informative
fragmentation peaks.
of the related silicon-bridged ferrocenyl derivative 4
previously reported.19
Syn th esis of th e Heter op en ta m eta llic 6. We have
also carried out the hydrosilylation reaction of 1 with
Ph2MeSiH in the presence of catalytic amounts of
1
Karstedt’s catalyst in toluene at 70 °C (Scheme 2). H
NMR spectroscopy was used to follow the progress of
the reaction, by monitoring the loss of the vinyl reso-
nances of 1. The reaction was completed in approxi-
mately 2 h. The resulting hydrosilylated product was
purified by column chromatography using a tetrahydro-
furan/hexane mixture (1/30) as eluent. The tetraphen-
yl-functionalized ferrocene 5 was isolated as an air-
stable orange oil. It is interesting to note that this
hydrosilylation reaction has been carried out under
conditions more forcing (higher temperature and longer
reaction times) than those used in the synthesis of 2.
This fact can be easily justified on the basis of the values
of the IR stretching frequencies of the Si-H bonds for
methyldiphenylsilane (ν(SiH) 2123 cm-1) and methyl-
dichlorosilane (ν(SiH) 2215 cm-1), which suggest that
the electronic environment about the reacting silicon
center in methyldichlorosilane is more suitable for
hydrosilylation than in methyldiphenylsilane. In fact,
it has been well-established that electron-withdrawing
substituents on the Si-H bond increase the rate of the
hydrosilylation process compared to the case of more
electron-donating groups.26
Although compound 3 has been isolated as small
orange crystals, unfortunately all attempts to grow
crystals suitable for X-ray diffraction studies have failed
so far. In the absence of the X-ray data we have used
the computer-generated molecular model in order to
gain insight into the structure of this pentaferrocenyl
molecule. Molecular modeling calculations of 3 show
that in its lowest energy conformation the four periph-
eral ferrocenyl units are oriented at ca. 100° relative to
one another, as shown in Figure 2. This arrangement
resembles that observed in the X-ray crystal structure
The π-coordinating ability of the outer arene rings of
5 toward transition metals offered a good chance to gain
an easy synthetic access to heterometallic molecules.
Thus, the pentanuclear molecule 6 was formed by
thermal treatment of 5 with an excess of Cr(CO)6, using
an approximately 9/1 mixture (v/v) of n-Bu2O and THF
as solvent. After chromatographic purification, the
desired 6 was isolated as a yellow solid.
(29) Guillaneux, D.; Kagan, H. B. J . Org. Chem. 1995, 60, 2502.

1,1′-Bis(dimethylvinylsilyl)ferrocene
Organometallics, Vol. 18, No. 12, 1999 2353
Sch em e 2
F igu r e 3. Cyclic voltammograms of 3 (A) in CH2Cl2 and
(B) in CH2Cl2/CH3CN (1/1 by volume) at a scan rate of 100
mV s-1 and (C) a differential pulse voltammogram of 3 in
CH2Cl2/CH3CN (1/1 by volume) at a scan rate of 10 mV
Several spectroscopic features were characteristic of
these molecules. For example, for the heterometallic 6,
the η6-coordination of the Cr(CO)3 moieties to the phenyl
rings resulted in the appearance of two intense ν(CtO)
bands at 1969 and 1893 cm-1 in the IR spectrum, as
well as a characteristic resonance at 233 ppm due to
the carbonyl carbon atoms in the 13C NMR spectrum.
In addition, the total absence of signals in the range
s-1
.
cyclic voltammogram displays the two diffusion-con-
trolled, reversible redox processes shown in Figure 3B.
The wave at the lowest potential remains broad and ill-
defined. The determination of the number of electrons
transferred in the complete oxidation of 3 was effected
by exhaustive coulometry measurements, carried out
past the anodic wave at the higher potential, resulting
in the removal of 5 electrons/molecule.
The differential pulse voltammogram (DPV) of 3 (in
CH2Cl2/CH3CN solution) shows two peaks of different
heights (Figure 3C). The first peak is broader than the
second and displays a shoulder (marked in Figure 3C
with an asterisk), suggesting two overlapped processes
differing by approximately 70 mV in potential. Integra-
tion of the peaks areas gives a first to second wave ratio
of 3:2. In the absence of any interactions between the
iron centers of the pentametallic 3 one would expect two
waves in a 1:4 ratio in the DPV response, corresponding
to the two different ferrocene environments present in
the molecule. Manners and co-workers recently found
that in the DPV measurements of a related tetraferro-
cenylsilane the resolution of the peaks was attained if
benzonitrile was used as solvent.30 Unfortunately, with
1
7.35-7.50 ppm in the H NMR spectrum of 6 provided
further proof of the complete coordination of Cr(CO)3
moieties to the four phenyl rings.
Electr och em istr y of 1, 3, a n d 5. The cyclic voltam-
mogram (CV) of the pentaferrocenyl molecule 3 in CH2-
Cl2 solution containing 0.1 M [(n-Bu)4N]PF6 (TBAH) as
supporting electrolyte is shown in Figure 3A. The CV
exhibits two separated oxidation waves, the first one
being broad and poorly resolved. In addition, a change
in solubility of 3 accompanied the change in oxidation
state, so that upon scan reversal after the oxidation
process at a higher potential, the reduction wave was
dramatically sharpened, giving rise to a cathodic strip-
ping peak. Thus, the complete oxidation of 3 in this
medium appears to result in the precipitation of the
oxidized molecule onto the electrode surface, and on the
reverse scan the molecule redissolves as it is reduced.
When acetonitrile is added to the CH2Cl2/electrolyte
medium, the cathodic stripping peak disappears and the

2354 Organometallics, Vol. 18, No. 12, 1999
Garc´ıa et al.
our pentanuclear 3, the use of benzonitrile as medium
did not provide a higher resolution of the oxidation
steps.
Formal potentials were calculated from the DPV peak
1
potentials, and the results obtained were E1/2 ) 0.41
2
V for the process corresponding to the first peak, E1/2
) 0.48 V for the second peak (observed as a shoulder),
3
and E1/2 ) 0.59 V for the peak at higher potential.
Assignment of the formal potentials observed in the
DPV of 3 to the corresponding electrochemical processes
has been carried out by comparison with the redox
potentials observed for the related dendritic molecule
7 previously described.19 This dendrimer, in which
F igu r e 4. Cyclic voltammogram of 6 in CH2Cl2/TBAH, at
a scan rate of 100 mV s-1
.
positive potential value determined for 1 and 5, com-
pared to that of the central ferrocene in 3, indicates that
in this case the removal of the electron is slightly more
difficult owing to the double positive charge generated
by the preceding step.
In summary, the pentametallic 3 exhibits three
1
oxidation steps. The first two-electron step at E1/2
)
0.41 V corresponds to simultaneous electron removals
from two nonadjacent outer terminal noninteracting
ferrocenyl moieties. The second one-electron process at
2E1/2 ) 0.48 V is centered on the disubstituted central
ferrocene, and finally two electrons are removed from
the remaining outer ferrocenyl centers neighboring
ferrocenyl units are also linked together by a bridging
silicon atom, serve as a valuable model, as there are
significant structural and electronic similarities among
the ferrocenyl moieties. The DPV of 7 shows two well-
separated waves of equal intensity at E1/2 ) 0.41 and
0.60 V vs SCE, indicating significant interactions be-
tween the ferrocene groups. On this basis, the first and
third redox potentials of 3 can be assigned to the
oxidation of the peripheral ferrocenes, as they are close
to those previously observed for 7. The redox behavior
observed for these molecules can be related to that found
in oligo- and polyferrocenylsilanes.31,32
3
those already oxidized at E1/2 ) 0.58 V. The separation
3
1
between the first and third waves, ∆E ) E1/2 - E1/2
,
provides a measure of the degree of interaction between
the outer iron centers. The obtained value, ∆E ) 170
mV, reveals significant electronic interactions between
the terminal ferrocenyl moieties.
Electr och em istr y of 6. The electrochemical behav-
ior of 6 has been examined using a nonnucleophilic
solvent (CH2Cl2) and TBAH as electrolyte. As illustrated
in Figure 4 the cyclic voltammogram of compound 6
reveals two reversible oxidation waves at E1/2 ) 0.60 V
and E1/2 ) 1.05 V vs SCE, respectively. Both oxidation
processes are diffusion-controlled with the anodic cur-
rent function i/v1/2 independent of the scan rate. The
ratio of the cathodic to anodic peak current is close to
unity for both systems and the peak potentials separa-
tion were 60 and 160 mV, respectively.
Controlled-potential electrolysis revealed that a single
electron is involved in the first oxidation step, and it
can be assigned to the oxidation of the central ferrocenyl
unit of 6. The E1/2 value of this first oxidation is
appreciably higher than the E1/2 found for the mono-
metallic monomers 1 and 5, and this is probably due to
the electron-withdrawing nature of the four peripheral
(η6-C6H5)Cr(CO)3 moieties.
To assign unambiguously the second oxidation peak
2
observed in the DPV of the pentametallic 3 at E1/2
)
0.48 V, we have also studied the electrochemical behav-
ior of the mononuclear molecules 1 and 5, because the
environment around the ferrocenyl unit in these mol-
ecules is similar to that of the central ferrocene in 3.
The CVs of 1 and 5 in CH2Cl2 solution are charac-
teristic of a reversible oxidation process with the
production of soluble stable products. Likewise, dif-
ferential pulse voltammetry showed an oxidation wave
at E1/2 ) 0.47 V for 1 and E1/2 ) 0.45 V for 5. The less
(30) MacLachlan, M. J .; Lough, A. J .; Geiger, W. E.; Manners, I.
Organometallics 1998, 17, 1873.
(31) (a) Rulkens, R.; Lough, A. J .; Manners, I.; Lovelace, S. R.; Grant,
C.; Geiger, W. E. J . Am. Chem. Soc. 1996, 118, 12683. (b) Foucher, D.
A.; Honeyman, C. H.; Nelson, J . M.; Zhong Tang, B.; Manners, I.
Angew. Chem., Int. Ed. Engl. 1993, 32, 1709.
Analysis of the cyclic voltammogram shows that the
anodic peak current of the second wave is approximately
4 times the ip value of the first oxidation step. Therefore,
this second oxidation peak can be attributed to a
(32) Dement’ev, V. V.; Cervantes-Lee, F.; Parkanyi, L.; Sharma, H.;
Pannell, K. H. Organometallics 1993, 12, 1983.

1,1′-Bis(dimethylvinylsilyl)ferrocene
Organometallics, Vol. 18, No. 12, 1999 2355
geometry has been calculated with MM2 using MM3 param-
eters to an average gradient <1. The conformation with
minimized energy was obtained from the optimized molecule
using the sequential search option in the software package.
Electr och em ica l Mea su r em en ts. Cyclic voltammograms
were recorded on a BAS-CV-27 potentiostat. CH3CN and CH2-
Cl2 (spectrograde) for electrochemical measurements were
freshly distilled from calcium hydride under nitrogen. The
supporting electrolyte was in all cases TBAH that was
purchased from BAS or Strem and was purified by recrystal-
lization from ethanol and dried under vacuum at 60 °C. The
supporting electrolyte concentration was typically 0.1 M. All
cyclic voltammetric experiments were performed using either
a platinum-disk working electrode (A ) 0.030 cm2) or a glassy-
carbon-disk working electrode (A ) 0.070 cm2), each of which
was polished prior to use with 1 µm diamond paste (Buehler)
and rinsed thoroughly with water and acetone. All potentials
are referenced to the saturated calomel electrode (SCE). A
coiled platinum wire was used as a counter electrode. In
general the concentrations of the solutions of the redox-active
molecules for cyclic voltammetry were in the range 10-4-10-3
M. The solutions were deoxygenated by purging with prepu-
rified nitrogen. No iR compensation was used. Differential
pulse voltammetry was done with a Polarecord-E-506 Metro-
hm, with a scan rate of 10 mV s-1, a pulse height of 10-20
mV, and a duration of 60 ms. DPV were recorded using CH2-
Cl2/CH3CN solutions of the ferrocenyl derivatives. Formal
potentials were calculated from the DPV peak potentials using
E1/2 ) Epk + Epulse/2, where Epulse is the pulse height. Coulo-
metric measurements were made with a PAR-379 digital
coulometer, using Pt gauze as the working electrode.
simultaneous multielectron transfer of four electrons
removed from the four terminal chromium centers. The
fact that the pentanuclear 6 exhibits this single-step
oxidation process at E1/2 ) 1.05 V is of relevance, as this
implies that the peripheral chromium tricarbonyl moi-
eties linked together by a silicon bridge do not es-
sentially communicate electronically with each other.
This fact contrasts interestingly with the case of 3, in
which appreciable interactions between the peripheral
ferrocenyl moieties are detected. Therefore, the nature
of arene rings seems to influence the degree of interac-
tion between metallic centers.33
Con clu sion s
We have established that 1,1′-bis(dimethylvinylsilyl)-
ferrocene can be used as an effective two-directional
starting core molecule for the synthesis of homo- and
heterometallic systems which are functionalized at their
periphery with ferrocenyl and (η6-C6H5)Cr(CO)3 moi-
eties. The degree of interaction between the electroactive
metal-based moieties linked together by a bridging
silicon atom depends on their chemical nature. The
extension of this synthetic methodology to the construc-
tion of higher generations of homo- and heterometallic
dendrimers is currently in progress.
Exp er im en ta l Section
Syn th esis of Com p ou n d s. Syn th esis of 1. A solution of
ferrocene (3.3 g, 17.8 mmol) and TMEDA (5.5 mL) in hexane
was treated with n-butyllithium (24 mL of 1.6 M solution in
hexane). An orange precipitate was formed, and the system
was stirred for 18 h. The dilithium salt Fe(η5-C5H4Li)2‚TMEDA
formed, was separated by filtration, and was washed with
hexane. The resulting pale orange precipitate was slurried by
addition of 50 mL of hexane and cooled to -78 °C. To this
stirred system was added dropwise a 20 mL hexane solution
of SiClMe2CHdCH2 (4.3 g, 35.7 mmol). After 30 min, the
mixture was warmed to room temperature and stirred for an
additional 10 h. The reaction mixture was filtered, and
volatiles were removed under vacuum. The oily residue was
subjected to column chromatography on silica using hexane
as eluent. The initial yellow band corresponding to a small
amount of ferrocene was discarded. A second major orange
band was collected, and solvent removal afforded the target
compound 1 as a reddish orange liquid. Yield: 4.1 g (65%).
Anal. Calcd (found) for C18H26Si2Fe: C, 61.04 (61.11); H, 7.34
Gen er a l Da ta . All reactions and subsequent manipulations
were carried out under an argon atmosphere by using con-
ventional Schlenk techniques. THF was distilled from sodium
benzophenone, CH2Cl2 and hexane were distilled from P4O10
,
and di-n-butyl ether was distilled from sodium. Dimethylvi-
nylchlorosilane, diphenylmethylsilane, ferrocene, and tert-
butyllithium (1.7 M solution in hexane and 1.5 M solution in
pentane) were purchased from Fluka and used as received.
Methyldichlorosilane (Fluka) and tri-n-butylstannyl chloride
(Aldrich) were distilled prior to use. N-Butyllithium (1.6 M
solution in hexane) was purchased from Aldrich and used as
received. Chromium hexacarbonyl (Aldrich) was sublimed prior
to use. Divinyltetramethyldisiloxane-platinum complex (3-
3.5% in xylenee; Karstedt’s catalyst), available from Petrarch
Systems Inc., was used as received. (Tri-n-butylstannyl)-
ferrocene was synthesized as described in the literature.29
Silica gel (70-230 mesh) and silanized silica gel (70-230
mesh) (Merck) were used for column chromatographic purifi-
cations.
1
(7.40). H NMR (CDCl3, 300 MHz): δ 0.31 (s, 12H, Si(CH3)2),
Infrared spectra were recorded on a Bomem MB-100 FT-IR
spectrometer. NMR spectra were recorded on a Bruker-AMX
(1H, 300 MHz; 13C, 75.43 MHz; 29Si, 59.3 MHz) spectrometer.
Chemical shifts are reported in parts per million (δ) with
reference to internal SiMe4 or to residual solvent resonances
δ 4.08 (m, 4H, C5H4), δ 4.31 (m, 4H, C5H4), δ 5.77 (dd, 2H,
CHdCH2 (cis)), δ 6.02 (dd, 2H, CHdCH2 (trans)), δ 6.31 (dd,
2H, CHdCH2). 13C NMR (CDCl3, 75.43 MHz): δ -1.98 (CH3),
δ 69.90, 71.36, 73.06 (C5H4), δ 131.64 (CH2), δ 139.02 (CH).
29Si NMR (CDCl3, 59.3 MHz): δ -10.05. IR (neat): ν(CdC)
1646 cm-1. MS (FAB; m/z (%)): 354.1 (M+, 100).
1
for H and 13C NMR (CDCl3: 1H, δ 7.27 ppm; 13C, δ 77.0 ppm).
29Si NMR spectra, referenced externally to SiMe4, 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.
Mass spectral analyses (positive FAB and EI) were con-
ducted on a VG Auto Spec mass spectrometer. Elemental
analyses were performed by the Microanalytical Laboratory,
Universidad Auto´noma de Madrid, Madrid, Spain.
Syn th esis of 2. HSiMeCl2 (1 g, 8.7 mmol) was slowly added
to a solution of 1 (1 g, 2.8 mmol) in 25 mL of toluene, containing
25 µL of Karstedt’s catalyst (3-5% Pt, in xylene), and the
solution was then heated to 40 °C. After the mixture was
stirred for 15 min at this temperature, the complete disap-
pearance of the vinyl resonances in the range 5.77-6.31 ppm
1
was confirmed by H NMR spectroscopy. The excess amounts
of HSiMeCl2 and toluene were removed under vacuum to afford
compound 2 as a moisture-sensitive viscous orange oil, which
was immediately used in the next reaction. Yield: 1.6 g (97%).
Anal. Calcd (found) for C20H34Si4Cl4Fe: C, 41.13 (41.25); H,
5.82 (5.93). 1H NMR (CDCl3, 300 MHz): δ 0.28 (s, 12H, Si-
(CH3)2), δ 0.75 (s, 6H, SiCl2CH3), δ 0.77 (m, 4H, Si(CH3)2CH2),
δ 0.98 (m, 4H, SiCl2CH2), δ 4.07 (m, 4H, C5H4), δ 4.32 (m, 4H,
Molecular mechanics calculations were made using the
Cache 3.11 software package for Windows. The optimized
(33) The lack of communication between (aryl)Cr(CO)3 units linked
by a bridging silicon atom has been also noted previously: Rieke, R.
D.; Tucker, I.; Milligan, S.; Wright, D. R.; Willeford, B. R.; Radonovich,
L.; Eyring, M. W. Organometallics 1982, 1, 938.

2356 Organometallics, Vol. 18, No. 12, 1999
Garc´ıa et al.
C5H4). 13C NMR (CDCl3, 75.43 MHz): δ -2.90 (Si(CH3)2), δ
4.28 (SiCl2CH3), δ 7.98 (Si(CH3)2CH2), δ 14.66 (SiCl2CH2), δ
69.95, 71.29, 73.01 (C5H4). 29Si NMR (CDCl3, 59.3 MHz): δ
0.21 (Si(CH3)2), δ 33.7 (SiCl2).
δ 4.22 (m, 4H, C5H4), δ 7.35 (m, 8H, C6H5), δ 7.50 (m, 12H,
C6H5). 13C NMR (CDCl3, 75.43 MHz): δ -2.81 (Si(CH3)2), δ
-5.02 (SiCH3), δ 6.41 (Si(CH3)2CH2), δ 9.05 (SiCH3CH2), δ
68.09, 71.05, 72.98 (C5H4), δ 127.76, 129.04, 134.51, 137.27
(C6H5). 29Si NMR (CDCl3, 59.3 MHz): δ -0.32 (SiC5H4), δ
-5.47 (SiC6H5). MS (FAB; m/z (%)): 750.4 (M+, 100).
Syn th esis of 3. A solution of (tri-n-butylstannyl)ferrocene
(6.4 g, 13.5 mmol) in 25 mL of THF was cooled to -78 °C and
treated with n-butyllithium (8 mL, 1.6 M solution in hexane).
The reaction mixture was stirred at that temperature for 90
min and then warmed to -30 °C, and a THF solution of 2 (1.6
g, 2.7 mmol) was added dropwise. The mixture was stirred
for 1 h, warmed to room temperature, and stirred for a further
24 h. The solvent was removed under vacuum, and the orange
residue was chromatographed on a silica gel column using
hexane and a hexane/THF mixture as eluents. Elution with
hexane produced a yellow band, which gave ferrocene. The
orange band eluted with hexane/THF (20/1) afforded compound
3 as an orange air-stable crystalline solid. Yield: 1.43 g (45%).
Anal. Calcd (found) for C60H70Si4Fe5: C, 60.95 (61.05); H, 5.92
Syn th esis of 6. A 100 mL, two-necked round-bottomed
flask equipped with a gas inlet and a straight-tube condenser
topped with gas inlet and bubbler was charged with 0.88 g (4
mmol) of Cr(CO)6, 0.6 g (0.8 mmol) of 5, n-Bu2O (90 mL), and
THF (10 mL). The mixture was stirred and heated to a gentle
reflux. The progress of the reaction was monitored by oc-
casionally cooling a sample of the mixture to room temperature
1
and recording the IR and H NMR spectra of the supernatant
solution. Over the course of the reaction, new carbonyl bands
at 1974 and 1904 cm-1 were observed to increase in intensity.
Likewise, in the 1H NMR (CDCl3) spectrum, the resonances
in the 7.35-7.50 ppm region progressively disappeared while
new resonances in the range 5.13-5.57 ppm were detected.
After 48 h, the reaction mixture was cooled to room temper-
ature and then to -10 °C for 3 h. The suspension was filtered
through a pad of silanized silica (3 × 3 cm) to remove the small
amounts of insoluble decomposition products and some unre-
acted Cr(CO)6. From the resulting light orange solution, the
solvent was removed under vacuum and the residue was
purified by column chromatography (2 × 30 cm) on silanized
silica, using a CH2Cl2/n-hexane mixture (1/3) and pure CH2-
Cl2 as eluents. The yellow band eluted with CH2Cl2 was
collected, and the desired product was precipitated by addition
of n-hexane. Analytically pure 6 was isolated as a light- and
1
(6.01). H NMR (CDCl3, 300 MHz): δ 0.26 (s, 12H, Si(CH3)2),
δ 0.45 (s, 6H, SiFc2CH3), δ 0.73 (m, 4H, Si(CH3)2CH2), δ 0.84
(m, 4H, SiFc2CH2), δ 4.05 (s, 20H, C5H5), δ 4.09 (m, 8H, C5H4),
δ 4.11 (m, 4H, C5H4), δ 4.26 (m, 4H, C5H4), δ 4.32 (m, 8H,
C5H4). 13C NMR (CDCl3, 75.43 MHz): δ -3.27 (SiFc2CH3), δ
-2.72 (Si(CH3)2), δ 8.64 (Si(CH3)2CH2), δ 9.50 (SiFc2CH2), δ
68.19 (C5H5), δ 68.08, 71.14, 72.98 (C5H4/C5H4), δ 70.50, 70.86,
73.37 (C5H5/C5H4). 29Si NMR (CDCl3, 59.3 MHz): δ -0.32
(Si(CH3)2), δ -4.48 (SiFc2). MS (EI; 70 eV: m/z (%)): 1182.0
(M+, 100), 684.0 ([SifcMe2(CH2)3SiMeFc2]+, 30.2), 591.7 (M2+
,
18.0), 497.9 ([SifcMe2(CH2)3SiMeFc]+, 33.6), 413.0 ([SiMeFc2]+,
81.3), 243.0 ([FcSiMe2]+, 53.51).
Syn th esis of 5. A mixture of 30 µL of a solution of
Karstedt’s catalyst (3-5% Pt in xylene) and 1 g (2.8 mmol) of
1 in toluene was stirred at room temperature for 30 min. A
solution of HMeSiPh2 (1.2 g, 6.3 mmol) in 15 mL of toluene
was then added dropwise, and the reaction mixture was heated
to 70 °C. After 2 h, the completeness of the hydrosilylation
reaction was confirmed by the disappearance of the resonances
corresponding to the vinyl group in the 1H NMR spectrum.
The excess amounts of HMeSiPh2 and the solvent were
removed under vacuum. The resulting orange residue was
redissolved in hexane and the solution purified by column
chromatography on silica. An orange band was collected using
a THF/hexane mixture (1/30) as eluent. Solvent removal
afforded the target product 5 as an air-stable orange oil.
Yield: 1.79 g (85%). Anal. Calcd (found) for C44H54Si4Fe: C,
70.49 (70.38); H, 7.20 (7.27). 1H NMR (CDCl3, 300 MHz): δ
0.23 (s, 12H, Si(CH3)2), δ 0.54 (s, 6H, SiCH3), δ 0.59 (m, 4H,
Si(CH3)2CH2), δ 0.97 (m, 4H, SiCH3CH2), δ 3.99 (m, 4H, C5H4).
air-sensitive yellow solid. Yield: 20%. Anal. Calcd (found) for
1
C
56H54O12Si4FeCr4: C, 51.94 (51.73); H, 4.17 (4.01). H NMR
(CDCl3, 300 MHz): δ 0.28 (s, 12H, Si(CH3)2), δ 0.59 (s, 6H,
SiCH3), δ 0.71 (m, 4H, Si(CH3)2CH2), δ 0.93 (m, 4H, SiCH3CH2),
δ 4.07 (m, 4H, C5H4). δ 4.29 (m, 4H, C5H4), δ 5.13 (m, 8H,
C6H5), δ 5.38 (m, 8H, C6H5), δ 5.57 (m, 4H, C6H5). 13C NMR
(CDCl3, 75.43 MHz): δ -2.51 (Si(CH3)2), δ -3.13 (SiCH3), δ
6.22 (Si(CH3)2CH2), δ 9.11 (SiCH3CH2), δ 71.09, 72.98 (C5H4),
δ 89.95, 96.05, 99.80 (C6H5), δ 232.96 (CO). IR (KBr): ν(C/O)
1969 and 1893 cm-1. MS (FAB; m/z (%)): 1295.3 (M+, 18.9),
1211.3 ([M - 3(CO)]+, 3.8).
Ack n ow led gm en t. We thank the Spanish Direccio´n
General de Ensen˜anza Superior e Investigacio´n Cien-
t´ıfica (DGES), Project PB97-0001, for the financial
support of this research.
OM990109J