Preparation and Redox Properties of Novel Polymerizable Pyrrole- and Allyl-Functionalized Cobaltocenium Monomers and Siloxane-Based Cobaltocenium Polymers

Article abstract of DOI:10.1021/om990527o

A series of novel cobaltocenium complexes functionalized with electrochemically and chemically polymerizable pyrrole or allyl substituents, [{η⁵-C₅H₅}Co{η⁵-C ₅H₄C(O)NH(CH₂)₃

Full text of DOI:10.1021/om990527o

4960
Organometallics 1999, 18, 4960-4969
P r ep a r a tion a n d Red ox P r op er ties of Novel
P olym er iza ble P yr r ole- a n d Allyl-F u n ction a lized
Coba ltocen iu m Mon om er s a n d Siloxa n e-Ba sed
Coba ltocen iu m P olym er s
Isabel Cuadrado,*,† Carmen M. Casado,† Francisco Lobete,† Beatriz Alonso,†
Blanca Gonza´lez,† J ose´ Losada,‡ and Ulises Amador§
Departamento de Quı´mica Inorga´nica, Facultad de Ciencias, Universidad Auto´noma de
Madrid, Cantoblanco 28049-Madrid, Spain, and Departamento de Ingenierı´a Quı´mica
Industrial, Escuela Te´cnica Superior de Ingenieros Industriales, Universidad Polite´cnica de
Madrid, 28006-Madrid, Spain
Received J uly 8, 1999
A series of novel cobaltocenium complexes functionalized with electrochemically and
chemically polymerizable pyrrole or allyl substituents, [{η5-C5H5}Co{η5-C5H4C(O)NH(CH2)3-
NC4H4}]PF6 (1), [{η5-C5H4C(O)NH(CH2)3NC4H4}2Co]PF6 (2), [{η5-C5H5}Co{η5-C5H4C(O)NHC6H4-
NC4H4}]PF6 (3), [{η5-C5H5}Co{η5-C5H4C(O)NHCH2CHdCH2}]PF6 (4), and [{η5-C5H5}Co{η5-
C5H4C(O)OCH2CHdCH2}]PF6 (5), have been prepared via condensation reactions. In a
similar way, the siloxane-based polymer 6 and the block copolymer 8, in which the amide-
linked cobaltocenium moieties are incorporated in the polymer backbone either as a part of
the main polymer chain or as pendant side groups, as well as the dimetallic model complex
[[{η5-C5H5}Co{η5-C5H4C(O)NH(CH2)3Si(CH3)2}]2O][PF6] (7), were prepared and characterized.
The molecular structure of the pyrrole-containing cobaltocenium 1 has been determined by
a single-crystal X-ray diffraction study. Cyclic voltammetric studies show that the stability
of the electrogenerated anionic species depends on the solvent and the nature of the
cyclopentadienyl substituents. Gold, platinum, and glassy-carbon electrodes have been
successfully modified by electrochemical polymerization of the pyrrole-functionalized
monomers 1-3, in acetonitrile solutions, resulting in detectable electroactive cobaltocenium
polymer films persistently attached to the electrode surfaces. Glassy-carbon electrodes coated
with films of the hydrophobic, siloxane-based, cobaltocenium-containing block copolymer 8
show redox activity in aqueous solutions when an ionic surface-active agent is added to the
film.
In tr od u ction
The first approach involves the use of chemically poly-
merizable metallocenyl monomers, which can be homo-
or copolymerized. On the other hand, the incorporation
of metallocenes in preformed organic or inorganic
polymers constitutes a very facile and versatile access
to novel organometallic macromolecules. An alternative,
less exploited approach involves the electrochemical
polymerization of metallocene derivatives containing
appropriate functional groups, directly onto electrode
surfaces. This is a simple and effective method, which
provides control of the properties of the resulting
polymer, including its conductivity, permeability, and
redox properties.
Metallocene-based polymers are an important cat-
egory of polymeric materials, which have attracted
increasing attention in the past few years, because of
the significantly different properties they possess in
comparison to conventional polymers.1 These include
thermal stability, novel redox characteristics, nonlinear
optical (NLO) effects, magnetic properties, and liquid
crystalline behavior. Likewise, metallocene-containing
polymers are interesting materials for the modification
of electrode surfaces that can be used for practical
applications and fundamental studies.
In general, two main strategies have been employed
for the synthesis of metallocene-containing polymers.
In this regard, molecules based on pyrrole have been
the subject of increasing interest in recent years, since
this chemical function appears exceptionally convenient
for achieving electropolymerization in the production of
electrodes modified by electroactive polymeric films.2
The pyrrole group is polymerized by an oxidative
polymerization mechanism that proceeds through an
electrochemically accessible radical cation intermediate.
* 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.
§ To whom inquiries regarding the X-ray data should be addressed
at the Departamento de Qu´ımica Inorga´nica y Materiales, Facultad
de Ciencias Experimentales y Te´cnicas, Universidad San Pablo-CEU,
28668-Boadilla del Monte, Madrid, Spain.
(1) For excellent recent reviews on metallocene-based polymers
see: (a) Peckham, T. J .; Go´mez-Elipe, P.; Manners, I. In Metallocenes;
Togni, A., Halterman, R., Eds.; Wiley-VCH: Weinheim, Germany,
1998; p 756. (b) Nguyen, P.; Gomez-Elipe, P.; Manners, I. Chem. Rev.
1999, 99, 1515. (c) Gonsalves, K. E.; Chen, X. In Ferrocenes: Homo-
geneous Catalysis-Organic Synthesis-Materials Science; Togni, A.,
Hayashi, T., Eds.; VCH: Weinheim, Germany, 1995.
(2) For reviews on functionalized pyrroles see for example: (a)
Deronzier, A.; Moutet, J .-C. Coord. Chem. Rev. 1996, 147, 339. (b)
Deronzier, A.; Moutet, J .-C. Acc. Chem. Res. 1989, 22, 249. (c) Curran,
D.; Grimshaw, J .; Perera, S. D. Chem. Soc. Rev. 1991, 20, 391.
10.1021/om990527o CCC: $18.00 © 1999 American Chemical Society
Publication on Web 10/29/1999

Cobaltocenium Monomers and Polymers
Organometallics, Vol. 18, No. 24, 1999 4961
Although a wide variety of transition-metal complexes
with pyrrole groups have been prepared, pyrrole mono-
mers containing organometallic entities remain re-
stricted to a few examples. To the best of our knowledge,
the only examples of pyrroles functionalized with orga-
nometallic redox-active centers reported until now
contain the ferrocene unit.3 However, only a few of these
ferrocene-containing pyrrole derivatives form electro-
active polymer films by direct anodic electropolymer-
ization. Cobaltocenium also constitutes an excellent
organometallic moiety to functionalize pyrrole systems
in order to achieve a rapid and direct deposition of the
resulting cobaltocenium polymers onto the electrode
surface. Cobaltocenium is a highly stable, positively
charged complex that undergoes a reversible monoelec-
tronic reduction to yield the uncharged, 19-electron
cobaltocene.4-9 In contrast to the well-developed chem-
istry of ferrocene-containing polymers, the incorporation
of the analogous, isoelectronic cobaltocenium system
into polymeric structures has been explored to a much
lesser extent.10 This is probably because the preparation
of cobaltocenium derivatives is considerably more dif-
ficult, since the cobaltocenium nucleus, once formed, will
not undergo electrophilic substitution.11
As a part of our research on new redox-active poly-
meric12 and dendritic13 organometallic systems, we
report here the synthesis and redox behavior of the first
examples of electropolymerizable cobaltocenium mono-
mers containing pyrrole groups, together with closely
related cobaltocenium derivatives functionalized with
allyl groups, which are potential candidates to prepare
polymers via addition reactions. Likewise, novel silox-
ane-based polymers containing cobaltocenium salts, as
well as a siloxane-bridged dimetallic model compound,
prepared by a similar synthetic route, are also described.
Resu lts a n d Discu ssion
Syn th esis of th e P yr r ole- a n d Allyl-F u n ction a l-
ized Coba ltocen iu m Mon om er s. The synthetic route
used to functionalize cobaltocenium moieties with pyr-
role derivatives takes advantage of condensation reac-
tions of the hexafluorophosphate salts of (chlorocarbonyl)-
cobaltocenium and 1,1′-bis(chlorocarbonyl)cobaltocenium
with amine-containing pyrroles. Recently, we have used
successfully a similar condensation strategy to prepare
a series of cobaltocenium-functionalized dendrimers,14
which in combination with â-cyclodextrins constitute a
novel type of host-guest system in which the formation
of high-molecular-weight supramolecular assemblies is
driven by the electrochemical reduction of the dendrim-
ers.
(3) (a) Zotti, G.; Zecchin, S.; Schiavon, G.; Berlin, A.; Pagani, G.;
Canavesi, A. Chem. Mater. 1995, 7, 2309. (b) Moutet, J .-C.; Saint-
Aman, E.; Ungureanu, M.; Visan, T. J . Electroanal. Chem. 1996, 410,
79. (c) Rose, T. L.; Kon, A. B. Inorg. Chem. 1993, 32, 781. (d) Eaves, J .
G.; Mirrazaei, R.; Parker, D.; Munro, H. S. J . Chem. Soc., Perkin Trans.
2 1989, 373. (e) Inagaki, T.; Hunter, M.; Yang, X. Q.; Skotheim, T. A.;
Okamoto, Y. J . Chem. Soc., Chem. Commun. 1988, 126.
(4) For recent examples of cobaltocenium derivatives see for example
refs 4-9: (a) Herberich, G. E.; Fischer, A.; Wiebelhaus, D. Organo-
metallics 1996, 15, 3106. (b) Herberich, G. E.; Englert, U.; Fischer, A.;
Wiebelhaus, D. Organometallics 1998, 17, 4769.
The condensation reactions of [{η5-C5H5}Co{η5-C5H4C-
(O)Cl}]PF6 and [{η5-C5H4C(O)Cl}2Co]PF6 with 1-(3-
aminopropyl)pyrrole and 1-(2-aminophenyl)pyrrole, in
chloroform solutions, at room temperature, and in the
presence of triethylamine as the base to neutralize the
acidic byproduct, afford the monosubstituted cobalto-
cenium salts 1 and 3, as well as the difunctional
derivative 2. The reactions are slightly exothermic and
(5) (a) Gloaguen, B.; Astruc, D. J . Am. Chem. Soc. 1990, 112, 4607.
(b) Alonso, E.; Valerio, C.; Ruiz, J .; Astruc, D. New J . Chem. 1997 21,
1139.
(6) (a) Beer, P. D.; Hesek, D.; Kingston, J . E.; Smith, D. K.; Stokes,
S. E. Organometallics 1995, 14, 3288. (b) Beer, P. D.; Drew, M. G. B.;
Graydon, A. R. J . Chem. Soc., Dalton Trans. 1996, 4129. (c) Beer, P.
D.; Drew, M. G. B.; Hazlewood, C.; Hesek, D.; Hodacova, J .; Stokes, S.
E. J . Chem. Soc., Chem. Commun. 1993, 229. (d) Beer, P. D.; Hesek,
D.; Hadacova, J .; Stokes, S. E. J . Chem. Soc., Chem. Commun. 1991,
270.
(7) Gilbert, A. M.; Katz, T. J .; Geiger, W. E.; Robben, M. P.;
Rheingold, A. L. J . Am. Chem. Soc. 1993, 115, 3199.
(8) Wang, Y.; Mendoza, S.; Kaifer, A. E. Inorg. Chem. 1998, 37, 317.
(9) Komatsuzaki, N.; Mitsunari, U.; Shirai, K.; Tanaka, T.; Sawada,
M.; Takahashi, S. J . Organomet. Chem. 1995, 498, 53.
(10) (a) Pittman, C. U., J r.; Ayers, O. E.; Suryanarayanan, B.;
McManus, S. P.; Sheats, J . E. Makromol. Chem. 1974, 175, 1427. (b)
Carraher, C. E.; Peterson, G. F.; Sheats, J . E.; Kirsh, T. Makromol.
Chem. 1974, 175, 3089. (c) Carraher, C. E.; Sheats, J . E. Makromol.
Chem. 1973, 166, 23. (d) Pittman, C. U. J .; Ayers, O. E.; McManus, S.
P.; Sheats, J . E.; Whitten, C. Macromolecules 1971, 4, 360. (e) See also
ref 1a.
(11) (a) Kemmitt, R. D. W.; Russell, D. R. In Comprehensive
Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W.,
Eds.; Pergamon Press: New York, 1982; Vol. 5, p 244. (b) Long, N. J .
Metallocenes. An Introduction to Sandwich Complexes; Blackwell
Science: Oxford, U.K., 1998.
(12) (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, 4327. (d) Mora´n, M.; Cuadrado, I.; Pascual, C.; Losada, J .
Organometallics 1993, 12, 811. (e) Mora´n, M.; Cuadrado, I.; Pascual,
C.; Casado, C. M.; Losada, J . Organometallics 1992, 11, 1210.
(13) (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) Cuadrado, I.; Casado, C. M.; Alonso,
B.; Mora´n, M.; Losada, J .; Belsky, V. J . Am. Chem. Soc. 1997, 119,
7613. (d) Casado, C. M.; Cuadrado, I.; Mora´n, M.; Alonso, B.; Barranco,
M.; Losada, J . Appl. Organomet. Chem. 1999, 13, 245. (e) Garc´ıa, B.;
Casado, C. M.; Cuadrado, I.; Alonso, B.; Mora´n, M.; Losada, J .
Organometallics 1999, 18, 2349.
take place rapidly, affording the desired cobaltocenium
(14) Gonzalez, B.; Casado, C. M.; Alonso, B.; Cuadrado, I.; Mora´n,
M.; Wang, Y.; Kaifer, A. E. Chem. Commun. 1998, 2569.

4962 Organometallics, Vol. 18, No. 24, 1999
Cuadrado et al.
Sch em e 1
F igu r e 1. Molecular structure of the pyrrole-functional-
ized cobaltocenium 1.
1
infrared spectroscopy, H and 13C NMR spectra, mass
spectrometry, and elemental analysis. Compound 1 was
further characterized by X-ray diffraction studies (see
below). H NMR spectra of 1-5 (in acetone-d6) show in
complexes in relatively high yields. In addition, Et3-
NHCl, which is formed as a byproduct, is more soluble
than the final reaction products in CHCl3 so that the
isolation of the desired pyrrole-containing cobaltocenium
complexes was facilitated. After appropriate purifica-
tion, the pyrrole-functionalized compounds were isolated
as air-stable yellow (1 and 3) and greenish (2) crystalline
solids.
1
all cases the pattern of resonances characteristic of
cobaltocenium derivatives in the expected region, along
with the proton resonances due to the organic groups
in the side chain. Thus, for example, for the pyrrole-
functionalized derivatives, two apparent triplets corre-
sponding to the R- and â-protons are observed, which
are centered at about 6.1 and 6.7 ppm for 1 and 2 and
at 6.3 and 7.1 ppm for 3. Likewise, the allyl group in 4
and 5 gives rise to an AA′KLM spin system pattern in
the 1H NMR spectra. The AA′ part due to the methylene
consists of a multiplet centered at 3.99 and 4.88 ppm
for 4 and 5, respectively. The three signals of the allyl
part include two close pseudoquartets for both dCHtrans
and dCHcis and a multiplet for the methine proton. The
FAB mass spectra of compounds 1-5 provided confir-
mation for the structural assignments and showed in
all cases the peak corresponding to the loss of the
counterion, together with several informative peaks
assignable to reasonable fragmentation products (see
Experimental Section).
X-r a y Str u ctu r e of 1. Single crystals of the pyrrole-
functionalized cobaltocenium derivative 1 suitable for
an X-ray diffraction study were grown by slow diffusion
of cyclohexane into a concentrated solution of the
compound in acetonitrile. The molecular structure of 1
is shown in Figure 1. Table 1 lists a summary of cell
constants and data collection parameters for the analy-
sis of 1.
The structure of 1 consists of discrete cations and
hexafluorophosphate anions. The two cyclopentadienyl
rings are planar and are nearly parallel to one another
(dihedral angle 2.41°). An unusual feature of this
molecule is that the cyclopentadienyl rings are almost
completely eclipsed, in contrast with what is observed
for carboxycobaltocenium hexafluorophosphate16 and
other cobaltocenium derivatives.6a,9 The Co-C(cyclo-
A similar condensation reaction was performed by
reacting allylamine with [{η5-C5H5}Co{η5-C5H4C(O)Cl}]-
PF6, which after purification yielded the desired allyl-
functionalized, amide-linked cobaltocenium 4 (Scheme
1). In this case, we have also attempted an alternative
synthetic route which involves a condensation reaction
between N-(trimethylsilyl)allylamine and (chlorocarbo-
nyl)cobaltocenium hexafluorophosphate in chloroform,
at room temperature. N-trimethylsilyl-substituted amines
are known to be one of the most reactive classes of
organosilane compounds and react with a variety of
electrophiles, such as carboxylic acid chlorides, yielding
the corresponding condensation products.15 This route
has several advantages over the conventional amine
route described above. In particular, the condensation
with the N-silylated amine proceeds under neutral
reaction conditions, as it avoids the liberation of HCl
generated in the absence of the silyl group. In addition,
the liberated trimethylsilyl chloride byproduct is highly
volatile and easy to remove from the reaction mixture,
and thus the desired amide-linked cobaltocenium salt
4 was cleanly obtained. In a similar way, the reaction
of O-(trimethylsilyl)allyl alcohol with (chlorocarbonyl)-
cobaltocenium hexafluorophosphate, under the same
reaction conditions, also afforded the desired ester-
linked product 5 (Scheme 1), which was isolated in high
yield as large yellow needles.
The structures of the novel cobaltocenium derivatives
were straightforwardly determined on the basis of
(15) Kricheldorf, H. R. In Silicon in Polymer Synthesis; Kricheldorf,
H. R., Ed.; Springer: Berlin, 1996; p 288.
(16) Riley, P. E.; Davis, R. E. J . Organomet. Chem. 1978, 152, 209.

Cobaltocenium Monomers and Polymers
Organometallics, Vol. 18, No. 24, 1999 4963
Ta ble 1. Cr ysta l a n d Refin em en t Da ta for
[{η5-C5H5}Co{η5-C5H4C(o)Nh (CH2)3NC4H4}]P F 6 (1)
formula
mol wt
CoC18ON2PF6H20
484.27
cryst dimens, mm
cryst habit and color
cryst syst
space group
cell dimens
a, Å
0.10 × 0.15 × 0.40
prismatic yellow
orthorhombic
Pbca (No. 61)
21.885(3)
b, Å
10.10(1)
c, Å
17.960(3)
R ) â ) γ (deg)
90.0
8
Z
V, Å3
D
3970(4)
1.62
calcd, g cm-3
F(000)
1968
temp, K
295
diffractometer
radiation
Enraf-Nonius CAD4
graphite-monochromated
Mo KR (λ ) 0.710 69 Å)
ω/2θ
scan technique
2θ range, deg
data collected
1-52
0 e h e 26, 0 e k e 12,
0 e l e 22
no. of unique data
no. of obsd rflns, I > 3σ(I)
Rint
4374
1912
decay
std rflns
<1%
3/45
F igu r e 2. Cyclic voltammograms of (a) 1 in DMF, (b) 1 in
CH3CN, (c) 4 in DMF, and (d) 4 in CH2Cl2. Unless
µ(Mo KR), cm-1
transmissn range
weighting scheme
max and av shift/error
max residual, e Å-3
R ) ∑||Fo| - |Fc||/∑|Fo|
10.1
0.65-0.90
unit
0.01, 0.001
0.2
0.062
0.064
1.2
otherwise indicated, the scan rate is 100 mV s-1
.
When the electrochemical reduction of 1 and 2 was
effected in acetonitrile (see Figure 2b), the ip,a/ip,c value
for the second process, at slow scan rates, is less than 1
and the cathodic current is higher than the diffusion-
controlled reversible value. In addition, at high scan
rates the current function (ip/v1/2) for this wave reaches
a limiting value that is the same as that of the
uncomplicated first reduction process but increases at
slower scan rates. These results are consistent with an
ECE mechanism in which the electrogenerated anion
could react with the solvent to give a product with a
less negative reduction potential. A similar behavior has
been observed by Geiger for the cobaltocene reduction
in acetonitrile solution, in which the formation of the
ring-addition intermediate {η5-C5H5}Co{η4-C5H5CH2-
CN} is postulated.17
The redox behavior, in DMF as solvent, of the allyl-
functionalized cobaltocenium compounds 4 and 5 is
different from that described above for the pyrrole
derivatives 1-3. The second reduction at about -1.6 V
vs SCE is irreversible, as shown by the absence of the
corresponding anodic peak in the reverse scan (see
Figure 2c). However, in CH2Cl2 at high scan rates these
compounds show partially chemically reversible reduc-
tions (Figure 2d), the ip,a/ip,c ratio being close to 1. The
instability of the monoanionic species generated in the
reduction of 4 and 5 could be related to the nature of
the substituents on the cyclopentadienyl ring.
2
Rw ) (∑w(|Fo| - |Fc|)2/∑w|Fo| )1/2
GOF (F)
no. of refined params
rfln/param ratio
262
7.3
pentadienyl ring) distances are in the range 1.989(12)-
2.036(10) Å, which are essentially similar to those found
in [{η5-C5H5}Co{η5-C5H4COOH}]PF6.16 Other bond dis-
tances and angles found in 1 do not differ significantly
from those of other cobaltocenium complexes.
Solu tion Red ox Beh a vior of Mon om er s 1-5. The
electrochemical behavior of the new cobaltocenium
derivatives 1-5 has been investigated in dichloro-
methane, acetonitrile, and dimethylformamide (DMF)
solution with n-Bu4NClO4 as supporting electrolyte.
The cyclic voltammograms (CVs) of the pyrrole-
functionalized cobaltocenium monomers 1-3 in DMF
solutions, over the range 0.0 to -2.0 V vs SCE, show
two reversible processes (waves A and B in Figure 2a)
characterized by peak-to-peak potential splittings (∆Ep)
of about 65-70 mV and essentially equal cathodic and
anodic peak currents. Furthermore, both electrochemi-
cal processes are diffusion-controlled with the peak
current linearly proportional to the square root of the
scan rate, v. Potentiostatic coulometry and comparisons
of limiting currents, obtained from rotating-disk-
electrode (RDE) voltammograms with that of the un-
substituted cobaltocenium hexafluorophosphate indicate
two successive one-electron transfers. The two observed
reduction waves can be easily assigned to the two
successive one-electron reductions of the cobaltocenium
moiety. These results indicate that for compounds 1-3,
in DMF solutions, reversible processes take place, and
stable neutral and monoanionic species are formed in
the time scale of the CV experiments.
Redox potential values for the new cobaltocenium
compounds 1-5 together with the observed values for
the unsubstituted cobaltocenium hexafluorophosphate
are indicated in Table 2. The electron-withdrawing
effect exerted by the carbonyl groups is clearly evident
in the substantial positive shift observed in the half-
(17) Geiger, W. E. in Laboratory Techniques in Electroanalytical
Chemistry; Kissinger, P. T., Heineman, W. R., Eds.; Marcel Dekker:
New York, 1996; p 683.

4964 Organometallics, Vol. 18, No. 24, 1999
Cuadrado et al.
cobaltocene grows in isosbestically at 1643 cm-1, indi-
cating a clean conversion. The shift to a lower frequency
in this ν(CdO) band is produced because the reduction
of the cobaltocenium unit of 4 inductively increases the
electron density on the amide group directly attached
to the cyclopentadienyl ring, resulting in a loss of
strength in the CdO bond.
Ta ble 2. Red ox P oten tia ls (V, vs SCE) of th e
Coba ltocen iu m Com p lexes a n d P olym er sa
compd
solvent
E1/2(A/A′) E1/2(B/B′)
Ep(B)
1
2
DMF
CH3CN
DMF
CH3CN
DMF
DMF
CH2Cl2
DMF
CH2Cl2
DMSO
DMF
-0.68
-0.60
-0.53
-0.58
-0.65
-0.69
-0.70
-0.61
-0.62
-0.61
-0.69
-0.65
-0.88
-1.62
-1.43
-1.53
-1.59
-1.56
3
4
Electr op olym er iza tion of P yr r ole-F u n ction a l-
ized Coba ltocen iu m Mon om er s. Figure 4a shows the
cyclic voltammogram of the pyrrole-containing cobalto-
cenium monomer 1 in acetonitrile solution containing
0.1 M n-Bu4NClO4, at a gold electrode, between -1.1
and +1.5 V vs SCE. The potential was first scanned in
the negative region, and the cyclic voltammogram shows
the reversible redox system A/A′ corresponding to the
monoelectronic reduction of the cobaltocenium moiety
to the neutral cobaltocene. Upon scan reversal, a large
irreversible oxidation peak, C, appears at +1.26 V vs
SCE, which could be assigned to the oxidation of the
pyrrole group. In fact, this oxidation takes place at a
potential value, which is in close agreement with that
observed for the free 1-(aminopropyl)pyrrole ligand,
under the same experimental conditions (+1.22 V vs
SCE). The subsequent cyclic voltammogram shows an
important increase in the peak current corresponding
to the cobaltocenium/cobaltocene redox couple. At the
same time, a new peak of lower intensity D appears at
the foot of the cobaltocenium reduction. Likewise, in the
anodic region, an irreversible peak E is observed, which
could be associated with the oxidation of the pyrrole
group.
-1.70
-1.68
-1.57
-1.70
5
6
7
8
-1.48
-1.66
-1.71
-1.85
DMF
DMF
[{η5-C5H5}2Co]PF6
a
At a glassy-carbon electrode.
Figure 4b shows the evolution of the cyclic voltam-
mogram of 1 during repeated potential scans over the
range -1.0 to +1.7 V vs SCE. The increase in the
current for the previously described cobaltocenium/
cobaltocene system upon continuous scanning indicates
that electrochemical polymerization of the monomer 1
rapidly occurs and that an electroactive polymeric film
grows on the electrode surface. Furthermore, in the
positive region, the wave centered at +1.26 V vs SCE,
corresponding to the oxidation of the pyrrole group, grew
in magnitude only during the early stages of deposition
and it reached an apparent steady-state value. At the
same time, the prepeak associated with this oxidation
becomes more anodic as the film grows. Similar pre-
peaks have been observed for some N-substituted pyr-
roles with large groups, and they have been related to
the oxidation of polypyrrole.18 The intensity of the
prepeak in the negative voltage region increases upon
cycling, and its potential shifts gradually to negative
values and finally merges with the reduction peak of
the cobaltocenium. This prepeak is ascribable to the
mediated reduction of the polypyrrole through the
reduced form of the cobaltocenium group.18a,c
F igu r e 3. (a) Infrared spectral changes observed upon
reduction of 4 in CH2Cl2/n-Bu4NPF6 at -1.0 V vs Ag
pseudoreference electrode in the spectroelectrochemical
cell. (b) FTIR absorbance difference spectrum of the start-
ing 4 and the electrogenerated reduction product.
wave potential value of monomers 1-5 in comparison
to the E1/2 value of pure cobaltocenium. Therefore, the
reduction of the new functionalized cobaltocenium
compounds 1-5 is thermodynamically easier than that
of [(η5-C5H5)2Co]PF6.
The formation of the neutral cobaltocene species,
generated by the monoelectronic reduction of the cat-
ionic species 1-5, has been evidenced by infrared
spectroelectrochemical experiments. As an example,
Figure 3 shows the spectral changes that accompany
the controlled-potential reduction of 4 in CH2Cl2/n-Bu4-
NPF6, in the thin-layer cell, at room temperature. With
the application of a reductive potential, the amide I ν-
(CdO) band at 1675 cm-1, corresponding to the cationic
compound 4, decreases in intensity while a new carbonyl
band corresponding to the electrogenerated neutral
After a period of scanning in a rigorously deaerated
solution of monomer 1, the electrodes thus coated were
removed from the monomer-containing solution, rinsed
with acetonitrile to remove any adhering solution, and
dried in air. Inspection of the electrode reveals the
presence of an insoluble colored (reddish brown) film.
(18) (a) Cosnier, S.; Deronzier, A.; Moutet, J .-C. J . Electroanal.
Chem. Interfacial Electrochem. 1986, 207, 315. (b) Daire, F.; Bedioui,
F.; Devynck, J . J . Electroanal. Chem. Interfacial Electrochem. 1987,
224, 95. (c) Cosnier, S.; Deronzier, A.; Moutet, J .-C. J . Electroanal.
Chem. Interfacial Electrochem. 1985, 193, 193.

Cobaltocenium Monomers and Polymers
Organometallics, Vol. 18, No. 24, 1999 4965
F igu r e 4. (a) Cyclic voltammograms, at a gold electrode, of 1 in CH3CN/0.1 M n-Bu4NClO4, at a scan rate of 100 mV s-1
.
(b) Evolution of the cyclic voltammogram during the oxidative electropolymerization of monomer 1 by repeated potential
scans (nine cycles) on a gold electrode in CH3CN/0.1 M n-Bu4NClO4. The inset shows the cyclic voltammogram of a Au
electrode modified with a film of poly-1, measured in CH3CN/0.1 M n-Bu4NClO4.
The voltammetric response of electrodes modified
with cobaltocenium-containing polymer films was ex-
amined in acetonitrile and aqueous electrolyte solutions.
A cyclic voltammogram of a gold electrode modified with
an electropolymerized film of monomer 1, obtained in a
clean acetonitrile solution containing only supporting
electrolyte, is shown in the inset of Figure 4b. A well-
defined redox process corresponding to the cobaltoce-
nium/cobaltocene system is observed at -0.6 V, which
is virtually identical with the redox potential of the
monomer 1 in solution. The redox wave is symmetric
and characteristic of a surface-confined redox couple,
with the expected linear relationship of peak current
with the potential sweep rate.19 For polymer films
examined at scan rates lower than 100 mV s-1, a peak
splitting ∆Ep of 10 mV, for the redox couple, was
observed and the ip,a/ip,c ratio was close to unity. These
voltammetric features unequivocally indicate the surface-
confined nature of the electroactive cobaltocenium-
containing polypyrrole film. The surface coverage of
electroactive cobaltocenium sites in the film, Γ, was
determined from the integrated charge of the cyclic
voltammetric wave, resulting in a value of 6 × 10-9 mol/
cm2. A similar electrochemical behavior is observed for
films of poly-1 examined in an aqueous electrolyte
solution. A remarkable feature of electrodes modified
with electropolymerized films of 1 is that they are
extremely durable and reproducible either in acetoni-
trile or aqueous electrolyte solutions. In addition, the
above-described results are essentially the same for
platinum and glassy-carbon electrodes.
F igu r e 5. Scanning electron micrograph of a polymer film,
obtained by electropolymerization of 1 (25 cycles) on a
platinum-wire electrode.
The microstructure of a film of poly-1 obtained by
anodic polymerization of the pyrrole-functionalized
monomer 1 on a platinum wire (0.25 mm of diameter)
was examined by scanning electron microscopy (SEM).
The SEM micrograph in Figure 5 shows that the
cobaltocenium-containing polymeric film has a compact
morphology of crossed fibers.
The pyrrole-functionalized cobaltocenium monomers
2 and 3 can be also electropolymerized under similar
experimental conditions. In the case of the difunctional
monomer 2, the presence of two polymerizable pyrrole
substituents attached to the cyclopentadienyl rings does
not seem to increase the efficiency of the electropoly-
merization process. Electropolymerized films of the
cobaltocenium-functionalized monomers 2 and 3 showed
(19) (a) Murray, R. W. In Molecular Design of Electrode Surfaces;
Murray, R. W., Ed.; Techniques of Chemistry XXII; Wiley: New York,
1992; p 1. (b) Abrun˜a, H. D. In Electroresponsive Molecular and
Polymeric Systems; Skotheim, T. A., Ed.; Dekker: New York, 1988;
Vol 1, p 97.

4966 Organometallics, Vol. 18, No. 24, 1999
Cuadrado et al.
Sch em e 2
similar voltammetric responses and similar stabilities
to the redox processes.
In conclusion, cobaltocenium-containing polypyrrole
homopolymers can be readily formed as stable films on
the electrode surfaces by electrochemical polymerization
of monomers 1-3. It is interesting to note that this
result contrasts with the electrochemical polymerization
of related N-substituted pyrrole ferrocene derivatives,
which can be grown as stable films only by copolymer-
ization with 1-methylpyrrole.3d The ease of preparation,
rapid polymerization rates, and electrochemical stability
either in aqueous and organic solvents make these
pyrrole-based cobaltocenium polymer films potentially
useful for applications in the fields of electrocatalysis
and molecular recognition of anions.
Syn th esis a n d Electr och em istr y of Siloxa n e-
Ba sed Coba ltocen iu m P olym er s. In the past few
years our group has been interested in the synthesis of
siloxane-based redox-active organometallic polymers.
Thus, we have reported siloxane polymers containing
ferrocene, [(η5-C5R4)Fe(CO)(µ-CO)]2 (R ) H, Me), as well
as [(η6-arene)Cr(CO)3] moieties, which exhibit interest-
ing redox properties.12d,12e Due to its resistance to strong
oxidizing agents and interesting electrochemical behav-
ior, cobaltocenium is an attractive moiety to incorporate
into polymeric backbones.10 To the best of our knowl-
edge, polysiloxane polymers containing cobaltocenium
units have not been prepared so far. With this in mind,
we are now particularly interested in the possibility of
obtaining cobaltocenium-containing polysiloxane mate-
rials, where the interesting electrochemical and chemi-
cal features of this organometallic moiety are combined
with the unique and valuable properties of siloxane
backbones.
On the other hand, reaction of [{η5-C5H5}Co{η5-
C5H4C(O)Cl}]PF6 with amino(propyl)methyl(3-5%)-
dimethylsiloxane(95-97%) copolymer, as a source of the
NH2 functionality, allows facile access to the block
copolymer 8, consisting of a poly(dimethylsiloxane)
chain, in which pendant amide-linked cobaltocenium
moieties are randomly distributed along the flexible
methylsiloxane backbone. After purification, polymer 8
was isolated as a yellow gum, which hardens and
solidifies on standing.
We have prepared two different types of siloxane-
based cobaltocenium-containing polymers. The polycon-
densation of 1,3-bis(3-aminopropyl)-1,1,3,3-tetrameth-
yldisiloxane with 1,1′-bis(chlorocarbonyl)cobaltocenium
hexafluorophosphate was effected under the same reac-
tion conditions as those used to prepare compounds 1-3
and afforded polymer 6, with a backbone consisting of
alternating dimethylsiloxane segments and cobaltoce-
nium moieties bonded through amide linkages (see
Scheme 2). The reaction has been carried out using the
minimum volume of solvent to dissolve the starting
products. These high-concentration conditions were used
to ensure maximization of the intermolecular condensa-
tion relative to the intramolecular cyclization process.
Polymer 6 was isolated as a shiny greenish solid, which
was found to be essentially insoluble in most common
organic solvents. The high insolubility of this material
precluded a complete characterization. Nevertheless, it
was found to be partially soluble in DMSO, and thus,
NMR characterization of the more soluble fraction could
be performed.
The dimetallic model compound 7 as well as the
polymeric cobaltocenium salts 6 and 8 were structurally
characterized by 1H, 13C, and 29Si NMR spectroscopy
as well as by elemental analysis and yielded data
1
consistent with the assigned structures. The H NMR
spectrum of 7 showed the resonances of the cyclopen-
tadienyl rings at 6.35, 5.98, and 5.91 ppm as well as
resonances assigned to the CH2CH2CH2 groups at 3.35,
1.67, and 0.61 ppm. The integration ratio of these
resonances was consistent with the assigned structure.
Broad, less well-resolved resonances were found in the
1H NMR spectra of both polymers 6 and 8 compared to
those of the corresponding model compound 7 but were
also consistent with the presence of backbones contain-
ing amide-linked cobaltocenium moieties and dimeth-
ylsiloxane segments. For the cobaltocenium-substituted
copolymer 8, the 1H NMR spectrum, together with
elemental analysis, was important for the estimation
of the degree of cobaltocenium functionalization. Thus,
Likewise, the condensation reaction of the same
difunctional amine with the hexafluorophosphate salt
of (chlorocarbonyl)cobaltocenium, in CHCl3 solution, at
room temperature and in the presence of Et3N, affords
the siloxane-bridged dimetallic model compound 7,
which has been prepared in order to aid the spectro-
scopic and electrochemical characterization of the poly-
mers.

Cobaltocenium Monomers and Polymers
Organometallics, Vol. 18, No. 24, 1999 4967
cyltrimethylammonium bromide was added to the poly-
mer film, the diffusion through the polymer film is
allowed and well-defined anodic and cathodic waves (see
for example Figure 6b), due to the reduction of the
cobaltocenium moieties in the polymer, appeared.
Su m m a r y
We have synthesized new cobaltocenium complexes
containing electrochemically and chemically polymer-
izable pyrrole and allyl substituents. Electrode surfaces
can be readily coated with stable and electroactive
cobaltocenium polymeric films upon oxidative electro-
chemical polymerization of the new pyrrole-functional-
ized monomers 1-3, resulting in detectable electroactive
material persistently attached to the electrode surfaces.
In addition, we have prepared novel redox-active, si-
loxane-based cobaltocenium polymers and block copoly-
mers. Electrodes coated with films of the hydrophobic
siloxane-based copolymer 8 show redox activity in
acetonitrile and also in an aqueous solution when an
ionic surface-active agent is added to the film. Work is
now focused on detailed studies of the applications of
electrodes modified with cobaltocenium-containing poly-
mer films in the fields of molecular recognition and
electrocatalysis.
F igu r e 6. Cyclic voltammograms of (a) a film of polymer
8 evaporatively deposited on a glassy-carbon electrode,
measured in CH3CN/0.1 M n-Bu4NClO4, and (b) a film of
polymer 8 + sodium n-dodecylbenzenesulfonate deposited
on a glassy-carbon electrode, measured in H2O/1 M KCl.
satisfactory results were obtained when integration of
the cobaltocenium and methyl protons was used, indi-
cating that all the pendant amine groups in the siloxane
chains have been derivatized with cobaltocenium moi-
eties. The 13C NMR spectra of 6-8 showed the expected
resonances for the carbon atoms in the molecules in
their different chemical environments. The 29Si NMR
spectra of both dimer 7 and polymer 6 show the expected
single resonance centered at about 8.3 ppm correspond-
ing to the dimethylsiloxane segment. Likewise, in the
29Si NMR of the block copolymer 8, in addition to the
resonances corresponding to the two different polysi-
loxane blocks at -18.82 and -21.87 ppm, a small
resonance was also detected at 7.33 ppm, which was
assigned to the terminal OSiMe3 units of the polymer
chain.
The electrochemical reduction of the dimetallic model
compound 7 and polymer 8 in DMF solutions is similar
to that observed for the pyrrole derivatives 1 and 2, and
the corresponding redox potentials are indicted in Table
2. In the case of the model compound 7, two simulta-
neous, but independent, one-electron transfers are as-
sociated with each reduction wave. This result indicates
the noninteracting character of the two equivalent
electroactive cobaltocenium moieties in the compound.
The redox properties of the polymer 8 have been also
studied as films evaporatively deposited on electrode
surfaces from a polymer-containing CH2Cl2 solution.
The polymer films were characterized by cyclic volta-
mmetry in fresh acetonitrile solutions containing only
supporting electrolyte. The deposited films exhibit
reproducible, well-defined reversible redox responses,
owing to the cobaltocenium/cobaltocene system, char-
acteristic of surface-confined redox couples (Figure 6a).
It is also interesting to note the redox response of films
of the block copolymer 8 in aqueous solution. In the CV
of glassy-carbon electrodes modified with a film of 8,
measured in H2O/KCl, only background current was
observed, indicating that the redox reaction of the
cobaltocenium moieties does not occur in the polymer
film. The absence of redox waves in an aqueous medium
is probably related to the highly hydrophobic character
of the poly(dimethylsiloxane) polymer backbone, which
hinders the diffusion of water and electrolyte ions into
the polymer film. However, when an ionic surface-active
agent such as sodium dodecylbenzenesulfonate or dode-
Exp er im en ta l Section
Ma ter ia ls a n d Equ ip m en t. All reactions were performed
under an inert atmosphere (prepurified N2 or Ar) using
standard Schlenk techniques. Solvents were dried by standard
procedures over the appropriate drying agents and distilled
immediately prior to use. Triethylamine (Merck) was distilled
over KOH under N2. The hexafluorophosphate salts of 1-(chlo-
rocarbonyl)cobaltocenium and 1,1′-bis(chlorocarbonyl)cobalto-
cenium were prepared as described in the literature.20 1-(3-
aminopropyl)pyrrole was prepared by reduction of 1-(2-
cyanoethyl)pyrrole21 with lithium aluminum hydride in diethyl
ether. The product was purified by distillation at 65-70 °C/
1.5 Torr. The following silicon-containing products were
purchased from Petrarch Systems: N-(trimethylsilyl)ally-
lamine, O-(trimethylsilyl)allyl alcohol, 1,3-bis(aminopropyl)-
1,1,3,3-tetramethyldisiloxane, and (aminopropyl)methyl(3-
5%)dimethylsiloxane(95-97%) copolymer. Allylamine and 1-(2-
aminophenyl)pyrrole were obtained from Aldrich and used as
received. Infrared spectra were recorded on a Bomem MB-100
FTIR spectrometer. NMR spectra were recorded on a Bruker-
AMX (1H, 300 MHz; 13C, 75.43 MHz; 29Si, 59.3 MHz) spec-
trometer. Chemical shifts are reported in parts per million (δ)
with reference to internal tetramethylsilane (SiMe4) or to
residual solvent resonances for 1H and 13C NMR (CDCl3: 1H,
δ 7.27 ppm; 13C, δ 77.0 ppm). 29Si NMR spectra, referenced
externally to tetramethylsilane, were recorded with inverse-
gated proton decoupling in order to minimize nuclear Over-
hauser 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. 3-Nitrobenzyl alcohol was
used as the matrix. Number-average molecular weights (Mn)
were obtained with an Osmomat 070 vapor-pressure osmom-
eter. Elemental analyses were performed by the Microana-
lytical Laboratory, Universidad Auto´noma de Madrid, Madrid,
Spain.
(20) Sheats, J . E.; Rausch, M. D. J . Org. Chem. 1970, 35, 3254.
(21) Patterson, J . M.; Brasch, J .; Drenchko, P. J . Org. Chem. 1962,
27, 1652.

4968 Organometallics, Vol. 18, No. 24, 1999
Cuadrado et al.
Electr och em ica l Mea su r em en ts. Cyclic voltammetric
experiments were performed on either a BAS CV-27 poten-
tiostat or a PAR 362 potentiostat. Coulometric measurements
were made with a PAR 362 potentiostat and a PAR 379 digital
coulometer. A PAR 377A coulometry cell system fitted with a
platinum-gauze working electrode was used. Electrochemical
measurements were performed in acetonitrile and dichlo-
romethane (both freshly distilled from calcium hydride under
nitrogen) and in dimethylformamide (distilled in vacuo and
stored over 4 Å molecular sieves). The supporting electrolyte
was in all cases tetra-n-butylammonium perchlorate (Fluka),
which was purified by recrystallization from ethyl acetate and
dried at 60 °C under vacuum. It was used in a concentration
of 0.1 M in all cyclic voltammetric measurements. A conven-
tional sample cell operating under an atmosphere of prepuri-
fied nitrogen was used for cyclic voltammetry. All cyclic
voltammetric experiments were performed using a platinum-
disk working electrode, a gold-disk electrode, or a glassy-
carbon-disk working electrode (for the three of them A ) 0.070
cm2), each of which was polished prior to use with either 1
µm diamond paste (Buehler) or 0.05 µm alumina/water slurry
and rinsed thoroughly with purified water and acetone. All
potentials are referenced to the saturated calomel electrode
(SCE). A coiled platinum wire was used as a counter electrode.
Solutions for cyclic voltammetry were typically 1.0 mM in the
redox-active species and were deoxygenated by purging with
prepurified nitrogen. No iR compensation was used. The
modification of electrode surfaces by electropolymerization of
the pyrrole-functionalized monomers 1-3 was effected by
electrochemical cycling as described earlier in the text. The
preparation of electrodes coated with evaporatively deposited
films of polymer 8 was accomplished by micropipetting a few
microliters of a dichloromethane solution of the polymer
containing about 1 mg/mL of the polymer onto the platinum
or glassy-carbon electrode surface and allowing the solvent to
evaporate to dryness. Infrared spectral changes during thin-
layer bulk electrolyses were measured by using a spectroelec-
trochemical cell as described previously.12e Infrared data were
collected with a Bomem MB-100 FTIR spectrometer. Bulk
electrolyses were controlled by a PAR 362 potentiostat.
electron density. Most of the calculations were carried out with
the X-ray 80 system.24
Syn th esis of [{η5-C5H5}Co{η5-C5H4C(O)NH(CH2)3NC4H4}]-
P F 6 (1). 1-(3-Aminopropyl)pyrrole (0.40 g, 3.2 mmol) and
triethylamine (0.40 g, 3.9 mmol) were dissolved in 20 mL of
dry chloroform and added dropwise under a nitrogen atmo-
sphere to (chlorocarbonyl)cobaltocenium hexafluorophosphate
(1.00 g, 2.5 mmol) in 30 mL of dry chloroform with stirring.
The reaction mixture was stirred at room temperature over-
night. After this time, the precipitate formed was separated
by filtration, washed several times with CHCl3 in order to
remove small amounts of the triethylamine hydrochloride
byproduct, and dried under vacuum. Compound 1 was isolated
as an air-stable yellow solid. Yield: 0.80 g, 65%. Recrystalli-
zation can be effected by slow diffusion of cyclohexane in a
concentrated solution of 1 in acetonitrile. Anal. Calcd for
C
18H20CoN2OPF6: C, 44.62; H, 4.16; N, 5.79. Found: C, 44.52;
H, 4.14; N, 5.62. FT-IR (KBr, cm-1): ν(NH), 3325; amide I,
1644; amide II, 1561; amide III, 1305, 830, 557. 1H NMR
(acetone-d6, 300 MHz): δ 2.07 (q, 2H, CH2), 3.37 (t, 2H, CH2-
NH), 4.04 (t, 2H, NCH2), 5.95 (s, 5H, C5H5), 5.98 (t, 2H, C5H4),
6.02 (t, 2H, C4H4N), 6.33 (t, 2H, C5H4), 6.76 (t, 2H, C4H4N),
8.09 (s, 1H, C(O)NH). 13C NMR (acetone-d6, 75.43 MHz): δ
31.94 (CH2), 38.37 (CH2NH), 47.60 (NCH2), 85.96 (C5H4), 86.71
(C5H4), 87.10 (C5H5), 108.62 (C4H4N), 121.25 (C4H4N), 162.15
(C(O)NH). MS (FAB; m/z (%)): 339.1 ([M - PF6]+, 100.0), 274.1
([M - PF6 - NC4H4]+, 3.5), 188.0 ([M - PF6 - C(O)NH(CH2)3-
NC4H4]+, 4.9).
Syn th esis of [{η5-C5H4C(O)NH(CH2)3NC4H4}2Co]P F6 (2).
This compound was prepared similarly to compound 1, starting
from 1,1′-bis(chlorocarbonyl)cobaltocenium hexafluorophos-
phate (1.00 g, 2.2 mmol), 1-(3-aminopropyl)pyrrole (0.61 g, 4.9
mmol), and triethylamine (0.75 g, 7.4 mmol). In this case, after
evaporation of the solvent under vacuum, the resulting crude
product was dissolved in CH2Cl2 and the solution washed with
water in order to dissolve the triethylamine hydrochloride
byproduct. The organic phase was separated and dried over
anhydrous MgSO4. The solvent was removed under vacuum,
to give 0.98 g (70% yield) of pure 2, which was isolated as a
bright greenish solid. Anal. Calcd for C26H30CoN4O2PF6: C,
49.20; H, 4.67; N, 8.93. Found: C, 49.28; H, 4.77; N, 9.01. FT-
IR (KBr, cm-1): ν(NH), 3417, 3239; amide I, 1660; amide II,
1551; amide III, 1300; PF6-, 840, 557. 1H NMR (acetone-d6,
300 MHz): δ 2.10 (q, 2H, CH2), 3.42 (t, 2H, CH2NH), 4.00 (t,
2H, NCH2), 5.98 (t, 2H, C5H4), 6.03 (t, 2H, C5H4), 6.11 (t, 2H,
C4H4N), 6.71 (t, 2H, C4H4N), 7.46 (s, 1H, C(O)NH). 13C NMR
(chloroform-d, 75.43 MHz): δ 30.54 (CH2), 38.43 (CH2NH),
47.59 (NCH2), 85.39 (C5H4), 86.67 (C5H4), 94.96 (C5H4), 108.48
(C4H4N), 120.68 (C4H4N). MS (FAB; m/z (%)): 489.2 ([M -
PF6]+, 30.3).
X-r a y Str u ctu r e Deter m in a tion Tech n iqu e. A summary
of the fundamental crystal data is given in Table 1. A yellow
crystal of prismatic shape and dimensions 0.10 × 0.15 × 0.40
mm3 was coated with an epoxy resin and mounted on an Enraf-
Nonius CAD4 diffractometer with a monochromatic Mo KR
radiation source (λ ) 0.710 69 Å). The cell dimensions were
refined by least-squares-fitting the θ values of 25 accurate
centered reflections within a 2θ range of 13-27°. Data were
collected at 295 K using the ω-2θ scan technique to a
maximum 2θ ) 52°, from (0,0,0) to (26,12,22) to yield 4374
unique reflections; among them 1912 were considered ob-
served, having I > 3σ(I). The stability of the crystal was
monitored every 100 reflections using 3 standard reflections;
no significant decay of their intensities was observed. The
intensities were corrected for Lorentz and polarization effects.
Scattering factors for neutral atoms and anomalous dispersion
corrections for Co and P were taken from ref 22. The position
of the heavy atom was obtained from the Patterson function.
The rest of the structure was solved by means of Fourier
synthesis. An empirical absorption correction23 was applied at
the end of the isotropic refinements. The hydrogen atoms were
included with fixed isotropic contributions at their calculated
positions determined by the molecular geometry. A final
refinement was undertaken with anisotropic thermal param-
eters for the non-hydrogen atoms. Since no trends in ∆F vs Fo
or (sin θ)/λ were observed, no special weighting scheme has
been applied. Final difference synthesis showed no significant
Syn th esis of [{η5-C5H5}Co{η5-C5H4C(O)NHC6H4NC4H4}]-
P F 6 (3). Compound 3 was prepared similarly to compound 1,
by reacting [(η5-C5H5)Co(η5-C5H4C(O)Cl)]PF6 (1.00 g, 2.5 mmol),
1-(2-aminophenyl)pyrrole (0.45 g, 2.8 mmol), and triethylamine
(0.40 g, 3.9 mmol). Purification of the reaction product was
achieved in this case by redissolving the yellow crude product
in acetone and the desired complex was precipitated by
addition of n-hexane. Yield: 0.58 g (45%). Anal. Calcd for
C
21H18CoN2OPF6: C, 48.64; H, 3.50; N, 5.41. Found: C, 48.83;
H, 3.36; N, 5.31. FT-IR (KBr, cm-1): ν(NH), 3268; amide I,
1653; amide II, 1538; amide III, 1303; PF6-, 836, 557. 1H NMR
(acetone-d6, 300 MHz): δ 5.88 (s, 5H, C5H5), 6.03 (t, 2H, C5H4),
6.33-6.36 (t, 2H, C5H4), 6.33-6.36 (t, 2H, C4H4N), 7.06 (t, 2H,
C4H4N), 7.42-7.49 (m, 3H, C6H4N), 7.77 (m, 1H, C6H4N). 9.43
(s, 1H, C(O)NH). 13C NMR (acetone-d6, 75.43 MHz): δ 85.17
(C5H4), 86.94 (C5H4), 87.32 (C5H5), 110.60 (C4H4N), 122.85
(C4H4N), 127.66 (C6H4N), 128.08 (C6H4N), 128.48 (C6H4N),
128.66 (C6H4N). MS (FAB; m/z (%)): 373.2 ([M - PF6]+, 100.0),
(22) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, U.K., 1974; Vol. IV, p 72.
(23) Walker, N.; Stuart, D., Acta Crystallogr. 1983, A39, 158.
(24) Stewart, J . M. The X-RAY80 System; Computer Science Center,
University of Maryland, College Park, MD, 1980.

Cobaltocenium Monomers and Polymers
Organometallics, Vol. 18, No. 24, 1999 4969
216.1 ([M - PF6 - NHC6H4NC4H4]+, 7.0), 188.1 ([M - PF6
-
3.19 (m, 2H, NHCH2), 5.89 (br, 2H, C5H4), 6.34 (br, 2H, C5H4),
8.31 (br, 1H, C(O)NH). 13C NMR (dimethyl sulfoxide-d6, 75.43
MHz): δ 1.43 (SiCH3), 16.27 (CH2Si), 23.79 (CH2), 43.53
(NHCH2), 86.15 (C5H4), 88.0. (C5H4), 95.56 (OC-C5H4), 161.16
(CO). 29Si NMR (dimethyl sulfoxide-d6, 59.3 MHz): δ 8.30.
C(O)NHC6H4NC4H4]+, 10.6).
Syn t h esis of [{η5-C5H 5}Co{η5-C5H 4C(O)NH CH 2CH d
CH2}]P F 6 (4). Two condensation methods were used for the
preparation of the compound 4.
Syn t h esis of [[{η5-C5H 5}Co{η5-C5H 4C(O)NH(CH 2)3Si-
(CH3)2}]2O][P F 6]2 (7). (Chlorocarbonyl)cobaltocenium (1.00 g,
2.5 mmol) was added to a chloroform solution, previously
stirred at room temperature, of triethylamine (0.51 g, 5.0
mmol) and 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisilox-
ane (0.31 g, 1.2 mmol). The reaction mixture was stirred
overnight. Subsequently, a precipitate was collected by filtra-
tion, washed several times with chloroform to remove small
amounts of triethylamine hydrochloride, and dried in vacuo.
Dimer 7 was isolated as a yellow solid. Yield: 0.57 g (47%).
Anal. Calcd for C32H44Co2N2O3Si2P2F12: C, 39.66; H, 4.54; N,
2.89. Found: C, 38.97; H, 4.32; N, 2.74. FT-IR (KBr, cm-1):
ν(NH), 3428, 3322; amide I, 1643; amide II, 1557; amide III,
1305; PF6-, 559. 1H NMR (acetone-d6, 300 MHz): δ 0.09 (s,
6H, SiCH3), 0.61 (m, 2H, CH2Si), 1.67 (m, 2H, CH2), 3.35 (q,
2H, NHCH2), 5.91 (s, 5H, C5H5), 5.98 (t, 2H, C5H4), 6.35 (t,
2H, C5H4), 8.16 (t, 1H, C(O)NH). 13C NMR (dimethyl sulfoxide-
d6, 75.43 MHz): δ 1.22 (SiCH3), 16.05 (CH2Si), 23.72 (CH2),
43.30 (NHCH2), 84.74 (C5H4), 86.49 (C5H4), 86.71 (C5H5), 95.01
(OC-C5H4), 161.89 (CO). 29Si NMR (dimethyl sulfoxide-d6, 59.3
MHz): δ 8.34. MS (FAB; m/z (%)): 823.0 ([M - PF6]+, 100.0),
678.0 ([M - 2PF6]+, 34.7).
Meth od 1. Allylamine (0.14 g, 2.5 mmol) and triethylamine
(0.30 g, 2.9 mmol) were dissolved in dry chloroform and added
dropwise under nitrogen to (chlorocarbonyl)cobaltocenium
(0.80 g, 2.0 mmol), in chloroform. The reaction mixture was
stirred at room temperature overnight. A precipitate was
formed during this time, which was separated by filtration,
thoroughly washed with CHCl3, and dried under vacuum to
afford 4 as a yellow crystalline solid. Yield: 0.45 g (53%).
Meth od 2. A solution of N-(trimethylsilyl)allylamine (0.30
g, 2.3 mmol) in chloroform was added with stirring under
nitrogen to (chlorocarbonyl)cobaltocenium (0.80 g, 2.0 mmol)
also in chloroform. Stirring was continued for 5 h. The
resulting yellow precipitate was filtered off, washed with
chloroform, and dried under vacuum. Yield: 0.59 g (65%).
Anal. Calcd for C14H15CoNOPF6: C, 40.30; H, 3.63; N, 3.36.
Found: C, 40.35; H, 3.53; N, 3.27. FT-IR (KBr, cm-1): ν(NH),
3322, 3353; amide I, 1650; amide II, 1551; amide III, 1241;
PF6-, 835, 557. 1H NMR (acetone-d6, 300 MHz): δ 3.99 (m,
2H, CH2), 5.14 (dq, 1H, CHdCH2 (cis)), 5.25 (dq, 1H, CHd
CH2 (trans)), 5.94 (m, 1H, CHdCH2), 5.95 (s, 5H, C5H5), 6.03
(t, 2H, C5H4), 6.37 (t, 2H, C5H4), 8.15 (s, 1H, C(O)NH). 13C NMR
(acetone-d6, 75.43 MHz): δ 42.89 (CH2), 84.97 (C5H4), 85.12
(C5H5), 86.35 (C5H4), 95.67 (C5H4), 116.60 (CHdCH2), 135.14
(CHdCH2). MS (FAB; m/z (%)): 272.1 ([M - PF6]+, 100.0).
Syn th esis of [{η5-C5H5}Co{η5-C5H4C(O)OCH2CHdCH2}]-
P F 6 (5). Compound 5 was prepared following method 2,
starting from (chlorocarbonyl)cobaltocenium (1.00 g, 2.5 mmol)
and O-(trimethylsilyl)allyl alcohol (0.70 g, 5.3 mmol). From the
reaction mixture a yellow solid was filtered, which after drying
under vacuum was identified as 5. The filtrate was cooled to
-30 °C, and yellow crystals of pure 5 were also isolated.
Yield: 0.90 g (86%). Anal. Calcd for C14H14CoO2PF6: C, 40.20;
H, 3.35. Found: C, 40.26; H, 3.10. FT-IR (KBr, cm-1): ν(Cd
Syn th esis of P olym er 8. Polymer 8 was prepared by
starting from (chlorocarbonyl)cobaltocenium (1.00 g, 2.5 mmol)
and (aminopropyl)methyl(3-5%)-dimethylsiloxane(95-97%)
copolymer (6.9 g) in a chloroform solution in the presence of
triethylamine. After evaporation of the solvent under vacuum,
the resulting residue was purified by repeated treatment with
dichloromethane/acetonitrile. Polymer 8 was isolated as a
yellow viscous oil which solidified on standing. Anal. Calcd for
n ) 5% and m ) 95%: C, 33.95; H, 7.19; N, 0.73. Found: C,
34.07; H, 6.81; N, 0.80. Mn (VPO, THF): 4900. FT-IR (KBr,
-
cm-1): ν(NH), 3420, 3320; amide I, 1641; amide II, 1561; PF6
,
1
O), 1730; PF6-, 832, 557. H NMR (acetone-d6, 300 MHz): δ
1
558. H NMR (acetone-d6, 300 MHz): δ 0.14 (s, 99H, SiCH3),
0.64 (m, 2H, CH2Si), 1.71 (m, 2H, CH2), 3.36 (m, 2H, CH2NH),
5.93 (s, 5H, C5H5), 6.00 (m, 2H, C5H4), 6.37 (m, 2H, C5H4), 8.01
(br, 1H, NH). 13C NMR (acetone-d6, 75.43 MHz): δ 1.02, 1.43
(SiCH3), 15.03 (CH2Si), 23.36 (CH2), 43.13 (NHCH2), 84.6
(C5H4), 86.56 (C5H4), 86.73 (C5H5), 95.31 (OC-C5H4), 161.49
(CO). 29Si NMR (acetone-d6, 59.3 MHz): δ 7.33, -19.78,
-22.43.
4.88 (m, 2H, CH2), 5.35 (dq, 1H, CHdCH2 (cis)), 5.48 (dq, 1H,
CHdCH2 (trans)), 6.05 (s, 5H, C5H5), 6.10 (m, 1H, CHdCH2),
6.12 (t, 2H, C5H4), 6.40 (t, 2H, C5H4). 13C NMR (acetone-d6,
75.43 MHz): δ 67.46 (CH2), 86.48 (C5H4), 87.37 (C5H5), 87.99
(C5H4), 90.05 (C5H4), 119.51 (CHdCH2), 132.69 (CHdCH2),
163.79 (C(O)O). MS (FAB; m/z (%)): 273.1 ([M - PF6]+, 100.0),
233.0 ([M - PF6 - CH2CHdCH2]+, 6.6).
Syn th esis of P olym er 6. A dry, deoxygenated chloroform
solution of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisilox-
ane (0.68 g, 2.7 mmol) and freshly distilled triethylamine was
added to 1,1′-bis(chlorocarbonyl)cobaltocenium (1.25 g, 2.7
mmol) in chloroform. After a few minutes with stirring, a slight
increase of the temperature was observed and a green solid
immediately appeared. The reaction mixture was stirred
overnight. The precipitate was collected by filtration, washed
thoroughly with chloroform to remove the triethylamine
hydrochloride, and dried in vacuo. Polymer 6 was isolated as
a green solid (1.1 g). Anal. Calcd for [C22H34CoN2O3Si2PF6]n:
C, 41.63; H, 5.40; N, 4.42. Found: C, 40.98; H, 5.02; N, 4.36.
FT-IR (KBr, cm-1): ν(NH), 3314; amide I, 1650; amide II, 1552;
amide III, 1292; PF6-, 559. 1H NMR (acetone-d6, 300 MHz): δ
0.05 (s, 6H, SiCH3), 0.52 (m, 2H, CH2Si), 1.54 (m, 2H, CH2),
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 financial support
of this research. We are grateful to Prof. Moise´s Mora´n
(Universidad Auto´noma de Madrid) and Prof. Angel E.
Kaifer (Miami University) for helpful discussions.
Su p p or tin g In for m a tion Ava ila ble: Tables of all bond
distances and angles, torsion angles, displacement parameters,
and atomic coordinates for 1. This material is available free
of charge via the Internet at http://pubs.acs.org.
OM990527O