Bis(ferrocenylsilyl)thiophenes and ferrocenylene(silylene) thiophene oligomers

Article abstract of DOI:10.1016/S0277-5387(99)00358-7

The reaction between 1,1'-dilithioferrocene and 2,5-bis (chlorodimethylsilyl) thiophene (I), leads to a series of cyclic oligomers of basic formulation [Fc-SiMe₂-TH-SiMe₂](n) (II); Fc = (η⁵-C₅H₄)₂Fe, TH = C₄H₂S. The material n = 2, IIa, has been completely characterized by spectroscopic and single crystal X-ray diffraction. Cyclic voltammetric analysis of IIa illustrates two reversible redox processes, indicating a significant interaction between the two ferrocenylene units despite the 5 atom bridge. By comparison, the monomeric analog Fc-SiMe₂-TH-SiMe₂-Fc (III), Fc = (η⁵-C₅H₅)Fe(η⁵-C₅H₄), prepared from the reaction of mono-lithioferrocene with I, exhibits a single redox process, even though there is the same bridge between the two Fe centers. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(99)00358-7

www.elsevier.nl/locate/poly
Polyhedron 19 (2000) 291–295
Bis(ferrocenylsilyl)thiophenes and ferrocenylene(silylene)thiophene
oligomers
*
Keith H. Pannell , Feng Wang, Hemant K. Sharma, Francisco Cervantes-Lee
Department of Chemistry, The University of Texas at El Paso, El Paso, TX 79968, USA
Received 26 July 1999; accepted 17 August 1999
Abstract
The reaction between 1,19-dilithioferrocene and 2,5-bis(chlorodimethylsilyl)thiophene (I), leads to a series of cyclic oligomers of basic
formulation [Fc-SiMe2-TH-SiMe2]n (II); Fcs(h5-C5H4)2Fe, THsC4H2S. The material ns2, IIa, has been completely characterized by
spectroscopic and single crystal X-ray diffraction. Cyclic voltammetric analysis of IIa illustrates two reversible redox processes, indicating a
significant interaction between the two ferrocenylene units despite the 5 atom bridge. By comparison, the monomeric analog Fc-SiMe2-TH-
SiMe2-Fc (III), Fcs(h5-C5H5)Fe(h5-C5H4), prepared from the reaction of mono-lithioferrocene with I, exhibits a single redox process,
even though there is the same bridge between the two Fe centers.
q2000 Elsevier Science Ltd All rights reserved.
Keywords: Cyclic oligomers; Thiophenes; Ferrocenes
1. Introduction
The interesting properties of polythiophenes are well stud-
ied [1] and recently the synthesis and study of thiophene-
substituted derivatives of the Group 14 elements has also
received attention due to their potential as electroactivemate-
rials [2–5]. We have an interest in similar ferrocenyl-substi-
tuted Group 14 materials [6–17], and now report studies
aimed at the introduction of both the ferrocene and thiophene
units into a silicon-containing molecular structure. We hope
to produce monomers, oligomers and polymers with inter-
esting structural and electrical properties. As a general pro-
cedure for the synthesis of such systems we have used the
chemistry outlined in Eqs. (1) and (2) in which either
monolithioferrocene or dilithioferroceneisreactedwitha2,5-
(chlorosilyl)thiophene (Ia RsMe; Ib RsPh).
Whereas the reaction of dilithioferrocene with I would, in
theory, yield polymeric materials, the use of monolithiofer-
rocene, [Fc]yLiq, was to provide monomers from which
the basic optical and electrochemical properties of the system
2,5-bis(ferrocenylsilyl)thiophene could be obtained.
2. Results and discussion
The reaction between 2,5-bis(chlorodimethylsilyl)thio-
phene, Ia, and dilithioferrocene, Eq. (1), resulted in the for-
mation of a series of low molecular weight cyclic oligomers.
We attempted to separate these materials by column chro-
matography and were able to obtain the first of this series,
IIa, ns2, as pure red crystals. The spectroscopic data for IIa
are recorded in Table 1 and its structure is presented in Fig.
1, and selected bond angles and lengths in Table 2.
* Corresponding author
0277-5387/00/$ - see front matter q2000 Elsevier Science Ltd All rights reserved.
PII S0277-5387(99)00358-7
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K.H. Pannell et al. / Polyhedron 19 (2000) 291–295
Table 1
NMR a, UV–Vis, and analytical properties of the new compounds
2,5-bis(hydrodimethylsilyl)thiophene
1H
0.26 (d, SiMe2); 4.76 (sept. SiH); 7.30 (thiophene)
13C
y2.64 (SiMe2); 136.7 (thiophenyl C3,4); 142.8 (thiophenyl C2,5)
y23.3
2128.7
29Si
IR (CCl4, cmy1
)
2,5-bis(hydrodiphenylsilyl)thiophene
1H
5.66 (SiH JSiHs206 Hz); 7.40–7.68 (phenyl, thiophene)
13C
128.1, 130.1, 132.9 (ipso), 135.5 (phenyl); 138.9 (thiophene C3,4); 140.0 (thiophene C2,5)
IR (hexane, cmy1
)
2136
2,5-bis(chlorodimethylsilyl)thiophene (Ia)
1H
0.76 (SiMe2); 7.52 (thiophene)
3.36 (SiMe2); 136.7 (thiophenyl C3,4); 143.3 (thiophenyl C2,5
15.2
13C
29Si
)
2,5-bis(chlorodiphenylsilyl)thiophene (Ib)
1H
7.42–7.72 (phenyl, thiophene)
128.2, 131.1, 132.4 (ipso), 134.9 (phenyl); 139.4 (thiophene C3,4); 141.5 (thiophene C2,5)
13C
[(ferrocenylenedimethylsilyl)thiophenylene]2 (IIa)
Analysis
Calc.: C, 56.5; H, 5.80. Found: C, 55.9; H, 5.88
0.27 (SiMe2); 3.93, 4.08 (ferrocenylene); 6.91 (thiophene)
0.43 (SiMe2); 70.3, 72.2, 74.2 (ferrocenylene); 136.1 (thiophene C3,4); 144.4 (thiophene C2,5
y9.7
279, 449
1H
13C
)
29Si
UV–Vis (THF) (nm)
[(ferrocenylenedimethylsilyl)thiophenylene]n (IIn)
1H
0.27, 0.40, 0.54 (SiMe2); 4.08, 4.17 (ferrocenylene); 7.34 (thiophene)
13C
y0.1, 2.1 (SiMe2); 68.7, 70.2, 72.1, 73.8 (ferrocenylene); 135.8 (thiophene C3,4); 145.2 (thiophene C2,5)
y4.85, y9.7, y10.4, y10.6, y15.2
279, 449
29Si
UV–Vis (THF) (nm)
2,5-bis(ferrocenyldimethylsilyl)thiophene (III)
Analysis
Calc.: C, 59.2; H, 5.67. Found: C, 58.4; H, 5.85
0.57 (SiMe2); 4.01 (C5H5), 4.13, 4.19 (C5H4), 7.43 (thiophene)
y0.1 (SiMe2); 68.7 (C5H5), 69.7 (ipso), 71.5, 73.6 (ferrocenyl); 136.0 (thiophene C3,4); 145.3 (thiophene C2,5)
y10.6
271, 448
1H
13C
29Si
UV–Vis (THF) (nm)
2,5-bis(ferrocenyldiphenylsilyl)thiophene (IV)
Analysis
1H
Calc.: C, 70.6; H, 4.93. Found: C, 69.9; H, 5.50
3.95 (C5H5); 4.22, 4.41 (C5H4); 7.30–7.60 (phenyl, thiophene)
65.8, 68.8, 71.4, 74.9 (ferrocenyl); 127.7, 129.6, 135.6 (phenyl), 138.7 (thiophene C3,4); 141.9 (thiophene C2,5
y16.9
13C
)
29Si
a Spectra were recorded in C6D6 with the exception of IV which was recorded in CDCl3.
The structure of IIa possesses normal bond lengths and
angles and the cycle shows no structural sign of ring strain.
The two ferrocene groups are completely eclipsed, as noted
in Fig. 1(b), and the two thiophene groups are positioned in
opposition to each other.
At the present time we have been unable to characterize
completely the remainder of the product obtained from the
reaction described in Eq. (1). Fast atom bombardment MS
indicated the presence of trimeric (m/es1147) and tetra-
meric (m/es1529) analogs of IIa and the NMR data
recorded in Table 1 are consistentwiththisobservation.How-
ever, other materials are also present, witness for examplethe
29Si NMR signals at y15.2 and y4.85 ppm. We continue to
study this system.
The spectroscopic data for III and IV are in accord with their
proposed structures and are recorded in Table 1. The single
crystal structure of III is recorded in Fig. 2, andrepresentative
bond lengths and angles are presented in Table 2. This com-
plex was synthesized to provide baseline data to facilitate the
analysis of polymeric and oligomeric analogs.
The related bond lengthsandanglesofIIacanbecompared
to those of III and it is immediately clear that there are no
truly significant differences between the two sets. The single
exception to this generality are the possibly shorter silicon–
thiophene–carbon bond lengths in IIa (Si1–C1s1.861(3)
˚
and Si2–C4as1.864(2) A) compared with those in III
˚
(Si1–C1s1.874(3) and Si2–C1s1.872(5) A). In both
structures there are essentially no dihedral angles between
the two cyclopentadienyl rings in the ferrocene units, and the
thiophene rings are planar with normal bond lengths and
angles. The key distinction between the two structures arethe
The reaction outlined in Eq. (2) was satisfactory for the
formation of monomeric 2,5-bis(ferrocenyldimethylsilyl)-
thiophene, III, and the diphenylsilyl analog IV, in goodyield.
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293
Fig. 2. Crystal structure of III.
exhibit more than a single redox process even though the
iron containing groups are nominally identical. We have
previously noted that in the a, v diferrocenyl oligosilanes,
Fc(SiMe2)nFc, when the bridging chain is equal or greater
than 4, the two ferrocenyl groups do not interact and only a
single redoxprocessisobservedviacyclicvoltammetry[11].
Shorter chains result in two distinct processes: an initial step
involving oxidation of alternate Fc groups, and a second step
where the presence of a neighboring ferrocenium ion raises
the oxidation potential of the remaining ferrocenylene
groups. The transmission of the electronic effects from a
ferrocenium ion to a neighboring unoxidized Fe center can
be a through bond inductive effect, or through space. Silicon
atom bridges and acetylenic bridgeseffectivelyfacilitatesuch
through bond interactions [11,18]. The degree to which the
ferrocene groups in IIa and III can interact in this manner
was investigated by cyclic voltammetry. Complex IIa exhib-
ited two discrete redox processes when the experiment was
performed in CH2Cl2; Eoxs0.51 V and Eoxs0.56 V,
Ereds0.48 V and Ereds0.41 V (relative to Ag/Agq). In
acetonitrile, a superior coordinating solvent in which the pos-
itive charge is better delocalized, only a single process was
observed, Eoxs0.56 V, Ereds0.48 V. By contrast, regardless
of the solvent, only a single process was observable when
complex III was examined, Eoxs0.56 V, Ereds0.46 V.
These results clearly show that the capacity for interaction
between the ferrocenium ion and the unoxidized ferroceny-
lene group can occur through space as well as via an atomic
backbone. It is not surprising that in III, where the two Fe
Fig. 1. Crystal structure of IIa: (a) regular view, (b) view to show eclipsed
ferrocenylene units.
Table 2
˚
Selected bond lengths (A) and angles (8) for IIa and III
˚
atoms are separated by )11 A, the two redox processes are
IIa
III
equivalent.
C9–Si1
C11–Si2
Si1–C1
Si2–C4a
1.857(3)
1.856(3)
1.861(3)
1.864(2)
C5–Si1
C15–Si2
Si1–C4
Si2–C1
1.843(5)
1.856(4)
1.874(5)
1.872(5)
3. Experimental
All reactionswereperformedwithdryoxygenfreesolvents
in N2 or Ar atmospheres. Analyses were perfromed by Gal-
braith Laboratories Inc.; NMR were recorded on a Bruker
250 MHz instrument. LRMS was obtained from theNebraska
Center for Mass Spectrometry. Electrochemical analysiswas
performed as previously reported, with tetraethylammonium
tetrafluoroborate as supporting electrolyte [11].
C9–Si1–C1
109.3(1)
109.1(1)
109.5(1)
111.5(1)
C4–Si1–C5
107.7(2)
111.4(2)
112.0(2)
110.3(2)
C11–Si2–C4a
C16–Si1–C15
C18–Si2–C17
C1–Si2–C15
C25–Si1–C26
C27–Si2–C28
two intramolecular Fe∆Fe distances. For IIa this distance is
˚
˚
7.57 A, whereas for III it is significantly longer at 11.28 A,
3.1. Synthesis of 2,5-bis(hydridodimethylsilyl)thiophene [2]
and this will impact many properties, vide infra.
One of the diagnostic features of polyferrocenyl and fer-
rocenylene complexes and materials is their capacity to
In a 250 ml flask, equipped with a reflux condenser, rubber
septum and dropping funnel was added 13.3 g (55 mmol) of
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2,5-dibromothiophene in 20 ml of THF to 2.90 g (119 mol)
of Mg and 0.4 g I2 in 100 ml of dry THF. The formation of
the Grignard was initiated by mild external heating with a
hair dryer and then an exothermic reaction occurred. After
complete addition, 3 h, the flask was cooled on an ice bath
and 10.4 g (110 mmol) of Me2SiHCl in 20 ml of THF was
added over 20 min. The reaction mixture was stirred over-
night and then the solvent removed in vacuo. The crude prod-
uct was extracted into hexane and filtered. Distillation of the
liquid residue after removal of the hexane yielded 6.1 g (30
mmol, 55%) of the title compound, b.p. 90oC/8 mm Hg.
3.3. Reaction of 2,5-bis(chlorodimethylsilyl)thiophene with
dilithioferrocene
To a 40 ml hexane slurry of 1,19-dilithioferrocenePtmeda
(prepared from ferrocene (3.0 g, 16 mmol), n-butyllithium
(24.4 ml of a 1.6 M solution) and 5.8 ml of freshly distilled
TMEDA in 150 ml of hexane) [19] was added dropwise 2.7
g (10 mmol) of bis-2,5(chlorodimethylsilyl)thiophene at
y788C. The mixture was stirred for 1 h at this temperature
and then permitted to warm to room temperature and stirred
overnight. After filtration the solvent was removed in vacuo
to produce a brown oily material which was dissolved in the
minimum of hexane and placed upon a 2=25 cm silica gel
column (60–200 mesh). Development withhexaneproduced
two distinct bands. The initial yellow band was collected and
after removal of solvents produced 50 mg (0.07 mmol, 14%)
of IIa as a red powder which was further purified by recrys-
tallization from hexane, m.p. 230–2348C. A second band
eluted with hexane yielded an orange–red oil, IIn.
3.2. Chlorination of 2,5-bis(hydridodimethylsilyl)thiophene
[2]
In a 100 ml side-arm flask, 3 g (15 mmol) of 2,5-
bis(hydridodimethylsilyl)thiophene was added slowly to a
catalytic amount of PdCl2 (0.2 g) in 40 ml of carbon tetra-
chloride. The reaction was monitored by IR spectroscopyand
after 30 min the Si–H stretching frequency at ;2128 cmy1
had disappeared. The solvent was removed in vacuo and the
liquid product was distilled to yield 2,5-bis(chlorodi-
methylsilyl)thiophene, (b.p. 125–130oC/14 mm Hg, 2.12 g,
7.8 mmol, 52%).
3.4. Synthesis of 2,5-bis(ferrocenyldimethylsilyl)thiophene
(III)
A solution of ferrocenyllithium (prepared from the reac-
tion of 9.28 ml of 1.6 M n-butyllithium with 1.0 g (2.4 mmol)
Table 3
Crystal and refinement data
IIa
III
Empirical formula
Color, habit
Crystal size (mm)
Crystal system
Space group
C18H22Si2SFe
orange prism
0.32=0.44=0.80
monoclinic
C28H32PSi2SFe
orange–yellow fragment
0.60=0.60=0.40
monoclinic
P21/c
P21/c
Unit cell dimensions
˚
a (A)
11.734(2)
11.999(2)
13.444(2)
21.429(5)
8.775(2)
14.824(4)
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
90.00
99.14(1)
90.00
1868.8(5)
90.00
106.95(2)
90.00
2666.4(11)
3
˚
Volume (A )
Z
4
4
2u range (8)
3.5–45
4.0–45
Scan type
v
v
Scan speed (8 miny1
)
3–20
3–15
Scan range w (8)
1.40
1.20
Standard reflections
3 measured every 97 reflections
3 measured every 97 reflections
Index ranges
h
k
l
0 to 12
y23 to 22
y2 to 12
y9 to 2
y14 to 14
y3 to 15
3794
Reflections collected
3189
Independent reflections
Observed reflections
Absorption correction
Min./max. transmission
Final R indices (observed data)
2462
3476
2286 (F)3.0s(F))
Semi-empirical
0.221/0.254
Rs3.07%, wRs5.07%
3195 (F)3.0s(F))
N/A
N/A
Rs4.75%, wRs7.32%
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295
of FcHgCl) was added dropwise to 1.0 g (3.7 mmol) of 2,5-
bis(chlorodimethylsilyl)thiophene in 30 ml of THF at
y788C. The mixture was stirred overnight and then the sol-
vent was removed in vacuo. The product was extracted with
hexane, and the solution filtered. After removal of the solvent
di-n-butylmercury was distilled to leave a gummy residue.
This was dissolved in the minimum of hexane and placed
upon a 10=2 cm silica gel column(60–200mesh)andeluted
with hexane. An orange band developed and was collected,
the solvent removed and the final residue recrystallized from
hexane to yield III, 1.2 g (2.1 mmol, 57%), m.p. 778C.
Also prepared by the same general route, in 65% yield,
was 2,5-bis(ferrocenyldiphenylsilyl)thiophene (IV) from
the reaction of ferrocenyllithium and 2,5-bis(chlorodi-
phenylsilyl)thiophene.
in Table 3 and selected bond lengths and angles are provided
in Table 2. The structures of IIa and III are illustrated in
Figs. 1 and 2, respectively.
4. Supplementary data
Crystallographic data for structures IIa and III are avail-
able from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK (fax: q44-1223-
336033; e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk), quoting the deposition numbers
CCDC 140477 (IIa) and CCDC 140478 (III).
Acknowledgements
3.5. Structural analysis of IIa and III
This research has been supported by the R.A. Welch Foun-
dation, Houston, TX (grant no. AH-546) and the NSF.
An orange crystal of approximate dimensions
0.32=0.44=0.80 mm (IIa) and an orange–yellow crystal
approximately 0.60=0.60=0.40 mm in size (III) were
mounted on glass fibers in a random orientation. Intensity
data were collected at room temperature for IIa and y1008C
for III, which decayed under the X-ray beam at room tem-
perature, using a Siemens/Bruker four circle diffractometer
with graphite-monochromated Mo Ka radiation,ls0.71073
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˚
A. Unit cell parametersandstandarddeviationswereobtained
by least-squares fit of 25 reflections randomly distributed in
reciprocal space in the 2u range of 15–308. The v-scan tech-
nique was used for intensity measurements in both cases. A
range of 1.48 in v and variable speed of 3.00 to 20.00 8 miny1
was used for IIa and a 1.28 v-range and a 3.00 to 15.008
miny1 speed for III. Background counts were taken with
stationary crystal and total background time to scan timeratio
of 0.5. Three standard reflections were monitored in both
cases every 97 reflections and showed no significant decay
for IIa and an average intensity decay of 8.2% for III even
at y1008C. The data were corrected for Lorentz and polari-
zation effects but only IIa was corrected semi-empiricallyfor
absorption giving a min./max. transmission ratio of 0.221/
0.254.
´
´
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Both structures were solved by direct methods and refined
using the PC-version of the SHELXTL PLUS crystallo-
graphic software by Siemens. Full-matrix least-squares
refinement minimizing 8w(FoyFc)2 was carried out with
anisotropic thermal parameters for non-hydrogen atoms. The
hydrogen atoms were placed at calculated positions (C–H
˚
0.96 A; UHs0.08) during refinements. The weighing
scheme has the form wy1ss2(F)qgF2 and the final R fac-
2
tors the form Rs8NFoyFcN/8Fo and Rws[wNFoyFcN /
[19] J.J. Bishop, A. Davison, M.L. Katcher, D.W. Lichtenberg, R.E.
Merrill, J.C. Smart, J. Organomet. Chem. 27 (1971) 241.
2
8wFo ]1/2. Relevant crystal and refinement data areprovided
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